Week 1 Overview of GI Function and Anatomy

Question 1

what accessory organs assist the GI tract?

Answer 1

salivary glands, pancreas, liver, gallbladder

Question 2

what are the 4 layers of the gut wall?

Answer 2

mucosa- simple squamous epithelium, lamina propria, muscularis mucosae
submucosa
external muscle layer- muscularis externae- circular inner, longitudinal outer- creates peristalsis
serosa

Question 3

describe the general structure of the alimentary canal

Answer 3

mouth, tongue, pharynx, oesophagus, stomach, small intestines (duodenum, jejenum, illium), cecum, large intestines (ascending, transverse and descending colon), rectum, anus

Question 4

what are peyers patches and which layer of the gut wall are they present?

Answer 4

aggregations of lymphocytes in lamina propria

Question 5

outline the broad functions of the various regions of the GI tract

Answer 5

mouth- port of entry for food
teeth- mechanically disrupt food
stomach- temporary store food, chemically digest it and kill pathogens within it - acid 
peristalsis- move food along tract
intestines- absorb nutrients 
rectum- eliminate residual waste

Question 7

describe the functions, nervous control (2 plaxuses), muscles present of the oesophagus

Answer 7

receives bolus of food from mouth
rapid peristaltic transport to stomach- 8-9 seconds
upper end- voluntary control- striated muscle
lower end- involuntary control- smooth muscle
myenteric plexus between outer muscle layers
submucosal plexus between submucosa and external muscle

Question 8

describe the digestive processes that continue in the somach

Answer 8

physical disruption- churning- 3 muscle layers and mucosal rugae
chemical disruption- by acid (HCL) and enzymes

Question 9

what are the overall functions of the stomach and how does this generally work?

Answer 9

• acts as food storage- eat faster than can digest
• wall relaxes so stomach pressure doesnt rise- receptive relaxation
• contracts rhythmically to mix and disrupt
• secretes acid and proteolytic enzymes to break down and disinfect
• secretes mucus to protect epithelia otherwise = ulcers
• produces hypotonic chyme by combining action of acid, enzymes and agitation
• delivers imcompletely digested chyme slowly to duodenum

Question 10

describe what digestive processes that occur in the mouth

Answer 10

physical disruption- mouth- teeth, tongue, muscle of mastication
chemical disruption- salivary amylase, lipase

Question 10

what are the functions of saliva?

Answer 10

start digestion- amylase and lipase
bacteriostatic- contains IgA- released through gut and resp
high Ca- protects teeth
assist swallowing- lubrication

Question 10

what occurs in the duodenum?

Answer 10

DILUTION AND NEUTRALISATION OF CHYME

• dilution as hypertonic - water drawn in from ECF to = isotonic
• liver releases bile via gallbladder- contains water, alkali and bile salts (emulsify fats)
• pancreas also secretes alkali to neutralise
• pancreas, liver and intestine secretes enzymes which act with the bile to complete digestion of chyme

Question 11

what do the enzymes from the pancreas and intestines do to complete digestion?

Answer 11

cleave peptides to AAs
cleave polysaccharides to monosaccharides
break down and reform lipids
break down nucleic acids

Question 12

what is required for successful absorption and what is absorbed where?

Answer 12

lots of energy- active process
large SA- folded gut, villi, micro-villi- adequate contact time
good blood supply, drainage
occurs in small intestines- more proximally
duodenum- iron
jejunum- most sugar, AAs and FAs
ilium- vit B12, bile acids and remainders
H2) still to be absorbed

Question 13

what occurs in the large intestines?

Answer 13

water recovery continues over 20hr transit

by the end content semi solid ready for expulsion in colon

Question 14

where contains most of the GIs bacteria?

Answer 14

colon- 99% anaerobic and most lost in faeces

Question 15

what are the 3 characteristics of a substance must be in order for us to absorb our nutrients?

Answer 15

sterile
neutral in pH
isotonic

Question 16

describe the fluid balance of the gut- what taken in/ produced and what sent out/ absorbed

Answer 16

ingest 1kg- 1L
mouth 1.5L of saliva 
stomach 2.5L gastric secretions
small intestine 9L of water/alkali
total= 14L    13 produced to deal with 1 ingested

absorption
small intestine absorb 12.5L
large intestine absorb 1.35L
leaving 0.15L of feaces

Question 17

explain what happens if fluid balance changes and why this is common

Answer 17

delicate balance dealing with large quantities why diarrhoea and constipation so common

• decreased absorption or increased secretion can=
• life threatening dehydration (depletion of body fluids), life threatening electrolyte imbalance

Question 18

describe the properties of the enteric (intestinal) nervous system and its relationship to the ANS

Answer 18

neural control

• somatic- innervating striated muscle
  
  • ingestion- mouth and first 1/3 oesophagus
  • excretion- last sphincter of anus
• ANS- controls rest
  
  • post ganglionic neurones from plexuses- one between muscle layers of gut wall and one beneath submucosa
  • gut nervous system- enteric system
  • range of neurotransmitters

Question 18

describe the role of hormones and other peptides which affect the motility and secreting in the gut- paracrine, endocrine control

Answer 18

paracrine control- substances act locally

• histamine- production of acid in stomach
• vasoactive substances- affect blood flow in gut

endocrine control- range of hormones control:

• secretion of stomach acids
• alkali secretions from liver and pancreas
• enzyme secretions