9.3 - Embryonic Development Flashcards
4 Stages of Sex
1) Excitement
- vasodilation causes engorgement of external genitalia
2) Plateau
- increases HR and RR
- in males, urethral sphincter contracts to prevent urine mixing with semen
3) Orgasm
- contraction
4) Solution
- body returns to pre-arousal state
fertilization is most likely to occur within 3 days leading up to fertilization
Pathway of Sperm
1) millions of sperm enter the female reproductive tract (only few reach occyte)
2) Capacitation - final maturation stage
- where female tract fluids expose the acrosome
3) Acrosome Reaction
- enzymes digest granulosa and zona pellucida
- Ca influx aids in sperm motility
4) Fusion
- sperm binds to oocyte receptors = enters oocyte = oocyte form ovum and polar body
5) Zygote
- sperm and ovum create zygote
Implantation Stages
Day 1 - 1st Cleavage & Polar Body Formation
- zygote divides into 2 blastomeres (no size increase)
- oocyte (completes meioiss II) and forms polar bodies
Day 2 - 4 Cell Stage
- 2nd cleavage = 4 blastomeres
Day 3 - Early Morula Formation
- 8-16 cells form solid ball
- cells compact (adhere closely) to enhance communication (enclosed in zona)
Day 4 - Advanced Morula Stage
- 16-32 cells
- cells begin differentiating
- outer layer - trophoblast
- inner layer - embryo proper
Day 5-6: Blastocyst Formation
- Blastoceal: fluid filled that absorbs in morula
- Inner Cell Mass: forms embyro proper
- differentiates into epiblast and
hypoblast
- Trophoblast: becomes placenta
- produces hCG
Implantation Stages
Day 7: Implantation
- blastocyst attaches to endometrium
Implantation is 3 Stages:
1) Apposition
- blastocysts loosely attaches to endometrium
- loose attachment = still has mobility = optimizes implantation location
2) Adhesion
- trophoblast adheres/binds to endometrium (facilitated by proteins/receptors)
- 2 trophoblast layers
1) Cytotrophoblast: single layer of
cells
2) Synctiotrophoblast:
multinucleated
- releases enzymes that
facilitates deeper implantation
3) Invasion
- Synctiotrophoblast enzymes digest exracellular matrix
- blastocysts deeply attaches to endometrium
- it invades blood vessels to establish maternal blood supply
Decidualization
- endometrial cells become decidualized cells which provide nourishment for embryo
Hormonal Support for Implantation
1) Synctiotrophoblast secretes hCG which signals corpus luteum to produce estrogen and progesterone
- maintains endometrial lining
- prevents menstruation
- hCG is detected in blood in urine
Embryonic Period
Gastrulation
- process of blastocyst becoming a gastrula (by forming 3 layers)
1) Ectoderm (outer)
- forms skin, nervous system, eyes, ears
2) Mesoderm
- bone, muscle, kidneys, connective tissue
3) Endoderm - inner
- lungs, thyroid, GI, GU
Neurulation
- gastrula becomes neurula
- neural plate folds = neural tube = brain and spinal cord
Structures
1) Neuroplate
- part of ectoderm
- source of nervous system cells
2) Neural Folds
- edged of neural plate
- converge into neural tube
3) Neural Groove
- part of neuroplate where folds fuse
4) Neural Crest
- formed by fused folds
- cells that migrate to form PNS
5) Neural Tube
- fused folds that are beneath the ectoderm
Heart Tube Formation
- occurs at week 3-4
- cardiac mesoderm fuses with heart tube
- heart tube is suspended in the pericardial cavity (by mesocardium that degenerates and allows it to move freely)
Heart Tube regions
1) Aortic roots = arterial outflow tracts
2) Truncus Arterious = aorta and pulomonary artery
3) Bulbus Cordis = R ventricle
4) Primitive Vebtricle = L ventricle
5) Primitive Atrium = forms L and R atria
5) Sinus Venous = receives venous blood
Hear Tube Elongation and Looping
- week 4 (day 23)
- as heart tube elongates, it loops to create an S shaped structure (bulbis and primitive ventricle shift positions)
Atria Formation
1) Sinous venous directs blood into primitive heart
- forms R and L sinus horns
2) Venous return shifts to right side of heart
- L horn: becomes coronary sinus (drains into R atrium)
- R horn: forms part of inferior vena cava
- Pulmonary veins incorporate into L atrium (provide path for oxygenated blood)
Aortic Arches
- develop at week 4
- arches are paired structures that remodel to form the major arteries of the heart
Seperation of the Heart
Atrial Seperation
1) Septum Primum - thin wall growing from atrium roof to endocardial cushions
2) Ostium Primum - temporary opening allowing blood flow bw L and R atria (before septum primum fuses)
3) Ostium Secondum - forms in septum primum as ostium primum closes
4) Septum Secunduum
- forms forum ovale: allows blood to bypass lungs from R to L atrium
Ventricular Seperation
1) muscular portion
2) membranous portion
3) Truncus arteriosus - endocardial cushions fuse and splits into aorta and pulmonary artery
Fetal Circulation
- shunts are essential to bypass organs that are not yet functional in fetus’
1) Foramen Ovale
- shunt bw L and r atria
- allows blood to bypass lungs
2) Ductus Arteriosus
- connects pulmonary artery to aorta
- bypasses lungs
3) Ductus Venosus
- connects umbilical vein to infeiror vena cava
- bypasses the liver
Umbilical Vein: carries oxygenated blood to fetus
Umbilical Artery: carries deoxygeneated blood back to placenta
Facial Development
Week 4-5: Facial Prominence
1) Cranial neural crest cells migrate to form features
2) Frontonasal: descends from the forebrain
3) Maxillary Prominence - forms upper jaw
4) Mandibular Prominence - forms lower jaw
Week 5: Nasal Development
1) Nasal Placodes - form nasal pits
2) Medial Nasal Process: forms nasal tip and primary palette
3) Lateral Nasal process: forms lateral nose
Week 6-7: Fusion of Facial Prominences
1) Media Nasal Process + Maxillary = upper lip and primary palette
2) Maxillary
- form cheeks and lateral upper lip
Palatogenesis
1) Primary Palette (Week 5-8)
- is formed from frontonasal and medial nasal processes
- develops upper jaw, teeth, and hard palette
2) Secondary Palette (Week 8-12)
- forms from palatine shelves (outgrowths of maxillary processes)
- mandable grows = allows palatine shelves to fuse above tongue
- palatine shelves fuse with primary palette and nasal septum to separate L and R nasal passages
Kidney Development
1) Pronephros (early, non-functional)
- week 4
- non-functional kidney that degenerates
2) Mesonephros
- week 4 -6
- forms glomeruli and tubules
- produces urine excreted into amniotic fluid
- mostly degenerates, becomes vas deferens in males
3) Metanephros (permanent)
- week 5
- uteric bud forms collecting system
- metaphoric mesenchyme forms nephrons
4) Nephron Formation
- week 8
- nephrons develop from mesenchyme to epithelial transformation
- bowmans capsule and glomerulus filter blood
- tubules concentrate ad reabsorb urine
5) Collecting System
- uteric bud becomes collecting ducts and renal pelvis
6) Kidney Migration and Rotation
- kidneys move from pelvis to abdomen
