Flashcards in Week 1.1 - Origin of the gametes Deck (57)
How many gametes are produced in a lifetime by oogenesis/spermatogenesis?
-approx 400 in oogenesis
-approx 200 million a day in spermatogenesis
Which gamete production is continuous and which is intermittent?
-Spermatogenesis is continuous
-Oogenesis is intermittent (once a month)
What are the two main functions of meiosis?
-Reduce chromosome number in gamete to 23
-Ensure every gamete is genetically unique
How many gametes produced from meiosis?
How does genetic variation arise in meiosis?
-Crossing over (exchange of DNA between to homologous chromosomes)
-Random segregation (Distribution of chromosomes among four gametes)
-Independent assortment (Two homologous chromosomes of a pair go to separate gametes
What is the sequence during differentiation in spermatogenesis?
-Germ cell -> spermatogonium -> primary spermocyte -> secondary spermocyte -> Spermatid -> spermatozoon
What is spermiogenesis?
-Maturation of a spermatid into spermatozoon
How long does spermatogenesis take?
What is the function of ad/ap spermatogonium?
-Ad spermatogonium replenishes germ cell stock
-Ap spermatogonium progress to spermatozoa
Where does spermatogenesis take place?
-Seminiferous tubules in testis
What are sertoli cells and where are they found?
-Cells which nourish the developing sperm
-Found lining the seminiferous tubules and interwoven between spermatogonia
Within the tubules, how is differentiation arranged?
-Germ cells line the basal lamina of a tubule and become more differentiated towards the lumen
What is the sertoli cell barrier (blood testis barrier)? Why is it important?
-Tight junction barrier between germline cells and spermatozoa
-Cellular environment for differentiation of sperm not suitable for germ cells
-Also prevents autoimmune response due to genetic differences in spermatozoa
Do all spermatogonia mature at the same time?
-No, different areas of the seminiferous tubule mature at different times
-Different groups mature together because cytoplasmic bridges join some spermatogonia together. This produces a spiral pattern of differentiation along the seminiferous tubule towards the lumen
What is spermatogenic wave?
-The distance between two identical stages of maturation along a tubule
What is a spermatogenic cycle?
-The time taken for the reappearance of the same stage in a given segment
-About 16 days
What is spermiation?
-Release of spermatids into the lumen of seminiferous tubules
Describe when and where spermatids mature into spermatozoa?
-when they are Released into lumen of seminiferous tubules they are carried to the rete testis and into the epididymis. They are remodelled as they do, finally becoming spermatozoa in the epididymis
When do the spermatozoa become motile?
-When they reach the epididymis
If sperm are non-motile until the epididymis, how do they get there?
-They are carried by sertoli cell secretions and peristaltic action
How much semen is produced per ejaculate?
What are the constituents of semen?
-Seminal vesicle secretions (70%)
-Secretions of prostate (25%)
-Bulbourethral gland secretions
What are seminal vesicle secretions comprised of?
What are prostatic secretions comprised of?
How many sperm per ejaculate?
What is the purpose of bulbourethral gland secretions?
-Neutralise acid in distal urethra
State the structures sperm passes on its way to ejaculation
-Pass seminal vesicles
-Passes through prostate
-Passes bulbourethreal glands
What comprises the ejaculatory ducts?
-The union of the vas deferens with the seminal vesicles
What is sperm capacitation?
-Final step before sperm become fertile
-Under the conditions of the female genitalia tract glycoproteins and cholesterol are removed from the plasma membrane of the sperm and there is activation of sperm signalling pathways
-Allows sperm to bind to zona pellucida of oocyte and initiate acrosome reaction