mammals

Question 1

what is the class of mammals?

Answer 1

mammalia

Question 2

what are the characteristics of mammals?

Answer 2

Mammals are members of class Mammalia → air-breathing vertebrate animals characterized by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young. Most mammals also possess sweat glands, specialized teeth, red blood cells with no nucleus, four chambered heart

Question 3

list difficulties of working with mammals

Answer 3

Small eggs
1000 times smaller than frogs

Produce very few eggs at ovulation
Fewer than 10 eggs at a time

Fertilized internally
Limited access

Ethically troublesome

Question 4

cumulus cells

Answer 4

surround oocyes
connected to oocytes via gap junctions
support and nourishment
attract, trap and select spermatozoa. 
eg.chemotaxis

Question 5

which cells forms cumulus oophorus?

Answer 5

cumulus cells

Question 6

function of gap junctions?

Answer 6

Supports oocyte growth and maturation
Provides substrates for glycolysis (e.g. Glucose, pyruvate)
Signals to oocyte to keep it viable and to keep it arrested at Prophase I of Meiosis I
Physical protection
Provide a physical barrier
Transfer reducing agents to oocyte to prevent oxidation
Removal of the cumulus cells before IVM reduces viability and fertilization potential of oocytes

Question 7

By which mechanism does oocyte mediate sperm interaction?

Answer 7

chemotaxis and retaining poor sperm while facilitating the movement of normal and hyperactivated sperm.

Question 8

which system control ovulation?

Answer 8

endocrine system

Question 9

define the endocrine system.

Answer 9

hormone system where chemicals are secreted into the blood.

Question 10

function of the follicle stimulating hormone in ovulation

Answer 10

to grow and mature follicles. they vary across the ovarian cycle .

Question 11

describe the negative feedback action of estrogen?

Answer 11

theca interna cells in the maturing follicle secrete estrogen, so estrogen levels increase toward the 12th day.

Question 12

effects of high levels of estrogen?

Answer 12

augments the ability of the ant pit to respond to GnRH (increase the number of GnRH receptors).

Question 13

effect of GnRH

Answer 13

an increasing level of LH and FSH

Question 14

LH/FSH surge

Answer 14

happens 24 hrs before ovulation begins, 16hrs before the peak.

Question 15

FSH surge

Answer 15

cuases the follicle to get bigger and biggger to the ppoint that it produces a thin-walled blisted on the ovary.

Question 16

LH surge

Answer 16

cause the mature follicle to be expelled from the ovary and trasnferred to the uterin tube by ciliated epithelial cells.

it also signals fot he production of proteolytic enzymes released by the follicle that cuase the degradation of the follicular tissue, allowing the cumulus-oocyte to become deposited in the peritoneal cavity.

Question 17

fimbrae

Answer 17

ends of fallopian tubes, swell with blood in response to sex hormones and sweep the cells into the fallopian tubes

Question 18

fertilization

Answer 18

it occurs in the fallopian tube in the area of the ampulla and undergoes its first cleavage 24hrs later

Question 19

cleavage in mammals

Answer 19

Slow (~12-24hrs) compared to others (e.g. flies = 10min)

Rotational cleavage (similar to C. elegans) (Fig 9.17)
Asynchronous from an early timepoint; do not all divide at the same time.
So, embryos frequently contain odd numbers of cells, ie. 3 or 6 blastomeres, instead of exponential 2-to 4-to 8-cell stages.
Zygotic genes are activated quite early

Mice → 2 cell stage; Human → 4 to 8 cell stage

Compaction→Blastomeres maximize their contact with each other by polarization and adhesion, forming a compact ball that is held together by tight junctions (following 3rd cleavage)

E-cadherins begin to become expressed
Embryonic cells start to adhere to each other very tightly (tight junctions), forming tiny holes between them call gap junctions for communication

Question 20

rotational

Answer 20

cleavage

Question 21

asynchronous

Answer 21

do not divide at the same time

odd number of cells; 3 0r 6 cells

Question 22

compaction

Answer 22

adhesion E-cadherins

formation of tight junctions and gap junctions

Question 23

morulla

Answer 23

8 cell embryo

totipotent

Question 24

trophoblast

Answer 24

trophoectoderm
descedants of the oute cells
participate in placental formation and implantation

Question 25

inner cell mass

Answer 25

come from innner cell mass
give rise to extraembryonic cells
pluripotent

Question 26

cavitation

Answer 26

sodium pumps are involved.

pump fluid into the cavity by osmosis

Question 27

the blasotcyst

Answer 27

32 -64 cells by the trophoblast

secrete fluid into morula to form a cavity.

Question 28

tubal pregnancy

Answer 28

premature hatching or implantation in the ovdicut cause life-threatening hemorrhage.

Question 29

how does implanation occur

Answer 29

The zona pellucida prevents the embryo from attaching to the fallopian tubes
To attach to the uterine wall the blastocyst must digest a small hole in the zona pellucida (trypsin protease  →                                                   contributed by the trophoblast)
Endometrium contains many molecules: collagen, laminin, fibronectin, cadherins, heparan sulfate etc.
Estrogen and progesterone (by Corpus luteum) causes the production of L-selectin (bind sugar polymers) and integrins (bind fibronectin, vitronectin, collagen, and laminin) to allow attachment
Wnt proteins (from the trophoblast or endometrium) result in the production of proteases: collagenase, plasminogen activator, stromelysin to allow the blastocyst to bury itself into the endometrial wall

Question 30

amnion

Answer 30

pouch in which an embryo develops. It is a defining characteristic of amniotes. The amnion is adjacent to the epidermis, formed by the ectoderm of the fetus, and is extremely elastic
Contains amniotic fluid → nourishing and protecting liquid
Contains fetal cells so you can assess genetic disorders through amniocentesis

Question 31

Chorion

Answer 31

(fetal portion of placenta)
Formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes.
The chorionic villi emerge from the chorion, invade the endometrium, and allow transfer of nutrients from maternal blood to fetal blood
Also induces the uterine cells to form decidua (maternal portion of placenta)

Question 32

day 15

Answer 32

primitive streak

Question 33

mammals and placental.

Answer 33

Placentals → a particular group of mammals (i.e. NOT marsupials or monotremes)
feeds the offspring during gestation
Humans are obviously placentals
Relevant from an embryological point of view
Massive divergence