Embryology

Question 1

Stem cells.

Answer 1

Question 2

Describe cleavage.

Answer 2

-within uterine tube
-unicellular zygote divides by mitosis or cleavage to become multicellular embryo
-each daughter cell = blastomere
-no increase in size due to zona pellucida

Question 3

Describe morula.

Answer 3

-in uterine tube
-blastomeres divide into ball of 16-32 cells in zona pellucida

Question 4

Describe a blastocyst.

Answer 4

-enters the uterus & hatches from zona pellucida = develops a cavity = ‘blastocoele’ = yolk sac
-differentiation of inner cell mass = embryo blast surrounded by outer cells = trophoblast

Question 5

Describe the blastocyst hatching.

Answer 5

-from zona pellucida
-accommodate implantation
-hatching due to pressure of expanding blastocyst & enzymatic dissolution of zona pellucida

Question 6

Describe the inner & outer cells of the blastocyst.

Answer 6

1. Inner - embryoblast (forms entire embryo)
2. Outer - trophoblast
   >expand to form extra embryonic membrane (amnion, yolk sac, allantois, chorion) related to placenta

Question 7

Describe the epiblast & hypoblast.

Answer 7

-embryoblast differentiates to form bilaminar disc of epiblast (dorsal) & hypoblast (ventral)

Question 8

Describe gastrulation.

Answer 8

3 germ layers

Question 9

Gastrulation summary.

Answer 9

Question 10

Describe the germ layer derivatives.

Answer 10

-inner -> embryoblast -> epiblast
-primary germ layers: ectoderm, mesoderm, endoderm
>ectoderm: epidermal, lining of oral, nasal cavity & anus, corneal epithelium, NS
>mesoderm: CT, muscle tissue, mesothelium, CVS, urogenital tract
>endoderm: epithelial lining & glands of digestive & respiratory system

Question 11

Describe the formation of notochord.

Answer 11

-derived from mesoderm
-transient structure
-provides direction
-basis for vertebral column
-provides direction & contributes to vertebra & intervertebral discs
-induces ectoderm to differentiate into neuroectoderm

Question 12

What are the functions of the notochord?

Answer 12

1. Primitive axis of embryo = rigidity
2. Basis for development of axial skeleton
3. Future site of vertebral bodies
4. Development of CNS

Question 13

Describe the formation of neural tube.

Answer 13

-derived from ectoderm
-basis for CNS
-cranial = brain
-caudal = spinal cord
-notochord = direction & contributes to formation of vertebral column

Question 14

Describe the mesoderm: intra-embryonic.

Answer 14

Question 15

Describe the mesoderm: paraxial

Answer 15

-somitogenesis
-differentiates into somitomeres on each side of neural tube
-differentiates further into somites

Question 16

What are the major somites?

Answer 16

-sclerotome: vertebrae, portions of skull, axial skeleton
-myotome: striated muscles of head, trunk, limbs
-dermotome: dermis of dorsal/back regions

Question 17

Segmented somites (picture).

Answer 17

Question 18

Describe mesoderm: intermediate.

Answer 18

-differentiate into urogenital system
>paired kidneys
>paired adrenal gland cortex
>paired gonads
>female & male reproductive ducts

Question 19

Describe mesoderm: lateral plate

Answer 19

-somatic (parietal) = dorsal & associates w ectoderm
>contributes to serous membranes lining the peritoneal, pleural, & pericardial cavities
-splanchnic (visceral) = ventral & associates with endoderm
>contributes to CVS, blood, kidneys, smooth muscles

Question 20

Describe mesoderm: extra-embryonic.

Answer 20

-derived from epiblast (originally from inner cell mass or embryoblast)
-contributes to formation of yolk sac, amnion, allantois & chorion
-vital functions in maternal-fetal protection, nutrient & waste exchange

Question 21

Placenta types. (Picture)

Answer 21

Question 22

Describe teratogens.

Answer 22

-any factor that causes congenital defects during fetal growth & development
>genetics
>radiation
>chemical agents (ex. Nicotine, drugs, alcohol
>infectious agents (ex. Aka bane virus, bovine viral diarrhea virus)
>hormones (ex. Anti-paramesoephric duct hormone in freemartins)

Question 23

Describe congenital defects of teratogens.

Answer 23

1. Reproductive
   -free Martin
   -cryptorchidism
2. Alimentary
   -cleft palate
   -atresia ani
3. Urinary
   -persistent urachus
4. Neuro
   -hydrocephalus
   -cerebellar hypoplasia
   -spina bifida
5. CVS
   -patent ductus arteriosus
   -ventricular septal defect
   -persistent R aortic arch
   -portocaval shunt
6. Respiratory
   -brachycephalic airway syndrome
7. Body wall
   -umbilical hernia

Question 24

Describe undifferentiated gonads.

Answer 24

1. Genital ridge: medial part of mesonephros (early kidney) & differentiate into capsule, stroma & CT of gonad
2. Coelomic epithelium: covers gentian ridge & differentiate into sex cords (sertoli or granulosa cells) of gonad
3. Primordial germ cells (PGC): unipotent cells that migrate from wall of yolk sac & differentiate into spermatogonia or oogonia between sex cords or sertoli or granulosa cells in testes or ovaries

Question 25

Describe differentiated gonads.

Answer 25

1. Paired testes: presence of Y chromosome (XY) = SRY gene that encodes for a testis determining factor & Sertoli cells produce AMH - Müllerian ducts degenerate & testes & wolffian ducts (Epididymus, vas deferens, ejaculatory duct, seminal vesicles) develop
2. Paired ovaries: absence of Y chromosome (XX), wolffian ducts degenerate & ovaries & Müllerian ducts (oviducts, uterus, cervix, cranial vag) develop

Question 26

Gonadal differentiation.

Answer 26

Question 27

Gametogenesis.

Answer 27