EMBRYOLOGY Flashcards
1
Q
What is included in the Prenatal/gestational period?
A
Embryonic period (first 8 weeks in humans)
Foetal period
2
Q
What is included in the embryonic period?
A
Week 1 = one germ layer
week 2 = two germ layers, flat
week 3 = three germ layers, folding into recognisable 3D body forms
weeks 4-8 = period of organogenesis (forming)
3
Q
what is included in foetal period?
A
- 3 months to birth (human)
- rapid increase in cell number (hyperplasia)
- growth in size (hypertrophy)
- biocehmical and functional maturation
- rudimental form of functioning in late foetal period for most organs
4
Q
what is different about marsupial neonates
A
- born way earlier
- develop a gut very early so they may process milk and suckle
5
Q
What is a syndrome
A
“packages” of congenital abnormalities that occur in several organ systems as the result of a single factor
6
Q
What causes congenital abnormalities? (broad):
A
- genetics
- environment
- combination
7
Q
what are the genetic causes of congenital abnormalities
A
- inherited or arise during generation of gametes
- defects in chromosomes -> aneuploidy, mutations
- defects in single genes
8
Q
environmental causes of congenital abnormalities (teratogens)
A
- chemicals (antibotics, hormones, vitamin A
- Infectious agents: viruses
- Radiation
- Mechanical factors
The embryonic period (through to 8 weeks human) is a critical period of susceptibility to teratogens
9
Q
what causes early embryonic death?
A
- usually due to implantation
- chromosomal abnormality
- hormonal imbalance
- maternal rejection
- failure of implantation and placentation
10
Q
process of early embryogenesis and implantation (mammals)
A
- ovum begins very large (80-120micro metres)
- cleavage division creates daughter blastomeres
- cleavage produces a solid ball of cells called a morula
- a cavity forms within the morula transfroming it into a blastula/blastocyst
- early cleavage occurs within zonea pellucida membrane until it ruptures and blastocyst “hatching”
- blastomeres compact towards the animal pole (cells forming) to form inner cell mass (embryoblastt) which will form the embryo
- outermost cells (trophoblast) will form the exttra embryonic tissue (membrane and placenta)
- uterine contractions space multiple blastocysts evenly
- implantation occurs at around 10-16 days depending on animal
11
Q
what determines pattern of cleavage
A
- varies between anmal groups depending on amount and distribution of yolk
12
Q
cleavage pattern in humans/mammals
A
- holoblastic cleavage
- whole cell divides (2, 4 , 6 etc)
13
Q
Cleavage pattern in birds (lots of yolk)
A
- So much yolk that cells can only party divide, creates animal pole and yolk is classed as vegetal pole
- Yolk is unevenly distributed towards a vegetal pole; smaller less yolky cells divide faster and form animal pole
14
Q
what is conceptus
A
refers to embryo with extra embryonic tissue
15
Q
explain implantation
A
- blastocyst with inner cell mass and trophoblast (outer layer) line up on outer epithelium of uterus
- trophoblast cells invade the uterus and amniotic cavity forms within blastocyst
16
Q
what are the sites of ectopic implantation
A
- Uterine tube
- Cervical opening of uterus
- Ovary
- Peritoneal cavity lining
16
Q
A
17
Q
Explain what Gastrulation is
A
- hollow blastula invaginates to form three layered embryo (triploblastic) with a primitive gut
18
Q
What are the 3 definitive germ layers formed during gastrulation
A
- ectoderm - epidermis and nervous
- endoderm - muscle, connective tissues
- mesoderm -> cavities in mesoderm will form primary coelom - gut, liver, lungs
19
Q
what are the two patterns of gastrulation?:
A
- protostomes = mouth first
- Deuterostomes = anus first, then mouth
20
Q
why is amphibian/frog gastrulation different?
A
- too much yolk -> means the embryo can’t turn inside out as usual
- must start with a hole/pit and cells move into the put inside the blastoceal
- then forms three layered triploblastic embryo
21
Q
What is the primitive streak?
A
- cells begn to gather at one end of the embryonic disk and aggregate into a mass and then streak across the surface
22
Q
explain simplified steps of gasttrulation
A
- embryo becomes one-dimensional layer of epithelial cells (embryonic disk)
- primitive streak forms along crainial-caudal axis
- epiblast cells migrate towards and then into prim streak, at the primitive streak undergo an epithelial to mesenchymal transition and ingress at the primitive streak to form the germ layers (now gastrula)
23
Q
process of body folding
A
- Initial body shape is formed by folding, which rearranges the three layered embryo
- Folding creates a single point at which the three germ layers are connected to the extraembryonic tissues (the umbilical stalk)
24
process of segmentation
- Serially repeating strips of mesoderm form somites
- present but subtle in adults
- paraxial mesoderm (alongside notocord) will become vertebral column + vertebral muscles)
25
process of heart development
1. heart develops from a pair of tubes (ventral aorti) -> fuse to form common chamber
2. inside the pericardium, heart expands faster than pericardium chamber so it is forced to bend as it grows -> tube starts to fold and twist, also begins to divide into chambers
3. bulbous cordis, single ventricle, primitive atrium and sinus venosus form
4. heart keeps twisting inside and atrium and ventricle partially divided. Truncus arteriosus forms leading to branched arches
5. endocondrial cushion forms, divides he common orifice between atrium and ventricle -> atrium and venticle seperate
6. septum prinum forms, grows down to cushion to divide left and right atria (top), septum secudrum also forms, two septi separating L+R atria
7. foramen primum forms, forming he one way valve
8. separation occurs in truncus arteriosus to separate aortic trunk and pulmonary trunk
26
what vessels are left from the branchial arch arteries that form in the embryo?
1. umbilical arteries -> round ligaments fo bladder
2. umbilical vein -> teres ligament of liver
3. ductus venosus -> if persists = portosystemic shunt
4. foram ovale = fossa ovalis
5. ductus arteriosus = ligamentum arteriosum
27
process of brain development
- early development dominated by the development of fluid-filled vesicles
- Initially 3 primary vesicles define the forebrain, midbrain and hindbrain
- forebrain vesicle = prosencephalon, midbrain = mesencephalon, hindbrain = rhombencephalon
- then vesicles divide to form 5 secondary vesicles
28
what are the 5 secondary vesicles that form the brain
1. forebrain forms telencephalon and diencephalon
2. midbrain forms mesencephalon = midbrain
3. hindbrain = metencephalon (cerebellum) and myelencephalon = medulla
29
how are the telencephalon and diencephalon formed?
telencephalon = smell, hippocampus, cerebrum -> created by expansion of 2 lateral vesicles
diencephaln = optic vesicle, thalamus and hypothalamus -> direct outgrowths for eyes, expansion of other centrally
30
how is the hindbrain formed
split by deep bend between met- and myelencephalon
31
explain formation of the eye
- forms from neurectofermal vesicle (optic cup -> future retina and optic cup) involuting and enveloping a surface ectodermal vesicle (future lens)
32
explain the structure of the pharyngeal arches
- from structures across throat and neck
- theoretically 6 arches but 5th never forms and 6tth is rudimentary
- each arch has thick mesodermal core which froms important cartilage, bone and vascular derivatives
- behind each arch is an external ectodermal pharangeal cleftt, and internal and endodermal pharyneal puch or groove
- ectodermal clefts would perforate to form functonal gills in fish, but not in mammals
33
what do the ectodermal clefts do in mammals?
- cleft 1 and pouch 1 form external ear and auditory tube
- puch 2 forms palatine tosils
- puch 3-6 form endocrine glands
34
what do the brachial arches do
- form basis for the lower jaw, ear ossicles, hyoid and laryngeal cartilages
- The mandible forms around the thin rode like Meckel’s cartilage
35
how does respiratory airway form
- bud off foregut as a tracheobronchial groove which closes to form a tracheobroncial tube
36
how does the midgut from?
- elongates and herniates extra embryonically into the tolk stalk for a short period
- gut twists counter clockwise at umbilcus
- further elongation of proximal part form jejunal colis
37
how is the urogenital area formed?
- terminal hindgut dilates to form cloaca connected to allantois
- cloaca divided by urorectal septum into urogenital sinus and anorectal canal
38
how do the kidneys form?
- intermediate mesoderm forms the urogenital ridge
- three successive pairs of kidneys form from cranial-caudal: pronephros, mesonephros and metanephros
- only the metanephrons form the definitive kidneys in adults
- mesonephric duct persists as male ductus deferens
- paramesonephric duct becomes uterus
- kindeys form form inductive interaction of two elements: the collecting elements and the excretory elements
- ureteric duct buds off mesonephric duct, then dilates to form renal pelvis and collecting ducts
- nephrons from within the metanephric cap
- collecting duct and nephron fuse -> if they fail = polysystic kidney
39
What causes cleft palate?
- falure of lateral palatne processes to fuse to each other and to nasal septum
- cannot generate negaive pressure in mouth to suckle -> milk in nasal cavity
- oral and nasal cavities fail to be separated
40
what causes peritoneopericardial hernia
- failure of normal septum transversum development
- normally forms the lower half of he diphragm and separates pericardial and peritoneal cavities
- abdominal pressure oushes abdominal contents into pericardium
41
