Higher Human Biology

1. Higher Human Biology Unit 2 Physiology & Health KEY AREA 2: Hormonal Control of Reproduction

2. Higher Human Biology We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Physiology & Health key areas : - Key Area 1 – Reproductive Organs Key Area 2 –Hormonal Control of Reproduction Key Area 3 – Biology of Controlling Fertility Key Area 4 – Ante- and Postnatal Screening Key Area 5 – Structure and Function of Arteries, Capillaries and Veins Key Area 6 – Structure and Function of the heart Key Area 7 – Pathology of Cardiovascular Disease (CVD) Key Area 8 – Blood Glucose Levels and Obesity

3. Physiology & Health Learning Intentions KEY AREA 2 – Hormonal Control of Reproduction • Hormonal influence on puberty • Hormonal control of sperm production • Hormonal control of menstrual cycle

4. 2a) Hormonal control of reproduction A hormone is a chemical that is produced at one site, and has an effect at another site Hormones are produced by endocrine glands and are secreted directly into the blood stream When a hormone reaches a target tissue, it brings about a specific effect Hormones produced in the hypothalamus and the pituitary gland control the onset of puberty, sperm production and the menstrual cycle

5. 2b) Hormonal influence on puberty At the beginning of puberty, the hypothalamus secretes a releaser hormone whose target is the pituitary gland The pituitary gland then produces hormones 1. FSH (follicle-stimulating hormone) (in males & females) 2. ICSH (interstitial cell-stimulating hormone) (in males) OR LH (luteinising hormone) (in females) The release of these hormones triggers the onset sperm production in men and the menstrual cycle in women (puberty).

6. 2c) Hormonal control of sperm production When FSH arrives in the bloodstream at the testes, it promotes sperm production in the seminiferous tubules When ICSH arrives in the bloodstream at the testes, it stimulates the interstitial cells to produce the male sex hormone testosterone Testosterone stimulates sperm production in the seminiferous tubules, and activates the prostate gland and seminal vesicles to produce their secretions Self-regulation of testosterone production As the concentration of testosterone builds up in the bloodstream, it reaches a level where it inhibits the secretion of FSH and ICSH by the pituitary gland This leads to a decrease in testosterone concentration, which then triggers the pituitary gland to again make FSH and ICSH and so on…… This self-regulating mechanism is called negative feedback control

7. 2d) Hormonal control of the menstrual cycle Lasts for approximately 28 days Menstruation is indicated by blood flow The first day of menstruation is called “Day 1” of the menstrual cycle There are 2 stages of the menstrual cycle (Follicular Phase and Luteal Phase) The Follicular Phase (1st half of the cycle) The Luteal Phase (2nd half of the cycle)

8. 2e) The Follicular Phase • FSH • stimulates development and maturation of a follicle • stimulates production of oestrogen by the follicle • Oestrogen • stimulates proliferation of the endometrium preparing it for implantation • affects the consistency of cervical mucus making it more easily penetrated by sperm • triggers a surge in the production of LH (around day 14) • LH • direct cause of ovulation (release of an egg from a follicle)

9. 2f) The Luteal Phase • LH • causes the follicle to develop into the corpus luteum • corpus luteum is a gland-like structure and starts to secrete progesterone • Progesterone • promotes further development and vascularisation of the endometrium preparing it for implantation if fertilisation occurs

10. 2g) The Luteal Phase- when fertilisation HAS NOT occurred • High levels of oestrogen and progesterone during the luteal phase trigger an inhibitory effect on the pituitary gland, so concentrations of FSH and LH drop as a result and no new follicles develop at this time (This is an example of negative feedback control) • Lack of LH leads to degeneration of the corpus luteum and therefore a subsequent drop in progesterone • the drop in progesterone triggers menstruation as the endometrium can no longer be maintained

11. The Embryo secretes a hormone called Human Chorionic Gonadotrophin (HCG) which has the same effect as LH. HCG maintains the corpus luteum which continues to secrete progesterone and prevents menstruation taking place. After about 6 weeks the placenta takes on the job of secreting progesterone. The presence of HCG in urine is the basis of pregnancy tests 2h) The Luteal Phase-when fertilisation HAS occurred

12. 2i) The menstrual cycle

13. Physiology & Health Questions KEY AREA 2 – Hormonal Control of Reproduction • Testing Your Knowledge 1 Page 130 Q’s 3 & 4 only 2. Quick Quiz

14. Pituitary Gland High concentrations of oestrogen & progesterone inhibit the pituitary gland FSH LH Ovaries • Direct cause of ovulation • Causes follicles to develop into corpus luteum • Corpus luteum secretes progesterone - Stimulates development/ maturation of follicles - stimulates follicles to secrete oestrogen Uterus/Endometrium • stimulates proliferation of endometrium • decreases cervical mucus viscosity • promotes further development of endometrium