14 - GI: Stomach

Question 1

General layers of the alimentary canal(1)

names, location, subsections (GN)

1) includes esophagus, stomach and intestines

Answer 1

innermost to outermost(1)
Mucosa
- epithelium
- lamina propria
- muscularis mucosa

Submucosa

Muscularis
- inner circular layer
- outer longituninal layer

Serosa (Visceral Peritoneum) or Adventitia
- mesothelium
- connective tissue (thin)

1) innermost meaning the side that touches food

Question 2

Purpose of alimentary canal layers

Answer 2

Mucosa: ease food passage, protective barrier of mucus
Submucosa: connect layers, houses blood/lymph vessels and nerves(1)
Muscularis: move food, houses nerves(1)
Serosa (organ in abdominal cavity) or Adventitia (thoracic c.): allow movement of organs and connect layers

1) different nerves in each

Question 3

Enteric nervous system (ENS)

basic purpose, components, relevant structures

Answer 3

helps to coordinate peristalsis
Components:
- myenteric plexus (between muscularis layers)
- submucosal plexus (in submucosa)

Facts:
- ~100 million neurons from esophagus to anus
- interstitial cells of Cajal act as ‘pacemakers of the gut’, they dictate the frequency of contractions and synchronize them
- regulate without spinal cord input

Question 4

ENS neural pathways

basic pathway of signals

Answer 4

interneurons connect the SM plexus and Myenteric plexus
- sensory neurons can detect stretch and ∆pH
- relays info through interneurons to motor neurons
- motor neurons output (enzyme production, contractions…)

PS and S systems alter the activity of each plexus
PS can act directly on effectors (specific regions instead of the entire plexus)

Question 5

Sympathetic innervation to GI tract

physiology GN

Answer 5

ganglia are distanced from organ
- sympathetic trunk to one of:
- celiac ganglion: upper GI
- superior mesenteric g. : small intestine
- inferior mesenteric g. : colon + rectum

Question 6

Parasympathetic innervation to GI tract

physiology GN

Answer 6

ganglia are on the organs
- vagus n. (X): most of GI
- pelvic splanchnic n.’s: sigmoid colon + rectum

Question 7

Peritoneum

structures, transverse layout (GN)

Answer 7

Peritoneum: epithelial lining in the abdomen
- parietal P. lines cavity wall
- double layer folds of peritoneum (eg: mesentery)
- visceral P. lines an organ

Question 8

Folds of the peritoneum

name, location, purpose (GN)

Answer 8

Falciform ligament: divides liver into L and R lobes, connects it to anterior wall and diaphragm
Greater Omentum: covers small intestines, contains plenty of fat
Lesser Omentum: between liver and stomach
Mesocolon: connects transverse colon to post. abdominal wall
Mesentery: connects small intestines to post. abdominal wall

all are double layers of peritoneum

Question 9

Which structures are retroperitoneal?

Answer 9

Fully:
- ascending and descending colon
- kidneys
- …others

Partially:
- duodenum (last 3/4)
- rectum (lower 2/3)
- pancreas (head + body)

Question 10

Which structures are intraperitoneal?

Answer 10

Fully:
- liver
- stomach
- jejunum, cecum
- appendix
- transverse colon
- sigmoid colon
- …others

Partial:
- rectum (upper 1/3)
- duodenum (first 1/4)
- pacreas (tail)

Question 11

Layers of the stomach

how it differs from the general layers of the GI tract (GN)

Answer 11

Mucosa:rugae (visible folds in mucosa) they allow the stomach to expand, flatten when expanded
- has gastric pits
- simple columnar epithelium

Submucosa: no change

Muscularis: innermost oblique layer added (3 muscle layers total)

Question 12

Anatomy of the stomach

purpose + quiz with goodnotes for locations

Answer 12

connect to esophagus

• Cardia: most proximal to esophagus
• Fundus: most superior section
• Body: expands to 1.5 to 2 litres
• Pyloric region:
  
  • pyloric antrum: most intense contractions (mix food)
  • pyloric canal: funnel to..
    -* pylorus:* deliver food slowly to…

to duodenum

Question 13

Important facts about the stomach

5

Answer 13

1. extremely acidic: pH of 1.5 - 3.5
2. denatures/digests proteins
3. blends food into chyme and delivers to duodenum
4. produces intrinsic factor (Vitamin B12 absorption)
5. absorbs some substances (alsohol, aspirin…)

Question 14

Blood supply to Stomach

quiz with GN

Answer 14

compare to diagram
- aorta
- celiac trunk
- R & L gastric a.
- R & L gastric-omental a.

Question 15

Venous drainage from Stomach

quiz with GN

Answer 15

compare to diagram
- hepatic portal v. (to liver, to hepatic v. to IVC) from:
- L & R gastric v.
- R gastro-omental v.
- splenic v.
- L gastro-omental v.
- short gastric v.’s

Question 16

Gastric pit

location, histology, names, secretions (GN)

Answer 16

in the rugae of the stomach
Cells (secretions):
- surface mucous cell (mucus)
- mucous neck cell (mucus)
- parietal cell (HCl & intrinsic factor)
- cheif cell (pepsinogen & lipase)
- G cell (gastrin)

Question 17

Gastrin role

feedback loop

Answer 17

• increases parietal and cheif cell activity (more secretions)
• tighten LES (so stomach acid doesn’t reflux)
• increase gastric motility (blend food)
• loosen pyloric sphincter

Question 18

HCl factory

GN diagram

Answer 18

• H2O + CO2
• H2CO3
• H+
  
  • exchange with K+ to gastric lumen
• HCO3-
  
  • exchange with Cl- to interstitial fluid
• Cl- transported to gastric lumen
• HCl (from H+ + Cl-)

Question 19

Phases of digestion

name, purpose, trigger, steps

Answer 19

Cephalic phase: prepare for food
trigger: thoughts of food, sense food (sight, smell, taste)
- parasympathetic output (vagus X) to submucosal plexus
- increase gastric secretions and contractions

Gastric phase: food breakdown
trigger: food in the stomach, detected by stretch and chemoreceptors (∆pH)
- enteric output to SM plexus and G cells
- increase gastrin production

Intestinal phase:
trigger: food in duodenum, detected by stretch and chemoreceptors (fatty acids and glucose)
- signals the stomach to release food or not
- CCK: slow movement to release food
- Secretin: slow digestion and movement
- enterogastric reflex, sympathetic output slows digestion

Question 20

Summary of gastric emptying control

promoting and inhibiting (GN)

Answer 20

Promotes:
- neural: parasympathetic
- hormonal: gastrin
- chyme composition: carbohydrates and water

Inhibits:
- neural: sympathetic & enterogastric reflex
- hormonal: CCK, Secretin
- chyme composition: high protein (slow), high fat (very slow)

Question 20

???Emesis

causes, reflex mechanism