embryo annexes Flashcards
what are the embryo annexes
- yolk sac
- amnion
- allantois
- umbilical cord
- chorion
- placenta
what is the function of the yolk sac
-hematopoiesis
-angeiogenesis
-gonocyte development
-forms primitive intestine
Process of cell formation stemming from the yolk sac
Cells are derived from the extraembryonic mesoderm of the VS wall (also called the islets of Wolff)
HEMOPOIESIS: cells become rounded, globular forming RBCs
ANGIOGENESIS: cells become flattened squamous forming vessel endothelium
when does the development of gonocytes occur
-primordial germ cells originate in embryo after 21 days in the YS wall
-migration of primordial cells occurs in week 5 in the genital ridges, causing them to priloferate
function of the amnion
- shock absorber
- allows embryo movement and development of MS system
- thermoregulation
- barrier to infections and contains fetal urine
Allantois def
the sac like structure in the embryo connecting stalk, lined by the endoderm
characteristic of the allantois in humans
RUDIMENTARY:
one portion regresses and another forms URACHUS (cord connecting umbilical region with the urinary bladder)
the part that regresses is replaced by CT –> Wharton’s jelly (mucous loose CT) contains allantois remnants
What is the blood vessel system of the umbilical cord
contains 2 arteries and 1 vein –> flow mirrors pulmonary circulation bcos it is different in its movement and contents:
ARTERIES: flow from embryo to the placenta: contain CO2, waste and deoxygenated blood
VEINS: flow from placenta to the embryo: contain nutrients and oxygenated blood
what is the advantage of umbilical cord post birth
can be stored bcos it contains hematopoietic cells within its blood vessels
what is the shape of the placenta
DISCOIDAL: thicker in the center an thinner in the lateral periphery
functions of placenta
Exhange of material between maternal and fetal circulation - FILTER
(includes: delivery of nutrients/ O2/antibodies, hormones, and the removal of waste products)
what are the placenta components
- EMBRYONIC COMPONENT: chorion forming the chorionic villi (STB, STB, EEM)
- MATERNAL COMPONENT: decidua basalis - the endometrium during pregnancy rich in glycolipids and lipids
Stages of development of chorionic villi
PRIMARY: 10/11 days, made of the first protrusions of the STB/ CTB membranes
SECONDARY: EEM grows and becomes incorporated into villi causing enlargement
TERTIARY: same as secondary but with blood vessels from the mesoderm extending into the vili
!! increase in size from primary to secondary
what would you see in a cross section of the 3 types of villi
primary: outer STB and inner CTB
secondary: outer STB, middle CTB and inner EEM
tertiary: same as secondary but the central EEM would contain blood vessels
what is present within the intervillus space
maternal blood supply (from the blood vessels) for contact with maternal circulation
Structure of the decidua
mucosa of the uterus during pregancy period having 3 REGIONS:
- decidua basalis (connects with villi to form the definitive placenta)
- decidua capsularis (capsule of the embryo)
- decidua parietalis (no contact with villi or embryo)
what happens to the three layers of the decidua over the course of the pregnancy
- D basalis forms the definitive placenta by connecting to the chorionic villi
- Fusion of the D capsularis nad parietalis to form the DECIDUA VERA (expelled during delivery)
Parts of the chorion
VILLOUS CHORION: region that has villi
SMOOTH CHORION: region that is absent of villi
Special chacteristics of the villi in the placenta
- CBT SHELLS: proliferation of the CBT to form anchoring regions to the D basalis
- Intravillous space containing the maternal blood that comes in contact with the wall of the villi for exchange and transport
How can we use embryo annexes to analyse the genetic profile of the embryo (2)
ANIOSCENTESIS: 14-18 weeks of pregnancy, transabdomical needle insertion into the amniotic cavity and extraction + analysis of amniotic fluid –> cells need culturing to stimulate proliferation
CVS (CHORIONIC VILLUS SAMPLING): 10-12 weeks of pregnancy, transvaginal needle insertion into placental mass and collection of villus cells.
Pressure in the diff components of the placenta
BASED ON BLOOD PRESSURE DIFFERENCES
70-80 mmHg in arteries of decidua
20-30 mmHg in the vein of embryo
8mmHg in the vein of decidua
how does placenta circulation work ()
- High blood pressure in arteries of decidua pushes maternal blood into the villus space in close proximity to embryo capillaries -> nutrient exchange
- Veins have lower blood pressure which favours entrance of blood back into the decidual veins from villus space -> waste product removal
what changes occur in placenta during the 3rd trimester and why (3)
REASON: increases the efficiency of the transport of tissue
- CBT dissapears and only a few cells remain
- STB decreases in thickness
- Dilation of capillaries in intervillus space
What is the disadvantage of the filter action of the placenta
toxins, drugs, alcohol, medication and some pathogens (HIV/syphillis) can also pass into the fetal circulation from the maternal which harms the baby
Action of the placenta as an endocrine gland (4)
- hCG - maintains the gravidic CL to keep producing progesterone
- progesterone - production after the gravidic CL has regressed
- relaxin: increases cervical dilation and flexibility of pelvis
- placental lactogen hormone -> preps the mammary glands for lactation
types of twins, their shared structures and when cell division occurs
- DIZYGOTIC: cell separation occurs very early, separate amniotic sacs, chorions and placenta
- MONOZYGOTIC:
2.1 DIAMNIOTIC: division occurs at the level of the blastocyst (2 inner cell masses), shared placenta but separate chorions and amniotic sacs
2.2 MONOAMNIOTIC: division occurs past the blastocyst (1 inner cell mass): shared placenta AND amniotic cavities
