Biology Chapter 3 Human Reproduction

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Graafian follicle.

Function:  Leydig’s cells synthesise and secrete male sex hormones testosterone (androgens).

Seminiferous tubules are highly coiled tubes. Each seminiferous tubule is lined on its inside by two types of cells called male germ cells (spermatogonia) and Sertoli cells. There are regions outside the tubules which are called interstitial spaces,  which contain small blood vessels and interstitial cells or Leydig cells .Other immunologically competent cells are also present.

 Seminiferous tubules.

The hormones involved in the regulation of spermatogenesis are -:

1. Gonadotropin releasing hormones (GnRH) released from the hypothalamus. It stimulates the  release of gonadotropins from pituitary.

2.  Follicular Stimulating Hormone (FSH). secreted by anterior pitutary which acts on sertoli cells and helps in spermatogenesis.

3 Lutenizing hormone (LH) secreted by anterior pitutary that stimulates the leydig cells to  synthesize and secrete androgens which help in spermatogenesis.

Seminal vesicles, a prostate and paired bulbourethral glands constitute the male accessory glands. Their main function is to aid in lubrication of penis  and maintain the vitality of the sperm as their secretion is rich in calcium, fructose and certain enzymes.

Male reproductive system of man

Female reproductive system.










   

The Spermatogonia(2N) or male germ cells on the inner lining of the seminiferous tubules divide mitotically and increase in number. They are diploid in nature having 46 chromosomes.
Some of the spermatogonia called Primary spermatocytes (2N) undergo first reduction division or Meiosis I to form  two equal cells called secondary spermatocytes(N) which are haploid in nature that is they have 23 chromosomes.
Secondary spermatocytes undergo second reduction division or Meiosis II and form four equal haploids cells called spermatids . 
The spermatids are transformed into sperms
(spermatozoa) by the process of spermiogenesis.

                       Process of Spermatogenesis

Structure of a mammalian sperm

A section through ovary

Oogenesis is the process of formation of mature female gametes.

The steps of oogenesis are- 

1. Oogenesis is iniatiated  during embryonic development in a female foetus. Millions of mother cells (oogonia) are formed in the foetal ovary. No new oogonia are formed after birth.

2 The oogonial cells which enter meiosis I are called primary oocytes .

3. The primary oocyte undergoes first meiotic division at puberty to form two unequal cells. Larger cell is called the secondary oocyte and smaller is called polar nuclei or first polar body.

4. The Secondary oocyte undergoes second meiotiv division and form two uneual cells. The larger being the Ova and smaller the second polar body.

5. Thus ovum or the female gaetiopfyte is formed.

Menstrual cycle is the cyclic changes of the endometrial wall of uterus.
The various events which occur during the mensrual cycle are-:

Menstruation Phase :
During this phase menstrual flow occurs. The  breakdown of endometrium lining of uterus and its blood vessels leads to discharge in form of  liquid  through the vagina. It lasts for 3-5 days.

Follicular phase 
During this phase the primary follicles grow to form mature Graafian follicles and the uterus wall regenrates simultaneously.  The secretion of the lutenizing hormone(LH) and the follicular stimulating hormone (FSH) brings about the changes in the uterus. The LH and FSH homones leads to the secretion of estrogen and follicular development respectively. It lasts upto 14th day.

Ovulation phase (14th day)
During this phase the Graafian follicle rupture to  and thereby  release ovum.

Luteal phase
During this phase the corpus luteum is formed from the remaining part of the Graafian follicle . the corpus luteum secrets progesterone which helps maintain the endometrium needed for implantation. In the absence of fertilization the corpus luteum degenerate. It is from 15th to 28th day. 

The mammalian sperm is covered by the plasma membrane all over . It is composed of the  parts
(i) Head - It consists of a haploid nucleus which is covered anteriorly by a cap called acrosome. The acrosome has many enzyme with helps the sperm to digest the wall around egg and fertilize it.
(ii) Neck forms the juncture between head and the middle piece.
(iii) Middle piece contains numerous mitochondria which provide energy for the motility of sperm.
(iv)Tail is the posterior-most part of sperm.

1. A sperm comes in contact with the zona pellucida layer of the ovum  and induces changes in the membrane which block the entry of more than one sperm.
2. The acrosomal secretions aid in the entry of sperm into the cytoplasm of the ovum through the
zona pellucida and the plasma membrane.
3. The seconday oocyte completes its meiotic division on the entry of sperm.
4. Meiosis of secondary oocyte is unequal and leads to the formation of a smaller second polar body and a larger ovum.
5.Finally the haploid nucleus of the sperms fuses with haploid ovum to form a diploid zygote.

1.A pair of testes 

2. Accessory ducts which include rete testis, vasa efferentia, epididymis and vas deferens.

3. Acessory glands which includes seminal vesicles, a prostate and paired bulbourethral glands.

4. The external genitalia or penis .

Functions of the following are:

(a) Corpus luteum -  It secretes progesterone that helps maintain endometrium wall of the uterus..

(b) Endometrium - It helps in implantation of the fertilized ovum. It undergoes cyclic changes that causes mentsruation.

(c) Acrosome - It helps the sperm to enter the zona pellucida layer of the ovum. It contains hyrdrolase enzymes which helps digest the wall of the ova and enter it.

(d) Sperm tail - It helps in motility of the sperm.

(e) Fimbriae- It helps in collecting the ovum after ovulation.

2. A pair of oviducts or fallopian tubes.
3. Uterus.
4. Cevix.
5. Vagina.
6. Vulva or the external genitilia. 

2. Mesoderm or the middle layer.

3.  Ectoderm or the outer layer.

The hormone involved in the induction of parturition is Oxytocin which stimulate stronger contraction of uterine walls which ultimately lead to the expulsion of the baby from the uterus, through birth canal.

During fertilization the sex of the child depends on whether the male gamete with X chromosome fertilizes the female gamete or the one with Y fuses with it. If the male gamete with X fuses with the female gamete it forms XX zygote that gives rise to a girl child. If Male gamete with Y fuses with the female gamete then XY zygote is formed which develops into a boy.
Thus scientifically  it the male which decides the sex of the child and not the female. So it is not right to blame women for giving birth to the child.

sexually

viviparous

internal

haploid

diploid

Ovulation

Fertilisation

Placenta

The correct statements are:
(a) Androgen are produced by Leydig cells. 
(c) Leydig cells are found in testis
(e) Oogenesis takes place in ovary. 

The menstrual cycle is a monthly cycle of changes in the ovaries and the lining of the uterus (endometrium), starting with the preparation of an egg for fertilization. The whole cycle takes around 28 days to complete. When the egg is not implanted in the uterus the endometrium of the uterus is shed and is released in the form of blood and mucous through the vagina. This is known as menses.
The hormones that regulate the menstrual cycle are follicle stimulating hormone (FSH), luteinizing hormone (LH), estrogen, and progesterone. During the follicular phase, the level of LH and FSH increases under the influence of RH (releasing hormone) from the hypothalamus. These stimulate the conversion of a primary follicle into a Graafian follicle. The level of LH increases gradually leading to the growth of follicle and secretion of estrogen. Estrogen inhibits the secretion of FSH and stimulates the secretion of luteinizing hormone. It also causes the thickening of the uterine endometrium. The increased level of LH causes the rupturing of the graafian follicle and release the ovum into the fallopian tube. The ruptured Graafian follicle transform into corpus luteum and starts secreting progesterone hormone during the luteal phase. Progesterone hormone helps in the maintenance and preparation of endometrium for the implantation of the embryo. High levels of progesterone hormone in the blood decrease the secretion of LH and FSH, therefore inhibiting further ovulation.

Endometrium is the inner glandular wall of the uterus. It undergoes cyclic changes during menstrual cycle. 

Myometrium is the middle wall of the uterus. It brings about strong contractions during the delivery of the baby.

It is not appropriate to blame women for producing female children because scientifically it is the father who determines the sex of the baby.

The scientific explanation for the following is:

The chromosome pattern in human females is XX and human males are XY. Males are heterogametic and produce two types of gametes one carrying X and the other carrying Y. The females are homogametic and produce same type of gamete carrying X chromosome. The sex of the child depends on the sperm that fuses with the ovum. If the fertilizing sperm has an X chromosome, then the baby would be a female and if a sperm with Y chromosome fuses with the ovum, it will develop into a male child. Thus, males are responsible for determination of the sex of a child. So, we should not blame women for the birth of a female child and stop ill-treating them.

Characteristics of Neanderthal man

(i) They possess a brain capacity of 1400 cc.
(ii) They were short but very strong with outward curved thigh bones.

(iii) They used hides to protect their body and to bury the dead. 

(a) Tissue culture is the technique that has helped scientists propagate the desired crops on a large scale in a short duration. The following steps are carried out to propagate crops by tissue culture:

i) Tissue culture is the process of developing a complete plant from a part of a plant. The plant part is called an explant.

ii) Explants can be grown in sterile conditions in special nutrient media to regenerate complete plants.

iii) Nutrient media contain a carbon source (such as sucrose), organic salts, vitamins, amino acids and phytohormones.

iv) Hence, propagation is achieved for a large number of plants in a short duration. This process is called micro propagation.

v) All the plants obtained by tissue culture are called somaclones since they are genetically identical to each other as well as the parent plant.

(b) Somatic hybrids are obtained by the method of somatic hybridisation. In this method, the somatic parts of two plants are hybridised. Protoplasts are isolated and fused to get a hybrid protoplast that grows further to form a new plant. For example, protoplasts of potato and tomato have been actually fused to form a pomato. But this plant is not commercially viable, as it does not have all the desired combination of characteristics for its commercial utilization

Parturition is the process of childbirth or the delivery of the foetus because of vigorous contraction of uterus at the end of the pregnancy which is after the 9 month gestation period. It is induced by a complex neuroendocrine mechanism. Fully developed foetus gives the signal which induces mild uterine contraction called foetal ejection reflex. This triggers results in release of oxytocin from maternal pituitary. The oxytocin results in stronger contractions of the uterine walls and the secretion of more and more oxytocin. The effect of oxytocin and uterine wall contraction leads to stronger contraction which leads to the expulsion of the foetus through the birth canal or parturition.

During the reproductive cycle of human female, placenta develops after the implantation of zygote in the uterus.

After implantation, finger like projection called chorionic villi appear on the trophoblast. The chorionic villi are surrounded by uterine tissues and maternal blood. It is this chorionic villi and the uterine tissue which interdigitate with each other and jointly form a structural and functional unit between developing embryo and maternal body called placenta.

The functions of placenta are as follows:

1) Nutrition: It helps to transport nutrients from mother's blood to foetus for its development.

2) Respiration: It provides oxygen to the foetus and removes CO₂ from the foetus.

3) Excretion: It helps in the removal of waste products from the foetus.

4) Immunity: It provides immunity to the foetus. Antibodies developed in mother's blood passes onto the foetus through the placenta.

5) Storage: It stores some fats, glycogen and iron.

6) Secretion of hormones: It secretes many hormones like oestrogen, progesterone, gonadotropin and placental lactogen that support the growth of the foetus.

Chorionic villi appear on the trophoblast after implantation. Chorionic villi interdigitate with the uterine tissues and jointly forms the placenta which is a structural and functional unit between developing embryo and maternal body.

Microscopic structure of human sperm

Function of Acrosome -

It contains enzymes that help the sperm to enter and to fertilise the ovum.

Function of Nucleus -

It stores the genetic information. It carries 23 chromosomes, out of which one is sex chromosome (either X or Y). Thus, it is responsible for determining the sex of the individual.

Function of Middle piece -

The middle piece contains several mitochondria, which produce energy for the movement of the tail and motility of the sperm.

(a) View of the female reproductive system of human

(b) Changes happening in ovary and uterus during menstrual cycle are caused by change in the levels of pituitary and ovarian hormones.

After menstrual phase gonadotropin i.e., Luteinising hormone (LH) and follicular stimulating hormone (FSH) are released from pituitary. Their level gradually increases during follicular phase and it stimulates development of follicles and secretion of estrogen by growing follicles.

Both LH and FSH attain peak on 13th & 14th day.

Rapid secretion LH causes ovulation on day 14.

During luteal phases Graafian follicle changes to corpus luteum which secretes Progesterone Progesterone maintains endometrium which is necessary for implantation.

Sertoli cells are found in testis. Its function is to provide nourishment to the germ cells.

(a) Fimbriae are the finger-like processes present at the end of the fallopian tubes

(b) Coleoptile is a conical sheath present in the monocot seeds; its function is to protect the developing plumule.

(c) Oxytocin is a hormone secreted by the posterior pituitary and it stimulates the contraction of uterine muscles during child birth (parturition).

(i) Figure 'f' illustrates ovulation. It represents the ovulatory stage of oogenesis.

(ii) The changes that cause ovulation are because of the change in level of the pituitary and ovarian hormones. The pituitary secrets two hormones called Follicle stimulating hormone (FSH) and Luteinizing hormone (LH). Estrogen is the ovarian hormone released during ovulation. The FSH and LH stimulate follicular development and secretion of estrogen from the primary follicles, the rapid secretion of LH induces graffian follicles to release and release ovum.

(iii) In anticipation of receiving the fertilised egg the primary follicles in the ovary grow to become graffian follicles and simultaneously the endometrium of the uterus regenerates and through proliferation and the blood supply is increased.

(iv) In the figure, (c) stage represents the secondary follicle and the (h) stage represents the degenerating corpus luteum.

The nucleus of the functional megaspore mother cell divides mitotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac. Subsequent mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages.

of the embryo sac. These mitotic divisions are strictly free nuclear in nature, that is, nuclear divisions are not followed immediately by cell wall formation. Among the eight nuclei, six are enclosed by cell walls and organised into cells, while the remaining two nuclei (called polar nuclei) are situated above the egg apparatus in a large central cell. Out of the six cells, three are grouped at the micropylar end, and constitute the egg apparatus out of which two are synergids and one egg cell. The other three cells are located at the chalazal end, and are called antipodals. All this leads to the organisation of the typical female gametophyte or embryo sac which is 8-nucleated and 7-celled.

(a) 
(b)

(i) Follicular phase: Follicular phase is also called the proliferative phase. During this phase the FSH released by the pituitary stimulates the growth of the primary ovarian follicle and also causes maturation of the primary oocyte in this follicle. The follicular cells of the Graafian follicle secrete oestrogen. Due to an increase level of estrogen the uterine endometrium becomes thick, more vascular and more glandular. This phase lasts for about 10 to 14 days, or until ovulation occurs. The luteinizing hormone (LH) released by the pituitary induces the mature Graafian follicle to burst and release the egg or ovum into the fallopian tube. This is called ovulation.

(ii) Luteal phase: The luteal phase is also called secretory phase or the post -ovulatory phase. It follows the ovulation. During this phase the corpus luteum continues to release the hormone, progesterone. It lasts for about 12 - 14 days and extends from the 16th - 28th day of the menstrual cycle.

(a) (i) Leydig cell are found adjacent to the seminiferous tubules in the testes. They synthesize and secrete testicular hormones called androgens (testosterone).

(ii) Sertoli cells are found in the seminiferous tubules. They act as nurse cell and provide nutrition to the male germ cells.

(iii) Primary spermatocytes are present in the testes. They are diploid cells that are derived from the spermatogonia. They undergo meiotic division to give rise to secondary spermatocyte and thereby male gamete-sperm.

(b) The male accessory glands include the seminal vesicles, prostate gland, and the bulbourethral glands whose secretions constitute the seminal plasma, which provides energy and motility to the sperms until they reach the ovum.

Prostate Gland: It stores and secretes an alkaline, milky fluid known as pre-ejaculate. The purpose of the alkalinity of the semen is to neutralize the acidity of the vaginal tract.

Bulbourethral glands: This gland secretes a viscous secretion during sexual arousal. This fluid helps to lubricate the urethra for easy passage of spermatozoa to pass through, and to help flush out any residual urine or foreign matter.

• The cycle starts with the menstrual phase, where the menstruation occurs. This is followed by the follicular phase. In this phase, the primary follicles mature into the Graafian follicles and the release of gonadotropins (LH and FSH) also increases. This causes follicular growth and the growing follicles produce oestrogen.
• The LH and FSH are at their peak in the middle of the cycle (14th day) and cause the rupture of the Graafian follicles to release the ovum. This phase is called the ovulatory phase.
• The remains of the Graafian follicles get converted into the corpus luteum that secretes progesterone for the maintenance of the endometrium.
• In the absence of fertilisation, the corpus luteum degenerates; thereby, causing the disintegration of the endometrium and the start of a new cycle.

Human testes are located outside the abdominal cavity for maintaining low temperature (2–2.5^o C lower than the normal internal body temperature) necessary for spermatogenesis.
The pouch in which they are present. is called Scrotal sacs.

(a) Fertilization occur in the fallopian tube of females in human.
The events that occur during this process are :

i. The sperms come in contact with zona pellucida  of the ovum.
ii. The sperm induces change in the membrane. 
iii. Blocks entry of other sperms / ensures only one sperm fertilizes the ovum / prevents polyspermy. 
iv. The secretion of acrosome helps the sperm to enter the cytoplasm of the ovum by degrading the wall of the ova. 
v. Entry of sperm induces completion of second meiotic division forming ovum and 2nd polar body 
vi. The haploid nucleus of Sperm and that of ovum fuses. 
vii. Fertilisation completes on the formation of diploid Zygote.
b. Method suggested for the couple :

In vitro fertilisation followed by embryo transfer (ET)
In this method, popularly known as test tube baby programme, ova from the wife/donor (female) and sperms from the husband/donor (male) are collected and are induced to form zygote under simulated conditions in the laboratory

During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and with the help of acrosomal secretions induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilise an ovum

Acrosome is a cap-like structure present in the anterior part of the head of the sperm. It contains the enzyme hyaluronidase, which hydrolyses the outer membrane of the egg, thereby helping the sperm to penetrate the egg at the time of fertilization.

(a) The signals for parturition originate from the fully developed fetus and the placenta which induce mild uterine contractions called foetal ejection reflex. This triggers release of oxytocin (birth hormone) from the maternal pituitary gland.

(b) The yellowish fluid colostrum secreted by mother during the initial days of lactation has abundant antibodies (IgA) that protects the infant or new born babies and develops resistance in them.

(a) The human testes are located outside the abdominal cavity in a pouch called scrotum. The scrotum helps in maintaining the low temperature of the testes (2 -2.5^o C lower than the normal internal body temperature) necessary for spermatogenesis.

(b) Honey bees are parthenogenetic organisms because in them an unfertilized egg develops into a new individual and there is no fertilization. This process of reproduction without fertilization is called parthenogenesis.

(a) Figure g illustrates corpus luteum. Rapid secretion of leutinizing hormone LH from pituitary gland induces the rupture of Graafian follicle and formation of corpus luteum.

(b) The corpus luteum secretes large amounts of progesterone and also estrogen which is essential for maintenance of the endometrium. Such an endometrium is necessary for implantation of the fertilised ovum and other events of pregnancy.

(c) Figure d is tertiary follicle which is characterised by a fluid filled cavity called antrum. The theca layer is organised into an inner theca interna and an outer theca externa. It is at this stage the primary oocyte within the tertiary follicle grows in size and completes its first meiotic division. It is an unequal division resulting in the formation of a large haploid secondary oocyte and a tiny first polar body. Figure e -is mature follicle or Graafian follicle. The secondary oocyte forms a new membrane called zona pellucida surrounding it.

(d) Diagram showing mature Graafian follicle

(a) The menstrual cycle is the regular natural change that occurs in the female reproductive system (specifically the uterus and ovaries) that makes pregnancy possible. The cycle is required for the production of ovocytes, and for the preparation of the uterus for pregnancy.
At the beginning of menstrual cycle, the brain signals the pituitary gland to produce a hormone called the follicle-stimulating hormone (FSH), which in turn signals the ovaries to begin forming and maturing eggs for this cycle. As these follicles mature, the level of estrogen in the body rises, indicating that an egg is ready. This first half of the menstrual cycle is called the follicular phase.

*When high estrogen levels signal an egg is ready, the pituitary gland then produces a luteinizing hormone (LH), triggering the ovary to release the mature egg by the process of ovulation. The day ovulation happens is the first day of the second half of the cycle, the luteal phase.

During the luteal phase of the menstrual cycle the ovaries (the corpus luteum) begin to increase the levels of progesterone in the body. Progesterone, secreted by ovary regulates and maintains the inner lining of the uterus both during menstrual cycle. Progesterone is a hormone that prepares the lining of the uterus for pregnancy. If the egg is fertilized and implanted, the body continues to produce progesterone and if not, then progesterone levels fall, and that month's menstrual period begins.

(b) The follicular phase is known as the Proliferative phase because the primary follicle grows into the mature Graafian follicle and the endometrium of the uterus regenerates through proliferation simultaneously. The hormones LH and FSH stimulate follicular development. 
(c) The primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. These changes in the ovary and the uterus are induced by changes in the levels of

pituitary and ovarian hormones. The secretion of LH and FSH increases gradually during the follicular phase, and stimulates follicular development as well as secretion of estrogens by the growing follicles. The LH surge induces rupture
of Graafian follicle and thereby the release of ovum (ovulation). The
ovulation (ovulatory phase) is followed by the luteal phase during which
the remaining parts of the Graafian follicle transform as the corpus
luteum. The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium.

(d) 
 

Breast-feeding is recommended in the initial period of an infant's growth because of the following reasons :
i. The colostrum in the milk contains antibodies which help the infant develop resistance against infections. 
ii. It provides the necessary nutrition to the baby.
iii. It protects the infant from allergies. 

(a) During coitus, the semen having sperms is released into the vagina.
i. It passes through the cervix of the uterus and reaches the ampullary-isthmic junction of the fallopian tube.

ii. The ovum is also released into the junction for fertilisation to occur.

iii. The process of fusion of the sperm and the ovum is known as fertilisation.

iv. During fertilisation, the sperm induces changes in the zona pellucida and blocks the entry of other sperms. This ensures that only one sperm fertilises an ovum.

v. The enzymatic secretions of the acrosomes help the sperm enter the cytoplasm of the ovum.

vi. This causes the completion of meiotic division of the secondary oocyte, resulting in the formation of a haploid ovum (ootid) and a secondary polar body.

vi. Then, the haploid sperm nucleus fuses with the haploid nucleus of the ovum to form a diploid zygote.

vii. Mitosis starts as the zygote moves through the isthmus of the oviduct (cleavage) and forms 2, 4, 8 and 16 daughter cells called blastomeres.

viii. The 8−16 cell embryo is called a morula, which continues to divide to form the blastocyst. The morula moves further into the uterus.

ix. The cells in the blastocyst are arranged into an outer trophoblast and an inner cell mass.
x. The trophoblast gets attached to the uterine endometrium and the process is called implantation. This leads to pregnancy.

xi. The inner cell mass gets differentiated to form the embryo.

(b) Placenta acts as an endocrine gland and produces the following hormones
i. Human chorionic gonadotropins (hCG), 
ii. human placental lactogen (hPL), 
iii. Estrogen and progesterone
iv. Relaxin (in the later stages of pregnancy).

These hormones support foetal growth and help in the maintenance of pregnancy. Hormones like oestrogen, progestogen, cortisol, thyroxine and prolactin are increased several folds in the maternal blood.

Blastocyst is the embryonic stage that gets implanted in the uterine wall of a human female.

Biofortification is an important method to develop crops with a higher level of vitamins minerals, protein and healthier fats which improve public health. 

(a) The sequence of secretion of the given hormones in a pregnant woman is:
FSH-LH-hCG-Relaxin

(b)

Attachment of the embryo /foetus to the uterine wall. It occurs after seven days of fertilization.

Yes, i do agree with the fact that breastfeeding is the best for newborn babies.

Mammary glands start producing milk at the end of pregnancy. The milk produced during the initial few days and lactation is called COLOSTRUM which contains several antibodies.

It helps in developing resistance for a newborn baby. It helps the baby fight of viruses and bacteria. Thus breast milk is packed with a disease-fighting substance that protects your baby from illness.

Breast milk also naturally contains many of the vitamins and minerals that a newborn requires. Also, it is easily digested - no constipation, diarrhoea and upset stomach.