Topic 11.4: Reproduction

Question 1

What is label A?

Answer 1

Spermatozoa

Question 2

What is label B?

Answer 2

Germline epithelium

Question 3

What is label C?

Answer 3

Sertoli cells

Question 4

What is label D?

Answer 4

Leydig cells

Question 5

What is the function of the testes and what are they composed of?

Answer 5

The testes are composed of seminiferous tubules which produce sperm

Question 6

What does the germline epithelium cells line and what will they divide to make?

Answer 6

Each tubule is surrounded by a basement membrane which is lined by germline epithelium cells

The germline epithelium will divide by mitosis to make spermatogonia

Question 7

What will spermatogonia divide by to make?

Answer 7

spermatogonia (which divide by meiosis to make spermatozoa)

Question 8

What are spermatozoa nourished by?

Answer 8

The developing spermatozoa are nourished by Sertoli cells

Question 9

What is the function of leydig cells?

Answer 9

Outside of the tubules are blood capillaries and interstitial cells (Leydig cells), which produce the male sex hormone, testosterone

Question 10

Outline the processes involved in spermatogenesis within the testes, including mitosis, cell growth, the two divisions of meiosis and cell differentiation (6)

Answer 10

Spermatogenesis describes the production of spermatozoa (sperm) in the seminiferous tubules of the testes

The first stage of sperm production requires the division of germline epithelium by mitosis

These cells (spermatogonia) then undergo a period of growth

This is followed by two meiotic divisions that result in four haploid daughter cells

These haploid cells then differentiate to form sperm cells

The developing sperm cells are nourished throughout by the Sertoli cells

Question 11

What is the role of LH in spermatogenesis?

Answer 11

LH: Stimulates the interstitial cells (Leydig cells) to produce testosterone

Question 12

What is the role of testosterone in spermatogenesis?

Answer 12

Testosterone: Stimulates the (second) meiotic division of spermatogonia and the maturation of spermatozoa through differentiation

Question 13

What is the role of FSH in spermatogenesis?

Answer 13

FSH: Stimulates the (first) meiotic division of spermatogonia

Question 14

What is label A?

Answer 14

corpus albicans

Question 15

What is label B?

Answer 15

corpus luteum

Question 16

WHat is label C?

Answer 16

secondary oocyte

Question 17

What is label D?

Answer 17

Mature (Graafian) follicle

Question 18

What is label E?

Answer 18

Germline epithelium

Question 19

What is label F?

Answer 19

Primordial follicles

Question 20

function of germline epithelium, primordial follicles, mature follicles and secondary oocyte (5)

Answer 20

The ovary contains follicles in various stages of development

Egg cells within primordial follicles have been arrested in prophase I and have yet to undergo meiotic division

Egg cells within mature follicles have begun meiotic division and are released from the ovary as secondary oocytes (arrested in prophase II)

The ruptured follicle develops into a corpus luteum that will, in time, degenerate into a corpus albicans

The germline epithelium functions as an epithelial layer separating ovarian tissue from the rest of the body - it is not involved in oocyte development

Question 21

Outline the processes involved in oogenesis within the ovary, including mitosis, cell growth, the two divisions of meiosis, the unequal division of cytoplasm and the degeneration of polar body (9)

Answer 21

Oogenesis describes the production of female gametes (ova) within the ovary

The process begins during foetal development, when a large number of cells (oogonia) are formed by mitosis before undergoing a period of growth

These cells begin meiosis but are arrested in prophase I until puberty

At puberty, some follicles continue to develop each month is response to FSH secretion

These follicles complete the first meiotic division to form two cells of unequal size

The cell with less cytoplasm is a polar body (which degenerates), while the larger cell forms a secondary oocyte

The secondary oocyte begins the second meiotic division but is arrested in prophase II (until fertilisation)

It is released from the ovary (ruptured follicle develops into corpus luteum) and, if fertilisation occurs, will complete meiosis

The second meiotic division will produce an ovum and a second polar body

Question 22

WHat is label A?

Answer 22

acrosome

Question 23

what is label B?

Answer 23

nucleus

Question 24

WHat is label C?

Answer 24

centriole

Question 25

What is label D?

Answer 25

mitochondria

Question 26

WHat is label E?

Answer 26

microtubules

Question 27

What is label F?

Answer 27

cortical granules

Question 28

What is label G?

Answer 28

zona pellucida (jelly coat)

Question 29

WHat is label H?

Answer 29

plasma membrane

Question 30

What is label I?

Answer 30

cytoplasm

Question 31

What is label J?

Answer 31

nucleus

Question 32

What is label K?

Answer 32

corona radiata (layer of cells which nourish egg)

Question 33

Outline the role of the epididymis in the production of semen (2)

Answer 33

Epididymis

Testicular fluids are removed, concentrating the sperm

Sperm mature and develop the ability to swim

Question 34

Outline the role of the seminal vesicle in the production of semen (2)

Answer 34

Seminal Vesicle

Adds nutrients (including fructose) for respiration

Secretes prostaglandins, causing contractions to the female system and helping sperm move towards the egg

Question 35

Outline the role of the prostate gland in the production of semen

Answer 35

Prostate Gland

Secretes alkaline fluid which neutralises vaginal acids (changes pH from 4 to 6 which aids sperm motility)

Question 36

What are two similarities between spermatogenesis and oogenesis?

Answer 36

Both processes result in the formation of haploid gametes

Both processes involve mitosis, growth and meiosis

Question 37

What is the difference in location between spermatogenesis and oogenesis?

Answer 37

spermatogenesis is in the testis; oogenesis is in the ovary

Question 38

What is the difference in number of gametes produced between spermatogenesis and oogenesis?

Answer 38

s- life long production (millions); o- fixed amount (only about 400 mature)

Question 39

What is the difference in gametes per germ cell between spermatogenesis and oogenesis?

Answer 39

s- 4; o- 1

Question 40

What is the difference in beginning of process between spermatogenesis and oogenesis?

Answer 40

s- begins at puberty; o- begins during fetal development

Question 41

What is the difference in timing of gamete formation between spermatogenesis and oogenesis?

Answer 41

s- continuous (any time); o- once a month (menstrual cycle)

Question 42

What is the difference in end of process between spermatogenesis and oogenesis?

Answer 42

s- fertility is life long but reduces; o- fertility stops at menopause

Question 43

What is the difference in timing of gamete release between spermatogenesis and oogenesis?

Answer 43

s- any time; o- monthly cycle

Question 44

What is the difference in meiotic divisions between spermatogenesis and oogenesis?

Answer 44

s- uninterrupted; o= arrested

Question 45

What is the difference in germ line epithelium between spermatogenesis and oogenesis?

Answer 45

s- involved in gamete production; o- not involved in gamete production

Question 46

Describe the process of fertilisation, including the acrosome reaction, penetration of the egg membrane by a sperm and the cortical reaction (10)

Answer 46

When the sperm enters the female reproductive tract, biochemical changes to the sperm occur in the final part of its maturation (capacitation)

The sperm is attracted to the egg due to the release of chemical signals from the secondary oocyte (chemotaxis)

Fertilisation generally occurs in the oviduct (fallopian tube)

To enter the egg membrane, the sperm must penetrate the protective jelly coat (zona pellucida) surrounding the egg via the acrosome reaction

The acrosome vesicle fuses with the jelly coat and releases digestive enzymes which soften the glycoprotein matrix

The membrane of the egg and sperm then fuse and the sperm nucleus (and centriole) enters the egg

To prevent other sperm from penetrating the fertilised egg (polyspermy), the jelly coat undergoes biochemical changes via the cortical reaction

The cortical granules release enzymes that destroy the sperm-binding proteins on the jelly coat

Now fertilised, the nucleus of the secondary oocyte completes meiosis II and then the egg and sperm nuclei fuse to form a diploid zygote

Question 47

Outline the role of hCG in early pregnancy (5)

Answer 47

The endometrium is a blood-rich environment in which an implanted zygote can grow and it is sustained by the hormone progesterone

If progesterone levels aren’t maintained (i.e. the corpus luteum degenerates), then the endometrium will be sloughed away (menstruation)

A fertilised zygote develops into a blastocyst that secretes human chorionic gonadotrophin (hCG)

hCG maintains the corpus luteum post-ovulation so that the blastocyst can remain embedded in the endometrium and continue to develop

Gradually the placenta develops and produces progesterone (at around 8 - 10 weeks), at which point the corpus luteum is no longer needed

Question 48

Outline early embryo development up to the implantation of the blastocyst

Answer 48

After fertilisation, the zygote undergoes several mitotic divisions to create a solid ball of cells called a morula (at around 4 days)

Unequal divisions beyond this stage cause a fluid-filled cavity to form in the middle - this makes a blastocyst (at around 5 days)

The blastocyst consists of:

An inner mass of cells (this will develop into the embryo)

An outer layer called the trophoblast (this will develop into the placenta)

A fluid filled cavity (called the blastocoele)

These developments all occur as the developing embryo is moving from the oviduct to the uterus

When the blastocyst reaches the uterus, it will embed in the endometrium (implantation)

Question 49

Explain how the structure and function of the placenta maintain pregnancy (6)

Answer 49

The placenta is a disc-shaped structure that nourishes the developing embryo

It is formed from the development of the trophoblast upon implantation and eventually invades the uterine wall

The umbilical cord connects the fetus to the placenta and maternal blood pools via open ended arterioles into intervillous spaces (lacunae)

Chorionic villi extend into these spaces and facilitate the exchange of materials between the maternal blood and fetal capillaries

Nutrients, oxygen and antibodies will be taken up by the fetus, while carbon dioxide and waste products will be removed

The placenta is expelled from the uterus after childbirth

Question 50

Explain how the hormonal role in secretion of estrogen and progesterone, maintain pregnancy (4)

Answer 50

The placenta also takes over the hormonal role of the ovary (at around 12 weeks)

Estrogen stimulates growth of the muscles of the uterus (myometrium) and the development of the mammary glands

Progesterone maintains the endometrium, as well as reduces uterine contractions and maternal immune response (no antibodies against fetus)

Both estrogen and progesterone levels drop near time of birth

Question 51

State that the fetus is supported and protected by the amniotic sac and amniotic fluid (4)

Answer 51

The fetus develops in a fluid-filled space called the amniotic sac

Amniotic fluid is largely incompressible and good at absorbing pressure, and so protects the child from impacts to the uterine wall

The fluid also creates buoyancy so that the fetus does not have to support its own body weight while the skeletal system develops

Finally, amniotic fluid prevents dehydration of the tissues, while the amniotic sac provides an effective barrier against infection

Question 52

WHat materials are exchanged from the maternal blood to the fetal supply? (9)

Answer 52

oxygen, glucose, lipids, water, minerals, vitamins, antibodies, hormones, amino acids

Question 53

What materials are exchanged from the fetal blood to the maternal blood? (4)

Answer 53

carbon dioxide, urea, hormones, water

Question 54

utline the process of birth and its hormonal control, including the changes in progesterone and oxytocin levels and positive feedback (9)

Answer 54

The process of childbirth is called parturition and is controlled by the hormone oxytocin

After nine months, the fetus is fully grown and takes up all available space in the uterus, stretching the walls of the uterus

This causes a signal to be sent to the brain, releasing oxytocin from the posterior pituitary

Oxytocin inhibits progesterone, which was inhibiting uterine contractions

Oxytocin also directly stimulates the smooth muscle of the uterine wall to contract, initiating the birthing process

The contraction of the uterine wall causes further stretching, which triggers more oxytocin to be released (causing even more contraction)

Additionally, the fetus responds to the cramped conditions by releasing prostaglandins which cause further myometrial contractions

As the stimulus causing oxytocin release is increased by the effects of oxytocin, this creates a positive feedback pathway

Contractions will stop when labour is complete and the baby is birthed (no more stretching of the uterine wall)