HUMAN REPRODUCTION

• during meiosis the chromosome number is halved from diploid to haploid • therefore gametes have the haploid chromosome number • two haploid gametes fuse during fertilisation to form a diploid zygote • the zygote develops into a multicellular diploid organism by mitosis

• produce and release sperm • produce male sex hormone, testosterone, that plays a role in spermatogenesis and the development of the secondary sexual characteristics

• temporarily stores sperm produced by the testes until it is mature and ready to fertilise the ovum

transports sperm, by means of peristaltic movements, from the epididymis to the urethra

transports both urine and sperm to the exterior

• the energy-rich secretion of the mucous membrane provides fructose, the main soruce of food for the sperm • the secretion also acts as a lubricant enhancing the motility of the sperm cells

• secretes prostate fluid that acts as a lubricant for the motility of sperm cells, protects sperm against the low pH in the urethra and vagina, protects sperm against infection

• the secretions of this gland contribute to greater mobility of the sperm • clears urethra of urine residue • lubricates the head of penis

transfers the sperm from the male to the female during copulation

• produce and release ova • produces hormones, oestrogen and progesterone

• transports the ovum as well as the developing zygote • the site of fertilisation and the first divisions of the zygote

• wall of the uterus consists of three layers, i.e. an outer serous layer, a muscular layer of smooth, involuntary muscle and the endometrium that lines the uterus on the inside • every month, the endometrium goes through cyclical changes where it thickens by becoming more vascular and glandular in preparation for the implantation of the fertilised ovum • the uterus narrows and opens to the vagina through the cervix, a neck region rich in glands that secrete cervical mucous

• increased muscle mass • development of a deeper voice • enlargement of the penis and sperm • production of sperm • development of sexual drive • increased production of sweat • increase in facial and body hair • skin becomes oily • behavioural changes

• increase in fat deposited below the skin • widening of hips • development of breasts • increase in height • development of ova in the ovaries • start of menstruation • growth of body hair • skin becomes more oily • behavioural changes

under the influence of testosterone, diploid cells in the seminiferous tubules of the testes undergo meiosis to form haploid sperm cells

• diploid cells in the ovary undergo mitosis to form numerous follicles. • at the onset of puberty and under the influence of FSH one cell inside a follicle enlarges and undergoes meiosis. • of the four cells that are produced, only one survives to form a mature, haploid ovum. • this occurs in a monthly cycle.

• head - contains the haploid cell nucleus with the male genetic material • acrosome - a sac at the front containing lytic enzymes that digest the protective jelly layer of the ovum to allow the sperm’s head and nucleus to penetrate the ovum’s membrane • middle portion/neck - contains many mitochondria that provides energy to the tail for locomotion • tail - performs whip-like movements that propel the sperm through the seminal fluid allowing it to swim towards the ovum

• jelly layer - provides protection to the early developmental stages of the fertilised ovum • haploid cell nucleus contains the female genetic material • cytoplasm - provides a reserve source of nutrients for the fertilised ovum

ovarian cycle and uterine cycle and progresses over a period of 28 days

• germinal epithelial cells that form the outer layer of the ovary divide by mitosis and form oogonia • each oogonium is surrounded by a granular layer. the oogonium together with its granular layer is known as the primary follicle • inside the primary follicle, the oogonia grow into primary oocytes • at 10-12 years, the hypophysis starts to secrete the hormone FSH, which stimulates development of primary follicles into graafian follicles.

• the developing follicles secrete increasing amounts of oestrogen • the primary oocyte divides by meiosis 1 into two cells: a larger cell, the secondary oocyte and a smaller cell, the polar body • the mature graafian follicle moves to the surface of the ovary where it forms a slight protuberance. the follicle increases in size as the production of follicle fluid increases and eventually the wall of the ovary ruptures to release an ovum into the fallopian tube • this release of an ovum is known as ovulation

• after ovulation the remains of the graafian follicle develop under the influence of LH, into a mass of yellow cells known as the corpus luteum • the corpus luteum secretes progesterone and a little oestrogen to maintain the endometrium for implantation • if the released ovum is not fertilised, the corpus luteum degenerates until only a small scar remains • if fertilisation does occur, the corpus luteum continues to function and maintain the endometrium until the 12th week of pregnancy

• the endometrium of the uterus is rich in glands and blood vessels • from puberty to menopause the endometrium undergoes monthly cyclical changes known as the uterine cycle • the female hormones oestrogen and progesterone are responsible for thickening the endometrium • if fertilisation does not occur, the thickened and vascularised tissue of the endometrium is not needed for implantation

• the upper layers of the endometrium break down; are shed and discarded together with the unfertilised, immature ovum to exit the body via the cervix and vagina • menstrual blood consists of endometrial tissue, blood and mucous • lasts for about 4-6 days • the endometrium in the uterus immediatly starts to thicken once more to prepare for the arrival of the next, possibly fertilised, ovum • if fertilisation occurs, the corpus luteum remains active and secretes hormones which maintain the endometrium, keeping it thick for implantation