Module 2B: Development of Lymphatic and Digestive System

Question 1

What is the primary function of the lymphatic system?

Answer 1

Returns interstitial fluid to the bloodstream and supports immune function

The lymphatic system plays a critical role in fluid homeostasis, fat absorption via lacteals, and immune surveillance.

Question 2

What fluid does the lymphatic system transport?

Answer 2

Lymph

Lymph is a clear fluid containing immune cells, proteins, and waste products.

Question 3

What are the components of the lymphatic system?

Answer 3

• Vessels
• Nodes
• Organs

These components work together to facilitate the return of interstitial fluid to the bloodstream.

Question 4

What happens to fluid from plasma in capillaries?

Answer 4

It diffuses into the interstitial space and becomes interstitial fluid

Most of this fluid is absorbed by tissue cells or resorbed into venous structures.

Question 5

What is the role of lymph vessels in interstitial fluid management?

Answer 5

Act as an overflow valve shunting accumulating interstitial fluid away

This helps prevent damaging increases in interstitial pressure.

Question 6

What are the two major lymphatic ducts and their drainage areas?

Answer 6

• Right lymphatic duct: drains right upper quadrant
• Thoracic duct: drains remainder of the body

The right lymphatic duct empties into the right subclavian vein, while the thoracic duct empties into the left subclavian vein.

Question 7

What is the embryonic origin of the lymphatic system?

Answer 7

Begins mesodermally as a bilaterally symmetrical network from cardinal veins

Selective atrophy and remodeling lead to an asymmetric drainage pattern.

Question 8

What is the thoracic duct’s primary role?

Answer 8

Drains lymph from most of the body

It forms from the fusion of multiple lymphatic plexuses.

Question 9

What are the two main hypotheses regarding the embryonic origin of the lymphatic system?

Answer 9

• Centrifugal hypothesis: lymphatic vessels sprout from veins
• Centripetal hypothesis: lymphatic vessels form de novo from mesenchymal precursor cells

Recent evidence suggests both mechanisms contribute to lymphatic development.

Question 10

What distinguishes capillary lymphatics from collecting lymphatics?

Answer 10

Capillary lymphatics have discontinuous junctions; collecting lymphatics have continuous junctions and intraluminal valves

Capillary lymphatics allow passive fluid entry, while collecting lymphatics facilitate unidirectional flow.

Question 11

What are primary lymphoid organs responsible for?

Answer 11

Sites of immune cell production and maturation

Examples include bone marrow and thymus.

Question 12

What are secondary lymphoid organs and their function?

Answer 12

Sites of lymphocyte activation

Examples include lymph nodes, spleen, and mucosa-associated lymphoid tissues.

Question 13

What is GALT and its role?

Answer 13

Gut-associated lymphoid tissue that provides immune defense in the gastrointestinal tract

It includes Peyer’s patches and mesenteric lymph nodes.

Question 14

When does the development of GALT begin in humans?

Answer 14

Around week 11–12 of gestation

This development is initiated by interactions between intestinal epithelium and lymphoid tissue inducer cells.

Question 15

What is the function of the cisterna chyli?

Answer 15

Major collecting reservoir for lymph from the intestinal trunk and lower body

It links gut immunity with systemic circulation.

Question 16

True or False: The thoracic duct empties into the right venous angle.

Answer 16

False

The thoracic duct empties into the left venous angle.

Question 17

Fill in the blank: The right lymphatic duct drains lymph from the _______.

Answer 17

Right upper quadrant

Question 18

What drives the postnatal maturation of GALT?

Answer 18

Postnatal antigen exposure

This includes exposure to microbiota and food.

Question 19

What is the primitive gut tube?

Answer 19

A blind-ending tube divided into three parts: foregut, midgut, and hindgut

The primitive gut tube is formed from the endoderm and plays a crucial role in the development of the gastrointestinal system.

Question 20

What does the foregut develop into?

Answer 20

Esophagus, stomach, proximal duodenum, liver, gallbladder, and pancreas

The foregut is the anterior part of the primitive gut tube.

Question 21

What is physiological herniation?

Answer 21

The process where intestinal loops enter the umbilical cord due to rapid elongation of the primary intestinal loop

Occurs during the 6th week of development.

Question 22

What are the components of the hindgut?

Answer 22

Distal third of the transverse colon, descending colon, sigmoid colon, rectum, and anal canal

The hindgut is the posterior part of the primitive gut tube.

Question 23

Fill in the blank: The embryonic period lasts from _____ weeks.

Answer 23

3 to 8 weeks

Question 24

What is the role of the endoderm in gut development?

Answer 24

Gives rise to the epithelial lining of the digestive tract

The endoderm also modifies to form secretory cells.

Question 25

What major anatomical feature does the mesoderm give rise to in the gut?

Answer 25

Muscle, connective tissue, and other components of the wall of the gut ## Footnote The mesoderm contributes to the stroma for the glands as well.

Question 26

True or False: The oropharyngeal membrane separates the stomodeum from the pharynx.

Answer 26

True

Question 27

What is the significance of the cloacal membrane in hindgut development?

Answer 27

It initially covers the region of the cloaca and separates the anal and urogenital tracts ## Footnote The cloacal membrane ruptures to form distinct openings.

Question 28

Describe the basic vertebrate body plan.

Answer 28

Bilaterally symmetrical structure organized along a central axis featuring: dorsal neural tube, notochord, segmented somites, and a ventral cavity containing internal organs ## Footnote This organization is fundamental for all vertebrate species.

Question 29

What are the embryologic milestones for week 4?

Answer 29

Embryonic folding creates foregut, midgut, and hindgut; oropharyngeal & cloacal membranes form ## Footnote Important for establishing the basic gastrointestinal structure.

Question 30

What does the midgut develop into?

Answer 30

Duodenum, jejunum, ileum, cecum, appendix, ascending colon, proximal two-thirds of transverse colon ## Footnote The midgut is supplied by the superior mesenteric artery.

Question 31

Fill in the blank: The gut tube undergoes _______ during embryonic development.

Answer 31

Elongation and rotation

Question 32

What is the role of the liver primordium during development?

Answer 32

Forms as an outgrowth of the endodermal epithelium at the end of the foregut ## Footnote Also known as the hepatic diverticulum.

Question 33

What is the origin of insulin-producing cells in the pancreas?

Answer 33

Beta cells in the islets of Langerhans ## Footnote They begin to appear by week 11 and insulin secretion starts by week 13.

Question 34

What does the urorectal septum separate?

Answer 34

The allantois and hindgut ## Footnote It plays a critical role in the development of the anal canal and urogenital sinus.

Question 35

What happens to the cloacal membrane during development?

Answer 35

It ruptures to form separate openings for the anal and urogenital tracts ## Footnote This occurs as the embryo develops and grows.

Question 36

What is situs inversus totalis?

Answer 36

A rare congenital abnormality characterized by a mirror-image transposition of abdominal and thoracic organs ## Footnote It results in failure to generate normal left-right laterality.

Question 37

What is the function of the greater omentum?

Answer 37

An apron-like structure created by the proliferation of the visceral mesoderm layer during stomach rotation ## Footnote It is involved in fat storage and immune response.

Question 38

What does the posterior anorectal canal become?

Answer 38

The rectum and anal canal

Question 39

What forms separate openings for the anal and urogenital tracts?

Answer 39

The cloacal membrane ruptures

Question 40

From where does the urinary bladder ultimately derive?

Answer 40

The cloacal region linked to the allantois

Question 41

What is a rectoperineal fistula?

Answer 41

A defect associated with abnormal urorectal septum development

Question 42

What is a urorectal fistula?

Answer 42

A defect associated with abnormal urorectal septum development

Question 43

What is an imperforate anus?

Answer 43

A defect associated with abnormal urorectal septum development

Question 44

What is a rectovaginal fistula?

Answer 44

A defect associated with abnormal urorectal septum development

Question 45

What is ectopia cordis?

Answer 45

The heart lies outside the thorax with a cleft in the thoracic wall

Question 46

What is gastroschisis?

Answer 46

Intestines herniate through the abdominal wall to the right of the umbilicus

Question 47

What is bladder exstrophy?

Answer 47

Closure in the pelvic region has failed

Question 48

What is cloacal exstrophy?

Answer 48

A larger closure defect with most of the pelvic region exposed

Question 49

What are the derivatives of the GI foregut?

Answer 49

* Oral cavity * Esophagus * Stomach * Duodenum (first part) * Liver * Gall bladder * Pancreas

Question 50

What are the derivatives of the GI midgut?

Answer 50

* Duodenum (2nd/3rd parts) * Jejunum * Ileum * Cecum * Appendix * Ascending colon * Transverse colon (proximal 2/3)

Question 51

What are the derivatives of the GI hindgut?

Answer 51

* Transverse colon (distal 1/3) * Descending colon * Sigmoid colon * Rectum * Upper portion of anus