Embryology

Question 1

Endoderm derivatives

Answer 1

Epithelial lining of:

GI tract, trachea, bronchi, lungs, liver, urinary bladder

Other:

thyroid, parathyroid, thymus

Question 2

Mesoderm derivatives

Answer 2

Muscles

Bone

Dermis

Connective tissue

Kidneys

Spleen

Cardiovascular structures

Blood

Gonads

Question 3

Ectoderm derivatives

Answer 3

Surface ectoderm: epidermis, sailvary glands, sweat glands, mammary glands

Neuroectoderm: CNS, retina

Neural Crest: ANS, dorsal root ganglia, cranial nerves, melanocytes, Schwann cells, adrenal medulla, bones of skull (pharyngeal arches)

Question 4

Organizing center

Answer 4

Instructs differentiation of cells

Ex: Primitive Node (anterior of primitive streak in humans, controls gastrulation; equivalent to Spemann’s organizing center in other animals), Isthmus Organizer (in midbrain-hindbrain isthmus; required for cerebellum development)

Question 5

Fertilization sequence of events

Answer 5

Secondary oocyte (in metaphase II) released from ovary –>sperm digest corona radiata –> one sperm penetrates zona pellucida –> block to polyspermy –> secondary oocyte completes meiosis II to make fertilized ovum and second polar body –> egg and sperm undergo rapid DNA synthesis –> nuclear membranes dissolve –> first mitosis

Question 6

Blastocyst

Answer 6

Created when fluid enters morula

Trophoblast: Outer sphere of cells

Embryoblast/Inner Cell Mass: cluster of cells on one inside edge of trophoblast

Question 7

Embryoblast/Inner Cell Mass

Answer 7

Gives rise to entire embryo

Epiblast: surrounds amniotic cavity; gives rise to entire body; (columnar cells); where primitive streak forms and gastrulation eventually occurs

Hypoblast: upper surrounding of exocoelomic cavity/primitive yolk sac (cuboidal cells)

Question 8

Trophoblast

Answer 8

Cytotrophobalst: cells divide and go outward to syncitiotrophoblast and fuse/lose cell membranes

Syncitiotrophoblast: no cell boundaries; secretes HCG; forms lacunae

Question 9

How does the embryo hijack the mother’s physiology?

Answer 9

Trophoblast secretes HCG to sustain the corpus luteum which secretes progesterone to sustain endometrium

After about 8 weeks, the placenta takes over progesterone production

Question 10

Placenta previa

Answer 10

An ectopic pregnancy where blastocyst implants too close to cervix and hemorrhaging occurs around 7 months (however can still have viable fetus)

Question 11

3 ways twinning can occur

Answer 11

1) Split at 2 cell stage: 2 amniotic cavities, 2 chorionic cavities, 2 placentas (RARELY happens)
2) Split at early blastocyst: 2 amniotic cavities, 1 chorionic cavity and 1 placenta
3) Split at late blastocyst: 1 amniotic cavity, 1 chorionic cavity, 1 placenta

Question 12

Sirenomelia

Answer 12

Cells moving into primitive streak lose steam at the end and fail to gastrulate properly, giving fused limbs (mermaid limbs)

Question 13

Sacrococcygeal teratoma

Answer 13

Caused by primitive streak persistence; tumor has bits of every germ layer; most common in female fetuses

Question 14

When are embryos most vulnerable to insult?

Answer 14

3-8 weeks

This is when body plan/organ systems are formed

Question 15

Axial mesoderm

Answer 15

Notochord

Question 16

Paraxial mesoderm

Answer 16

Somites create sclerotome (bone and cartilage of vertebral column), myotome (skeletal muscles), dermatome (dermis)

Question 17

Intermediate mesoderm

Answer 17

Kidney

Question 18

Lateral plate mesoderm

Answer 18

Creates mesothelial/serous membranes (peritoneum, pericardium, lung pleura); splits into two divisions and coelomic cavity forms in between them

Parietal/Somatic mesoderm: body wall

Visceral/Splachnic mesoderm: surrounds endodermal organs

Question 19

Extraembryonic mesoderm

Answer 19

Anybody know what this turns into?

Question 20

How does the neural plate begin to form?

Answer 20

Notochord induces it to

Question 21

Forebrain

(Procephalon)

Answer 21

Telencephalon: oflactory nerve

Diencephalon: optic nerve

Question 22

Midbrain

(Mesencephalon)

Answer 22

Cranial nerve III (occulomotor)

Question 23

Hindbrain

(Rhombencephalon)

Answer 23

8 Rhombomeres

Cranial nerves IV to XII

Question 24

Foregut

Answer 24

Epithelium of…

Pharyngeal pouch derivatives: thyroid, parathyroid, thymus, tonsils

Esophagus

Trachea

Lung buds

Stomach

Liver

Gall bladder

Pancreas

Duodenum

Question 25

Midgut

Answer 25

Epithelium of... Posterior duodenum Small intestine Transverse colon (part of it)

Question 26

Hindgut

Answer 26

Epithelium of... Colon Rectum Urinary bladder Prostate Urethra

Question 27

Examples of epithelial-mesenchymal transition

Answer 27

1) Gastrulation at primitive streak 2) Neural crest migration 3) Lateral plate forming mesothelium lining of peritoneum (mesenchymal TO epithelial...opposite!) 4) Note: also happens in cancer invasion when cells detach from each other and attach to basement membrane

Question 28

When does basic organogenesis of the fetus complete?

Answer 28

End of 1st trimester Most sensitive to teratogens during 1st trimester

Question 29

Fetus' genetalia differentiated

Answer 29

14 weeks

Question 30

When does surfactant secretion begin and why is that relevant?

Answer 30

24 weeks Note: at ~26 weeks (beginning of 3rd trimester) CNS matured enough to support rhythmic breathing so after this point, viable fetus can be born

Question 31

Morphogen gradient responsible for dorsal-ventral axis

Answer 31

BMP High on ventral side (induces epidermis and lateral plate--most ventral) (BMP signals through protein kinase receptor that activates Smad TFs)

Question 32

Genes responsible for anterior-posterior axis

Answer 32

Hox genes

Question 33

How do chordin and noggin act?

Answer 33

BMP antagonists that bind BMP and stop it from signaling Act on dorsal side to inhibit BMP

Question 34

Hox gene vs. Homeodomain vs. Homeobox

Answer 34

Hox: gene Homeodomain: structural motif in the protein that can bind to DNA Homeobox: DNA that encodes the homeodomain

Question 35

How does retinoic acid affect Hox gene transcription?

Answer 35

RA activates Hox gene transcription by binding receptor and translocating into nucleus RA sequentially activates Hox gene expression: anterior to posterior

Question 36

Retinoic acid teratogenesis

Answer 36

Hox genes not usually expressed in most anterior pharyngeal arch (containing rhombomeres 1 and 2) but excess RA causes Hox expression there Causes cleft palate, micrognathia, etc

Question 37

RU 486

Answer 37

Progesterone receptor antagonist Used in first months of pregnancy, but not after because at that point placenta is making progesterone, and can't block that

Question 38

Malformation

Answer 38

Results from abnormal formation of a structure (usually during embryogenesis)

Question 39

Deformation

Answer 39

Results from impact of mechanical forces on normally-formed structure (usually during fetal period)

Question 40

Disruption

Answer 40

Results from destruction of previously normally formed structure

Question 41

Dysplasia

Answer 41

Results when normal structures are made out of abnormal tissues