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Mammalian physiology > Digestive System > Flashcards

Digestive System Flashcards

1
Q

anatomy of the digestive tract

A
  • digestive system begins with oral cavity (mouth and pharynx) which serves as a receptacle for food
  • swallowed food enters gastrointestinal tract (GI tract) consisting of esophagus, stomach, small intestine, and large intestine
  • portion of the GI tract running from the stomach to the anus is also called the gut
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2
Q

digestion

A

chemical and mechanical breakdown of food
- takes place primarily in lumen of gut

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3
Q

accessory glandular organs

A

salivary glands, liver, gallbladder, and pancreas

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4
Q

digestion begins with chewing and secretion of saliva by three pairs of salivary glands:

A

(1) sublingual glands - under the tongue
(2) submandibular glands under the mandible (jawbone)
(3) parotid glands lying near the hinge of the jaw

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5
Q

esophagus

A

narrow tube that travels through the thorax to the abdomen
- walls are skeletal muscle but transition to smooth muscle

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6
Q

sections of stomach

A
  • upper fundus
  • central body
  • lower antrum
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7
Q

pyloric valve

A

guards the pylorus or opening between stomach and small intestine

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8
Q

chyme

A

stomach continues digestion by mixing food with acid and enzymes

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9
Q

where does most of digestion take place?

A

small intestine

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10
Q

sections of small intestine

A
  • duodenum
  • jejunum
  • ileum
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11
Q

how is digestion carried out?

A

intestinal enzymes, aided by exocrine secretions from two accessory glandular organs - pancreas and liver

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12
Q

sphincter of Oddi

A

keeps pancreatic fluid and bile from entering small intestine except during a meal

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13
Q

colon

A

proximal section of large intestine

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14
Q

what happens in the colon?

A

watery chyme becomes semisolid feces, as water and electrolytes are absorbed out of the chyme and into the extracellular fluid

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15
Q

rectum

A

terminal section of the large intestine

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16
Q

4 layers of GI tract

A

(1) inner mucosa facing lumen
(2) submucosa
(3) layers of smooth muscle known collectively as muscularis externa
(4) covering of connective tissue called serosa

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17
Q

Mucosa include:

A

(1) transporting epithelial cells into the small intestine
(2) endocrine and exocrine secretory cells
(3) stem cells

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18
Q

mucosal (apical) surface

A

cells secrete ions, enzymes, mucus, and paracrine molecules into lumen

19
Q

serosal (basolateral) surface

A

substances being absorbed from lumen enter ECF

20
Q

mucosa: mucosal epithelium

A
  • the cell to cell junctions tie GI epithelial cells together
  • in stomach+colon junctions have a tight barrier
  • in small intestine junctions are leaky
  • stem cells are rapidly dividing
21
Q

mucosa: lamina propia

A
  • subepithelial connective tissue: nerve fibers, blood vessels, and lymph vessels
  • immune cells patrolling for invaders that enter through epithelium
  • lymphoid tissue adjoining epithelium form small nodules and large Peyer’s patches
22
Q

mucosa: muscularis mucosae

A
  • thin layer of smooth muscle separates the lamina propria from the submucosa
  • contraction of muscles in this layer moves the villi back and forth
23
Q

submucosa

A
  • middle layer of gut wall
  • connective tissue with larger blood and lymph vessels running through it
  • also contains submucosal or meissner’s plexus on of the major nerve networks of enteric nervous system
24
Q

muscularis externa

A
  • outer wall of Gi tract consists of 2 layers of smooth muscle: inner circular layer and outer longitudinal layer
25
Q

contraction of circular layer

A

decreases diameter of lumen

26
Q

contraction of longitudinal layer

A

shortens tube

27
Q

myenteric plexus/Auerbach’s plexus

A

second nerve network
- lies between longitudinal and circular muscle layers
- controls and coordinates motor activity of muscularis externa

28
Q

serosa

A
  • outer covering of entire GI tract
  • connective tissue membrane that is a continuum of the peritoneal membrane lining the abdominal cavity
29
Q

four processes of digestive system

A
  • digestion
  • absorption
  • secretion
  • motility
30
Q

secretion

A

movement of material from cells into lumen or ECF

31
Q

digestion

A

chemical and mechanical breakdown of food into absorbable units

32
Q

absorption

A

movement of material from GI lumen to ECF

33
Q

motility

A

movement of material through the GI tract as a result of muscle contraction

34
Q

challenges of digestive system

A
  • autodigestion
  • mass balance
  • fluid loss
  • defense
35
Q

autodigestion

A

if protective mechanisms against autodigestion fail, raw patches known as peptic ulcers develop

36
Q

mass balance

A

matching fluid input with output, dehydration

37
Q

fluid loss

A

vomiting, diarrhea, loss of blood pressure

38
Q

defense

A

GI tract is assisted by an array of physiological defense mechanisms, including mucus, digestive enzymes, acid, and the largest collection of lymphoid tissue in the body, the gut-associated lymphoid tissue (GALT)

39
Q

mass balance in GI tract

A
  • gastrointestinal epithelial cells are polarized, with distinct apical and basolateral membranes
  • water follows osmotic gradient created by transfer of solutes from one side of epithelium to other
  • water moves through the epithelial cells via channels or through leaky junctions between cells
40
Q

digestive enzymes

A
  • enzymes are secreted by exocrine glands (salivary glands and the pancreas) or epithelial cells in stomach and small intestine
  • enzymes are proteins synthesized on rough ER packaged by Golgi complex into secretory vesicles, stored in cell until needed and released by exocytosis
  • many intestinal enzymes remain bound to apical membranes of intestinal cells anchored by transmembrane protein “stalks” or lipid anchors
  • some digestive enzymes are secreted in an inactive proenzyme form known collectively as zymogens
41
Q

mucus

A
  • viscous secretion composed primarily of glycoproteins collectively called mucins
  • made in specialized exocrine cells called mucous cells in the stomach and salivary glands, and goblet cells in the intestine
  • the signals for mucus release include parasympathetic innervation , variety of neuroproteins found in enteric nervous system and cytokines from immunocytes
  • parasitic infections and inflammatory processes in the gut also cause substantial increases in mucus secretion
42
Q

tonic contractions

A

sustained for minutes or hours, they occur in some smooth muscle sphincters and in the anterior portion of the stomach

43
Q
A

Mammalian physiology (2 decks)

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