Early Pregnancy Flashcards
What does syngamy mean?
Fusion of male and female pronuclei
What does is an Ootid?
Large single cell comprising male and female pronuclei after fertilization
What is a Zygote?
Product of a fertilized oocyte from haploid gametes to a diploid cell (single cell embryo that eventually divides)
What is an embryo?
Early stage of development following zygotic cellular cleavage
What are Blastomeres?
Individual cells within and embryo as a result of an embryonic cleavage
What is the Morula?
An embryo that contains a minimum of 8 cells but has only one totipotent cell type
What are blastocyst?
Stage of embryo development identified by a blastocele cavity and two distrinct cell lineages
What is the fetus?
Stage of advanced embryo development when the embryo begins to form recognizable structures
What is Conceptus?
Structures that make up the product of conception that are stage dependent and include the embryo, extraembryonic membranes, fetus, and placenta.
How does the process of Preattachment development of the embryo go?
Goes from ootid-> through syngramy-> to Zygote-> 2-celled embryo-> turns to Morula (4-8 cells) -> goes to Early blastocyst-> Hatching Blastocyst-> Hatched blastocyst.
What is cleavage?
1.Increases # of cell
2.Increases cell mass
3.forms blastomeres
What occurs with inner cells?
- They develop gap junctions
- Groups of cells form
What do outer cells do?
Cell to cell adhesions called tight junctions. (alters permeability of outer cells-> fluid accumulation)
Where are tight junctions?
They are between outside cells
Where are gap junctions?
They are between inside cells
What do outter cells pump? What occurs when they pump this substance?
- Outer cells pump Na+ into the embryo
- H2O accumulation
What 2 cell populations are in the blastocyst?
- Inner cell mass -> Embryo proper (fetus)
- Trophoblast -> Chorion (outer placental layer)
What is the Blastocoele?
Fluid filled cavity
What is Hatching?
Blastocyst leaves protective zona
When it comes to the hatching of the blastocyst what 3 forces is it governed by?
- Blastocyst growth & fluid accumulation: increases pressure
- Enzyme production by trophoblastic cells : weaknes zona
- Blastocyst contraction: Intermittent pressure pulses
How does the timeline of bovine embryo development and elongation occur?
- Day 1 cell
- After 3 days turns into 8-16 cell (embryonic genome activation) consists of totipotent cells
- After 5 days the D5 Morula forms
- After Day 7 it turns into a D7 Blastocyst.
What occurs when an embryo hatches?
- Blastocyst are free floating in uterus until later attachment
- Dependent on uterine environment for survival
- Adequate lutela progesterone increases uterine secretions
When does the process of the uterus normally occur?
Occurs around 4 days and 1/2 when the process is in the uterus.
What occurs after the blastocyst hatches?
- The conceptus undergoes massive growth usually in the form of elogation
- The blastocyst begins to form extraembryonic membranes (amnion, chorion, allantochorion)
- In primates, the blastocyst implants into the uterus quickly and then forms membranes
What does the gravite horn contain?
Contains the fetus or the pregnancy
What are the 4 extrambryonic membranes in the embryo?
- Yolk sac
- Chorion
- Amnion
- Allantois
What is the Endoderm (inside)?
- Interior linings of our two tubes
- GI tract
- Respiratory tract
- Endocrine glands
- Urinary tract
What is the Mesoderm (middle)?
- Connective tissue
- Muscle
- Gonad (not gametes)
- RBC (red blood cells)
What is the Ectoderm (outside)?
Nervous system and skin
Where does the pimitive endoderm begin to form?
It begins to form beneath the inner cells mass
Where does the mesoderm begin to form ?
It forms between the embryo proper and the primitive endoderm
When does the yolk sac form?
Formed when the primitive endoderm completes formation
Till when does the mesoderm grow?
Continutes to grow surrounding the yok sac until it gains wing-linke structures
In the stage of when the allantois is now formed what occurs within the structure?
- The mesoderm now surrounds the yolk sac and developing allantois
- The allantois is simply a diverticulum from the primitive gut that collects embryonic waste
- The mesoderm fuses with the trophectoderm cells to form the chorion, which will be the outer layer of the placenta.
What occurs to the yolk sac over time when the allantois grows?
- The yolk sac regresses
- The allantois expands
- Amnion almost completely surrounds the embryo to help protect the embryo proper
At the end what occurs to the Amnion and the Chorion?
- Amnion completely fuses to form a double sac around the embryo
- Allantois and chorion will eventually fuse to form the allantochorion
What would occur if mom did not know she was pregnant (body wise)/ carrying an embryo?
- Mother’s body would terminate pregnancy
- Cycle again
How does the maternal recognition of pregnancy determine an embryo’s survival?
- Biochemical signals prevent luteuolysis and it results in maintancne of pregnancy.
What are the requirements for pregnancy to continue?
- Preventation of luteyolysis
- Maintenance of progesterone for embryo attachment to the uterine endometrium
What prevents the CL from being regressed and maintaining its P4 secreition?
Small point during production of progesterone alerts the body to not regress the CL.
What must be prevented so that the uterus does not secrete PGF2alpha?
Oxytocin production from the CL must be prevented.
What 2 species does not have a pregnancy recognition factor?
- The bitch
- The queen
What are the pregnancy recognition factors for:
Cow
Ewe
Mare
Sow
Woman
- bIFN-t (btp-1)
- oIFN-t (otp-1)
- proteins/estrogens (?)
- Estradiol
- hCG
What do blastocysts signals do?
Blastocysts secrete signals that block production of PGF2alpha from the endometrium
What are secreted by trophoblasts amd what do they do?
- Secrete proteins known as interferon taus (INF-t)
- Inhibit production of oxytocin receptors so they can’t stimulate PGF2 alpha synthesis.
What do INF-taus cause?
- Cause secretion of proteins from the uterine glands
- Creates a hospitable environment for the conceptus
How does the maternal recognition in pigs happen?
- When pigs are not pregnant oxytocin from various sources cause PGF2alpha synthesis in the uterus
- Drains out into the uterine vein and traget the CL for luteolysis (endocrine)
How does estradiol secretion by blastocyst affect the way pigs produce their hormones?
- Estradiol secretions by blastocyst reroutes PGF2alpha into the uterine lumen in an exocrine fashion
- Destroys and cannot cause luteolysis
What is needed to maintain pregnanct in pigs?
- Needs 2 conceptuses per horn (required to maintain pregnancy)
- Meeds a good amount of estradiol if not prostaglandin comes in.
Maternal recognition of pregnancy in pig steps
- Sow secretes PGF2alpha unlike the cow, but it is simply rerouted
- Estrogen production by the conceptus does not inhibit PGF2alpha, it simply redirects in an exocrine fashion away from capillaries
- E2 stimulates contradictions to help disperse piglets in uterine horns.
- Porcine conceptuses produce interferons but they do not help to maintain pregnancy
How does maternal recognition of pregnancy in horse occur?
- Conceptus must translocate over uterus to prevent PGF2alpha secretion
- Conceptus does not elongate as in other species
- conceptus must migrate 12-14 times per day, inhibits PGF2alpha
How does maternal recognition work in humans?
- huamns produce LH-like proteins (human chorionic gonadotropin)
- Conceptus secretes hCG
- Inhibits intraovarian luteolysis
How does maternal recognition work in pregnancy of cats and dogs?
- Cats and dogs have no signal from conceptus
- dogs have a longer length of diestrus similar to gestation - no CL difference
- Cats with no mating, CL does not form, since cats are induced ovulators. CL will form even from sterile males but CL will be maintained in a pseudopregnancy, meaning no signal from conceptus is required.
