Gametogenesis Flashcards
What is gametogenesis?
The making of sex cells, spermatogenesis or oogenesis
What process is required for gametogenesis?
Meiosis, one parent cell makes for genetically different, haploid daughter cells
Where is sperm formed in most species?
Highly specialised organs, gonads
Describe spermatogenesis
Sperm are produced from spermatogonial stem cells. Spermatogonial cells divide by mitosis initially, producing the diploid primary spermatocytes. In total, each primary spermatocyte gives rise to four sperm cells
Where does spermatogenesis occur in insects and mammals?
Insects = occurs within the cysts in testes Mammals = occurs seminiferous tubules in the testes
What is the direction of spermatogenesis in insects and mammals?
Insects = from distal to proximal Mammals = from periphery to lumen
When does spermatogenesis begin in insects and mammals?
Insects = starts in larval stage Mammals = From puberty
How long does spermatogenesis last in insects and mammals and how many sperm are produced per day??
Insects = Produced in a few days, 10 000 per day Mammals = Produced in 74 days, 300 000 000 per day
Where is sperm stored in insects and mammals?
Insects = Stored in the seminal vesicle Mammals = Stored in epididymis for <4 weeks or reabsorbed
Where does semen come from in insects and mammals?
Insects = Semen from accessory glands Mammals = semen from seminal vesicles and prostate glands
What is sperm gigantism?
Sperm length exceeds body length
What is sperm heteromorphism?
The simultaneous production of two or more distinguishable types of sperm by a single male
What is oogenesis?
A primary oocyte gives rise to a single oven, begins in the female embryo
Where does oogenesis occur in insects and mammals?
Insects = From distal to proximal Mammals = Within a follicle
How long oogenesis last in insects and mammals and how many are produced per day?
Insects = Starts in larval stage, eggs are produced in a few days <100 eggs per day Mammals = 400 000 follicles at birth and no more are produced, but ovulation begins in puberty, one egg per month produced
Where are eggs released into in insects and mammals?
Insects = released into uterus for fertilisation Mammals = Follicle ruptures, oocyte enters fallopian tube for fertilisation
What happens if an egg isn’t fertilised in mammals?
If not fertilised, degenerates and prepared uterus lining (thick, vascular endometrum lining) sloughs away
What controls gametogenesis?
Hormones. At puberty, hypothalamus secretes gonadotrophin- releasing hormone (GnRH)
GnRH stimulates FSH (follicle stimulating hormone) and LH (lutenizing hormone) from the anterior pituitary cells.
How do FSH and LH affect spermatogenesis?
FSH – stimulates development of seminiferous tubules (where sperm form) and spermatogenesis acting together with testosterone by stimulating Sertoli cells
LH – stimulates Leydig cells to secrete testosterone which stimulates spermatogenesis
How do FSH and LH affect oogenesis?
FSH – stimulates development of follicles and secretion of estrogens
LH – stimulates maturation of follicles and release of ova at ovulation
What is the role of oestrogen and progesterone
Estrogen – enhances growth of follicles, grows endometrium
Progesterone – grows and maintains endometrium for pregnancy, secretes nutrients for embryo
Fluctuate in 28 d cycle in humans
What do embryonic placental cells secrete if fertilised?
chorionic gonadotropin to rescue the corpus luteum and maintains its function
How does the birth control pill work?
By negative feedback to FSH and LH
When does menstruation occur?
When oestrogen and progesterone levels are low
