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
Amniotic Sac and Fluid
Amniotic Sac = Chorion + Amnion
Amniotic Fluid
- volume increases with length of pregnancy
1. Oligohydramnious - insufficient fluid (can cause low birth weight)
2. Polyhydramnious - too much fluid (can cause neural tube defects)
how Fluid is Produced
1) maternal blood crosses amnion
2) fetal circulation - fetal drinks fluid then urinates
Functions of Amniotic Fluid
1) Provides space for embryo to grow
2) Protects from injury via cushioning from trauma
3) Supports temp regulation
4) Promotes fetal and musculoskeletal development
5) Prevents umbilical cord compression
Umbilical Cord
- formed by the amnion (wk 5)
- has 2 umbilical arteries and 1 umbilical vein
Umbilical Arteries: carry deoxygenated blood and waste from fetus to placenta
Umbilical Vein: carries oxygenated blood from placenta to fetus
Whartons Jelly: cushions and protects vessels from compression/twisting
Placenta
- exchanges waste and nutrients bw fetus and mother
- large porteins (clotting factors, IgM) do NOT cross
Hormone Production
1) hCG: maintain corpus luteum and supports progesterone and estrogen production
2) Human placental lactogen (HPL)
- regulates glucose, protein, fat levels
3) Relaxin - relaxes pelvis and cervix
4) Estrogen
- supports growth of uterus
- preps breast for lactation
5) Progesterone
- maintains uterine lining
- supports immune tolerance
- prevents contractions
