Embryology

Question 1

Epiblast

Answer 1

The thicker layer, consisting of high columnar cells. Eventually forms the three definitive germ layers

Question 2

Hypoblast

Answer 2

Consisting of small cuboidal cells. Becomes part of the yolk sac.

Question 3

Capacitation

Answer 3

Removal of seminal proteins from the surface
-Penetration through corona radiata

Question 4

Acrosome reaction

Answer 4

-Release of acrosomal enzymes (acrosin, etc.)
-Penetration of sperm through zona pellucida

Question 5

Fusion of the plasma membranes of sperm and oocyte

Answer 5

Changes in zona pellucida inactivates sperm receptors and prevents polyspermy.

Question 6

Inner cytotrophoblast

Answer 6

Makes cells mitotically active
-Forms new cytotrophoblast and synctiotrophoblast

Question 7

Syncytiotrophoblast

Answer 7

Secretes and Invades:
-Secrete human chorionic gonadotrophin (HCG)-early pregnancy tests

Question 8

Epiblast

Answer 8

The thicker layer, consisting of high columnar cells.

Question 9

Hypoblast

Answer 9

Consisting of small cuboidal cells. Becomes part of the yolk sac.

Question 10

Limb buds appear at week:

Answer 10

week 4

Question 11

Hand & foot plates formed at week:

Answer 11

week 5

Question 12

Digital rays appear
-Tissue between digital rays undergoes apoptosis
-Form notches at week:

Answer 12

Week 6

Question 13

Upper limbs bend at elbow
-Fingers are short and webbed at week:

Answer 13

Week 7

Question 14

Digits are distinct and separated at week:

Answer 14

Week 8

Question 15

Limb extend ventrally
Hand plates & foot plates face each other at day:

Answer 15

48 days

Question 16

Upper limbs bent at elbows
Hands curved over thorax at day:

Answer 16

51 days

Question 17

Soles of feet face medially at day:

Answer 17

54 days

Question 18

Elbows point caudally
Knees point cranially at day:

Answer 18

56 days

Question 19

When does osteogenesis of the long bones begin?

Answer 19

7th week of embryological development (primary ossification centers)

Question 20

What is the epiphyseal plate?

Answer 20

The growth plate between diaphysis and epiphysis
-Adds length to the bone
-Persist until growth period is over

Question 21

Epiphysis is formed by:

Answer 21

Secondary centers of ossification

Question 22

The diaphysis is formed by:

Answer 22

The primary center of ossification (appear by 7th-8th week)

Question 23

Dermatomes are derived from which embryological structure?

Answer 23

Neural crest cells: which are also precursors of Schwann cells
-They also form the neurolemma and myelin sheaths

Question 24

Cutaneous syndactyly

Answer 24

The most common limb defect in which there is webbing of the digits (failure of webs to degenerate between 2 or more digits)

Question 25

Osseous syndactyly

Answer 25

Fusion of the bones-failure of development of notches between the digital rays (bones are fused together)

Question 26

Polydactyly

Answer 26

Supernumerary digits Disruption of the anteroposterior pattern Inherited as a dominant trait

Question 27

Congenital Talipes (Club Foot)

Answer 27

Talipes equinovarus (most common type) Sole of the foot is turned medially and the foot is inverted -Multifactorial pattern of inheritance

Question 28

Amelia

Answer 28

-Complete absence of limbs -Suppression of limb bud development in the 4th week

Question 29

Meromelia

Answer 29

-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

Question 30

Cleft hand and cleft foot (ectrodactyly)

Answer 30

-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

Question 31

Amniotic Band Syndrome

Answer 31

-Tears in the amnion result in amniotic bands -May encircle fetal limbs & digits -Ring Constrictions -Amputations -Cause unknown

Question 32

VACTERL

Answer 32

Vertebral defects Anal atresia Cardiac defects Tracheo-esophageal fistula Renal anomalies Limb abnormalities

Question 33

Gene that initiates the process of limb development

Answer 33

The Homeobox (HOX)

Question 34

Activation of the mesenchyme induces formation of an :

Answer 34

apical ectodermal ridge (AER)

Question 35

Diaphysis

Answer 35

Formed by primary ossification center (primary bone, long bone)

Question 36

Epiphysis

Answer 36

Formed by secondary ossification center (top of the bone)

Question 37

Epiphyseal plate

Answer 37

Growth plate between diaphysis and epiphysis, adds length to the bone, persist until growth period is over