lecture 32

Question 1

upper esophageal sphincter

Answer 1

• separates pharynx of the throat and top of esophagus
• will relax when swallowing so food can reach esophagus

Question 1

sphincters of GI tracts

Answer 1

• are rings of smooth muscle that are tonically constricted to adjacent organs unless there is a stimulus for them to relax
• serve as one way valves

Question 2

lower esophageal sphincter

Answer 2

• separates esophagus from stomach
• can spontaneously relax allowing acid stomach contents to splash back up into esophagus and burn esophageal wall resulting in heart burn or adic reflux

Question 3

pyloric sphincter

Answer 3

• separates stomach from small intestine
• contents will remain in stomach till its done with them
• contents leave in the form of chyme through pyloric sphincter into the duodenum of the small intestine where chemical digestion will continue and absorption of most substances will begin

Question 4

Ileocecal sphincter

Answer 4

• separates small intestine and large intestine
• found at the start of the large intestine

Question 5

Internal and external anal sphincters

Answer 5

• have voluntary conscious control over the external anal sphincter but not the internal

Question 6

Name the structures that a carbohydrate would pass through from beginning to end of GI tract

Answer 6

1. oral cavity
2. esophagus
3. stomach
4. small intestine
5. large intestine
6. rectum

Question 7

The GI tract

Answer 7

• main role is to transfer nutrients and water from food into body
• 4.5m continuous hollow tube from mouth to anus
• anything a part of your GI tract or anything in the lumen is considered external environment. To become internal we need to cross the wall of the GI tract through the process of absorption happening in the small intestine
• accessory glands and organs are functionally associated with the GI tract, but material does not pass through them (salivary glands, liver, gallbladder, pancreas)

Question 8

what are the 4 tissues that make up the wall of GI tract in the stomach and small intestine (inside to outside)

Answer 8

1. mucosa
2. submucosa
3. muscularis externa (longitudinal muscle and circular muscle)
4. serosa

Question 9

mucosa

Answer 9

• the innermost layer

Question 10

what is the mucosal layer comprised of?

Answer 10

• epithelium that lines the GI tract
• transporting epithelium cells (absorption of glucose)
• secreting epithelium cells (secrete carbohydrates, mucous (HCO3- to neutralize stomach acids)
• stem cells because cells turn over quick because they’re facing a harsh environment
• lamina propria that epithelium cells adhere too contain glands, lymph vessels, blood supply and nerve fibers
• muscularis mucosae is a thin layer of smooth muscle that separates mucosa from submucosa and can contract to alter SA of mucosa for absorption

Question 11

what is the submucosa comprised of

Answer 11

• loose connective tissue that contains nerve trunks, lymph vessels and blood supply
• in this layer the small intestine also has the submucosal plexus

Question 12

Muscularis externa

Answer 12

• has 2 layers of smooth muscle which are circular muscle (constrict lumen) and longitudinal muscle (shorten tract)
• alternating contraction of these 2 muscle give rise to type of contraction that occurs in small intestine called segmental
• stomach has extra layer called oblique layer (runs diagonal)
• myenteric plexus is located just in between these 2 muscle layers

Question 13

serosa

Answer 13

• outer layer covering the entire GI tract
• largely connective tissue
• comprised of secretory epithelium that allows for lubrication so we don’t get friction when all these different types of muscle contractions are happening
• protects and suspends GI tract within abdominal cavity

Question 14

The 4 basic GI processes

Answer 14

• secretion: movement of material from cells to lumen (saliva, gastric juice, pancreatic enzymes
• digestion: mechanical or chemical digestion of food into absorbable bits
• absorption: movement of material from GI lumen to ECF
• motility: movement throughout GI tract as a result of muscle contractions

Question 15

peristaltic contactions

Answer 15

• propel contents forward
• regulates motility

Question 16

segmental contractions

Answer 16

• mix and mash food back and forth
• happening in small intestine
• important for mechanical digestion

Question 17

what are the GI secretions and where do they come from

Answer 17

1. saliva - slaivary glands
2. gastric juices - stomach
3. bile - liver
4. pancreatic enzymes (pancreas)
5. mucous, Na+, H+, K+, Cl- and HCO3-

Question 18

The enteric nervous system

Answer 18

• a self sufficient circuit that runs your gut
• normally receives input from ANS
• regulates digestive processes, secretion, motility and how long something spends in your stomach before you shuttle it along in your small intestine

Question 19

short reflexes

Answer 19

• involves only your enteric nervous system

Question 20

long reflexes

Answer 20

• involves autonomic input (the brain)

Question 21

what system inhibits GI motility and secretions

Answer 21

the sympathetic nervous system

Question 22

what system stimulates GI motility and secretions

Answer 22

the parasympathetic nervous system