mammals Flashcards
what is the class of mammals?
mammalia
what are the characteristics of mammals?
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
list difficulties of working with mammals
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
cumulus cells
surround oocyes connected to oocytes via gap junctions support and nourishment attract, trap and select spermatozoa. eg.chemotaxis
which cells forms cumulus oophorus?
cumulus cells
function of gap junctions?
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
By which mechanism does oocyte mediate sperm interaction?
chemotaxis and retaining poor sperm while facilitating the movement of normal and hyperactivated sperm.
which system control ovulation?
endocrine system
define the endocrine system.
hormone system where chemicals are secreted into the blood.
function of the follicle stimulating hormone in ovulation
to grow and mature follicles. they vary across the ovarian cycle .
describe the negative feedback action of estrogen?
theca interna cells in the maturing follicle secrete estrogen, so estrogen levels increase toward the 12th day.
effects of high levels of estrogen?
augments the ability of the ant pit to respond to GnRH (increase the number of GnRH receptors).
effect of GnRH
an increasing level of LH and FSH
LH/FSH surge
happens 24 hrs before ovulation begins, 16hrs before the peak.
FSH surge
cuases the follicle to get bigger and biggger to the ppoint that it produces a thin-walled blisted on the ovary.
LH surge
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.
fimbrae
ends of fallopian tubes, swell with blood in response to sex hormones and sweep the cells into the fallopian tubes
fertilization
it occurs in the fallopian tube in the area of the ampulla and undergoes its first cleavage 24hrs later
cleavage in mammals
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
rotational
cleavage
asynchronous
do not divide at the same time
odd number of cells; 3 0r 6 cells
compaction
adhesion E-cadherins
formation of tight junctions and gap junctions
morulla
8 cell embryo
totipotent
trophoblast
trophoectoderm
descedants of the oute cells
participate in placental formation and implantation
inner cell mass
come from innner cell mass
give rise to extraembryonic cells
pluripotent
cavitation
sodium pumps are involved.
pump fluid into the cavity by osmosis
the blasotcyst
32 -64 cells by the trophoblast
secrete fluid into morula to form a cavity.
tubal pregnancy
premature hatching or implantation in the ovdicut cause life-threatening hemorrhage.
how does implanation occur
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
amnion
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
Chorion
(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)
day 15
primitive streak
mammals and placental.
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
