1. Reproduction Structure of the Testis Under a light microscope the
testes are seen to consist of a
network of seminiferous
tubules, in between which
are interstitial cells, cells of
Leydig and blood capillaries.
Development of spermatozoa
takes place from the outside
of the tubule. Once they have
differentiated, spermatozoa
are nourished by Sertoli cells.
They leave the tubule via the
lumen.

2. Spermatogenesis Spermatogenesis is the process of producing spermatozoa and involves mitosis, meiosis and cell differentiation. Mitosis produces large numbers of spermatogonia. These grow into primary spermatocytes. These undergo the first meiotic division to produce secondary spermatocytes. These undergo the second meiotic division to become spermatids. These have the correct amount of DNA, but must first differentiate and mature into spermatozoa. This final maturation takes place with the aid of the Sertoli cells. Animation: Spermatogenesis (Quiz 2)

3. Hormonal control of Spermatogenesis FSH – produced in the pituitary gland. - stimulates sperm production in the seminiferous tubules. - stimulates division and maturation of Sertoli cells. LH – produced in the pituitary gland - stimulates the interstitial cells (Leydig cells) to produce testosterone. Testosterone – promotes spermatogenesis. The Ovaries The ovaries contain follicles in different stages of development. Each follicle contains developing oocytes. As well as producing oocytes, the ovaries secrete the female sex hormones oestrogen and progesterone.

4. Ovary – cross section

5. Oogenesis Oogenesis is the development of egg cells
Oogenesis Oogenesis is the development of egg cells. It involves mitosis, cell growth, and meiosis. Mitosis produces oogonia which grow into primary oocytes. The first meiotic division produces one secondary oocyte and a polar body. The polar body contains DNA but very little cytoplasm – most cell material goes into the secondary oocyte. The second meiotic division of the oocyte produces the ovum and another polar body. The original polar body also divides. The three resulting polar bodies degenerate. This second meiotic division only takes place after the ovum has been fertilised in the fallopian tube.

6. Mature sperm cell.
The acrosome contains enzymes needed to
penetrate the tough outer layer of the ovum
the zona pellucida. The rest of the head
contains the genetic information in the
nucleus.
The midpiece contains many mitochondria
needed to power the tail.
Mature egg.
Just inside the plasma membrane of the egg are
cortical granules containing enzymes that will be
released at fertilisation.
There is also a jelly coat just outside the zona
pellucida which contains protein receptors.

7. Role of the epididymis, prostate and seminal vesicles
Role of the epididymis, prostate and seminal vesicles. Sperm cells produced in the seminiferous tubules travel to the epididymis where they finish maturation and become motile. Fluid from the Sertoli cells is reabsorbed so that the sperm are concentrated. Only 10% of the semen ejaculated is made up of sperm cells. Most of the fluid part of the semen is produced by the seminal vesicles. The fluid they contribute contains fructose for energy and prostaglandins which cause contractions of the female system. These help the sperm move towards the fallopian tubes. Fluid produced in the prostate is alkaline and this helps to neutralise the acidic environment in the female reproductive tract. The presence of the prostate secretion raises the pH from 4 to 6, which is the optimum pH for sperm motility. Cowper’s gland produces a small volume of clear fluid which plays a role in lubrication.

8. Comparison of Spermatogenesis and Oogenesis.
1. Differences
2. Similarities
Both produce haploid gametes by meiosis
Both occur in the gonads
Both start at puberty and are controlled by hormones
Spermatogenesis
Oogenesis
No. of gametes produced
Very large no. of spermatozoa
Limited number of ova
No of gametes produced from one germ cell
Four
One
Time of formation from puberty
Continuously
Once a month
Time span of production
Does not stop
Stops at menopause
Release of gametes
Any time
Monthly cycle

9. Fertilization Refers to the fusion of the sperm and the egg
Fertilization Refers to the fusion of the sperm and the egg. When the secondary oocyte is released at ovulation, it is surrounded by two layers – the corona radiata (layer of follicle cells) and the zona pellucida – an amucoprotein (complex of protein and polysaccharide). If a sperm cell touches the cells of the corona radiata, the membrane of the acrosome fuses with the membranes of the follicle cells, releasing the proteolytic enzyme which digests the follicle cells. This is called the acrosome reaction. The head of the sperm can now penetrate this layer. Fertilization: A Sweet Love Story - YouTube The sperm cell reaches the zona pellucida. Within its thick, jelly layer are receptors which bind to the sperm cell, allowing it to pass through. The head of the sperm fuses with the membrane of the secondary oocyte and the cortical granules release enzymes to thicken the zona pellucida to form a thick barrier which cannot be penetrated by other sperm cells. This is called the cortical reaction and ensures that the ovum can only be fertilized by one sperm cell.

10. Early Pregnancy About 8 days after fertilization, the blastocyst (bundle of about 64 diploid cells produced by mitosis of the zygote) embeds itself into the endometrium. The outer cells of the blastocyst – trophoblast cells – start to secrete human chorionic gonadotrophin hormone, HCG. This hormone sustains the corpus luteum, allowing it to continue to produce progesterone. This will ensure that the thick wall of the endometrium is maintained. From Fertilization to Implantation – YouTube In time, the placenta starts to secrete progesterone and after about 10 weeks of pregnancy, the corpus luteum is no longer needed. HCG is secreted in urine and is used to detect pregnancy. A pregnancy stick contains an area of antibodies against the HCG which have pigment attached. As the urine flows up the stick due to capillary action, the HCG attaches to the antibodies and picks up the pigment. Further up the stick, a second group of antibodies are fixed in a line. When the HCG/antibody complex reaches this group of antibodies, they react, and a blue line forms. Early embryo development Shortly after fertilization, the haploid male and female gametes line up across the equator and undergo their first mitotic division. The division is not followed by growth and is called a cleavage division.

11. Further cleavage divisions lead to the formation of a ball of cells called the morula, which reaches the uterus about 4 days after fertilization. Slightly unequal divisions follow, causing a fluid filled space to form in the middle. The structure is now referred to as a blastocyst and will implant in the endometrium about 7-8 days after fertilization. As implantation occurs, the trophoblast grows trophoblastic villi into the endometrium and will absorb nutrients from it. This is an adequate supplier for about two weeks, after which the placenta takes over.

12. Placenta structure and function In the placenta, oxygen and glucose from the mother’s blood diffuse into the baby’s blood, and CO2 and other waste, including urea, diffuse from the baby’s blood to the mother. Mineral ions and amino acids are actively transported across the placenta, and water follows by osmosis. Antibodies cross freely so that the baby is initially protected from infection.

13. The placenta is a barrier to bacteria, however, some viruses can cross it. The mother and foetus each have their own blood and circulation. Materials are exchanged, but the blood does not mix. Often, babies have different blood groups to their mother. Between the first two and ten or so weeks of pregnancy, HCG is secreted by the placenta. Its role is to maintain the corpus luteum, which continues to produce progesterone and estrogen in order to maintain the thick lining of the uterus. After about 16 weeks, the corpus luteum breaks down and the placenta takes over the function of estrogen and progesterone production. Progesterone helps to maintain the pregnancy by reducing coordinated contractions of the uterus and by reducing the mother’s immune response so that antibodies against the baby are not produced. Estrogen stimulates the growth of the uterine muscles and the mammary glands. Estrogen and progesterone levels drop at the time of birth, which allows lactation (previously inhibited by progesterone). The role of the amniotic sac and fluid. The foetus is surrounded by amniotic fluid contained within the amniotic sac. The fluid protects the foetus from bumps. Later in pregnancy, the baby drinks the fluid and urinates in it. It is constantly filtered and replenished by the mother.

14. The hormonal control of birth
The hormonal control of birth. 38 weeks after conception, the baby is ready to be born. Progesterone levels fall and this leads to coordinated contractions which start at the top of the uterus and work down to the cervix. The posterior pituitary releases oxytocin which relaxes the fibres that join the bones of the pelvis. Oxytocin also stimulates contractions. The pushing of the baby’s head against the cervix leads to further release of oxytocin, which leads to further contractions. This positive feedback loop continues until the cervix is fully dilated. This signals the end of labour and expulsion begins. The first stage of birth, labour, can take many hours but expulsion is usually quite fast. Powerful contractions push the baby out of the uterus. Residual contractions push the placenta from the uterine wall and the feedback loop involving oxytocin is broken. That, my friends, is all.