Gametogenesis Flashcards
What is a gamete?
The cells responsible for reproduction - sperm and ova - these are haploid cells derived as a product of meiosis containing half the normal amount of DNA and they fuse together to form a diploid zygote
How does genetic variation occur?
genetic variation ensures each gamete is genetically unique
- crossing over
- independent assortment
- random segregation
What are the differences between men and women in regards to their fertility?
women only have about 400 ova in a lifetime - they are present at birth but are stimulated by fertilisation
men produce a large number or sperm (200 million) per day so their reproductive potential is pretty much unlimited
Where does spermatogenesis occur?
seminiferous tubules
Why are spermatifus at different levels of maturation at different sections of the seminiferous tubules?
if all were at the same stage then men would need to wait until fill maturation - and as women are only fertile for short periods of time this is not beneficial for fertilisation
What is the spermatogenic cycle?
the length of time it takes for spermatids at the same stage in the cycle to show up again when looking at a specific point along the seminiferous tubules
What is the spermatogenic wave?
to distance between groups of spermatids at the same level of maturation
What is spermiogenesis?
the process by which spermatids become spermatozoa
When does spermiogenesis take place?
once the spermatids have been released into the lumen of the seminiferous tubules
What happens to the spermatozoa as they pass down the seminiferous tubules?
they remodel as the pass through the retentions testis to mature - non motile spermatids become mobile by the time they reach the epidydimis
How do spermatids move if they aren’t mobile?
peristaltic contractions and secretions by the sertoli cells
Why do sperm need mitochondria?
they need energy (ATP) and use fructose as their metabolic fuel - flagella tail provides motility for the sperm
What do the seminal vesicles secrete?
AA, citrate, fructose, prostaglandins
Why is fructose used instead of glucose?
to reduce competition with bacteria
What do the prostatic glands produce?
proteolytic enzymes and zinc - less zinc more fertility
What do the coppers glands produce?
mucoproteins to help lubricate and neutralise acidic urine in distal urethra
What is sperm capacitation?
final maturation step required before sperm becomes fertile
Where does capacitation occur and why?
in the female genital tract as the conditions there stimulte;
- removal of glycoproteins and cholesterol fro sperm membrane
- activation of sperm signalling pathways
- allow sperm to bind to zone pellucid of oocyte and initiate acrosome reaction
What is oogenesis?
the process of oocyte maturation in the ovary
Where do germ cells come from?
arise from the yolk sac
How is an oocyte transported?
the fimbrae sweep over the surface of the ovary and the uterine tube begins to contract rhythmically so the oocyte is carried to the tube by the swelling movements of the frimbriae - oocyte then propelled by peristaltic muscular contractions of the tube and by cilia in the mucosa
How is an oocyte transported?
the fimbrae sweep over the surface of the ovary and the uterine tube begins to contract rhythmically so the oocyte is carried to the tube by the swelling movements of the frimbriae - oocyte then propelled by peristaltic muscular contractions of the tube and by cilia in the mucosa
What happens to the CL if no fertilisation occurs?
the CL degrades and forms a mass of fibrotic scar tissue called the corpus albicans - progesterone production decreases so menstruation follows
What happens to the CL is fertilisation occurs?
HCG produced by the embryo prevents CL degenerating and the CL grows to form the CL of pregnancy which secretes progesterone until the placenta becomes adequate to secrete it itself
