Embryology Flashcards
Epiblast
The thicker layer, consisting of high columnar cells. Eventually forms the three definitive germ layers
Hypoblast
Consisting of small cuboidal cells. Becomes part of the yolk sac.
Capacitation
Removal of seminal proteins from the surface
-Penetration through corona radiata
Acrosome reaction
-Release of acrosomal enzymes (acrosin, etc.)
-Penetration of sperm through zona pellucida
Fusion of the plasma membranes of sperm and oocyte
Changes in zona pellucida inactivates sperm receptors and prevents polyspermy.
Inner cytotrophoblast
Makes cells mitotically active
-Forms new cytotrophoblast and synctiotrophoblast
Syncytiotrophoblast
Secretes and Invades:
-Secrete human chorionic gonadotrophin (HCG)-early pregnancy tests
Epiblast
The thicker layer, consisting of high columnar cells.
Hypoblast
Consisting of small cuboidal cells. Becomes part of the yolk sac.
Limb buds appear at week:
week 4
Hand & foot plates formed at week:
week 5
Digital rays appear
-Tissue between digital rays undergoes apoptosis
-Form notches at week:
Week 6
Upper limbs bend at elbow
-Fingers are short and webbed at week:
Week 7
Digits are distinct and separated at week:
Week 8
Limb extend ventrally
Hand plates & foot plates face each other at day:
48 days
Upper limbs bent at elbows
Hands curved over thorax at day:
51 days
Soles of feet face medially at day:
54 days
Elbows point caudally
Knees point cranially at day:
56 days
When does osteogenesis of the long bones begin?
7th week of embryological development (primary ossification centers)
What is the epiphyseal plate?
The growth plate between diaphysis and epiphysis
-Adds length to the bone
-Persist until growth period is over
Epiphysis is formed by:
Secondary centers of ossification
The diaphysis is formed by:
The primary center of ossification (appear by 7th-8th week)
Dermatomes are derived from which embryological structure?
Neural crest cells: which are also precursors of Schwann cells
-They also form the neurolemma and myelin sheaths
Cutaneous syndactyly
The most common limb defect in which there is webbing of the digits (failure of webs to degenerate between 2 or more digits)
Osseous syndactyly
Fusion of the bones-failure of development of notches between the digital rays (bones are fused together)
Polydactyly
Supernumerary digits
Disruption of the anteroposterior pattern
Inherited as a dominant trait
Congenital Talipes (Club Foot)
Talipes equinovarus (most common type)
Sole of the foot is turned medially and the foot is inverted
-Multifactorial pattern of inheritance
Amelia
-Complete absence of limbs
-Suppression of limb bud development in the 4th week
Meromelia
-Partial absence of limbs
-Disturbance of limb development during 5th week
*Defects are caused by: Genetic factors, mutant genes, environmental factors, vascular disruption and ischemia
Cleft hand and cleft foot (ectrodactyly)
-Absence of one or more central digits (Failure of development of one or more digital rays)
-Remaining digits are partially or completely fused leading to lobster-claw like deformities
Amniotic Band Syndrome
-Tears in the amnion result in amniotic bands
-May encircle fetal limbs & digits
-Ring Constrictions
-Amputations
-Cause unknown
VACTERL
Vertebral defects
Anal atresia
Cardiac defects
Tracheo-esophageal fistula
Renal anomalies
Limb abnormalities
Gene that initiates the process of limb development
The Homeobox (HOX)
Activation of the mesenchyme induces formation of an :
apical ectodermal ridge (AER)
Diaphysis
Formed by primary ossification center (primary bone, long bone)
Epiphysis
Formed by secondary ossification center (top of the bone)
Epiphyseal plate
Growth plate between diaphysis and epiphysis, adds length to the bone, persist until growth period is over
