Microanatomy: ovaries and fallopian tubes

Question 1

Micro of follicles at different phases 1

Answer 1

• Most follicles in the cortex of the ovary are primordial, and they have no surrounding granulosa layer
• Some follicles will have the beginnings of a granulosa layer (primary follicles)
• Majority of primary follicles will not become graafian and instead will become atretic
• Starting at primary follicles and on the oocyte is surrounded by a pink band (btwn it and the granulosa cells) called zona pellucida
• Zona pellucida is a glycoprotein coat secreted by both oocyte and granulosa cells, it serves to protect the embryo and prevent more than 1 sperm from fertilizing the oocyte

Question 2

Micro of follicles at different phases 2

Answer 2

• Granulosa cells proliferate under control of FSH, theca cells surround the follicle and look like stromal cells
• The BM is beneath the theca cells, no blood vessels cross the BM so oocyte/granulosa nutrition is from diffusion across BM
• Antrum formation (very large follicle) occurs when there is massive proliferation of granulosa cells and follicular fluid accumulation

Question 3

Oogenesis

Answer 3

• Primordial germ cells give rise to oogonium (happens before birth)
• Oogonium proliferates via mitosis into oocytes, which undergo meiotic DNA replication but are arrested (into primordial oocytes, diploid) before the first meiotic division
• Most oocytes are lost by atresia before puberty

Question 4

Secondary oocyte genesis

Answer 4

• At puberty some primordial oocytes begin to mature into primary oocytes and menstrual cycle begins
• During the pre-ovulatory LH surge the pre-ovulating oocyte undergoes the first meiotic division, creating a secondary oocyte (haploid, but 2 copies of chroms) and a polar body

Question 5

Mature ovum genesis 1

Answer 5

• Upon fertilization of sperm the secondary oocyte undergoes the second division, creating the mature ovum (haploid, 1 copy) and a second polar body
• Polar bodies contain nothing but DNA, and the first polar body may or may not undergo another division

Question 6

Mature ovum genesis 2

Answer 6

• This process is to protect the secondary oocyte/ovum from the immune system, since haploid cells do not express nl surface proteins and the secondary oocyte/ovum would be attacked by the immune system if it was present for long enough time
• Since the oocyte remain diploid until just prior to ovulation, it is only haploid until fertilization or menstration (a short time and thus its not attacked by immune system)

Question 7

Antral follicle/graafian follicle 1

Answer 7

• Granulosa cells can be mural (on wall of follicle, closely associate w/ BM) or cumulus oophorus (associated w/ oocyte)
• Mural granulosa cells and theca cells remain after ovulation, and become CL
• Cumulus ephors cells die after ovulation
• Cumulus oophours cells extend contacts down pores in zona pellucida to communicate w/ oocyte

Question 8

Antral follicle/graafian follicle 2

Answer 8

• This means in females gametogenesis and steroidogenesis are linked: when gamete production is lost so is E2/P production (not true in males)
• Around day 12-13 the most mature graafian follicle (almost free-floating oocyte w/in follicular fluid) will be just under the thinning ovarian cortex, where rupture site (stigma) will occur
• Other developing follicles undergo atresia at any phase of follicular development

Question 9

Luteal phase micro

Answer 9

• The (mural) granulosa cells and theca cells form the corpus luteum, which has a high degree of vascularity to ensure transport of the E2/P produced
• Granulosa and theca cells (in both follicular and luteal phases) have classic steroidogenic morphology: lots of SER/mito, no secretory granules, some have lipid droplets
• If no implantation occurs there is luteolysis- death of granulosa and theca cells
• CL becomes corpus albicans- primarily composed of collagen

Question 10

Fallopian tube 1

Answer 10

• Part closest to ovary is infundibulum, and the width of the tube gets progressively smaller as it approaches the uterus
• At the ovarian end of the infundibulum are fimbriae, to sweep the ovary into the tube (they move over the ovary near ovulation)
• After the infundibulum is the ampulla, then the isthmus
• The infundibulum and ampulla have lots of mucosal folds, isthmus has few
• Fertilization should occur in tube, and usually occurs in the ampulla
• Oocyte is moved along the tube by ciliary beating w/in the tube, sperm are moved by fluid flow

Question 11

Fallopian tube 2

Answer 11

• Cells lining the tube are simple columnar epithelia either w/ cilia (basal bodies) or are mucus secreting (peg cells)
• Basal bodies have a dark membrane under the cilia, peg cells do not
• Both cilia and peg cells mucus secretion are stimulated by E2
• Isthmus is narrowest (from lots of SmM) to prevent bad sperm from getting in, can also store sperm for several days
• Utero-tubal junction (UTJ) contains the fewest mucosal folds