Hormonal control of Reproduction

Learning Outcomes   Pituitary gland is stimulated to release FSH, LH, and ICSH by a releaser hormone produced in the hypothalamus Hormonal control of sperm production FSH promotes sperm production ICSH stimulates the production of testosterone Testosterone stimulates sperm production Testosterone activates the Seminal vesicles and Prostate Gland As testosterone concentration increases to a certain level this inhibits FSH and ICSH secretion Testosterone level decreases Pituitary releases FSH and ICSH again – This self-regulating mechanism is ‘negative feedback control’

Hormones Hormones are ‘chemical messengers’ produced by Endocrine Glands Hormones are secreted into the bloodstream When they reach a ‘target organ’ they bring about a specific effect In reproduction, hormones control – the onset of puberty sperm production the menstrual cycle

Hypothalamus Brain Pituitary

Onset of Puberty At puberty the Hypothalamus secretes a releaser hormone whose target is the Pituitary Gland The pituitary responds by producing two hormones The first is FSH, follicle stimulating hormone In males, the second is ICSH (interstitial cell-stimulating hormone) In females, the second is LH (luteinising hormone)

Hormonal control of sperm production FSH promotes sperm production in the seminiferous tubules ICSH stimulates the interstitial cells to produce the hormone Testosterone Testosterone – stimulates sperm production activates the Seminal Vesicles and Prostate Gland to produce secretions

Seminiferous tubules – sperm production here Coiled Tubes Leading to sperm duct Seminiferous tubules – sperm production here

Negative Feedback Control As testosterone concentration builds up in the bloodstream it reaches a level that inhibits FSH and ICSH secretion This leads to a decrease in testosterone concentration As a result, the pituitary gland releases FSH and ICSH again This type of self regulating mechanism is called negative feedback

Pituitary hormones and Ovaries FSH stimulates the development and maturation of each follicle It also stimulates the ovary to secrete the female sex hormone Oestrogen LH triggers ovulation It also brings about the development of the corpus luteum from the follicle The corpus luteum then secretes the sex hormone Progesterone

Ovary- secretes Oestrogen Mature Follicle Corpus luteum -progesterone Ovulation

Oestrogen Oestrogen stimulates the proliferation of the Endometrium, the inner layer of the uterus This prepares the uterus for implantation of an embryo High levels of oestrogen stimulates the cells lining the cervix to secrete a watery mucus easily penetrated by sperm The highest concentration of oestrogen is just before ovulation (increases chance of fertilisation)

Progesterone Oestrogen also stimulates the production of LH by the pituitary Progesterone – promotes the further development and vascularisation of the endometrium, in preparation to receive a blastocyst progesterone inhibits the secretion of FSH and LH by the pituitary

Try these questions . . . . Name three reproductive processes that hormones control Name two female hormones produced by the pituitary What does testosterone do? What does high levels of oestrogen do to the cells lining the cervix? Name the two hormones that progesterone inhibits

Answers . . . . the onset of puberty, sperm production, the menstrual cycle FSH and LH Stimulates sperm production and activates the Seminal Vesicles and Prostate Gland to produce secretions High levels of oestrogen stimulates the cells lining the cervix to secrete a watery mucus easily penetrated by sperm FSH and LH by the pituitary gland

Glossary CORPUS LUTEUM – the ‘yellow body’ which forms from the follicle after ovulation ENDOMETRIUM – the lining of the uterus FOLLICULAR PHASE – phase of the menstrual cycle during which follicles in the ovary mature. This phase ends at ovulation FOLLICLE STIMULATING HORMONE (FSH) – a pituitary hormone which stimulates the development of a ball of cells round the ovum INTERSTITIAL CELLS – cells found between the seminiferous tubules of the testes, which produce testosterone INTERSTITIAL CELL STIMULATING HORMONE (ICSH) - hormone produced by the anterior lobe of the pituitary gland that, in the male, stimulates the interstitial cells of the testes to produce testosterone LUTEAL PHASE – stage of the menstrual cycle which occurs after ovulation and before a period starts. During this phase, the lining of the womb thickens.

LUTENISING HORMONE (LH) – a pituatry hormone which stimulates ovulation OESTROGEN – a hormone involved in the menstrual cycle with a variety of functions PROGESTERONE – a hormone produced by the corpus luteum, involved in the menstrual cycle PROSTATE – gland of the male reproductive system which contributes fluid to the semen SEMINAL VESICLE – a gland of the male reproductive system which contributes fluid to the semen SEMINAL FLUID (SEMEN) – fluid which carries the sperm from the testes out of the penis during ejaculation SEMINIFEROUS TUBULES – tubules of the testes in which sperm are made TESTOSTERONE – a sex hormone which promotes male characteristics and sperm production