Component 2.3 - The Menstrual Cycle, placenta, umbilical cord Flashcards
What is the function of the gonadotropic releasing hormone and where is it secreted by?
It is secreted by the hypothalamus and stimulates the anterior pituitary gland to secrete FSH and LH
(Positive feedback by GnRH)
What is the function of FSH?
It stimulates the development of the primary follicles in the ovary (secreted from the anterior pituitary gland)
Also stimulates the thecal cells to produce oestrogen
What is the role of LH?
1) High concentration, secreted by the anterior pituitary gland causes graafian follicle to release secondary oocyte and be converted to corpus luteum
2) Positive feedback by oestrogen causes LH concentration to increase
3) Has a positive feedback on FSH
What does the Graafian follicle secrete after it has released the secondary oocyte?
Oestrogen and progesterone
What are the roles of oestrogen?
1) Triggers the rebuilding of the endometrium
2) Inhibite FSH secretion by negative feedback (this also brings its own conc down)
3) Stimulates LH production by positive feedback
What is the role of progesterone?
1) It maintains the newly built endometrium
2) It has a negative feedback on FSH and LH
What happens if there is no implantation?
The falling concentrations of FSH and LH cause the corpus luteum to degenerate so progesterone production declines.
Endometrium no longer being rebuilt or maintained and so it is shed.
FSH secretion is no longer inhibited and another menstrual cycle is initiated
How does the blastocyst transform?
The trophoblast becomes the chorion (outer membrane surrounding the embryo) and the placenta.
The inner cell mass forms the embryo and the amnion
How do trophoblastic villi change after the chorion has developed?
Chorion cells move into trophoblastic villi which form much larger chorionic villi. They contain capillaries which connect the embryo to the uterus wall.
What are the 5 major roles of the placenta?
1) An endocrine organ
2) Exchange of materials
3) A barrier between the mother’s and foetus’s circulation
4) Protection against the mothers immune system
How does the placenta provide protection against the mothers immune system?
The mother does not make an immune response against the foetus.
The cells of the chorionic villi fuse so there are no spaces between them making a syncitium so no WBCs can get into foetal blood
Why is it important that the placenta provides a barrier between the maternal and foetal circulation?
Protects foetus from changes in maternal blood pressure
Protects foetal capillaries from high blood pressure
How does the placenta exchange between the mother’s and foetus’s blood?
Distance between intervillous spaces which contain the mother’s blood and the chorionic villi is very small so transport can occur
Concentration gradient maintained by counter current flow
How are the umbilical artery and the pulmonary artery similar?
They both carry deoxygenated blood.
The umbilical artery is called an artery because it is coming away from the foetus’s heart.
How does the foetus get nutrients?
The blood of the foetus comes to the placenta in the umbilical artery. The blood exchanges at the chorionic villi and then goes back in the umbilical vein high in nutrients.
