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

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

Physiology & Health Learning Intentions KEY AREA 2 – Hormonal Control of Reproduction a)Hormonal onset of puberty b)Hormonal control of sperm production c)Hormonal control of menstrual cycle

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

2b) Hormonal onset of puberty At puberty, the hypothalamus secretes a releaser hormone whose target is the pituitary gland The pituitary gland then produces 2 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

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

2d) Hormonal control of menstrual cycle When FSH arrives in the bloodstream at the ovaries it:- -Stimulates the development and maturation of each follicle and -Stimulates the ovary tissue to secrete the sex hormone oestrogen When LH arrives in the bloodstream at the ovaries it:- -Triggers ovulation - Brings about the development of the corpus luteum from the follicle - Stimulates the corpus luteum to secrete the sex hormone progesterone

2e) Influence of ovarian hormones (Oestrogen & Progesterone) When the ovary wall secretes oestrogen it:- -Stimulates proliferation (cell division) of the inner layer of the uterus, called the endometrium -This effects the repair of the endometrium following menstruation and prepares it for implantation -Stimulates the secretion of LH by the pituitary gland When the corpus luteum secretes progesterone it:- - Promotes the further development and vascularisation of the endometrium into a spongy layer rich in blood vessels, making it ready to receive a blastocyst (embryo) if fertilisation occurs -Inhibits the secretion of FSH and LH by the pituitary gland

2f) 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 (1 st half of the cycle) The Luteal Phase (2 nd half of the cycle)

2f) The menstrual cycle – The Follicular Phase FSH released from the pituitary gland, arrives in the ovary and stimulates:- Development & maturation of a follicle Production of oestrogen by the ovarian tissues As the concentration of oestrogen builds up, it stimulates proliferation (cell division) and repair of the endometrium High concentrations of oestrogen trigger the production of LH and FSH by the pituitary gland at approximately “Day 14” The surge of LH directly causes ovulation by causing the follicle to rupture and release the ovum The ovum then moves along the oviduct, and over this very short period of 2-3 days, fertilisation may occur if the ovum meets a sperm

2f) The Menstrual Cycle – The Luteal Phase LH stimulates the follicle to become the corpus luteum The corpus luteum (gland-like structure) secretes progesterone and oestrogen The rise in progesterone concentration stimulates further development of the endometrium so it becomes thick, spongy and has an increase in vascular blood vessels, making it ready to accept and nourish a blastocyst if fertilisation takes place and the blastocyst becomes implanted. High levels of oestrogen and progesterone during this luteal phase trigger an inhibitory effect on the pituitary gland, so concentrations of FSH and LH drop as a result and no new follicle develop at this time (This is an example of negative feedback control)

2f) The Menstrual Cycle – The Luteal Phase If fertilisation HAS NOT occurred:- The drop of LH leads to the degeneration of the corpus luteum by approximately “Day 22” This drop of LH, is followed by a rapid drop in progesterone and oestrogen By approximately “Day 28”, these ovarian hormones are at such a low level that the endometrium can no longer be maintained and menstruation begins Menstruation lasts a few days Menstruation involves the loss of the inner layer of the endometrium accompanied by a small volume of blood for a few days

2f) The Menstrual Cycle – The Luteal Phase If fertilisation HAS occurred:- The Embryo secretes a hormones 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

2f) The menstrual cycle

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