Digestive System

Question 1

anatomy of the digestive tract

Answer 1

• 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

Question 2

digestion

Answer 2

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

Question 3

accessory glandular organs

Answer 3

salivary glands, liver, gallbladder, and pancreas

Question 4

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

Answer 4

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

Question 5

esophagus

Answer 5

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

Question 6

sections of stomach

Answer 6

• upper fundus
• central body
• lower antrum

Question 7

pyloric valve

Answer 7

guards the pylorus or opening between stomach and small intestine

Question 8

chyme

Answer 8

stomach continues digestion by mixing food with acid and enzymes

Question 9

where does most of digestion take place?

Answer 9

small intestine

Question 10

sections of small intestine

Answer 10

• duodenum
• jejunum
• ileum

Question 11

how is digestion carried out?

Answer 11

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

Question 12

sphincter of Oddi

Answer 12

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

Question 13

colon

Answer 13

proximal section of large intestine

Question 14

what happens in the colon?

Answer 14

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

Question 15

rectum

Answer 15

terminal section of the large intestine

Question 16

4 layers of GI tract

Answer 16

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

Question 17

Mucosa include:

Answer 17

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

Question 18

mucosal (apical) surface

Answer 18

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

Question 19

serosal (basolateral) surface

Answer 19

substances being absorbed from lumen enter ECF

Question 20

mucosa: mucosal epithelium

Answer 20

• 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

Question 21

mucosa: lamina propia

Answer 21

• 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

Question 22

mucosa: muscularis mucosae

Answer 22

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

Question 23

submucosa

Answer 23

• 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

Question 24

muscularis externa

Answer 24

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

Question 25

contraction of circular layer

Answer 25

decreases diameter of lumen

Question 26

contraction of longitudinal layer

Answer 26

shortens tube

Question 27

myenteric plexus/Auerbach's plexus

Answer 27

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

Question 28

serosa

Answer 28

- outer covering of entire GI tract - connective tissue membrane that is a continuum of the peritoneal membrane lining the abdominal cavity

Question 29

four processes of digestive system

Answer 29

- digestion - absorption - secretion - motility

Question 30

secretion

Answer 30

movement of material from cells into lumen or ECF

Question 31

digestion

Answer 31

chemical and mechanical breakdown of food into absorbable units

Question 32

absorption

Answer 32

movement of material from GI lumen to ECF

Question 33

motility

Answer 33

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

Question 34

challenges of digestive system

Answer 34

- autodigestion - mass balance - fluid loss - defense

Question 35

autodigestion

Answer 35

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

Question 36

mass balance

Answer 36

matching fluid input with output, dehydration

Question 37

fluid loss

Answer 37

vomiting, diarrhea, loss of blood pressure

Question 38

defense

Answer 38

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)

Question 39

mass balance in GI tract

Answer 39

- 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

Question 40

digestive enzymes

Answer 40

- 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

Question 41

mucus

Answer 41

- 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

Question 42

tonic contractions

Answer 42

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