The 4 hormones Oestrogen – secreted by the ovary Progesterone – secreted by the ovary and corpus luteum The gonadotrophins secreted by the pituitary gland Follicle stimulating hormone (FSH) Luteinising hormone (LH)

1.An increase in FSH from the pituitary gland stimulates the development of one or more follicles 2.Increases in FSH also stimulates oestrogen production (and small amounts of prog) from the ovaries. 3.Oestrogen stimulates the maturation of the follicles. 4.Oestrogen also stimulates the endometrium layer to thicken.

4. After about 12 days oestrogen rises to a peak causing LH and FSH to rise which triggers ovulation. 5. A peak in LH also causes the formation of the corpus luteum from the ruptured Graafian follicle. 6. The corpus luteum now secretes oestrogen and high levels of progesterone

If pregnancy does not occur 7. High Levels of Progesterone maintains the thickness of the endometrium. (secretory phase) 8. After FSH and LH levels drop causing the corpus luteum to degenerate and the levels of progesterone and oestrogen to fall after about 14 more days. 9. This cause the menstrual phase in which the outer layers of the endometrium are shed. (period)

If pregnancy does occur Progesterone and oestrogen levels stay high and the endometrium layer is maintained. The ovary at first secretes these hormones but later (3 months) the placenta will take over this role.

Hypothalamus secretes GnRH (gonadotrophin releasing hormone) which controls the secretions from the pituitary gland Pituitary Gland – secretes FSH and LH Increases in FSH at the start of the cycle stimulates Oestrogen production from the ovaries low levels of oestrogen inhibits FSH and prevents the stimulation of any more follicles Negative feedback High levels of oestrogen (day 12) stimulates FSH Positive feedback This triggers very high levels of FSH and LH causing ovulation This triggers the formation Of the corpus luteum which Secretes high levels of prog Which in turn inhibits LH and FSH secretion from the pituitary gland

Zygote – fertilized ovum

Morula – a mass of 16 cells (day 3)

Blastocyst – hollow structure - begins to implant in endometrium (fully implanted 10 days after fertilization

Outer wall of blastocyst – makes the trophoblast which will go on to form the placenta. Inner mass becomes the yolk sac and amniotic cavity

Endoderm  digestive and respiratory tracts Mesoderm  skeletal tissues and bones Ectoderm  skin and nervous tissue. Inner cell mass will later form the tissues of the baby and differentiate into the primary germ layers Germ cells are very useful for research and a new legal bill is currently being passed to determine if it is legal to use them.

Neurulation

Birth or labour Stage 1 – onset of uterine contractions until dilation of the cervix Stage 2 – max dilation of the cervix until baby gets out – this is the ouch bit!! Stage 3 – expulsion of the placenta through the vagina (yummy – nice fried I’ve heard)

More hormones Oxytocin secreted by pituitary gland causes the contractions of the uterine muscle. It is thought that it is a hormone produced by the baby’s hypothalamus (ACTH) which stimulates the production of oxytocin by stimulating the fetal adrenal glands and producing cortisol which then passes into the mothers blood across the placenta (only proven in sheep and goats!!)

Lactation Prolactin (secreted from the pituitary gland) stimulates milk production Suckling stimulates oxytocin production from the pituitary gland which causes the myoepithelial cells to contract and expel milk through the mammary glands.