D3.1 Reproduction HL(only human)

Question 1

Which hormone produced by the hypothalamus affects the production of FSH and LH in the pituitary gland?

Answer 1

Gonadotrophin releasing hormone (GnRH)

Question 2

What is the pituitary gland?

Answer 2

A gland located at the base of your brain.

Question 3

How does the hypothalamus control the secretion of the hormones made in the anterior pituitary gland?

Answer 3

The hypothalamus sends a hormone to the target cells that makes them receptive to hormones produced by the anterior pituitary gland?

Question 4

Which hormone(s) secreted by the posterior pituitary gland increase the sex hormone production in male and female reproductive systems?

Answer 4

FSH and LH

Question 5

What is the effect of estradiol (oestrogen) and testosterone on puberty?

Answer 5

It is going to cause the secondary sexual characteristics in male and females

Question 6

What are the secondary sexual characteristics in human females during puberty?

Answer 6

Question 7

What are the secondary sexual characteristics in human males during puberty?

Answer 7

Question 8

What is Gametogenesis?

Answer 8

Is the formation of haploid gametes, occurs through meiosis and is an integral aspect of sexual reproduction.

Question 9

What are the two types of gametogenesis?

Answer 9

Gametogenesis in males is referred to as Spermatogenesis and in females, as Oogenesis. While the basic mechanism in both the processes remains the same, there are variations in the numbers of sperm and eggs produced in each cycle.

Question 10

What are the three phases in both Oogenesis and Spermatogenesis?

Answer 10

multiplication phase, growth phase, maturation phase

Question 11

What happens in Oogenesis and Spermatogenesis? (diagram)

Answer 11

Question 12

When does Spermatogenesis occur?

Answer 12

Spermatogenesis in males occurs with the onset of puberty.

Question 13

What are the sites of sperm production?

Answer 13

Within each testis are the highly coiled seminiferous tubules – these are the sites for sperm production.

Question 14

Where is testosterone produced?

Answer 14

Between the seminiferous tubules are the Leydig (interstitial cells) cells, which produce testosterone.

Question 15

What are basement membrane lined with?

Answer 15

The basement membranes are lined by the spermatogonia.

Question 16

What are the different phase of spermatogenesis?

Answer 16

1. Spermatogonia to primary spermatocytes (multiplication phase)
2. Primary spermatocyte to secondary spermatocyte (growth phase)
   3.Secondary spermatocyte to spermatids (maturation phase)
   4.Spermatid to sperm (spermiogenesis)

Question 17

What happens during the multiplication phase(spermatogonia to primary spermatocytes) of spermatogenesis?

Answer 17

The spermatogonia are diploid cells (2n) and have 44 autosomes and two sex chromosomes. Spermatogonia divide mitotically to produce more cells. Some of these cells continue dividing, others move away from the basement membrane and differentiate to form the primary spermatocyte. The primary spermatocyte is a diploid cell.

Question 18

What happens during the growth phase(primary spermatocytes to secondary spermatocytes) of spermatogenesis?

Answer 18

Primary spermatocytes undergo the first meiotic division to produce the secondary spermatocytes. A single primary spermatocyte (2n) produces two secondary spermatocytes (n), each with 22 autosomes and either an X or a Y sex chromosome. Crossing over and independent assortment of chromosomes brings in genetic variation.

Question 19

What happens during the maturation phase(secondary spermatocytes to spermatids) of spermatogenesis?

Answer 19

Each secondary spermatocyte completes the second meiotic division to produce two spermatids. There is no change in the chromosome number, that is, both the secondary spermatocyte and the spermatids are haploid.

Question 20

What happens during spermiogenesis (spermatids to sperm) of spermatogenesis?

Answer 20

The spermatids undergo differentiation to form the sperm or spermatozoa. The process, called spermiogenesis, is supported by the secretions of the Sertoli cells of the seminiferous tubules.

Question 21

When does Oogenesis occur?

Answer 21

Unlike in males, the process of oogenesis begins during foetal development.

Question 22

What is the beginning of Oogenesis?

Answer 22

Oogenesis begins with diploid oogonia. The oogonia undergo mitosis. Some of the oogonia develop to form primary oocytes. The diploid primary oocyte begins meiosis I; however, this is arrested at prophase 1. At the time of birth, each ovary has numerous follicles each containing primary oocytes. Many of these follicles degenerate from birth to puberty.

Question 23

What happens after the onset of puberty in oogenesis?

Answer 23

The onset of puberty marks the beginning of the menstrual cycle. Under the influence of the hormones, many of the follicles start growing; however, only one matures. The primary oocyte now competes the first meiotic division resulting in formation of two haploid cells. Due to unequal division of the cytoplasm, these cells differ in size and are termed as the secondary oocyte (n) and the first polar body (n). The first polar body disintegrates. The secondary oocyte begins meiosis II but this is arrested at metaphase II. At the time of ovulation, the secondary oocyte is released from the ovary.

Question 24

What happens after fertilisation in oogenesis?

Answer 24

If fertilisation occurs, the secondary oocyte (n) completes meiosis II forming the ovum (n) and the second polar body (n). If fertilisation does not occur, the secondary oocyte is discharged from the body during the menstrual flow.

Question 25

What are the differences between spermatogenesis and oogenesis?

Answer 25

Question 26

What is role of testosterone? Where is it secreted? How is the secretion controlled?

Answer 26

Testosterone is the primary male hormone. It is secreted by the testes. The secretion of testosterone is controlled by a negative feedback mechanism that involves the hypothalamus and the anterior pituitary.

Question 27

How do the levels of testosterone change in a life time and why?

Answer 27

The level of testosterone remains fairly low in early childhood. Puberty is initiated by the release of gonadotropin-releasing hormone (GnRH) by the hypothalamus.

Question 28

What is the role of gonadotropin-releasing hormonre (GnRH)?

Answer 28

GnRH, in turn, acts on the anterior pituitary, stimulating the release of follicle-stimulating hormone (FSH) and luteinising hormone (LH). Both LH and FSH are carried by the blood to the testes.

Question 29

What is the role of LH and FSH in male hormones?

Answer 29

LH stimulates the release of testosterone by the Leydig cells while FSH plays a role in the production of sperm by stimulating the Sertoli cells.

Question 30

What does a surge of testosterone lead to?

Answer 30

The surge in the level of testosterone leads to the development of secondary sexual characteristics like growth of reproductive organs, an increase in height and musculature, deepening of the voice and development of hair – particularly on the face, underarms and pubic region.

Question 31

What happens when levels of testosterone in the bloodstream increase?

Answer 31

As the levels of testosterone in the bloodstream increase, the release of GnRH from the hypothalamus is inhibited, which, in turn, inhibits release of FSH and LH by the anterior pituitary. Testosterone acts directly on the anterior pituitary too. Inhibin secreted by the Sertoli cells also inhibits the production of FSH.

Question 32

What are the steroid hormones in women? And where are they secreted from?

Answer 32

In females, steroid hormones – including oestradiol and progesterone – are the primary female hormones secreted by the ovaries.

Question 33

Why causes puberty occur in females?

Answer 33

As in males, puberty in females begins with GnRH stimulating the release of FSH and LH from the anterior pituitary. These, in turn, cause release of the female sex hormone.

Question 34

What is the negative and positive feedback loop for hormones?

Answer 34

Question 35

What onsets the development of secondary sexual characteristics in females?

Answer 35

An increase in the level of oestradiol leads to the development of secondary sexual characteristics in females like maturation of the ovaries, development of the breasts and development of body hair, as well as the onset of the menstrual cycle.

Question 36

How does the sperm bind to the egg?

Answer 36

Millions of sperm enter the female reproductive system. The sperm that eventually manage to reach the vicinity of the egg have to traverse through the jelly-like zona pellucida. They begin the journey by binding to specific binding sites on the zona pellucida. Then the hydrolytic enzymes released by the acrosome digest and soften the layer, helping the sperm to push their way through. This is known as the acrosome reaction.

Question 37

What is the acrosome reaction?

Answer 37

Hydrolytic enzymes released by the acrosome digest and soften the zona pellucida, assisting fertilisation.

Question 38

What is the polyspermy?

Answer 38

Polyspermy is the fusion of more than one sperm with the egg, resulting in a non-viable zygote. The egg needs to be safeguarded against polyspermy.

Question 39

What mechanism have been put in place to prevent polyspermy?

Answer 39

• The plasma membrane of the fertilised egg becomes impermeable to the entry of sperm due to changes in the membrane potential.
• The cortical granules fuse with the plasma membrane and release their contents into the space between the plasma membrane and the zona pellucida by exocytosis. This is known as the cortical reaction and has a two-fold effect. The enzymes of the cortical granules destroy the sperm receptors on the zona pellucida preventing the binding of other sperm. In addition, the zona pellucida hardens, stopping the sperm from moving towards the egg.

Question 40

What is the result of fertilization?

Answer 40

Fertilisation results in the formation of a single-celled diploid zygote.

Question 41

What happens after fertilization to the zygote?

Answer 41

After fertilization, the zygote and the membranes that surround it, are moved towards the uterus by the cilia found in the Fallopian tube. During its journey to the uterus, the zygote undergoes five or six rapid mitotic cell divisions but does not increase in size. Each daughter cell produced by cleavage is called a blastomere (blastos = “germ,” in the sense of a seed or sprout).

Question 42

What happens approx. 3 days after fertilization?

Answer 42

Approximately 3 days after fertilization, a 16-cell embryo reaches the uterus. The cells that had been loosely grouped are now compacted and look more like a solid mass. The name given to this structure is the morula (morula = “little mulberry”). Once inside the uterus, the embryo floats freely for several more days. It continues to divide, creating a ball of approximately 100 cells. The uterus wall is thickening during this time.

Question 43

What happens after day 4 to the zygote?

Answer 43

Around Day 4, the dividing cells rearrange themselves to form two layers: an outer trophoblast and the inner cell mass. A fluid-filled cavity develops in the centre called the blastocoel. At this point the embryo is known as a blastocyst. It would help you to remember that while the morula is a solid ball of 16 cells, the blastocyst is a hollow ball of 32 cells.

Question 44

What is a blastocyst?

Answer 44

The ball of now tightly bound cells starts to secrete fluid and the cells organize themselves around a fluid-filled cavity, called the blastocoel. This developmental stage, is referred to as a blastocyst.

Question 45

What is a trophoblast? And do they develop?

Answer 45

Within this structure, a group of cells forms into an inner cell mass, which will become the embryo. The cells that form the outer shell are called trophoblasts (trophe = “to feed” or “to nourish”). These cells will develop into the chorionic sac and the foetal portion of the placenta (the organ of nutrient, waste, and gas exchange between mother and the developing offspring).

Question 46

What happens to trophoblast and inner cell mass?

Answer 46

The trophoblast will eventually differentiate into structures that would help in the attachment or implantation of the embryo to the endometrium of the uterus. The inner mass of embryonic cells is totipotent during this stage, meaning that each cell has the potential to differentiate into any cell type in the human body. Totipotency lasts for only a few days before the cells’ fates are set as being the precursors to a specific cell line.

Question 47

What happens to blastocyst at the end of the first week after fertilisation?

Answer 47

The blastocyst now sheds the zona pellucida in a process called hatching. At the end of the first week, the blastocyst comes in contact with the uterine wall (endometrium) and adheres to it, embedding itself in the uterine lining via the trophoblast cells. This is the beginning of the process of implantation, which signals the end of the pre-embryonic stage of development. Implantation can be accompanied by minor bleeding.

Question 48

What happens to blastocyst if it doesn’t attached to uterine wall?

Answer 48

The blastocyst typically implants in the fundus of the uterus or on the posterior wall. However, if the endometrium is not fully developed and ready to receive the blastocyst. A significant percentage (50–75 percent) of blastocysts fail to implant; when this occurs, the blastocyst is shed with the endometrium during menstruation. The high rate of implantation failure is one reason why pregnancy typically requires several ovulation cycles to be successfully achieved.

Question 49

What happens when an implantation is successful?

Answer 49

When implantation is successful and the blastocyst adheres to the endometrium, the superficial cells of the trophoblast fuse with each other, forming a multinucleated body that digests endometrial cells to firmly secure the blastocyst to the uterine wall. In response, the uterine mucosa rebuilds itself and envelops the blastocyst.

Question 50

What stop the break down of the corpus luteum to keep endometrial lining, after fertilisation?

Answer 50

Soon after implantation, the cells of the trophoblast (that will eventually form the placenta), start secreting a hormone called human chorionic gonadotropin (hCG). This hormone maintains, enlarges the corpus luteum so that it continues to secrete progesterone and estrogen to suppress menstruation. These functions of hCG are necessary for creating an environment suitable for the developing embryo. As a result of this increased production, hCG accumulates in the maternal bloodstream and is excreted in the urine. Implantation is complete by the middle of the second week. By the third month, the placenta takes over the role of the corpus luteum and starts secreting progesterone and oestradiol needed for maintaining the pregnancy.

Question 51

How do pregnancy kit work?

Answer 51

Pregnancy test kits are designed to detect the presence of hCG in a woman’s urine. The test kit consists of a pregnancy test stick coated with monoclonal antibodies specific to hCG. When a woman urinates onto the pregnancy stick, hCG – if present in her urine – binds to the monoclonal antibodies on the stick. This results in a change in the colour indicating a positive pregnancy. A few days after implantation, the embryo (trophobalst) secretes enough hCG to give a positive pregnancy test.

Question 52

What happens once the blastocyst has implanted?

Answer 52

Once the blastocyst is implanted, the extraembryonic membrane starts forming.

Question 53

What are the two structures that the extraembryonic membrane form?

Answer 53

One of the extraembryonic membranes forms the umbilical cord. Yet another forms the chorion.

Question 54

What is an umbilical cord?

Answer 54

A rope-like structure attaching the foetus to the placenta, enabling the movement of food and oxygen from the mother to the foetus.(At start connects the embryo to the wall of the uterus)

Question 55

What forms by the 14th day to the extraembryonic membrane? And what does this represent?

Answer 55

By the 14th day, the chorionic villi (finger-like projections of the chorion) start forming. These represent the beginning of the placenta.

Question 56

What is the placenta?

Answer 56

The placenta is a spongy tissue composed of both maternal tissue and embryonic tissue that begins to form by the fourth week of pregnancy. All the exchanges between the mother and embryo take place through the placenta.

Question 57

What is the maternal portion of the placenta?

Answer 57

The maternal portion of the placenta is the uterine endometrium.

Question 58

What is the embryonic portion of the placenta?

Answer 58

The embryonic portion of the placenta is the chorionic villi or the finger-like projections of the chorion.

Question 59

How does the maternal blood interact with the embryonic portion of the placenta?

Answer 59

The chorionic villi extend into the intervillous space and increase the surface area. Maternal blood from the open endometrial arteries pools in the intervillous spaces (and of course, returns by the endometrial veins). Thus the chorionic villi are bathed in maternal blood. It is important to remember that while the chorionic villi are surrounded by maternal blood, the maternal and foetal circulatory systems are not connected.

Question 60

How does the foetus obtain oxygen and nutrients?

Answer 60

The maternal blood is rich in oxygen and nutrients. These diffuse from the maternal blood that collects in the intervillous spaces to the foetal blood vessels in the chorionic villi of the placenta. The oxygen and nutrients then travel down the umbilical cord, entering the foetal circulation. Waste and carbon dioxide produced by the developing embryo travel from the umbilical blood vessels to the placenta. Here they diffuse into the maternal blood present in the intervillous space of the placenta. These waste products are then removed by the mother.

Question 61

Apart from its role in exchange of material between the mother and the foetus, what is the other role of the placenta?

Answer 61

The placenta acts as an endocrine gland secreting progesterone and oestradiol to maintain the pregnancy.

Question 62

Why are these such differences between pregnancies in these groups of mammals?

Answer 62

In placental mammals, the growing foetus is nourished by the placenta. This, in turn, permits a longer pregnancy ensuring that the offspring completes most of its development within the uterus. On the other hand, marsupials do not have a placenta and hence the offspring is born immature.

Question 63

When is the term embryo and foetus used during pregnancy?

Answer 63

The term embryo is used until about 11 weeks of pregnancy; thereafter the term foetus is used.

Question 64

How long does a typical pregnancy in humans last?

Answer 64

A typical pregnancy lasts for 40 weeks

Question 65

What is parturition or childbirth?

Answer 65

Parturition or childbirth is the process by which the foetus is expelled from the body.

Question 66

What hormone maintains pregnancy? And what is it’s role?

Answer 66

Pregnancy is maintained by progesterone that is initially secreted by the corpus luteum and later by the placenta. The progesterone prevents uterine contractions.

Question 67

What happens to the levels of progesterone at the seventh month of pregnancy?

Answer 67

By the seventh month of pregnancy, in anticipation of the eventual expulsion of the baby, the levels of progesterone plateau and then start declining.

Question 68

What does the growth of the baby cause around the seventh month?

Answer 68

The growth of the baby causes the walls of the uterus to stretch. The stretch is detected by receptors present on the uterine wall.

Question 69

What doe the stretch of the uterine wall in the seventh month cause?

Answer 69

The stretching of the uterus exerts a physical stress on both the baby and the mother, causing the secretion of stress hormones like cortisol.

Question 70

What does the rise in stress hormones like cortisol cause?

Answer 70

The rise in the levels of stress hormones stimulates the release of an oestrogen called oestriol.

Question 71

What is the role of the hormone oestriol, in pregnancy?

Answer 71

Oestriol inhibits the production of progesterone by the placenta. It also makes the smooth muscles of the uterus more receptive to oxytocin.

Question 72

What happens when oxytocin is released during pregnancy?

Answer 72

When oxytocin is released, by the posterior pituitary, it causes uterine contraction initiating parturition. The foetus responds by secreting prostaglandins, which, in turn, intensifies the uterine contraction. This causes the posterior pituitary to release more oxytocin. Thus a positive feedback loop eventually leads to the expulsion of the baby down the birth canal and out of the body and pushing out of the placenta.

Question 73

What is the onset of menopause marked by?

Answer 73

The onset of menopause is marked by a decrease in the levels of oestradiol and progesterone. This results in a range of physical symptoms like hot flashes and vaginal dryness.

Question 74

What is Hormone Replacement Therapy or HRT?

Answer 74

Hormone replacement therapy or HRT is a treatment that relieves the symptoms of menopause. In HRT, the person undergoing treatment is given medication that contains low doses of oestradiol or a combination of oestradiol-progestin (progestin is a synthetic derivative of progesterone). Current research is still ambiguous on the benefits of HRT.