GI Tract

Question 1

Processes

Answer 1

• Ingestion: to take in food
• Mastication: chewing (mechanical breakdown of food)
• Deglutition: swallowing
• Digestion: chemical breakdown of food
• Absorption: passage of food from the digestive tract lumen to the blood
• Peristalsis: the “milking” action of smooth muscle; mainly propels food
• Segmentation: “mixing” action of smooth muscle, separate muscle segments contract at the same time
• Defecation: the formation and excretion
  of solid waste

Question 2

Swallowing Mechanisms

Answer 2

• Buccal phase
• Pharyngeal phase
• Esophageal phase

Question 3

Layers of Digestive Tract Wall

Answer 3

• Mucosa
• Submucosa
• Muscularis externa

Question 4

Mucosa

Answer 4

The absorptive layer, lines the lumen, folded to 600x its length in some areas 
(3 major components):
- Mucosal epithelium
- Lamina propria
- Muscularis mucosae
- Serosa

Question 5

Mucosal Epithelium

Answer 5

Columnar epithelium (stomach, intestines) or stratified squamous
– Crypts of Leiberkuhn: folds in the mucosa, source of new epithelial cells

Question 6

Lamina Propria

Answer 6

Loose CT of the mucosa, with capillaries that receive absorbed nutrients
– lymphatic tissue: capillaries and lymphatic nodules involved in absorption of fat

Question 7

Muscularis Mucosae

Answer 7

A thin layer of smooth muscle that keeps the folds of the mucosa folded

Question 8

Submucosa

Answer 8

Tissue: dense irregular CT
– Peyer’s Patches: aggregates of lymph nodes, significant protection against intestinal infections
Meissner’s plexus: nerve supply to the muscularis mucosae
Brunner’s (intestinal) glands (duodenum only)

Question 9

Muscularis Externa

Answer 9

Mainly a double layer of smooth muscle, propels and mixes digestive contents
– circular layer: thick inner layer, muscle fibers describe a circle
– longitudinal layer: thin outer layer, muscle fibers run along the length of the GI tract
– Auerbach’s (Myenteric) plexus: nerve supply to the muscularis externa

Question 10

Serosa

Answer 10

Outer wall of the GI tract, visceral peritoneum, loose CT + simple squamous epithelium

Question 11

Mouth and Pharynx

Answer 11

• Tongue: a muscular soft organ, involved in moistening/mixing food, taste, speech
• Lingual tonsils: aggregates of lymph nodes located on the posterior/superior aspect
• Frenulum linguae: an inferior attachment of the tongue to the lower jaw
• Papillae: microscopic folds in the tongue containing taste buds

Question 12

Heterodont Dentition

Answer 12

Having “varied” teeth

• Diphyodont: having 2 sets of teeth within 1 life time
• Dental formulas (I - C - P - M in each quadrant)

Question 13

Deciduous Teeth

Answer 13

2-1-0-2:

2 incisors, 1 canine, 0 premolar, and 2 molars in each quadrant

Question 14

Permanent Teeth

Answer 14

2-1-2-3:

2 incisors, 1 canine, 2 premolars, 3 molars in each quadrant

Question 15

Salivary Glands

Answer 15

Release water, lysozyme, digestive enzymes, mucus
• buccal: in cheeks
• parotid: largest, anterior to the ear (pure serous)
• submandibular (submaxillary) inferior and medial to mandible (contain serous/mucus cells)
• sublingual: inferior to the tongue (mostly mucus)

Question 16

Esophagus

Answer 16

Function to move food to the stomach
• lining epithelium: stratified squamous epithelium
• muscle layer:
– 1st third: skeletal m.
– 2nd third: a mixture of skeletal and smooth m.
– 3rd third: smooth m.

Question 17

Stomach

Answer 17

A large, muscular distendible portion of the GI tract
• Epithelial lining = simple columnar epi
• 3 layers of smooth muscle: longitudinal, circular and oblique
• Where peristalsis continues and segmentation begins

Question 18

Rugae

Answer 18

Macroscopic folds in the stomach, luminal lining, flatten when the stomach is full. Also found in the gall bladder and urinary bladder

Question 19

Gastric Glands & Pits

Answer 19

• Gastric glands: microscopic folds, secrete gastric juice

- Gastric pits: openings from gastric glands to gastric lumen

Question 20

5 Cell Types of Stomach

Answer 20

– chief (zymogenic) cells: secrete protein breaking enzymes
– parietal cells: secrete stomach acid
– mucus cells: secrete mucus

Question 21

Enteroendocrine Cells of Gastric Glands

Answer 21

– G-cells: secrete hormones to support stomach activity

– Argentaffin cells: secrete histamine and serotonin to support stomach activity

Question 22

Small Intestine

Answer 22

~ 3 meters long, responsible for most digestion/absorption
3 histologically different regions:
- duodenum
- jejunum
- ileum

Question 23

Folds That Increase Intestinal Surface Area

Answer 23

– plicae circularis-macroscopic permanent folds (permanent until death) (increase 2 x)
– villi-fingerlike projections on plicae (increase 10 x)
– microvilli-submicroscopic folds on apical membranes of columnar cells (increase 20-30 x)

Question 24

Duodenum

Answer 24

25 cm, responsible for 95% of digestion and absorption
• mucous glands (not present in jejunum)
• ampullae-enlargements allowing for openings from pancreatic and bile ducts
– hepatopancreatic (sphincter of Oddi)
– accessory

Question 25

Jejunum

Answer 25

1 m long, histologically similar to duodenum, finishes what was started in the duodenum

Question 26

Ileum

Answer 26

2m long, mainly water, mineral, vitamin absorption

Question 27

Liver

Answer 27

Responsible for detoxifying nutrients, supplying bile to the duodenum, supplying vitamins, supplying hormones - Falciform ligament: suspends liver from diaphragm - Ligamentum teres hepatis: extends from falciform ligament to umbilicus (remnant of umbilical vein)

Question 28

Gallbladder

Answer 28

Stores bile

Question 29

Pancreas

Answer 29

* acinar cells (exocrine): secrete most digestive enzymes and bicarbonate * pancreatic ducts: collect enzymes, bicarb, pass them onto the duodenum * pancreatic islets (Islets of Langerhans) (endocrine): secrete hormones (insulin)

Question 30

Endocrine Portion of the Pancreas

Answer 30

* pancreatic islets (Islets of Langerhans): * approximately 1 million in the human pancreas * 2 major cell types alpha and beta * control blood sugar

Question 31

Large Intestine

Answer 31

• regions (7): cecum, ascending, transverse, descending, sigmoid, rectum, anus - lining epithelium - haustra - haustral churning - taenia coli - epiploic appendages

Question 32

Lining Epithelium

Answer 32

Mostly simple columnar, stratified squamous in the anal canal

Question 33

Haustra & Haustra Churning

Answer 33

Haustra: sacs or pouches seen along the length of the large intestine Haustra Churning: contraction of the haustra, mixes feces, max absorption of water

Question 34

Taenia Coli

Answer 34

3 distinct bands of smooth muscle (longitudinal) running the length of the large intestine

Question 35

Rectum & Anus

Answer 35

* rectum: stores feces until defecation | * anus: contains 2 sphincter muscles controlling passage of feces to the exterior