Sexual reproduction in Human beings

Learning outcomes Identify on diagrams of the male reproductive system and give the functions of testes, scrotum, sperm ducts, prostate gland, urethra and penis Identify on diagrams of the female reproductive system and give the functions of ovaries, oviducts, uterus, cervix and vagina Compare male and female gametes in terms of size, numbers and mobility Describe the menstrual cycle with reference to the alternation of menstruation and ovulation, the natural variation in its length, and the fertile and infertile phases of the cycle

Learning outcomes: Describe fertilisation and early development of the zygote simply in terms of the formation of ball of cells which becomes implanted in the wall of uterus

Male reproductive organ

The male reproductive system Testes (testis) Organ that produce the gametes and male sex hormone (testosterone) The testis constantly divide to produce up to 100,000,000 sperms per day. The testis work more efficiently at just below body temperature, so they are held outside the body in scrotum.

The male reproductive system Storage duct/ epididymis Sperms are stored in the storage duct temporarily in an inactive form before it enters the sperm duct.

The male reproductive system Sperm ducts/ Vas deferens Tubes which carry the sperm away from the testes

The male reproductive system Seminal vesicle/ Prostate gland Is about the size of the golf ball It adds a nutrient fluid and enzyme (seminal fluid) in which it activates the sperms to swim Sperms + seminal fluid = semen

The male reproductive system Urethra The urethra is a tube that carries both urine and semen along the penis to be released from the body but at different times.

The male reproductive system Penis It is an organ for introducing sperms into the female. It contains spongy tissue which fills with blood to make the penis firm (an erection).

QUICK CHECK! State the functions of: Testes Scrotum Sperm ducts Prostate gland Urethra penis

Female reproductive organs

The female reproductive system Ovaries Female gonads Making and releasing the female gametes The female releases one ovum every four weeks

The female reproductive system Oviducts/ Fallopian tube Are tubes which carry the ova from the ovaries They are lined with cilia together with a little muscular assistance, help to move the ova gently along. The egg is fertilized in the oviduct.

The female reproductive system Uterus/ Womb A pear shape organ The wall contain involuntary muscle The embryo develops in the uterus during pregnancy

The female reproductive system Cervix Cervix is the “neck” of the uterus, where the uterus joins the vagina.

The female reproductive system Vagina it is part of the female system which receives the penis during the sexual intercourse It is muscular and stretchable

QUICK CHECK! Ovaries Oviducts Uterus Cervix vagina State the functions of: Ovaries Oviducts Uterus Cervix vagina

Checkpoint 1: Name the organ/ organs that carry out the function: Store matured sperms Carries both sperm and urine Produces cells with only half the number of chromosome Produces the male sex hormone Receive sperm Egg must be fertilised here for pregnancy to take place.

Female gametes vs male gametes

Female gametes vs male gametes Released in millions Able to move Very small (0.05 mm) Very little cytoplasm Nucleus contains either an X or a Y chromosome Female gametes Released one per month Unable to move by their own Comparatively large (o.1mm in diameter) A lot of cytoplasm which contains nourishment for the zygote if the ovum is fertilised Nucleus always contains an X chromosome

QUICK CHECK! Compare the human male and female gametes in terms of size, numbers and Movement In each case, suggest reasons for the differences you describe.

Human reproductive system Menstrual cycle

Menstrual cycle The average menstrual cycle is about 28 days. Begins with puberty, ends with menopause. Menstrual cycle is the alternation of menstruation and ovulation.

Menstrual cycle Menstruation: The spongy lining then peel away , damaging the blood capillaries. The lining is passes out of the vagina, together with the blood. Menstrual period. It lasts for about 5 days Repair of uterine lining: Over a period of 14 days, the walls of the female’s uterus develop a spongy lining Ovulation: On day 14th, ovulation occurs. The ovum passes down the oviduct. If the ovum is not fertilised by sperm, it passes through the uterus and vagina and out of the vulva. Thickening of the lining Lining continues to thicken for the next 10 – 12 days before it begins to break down.

Menstrual cycle The fertile period is from day 11 to day 17, because ovulation has occurred. Ovum can survive for 2-3 days and allowing for the possible survival of sperms in the oviduct. The rest of the time is considered infertile period.

Factors affecting menstrual cycle Stress Unbalanced diet/ malnutrition Mental fatigue Illness These factors can alter or stop the menstrual cycle

Menstrual cycle There are many developing follicles in the ovary. The young follicles are called primary follicles A primary follicles are matured into a mature follicle called Graafian follicle. The mature follicle releases hormone oestrogen that brings about the repair and growth of the uterine lining. During the ovulation, the one egg is released.

Summary

Menstrual cycle The ovary secretes progesterone after ovulation. Progesterone causes the uterine lining to remain thick and soft and to become well supplied with blood vessels. This is important for preparation of the implantation of embryo.

Menstrual cycle If no fertilisation occur, progesterone continues to be secreted for about ten days. Then stop producing progesterone and this will cause the onset of menstruation.

Fertilization and development of embryo Reproduction Fertilization and development of embryo

Fertilization The egg released is surrounded by a few layers of follicle cells. As the sperm swim toward the egg, it will release enzymes that digest the follicle cells. Only one sperm enters the egg. The fusion of the nuclei to form the zygote is called fertilization. The fertilization occurs in oviduct.

Development of embryo The zygote passes along the oviduct to the uterus and it begins to divide by mitosis to form a ball of cells that called embryo. The embryo becomes embedded in the uterine lining. This is called implantation.

Development of embryo placenta Finger –like projections (villi) to provide large surface area for diffusion Allow dissolved food substances (glucose, amino acid, mineral salts) and oxygen to diffuse from mother blood to the embryo Allow metabolic waste (urea and carbon dioxide) to diffuse from embryo to mother’s blood Allow the antibodies to diffuse to the embryo Produce progesterone umbilical cord Contain umbilical vein and two umbilical arteries bring dissolved oxygen and nutrients by the umbilical vein to the foetus removing waste via umbilical arteries. amniotic fluid Provide the buoyancy to the foetus, thus protect it from shock and mechanical injuries Maintains a relatively constant environment for the foetus.

Development of embryo The exchange of the material between the foetus and the placenta. Page 349

Development of embryo Page 349

Development of embryo The time between conception and birth is nine months. The nine months is known as the gestation period. At the end of the gestation period, contraction of the uterus walls causes the rupture of the amniotic sac. The birth of the baby is followed by the ejection of the placenta.

Thinking room? How are identical twins come about? Why do they always - look alike and same sex?

IVF A woman with blocked oviducts cannot have a baby in the normal way but can now have a ‘test-tube’ baby. A doctor, using a fine tube through the body wall, sucks up several eggs from the ovary, puts them in a dish and mixes them with sperm. The eggs are then kept for a few days before they are put back into the woman’s uterus via the cervix. Describe what can normally happen in the oviduct. Why does the doctor get the eggs from the ovary through the body wall and not through the vagina and uterus? Why must the sperms be mixed with eggs before they are put back in the woman? Why do you think the eggs are kept for a few days before they are put back into the uterus? Why is the term ‘test-tube baby’ inaccurate?