GI Lecture 1 Flashcards
(84 cards)
1
Q
Give route of digestion
A
- Mouth/Oropharynx
- Esophagus
- Stomach
- Intestines (large and small)
2
Q
In the intestines, what part is primary site for nutrient absorption?
A
Small intestine
3
Q
What part of digestion route has important mixing function
A
stomach
4
Q
What are some accessory glands (3)
A
- Salivary glands
- Pancreas (we’re focusing on exocrine fxn but there is endocrine fxn)
- Liver
5
Q
When lipids are consumed, how are they taken up and absorbed?
A
taken up as triglycerides
Absorbed as FA and monoglycerides
6
Q
When proteins are consumed, how are they taken up and absorbed?
A
Taken up as large proteins
Absorbed as AA and (di or tri) peptides
7
Q
When carbohydrates are consumed, how are they taken up and absorbed?
A
Ingested as starch, disaccharides, and monosaccharides
Absorbed as monosaccharides
this varies among species
8
Q
Sphincters of digestive system
A
Upper and lower esophageal
Pyloric
Ileocecal
Internal and external
9
Q
Where is ENS located
A
SOLEY in GI tract
10
Q
What plexuses make up ENS
A
Myenteric (between circular and longitudinal muscle layers)
Mucosa of SI and LI
11
Q
Can ENS be modified by structures outside GI tract?
A
Yes
Brain can modify external and internal output
12
Q
Can ENS fxn w/o spinal cord or brain
A
YES
13
Q
When AP reach threshold, what happens?
A
Impulses are able to occure and neurotransmitter is released
14
Q
What types of neurons are in ENS
A
Sensory afferent neurons
Interneurons
Efferent secretomotor neurons
15
Q
What is myenteric plexus mainly concerned with?
A
Motor activity along gut and regulating enzyme output of adjacent organs
16
Q
When myenteric plexus is stimulated what happens
A
Increases tone of gut wall
Increase intensity and rate of contractions
Increase conduction of contractions
17
Q
When myenteric plexus is inhibited what happens?
How?
A
Has inhibitory arm that inhibits sphincter muscles that allows particles to leave one area (stomach) to another area (SI)
18
Q
What is submucosal plexus mainly in control of
A
Senses LOCAL functions of gut
19
Q
What does submucosal plexus regulate?
A
Specific small areas in gut to help local secretion, local absorption, local contraction, and local SA of internal gut wall.
20
Q
ENS neurotransmitters
A
Achl (stimulatory)
Noepinephrine (inhibitory)
21
Q
Parasympathetic ANS
-divided into (controlled by and controls)
A
Cranial division
- Vagus n
- Stomach and pancreas, not really intestines
Sacral division
- Pelvic n
- Aboral half of large intestine
22
Q
Parasympathetic ANS neurons
A
Preganglionic neurons project to myenteric and submucosal nervouse system
23
Q
Parasympathetic ANS is stimulated by
A
Achl
24
Q
Sympathetic ANS neurons
A
Postganglionic neurons to all areas of GI tract and terminate on ENS
25
Sympathetic ANS ihibited via
Noepinephrine
26
Types of reflexes in GI tract
- Reflexes entirely within ENS (local distention/local motor)
- Reflexes from gut to prevertebral sympathetic ganglia and back for global effect
- Reflex to spinal cord/brain stem then back to GI tract (general overall regulation of GI secretion and motility
27
Give examples of reflexes from gut to prevertebral sympathetic ganglia
- Gastro-colic reflex (stomach signal colon evacuation)
- Enterogastric reflex (Colon and SI inhibit stomach motility and secretion)
- Colonileal reflex (Colon to SI to decrease SI motility and slow further filling the colon)
28
GI Endorcrine regulation
- How are cells dispersed
- How are prodcuts secreted
GI endocrine cells are dispersed and not concentrated in a gland.
Products (hormones) are secreted in bloodstream and can affect other organs
29
Gastrin
- What is it
- What does it do
Protein that is released from cells in stomach and enters bloodstream (endocrine) and delivered to parietal cells of stomach.
Stimulates H+ secretion and stimulates mucosal growth
30
Cholecystokinin (CCK)
- What is it
- What does it do
Secreted by cells in SI in response to fat or fat breakdown products in intestine
Stimulates increased contractions of gallbladder, increases pancreatic secretions, and decreases stomach motility to allow more time for chyme in SI
31
Secretin
- What is it
- What does it do
Secreted in cells in SI in response to acidic gastric contents in SI
Stimulates gastric/pancreatic secretions and inhibits effects on acid secretion and motility in GI tract
32
Important protein hormones in GI tract
```
Gastrin (stomach)
Secretin (SI)
CCK (SI)
Gastric inhibitory peptide
Trophic hormone
```
33
Gastric inhibitory peptide
Secreted by upper SI in response to FA and AA locally
Decreases motor activity in stomach and stimulates insulin secretions
34
Trophic hormone
- What is it
- Relationship between
Hormone in gut that helps maintain microvillia and helps microvilli grow and regenerate.
Potential interactions among ENS and endorcrine system
35
Types of communication in GI
Endocrine=communicate via bloodstream
Paracrine=communicate with adjacent neighbor
Autocrine=communicate with yourself
Neurocrine=communicate via neurons
36
Describe immune system of GI
Has autonomous immune system: gets mucosa richly populated with immune cells. When antigens are detected, cytokines will be released to generate inflammation response.
37
Blood flow from GI tract
Venous blood from gut, spleen, and pancreas flow into liver via portal vein
This allows for nutrients to pass to liver first and liver acts as buffer for nutrients so liver can remove bacteria from blood. Detoxes blood.
38
Interstitial cells of cajal
- What are they
- Electric activity
- Why slow waves?
Specialized cells at jxn btwn circular and longitudinal muscles that extend length of GI tract and act as pacemakers
Electrical activity appears spontaneous
Connected to cells electrically
Amplitude and frequency of their slow waves modulated by nervous and endocrine system.
39
Control of gut muscle contractions
- Length of waves
- Unique?
Slow waves of depolarization that covers large area of muscle cells since they are connected electrically.
Occurs in absence of AP
40
Smooth muscle contractions (Explain)
Will only contract when AP is present and AP can only occur during PEAK of slow wave. SM can only contract once during slow wave. When AP is present individual muscles will work together.
41
Functional types of movements in GI
| -Give 2 and fxn
Propulsive movements
-->Cause ingesta to move progressively through GI tract
Mixing movements
-->Keeps GI contents mixed and exposes SA of digestible material to SA of gut for absorption and digestive enzymes.
42
Peristaltic wave
- Type
- Describe
Basic movement of GI tract and example of propulsive movement
Distention of gut lumen occurs and contraction rings form on distention. Peristaltic contraction moves towards distended segment and there's relaxtion of smooth muscle that "leads" peristaltic wave in aboral direction thanks to myenteric plexus. Without myenteric plexus, peristalsis contraction is weak.
CAN move oral and aborally
43
Stimuli for peristalsis
Local distention of gut wall (stretching of wall)
Irritation of gut lining (causing distention)
PANS
44
Mixing movement
- What is it
- How
- Influenced
Intermittent contractions that only last a few seconds but result in chopping, mixing, shearing of food.
Can happen when there's peristaltic wave against closed sphincter or there's specific contraction of circulat muscle layer that's not propagated
Influenced by PANS, SANS, ENS
45
Prehension
Directing food into GI tract (feet, tongue, teeth)
46
Chewing reflex
- Controlled by
- Explain
Controlled by brainstem
When food is in mouth, there's relaxation of jaw muscles. As jaw drops, strecth receptors in jaw muscles are stimulated and there's contraction of jaw muscles.
47
Deglutition (swallowing)
| -Stages
1st=voluntary=bolus entering mouth up to soft palate
2nd=pharyngeal=through pharynx
3rd=Esophageal=through esophagus
48
Deglutition
- Controlled by
- How does it work
Controlled by lower motor neurons and efferents travel in CN 7,10,12,9
Bolus goes through esophagus via peristaltic wave and respiration is inhibited when swallowing (glottis closed)
49
Resting esophagus
- How is it normally
- Describe
Normally closed via sphincters
Closed sphincters prevent gastric contents from refluxing into esophagus. Lower sphincter is formed by entrance of stomach. Stomach distention closes esophagus. DUring deglutition, esophageal muscles shorten to help align esophagus and stomach.
50
Megaesophagus
- What
- Who's predisposed?
When there's fibrous band of tissue that wraps around esophagus that should have disappeared during development. There's vascular ring anomaly in blood vessels around esophagus. Nerve damage can result
-Great Danes, Irish Setters, German Sheperd
51
Motor functions of stomach (3)
Store food
Mix food
Release chyme
52
3 functional areas of stomach
Fundus (esophageal end)
Corpus (mixing area for saliva and gastric secretions)
Anthrum (gastric/pyloric pump) regulates propulsion of food through pyloric sphincter
53
Proximal portion of stomach
- Purpose
- Reflexes
Stores food
Very little mixing occurs here. Food in layers
Adaptive relaxation reflex=ability of stomach to expand to accept large quantities of food
Vag-vasal reflex=no pressure build up, sensory info up vagus, relaxation of stomach from vagus
54
Vagotomy
In proximal portion of stomach, cut vagus nerve to reduce rate of gastric secretion and prevent stomach from expanding and builds up intraluminal pressure to feel "full"
55
Distal stomach
- Contractions
- Particle movement
Peristaltic contractions are more frequent.
Only smallest particles and fluids are passed into SI. Large particles are ground and ejected back toward antrum and corpus (retropulsion)
56
Proximal vs Distal stomach control
- Under what influence
- What n regulates
- Explain
Under endocrine and nervous control
Vagus n regulates
Proximal= vagus suppresses contractions allowing relaxation (unknown neurotransmitter)
Distal=vagus stimuates intense peristaltic activity (mediated by Achl)
57
Control of stomach emptying
- What must NOT happen
- Type of control
- Most potent control
Rate of stomach emptying must not exceed small intestine digestion/absorption
More negative control than positive control
Most potent control by small intestine, NOT stomach
58
Promotion of stomach emptying
- Promoted by
- Effects of stretched stomach wall
-Promoted by greater volume of food and NOT increased pressure thanks to adaptive reflex. Promoted by STRETCH IN STOMACH WALL.
Stretching of stomach walls causes myenteric reflex in stomach wall, increases activity of pyloric pump, inhibits closure of pyloric sphincter, stimulates gastrin secretion.
59
Inhibition of stomach emptying
- Regulated by
- Reflex involved and exaplain
Regulated primarily via SI intestine mechanism
Involves enterogastric reflex
- >Directly from duodenum to stomach via ENS
- >Through extrinisic n via SAND inhibitory n fibers in stomach
- >Via vagus n to inhibit activity
60
Things that can initiate enterogastric reflex to slow stomach emptying (6)
```
Distention of duodenum
Irritation of duodenal mucosa
pH of chyme entering duodenum
Osmolaity of chyme
Breakdown products of proteins
Breakdown products of fats (hormonal)
```
61
Hormonal control of stomach emptying
- Primary stimulus
- Protein hormones involved
Primary stimulus is presence of fat products in SI
CCK (from jejnum) is primary regulator and blocks stomach motility caused by gastrin.
Secretin released from acid in duodenum
62
Mechanism of hormonal action to inhibit stomach emptying
Inhibits action of pyloric pump
| Increases closure of pyloric sphincter
63
Interdigestive motility
Altered motility to clear stomach particles that didn't pass pyloris
-VERY strong peristaltic waves and plyoric sphincter is more open than previously (1 hour intervals)
64
Differences between regurgitation and vomiting
Vomiting has anticipatory salivation, retching, and abdominal contractions. Regurgitation does not
Vomiting has low pH and bile present. Regurge has high/neutral pH and absence of bile.
Vomiting lacks sausage shape vomit and undigested food. Regurge has undigested food and sausage shaped vomit.
65
Vomiting
- Involves
- How
Involves emetic/vomiting center of medulla and receives afferents from vagus and SANS.
Upper GI becomes distended (stimulus) and contractions from duoednum occurs to open lower esophageal sphincter. Abdominal contractions increase intragastric pressure to force vomit through lower esophageal sphincter.
66
Vomiting without GI irritation
Can be due to nervous signals (motion sickness) or specific chemical induction (drugs)
67
T/F Peristaltic waves occur in all parts of SI
T
68
Where are peristaltic waves faster in stomach?
Proximal
69
What controls SI movements?
Nervous and hormonal regulation (gastrin, CCK, insulin)
| Gastroeneteric reflex
70
Inhibitory hormonal secretions that controls SI movement
Secretin and glucagon
71
Digestive vs Interdigestive Phase
Peristatltic waves are more powerful in ID phase and extend further in SI
ID phase includes migrating motility complex that controls bacterial population in upper gut.
Peristaltic rush is also involved to eliminate noxious agents in SI in ID phase
72
3 Fxns of Colon
Absorb water and electrolytes (transition from chyme->solid poop)
Storage of fecal matter until elimination (distal half)
Species dependent fermentation (microbial digestion)
73
Mixing and propulsive movement of LI
Simultaneous contractions of circular and longitudinal muscles that form bulges called haustrations. Fecal matter is then pressed and rolled by exposing fecal surface to LI lumen to extract water from feces
74
Propulsive movements of LI
- Impeded by
- movement
Impeded by haustrations and antiperistaltic direction
| Movement in oral and aboral direction
75
Control of LI motility
| -wave origins
Colonic slows waves are generated in circular muscle and moves to longitudinal layer and controlled by pacemaker area that can CHANGE.
76
Cholinergic drugs in LI motility
Prolongs slow wave duration and increases incidence of spike burst and contraction
77
Adrenergic drug in LI motility
Decrease spike activity
78
Stimulatory and inhibitory hormone in LI motility
Stimulatory=gastrin and CCk
| Inhibitory=secretin
79
Constipation
Increase in colon motor activity and too much movement in oral direction
80
Diarrhea
Decrease in colon motor activity and too much movement in aboral direction
81
Defecation
| -Type or reflex
Rectosphincteric reflex
- Feces in rectum
- Peristaltic contractions in rectum
- Reflex relacation of internal sphincter
- Faciliated by adbominal muscle contraction against closed glottis
82
Defacating uses what n
Sacral portion of spinal cord
- Psym efferent impulses via pelvic n to relax internal sphincter
- Voluntary signals via pudendal n to control external sphincter
83
Internal anal sphincter
- type of muscle
- innervatino
Extension of circular muscle layer that remains constricted
PANS from pelvic n in sacral region for relaxation
SAN from hypogastric n for constrictino
84
External anal sphincter
- innervation
- type of muscle
Pudendal n
| Skeletal muscle fibers under voluntary control
