Unit 2 - Physiology and Health Chapter 10 - Hormonal Control of Reproduction

Where is your pituitary gland?–Hormonal Control. The Pituitary gland is located in the centre of the brain and produces many hormones Hormones are chemical messengers produced by an animal’s endocrine glands and secreted directly into the bloodstream. When a hormone reaches a certain target tissue, it brings about a specific effect.

Pituitary gland Pituitary gland is a gland that produces many hormones. Two of these are called GONADOTROPIC hormones because their target are the gonads (reproductive organs). FSH –Follicle stimulating hormone. In men - ICSH – Interstitial Cell Stimulating hormone. In women – LH – Luteinising hormone These hormones are released at puberty. 12/11/2018

Influence of testosterone Testosterone stimulates sperm production. It also activates the prostrate gland and seminal vesicles to produce their secretions. SELF REGULATION OF TESTESTORONE 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 anterior pituitary. This leads to a decrease in testesterone concentration, soon followed by a resumption of the activity by the anterior pituitary. This makes gonadotropic hormone again and the cycle starts again. 12/11/2018

Influence of pituitary Hormonal on testes – negative feedback! This type of self-regulating mechanism is called NEGATIVE FEEDBACK CONTROL. ICSH FSH in the bloodstream promotes sperm production in the seminiferous tubules. ICSH stimulates interstitial cells to produce male sex hormone TESTOSTERONE 12/11/2018

Female Reproductive System Made up of uterus, oviducts, ovaries and vagina. Functions: produces ova (eggs). Receives sperm from penis. 12/11/2018

FYI - Eggs Evidence suggests that eggs are formed in foetal life. About 400,000 immature eggs reside in each ovary at puberty. The menstrual cycle, as a biologic event, allows for ovulation of one egg typically each month. Thus over her lifetime a woman will ovulate approximately 400 to 450 times. All the other eggs dissolve. As a woman's total egg supply is formed in foetal life, to be ovulated decades later, it has been suggested that this long lifetime may make the chromatin of eggs more vulnerable to division problems, breakage, and mutation than the chromatin of sperm, which are produced continuously during a man's reproductive life. This possibility is supported by the observation that foetuses and infants of older mothers have higher rates of chromosome abnormalities than those of older fathers.

The Female reproductive system continued. The role of the female in reproduction is not only to produce gametes but also…. Houses and provides nutrients (food and oxygen) to the developing zygote (fertilized egg) and later the embryo and foetus. Remove its waste products. Gives birth to the offspring. After delivering into the world, provide it with continued supply of food for a period of time.

The Ovaries The ovaries are the site of ova production by meiosis Ova are contained in a developing Graafian follicle The Graafian follicle secretes the hormone oestrogen After ovulation, the Graafian follicle becomes the corpus luteum which secrete progesterone

Corpus Luteum SEE SCHOLAR – Maturation of ova simulation http://courses.scholar.hw.ac.uk/vle/scholar/session.controller?action=viewContent&contentGUID=f65bd0a3-3b06-6409-554b-934e6eb2195a Graafian follicle developing OVARY egg Immature Graafian follicle

Graafian Follicle ovum Graafian follicle follicular liquid 12/11/2018

Pituitary Hormones & the Ovaries F.S.H (Follicle Stimulating Hormone) Stimulates the development of eggs (inside the structures called follicles) and the development and maturation of Graafian Follicle Stimulates ovary to produce the hormone oestrogen L.H (Lutenising Hormone) Triggers ovulation Brings about the development of the corpus luteum from the follicle Stimulates corpus luteum to produce progesterone Gonadotrophic hormones (FSH/LH) and ovarian hormones (Oestrogen/Progesterone) interact to control the female menstrual cycle.

Effect of Ovarian Hormones on the Uterus &Pituitary Gland Gonadotrophic hormones (FSH/LH) and ovarian hormones (Oestrogen/Progesterone) interact to control the female menstrual cycle. During puberty the anterior pituitary gland begins to secrete FSH & LH. These hormones are transported to the ovaries in the blood Oestrogen and Progesterone are called the ovarian hormones since they are produced by the ovary. Oestrogen stimulates proliferation (cell division) of the lining of the uterus - the endometrium. And it is responsible for the repair after menstruation. stimulates secretion of LH by the anterior pituitary gland Progesterone Promotes the thickening of the endometrium Promotes vasularisation (many blood vessels), to create a spongy layer(of the endometrium) Inhibits secretion of FSH and LH by the anterior pituitary gland

Continual Fertility vs Cyclical Fertility Continual Fertility in Males high level of testosterone has a negative feedback effect on the secretion of FSH and ICSH by the pituitary gland relatively constant levels of testosterone, FSH and ICSH Cyclic Fertility in Females fluctuating levels of FSH, LH, oestrogen and progesterone only fertile for a few days before and after ovulation 12/11/2018

Menstrual cycle – intro. The ovarian hormones oestrogen and progesterone, and the pituitary hormones FSH and LH interact with each other to coordinate the menstrual cycle. The menstrual cycle is a repeating series of changes in the levels of the above hormones which is accompanied by changes in the development of the Graafian follicle and the lining of the uterus (the endometrium). The average length of a cycle is 28 days, although it can vary greatly from one individual to another. The first day of menstruation, that is the start of the monthly 'period', is usually regarded as day 1 of the cycle.

Menstrual cycle- Hormonal Control (a) changes in levels of the pituitary hormones FSH and LH; (b) development of the Graafian follicle; (c) changes in the levels of the ovarian hormones oestrogen and progesterone (d) changes in the thickness of the endometrium.

The menstrual cycle can be divided into two parts: Follicular Phase First half - from day 1 (the start of menstruation) to about day 14 (when ovulation occurs) Luteal Phase Second Half - from day 14 to day 28, when menstruation begins again. FOLP

Menstrual cycle - Follicular Phase FSH from the pituitary gland stimulates the development and maturation of the Graafian follicle produces oestrogen by the ovary; As the concentration of oestrogen increases: stimulates the repair of the endometrium after menstruation stimulates the pituitary to secrete LH; Concentrations of LH gradually increase until there is a sharp increase around day 12 or 13. This peak of LH concentration causes ovulation (the release of an ovum) around day 14 in the cycle

Menstrual cycle - Luteal Phase LH causes: the Graafian follicle to develop into the corpus luteum stimulates the corpus luteum to secrete progesterone; Increasing progesterone levels promote….. the thickening and vascularisation (build up of blood vessels) of the endometrium, in preparation for the implantation of a fertilised ovum; high levels of progesterone inhibit the secretion of FSH and LH by the pituitary gland; As the levels of LH decrease the corpus luteum begins to degenerate (around day 22). This causes the levels of progesterone to decrease until by around day 28 of the cycle the endometrium can no longer be maintained. endometrium breaks down and is passed out of the body (menstruation). The decrease in progesterone levels removes its inhibitory effect on the pituitary gland, which begins to secrete more FSH again. As the levels of FSH rise the cycle begins again.

Menstrual cycle – Changes Two other changes which take place during the menstrual cycle are changes to the cervix body temperature.

Menstrual cycle – Changes to the Cervix The changes which occur to the cervix play a role in fertility. The cells of the cervix secrete mucus. High levels of oestrogen stimulate these cells to produce a thin and watery mucus and cervix becomes slippery and stretchy which is easily penetrated by sperm. Since the highest levels of oestrogen occur just before ovulation, the production of thin mucus at this time increases the chances of fertilisation. High levels of progesterone, on the other hand, cause the mucus secreted by the cervical cells to become thicker and, if pregnancy occurs, change into a semi-solid 'plug', which helps to protect the developing embryo against infection.

Diagram of changes to the cervix during menstrual cycle. 12/11/2018 Mrs Smith Ch15 Sex organs and hormonal control

Menstrual cycle – Changes to the Cervix The thin and watery mucus of the cervix not only make it easier for sperm to swim. It also helps the sperm to point in the correct direction ready for their passage through the reproductive tract which stops this happening. This is further assisted by muscular contractions of the uterus and oviduct caused by prostaglandins present in seminal fluid

Menstrual cycle – Changes to Body Temperature A woman's body temperature rises by as much as 0.5°C at ovulation. These changes in body temperature and the viscosity of cervical mucus can be used as indicators of ovulation and forms the basis of the rhythm method of birth control (see later).