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Histology > Lecture 41 > Flashcards

Lecture 41 Flashcards

1
Q

3 types of follicles (maturation of oocytes and production of steroid hormones takes place in ovarian follicles)

A
  1. Primordial Follicles
    - Primordial: lie dormant in ovary throughout reproductive life of a female
    - Under hormonal stimulation, the primoridal follicles grow and change shape
  2. Growing Follicles
    a) Primary Follicles
    b) Secondary (Antral) Follicles
  3. Mature or Graafian Follicles
    - Graafian follicles will release oocyte into fallopian tube during ovulation
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2
Q

Precursor of Estrogen and progesterone

A

Estrogen and progesterone has androgens as precursor

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3
Q

Ovary - general organization

A

Cortex on outside, medulla on inside.
- All ovarian follicles in cortex.
- Medulla contains stroma of CT, blood vessels. Blood supply goes into
medulla and then branches into cortex

Primordial follicle to unilaminar primary follicle to multilaminar primary follicle to secondary (antral) follicle to graafian follicle

After oocyte has left, it produces corpus luteum (steroid hormone-producing gland that supports the uterus for implantation and during pregnancy)

If pregnancy does not occur, corpus luteum involutes and cells die to form scar called corpus albicans. Small scar if no pregnancy

Corpus hemorrhagicum is the period

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4
Q

Ovarian cortex details

A

Ovary is covered by cuboidal ep called germinal ep. Germinal ep is bw peritoneal cavity and ovary.

  • Female germ cells are born in yolk sac and migrate into cortex of ovary
  • DICT under germinal ep is called tunica albuginea

The ovarian cortex contains numerous primordial follicles, each housing a primary oocyte
- Oocyte has nucleus and cytoplasm surrounding it. It also has flat layer of cells surrounding the oocyte.

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5
Q

Primordial ovarian follicle

A
  • Primary Oocyte: arrested in prophase Meiosis I
  • chromosomes are visible in nucleus
  • has squamous follicular cells on outside. These are support cells, they nourish the oocyte, and they sit on a basement membrane.
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6
Q

Number of immature, primary and mature oocytes throughout life

A
  • During life time of female, as the follicle develops in mother, about 5 million immature oocytes or germ cells are migrating
    from yolk sac into the cortex of the ovary
  • These cells spend significant amount of time in this stage, up to 40 years
  • Of those 5 million primary oocyte, which are arrest at the first meiotic division, once a female is born there are about 400,000 left.
  • Most of them die during development.
  • During the reproductive female lifespan, about 500 mature and undergo further development
  • During reproductive life span of women, several of the primordial ovarian follicle will further develop into primary unilaminar
    follicle.
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7
Q

Primary unilaminar follicle

A

Primary follicles contain primary oocytes surrounded by a monolayer of cuboidal follicular granulosa cells. The zona pellucida develops.
- Oocyte is also arrested in prophase of meiosis I

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8
Q

Zona pellucida

A
  • eosinophilic layer develops bw cuboidal follicular cells and oocytes during the stage of primary unilaminar follicle. and it remains in tact until fertilization.
  • this layer is made up of glycoproteins that are made by the oocyte.
- there are also sperm receptors here, so the
acrosomal reaction (enzyme reaction that occurs as sperm binds to allow the spermatozoa to penetrate) can occur.
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9
Q

Primary multi laminar follicle

A
  • granulosa cells have divided rapidly to form a multilayer coat
  • Zona pellucida is penetrated by cytoplasmic processes of the follicular granulosa cells
  • the granulosa cells support the oocyte with signals and nourishment
  • Oocyte and Granulosa Cells communicate through gap junctions through zona pellucida

Order (outside to in): granulosa cells, zona pellucida, oocyte

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10
Q

Secondary antral follicle

A
  • formation of antrum due to liquid secreted by granulosa cells
  • material inside antrum has lots of glycoproteins and is called the liquor folliculi
  • oocyte is still arrested at prophase of meiosis I
  • it is a primary oocyte within a secondary follicle
  • on the layer of granulosa cells, surrounding the secondary follicle, there is a dark pink line, which is the basement membrane bw granulosa cells and remaining tissue
  • cells that surround the follicle form 2
    distinct layers called theca interna and theca externa
  • theca externa is made of CT with collagen, fibroblasts, has stroma cells
  • theca interna developed to produce and secrete androgens. they are steroid-
    hormone producing cells
  • androgens are passed on to the granulosa
    cells. Most androgens are absorbed by granulosa cells. Very little ends up in the surrounding vascular system
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11
Q

Theca cells

A

Granulosa Cells convert Androgens received from Theca Interna Cells into Estradiol.
•LH triggers androgen production in Theca Cells
•FSH triggers Estradiol production in Granulosa Cells

  • theca interna cells have lots of cholesterol. this is a steroid hormone producing cell
  • theca interna cells take up cholesterol, stimulated by LH and produce androgens that they pass on across the basement membrane to the granulosa cells
  • androgens are immediately changed by aromatase enzymes into estradiol
    or estrogen. this activity needs FSH. FSH binds to receptors on the granulosa cells to convert androgens to estrogens.
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12
Q

Mature graafian follicle

A
  • the follicle becomes very big, antrum fills with lots of liquid, it creates some hydrostatic pressure that helps to expel the oocyte
    during ovulation
  • There is granulosa cell layer. There are capillaries within theca interna cell laye. There is theca externa that is CT layer
  • this follicle expels the oocyte
  • oocyte is attached to the rest of the granulosa cell layer by protrusions called cumulus oophorus.
  • this is the connecting piece of the oocyte to the remainder of the layer of granulosa cells
  • the granulosa cells also surround the oocyte, forming a covering called the corona radiata.
  • during ovulation, the oocyte separates from the cumulus oophorus and carries with it the corona radiata
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13
Q

Ovulation and LH surge effects

A
  • 12-24 hours before ovulation, a surge of LH from pituitary gland triggers completion of Meiosis I

LH triggers a few events:
- induce the capillaries that you find in the theca interna to proliferate (Angiogenesis of blood vessels)
- androgenesis occurs and they are sprouting into the granulosa cell layer. There’s some bleeding occurring, filling the antrum. This is Called the corpus hemorrhagicum
- There are enzymes released in the CT, induced by the LH surge, that soften up the tissue so there is a weak spot that breaks open and the oocyte is released
- in response to high LH levels, the oocyte immediately finishes meiosis I and enters meiosis II
— the product of meiosis I is 2 cells. 1 cell will be the ovum (secondary oocyte), the second cell is very small and has a lil bit of genetic material and is called the first polar body.
— the first polar body appears after ovulation.
— Now we have a secondary oocyte (ovum) that immediately arrests in metaphase of meiosis II. A meiotic spindle of second meiosis forms and stays like that until fertilization occurs.
- the breakdown of tunica albuginea is mediated by the theca externa releasing enzymes. during ovulation, cells in theca externa are stimulated to breakdown the CT by enzymatic digestion in response to
LH surge

The graafian follicle, after ovulation, is initially called corpus hemorrhagicum bc it is filled with a lil bit of blood.

  • the oocyte has left, its being expelled through surface of ovary.
  • there is still germinal ep on outside of corpus hemorrhagicum
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14
Q

Pathway from primary oocyte to sperm entry

A
  1. Primary Oocyte arrested at Prophase of Meiosis I (fetal ovary to puberty)
  2. Completion of Meiosis I during ovulation
  3. Secondary Oocyte arrested at Metaphase of Meiosis II. Has first polar body
  4. Completion of Meiosis II following sperm entry. Has 2 polar bodies
    - if you look at oocyte in Petri dish and you see 2 polar bodies, you know that the oocyte has been fertilized
    - eventually the male and female nuclei fuse to form zygote or embryo
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15
Q

Oocyte through Fallopian tube

A

During ovulation, the primary oocyte completes meiosis I, and travels through the oviduct as secondary oocyte (ovum), then arrested at metaphase of meiosis II. The ovum completes meiosis II only upon sperm entry. Cleavage of the zygote commences in the oviduct (fallopian tube)

Fertilization occurs within fallopian tube. Then cell division occurs. Then there is blastocyst that enters the uterus through the Fallopian tube and then implants on the wall of the uterus

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16
Q

Corpus luteum and corpus albicans, if pregnant or not

A

After a while, the Corona radiata will disappear, but there is still zona pellucida. The sperm receptors are part of the zona pellucida, so the spermatozoa dont have to navigate through the corona radiata cells

After oocyte has left, there is process called luteinization (elements of ovarian follicle, theca interna and granulosa cells, develop into the corpus luteum). This is part of the graafian follicle that expelled its oocyte and the remaining granulosa cells transform into an endocrine organ (corpus luteum) that makes a lot of progesterone. This corpus luteum is so large that it pushes into the medulla and takes up a lot of room. It becomes very large during pregnancy

If not pregnant, no fertilization, no implantation, the corpus luteum does not become that big. It does make progesterone after ovulation to support implantation just in case, but without implantation, there is
no feedback bw uterus and ovary, and the corpus luteum will disappear

If preggo, hormones produced by the placenta, such as human Chorionic
gonadotropin, will tell the cells to continue to make progesterone to support the placenta. Then the corpus luteum will get big

After birth, corpus luteum is not required anymore to make progesterone, but it becomes a scar, called corpus albicans. These large scars are indicative of pregnancy. Physicians can look at ovary
and count the number of scars and can tell how many pregnancies a woman has had (based on number of corpus albicans present).

17
Q

Corpus luteum

A

2 layers
•Granulosa Cells become Granulosa Lutein Cells
•Theca Interna Cells become Theca Lutein Cells

  • the granulosa lutein cells continue to make estrogen
  • LH hormone induces production of progesterone from both theca lutein
    cells and granulosa lutein cells
  • Progesterone then enters
    capillaries, which are found throughout the corpus luteum
  • corpus luteum is highly vascularized, perfused by capillaries and is endocrine organ and receives lots of progesterone and estrogen

There is corpus luteum with some antrum in the middle. If you look at the cell layer on the outside of antrum, there are 2 cell types:

  1. granulosa lutein cells are large with lots of cytoplasm
  2. theca lutein cells are smaller, darker stained and migrate into granulosa lutein cell layer. They are forming strands of cells with smaller nuclei but less cytoplasm.
18
Q

Corpus albicans

A

Scar tissue, remnant of Corpus Luteum

Corpus albicans is result of deteoriartion of corpus luteum. If we have large corpus luteum, the remaining tissue (scar) will also be large.

Inner is mostly extracellular matrix, white-ish, with some nuclei, and it is surrounded by stroma of the ovary.

The scar is called corpus albicans. During the normal development of ovarian follicles, quite a few follicles cease developing (5 or 10 follicles develop every month, but at 1 point, they stop developing, so there is a bit of competition bw developing follicles. Only 1 or 2 will finish development and ovulate in
humans)

The remaining follicles that dont make it also form little scars and are called atretic follicle (or follicular atresia) (small remnant of follicle that fails to develop). Atresia is process by which follicles die, can see this as pyknotic dying nuclei, then there is a lil scar tissue forming. The atretic follicle is everywhere in ovary but don’t form a significant scar

19
Q

Ovarian cycle

A

Pituitary gland makes FSH and LH. Both of these regulate the maturation and development of ovarian follicles.

First half of menstrual cycle is when follicles develop and is called Follicular Phase aka Estrogenic phase bc this is where the
follicles make lots of estrogen. In response, estrogen levels rise in the blood
- Estrogen secreted by growing follicles

As estrogen levels rise, that is a trigger for the pituitary gland to have a surge of LH. There is also a lil FSH surge, but it is mostly LH surge. LH surge induces ovulation

As a response, the increase in LH induces the corpus luteum to produce progesterone.

Second half of menstrual cycle is called progestational stage AKA luteal phase

  • Estrogen and Progesterone secreted by Corpus Luteum
  • occurs after ovulation

Histology (25 decks)

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