Gonads 1 Flashcards
Describe the change in number of oogonia in women throughout life.
Maximum (24 weeks gestation) - 6-7 million
Birth - 2 million Puberty - 400,000
300-400 mature eggs released Menopause - 0
What is the process by which oogonia degenerate and die?
Atresia
Describe the steps in spermatogenesis.
Germ cells divide to produce spermatogonia. Spermatogonia remain dormant until puberty where a rise in FSH triggers division of spermatogonia to produce more spermatogonia and primary spermatocytes (still diploid). Primary spermatocytes enter first meiotic division to form secondary spermatocytes(haploid). Secondary spermatocytes enter second meiotic division to form spermatids. Spermatids mature into spermatozoa.
What stimulates the spermatogonia to proceed to the next stage and when does this happen?
FSH release during puberty
How long does the process of spermatogenesis take place?
70 days
Describe the steps in oogenesis.
Germ cells divide to produce oogonia. Oogonia divide mitotically to produce primary oocytes (diploid). Primary oocytes enter the first meiotic division straight away but are halted in prophase of the first meiotic division. The oocytes form a layer of cells around them, forming primordial follicles. These cells remain dormant for 12-50 years. More cells die of atresia. Puberty - release of FSH rescues a group of the dormant cells and they continue development. They complete the first meiotic division around the time of ovulation. If fertilisation takes place, they will complete the second meiotic division to form an ovum.
What is produced after the first meiotic division is complete?
Secondary oocyte + first polar body
What is required to complete the second meiotic division?
Fertilisation
What is produced after the second meiotic division is complete?
Ovum + second polar body
Describe the passage of sperm from production to release.
Sperm is produced in seminiferous tubules. It moves to the rete testis where it is concentrated. It then moves via the vasa efferentia to the epididymis for storage (nutrients are secreted here and they attain their motility). It is ejected via the vas deferens (which has smooth muscle around it) and then via the urethra.
Describe the structure of seminiferous tubules.
Spermatogonia around the outside Underlying this is a layer of Sertoli cells.
The lumen of the seminiferous tubule is on the inside
What important cell type lies outside the seminiferous tubules? What do they produce?
Leydig cells - they produce LH receptors and in response to this it produces testosterone which is needed for spermatogenesis to take place
How do spermatogonia pass through the Sertoli cell barrier?
They move into the Sertoli cells and are enclosed in the cytoplasm of the Sertoli cells. The Sertoli cells provide structural and metabolic support for the spermatogonia and help them develop. They then enter the lumen.
Describe which receptors are expressed by Sertoli cells and Leydig cells.
Sertoli Cells - FSH receptor and Androgen receptor Leydig Cells - LH receptor
What is inhibin and what cells produce this?
Inhibin inhibits the release of FSH and is produced by Sertoli cells