Ch15: Sex Organs & Hormonal Control Higher Human Biology

Male Reproductive System Testes are the site of: sperm production manufacture of the male sex hormone testosterone

Sperm Production Sperm are formed by meiosis in the tiny seminiferous tubules of the testes, which unite forming coiled tubes that connect to the sperm duct. Sperm duct

Sperm forming by meiosis

Pathway of sperm

Pathway of sperm during sexual intercourse Image source: www.fertility.com Sperm are motile. This requires a fluid medium & a source of energy.

Testosterone ….the male sex hormone Produced by interstitial cells, in the tissue between the seminiferous tubules of the testes Released directly into the bloodstream Image source: http://faculty.une.edu

Seminal Vesicles Males have 2 seminal vesicles, which secrete a thick liquid rich in: fructose – a sugar that provides sperm with energy for motility prostaglandins – hormone-like compounds that stimulate contractions of the female reproductive tract. Help sperm to move more quickly towards the egg.

Prostate Gland Secretes a thin lubricating liquid containing enzymes. The enzymes keep the fluid at the optimum viscosity (thickness) for sperm motility. Semen is a milky liquid composed of: sperm, fluid from seminal vesicles fluid from prostate gland

Female Reproductive System Oviduct / Egg tube Where the egg is fertilised Ovary Produces eggs Uterus lining Lining of the womb Uterus / Womb Where the baby grows Cervix The neck of the uterus which connects to the vagina. Vagina The penis is put here when mating.

Developing Egg Eggs are formed by meiosis in the ovaries. Each ovum (egg) is contained by a developing Graafian follicle which secretes oestrogen (a hormone). After ovulation (release of the egg), the Graafian follicle develops into a corpus luteum which secretes the hormone progesterone.

Image source: http://resources.schoolscience.co.uk

Hormones Hormones are chemical messengers, produced in the endocrine (ductless) glands (e.g. pituitary and thyroid glands) then secreted into the bloodstream. Pituitary gland When a hormone reaches its target tissue it brings about a specific effect Thyroid gland

Gonadotrophic hormones The gonads (reproductive organs) are the target organs of two of the hormones produced by the pituitary gland, thus these hormones are called gonadotrophic hormones: FSH: follicle-stimulating hormone ICSH: interstitial cell- stimulating hormone (males) LH: Luteinising hormone (females) These hormones begin to be released from the anterior pituitary at puberty.

Male Gonadotrophic hormones promotes sperm production in the seminiferous tubules The functions of the testes are regulated by these hormones: Anterior (front) lobe FSH In bloodstream Testosterone stimulates interstitial cells to produce testosterone ICSH Activates secretion from prostate gland + seminal vesicles

Self Regulation of Testosterone The body has self-regulating mechanisms, called negative feedback control, that allows the body to correct changes. When the concentration of testosterone gets to a certain level it inhibits the secretion of FSH & ISCH, which in turn causes a decrease in testosterone concentration.

Negative Feedback Control When a factor affecting the body’s internal environment deviates from its norm (or set-point) the body responds to correct the change. Image source: www.hw.ac.uk

Female Gonadotrophic hormones FSH stimulates: Development and maturation of each Graafian follicle Secretion of oestrogen from ovary tissue LH triggers: Ovulation Development of corpus luteum Secretion of progesterone Oestrogen & Progesterone are the ovarian hormones.

Oestrogen Oestrogen stimulates: Image source: www.beliefnet.com Oestrogen Oestrogen stimulates: cell division (proliferation) of the endometrium (inner layer of the uterus) allowing it to repair after menstruation. the secretion of LH by the anterior pituitary

Progesterone Progesterone stimulates: the thickening of the endometrium inhibits the secretion of FSH & LH by the anterior pituitary

Effect of Hormones in females GnRH = Gonadotrophin Releasing Hormone

Menstrual Cycle 28 day cycle Endometrium Ovulation Image source: www.medicine4faith.net 28 day cycle each cycle continuous with previous cycle and next cycle 2 phases View the animation on menstruation: http://resources.schoolscience.co.uk/abpi/new/resources/hormones/horm4.asp follicular phase luteal phase

Menstrual Cycle: Follicular Phase First half of cycle FSH from pituitary stimulates development & maturation of a Graafian follicle and production of oestrogen from ovarian tissues Repair & proliferation of the endometrium (due to increase in Oestrogen) At day 14 - high Oestrogen levels cause a surge in the production of LH (& FSH) causing ovulation.

Ovulation Occurs on day 14 Surge in LH causes the wall of the Graafian follicle to rupture & release the egg after ovulation the egg moves along the oviduct for 3-4 days the egg can be fertilised if it meets a sperm Ruptured follicle Protective cells Egg

Menstrual Cycle: Luteal Phase Second half of cycle LH stimulates Graafian follicle to become corpus luteum, which then secretes oestrogen & progesterone Endometrium becomes thick, vascular & spongy, due to increase in progesterone, ready to accept & nourish the embryo if fertilisation has occured FSH drops due to high oestrogen + progesterone so no new follicles LH oestrogen FSH

Menstrual Cycle: Luteal Phase LH oestrogen FSH Low LH causes degeneration of corpus luteum (day 22) Followed by rapid drop in progesterone (& oestrogen) If NO fertilisation, Menstruation begins at Day 28 because the ovarian hormones (oestrogen + progesterone) are so low that the endometrium can’t be maintained

Why do pregnant women not menstruate? The fertilised egg secretes a hormone called human chorionic gonadotrophin (HCG) which maintains the corpus luteum which secretes progesterone preventing menstruation. Image source: staff.um.edu.mt After 6 weeks the placenta secretes progesterone instead. Pregnancy tests, test for the presence of HCG in urine.

Image source: www.fertilityet.org.uk to transport, nourish & filter sperm Endometrium (food lining) develops Endrometrium (+ some blood) is discharged Role of cervix The cells that line the cervix secrete mucus which lubricates the vagina. High levels of oestrogen stimulate these cells to secrete a watery mucus which help sperm enter the reproductive tract. High levels of progesterone cause the cervical mucus to thicken. During pregnancy this forms a semi-solid plug to protect the fertilised egg from infection. Prostaglandins in the semen also help transport the sperm by inducing muscular contractions in the uterus & oviduct.

Body Temperature Image source: http://en.wikipedia.org Body temperature rises by 0.5°C at ovulation and stays high during the luteal phase. Changes in viscosity of cervical mucus & body temperature are used by some people as indicators for the rhythm method of birth control.

Continuous v Cyclical Fertility Male fertility is continuous because they secrete a steady level of testosterone and produce a steady quantity of sperm. Female fertility is cyclical due to the delicate balance of gonadotrophic and ovarian hormones. Females are usually only fertile for 3-4 days immediately after ovulation.