3- HUMAN REPRODUCTION

CHAPTER NO.3 HUMAN REPRODUCTION

A19

INTRODUCTION

Hi Students, The First Two Chapters Of Your Syllabus Have Been Completed. You Have Studied About Different Types Of Reproduction And Sexual Reproduction In Flowering Plants.Now We Shall Discuss In Detail About Sexual Reproduction In Human

Beings In This Chapter No.03.

As animals became more complex, specific organs and organ systems developed to support specific functions for the organism. The reproductive

structures that evolved in land animals allow males and females to mate,

fertilize internally, and support the growth and development of offspring.

The reproductive tissues of male and female humans develop similarly in uterus of mother until a low level of the hormone testosterone is released from male gonads. Testosterone causes the undeveloped tissues to differentiate into male sexual organs. When testosterone is absent, the tissues develop into female sexual tissues. Primitive gonads become testes or ovaries. Tissues that produce a penis in males produce a clitoris in females. The tissue that will become the scrotum in a male becomes the labia in a female; that is, they are homologous structures.

In this chapter we will study about ;

Human Reproductive Systems and Their Functions.

MALE REPRODUCTIVE SYSTEM

Male reproductive system is located in the pelvis region. It consists of :

a pair of testis, glands, accessory ducts and external genitalia.

TESTES:

Smooth organ situated outside the abdominal cavity within a pouch called scrotum.

The scrotum helps in maintaining the low temperature of the testis which is 2-2.5°C which is below than the normal internal body temperature.

Each testis is 4 to 5 cm in length and 2 to 3 cm in width in adults.

Each testis contains about 250 compartments called testicular lobules.

Each testicular lobule contains one to _ three highly coiled seminiferous tubules, in which sperms are produced.

The wall of each seminiferous tubule is lined by two types of cells called male germ cells (spermatogonia) and Sertoli cells.

The male germ cells undergo meiosis leading to sperm formation and Sertoli cells provide nutrition to the germ cells.

The regions outside the seminiferous tubules called interstitial spaces contain small blood vessels and interstitial cells or Leydig cells.

Leydig cells synthesize and _ secrete’ testicular hormones

called androgens.

ACCESSORY DUCTS:

The male accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens.

The seminiferous tubules of the testis open into the vasa efferentia through rete testis.

o The vasa efferentia leave the testis and open into epididymis located

along the posterior surface of each testis.

The epididymis leads to vas deferens that ascends to the abdomen and loops over the urinary bladder.

Vas deferens receives a duct from seminal vesicle and opens into urethra as the ejaculatory duct.

The urethra originates from the urinary bladder and extends through the penis to its external opening called urethral meatus.

ACCESSORY GLANDS:

The male accessory glands include paired seminal vesicles, prostate gland and paired bulbourethral glands.

Accessory glands secrete seminal plasma which is rich in fructose,calcium and some enzymes

Secretion of bulbourethral gland also helps in lubricating the penis.

EXTERNAL GENITALIA:

The penis is the male external genitalia.

Some special tissues make up the penis which helps in the erection of

the penis.

The enlarged end of penis called the glans penis.

Eoreskin, a loose fold of tissue covers the glans penis.

LET US KNOW WHAT WE HAVE LEARNT!

PART- A: VERY SHORT ANSWER TYPE QUESTIONS:

a) MCQs:

1. Which of the following organ is known as male reproductive

gland?

A. Scrotum

B. testes

C. seminal vesicles

D. penis

2. Where the scrotum lies?

A. below the pubic symphysis

B. above the pubic symphysis

C. behind the pubic symphysis

D. in front of pubic symphysis

3. Which of the following comes under the functions of male reproductive system?

A. production of spermatozoa

B. delivery of spermatozoa in semen

C. maturation

D. all of the above

4. Which layer of testis divides the glandular structure of testis into

lobules?

A. tunica vaginalis

B. tunica albuginea

C. tunica vasculosa

D. both A and B

5. Which organ suspends the testes in the scrotum?

A. seminal vesicles

B. spermatic cords

C. scrotum itself

D. ejaculatory ducts

b) TRUE/FALSE:

1. An alternate name for the primary reproductive organs is "gametes."

2. The two main functions of the testes are to produce "sperm cells" and hormones associated with the reproductive process.

3. The tightly coiled tubules known as "interstitial tubules” are the places

where sperm cells are produced.

c) FILLIN THE BLANKS:

1. The gland secretes a milky, slightly acidic fluid that plays a role in activation of the sperms.

2. The produces 70% of the fluid in semen.

ANSWER KEY: PART-A

a) MCQs:

1. (b) Testes are the glands as they secrete hormones.

2. (a) Below the pubic symphysis-joint between pubic bones of two sides.

3. (d) All are in the process of spermatogenesis.

4. (b) Tunica albugenea.

5. (b) Spermatic cord; consists of an artery, a vein, a lymph vessel, a nerve, cremaster muscle and a vas deferens.

b) TRUE/FALSE:

1. False: Gonads

2. True

3. False: Seminiferous tubules.

c) FILLIN THE BLANKS:

1. Prostate

2. Seminal vesicle

PART-B: SHORT ANSWER TYPE QUESTIONS:

1. Why are humans testes located outside the abdominal cavity? Name the pouch in which they are present.

2. Write the location and functions of following in human testes.

(i)Sertolicells

(ii) Leydig cells

3. State the role of the epididymis in male fertility.

PART-C: LONG ANSWER TYPE QUESTION ANSWERS:

1. Draw a labelled diagrammatic view of human male reproductive system.

A20

INTRODUCTION

HUMAN FEMALE REPRODUCTIVE SYSTEM:-It is a system of sex organs and accessory glands specialized in formation and fertilization of ovum, its growth and nourishment to form foetus and subsequent delivery of fully formed young one.The female reproductive system is made up of the internal and external sex organs that function in reproduction of new offspring.

It consists of:

1. Ovaries- one pair

2. Fallopian tubes / Oviducts- one pair

(i) Infundibulum

(ii) Fimbriae

(iii) Ampulla

(iv) Isthmus

(v) Uterine part

3. Uterus (Mother’s womb)

(i) Uterus

(ii) Cornua

(iii) Body

(iv) Cervix

4. Vagina

1. OVARIES:-

They are the primary sex organs in female.

They are present in upper pelvic cavity.

There are pair of ovaries which appear like unshelled almond, length (2-4cm).

Ovaries are attached to uterus with the help of ovarian ligaments.

The broad ligaments are attached to ovary by double fold of peritoneum called mesovarium.

2. FALLOPIAN TUBE / OVIDUCT:-

They are 10-12 cm long and consist of following parts:-

(i) INFUNDIBULUM: = The part of fallopian tube closest to ovary is called

infundibulum. It is funnel like.

(ii) FIMBRIAE: - The finger like projection called fimbriae.Function of Fimbriae: - Fimbriae helps to collect ovum after ovulation.

(iii) AMPULLA: - Widest and longest part of fallopian tube.

(iv) ISTHMUS: - Narrow, short and thick walled part.

(Vv) UTERINE PART: - With the help of which the uterus attaches to the fallopian tube.

Function of Fallopian tube:-

It conveys the egg from ovary to uterus.

Fertilization takes place in the ampullary region of fallopian tube.

3. UTERUS (MOTHER’S WOMB) :-

Itis hollow muscular, inverted, pear shape.

Uterus is divided into following parts:-

{1} Uterus:- Dome shaped part.

(ii) Cornua:-Upper corners.

(iii) Body:- Main part of uterus.

It communicate above with body of uterus and below with vagina.

Function of uterus :- The development of foetus takes place inside the uterus.

4. VAGINA:-

Itis 10 cm long tube that extends from cervix to the outside of body.

The opening of vagina is called vaginal pore (orifice ).

Through which menstrual fluid passes out and delivery of baby takesplace.

The male copulatory organ release semen through this pore.

The vaginal pore is covered by amembrane, called Hymen.

Function of Fallopian tube:-

It conveys the egg from ovary to uterus.

Fertilization takes place in the ampullary region of fallopian tube.

3. UTERUS (MOTHER’S WOMB) :-

Itis hollow muscular, inverted, pear shape.

Uterus is divided into following parts:-

{1} Uterus:- Dome shaped part.

(ii) Cornua:-Upper corners.

(iii) Body:- Main part of uterus.

It communicate above with body of uterus and below with vagina.

Function of uterus :- The development of foetus takes place inside the uterus.

4. VAGINA:-

Itis 10 cm long tube that extends from cervix to the outside of body.

The opening of vagina is called vaginal pore (orifice ).

Through which menstrual fluid passes out and delivery of baby takesplace.

The male copulatory organ release semen through this pore.

The vaginal pore is covered by amembrane, called Hymen.

LET US KNOW WHAT WE HAVE LEARNT!

PART-A VERY SHORT ANSWER TYPE QUESTIONS

a) MULTIPLE CHOICE QUESTIONS:--

1. The primary sex organ of female reproductive system is:

(a) fallopian tube

(b) ovaries

(d) cervix

2. Which part of the fallopian tube has finger like projection?

(a) fallopian tube

(b) ampulla

(d) fimbriae

3. Progesterone us secreted by:

(a) thymus

(b)thyroid

(c)testis

(d) corpus luteum

4. Which of the following is the largest widest part of the fallopian tube:

(a)ampulla

(b)isthmus

(c)fimbriae

(d) luteum

5.The outer layer of uterus is:

(a) perimetrium

(b)encometrium

(c)myometrium

(d) endometrium

b) TRUE/FALSE:--

1. Fertilization occurs in the oviduct.

2. Isthmus is narrow, short and thick walled part of fallopian tube.

3. Fimbriae help to collect ovum after ovulation.

c) FILL IN THE BLANKS:-

1. The opening of vagina is called ...............

2. The vaginal pore is covered by a membrane, called ................

ANSWER KEY: PART-A

a) MULTIPLE CHOICE QUESTIONS

1. (b) Ovaries. (Ovaries are the primary sex organs that produce the female

gametes (ovum) and several steroid hormones (ovarian hormones)).

2. (d) Fimbriae. (The ends of the fallopian tubes close to the ovaries are

covered with finger like projection called fimbriae).

3. (d) Corpus luteum. (Progesterone is secreted by the ovarian corpus luteum

during the first ten weeks of pregnancy, followed by the placenta in the later

phase of pregnancy).

4. (a) Ampulla. (The largest part of the fallopian tubes is referred to as the

ampulla. Ampulla has a diameter of 1cm at its widest point and is 5cm long).

5. (a) Perimetrium.(The perimetrium is the outer serous layer of the uterus.

b) TRUE/FALSE

1. (a) True (Fertilization takes place in the ampullary region of fallopian tube).

2. (a) True (Isthmus is narrow, short and thick walled part of fallopian tube).

3. (a) True (Fimbriae helps to collect ovum after ovulation).

c) FILLIN THE BLANKS

1. Vaginal pore.

2. Hymen.

(B) SHORT ANSWER TYPE QUESTIONS

1. What is the function of fimbriae?

2. What is the function of endometrium?

3. What is the function of fallopian tube?

(C) LONG ANSWER TYPE QUESTIONS

1. Explain the female reproductive system with the help of well labeled

diagram.

A21

INTRODUCTION

SPERMATOGENESIS

The process of formation of haploid spermatozoa or sperms, from diploid

spermatogonia, inside the eminiferoustubule of testis in male is called

spermatogenesis. It starts at puberty.

SPERMATOGENESIS is divided into two parts:-

1. Formation of spermatid

2. Spermiogenesis

1. FORMATION OF SPERMATID:

(a) Multiplication phase

(b) Growth phase

a) MULTIPLICATION PHASE:-

At sexual maturity, the undifferentiated germ cells divide several time by

mitosis to produce a large number of spermatogonia.

Spermatogonia (2N) are of two types :-

(i) Type A spermatogonia

(ii) Type B spermatogonia

2. TYPE B SPERMATOGONIA are precursors of sperm. They stop dividing and undergo growth.

b}) GROWTH PHASE:-

Each type B spermatogonia grow in size and form primary spermatocyte.

c)MATURATION PHASE:-

Each primary spermatocyte undergoes meiosis-1 which is a reductional

division and forms secondary spermatocyte which are haploid.

Each secondary spermatocyte undergoes meiosis-l and form spermatid.

2. SPERMIOGENESIS:-

The transformation of spermatid into spermatozoa is called spermiogenesis.

SPERMIATION :-

After spermiogenesis the sperm head become embedded in the sertoli cells.

Later on they are removed from seminiferous tubule. This phenomenon is called spermiation.

SIGNIFICANCE OF SPERMATOGENESIS

During spermatogenesis, one spermatogonium produce four sperms.

Sperms have half the number of chromosomes.

After fertilization, thediploid chromosome number is restored in the zygote.

It maintain thechromosome number of the species.

During meiosis-l crossing over takes place which brings about variation.

Spermatogenesis occurs in various organisms. Thus it supports the evidence of the basic relationship of the organisms.

LET US KNOW WHAT WE HAVE LEARNT!

PART- (A) VERY SHORT ANSWER TYPE QUESTIONS

a) MULTIPLE CHOICE QUESTIONS:

1. What happens during spermatogenesis

(a)meiosis

(b) mitosis

(d) none of these

2. The nature of spermatid

(a) haploid

(b) diploid

(d) none of these

3. Diploid primary germ cells in male is

(a) spermatogonia

(b) oogonia

(d) ovary

4. Which of the following form stem cells

(a) type A spermatogonia

(b) type B spermatogonia

(c)bothA&B

(d) None of these

5. Asingle primary spermatocyte finally produced how many sperms

(a)2

(b)4

(d)8

b) TRUE/FALSE

1. During spermiogenesis, spermatids differentiate into spermatozoa.

2. During spermatogenesis, one spermatogonia produces 2 sperms.

3. Type B spermatogonia are precursor of sperm .

c) FILL IN THE BLANKS

1. The process of formation of sperms is called ............

2.The transformation of spermatids into spermatozoa is called ..........

ANSWER KEY: PART-A

A) MULTIPLE CHOICE QUESTIONS

1.(c) Meiosis and mitosis (Both meiosis and mitosis happens during spermatogenesis).

2.(a) Haploid (Spermatozoa are highly specialized haploid cells).

3.(a) Spermatogonia (Diploid primary germ cells in male is spermatogonia).

4.(c) Type - A spermatogonia (Type A spermatogonia are stem cells).

5.(b) 4 (By mitotic division, the primary spermatocyte produces two secondary spermatocytes and two secondary spermatocytes produce four haploid cell and four spermatozoa).

B) TRUE/FALSE

1. (a) True (The spermatids are transformed into spermatozoa (sperm) by

the process of spermiogenesis.

2. (b) False (During spermatogenesis, one spermatogonia produces four sperms.

3. (a) True (Type - B spermatogonia are precursor of sperm).

C) FILL IN THE BLANKS

1. Spermatogenesis (The process of formation of sperms is called spermatogenesis.

2. Spermiogenesis (The transformation of spermatids into spermatozoa is called spermiogenesis).

PART-(B) SHORT ANSWER TYPE QUESTIONS

Ques 1. What is spermatogenesis?

Ques 2. Define spermiogenesis and spermiation.

Ques 3. What is the significance of spermatogenesis?

PART-(C) LONG ANSWER TYPE QUESTIONS

Ques 1. Explain the process of spermatogenesis.

A22

INTRODUCTION

SPERMS are male gametes. They are formed inside the primary sex organs in males; TESTIS, by the process of spermatogenesis. Sperms are produced in very large number.

They are very motile structures. Human sperm is about 60 pm long and about 3.5 pm broad.

It is necessary to reach the sperm up to the ovum (female

gamete) and fertilization to take place.

STRUCTURE OF SPERM

The mammalian sperm cell can be divided in 4 parts:

HEAD, NECK, MIDDLE PIECE AND TAIL

Head: It contains the nucleus with densely coiled chromatin fibres,surrounded anteriorly by a thin, flattened sac called the acrosome,which contains enzymes used for penetrating the female egg. It also

contains vacuoles.

Neck: The neck or connecting piece is 0.3 um long and contains one Proximal centriole and one Distal centriole.

Middle piece: The middle piece is 5-7 um long and has a central filamentous core with many mitochondria spiralled around it, used for ATP production for the journey through the female cervix uterus and uterine tubes.

Tail: Tail, also called the flagellum, is the longest part and capable of wave like motion that propels sperm for swimming and aids in the penetration of the egg. The tail was formerly thought to move

symmetrically in a helical shape. However, a 2020 study by the University of Bristol stated that the tail moves in a more complicated manner, combining asymmetrical standing and travelling waves as

well as rotating the entire body to achieve a perceived symmetry.

During fertilization, the sperm provides three essential parts to the oocyte:

(1) A signalling or activating factor, which causes the metabolically dormant oocyte to activate.

(2) The haploid paternal genome.

(3) The centriole, which is responsible for forming the centrosome and microtubule system.

LET US KNOW WHAT WE HAVE LEARNT!

PART-A: VERY SHORT ANSWER TYPE QUESTIONS:

A) MCQs:

Q1. The body of sperm is covered by

a) Head

b) Cell membrane

c) Cell wall

d) Cytoplasm

Q2. What part of sperm holds the haploid chromatin?

a) Acrosome

b) Head

c) Tail

d) Neck

Q3. Which of the following is not an essential feature of sperms that determine the fertility of a male?

a) Sperm count

b) Sperm motility

c) Sperm height

d) Sperm production rate

Q4. Head of the sperm contains which kind of nucleus?

a) Diploid

b) Triploid

c) Haploid

d) Tetraploid

FILL IN THE BLANKS:

1. Head of the sperm is called .

2. Tail of the sperm is used for .

3. Part contains mitochondrion.

TRUE OR FALSE

1. Sperm is male gamete produced from single cell.

2. Nucleus helps the sperm to propel towards egg.

3. Nucleus of sperm holds DNA.

ANSWER KEY: PART-A

a) MULTIPLE CHOICE QUESTIONS

A1: b

Explanation: As in the case of any other cell, sperms are enveloped by a

phospholipid bilayer, which is also called as plasma membrane or cell membrane.

A2:b

Explanation: The haploid nucleus is present in the head. Acrosome is the cap like structure of head which helps it to fertilize the ovum.

A3: c

Explanation: Sperm count is essential as it determines the probability of a sperm encountering the egg. Sperm motility is essential to ensure the passage of sperms through the genital tract, uterus and oviduct. Sperm production rate determines the number of healthy coitus a male can

have. Sperm height is not a determining factor of fertility.

A4: c

Explanation: Nucleus is Haploid in sperm before fertilisation.

A5: b

Explanation: Tail helps the sperm to swim in a fluid medium.

b) FILL IN THE BLANKS:

Ans: 1. Acrosome

Ans: 2. Locomotion

Ans: 3. Middle piece

c) TRUE/ FALSE:

1. False, it is produced by meiosis from germ cells.

2. False, tail helps to propel toward egg.

3. True.

PART-B: SHORT ANSWER TYPE QUESTIONS:

Q1. How does the structure of a sperm relate to its function?

Q2. Describe the structure of mammalian sperm in brief.

Q3. What are the 4 main parts of a sperm?

ANSWER KEY: PART-B

A1. The head contains the genetic material for fertilisation in a haploid nucleus. The acrosome in the head contains enzymes so that a sperm canpenetrate an egg. The middle piece is packed with mitochondria to release energy needed to swim and fertilise the egg. The tail enables the sperm to

swim.

A2. Sperm is composed of a head, neck, middle piece and tail. Whole body of sperm is enclosed by plasma membrane. The head contains as elongated haploid nucleus, the anterior portion is covered by a cap like

structure called as acrosome. This acrosome is filled with enzymes that help fertilisation of the ovum.

A3. The head of the sperm contains the nucleus. The nucleus holds the DNA of the cell. The neck contains two centrioles. The proximal centriole provide Microtbule organiser after fertilization and distal centriole provide flagellum for sperm movement.The middlepiece of the sperm is packed with mitochondria. Mitochondria are organelles in cells that produce energy. The tail of the sperm moves like a propeller, around and around.This tail has a long flagella that pushes the sperm forward.

PART-C: LONG ANSWER TYPE QUESTIONS:

Q1. Explain the structure of Human sperm with appropriate labelled

diagram?

ANSWER KEY: PART-C

A1. For answer, refer to page no. 2 & 3.

A23

INTRODUCTION

Ovum or egg is the female gamete produced in the primary sex organ or gonad; OVARY of female mammal. The process of formation of haploid egg or ovum from diploid sex or germinal cell is called oogenesis. Oogenesis starts in females by the time female foetus is only 25 weeks old, in the womb of her mother. It is interesting to note here that mature ovum or ootid is formed only after its meeting with the sperm in the fallopian tube.

OOGENESIS:

It is a growth process in which primary egg cell which we call as ovum

becomes a mature ovum.

The three phases are MULTIPLICATION STAGE, GROWTH STAGE and MATURATION STAGE.

It produces oocytes and ultimately yields mature ovum.During embryogenesis, in development at the time of the gastrulation a small group of cells are "put aside" to later form oocytes and spermatozoa. This population of cells is described as the primordial germ cells {(PGCs).

These cells also migrate initially into the posterior endoderm that forms the hind gut and from there into the genital ridge that will be the site of the developing gonad, from this time there occurs a multiplication phase leading to the formation of oogonia which is diploid in nature.

PROCESS OF OOGENESIS

The process of formation of a mature gamete or ovum is called oogenesis. Oogenesis consists of the following three phases:-

1. Multiplication Phase: Oogenesis is initiated during the embryonic development stage when a couple of million gamete mother cells (oogonia)are formed within each foetal ovary. No more oogonia are formed and added after birth. These cells start mitotic division and change into primary oocytes.

2. Growth Phase: Each primary oocyte then gets surrounded by a layer of granulosa cells. This structure is called primary follicle. A large number of these follicles degenerate during the phase from birth to puberty. At puberty only 60 to 80 thousand primary follicles are left in each ovary. The primary follicle gets surrounded by more layers of granulosa cells to form secondary follicle.

3. Maturation Phase: In the maturation phase, the secondary follicle soon

transforms into tertiary follicle. The primary oocyte within the tertiary

follicle grows in size and completes the first meiotic division to form a

large haploid secondary oocyte and a tiny first polar body. In second meiotic division secondary oocyte change into ovum and second polar body release. The tertiary follicle changes into a mature follicle. The graffian follicle which ruptures to release the ovum from the ovary by a

process called ovulation.

LET US KNOW WHAT WE HAVE LEARNT!

PART-A VERY SHORT ANSWER TYPE QUESTIONS

a) MCQs:

Q1. The stage of the cell cycle at which primary oocyte are arrested?

a) Prophase |

b) Metaphase |

c) Prophase Il

d) Metaphase II

Q2. How many chromatids are present in Secondary Oocyte?

a) 46

b) 23

c) 48

d) 92

Q3. The division of primary oocyte into the secondary oocyte and first polar body is an example of:

a) Symmetric division

b) asymmetric division

c) Cell death

d) asexual reproduction

Q4. Secondary oocyte divides into:

a) Ovum and first polar body

b) Ovum and second polar body

c) First polar body and second polar body

d) Primary oocyte and second polar body

Q5. How much number of mature ova is produced from one oogonium in

oogenesis?

a) Four

b) Six

c) One

d) Two

b) FILL IN THE BLANKS:

1. The process of release of ovum from mature follicle is called

2. The mature follicle release female hormone estrogen.

3. Oogenesis takes place in .

4. The matured ovum isreleased from «tj.

c) TRUE/ FALSE

1. Product of oogenesis is four mature egg.

2. Longest phase of oogenesis is multiplication phase.

3. Two polar bodies are formed during oogenesis.

ANSWER KEY: PART-A

a) MCQs:

Al:a

Explanation: Oogonia are formed during foetal development. Soon they start

undergoing meiosis but are arrested at Prophase | awaiting further cues of

division. Oogonia at this stage are called primary oocytes.

A2: a

Explanation: Secondary oocyte is formed after the first round of meiosis and

thus has a haploid set of chromosomes i.e., 23 chromosomes. But eachchromosome has two daughter chromatids, thus making a total of 46 chromatids. Ova are formed after the second round of meiosis, and each

chromosome gets a single chromatid, thus having a total of 23 chromatids.

A3: b

Explanation: Asymmetric division refers to the unequal distribution of cytoplasm between the daughter cells. Primary oocyte undergoes the first round of meiosis, producing a large haploid secondary oocyte and a tiny first polar body. Thus this is an instance of asymmetric division.

A4: b

Explanation: Secondary oocyte is formed as a result of the asymmetric division of primary oocyte, which also produces a tiny first polar body.Secondary oocyte further undergoes another asymmetric division producing a larger ovum and a

smaller second polar body.

A5: c

Explanation: Only one matured ovum is produced in oogenesis.

b) FILL INTHE BLANKS:

1. Oogenesis

2. Graffian

3. Ovaries

4. Secondary oocyte.

c) TRUE /FALSE :

1. False, product is 1 mature egg.

2. False, longest phase is growth phase.

3. True.

PART-B SHORT ANSWER TYPE QUESTIONS

Q1. What is the process of oogenesis?

Q2. How many stages are there in oogenesis?

Q3. What is the importance of oogenesis in females?

PART-C LONG ANSWER TYPE QUESTIONS

Q1. Explain Oogenesis with the help of diagrams.

A24

INTRODUCTION

WHAT IS OVUM: -It is the single cell released from either of the female primary

reproductive organs like ovaries. It is capable of developing into new organism, when fused with the sperm cell. It is known as ovum. The plural of ovum is ova.

Ovum is the name given to the haploid female reproductive gametes. Ova

are produced by both animals and land plants like Embryophytes.

The ova are developed from the primitive germ cells which are imbedded in the substance of the ovaries, through the process of oogenesis.

Each primitive germ cell gives rise, by repeated mitotic divisions, to a

number of smaller diploid cells termed odgonia, from which the diploid primary oocytes are developed.

Human ova are extremely minute, measuring about 0.2 mm. in diameter These are enclosed within the egg follicles of the ovaries. As a rule, each follicle contains a single ovum, but sometimes two or more are present.

By the enlargement and subsequent rupture of mature follicle at the surface of the ovary, an ovum is liberated (ovulation), at its secondary oocyte (haploid) state and conveyed by the uterine tube to the cavity

of the uterus.

Unless it be fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being.

In appearance and structure the ovum differs little from an ordinary cell,

ITHAS SEVERAL PARTS:-

The cell substance is known as the yolk or odplasm.

The nucleus as the germinal vesicle.

The nucleolus as the germinal spot.

The ovum is enclosed within a thick, transparent envelope, the zona

striata or zona pellucida, adhering to the outer surface of which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata.

1. YOLK

The yolk comprises: -

(1) The cytoplasm of the ordinary animal cell with its spongioplasm and hyaloplasm; this is frequently termed the formative yolk.

(2) The nutritive yolk or deutoplasm, which consists of numerous rounded granules of fatty and albuminoid substances imbedded in the cytoplasm.

In the mammalian ovum the nutritive yolk is extremely small in amount, and is of service in nourishing the embryo in the early stages of its development only.Human ovum is Alecithal i.e,without yolk.

Acentrosome and centriole are present and lie in the immediate neighborhood of the nucleus.

2. GERMINAL VESICLE. —

The germinal vesicle or nucleus is a large spherical body which at first occupies a nearly central position.

It becomes eccentric as the growth of the ovum proceeds.Its structure is that of an ordinary cell-nucleus.

It consists of a reticulum or karyomitome, the meshes of which are filled with karyoplasm, while connected with, or imbedded in, the reticulum are a number of chromatin masses or chromosomes, which may present the appearance of a skin or may assume the form of rods or loops.

The nucleus is enclosed by a delicate nuclear membrane, and contains in

its interior a well-defined nucleolus or germinal spot.

3. COVERINGS OF THE OVUM: —

The zona striata or zona pellucida is a thick, non cellular, glycoprotein

rich membrane. It carries receptor proteins,zp1,zp2,zp3 to attach sperm.

It transfer nutrients to egg.

It persists for some time after fertilization has occurred, and may serve

for protection during the earlier stages of segmentation.

It is not yet determined whether the zona striata is a product of the

cytoplasm of the ovum or of the cells of the corona radiata, or both.

The corona radiata consists or two or three strata of cells; they are derived from the cells of the follicle, and adhere to the outer surface of the zona striata

when the ovum is set free from the follicle; the cells are radially arranged

around the zona, those of the innermost layer being columnar in shape.The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist

in protecting and nourishing the ovum.

The ovum has two poles; animal pole and vegetal pole. Two polar bodies occur near the animal pole in periviteline space.

LET US KNOW WHAT WE HAVELEARNT!

PART-A VERY SHORT ANSWER TYPE QUESTIONS

a) MULTIPLE CHOICE QUESTIONS:--

1. Fertilization of ovum in human beings occur in:

(a) fallopian tube

(b) cervix

(d) none of these

2. Cleavage in mammals is?

(a) Holoblastic equal

(b) Holoblastic unequal

(d) discoidal

3. Fertilizin is a chemical substance produced from:

(a)Polar bodies

(b) middle piece of sperm

(c)Mature egg

(d) acrosomes

4. Mature ovum in human being is surrounded by:

(a) Plasma membrane

(b)Vitelline membrane

(d) all of these

5. Human eggs are:

(a) alecithal

(b) microlecithal

(d) macrolecithal

b) TRUE/FALSE:--

1. Human egg has a head, middle piece and tail.

2. Egg laid after fertilisation is made up of a single cell.

3. The ova are developed from the primitive germ cells which are imbedded inthe substance of the ovaries.

c) FILL IN THE BLANKS:--

1. Outer to the zona pellucida, there is very thick cellular layer..............

2. The side of the ovum which extrudes polar bodies is termed the................

ANSWER KEY: PART-A

a) MULTIPLE CHOICE QUESTIONS

1. (a) Fallopian tubes. (In human beings, fertilization takes place in the ampulla- isthmus junction of the oviduct).

2. (a) Holoblastic cleavage. (The cleavage in which COMPLETE zygote divides into equal blastomers is called holoblastic equal).

3. (c) Fertilizin. (Ovum secretes a chemical named fertilizin composed of

glycoprotein = monosaccrides +amino acids).

4. (d) All of these. (The ovum is round ,non motile cell. It is almost free of

yolk and has abundant cytoplasm called ooplasm and is surrounded by plasma membrane).

5. (a) alecithal. (The human ovum is almost free of yolk).

b) TRUE/FALSE

1. False: Hint: Head, neck, middle piece and tail are the parts of a sperm.

2. True: Hint: Single celled structure after fertilization is called zygote.

3. True: Hint: Primitive germ cells develops into oogonia.

c) FILL IN THE BLANKS

{. Corona radiata.

2. Animal pole.

(B) SHORT ANSWER TYPE QUESTIONS

1. What are fertilizin molecules. ?

2. What is the meaning of ovum?

3. Can you see a human ovum?

(C) LONG ANSWER TYPE QUESTIONS

1. Explain the structure of ovum with the help of well labeled diagram.

A25

INTRODUCTION

WHAT IS MENSTRUAL CYCLE?

In her life cycle, a woman’s body is vulnerable to a variety of changes. The

cycle of these changes takes place in women every month, positively for pregnancy is called menstrual cycle.When an ovum is unfertilized, the uterus lining sheds and leads to hemorrhage, called menstruation.

Ina girl, menstruation starts from the age of 10 to 15 when she attains puberty and this beginning is known as menarche.

The ending of menstruation is known as menopause which takes place at the age range of 50s.

The first day of bleeding is marked as the first day of a menstrual cycle and

period from one menstrual cycle to another can vary from 28 to 30 days.Before discussing the different phases of menstrual cycle, it is important to

have a glimpse of female reproductive system and organs involved in this

cycle. They mainly include:

Pair of ovaries which store, nourish and release ova.

Uterus (womb), where implantation of a fertilized egg takes place and the foetus develops.

Pair of the fallopian tube connecting the ovaries and uterus.

The count of the ovum in each ovary is decided and fixed before the birth of a girl. As she reaches puberty, hormones stimulate the development and release of one ovum per month from one ovary

alternatively. This continues till menopause.

There are four phases: menstruation, the follicular phase, ovulation and the

luteal phase.

1. MENSTRUATION:Menstruation is the elimination of the internal lining of the uterine wall along with other secretions from the body through the vagina.It usually lasts three to seven days but this could change to more or less days from month to month and depending on each woman.

2. THE FOLLICULAR or PROLIFERATIVE or ESTROGEN PHASE:

The follicular phase starts on the first day of menstruation and ends with ovulation.

During this phase the pituitary gland (situated at the base of the brain)

releases a follicle (cyst) stimulating hormone, under the influence of

GnRH (gonado trophin releasing hormone) from hypothalamus.

This hormone produces 10 to 20 follicles in the ovary and each follicle houses an immature egg.

These follicles produce the hormone estrogen, which in turn thickens

the lining of the endometrium in preparation to receive a fertilized egg.

Often, only one follicle keeps growing and travels to the ovarian surface while the remaining follicles gradually fade and are absorbed back into the body.

3. OVULATION:

Ovulation occurs 12 to 16 days before the following period but not necessarily in the middle of the cycle.

The term “ovulation” indicates the release of a mature egg by one of the ovaries.

The release of estrogen during the follicular phase causes the brain

to produce a gonadotrophin- releasing hormone that prompts the pituitary gland to produce raised levels of luteinizing hormone (luteotropic hormone). FSH and LH levels are the maximum .

This extracts the mature egg from the follicle (cyst) and transports it from the ovary to the fallopian tube.

If fertilization does not occur during this phase, the egg continues to the uterus and dissolves within 6 to 24 hours.

4. THE LUTEAL or SECRETORY or PROGESTERONE PHASE:

During this phase, the GRAFFIAN follicle from which the mature egg burst out (now called the yellow body of the ovary or corpus luteum)releases a large quantity of progesterone and some estrogen.

The two hormones help in thickening the lining of the uterus endometrium and maintain its thickness.

If fertilization does not occur, the yellow body degrades (corpus albicans) and progesterone levels decrease, leaving the lining unstable.

The lining then falls away and a new menstrual cycle period begins.

COMMON ISSUES ACCOMPANYING THE MENSTRUAL CYCLE:

CRAMPS:Many women experience stomach spasms during the first few days of their cycle. They occur because of chemicals in the body that cause the uterine muscles to contract to help shed the uterine lining.

DYSMENORRHEA (PAINFUL PERIODS):

It is the most common menstruation problem. The pain varies from one woman to the other.

LET US KNOW WHAT WE HAVELEARNT!

PART-A VERY SHORT ANSWER TYPE QUESTIONS

a) MULTIPLE CHOICE QUESTIONS: -

1. Corpus luteum secretes:

(a) Progesterone

(b) estrogen

(d) FSH(d) MSH

3. A human female reaches menopause around the age of:

(a) 50 years

(b) 15 years

(d) 25 years.

4. First Menstrual cycle at the time of puberty is called:

(a) Ovum

(b) Sperm

(d) Menarche

5. Progestrone is secreted during:

(a) Follicular phase

(b) Menstrual phase

(d) Secretory phase

b) TRUE/FALSE: -

1. Menstrual cycle ceases during pregnancy.

2. The process of release of ovum from a mature follicle is called menopause.

3. Menstrual cycle is found in non-primitive.

c) FILL IN THE BLANKS: --

1. Ovulation is induced by a hormone called

2. The mature follicle is called

ANSWER KEY: PART-A

a) MULTIPLE CHOICE QUESTIONS

1. (a) Progesterone It is essential for maintenance of the endometrium, to

maintain pregnancy.

2. (a) FSH.

3. (a) 50 years

4. (d) Menarche the last menstrual cycle is called Menopause.

5. (d) Secretory phase.

b) TRUE/FALSE

1. True

2. False ; it is called Ovulation.

3. True

c) FILL IN THE BLANKS

1. Luteinizing hormone (LH).

2. Graffian Follicle.

c) FILL IN THE BLANKS: --

1. Ovulation is induced by a hormone called

2. The mature follicle is called

ANSWER KEY: PART-A

a) MULTIPLE CHOICE QUESTIONS

1. (a) Progesterone It is essential for maintenance of the endometrium, to

maintain pregnancy.

2. (a) FSH.

3. (a) 50 years

4. (d) Menarche the last menstrual cycle is called Menopause.

5. (d) Secretory phase.

b) TRUE/FALSE

1. True

2. False ; it is called Ovulation.

3. True

c) FILL IN THE BLANKS

1. Luteinizing hormone (LH).

2. Graffian Follicle.

A26

INTRODUCTION

FERTILIZATION:

Fusion of a haploid male gamete (sperm) and a haploid female gamete (ovum) to form a diploid cell, the zygote is called fertilization. It may be (external) outside the body of mother or (internal) inside the body of mother.

It is a physiochemical process.

Fertilization can only occur if the ovum and the sperm meet.

This is the reasons why all copulations do not lead to fertilization and pregnancy.

FERTILIZATION IN HUMANS:

Fertilization is internal in humans.

It takes place in the ampullary region of fallopian tube.

Ovum in the secondary oocyte stage, released by the ovary in ovulation.

During coitus a large number of sperms get inseminated in the female genital

tract, vagina.

Hormones Prostaglandins in semen and Oxytocin in females leads to certain

movements in the genital tract of the female to reach the sperms to the oviduct.

CAPACITATION of the sperms (washing of cholesterol vesicles covering sperm

head, entry of calcium ions into sperms.) is done in the female genital tract.

STEPS OF FERTILIZATION:

1.PENETRATION OF THE SPERM INTO OVUM:

The sperm comes in contact with the egg in ampulla — isthmus junction of the oviduct.

Asperm comes in contact with Zona Pellucida layer of the ovum.

Compatibility reaction between fertilizin on the egg surface and antifertilizin

on the sperm surface takes place.

Optimum pH, Mg** and Ca?’ are required for fertilisation.

In Cortical reaction Ca** wave expel cortical granules. Plasma membrane

becomes Fertilisation membrane. No other sperm can enter now.

In Zona reaction chemicals extruded from the egg lie on zona pellucida and

prevent attachment of any other sperm.

2. ACTIVATION OF OVUM:

The entry of sperm leads to completion of Meiosis || of the secondary oocyte

that results in the formation of haploid ovum (Ootid) and a second polar body.

3. FUSION OF SPERM AND EGG NUCLEUS:

The haploid sperm nucleus fuses with the haploid nucleus of ovum to form a

diploid zygote.

SEX OF THE BABY:

The sex of the offspring is determined at the time of fertilization.

The sex chromosome pattern in human females is XX and that of human male is XY.

All haploid female gametes have only one type of sex chromosomes X (homogametic)

All the haploid male gametes have two types of sex chromosomes X or Y (heterogametic).

After the fusion of male and female gametes the zygote carries either XX or XY depending upon the sperm carrying X or Y fertilizes the ovum.

The zygote carrying XX would be female baby and XY would be male baby. That is why; FATHER is responsible for the sex of the child.

LET US KNOW WHAT WE HAVE LEARNT!

PART: A VERY SHORT ANSWER TYPE QUESTIONS

A) MULTIPLE CHOICE QUESTIONS:

1. In the absence of acrosome the sperm:

a) Cannot get food.

b) Cannot swim.

c) Cannot penetrate the egg.

d) Cannot get energy.

2. The part of fallopian tube closest to ovary is:

a) Ampulla.

b) Isthmus.

c) infundibulum.

d) Cervix.

3. What happens during fertilization in humans after many sperms

reach close to the ovum:

a) Compatibility reactions between acrosome and zona pellucida help

one sperm to enter the ovum.

b) All sperms expect the one nearest to the ovum lose their tails.

c) Cells of corona radiata trap all the sperms except one.

d) Only two sperms nearest the ovum penetrate zona pellucida.

4. Fertilization in humans is practically feasible only if:

a) Ovum and the sperms are transported simultaneously to ampullary-isthmic junction of fallopian tube.

b) Ovum and the sperms are transported simultaneously to ampullary-isthmic junction of the cervix.

c) The sperms are transported into cervix within the 48 hours of the release of ovum in uterus.

d) The sperms are transported into vagina within the just after the release of ovum in fallopian tube.

B)FILL IN THE BLANKS:

1. Fertilization is in humans.

2. Male and female gametes are .

3. Zygote is .

4. The fusion of male and female gametes is called .

C) TRUE/FALSE:

1. The site of fertilization is in the ampula.

2. Mother has Y chromosome, responsible for reproduction of male child.

ANSWER KEY: PART-A

A) MULTIPLE CHOICE QUESTIONS:

1.C

2.C

3.A

4.A

B) FILL IN THE BLANKS:

1. Internal.

2. Haploid.

3. Diploid.

4. Fertilization.

C) TRUE/FALSE

1. False: The site of fertilization is ampula-isthmus junction.

2. False: Father has Y chromosome, responsible for reproduction of male

child.

PART:B SHORT ANSWER TYPE QUESTIONS

1. How is polyspermy prevented?

2. How the sex of the baby is determined?

3. Why all copulations do not lead to fertilization?

PART:C LONG ANSWER TYPE QUESTIONS

1. Define Fertilization. Explain the process of Fertilization.

2. What are the functions of

a) Acrosome

b) Fimbriae

c) Endometrium

d) Sperm tail

A27

INTRODUCTION

As you know the first diploid cell of life, formed after fertilisation is ZYGOTE. After this the zygote changes to embryo; EMBRYOGENESIS. For this the zygote divides by MITOSIS. This division of zygote is called cleavage.Cleavage is the series of rapid mitotic division of the zygote which convert the single cellular zygote into a multicellular structure, called blastula

(blastocyst).

SITE OF CLEAVAGE: Medial to the Ampula in fallopian tube.

TYPE OF CLEAVAGE: In Human beings the cleavage is of HOLOBLASTIC type. In this whole of the Zygote undergoes division.

Zygote undergoes mitotic division (cleavage) as it moves through

the isthmus towards the uterus and forms 2, 4, 8, 16 daughter cells called blastomeres.

The embryo with 8-16 blastomeres is called a morula.

It has mulberry like appearance.

Inner cell mass — embryo proper.

Outer cell mass — protective and nutritive coverings of the embryo

Presence of Zona pellucida.

In blastocyst, blastomeres are arranged into trophoblast (outer layer)and inner cell mass attached to trophoblast.

The inner cell mass gives rise to embryo.

The cell of trophoblast (Gr. Trophe -nourishment) help to provide nutrition to the embryo.

The cells of the trophoblast later form the extraembryonic membranes namely chorion and amnion and part of the placenta.

The cells of the trophoblast which are in contact with the inner cell mass are called Cells of Rauber.

SIGNIFICANCE OF CLEAVAGE

The distribution of the cytoplasm of the zygote, amongst the blastomeres.

Increased mobility of the protoplasm.

The restoration of cell size and the nucleocytoplasmic ratio characteristic of the species.

Unicellular zygote is converted into multicellular embryo.

IMPLANTATION / NIDATION

Implantation is the attachment of the blastocyst to the endometrium of

uterine wall.

It occurs after 7 days of fertilization and takes three days.

As the blastocyst implants, usually in either the posterior portion of the

fundus or the body of the uterus in the region of embryonal knob., it orients with the inner cell mass towards the endometrium.

After implantation, the endometrium is known as the DECIDUA.

The uterine cells undergo rapid division and partially covers the blastocyst.

LET US KNOW, WHAT WE HAVE LEARNT!

PART: A- VERY SHORT ANSWER TYPE QUESTIONS

A) MCQs:

1. The cavity present in the blastula is called:

a) Coelom

b) Fluid

c) Blastocoel

d) Blastopore

2. Eight to sixteen cell stage embryo is called:

a) Blastomere

b) Zygote

c) Morula

d) Blastula

3. The last process that leads to pregnancy is called:

a) Fertilization

b) Cleavage

c) Lactation

d) Implantation

4. Which layer of blastomere gets attached to the endometrium of the uterus?

a) Blastomere

b) Trophoblast

c) Blastocoel

d) Inner cell mass

5. The daughter cell formed as a result of cleavage of a zygote are called:

a) Blastocyst

b) Blastula

c) Blastomeres

d) Blastocoel

B) FILL UPS:

a) The embryo with 8-16 blastomeres is called a .

b) Implantation is the attachment of the to the uterine wall.

C) TRUE/FALSE:

a) Beginning of embryonic development in the egg is indicated by cleavage.

b) Cell division that occurs in zygote is called implantation.

c) The hollow ball of cells formed from cleavage is called blastula.

ANSWER KEY: PART-A

A) MCQs:

1. (C) — The cell division after the morula leads to the formation of a cavity called blastocoel.

2. (D) —Zygote divides rapidly via the process of cleavage to form 8 to 16 celled embryo called morula.

3. (D) — Fertilization is one of the first process that leads to pregnancy. Implantation is the attachement of developing embryo to the uterine wall. This is the last step that leads to pregnancy.

4. (B) — The blastomere is composed of internal inner mass of cells and external layer of cells called trophoblast. The trophoblast attaches to the endometrium.

5. (C)- The zygote undergoes cleavage producing an exponential increase in cell mass. These new daughter cells are called

blastomeres.

B) FILL UPS:

a) The embryo with 8-16 blastomeres is called a morula.

b) Implantation is the attachment of the blastocyst to the uterine wall.

C) TRUE/ FALSE:

a) True: The first Mitotic division.

b) False: It is called Cleavage.

c) True: It is also known as BLASTOCYST.

PART-B SHORT ANSWER TYPE QUESTIONS

1. Give the significance of cleavage.

2. Draw the well labelled diagram of blastocyst formation before implantation.

3. What is implantation? Give the other name of implantation.

PART-C LONG ANSWER TYPE QUESTIONS

1. What is a cleavage? Give the site of cleavage. Explain the process of formation of morula from zygote through series of cell division.

A28

INTRODUCTION

After fertilization zygote is formed. The zygote needs proper embedding in the

uterus to start embryogenesis. There are different steps in the formation of

embryo from the zygote. These are Implantation, Gastrulation and

Organogenesis.Let us discuss these one by one.

IMPLANTATION:

It is the attachment of the blastocyst to the uterine wall. It occurs after 7 days of

fertilisation

STEPS FOR IMPLANTATION:

1.Trophoblast develops into two layers in region of contact between blastocyst

and endometrium of the uterus, these are:- syncytiotrophoblasts,cytotrophoblasts respectively.

2.The blastocysts sinks into a pit formed by endometrium and gets completely

buried into it.

3. The cells of inner cell mass differentiate into two layers called epiblasts and hypoblasts, together forming embryonic discs .

4. The trophoblastic cells secerets human chorionic gonadotropin [hCG]

Which maintain the corpus luteum and stimulates it to secrets progesterone.

5. It undergoes mainly in three stages. Apposition, Adhesion and Invasion.

Apposition:( blastocyst contacts the implantation site of the endometrium.)

Adhesion :( trophoblast cells of the blastocyst attach to the receptive endometrial epithelium. }

Invasion : (trophoblast cells cross the endometrial epithelial basement membrane

and invade the endometrial stroma.)

6. Soon after implantation, trophoblast secrets enzymes and causing changes in

endometrium of uterus called decidualization. There are three kinds of decidua [a portion of modified endometrium of uterus] developed in implantation.

{i} DECIDUA BASALIS:It is the portion between the chorion and the myometrium

of theuterus.

{i}DECIDUA CAPSULARIS:it is the portion of endometrium between the embryo anduterine cavity.

{iij}DECIDUA PARIETALIS:It is the portion of modified endometrium that lines the

entirepregnant uterus except for the area where that placenta is forming.Therefore, implantation starts after ovulation and leacis to preqnancy. pregnancy is the condition of having a developing embryo Inside the wonib of the mother}

GASTRULATION:

It is the transformation of the blastocysts into the gastrula with primary germ layers by re-arrangment of the cells is called gastrulation. It involves cell movements that help to attain new shape and morphology of the embryo.Thesecell movements are called morphogenetic movements. In all the triploblastic animals three germ layers namely Ectoderm, Mesoderm and Endoderm are formed by the morphogenetic movements.

1} FORMATION OF EMBRYONIC DISC :-Blastocysts consists of inner cell mass

and trophoblasts . The inner cell mass contains cells called stem cells which have

the potency to give rise to all tissues and organs .The cells of the inner mass

differentiated into two layers hypoblasts(smaller cuboidal cells ),epiblasts(layer of larger columnar cells),together forming embryonic disc(embryonic knob).

2} FORMATION OF AMNIOTIC CAVITY: A space appears between epiblast and trophoblast, called amniotic cavity filled with amniotic fluid. The roof of this cavity is

formed by amniogenic cells derived from the trophoblast, while its floor is formed

by the epiblast.

3}FORMATION OF EXTRA EMBRYONIC COELOM: The cells of trophoblast give rise to the mass of the cells called extra embryonic mesoderm, which is differentiated into two layers ,inner splanchnopleuric extra embryonic mesoderm layer and outer somatopleuric extra embryonic mesoderm layer.Both these layers enclose the extra embryonic coelom.

4} FORMATION OF CHORION AND AMNION: At this stage, two very important embryonic membranes ,chorion and amnion, are formed :

The chorion is formed by somatopleuric extra embryonic mesoderm inside and

trophoblast inside .It forms foetal part of placenta. It produces human chorionic

gonadotropin (hCG) and important hormone of pregnancy.The amnion is formed by amniogenetic cells inside and somatopleuric extra embryonic mesoderm outside. The amnion surrounds the embryo creating the

amniotic cavity that is filled with amniotic fluid which serves as a shock absorber for the foetus , regulates foetal body temperature and prevents desiccation.

5) FORMATION OF YOLK SAC: Flattened cells arising from the hypoblasts spread and line inside the blastocoel. These are endodermal cells of primary yolk sac .|t becomes much smaller than before and is now called secondary yolk sac after the appearance of extra embryonic coelom .The secondary yolk sac consists of outer splanchnopleuric extra embryonic mesoderm and inner endodermalcells .The yolk sac is a source of blood cells in humans , (functions as a shock absorber and helps prevent desiccation of embryo )otherwise it is non functional in human.

6} FORMATION OF PRIMITIVE STREAK:A primitive streak is a faint groove on

the dorsal surface of the epiblasts is formed . It elongates from the posterior to

the entire part of the embryo .The primitive streak clearly establishes the head and the tail ends of the embryo as well as its right and left sides .

7} FORMATION OF GERM LAYERS: After the formation of the primitive streak

cells of the epiblast move inward below the primitive streak and detach from the

epiblast this inverting movement is called invagination.(i)once the cells have

invaginated ,some of them separate from the hypoblast forming the endoderm .

endoderm develops first during embryonic development (ii)other cells remain

between the epiblast and newly formed endoderm forms the mesoderm (iii) cells

remainning in the epiblast form ectoderm .

FATE OF THREE GERM LAYERS: Each germ layer forms specific tissues, organsand organ - systems. The three germ layers produce tissues, organs and organ-system in following manner:

1. Ectoderm: It forms:

(i) Epidermis of skin, epidermal derivatives like epidermal glands, hair, nail etc.

(ii) Nervous system,

(iii) Medulla of adrenal gland, posterior and intermediate lobes of pituitary gland,

pineal gland,

(iv) Eye (conjunctiva, cornea, lens, retina, iris and ciliary muscles),

(v) Internal ear,

(vi) Nasal and olfactory epithelia,

(vil) Enamel of teeth,

(viii) Epithelium of fore gut and hind gut

(ix) Some glands—sweat glands, oil glands, mammary glands, salivary glands and

lacrimal glands.

2. Mesoderm: It forms:

(i) Dermis of skin,

(ii) Muscles except iris and ciliary muscles,

(iii) Connective tissues,

(iv) Kidneys,

v) Gonads,

(vi) Notochord,

(vii) Heart, blood and lymph vessels,

(viii) Urinary and reproductive ducts

ix) Most of skeleton,

(x) Coelomic epithelium,

(xi) Pericardium and pleura,

(xii) Dentine of teeth,

(xiii) Cortex of adrenal gland,

(xiv) Mesenteries,

(xv) Sclera and choroid of eyes,

(xvi) Wall of the gut except its lining.

3. Endoderm: It gives rise to:

(i) Lining of gut except for gut and hind gut,

(ii) Some glands—pancreas, liver, gastric glands, intestinal glands, thyroid,

parathyroid, thymus and larger part of prostate,

(iii) Inner layer of tympanic membrane,

(iv) Lining of middle ear,

(v) Trachea, bronchi and lungs,

(vi) Urinary bladder,

(vii) Urethra

FOETAL MEMBRANES :

After gastrulation the growing embryo develops four membranes called extra

embryonic or foetal membranes

Foetal membranes present in humans are the AMNION, CHORION,ALLANTOIS and YOLKSAC.

AMNION is the innermost layer that surrounds the embryo and is filled with the

amniotic fluid that absorbs the shock and protects the embryo from mechanical

stress.

The CHORION is the outermost layer that is composed of trophoblast cells and mesoderm, it is responsible for the formation of the placenta.

The ALLANTOIS is reduced in nature. It is present as a bag like structure near yolk

sac.

The YOLK SAC had a nutritive function in reptilia, aves and other egg-laying mammals but in humans, these are done by the placenta, yolk sac acts as a precursor for blood cells.

ORGANOGENESIS:

It is the phase of embryonic development that starts at the end of gastrulation

and continues until birth. In this stage the germ layers formed from gastrulation

form internal organs of the organism. It begins in the third week of pregnancy. The

first sign of organogenesis is NOTOGENESIS (differentiation of notochord)followed by appearance of rudiments of nervous system. It begins with the development of a fold of ectoderm called neural plate. It is primordium of nervous system. Soon rudiments of other organs also begin to appear. With the beginning of organogenesis, the embryo is converted into foetus. As we know pregnancy is the time from conception to birth. In human beings it is approximately nine months _+ seven days. Pregnancy is mainly divided into

three - months periods called trimesters. After first month of pregnancy embryo’s

heart is formed. By the end of second month, limbs and digits develop and major

organs including external genitals develop, by the end of 12 week. By the end of

about 24 weeks the body is covered with fine hair ,eyelides and eyelashes are

formed.The foetus is fully developed by the end of 9 months into the placenta .

PLACENTA :-

It is a foetal - maternal connective that develops during pregnancy and forms a

temporary association between foetal and mother tissues for supporting the

foetus during its development . Foetus is connected to placenta by a long flexible

string called umbilical cord. It is mainly formed of Allantosis and is covered by

Amniotic Epithelium. The foetal part is formed of Chorion but vesssels derived

from Allantosis extend into it. It sends out a number of fingers like outgrowths

called chronic villi, therefore human placenta is called Metadiscoidal Placenta.

LET US KNOW WHAT WE HAVE LEARNT!

(A) VERY SHORT ANSWER TYPE QUESTIONS:

Fillin the blanks

1. The end product of gastrulation is called ...............

2. Yolk sac is...............in humans.

3. After the first month of pregnancy............ is formed.

True /false

1.Trophoblast is the outermost layer of cells of gastrula.

2.The cell movements during gastrulation is called morphogenetic movements.

3.Hypoblasts and epiblasts together form embryonic disc

MCQ's

1. Mesoderm gives rise to all the structures except__.

(a) Gonads

(b) Circulatory system

(d) Muscular system

2. In human females, the fertilized eggs get implanted inthe uterus after___.

(a) One month of fertilization

(b) Two months of fertilization

(d) Three weeks of fertilization

3. Foetus is connected to placenta by a long flexible string called:

(a) umbilical cord

(b) chorionic villi

(d) amnion

4. Implantation is the process of .

(a) Attachment of blastocyst to the uterine wall

(b) Egg movement

(d) Egg fertilization

5. Amniotic fluid protects foetus from:

(a) degeneration

(b) jerks

(d) none

(B) SHORT ANSWER TYPE QUESTIONS

1. Write a short note on chorion and amnion .

2. Define implantation and gastrulation .

3. Define organogenesis.

(C) LONG ANSWER TYPE QUESTIONS

1. Evaluate the fate of ectoderm.

2. Define and explain foetal membranes.

ANSWER KEY: PART-A

FILL IN THE BLANKS

1. gastrula

2. Non-functional (because yolk is not stored. It helps in synthesis of blood, corpuscles in the early embryo. Then it shrinks)

3. Embryo’s heart

TRUE / FALSE

1. False ( because trophoblast is the outermost layer of blastula)

2. True

3. True

MCQ’s

1.(c) (because nervous system developed by ectoderm.)

2.(c) (because It takes about 6-12 days for the fertilized egg to travel to the uterus and attach to the uterus in a process known as implantation)

3.(a) (umbilical cord which helps in the transport of substances to and from the

embryo)

4 (a)

5.(b) (in this fluid foetal cells float hence it act as shock absorber and thus

protects from jerks.)

A29

INTRODUCTION

As you know by the end of pregnancy the foetus is fully developed and is

ready for delivery.

PARTURITION:

MEANING: - The process of child birth is called parturition. It occurs at the

end of pregnancy .The duration of pregnancy is 9 months # 7 days in case of Human Female. The period after fertilization from conception to child birth,called gestation period.

PROCESS: - The process of parturition is induced by nervous system and endocrine system. The signal for child birth originates from foetus and placenta. Fully grown foetus and placenta induce uterine contractions called foetal ejection reflux. It causes the release of two hormones

OXYTOCIN & RELAXIN.

OXYTOCIN: - It promotes uterine contractions.

RELAXIN: - It dilates uterine cervix.

PARTURITION or Child birth begins with contraction of uterus which is also

called labour pains.

STAGES OF PARTURITION:

1. STAGE OF DILATION: - It is the stage of complete dilation of cervix from onset of labour pains. It causes opening of cervix. Amniotic sac ruptures.Amniotic fluid comes out through the vagina. This stage lasts 6-12 hours.

2. STAGE OF EXPULSION: - It is the stage from cervical dilation to delivery of

the child. The baby passes through the cervix and vagina and is born. It lasts

10 minutes to several hours.

3. PLACENTAL STAGE: - After the birth of child placenta comes out of uterus .It

is called placental stage. Now the uterine contractions constrict blood vessels

that were torn during delivery there by reducing the possibility of excessive

blood loss.

In about 28-35 days uterus returns to its normal size.Sometimes there is birth of embryo or foetus at about 20 weeks of gestation. It is called abortion. It may occur from natural causes or induced.

MEANING: - The production of milk in the mammary glands is called lactation. In

humans the process of feeding milk is also called breast feeding.

PERIOD: - Mammary glands undergo differentiation during pregnancy and starts

producing milk at the end of pregnancy and after the birth of child.

ROLE OF HORMONES:

PROLACTIN: - After the birth of child Prolactin is released by pituitary gland. It causes secretion and storage of milk.

OXYTOCIN: - Ejection of milk is stimulated by Oxytocin.

COLOSTRUM: - It is the first milk produced by mammary glands just after the child's birth. It is yellowish in colour. It is rich in protein. It also contains

antibodies like IgA which provides immunity to new born.

COMPOSITION OF MILK: - It contains Fat, Milk Protein, Lactose Sugar,Mineral Salts and Vitamins. A woman secretes 1-2 litres of milk per day.

IMPORTANCE OF BREAST FEEDING:-

1. It is easily digestible.

2. It promotes healthy growth and development of new born.

3. It provides immunity to the new born.

4. Itis also a mean of birth control.

LET US KNOW WHAT WE HAVE LEARNT!

PART-A: VERY SHORT ANSWER TYPE QUESTIONS

MCQs:-

1. Hormone responsible for uterine contraction:

(a)Oxytocin

(b) Relaxin

(d) Estrogen

2. Duration of gestation period in human beings is:

(a) 7 Months +9 days

(b) 6 Months +9 days

(d)none of these

3. Function of Oxytocin is to help in:

(a) Child birth

(b) Growth

(d) Ovulation

4. Process of parturition is induced by:

(a) Nervous system

(b) Endocrine System

(d) None of these

5. Milk is produced by:

(a) Pituitary gland

(b) mammary glands

(d) none of these

TRUE / FALSE:

1. Colostrum is the first milk produced after child birth.

2. Oxytocin is also called birth hormone.

3. Prolactin is Hormone responsible for dilation of uterine cervix.

FILL UPS:

1. Duration from pregnancy to birth is called .

2. Ejection of milk is stimulated by hormone.

ANSWER KEY: PART- A

MCQs:

1. (a) Oxytocin is also known as Birth Hormone.

2. (c) The period from fertilization, conception and child birth.

3. (a) Oxytocin is also known as Birth Hormone, helps in contraction of uterus.

4. (c) Nervous system and the system of hormones; Endocrine system.

5. (b) Mammary glands in female secrete milk for baby after parturition.

TRUE /FALSE:

1. True

2. True

3. False (It causes secretion and storage of milk).

FILL UPS:

1. Gestation period.

2. Oxytocin

PART-B: SHORT ANSWERS TYPE QUESTIONS:-

Q1. What is lactation? Name the hormones responsible for it.

Q2. Why breast feeding is recommended during the initial period of child’s

growth?

Q3. What is Colostrum? Which antibody it contains?

PART-C: LONG ANSWERS TYPE QUESTIONS:-

Q1. What is parturition? Explain the stages of parturition.

2. At menopause, there is rise in urinary excretion of:

(a) FSH

(b) STH

1. TYPE ASPERMATOGONIA are stem cells and keep dividing.

Chapter 3 Human Reproduction

Plus Two

Saturday 30 January 2021

Chapter 3 Human Reproduction

Chapter 3 Human Reproduction

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