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Human Embryology > Weeks 4-8 > Flashcards

Weeks 4-8 Flashcards

1
Q

What is the 4th-8th week period called

A

Organogenetic period

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2
Q

Mesoderm vs mesenchyme

A

Mesoderm: derived from the mesodermal germ layer

Mesenchyme: any loose connective tissue; may be derived from the mesoderm, neural crest, etc

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3
Q

Mesoderm cells to blood vessels signalling pathway

A
  • FGF2 binds to FGFR creating mesoderm cells
  • VEGF binds to VEGF-R2 and creates hemangioblasts around mesoderm cells.
  • VEGF binds to VEGF-R1 to create tube formation.
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4
Q

Hemangioblasts can become…..

A
  1. Angioblasts (outside cells) which create:
    - endothelial tube
  2. hematopoetic stem cells (HSC) which create:
    - myloid -RBC,WBC, macrophages
    - Lymphoid-B cells abd T cells
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5
Q

Mesoderm cells can differentiate into these types

A

Hermangioblasts, angioblasts and HSC

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6
Q

Vasculogenesis

A

Blood vessel formstion begins in the extraembryonic mesoderm of the yolk sac, connecting stalk and chorion and eithin the embryo a few days later.

  • mesoderm cells differentiate to angioblasts
  • aggregate to form blood islands which become endothelial lined channels
  • new vessles sprout (angiogenesis)
  • adjacent mesoderm becomes muscle
  • inital blood crlls form from endothelial cells
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7
Q

Embryonic period

A

Important period of development as the beginning of all organ systems appear during this time

  • each organ system has a particular critical period
  • by the end of the embryonic period, the embryo appears human
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8
Q

Folding of the embryo

A
  • during the 4th week, the shape of the emrbyo changes
  • flat trilainar embryo becomes cylindrical in shape
  • folding results from the rapid growth of the neural tube and amniotic cavity but not yolk sac
  • folding occurs in the longitudinal and transverse planes
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9
Q

Folding in the longitudinal plane

A
  • redults in the head and tail ends of the embryo swinging ventrally
  • the septum transversum, primitive heart and orophsryngeal membrane turn onto ventral surface
  • somatopleure becomes face and chest wall
  • part of yolk sac is incorporated as the foregut
  • the tail fold occurs after head fold
  • during the tail fold, part of the yolk sac is incorporated as the hindgut
  • the connecting stalk moves to the ventral surface
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10
Q

Folding in the transverse plane

A
  • the sides of the embryonic disc roll ventrally forming a cylindrial embryo
  • part of the yolk sac is incorporated as the midgut
  • the splanchnopleure forms the wall of the gut
  • the somatopleure forms the body wall
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11
Q

Major events in order so far….. (Up to week 4)

A

-cleavage, implantation,gastrulation, neurluation, folding of the embryo

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12
Q

Neural tube defects
(Due to lack of closure of different reguons of thr neural tube)
-If anterior neuropore doesnt close…
-if posterior neuropore doesnt close…

A

Anencephaly (missing parts of brain, skull)

Slina Bifida (Incomplete closing of the spine)

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13
Q

Waht can prevent NTD’s during pregnancy?

A

Folic Acid

  • all women of childbearing age should take folic acid
  • 400 ug/day
  • 4000 ug/day when trying to concieve if history of NTD’s in family
  • prevents 70% of NTD’s
  • must be started 3 months prior to conception so all women of childbearing age should have 400ug/day
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14
Q

Control of development

A

During embryonic development, certain embryonic tissues act as inductors and influence the development of adjacent tissues

  • some signal passes from the inducing tissue to the induced tissue such as
  • a diffusible molecule
  • the extracellular matrix
  • physical contact
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15
Q

Examples of control of development

A
  • notochord and neural tube: notochord secretes FGF and shh to form neural plate which then forms neual groove and then neural tube.
  • lens formation: Les vesicles induced to form by optic cup location
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16
Q

The placenta is a _____ organ

A

Fetomaternal

  • fetal component is the villus chorion
  • maternal component is the decidua basalis of the endometrium
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17
Q

Maternal and fetal blood flow very close together bht normally ______

A

Do not mix

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18
Q

Blood flows from the fetus to the placenta via ______ (rest of path)

A

2 umbilical arteries—->capillaries of the chorionic villi—->exchange occurs——>veins—->unbilical vein—-> fetus

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19
Q

Maternal blood goes to the olacenta via _______ endometrial arteries though _______

A

80-100

Intervillous spaces——> endometrial veins

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20
Q

Exchange occus across the placental membrane in these ways

A

Diffusion
Facilitated diffusion
Active transport
Pinocytosis

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21
Q

Hemolytic disease of the newborn (Erythroblastosis fetalis)

A
  • usually results from Rh incompatibility between an Rh- mol and an Rh+ fetus.
  • Rh- person does not have Rh antigen on RBC nor anti-Rh antiobdies in plasms
  • if Rh- person is exposed to Rh+ blood, they will produce anti-Rh antibodies
  • anti-Rh antibodies corss the placenta and lyse fetus’s Rh+ RBC
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22
Q

Decidua refers to

A

The gravid endometirum, the functional layer of the endometrium in a pregnant women that separates from the remainder of the uterus after childbirth (second birth)

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23
Q

3 main regions of the decidua

A

Decidua basalis-part of the decidua deep to the conceptus that forms the maternal part of the placenta

Decidua capsularis-the superficial part of the decidua overlying the conceptus

Decidus parietalis- all the remaining parts of the decidua

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24
Q

Twins and fetal membranes

A

Twins that originate from 2 zygotes are dizygotic (DZ) twins or fraternal twins

Twins that originate from ine zygote are Monozygotic (MZ) twins or identical twins

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25
Q

Amniotic cavity expands and occupies all ____

A

Chorionic space and fuses with the chorionic cavity including the membrane to create a amniochorionic cavity

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26
Q

How many umbilical arteries and veins are there?

A 
2 arteries (oxygenated blood) 
1 vein
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27
Q

When are each chorionic villi types present?

A

Primary- end of second week (begin to branch)

Secondary-cover the surface of chorionic sac

Tertiary-blood vessels visbile in them

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28
Q

Digestive tract includes

Accessory digestive organs include

A

Mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum and anus

Liver, gall bladder and pancreas

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29
Q

Primitive gut is a ____consisting of the

A

Straight tube

Foregut
Midgut
Hindgut

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30
Q

Throughout the digestive tract…
Endoderm gives rise to

Splanchnic mesoderm gives rise to

A

Epithelium and glands

Connective tissue and muscle of the wall

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31
Q

Umbilical arteries bring?

A

Deoxygenated blood

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32
Q

The midgut remains attached to the yolk saf via the

A

Vitelline Duct or omphaloenteric duct

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33
Q

Derivities of the foregut

A

Pharynx to half of duodenum

Esophagus-develops causal to pharynx

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34
Q

The esophagus is separated from the trachea by the

A

Tracheoesdophageal septum

35
Q

Esophageal artresia

A

1/3000 births

Results from improper division of the trachea and espohagus (usally occurs with a tracheoesophageal fistula (opening) or failure of the espohagus to recanalize in 8th week

36
Q

How are gut regions established?

A 
From pharynx to colin there is an increasing gradient of retinoic acid! 
SOX2-specifies esophagus and stomach 
PDX1-specifies Doudenum 
CDXC-Small intestine 
CDXA-Large intestine

Morphogens

37
Q

Dorsal mesentery suspends…

Ventral mesentery forms from the____ and develops into the

A

The gut tube from the posterior body wall

Septum transversum

Lesser omentum

38
Q

3 blood vesseld in developing gut

A

Celiac arterial trunk - supplies foregut

Superior mesenteric artery -supplies midgut

Inferior mesenteric artery- supplies hindgut

39
Q

Mesentery

A

Connective tissue holding in place structures

40
Q

Dorsal mesogastrium

A

Holds stomach to dorsal body wall

41
Q

Which region of the stomach grows faster?

A

Dorsal region

42
Q

Liver grows rapidlt and tskes up most of the peritonial space, and splits the _________ into 2 spaces______

A

Ventral mesentery

  1. Lesser omentum-between liver and stomach
  2. Faciform ligament-between liver and ventral wall
43
Q

Lesser omentum has two ligaments____

A

Caudal part-Heptoduoderal ligament

Crabial part-Hepatogastric ligament

44
Q

Foregut endoderm proliferates to form____

A

Buds for lungs, liver, gall bladder and pancreas

45
Q

Where does the stomach develop from

A

The distal portion of the foregut

  • in 4th week a dilation occurs
  • enlarges and lies ventrally
  • dorsal border grows faster than ventral
  • dorsal border becomes the greater curvature of the stomach
  • ventral border becomes the lesser curvature of the stomach
46
Q

Congrnital pyloric stenosis

A

1/150 Males
1/750 Females

  • abdnormal thickening of the pyloric sphincter
  • restricts movement of materials from stomach into the small intestine
  • stomach becomes distended and projectile vomitting occurs

Stenosis=partial blockage

47
Q

Stomach rotation

A
  • Stomach rotates 90° clockwise around a longitudinal axis
  • ventral border moves to the right and doesal border to the left
  • before rotation, the cranial and causal ends of the stomach were in midline.
  • after rotation, the cranial end is on the left and the caudal end is on the right and the long adis is almost horizontal
48
Q

What happens to the mesentery during stomach rotation?

A

Messntsry also rotates 90°, mesentery has spaces that fuse and form a cavity

Now it is called the greater omentum (apron that hangs over) instead of dorsal mesogastrium

49
Q

Omental Bursa

A
  • isolated clefts develop in the mesenchyme forming he thick dorsal mesogastrium.
  • the clefts fuse and form a single cavity=omental bursa or lesser perioneal sac
  • as stomach enlarges, the onental bursa expands and acquires an inferior reccess of the omental bursa between the lsyer of the elongated dorsal mesogastrium and is called greater omentum.
  • membrane overhangs the developing small intestine
50
Q

Alimentary system

A

Digestive tract frim mouth to anus

51
Q

When does the prinordial gut form

A

Fourth week

52
Q

Espohageal stenosis

A

Incomplete canalization of the espohagus during the 8th week

-no apoptosis

53
Q

Development of duodenum begins when and where

A

Early in the 4th week, and develops from the caudal or distal part of the foregut
-grows rapidly forming a c-shaped loop that projects ventrally

54
Q

During the 5th and 6th weeks, the lumen of the duodenum becomes progressively _____-

A

Smaller and is temporaily obliterated because of the proliferation of its epithelial cells

Normal vacuolation occurs as the epithelial cells degenerate, as a result, the dupdenum normally becomes recanalized by the end of the embruonic period

55
Q

Duodenal stenosis

A

Partial occlusion of the duodenal lumen

  • usually results from incomplete recanalization of the duodenum resutlint from defective vacuolization
  • bile duct is connected to duodenum therefore the stomachs contents usually contain bile are often vomited

similar symptoms to pyloric stenosis

Can also be determined by ultrasound

56
Q

Duodenal artresia

A

Fully blocked duodenum

Recanalization fails to occur

Occurs almost always at the junction between the bile and pancreatic ducts

Amnitoic fluid builds up as it can not pass through

57
Q

Liver and gull baldder development begins when

A

4th week as an endodermal outgrowth from the foregut

  • liver bud or hepatic diverticulum
  • bud projects into splanchnic mesoderm and divides into cranial and caudal parts
58
Q

What layer gives rise to the heptaocytes

A

Endoderm

Hapato=liver
Cytes=cells

59
Q

Cell types like hemopoietuc tissue, fibrous tissue and kupffer cells are derived from?

A

Mesoderm

60
Q

The liver grows so rapidly that by week 8 the liver makes up what percent of the fetal body weight?

A

10%

61
Q

When does hematopoiesis begin in the liver? And when does bile formation occur?

A

Week 6 -hematopoietic cells migrating from the dorsal aorta to the liver

Week 12

62
Q

Liver primordium is the ____ part

Gall bladder and cystic duct are the ____ part of the diverticulum

A

Larger, causal

Smaller, caudal

63
Q

Liver bud outgrowth is induced by….?

A
  • secreted factors from cardiac mesoderm (FGF’s) and septum transversum (BMP’s)
  • initially, all of foregut can form liver, but is inhibited everywhere but at the site of liver bud outgrowth by factors secreted by surrounding tissue (noncardiac mesoderm, ectoderm, and notochord)
  • fibroblast growth factors (FGF), secreted by cardiac mesoderm, inhibit the inhibitors and stimulate bud growth.
  • BMP’s enhance the action of FGF’s
  • later hepatocyte-specific genes regulate liver cell differentiation.
64
Q

The pancreas develops where and from what?

A

Endodermal cells form dorsal and ventral pancreatic buds at caudal end of foregut. Week 4

As duodenum rotates, the vental bud is carried dorsally to lie posterior to the dorsal bud

65
Q

By week 5 which pancreatic bud is bigger

A

Dorsal

66
Q

During week 6 the pancreas is rotated 90° causing

A

2 buds to become closer and fuse into one pancreas and 1 drainage site

67
Q

Derivatives of the midgut

A

Include the small intestine (part of duodenum, jenunum, and ileum), proximal protions of the large intestine (caecum and appendix, ascending colon and 2/3 of the transverse colon)

68
Q

As the midgut elongates, it forms a U-shaped loop that projects through the ______ into the _____

A

Umbilical cord

Extraembryonic coelom

69
Q

Midgut undergoes _______ in the 6th week because there isnt enough room into the abdominal cavity (large liver and 2 sets of kidneys)

A

Physiological herniation

Midgut enters yolk sac

70
Q

Midgut loop has a _____ and _____ limb

A

Cranial- grows rapidly and gives rise to loops of the small intestine

Caudal-gives rise to parts of the large intestine

71
Q

During herniation, loop rotates 90°________ and causes…

A

Counterclockwise around the axis of the superior mesenteric artery

-cranial limb to the right and caudal limb to the left

72
Q

Midgut returns to the abdomen (hernia reduced) in the ____ week

A

10th
-enlargement of tthe abdominal cavity, and the relative decrease in the size of the liver and kidneyes are contributing factors in intestinal return

73
Q

The midgut goes through how many rotations?

A

3-90° counterclockwise rotations

74
Q

After the rotations of the midgut are complete, the intestines become fixed in position by____

A

Fusion of the mesenteries with the abdominal wall

75
Q

Congenital omphocele

A
  • midgut herbia is not reduced and intestines remain in proximal part of umbilical cord (1/5000)
  • can be born woth intestines put of body if ruptured (gastroschisis)
76
Q

Ileal diverticulum

A

Connection between midgut and yolk sac remains to birth (2-4%)

77
Q

Derivatives of the hindgut

A

Distal portion of transverse colon, descending colon, sigmoid colon, rectum and superior anal canal

78
Q

Cloaca

A
  • Is the expanded terminal part of the hindgut
  • is an endoderm-lined chamber that is in contact with the surface ectoderm at the clocal membrane
  • membrane is composed of endoderm of the cloaca and ectoderm of the proctodeum or anal pit
79
Q

Partitioning of the Cloaca

A
  • by 7th week, urorectal septum (mesenchyme) divides cloaca into vental urogenital sinus and dorsal GI part.
  • anal membrane ruptures at the end of the 8th week which brings digestive tract into communication with amniotic cavity
80
Q

The superior two thirds of the adult anal canal are derived from the

A

Hindgut

81
Q

By end of week 8, the fetus can now take in amniotic fluid and

A

Dispose of it

82
Q

The proctodeum and hingut connect where

A

Pectinate line

Proctodeum=ectoderm
Hibgut=endoderm

Communiction between germ layers since there isnt room for mesoderm

83
Q

Annular pancreas

A

Ring like annular part of the pancreas consists of a thin, flat band of the duodenum which may cause obstruction to the dupdenum

Human Embryology (6 decks)

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