Reproductive Organs and Hormones

Unit 2

What you should know

• The structure and function of reproductive organs and gametes and their role in fertilisation.

• Gamete production in the testes. The roles of seminiferous tubules, interstitial cells, testosterone, prostate gland and seminal vesicles.

• Gamete production in the ovaries to include maturation of ova and the development of a follicle. Site of fertilisation in the oviduct and zygote formation.

Reproductive Organs and Gametes

• Prior Knowledge– Reproductive organs produce gametes– Male gamete- sperm– Female gamete- egg/ova– Male reproductive organ- testes– Female reproductive organ-ovary

Production of Gametes

• A germ line is the sex cells (eggs and sperm) that are used by sexually reproducing organisms to pass on genes from generation to generation.

• Gametes are produced by germline cells

MALE REPRODUCTIVE SYSTEM

PUBIC BONE

BLADDER

URETER

RECTUM

PENIS

ERECTILE TISSUE

URETHRA

TESTIS SCROTUM

EPIDIDYMIS

VAS DEFERENS

COWPER’S GLAND

SEMINAL VESICLE

PROSTATE GLAND

TESTES

SEMINIFEROUS TUBULE

INTERSTITIAL CELLS

TESTES• Seminiferous tubules – produce sperm

• Interstitial cells– secrete testosterone

Interstitial cells

Accessory Glands• Seminal vesicles and the prostate gland

• Semen consists of 10% sperm and 90% fluid and as sperm pass down the ducts from testis to penis, (accessory) glands add various secretion

• The prostate gland and seminal vesicles secrete fluids that maintain the mobility and viability of the sperm. This fluid is called semen

– Seminal vesicles secrete a fructose rich liquid, which provides energy for the mobility of the sperm

– The liquid also contains hormone like compounds (Prostaglandins) which stimulate contractions of the female reproductive tract

– Prostate gland secretes a thin lubricating liquid containing enzymes which regulate the viscosity of semen

FEMALE REPRODUCTIVE SYSTEM

VAGINA

CERVIXUTERUS

ENDOMETRIUMOVARY

OVIDUCT

THE OVARIES

• The ovaries contain immature ova in various stages of development

• Each ova is surrounded by a follicle that protects the developing ovum and secretes hormones

• Mature ova are released into the oviduct where they may be fertilised by sperm to form a zygote

GRAAFIAN FOLLICLE

You should know

• The structure and function of reproductive organs and gametes and their role in fertilisation.

• Gamete production in the testes. The roles of seminiferous tubules, interstitial cells, testosterone, prostate gland and seminal vesicles.

• Gamete production in the ovaries to include maturation of ova and the development of a follicle. Site of fertilisation in the oviduct and zygote formation.

Hormonal Control

What You Should Know• Hormonal onset of puberty. Pituitary gland releases follicle

stimulating hormone (FSH), luteinising hormone (LH) or interstitial cell stimulating hormone (ICSH) via the hypothalamus

• Hormonal control of sperm production. FSH promotes sperm production and ICSH stimulates the production of testosterone. Testosterone also stimulates sperm production and activates the prostate gland and seminal vesicles. Negative feedback control of testosterone by FSH and ICSH.

• Hormonal control of the menstrual cycle. Development of a follicle and the endometrium in the uterus. Roles of FSH, LH, oestrogen and progesterone in the menstrual cycle. Development of a follicle, the corpus luteum and the endometrium. Follicular and luteal phases. Blastocyst implantation. Negative feedback control through pituitary gland, FSH and progesterone, leading to menstruation.

•

Hormones• Hormones are chemical messengers produced by cells that bind to

receptors on the plasma membrane of other cells or enter other cells and alter the metabolic function of these cells.

• In response to a signal from the brain, hormones are secreted directly into the blood by the glands that produce and store them. These glands make up what is known as the endocrine system

• The testes and ovaries, or "gonads", are endocrine glands. – In males, testes produce sperm and secrete the male sex hormone

testosterone; – in females, ovaries produce eggs and the female hormone oestrogen.– It is these hormones that determine secondary sex characteristics like

muscle mass and facial hair. They also help to orchestrate sperm production, menstruation and pregnancy.

Hormonal Onset of Puberty• At puberty the hypothalamus

secretes a releaser hormone that targets the pituitary gland

• Releaser hormones cause the release of other hormones to start and stop

• The pituitary gland is stimulated to release– follicle stimulating hormone (FSH)– Luteinising hormone (LH) in women– Or interstitial cell stimulating hormone

(ICSH) in men– These hormones control the onset of

puberty

Hormonal Control of Sperm Production

Male Hormones• FSH (follicles stimulating hormones)

promotes spermatogenesis in seminiferous tubules

• ICSH (Interstitial cell-stimulating hormone) stimulates interstitial cells to produce male hormones (eg testosterone)

• Testosterone also stimulates sperm production and activates the prostate gland and seminal vesicles

• FSH and ICSH exhibit negative feedback control on the pituitary gland decreasing the level of testosterone produced by the interstitial cells

NEGATIVE FEEDBACK CONTROL

• High levels of testosterone have an inhibitory effect on the pituitary gland

• Inhibits secretion of FSH and ICSH

• Thus, levels of testosterone fall

• Inhibitory effect on pituitary ceases

• FSH and ICSH secretion increases

• Levels of testosterone increase

SELF REGULATION OF TESTOSTERONE

Testosterone

PITUITUARY GLAND

SEMINIFEROUS TUBULES INTERSTITIAL CELLS

FSH ICSH

StimulatesInhibits

Hormonal Control of the Menstrual Cycle

MENSTRUAL CYCLE

• Takes on average 28 days• Menstruation is day 1 to 5 of

the cycle• Endometrium starts to repair• Ovulation day 14• Endometrium thick and spongy• Menstruation in absence of

fertilised egg• Consists of 32 phases-

Follicular phase & Luteal phase

• FSH– Causes development of follicles in ovary– Stimulates secretion of oestrogen by the

follicle

• oestrogen stimulates proliferation of the endometrium preparing it for implantation and affects the consistency of cervical mucus making it easier for sperm to penetrate

Follicular Phase

Luteal Phase

• LH– Peak levels of oestrogen stimulate a surge in

the secretion of LH which triggers ovulation– Causes Graafian follicle to rupture (ovulation)– Causes development of the corpus luteum

from the follicle– Stimulates the corpus luteum to secrete

progesterone

• Progesterone promotes further development and vascularisation of the endometrium preparing it to receive a blastocyst if fertilisation occurs

• Ovum dies after 36 hours

Negative Feedback Effect of Ovarian Hormones on the Pituitary

• High levels of oestrogen and progesterone have an inhibitory effect on the pituitary gland

• Decrease the levels of FSH and LH which prevents further follicles from developing

• The lack of LH leads to degeneration of the corpus luteum

• A drop in progesterone leads to menstruation

Menstrual Cycle

FERTILISATION

FERTILISATION