6. Reproductive organs Flashcards
Why sex?
= Sex increases genetic variation
- enhances the efficiency of natural selection
- allows faster rates of adaptions
- combines different beneficial mutation in
Meiosis
- formation of sex cells
- occurs in animals, plants and fungi
- recombination and crossing over occurs in prophase
- produces 4 haploid daughter cells
- daughter cells are genetically different
Functions of the reproductive systems
- Production of Gametes
- Production of Sex hormones
- Fertilisation - unites 2 gametes to form a diploid (2n) with a full set of chromosomes
- Development and nourishment of baby
What are gametes
= egg and sperm are haploid (n) and have 23 chromosomes
- each gamete is genetically unique due to genetic recombination in prophase 1
What is oogenesis ?
= the process of producing oocytes in the ovaries and starts during foetal development and stops before birth
- on pause until puberty
1st meiotic division before ovulation - 2nd meiotic division if fertilisation stressful
What is spermatogenesis?
= the process of producing sperm in the testes begins at puberty
Hormonal feedback mechanisms
Day 1-10
- oestrogen (and inhibit) initially inhabit anterior pituitary secretions of FSH and LH by negative feedback
- the pituitary is inhibited by low levels of oestrogen but stimulated by high levels of oestrogen
- as the follicle matures it releases its own oestrogen
- the pituitary is inhibited by low levels of oestrogen but stimulated by high levels of oestrogen
Day 14-25
- corpus liuteum secretes progesterone, a littler oestrogen and inhibit which inhibit LH and FSH secretion from pituitary by negative feedback system
The female reproductive cycle
phases:
1. menstual
2. preovulatory
3. ovulation
4. post ovulatory
- feedback is important in regulating hormonally controlled cycles
- the high levels of oestrogens during the last part of the preovulation phase have a positive feedback effect on cells secreting LH and GnRH thus bringing about ovulation
There are many hormonal interactions between the ovarian and uterine cycles
Female hormones
- Oestrogen - promotes development and maintenance of female reproductive structures
- progesterone - works with oestrogen to prepare endometrium for implantation
- relaxin - Inhibits contractions of uterine smooth muscle
- during labour increases flexibility of pubic and dilates cervix
- inhibit - FSH, GnRH and LH
ovaries
= paired glands that produce gametes and hormones (oestrogen, inhibin and relaxin)
- located each side of uterus
- produce two oestrogen (oestradiol and estrone)
Fallopian tube
= Extends laterally from each side of the uterus, open to peritoneal cavity, terminates in fibriam near each ovary
- site of fertilisation
- pathway for the sperm to reach the ovum and for the secondary oocytes and fertilised ova to travel to the uterus
The uterus
Three layers
- serosa - outermost layer
- myometrium (3 muscle layers
- the endometrium - inner layer (shed each month)
Follicles
- contain oocytes in various stages of development
- a mature follicle is ready to rupture and expel the secondary oocyte
Vagina
- receives penis
- outlet for menstrual fluid and baby
What is the effect of the follicle stimulating hormone on females:
- FSH stimulates follicles to develop in the ovarian cortex. Each ovarian follicle consists of an oocyte (immature ovum) surrounded by cells.
- If there is only one layer of cells surrounding the oocyte these surrounding cells are called follicle cells, if there is more than one layer they are called granulosa cells
What is the effect of the follicle stimulating hormone on males?
- FSH activates cells surrounding the seminiferous tubules (called sustentacular or Sertoli cells) In the testes to bind testosterone and stimulate spermatogenesis
Testes
- produce sperm from puberty which are delivered to exterior of body through a system of ducts
- sperm are formed seminiferous tubules and testes
Penis
- delivers semen to vagina
- erection is brought on by parasympathetic innervation leading to vasodilation of arterioles in erectile tissue
- large amounts of blood enter the tissues into dilated
Spermatogenesis
- Spermatogenesis begins with spermatogonia (diploid stem cells) –> diploid primary spermatocytes –> meiosis I to become secondary haploid spermatocytes –> meiosis II to become spermatids
Hormones in males and what is its effect
Testosterone
- Completes spermatogenesis (FSH initiates spermatogenesis)
- Stimulates the formation and maintenance of male reproductive organs
- Promotes secondary sex characteristics (bigger bones and muscles, deep voice, hair, higher metabolic rate)
- Is responsible for libido and aggression
Hormonal feedback mechanisms in males
- Inhibin (secreted when sperm count is high) inhibits anterior pituitary secretion of FSH (and possibly hypothalamic secretion of GnRH
- High testosterone inhibits hypothalamic secretion
