midterm 2 Flashcards
what is the amniotic cavity?
Cells of ICM form two-layered Embryonic disk and a space called the amniotic cavity
what do Trophoblast form?
Trophoblast forms cytotrophoblast, syncytiotrophoblast, & chorion
what are the 2 layers of the Embryonic disc ?
Epiblast, Hypoblast
what is the Epiblast?
will become the embryo proper
what is the Hypoblast?
forms extraembryonic membrane: yolk sac
what does the Cytotrophoblast do?
1) adheres to endometrium
& burrows through uterine wall
2) secretes factors to attract maternal blood vessels
3) remodels the maternal blood vessels
what does the Syncytiotrophoblast do?
multinucleated body that digests uterine tissue
what does the Chorion
do?
1 - embryonic contribution to the placenta
2 - membrane that surrounds all others
what is the Amniotic cavity filled with ?
amniotic fluid
Functions of amnion ?
1) cushion and shock absorber
2) temperature regulator
Functions of the yolk sac ?
1) supplies some nutrients absorbed from trophoblast
2) primitive blood circulation for 2nd and 3rd week
3) after week 4 greatly reduces in size as placenta takes over nourishment function
4) source of blood cells and primordial germ cells
what is the allantois?
allantois is outpocketing that serves as primitive excretory duct that eventually become part of urinary bladder
what happens in Embryogenesis and gastrulation?
1) two layers to three layers via gastrulation
2) pluripotency to multipotency
3) primitive streak or indentation visible on dorsal surface of embryo
4) cells migrate toward and thru primitive streak and form two layers
what are the 2 layers formed in Embryogenesis and gastrulation?
Endoderm , Mesoderm
what is the endoderm?
displaces hypoblast
what is the Mesoderm?
second layer to migrate in fills middle layer and becomes
What is the ectoderm?
cells of epiblast that did not migrate thru become ectoderm
what does the endoderm layer become ?
1) digestive system
2) Liver
3) Pancreas
4) Lungs inner layers
what does the mesoderm layer become ?
it becomes the dermis of the skin
- circulatory system
- Lungs (epithelial layers)
- Skeletal System
- Muscular System
what does the ectoderm layer become ?
1) Hair
2) nails
3) skin (epidermis)
4) nervous system (CNS)
How does the placenta connect to the embryo?
umbilical cord
Umbilical cord
- two arteries that carry deoxygenated blood and waste from the fetus
- single vein that carries nutrients and oxygen from mom to fetus
what are tissues from the embryo called?
chorion
what is the chorion?
- chorionic membrane with finger-like villi
- burrow into endometrium and remodel maternal blood vessels
- fetal mesenchymal cells derived from mesoderm fill villi and differentiate into blood vessels, including those of the cord
what tissue comes from the mom?
decidua basalis portion of endometrium
A
B
Label
A
A
3 main functions of the placenta ?
Nutrition & digestion, respiration, endocrine function
Nutrition & digestion functions of the placenta ?
- Mediates diffusion of maternal glucose, amino acids, fatty acids, vitamins and minerals
- stores nutrients during early pregnancy to accommodate for increased fetal demand later in pregnancy
- excretes and filters fetal nitrogenous wastes into maternal blood
Respiration functions of the placenta ?
Mediates maternal to fetal oxygen transport and fetal to maternal CO2 transport
endocrine functions of the placenta ?
- secretes several hormones; hCG, estrogens, progesterone, to maintain pregnancy and stimulate maternal and fetal development
- mediates the transmission of maternal hormones into fetal blood and vice versa
how does maternal blood get to fetal blood?
maternal blood -> chorionic epithelial cells -> fetal connective tissue -> fetal endothelial cells -> fetal blood
does maternal blood interact with fetal flood?
NO, there is no direct intermingling
what substances use simple diffusion in the placenta?
O2, CO2, lipid-soluble
what substances use facilitated diffusion in the placenta?
carbohydrates, vitamins
what substances use active transport in the placenta?
Amino acids, iron
Benefit of the separation of maternal and fetal blood?
prevents the mother’s cytotoxic T cells from reaching and subsequently destroying the fetus, which bears “non-self”
antigens. Further, it ensures the fetal red blood cells do not enter the mother’s circulation and trigger antibody development
(if they carry “non-self” antigens)—at least until the final stages of pregnancy or birth.
what percentage of identical have separate chorions, amnions
33
what percentage of identical have common chorion, separate amnions
66
what is Placenta previa?
Placenta previa can result if an embryo implants close to the internal
os of the uterus (the internal opening of the cervix). As the fetus grows, the placenta can partially or completely cover
the opening of the cervix (Figure 28.7). Although it occurs in only 0.5 percent of pregnancies, placenta previa is the
leading cause of antepartum hemorrhage (profuse vaginal bleeding after week 24 of pregnancy but prior to childbirth).
when does Organogenesis occur ?
during Embryonic Period
What are the 2 pain processes that occur?
Neurulation, Somitogenesis
What is Neurulation?
formation of neural tube
What is Somitogenesis?
segmentation of meswodermal cells in developing trunk axial skeleton/muscles
where do the brain structures form?
At the anterior end of the neural tube
how is Tube-within-tube gut produced ?
through folding
Formation of heart?
formation of the heart starts with the tube
what other systems are produced?
urogenital, rudiments of pulmonary, limb bud, eye pits, facial structures
which cells help with the development of the nervous system?
neuroectodermal cells
what are 3 important features?
Notochord, neural plate, neural tube
what is the function of the Notochord?
signals the overlying ectoderm in dorsal midline to thicken and form neural plate
what happens to the neural plate?
Edges of the neural plate, the neural folds, bend toward each other (due to cytoskeletal changes in cells). The ends meet and neural tube disconnects
what are frees special cells called ?
Neural Crest
- Sometimes called 4th Germ Layer
- Migrate all over to form many important structures
what develops from the neural tube?
brain and spinal chord
Explain the stages of neurulation
1) Neuroectodermal tissues differentiate from the ectoderm and thicken to form the neural plate. the border of the neural plate separates it from the ectoderm.
2) The neural plate then bends dorsally with the two ends joining together to form the neural crest
3) the closure of the neural tube disconnects the neural crest from the epidermis. The neural crest cells will differentiate to form most of the PNS
4) The notochord degenerates and only persists as the nucleus pulposus. Other mesodermal cells differentiate into somites, these are precursors of the axial skeleton and skeletal muscle.
what can cause neural tube defects?
- Deficiency in maternal folate (folic acid) in the 1st weeks of pregnancy can cause neural tube defects
list some neural tube defects
1) Spina Bifida - Failure of posterior neuropore closure
2) Anencephaly: Failure of anterior neuropore closure
what is the Neural Crest?
Population of migratory cells left over from neurulation
what does the neural crest contribute to?
- peripheral nervous system
- septum that partitions the outflow tracts of heart into two major vessels that separate systemic and pulmonary circulation
what are Somites?
One either side of neural tube, the mesoderm splits into temporary segmented structures called somites.
What do somites form?
- vertebral column
- muscles of ribs, vertebral column, and limbs
- dermis of skin
how does embryonic folding occur?
- From a flat disc to 3-d cylinder by end of week 4
- Tube-within-tube body plan
- Expansion, folding, and fusion of edges of embryo
- Inner tube is future gastrointestinal tract
which system is the first fully-functional system to develop?
Circulatory system
at how many weeks does the heart start beating?
4
how is the heart formed?
- Cranial mesodermal cells condense into paired tubes that fuse to form single heart tube connected via capillaries to chorionic villi
- Rudimentary Tube loops upon itself
- Begins to beat and pump blood
> Initially RBCs produced in liver, eventually will come from bone marrow - Partitions to form 4 rudimentary chambers
> right and left atria
> right and left ventricles
what happens to the embryo at 7 weeks?
- GI system develops too rapidly for abdomen, intestines temporarily loop into umbilical cord
- the Webbing removed between digits on paddle-shaped hands and feet
- Facial structure includes nostrils, outer ears, and lenses on eyes
- Major brain structures in place
- External genitalia ambiguous
what happens to the embryo at 8 weeks?
- All major organs and external body structures have begun to form.
- The embryos’s heart beats with a regular rhythm.
- The arms and legs grow longer, and fingers and toes have begun to form.
- The sex organs begin to form.
- The eyes have moved forward on the face and eyelids have formed.
- The embryo is 3 cm long and weighs 8 g.
- At the end of eight weeks, the embryo looks more like a human and is now called a fetus.
what happens to the embryo at 9 weeks?
- Continued cell proliferation and differentiation in immature organ systems
- Sexual Differentiation
- Fetal circulatory system and shunts
when do secondary sexual characteristics develop?
During Puberty
Factors biological sex is based on
- Presence or absence of Y chromosome
- Type of gonads
- Sex Hormones
- Internal reproductive anatomy
- External genitalia
what is Sex determination ?
Specification of the gonads as either testes or ovaries
XY
SRY gene on Y chromosome directs development of testes
NO SRY gene?
Ovaries development