5 - Gametogenesis Flashcards
How is genetic variation ensured during meiosis?
- Independent assortment
- Random segregation
- Crossing over (in bivalents)
What are the differences between male and female gametes?
What is spermatogenesis and where/how does it occur?
- Haploid cells from germ cells
- In seminiferous tubules
- Spermatogonia in basal compartment divide by mitosis to form two primary spermatocytes, one replacing spermatogonia and one undergoes meiosis I to form secondary spermatocytes
- Meiosis II to make 4 spermatids
What is the blood-testes barrier?
- Basal compartment = spermatogonia
- Adluminal compartment = spermatids
- Leydig cells, next to sertoli cells, secrete testosterone
- Barrieer prevents autoimmune destruction of genetically diverse sperm
What are the two different types of spermatogonium?
D = dark (quiescent state if needed)
P = pale
What is a spermatogenic cycle and wave?
Cycle: time taken for spermatids at the same stage in the cycle to reappear within a given segment. approx 16 days
Wave: distance between groups of spermatids at the same level of maturation.
Allows male to always be fertile
What is spermiogenesis?
- Spermatids become spermatazoa (mature sperm)
- In lumen of seminiferous tubule non-motile sperm becomes motile
- Process complete by epididymis
What is the structure of a sperm?
- Head: nucleus and acrosome layer for when touches ova
- Tail: motility. lots of mitochondria for ATP to provide energy for the flagella
What is sperm capacitation?
- Occurs in female reproductive tract
- Spermatozoa now fertile
- Acrosome reaciton allows it to get through zona pellucida
Where is the derivatives of semen?
- Fructose: to stop competition with lactobacilli for glucose
- Zinc: high conc means low motility
What is the process of oogenesis before birth?
- Germ cells from yolk sac go to ovary and form oogonia, which proliferate by mitosis
- All enter meiosis I and stop at prophase = primary oocytes
- End of 3rd month surrounded by flat epithelial cells called follicular cells = primordial follicles
- Oogonia already undergoing atresia at this point
After birth how does oogenesis continue in general?
Describe the three phases of a maturing oocyte.
- Preantral: 15-20 follicular cells change from flat to cuboidal stratified. Called granulosa cells. These cells secrete glycoprotein on oocyte to form zona p. Primary follicle
- Antral: Fluid filled spaces between granulosa cells. Collective space called antrum, secondary follicle. Outer fibrous layer forms theca interna and externa.
- Preovulatory: LH surge so follicle completes meiosis I. One chosen to go to maturity - Graafian follicle. Will start meiosis II 3hrs before ovulation but stops in metaphase. Only completes meiosis II if fertilised, polar bodies discarded. No fertilisation the oocyte degrades after 24 hours
What other cells are released with the ova?
How does the process of actual ovulation occur?
Once the oocyte has left the ovary, what happens to the left over theca interna/externa cells?
- Dies after 14 days and forms a mass of scar tissue called corpus albicans
How is the oocyte transported down the uterine tube?
What happens to the corpus luteum if fertilisation occurs?
What are the main differences between oogenesis and spermatogenesis?
What is the histological structure of an ovary?
Label the following histological images to explain what follicle is being shown in the ovary.
What does the corpus luteum look like histologically?
