Reproduction 3 Flashcards by o e

Which hormone is important during the first part of the menstrual cycle?

FSH -> it drives the follicular growth from Primary follicle to mature follicle (Graafian follicle)

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When does a follicle cell become dominant?

Out of 6-20 follicles, 1 becomes dominant on day 7

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What does the dominant follicle secret?

Low level of Estrogen -> negative feedback

Estrogen -> Estrogen level increases and causes negative feedback to FSH -> other follicles die (follicular atresia)

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What is the consequence of the growth of the dominant follicle?

It secrets more Estrogen -> now causing positive feedback on FSH and LH -> FH and LH surge on day 14

High level of Estrogen -> positive feedback

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What happens on day 14?

The LH surge is responsible for ovulation -> the mature Graafian follicle burst and allows the oocyte to go off the surface of the ovary

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What happens to the ruptured follicle?

LH (luteinizing hormone) causes the ruptured follicle to become corpus luteum

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What does the corpus luteum do?

The luteal phase starts, and the corpus luteum secretes estrogen and progesterone + Inhibin

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What are the functions of estrogen, progesterone, and Inhibin

Negative feedback to Hypothalamus and anterior pituitary -> no release of Gonadotropins (FSH and LH) -> no development of new follicles

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What happens to the Endometrium when estrogen is secreted?

Endometrium becomes thick and proliferative caused by estrogen so that the oocyte can get implanted and eventually fertilized, and progesterone provides a nutritious environment in the endometrium (becomes secretory) for a conceptus being implanted

Time window: 12-24 hr for the egg and 72 hr for the sperm

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What happens if no fertilization occur?

If there is no signal at around day 25 that a pregnancy has occurred the corpus luteum degenerates -> estrogen, progesterone, and inhibin will decrease until day 28

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What happens if the corpus luteum degenerates?

It becomes the white corpus albicans

Loss of negative feedback to the Hypothalamus, anterior pituitary, and Gonadotropin release
Loss of estrogen and progesterone release -> Endometrium gets shed

-> Corpus luteum in form of Menses will pour out -> which is DAY 1

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What are some effects of estrogen?

-Proliferative endometrium, watery cervical
mucus -> makes penetration of sperm easier
-Internal & external reproductive organ growth
-Bone growth in youth/ prevent bone loss (also stops bone growth in females)
-Fat distribution
-has anti-acne effect -> stimulation of fluid from sebum glands#

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What are some estrogen molecules?

-Estradiol: 2x OH
-Estrone: Ketone group
-Estriol: 3x OH

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What is the Menopause?

Ovulation gradually stops at the age of 51 due to loss of estrogen production

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What are symptoms of the Menopause?

Hot flashes -> estrogen provides some feedback to hypothalamus in regulating body temperature -> lost in Menopause bc of the drop of estrogens -> small temperature changes can cause major symptoms

-Bone loss (estrogen is antiresorptive - bc osteoclasts.. -> loss of bone density)
-mood swings
-increase in CV risk

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What is considered pregnancy?

Fertilization of secondary oocyte to the infant is born

Gestation is measured from the last menstrual period until birth
-> so for gestation you will add 2 weeks, bc fertilization can only occur 2 weeks after day 1 of menstrual cycle

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Stages of pregnancy:

Preembryo: Conceptus from fertilization until 2 weeks old

Embryo: Conceptus during the 3rd through the 8th week

Fetus: Conceptus - from 9th week until birth

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What is fertilization?

sperm fuses with an oocyte to form a zygote
oocyte is viable for 12-24 hr
sperm is viable for 24-72 hr

it must occur 3 days before ovulation or 1 day after ovulation

Why do most of the sperm cells not make it to the uterus?

-Leak out of vagina
-acidic vaginal environment
-stuck in the mucus
-destroyed by phagocytic leukocytes
-out of 300 million -> 100-200 make it

How can sperm motility be supported by the female?

During orgasm females produce oxytocin and prostaglandin, causing contraction of the uterine that will aid in sperm motility

How does the sperm penetrate the oocyte?

Sperm binds to the zona pellucida and undergoes the acrosomal reaction -> the enzymes in the acrosome pocket will be released helping to digest the coatings of the oocyte

How is the fertilization of only 1 sperm cell ensured?

Block to Poly -> once one sperm cell penetrates the oocyte it causes the cortical granules the release its content (green) -> a fertilization membrane is formed and blocks all the other sperm cells

What happens to the oocyte after the sperm enters the egg?

-Oocyte completes 2nd meiotic division -> Nuclei of sperm and egg unite

-Egg enzymes are activated to drive the process of zygote cell division and development -> during cell divisions it migrates through the uterine (Fallopian) tube towards the uterus

What are the stages of cell division?

1st stage (Morula): The zygote undergoes cell division without cell growth -> period of cleavage - the cells divide into smaller cells

Continued growth becomes blastocytes with hollow core (embryoblast) and cells outside of the ball -> Throphoblast cells

What do Throphoblast cells and Embryoblast cells differentiate into?

Trophoblast: The baby portion of the placenta -> chorion Embryoblast: becomes the embryo -> Fetus

What do Throphoblast cells and Embryoblast cells differentiate into?

Trophoblast: The baby portion of the placenta -> chorion Embryoblast: becomes the embryo -> Fetus

When does implantation occur?

On day 6-7 after ovulation, when Blastocytes (with Throphoblast and Embryoblast) are formed (Blastocytes are implanted during IVF)

What about twins?

-Fraternal twins: 1-2% of ovulations results in the release and development of more than one oocyte + if they are penetrated by sperm cells -> TWINS -Identical twins: Separation of cells during the period of cleavage - as all cells are totipotent

Explain the process of Implantation:

6-7 days after ovulation the Trophoblast adheres to the Endometrium -> proteolytic enzymes help to bury the Blastocyte into uterine -> Throphoblast forms the placenta/chorion -> Embryoblast forms the Embryo

What can happen in this period - related to the menstrual cycle?

Minimal pour out of blood -> 2 weeks earlier than expected (in case a normal cycle is expected), bc normal cycle with pour out of menses would occur 2 weeks later

REMINDER: When does the corpus luteum start to degenerate and would cause to shed of the endometrium?

On day 25 -> loss of negative feedback to production of FSH and LH from anterior pituitary -> loss of secretion of estrogen, progesterone, and inhibin -> shedding of the endometrium

What do Trophoblasts secrete?

hCG (human chorionic gonadotropin) prevents menstruation h - human c - chorionic (thromboblast) g - the acts like gonadotropin LH

How is menstruation prevented by hCG?

Binding of LH receptors and thereby acting as LH -> gives the body signal to keep the corpus luteum present Effect: Estrogen and progesterone still be produced -> endometrium stays proliferative and secretory (menses will be skipped a week later) and the negative feedback will still be active, no development of new follicles

What is hCG also used for?

ELISA pregnancy test -> bc it is only released when a female is pregnant (binds to the same receptor as LH, but still looks different enough to be detected and differentiated from LH by the ELISA)

What is the placenta and its role?

It is a highly vascularized structure surronding the embryo and endometrium -> allow exchange of nutrients, gases, and wastes

When is the placenta fully formed and what is its function then?

3rd month of gestation, it will take the role of corpus luteum in secreting estrogen and progesterone -> which will provide negative feedback to the anterior pituitary -> no FSH and LH -> no development of new follicles?

What are chorionic villi and Lucanae/sinuses?

chorionic villi: extensions of the chorion dipping into the endometrium Lucanae/sinuses: area of pooled maternal blood, exposed by digested maternal blood vessel caused by proteolytic enzymes of chorionic villi

How does the exchange between fetal and maternal blood occur?

Trophoblast/chorion: chorionic villi have released proteolytic enzymes to burry into the endometrium and also digested the maternal blood vessels -> causing the maternal blood to be pooled around this area

In terms of administering drugs to pregnant women: What barriers need to be crossed to reach the fetus's blood?

The maternal blood is pooled and open, to reach the blood of the fetus only the membrane of the chorionic villi and the capillaries inside the villi has to be crossed

Why is the blood in the Lucanae/sinuses is considered pooled?

Because it is a mix of oxygenated (from arteries) and deoxygenated (from veins) maternal blood -> there is nothing separating them

How does the pooled maternal blood travel to the fetus?

Vein = TO the FETAL heart (AWAY from the MOTHER's HEART) Arteries = AWAY from the FETAL heart (TO the MOTHERS HEART) Through the Umbilical vein carrying the blood to the fetal heart Deoxygenated blood from the fetus is transported by the umbilical arteries to the heart of the mother

How are the umbilical arteries and veins directed to the fetus

Umbilical core, carrying the umbilical vein and aretery

What is the amnion?

Located between Embryo and Chorion, filled with amnion fluid, eventually fuses with inner surface of chorion