The reproductive system Flashcards
The reproductive system consists of consists of:
*Gonads: Pair of testes in male, ovaries in female – produce gametes and secrete sex steroid hormones
*Reproductive tract: System of specialised ducts for transport or housing gametes
*Accessory sex glands: Produce supporting secretions into the tract:
Male: Testes outside the body to stay cool accessory glands produce secretions to nurture the sperm and allow it to swim effectively and tract for sperm conveyance
Female: ovaries produce ova which travel down the fallopian tubes into the uterus for fertilisation (which will then house the developing embryo) by sperm which enter through the vagina
Hormones and reproduction
(see diagram)
*Gonads serve 2 main functions
–Gametogenesis
–Production/secretion of steroid sex hormones
*3 types of sex hormone
–Androgens
–Oestrogens e.g. oestrodiele
–Progestogens e.g. progesterone
*Functioning of gonads controlled by hypothalamus and anterior pituitary under influence of higher brain centres (in the cortex)
*GnRH from hypothalamus acts on pituitary to release gonadotrophins LH and FSH which reach the gonads through the blood stream to cause gametogenesis and production/secretion of sex hormones
Spermatogenesis
Sperm: head has an acrosomal vesicle of enzymes to break into the egg, nucleus carries genetic info, dense fibres in flagellum used to propel the sperm forward
*spermatogenesis is a complex process generating huge numbers of cells
*3 major steps
–Mitotic division
–Meiotic division
–Cytodifferentiation
*Cells formed highly specialised to carry genetic material a considerable distance (through the female tract)
*spermatozoan keep close association with sertoli cells during development
–Functions of sertoli cells – to allow spermatozoa to mature (see year 1)
Spermatogenesis: 1 spermatogonium = 4 spermatozoa
(see diagram)
Oogenesis
When a female is born she contains all her eggs – a finite resource.
Around puberty one primary oocyte will mature starting menstrual cycling.
Last cycle occurs at menopause.
Only ~400 of a females oocytes mature into ova in her lifetime.
1 oocyte = 1 ovum
(see diagram)
Each oocyte cycle consists of ovarian and uterine events:
Ovarian events
*Follicular phase
(Ovulation)
*Luteal phase – corpus luteum tissue present – this is shed in menstruation
Uterine events
*Proliferative phase – endometrial lining thickens
*Secretory phase – greater blood supply to support a fertilised ovum until the placenta forms
Hormonal control of ovulation (summary)
Hypothalamus secretes GnRH: stimulates anterior pituitary to secrete FSH and LH
*LH surge caused by switch of oestrogen feedback from negative to positive feedback
*ovulation : high progesterone prevents further positive feedback from oestrogen on LH
^initially follicle is secreting oestrogen (before ovum leaves follicle)
Around mid-cycle oestrogen peak
Ovum leaves follicle causing rise in oestrogen and progestrone and corpus luteum develops
If fertilisation does not occur oe and prog decrease and menstruation occurs
Best chance of getting pregnant before/during ovulation
Reproductive potential
Human life-cycle often considered in 5 phases:
1- embryonic/foetal development – no lung use – placenta area of gas exchange
2- Infancy & childhood
3-puberty & adolescence
(^1-3 development)
4-Adulthood (relatively stable)
5-late adulthood / old age (deterioration)
What do we mean by puberty?
*Physiological changes
*Morphological changes
*Behavioural changes
In endocrine terms:
processes leading to maturation of the hypothalamo-pituitary gonadal axis
Peripuberty
^ means around the time of puberty
Peripuberty
–Inc in activity of hypothalamic pulse generator leads to inc secretion of pituitary gonadotrophins (FSH&LH)
–Rise in sex steroids leads to secondary sexual development, growth spurt and fertility
Factors affecting time of onset
–Nutrition
–Genetic influences (especially in females: age of first menstruation is similar to mother)
–General health
–Attainment of critical body weight
Average age and stage of puberty 9 ½ - 14 ½ female growth spurt etc.
Most girls have their menstrual cycle start around age 14
Spikes in LH secretion during sleep observed in early-mid and mid-late puberty after which levels drop and become more stable (although still higher than in childhood)
Reproductive potential
*Once HPG sufficiently “mature” then ovulation /gametogenesis will occur
*In females cycles will continue until menopause in the female- natural loss of reproductive function due to decline in ovarian reserve
^schematic to show changes (not highly accurate) but observable fall in pro and oe and greater levels of gonadotrophin occur after menopause – as greater levels of LSH were required to stimulate an ova.
Changing ratio of hormones is a useful predictor of ovarian reserve. Measuring gonadotrophin levels may be able to predict menopause or FSH or LH
Early menopause can shorten lifespan raised FSH and reduced LH can diagnose this.
Puts a woman at risk of heart conditions and osteoporosis – treated by HRT.
(Polycystic ovarian syndrome can be diagnosed from elevated LH and lowered FSH levels)
Symptoms of menopause
*Vasomotor
- Hot flushes
- Night sweats
- Headaches
- Palpitations
*Psychological
- Depression, anxiety
- Irritability
- Insomnia
- Fatigue
*Urogenital - change in vaginal pH and vaginal atrophy
*Bone loss (long-term consequence: osteoporosis)
Treatment of menopause
Hormone replacement therapy (HRT) with oestrogen and progesterone
–Systemic
Pills, patches, implants, nasal spray (circulate in blood)
–Local
Creams, pessaries, vaginal ring (in vaginal area)
Alternative remedies
–To alleviate symptoms
Phytoestrogens: soya
Phytoprogestogens: wild yam etc.
Women who exercise may maintain a better hormone profile too
Treatment of menopause:
Oestrogenic and progestogenic side-effects
Oestrogenic side-effects
*Breast tenderness
*Bloating
*Nausea
*headache
Progestogenic side-effects
*Depression, mood swings
*Skin changes
*Abnormal bleeding
Increased risk of:
breast/ endometrial cancer, blood clots or stroke
Benefits of HRT:
Potentially lower risk of osteoporosis and Alzheimer’s disease
Contraception: the ideal contraceptive should be…
*Reliable / effective
*Reversible
*Available
*Acceptable (to every culture)
*Low cost
*Safe
–No risk
–No side effects
*Doesn’t rely on memory
Methods of contraception (and failure rates)
We are most fertile mid-cycle but not every woman has a 28 day cycle and there are many individual variations between women.
*Hormone releasing (0.1-3%)
–COC (combined oral contraceptive) , POP (progestrone only pills)
–CC Patch , vaginal ring
–Emergency pills
–Injectables , subdermal implants
–IUS (inter uterine hormonal device)
Hormone releasing side effects:
- Risk of deep vein thrombosis
- Risk of breast cancer
- Headaches, nausea and weight gain are common
*IUD (0.2-2%) (not hormonal)
- A copper coil – local inflammatory action impedes sperm transport, copper is toxic to sperm
*Sterilisation
–Vasectomy (0.1%)
–Tubal ligation (0.5-2%)
*Natural methods (high failure rate ~10%)
*Barrier methods
–Diaphragm / cap (6%)
–Male condom (3-5%)
