GI S1 - Intro

Question 0

What is secreted to aid digestion?

Answer 0

HCl, bile and a variety of enzymes

Question 1

Define digestion

Answer 1

The breakdown of ingested food into molecules small enough to be absorbed by the body

Question 2

What are the physical processes which aid digestion?

Answer 2

Mechanical chewing of food

Peristalsis

Question 3

Define peristalsis

Answer 3

The contraction of the smooth muscle components of the alimentary tract walls to mix the food and move it from mouth to anus

Question 4

What are the four functions of the alimentary tract?

Answer 4

Secretion
Digestion
Motility
Absorption

Question 5

Give an overview of fluid movement in the alimentary tract

Answer 5

~1kg food is mixed with ~1.5L saliva and ~6L secretions from the stomach, liver, pancreas and intestines.
All but ~1.5L of this is re absorbed in the small intestine.
The large intestine reabsorbs more fluid to leave ~150g of solid faeces

Question 6

What are the four layers of the alimentary tract between the oropharynx and the anus

Answer 6

The mucosa
The submucosa
The muscularis externa
The serosa/adventitia

Question 7

What does the mucosa/mucous membrane consist of?

Answer 7

A thin layer of lining epithelium
The lamina propria (connective tissue)
Muscularis mucosa (a thin layer of smooth muscle)

Question 8

Describe the submucosa and its contents

Answer 8

A zone of fibro-elastic tissue with blood vessels, nerves, leukocytosis and fat cells

Question 9

Describe the muscularis externa

Answer 9

Composed of an inner circular and an outer longitudinal layer of smooth muscle with the myenteric plexus lying between the layers

Question 10

What is the serosa/adventitia?

Answer 10

A thin outer layer of connective tissue on the alimentary tract

Question 11

How are motility and secretion regulated in the alimentary tract?

Answer 11

The autonomic nervous system

Hormones

Question 12

What controls movement in the alimentary tract?

Answer 12

It’s entirely autonomic apart from the voluntary actions of chewing, swallowing and defecating.

Question 13

Describe the enteric nervous system

Answer 13

Made up of two plexuses in the wall of the gut. These can function independently of the CNS but their activity may be altered by both branches of the ANS.

Question 14

Briefly describe hormones in the walls of the gut

Answer 14

A dozen or more peptide hormones are released
These can be paracrine or endocrine and act to affect secretions and motility in different parts of the gut
Two main groups:
-Gastrin
-Secretin

Question 15

Briefly describe the process of swallowing

Answer 15

A complex set of contractions which cause formation of a “bolus” of food in the mouth, then propel this bolus to the larynx, from where it proceeds rapidly down the oesophagus to the stomach

Question 16

How may swallowing be impaired?

Answer 16

Blockage of the oesophagus by a tumour
Anaesthesia
Neurological deficits
Problems with the musculature

Question 17

What is a common result of problems swallowing?

Answer 17

Aspiration of food into the lungs, which is very dangerous

Question 18

Define dysphagia

Answer 18

Difficulty swallowing

Question 19

How may compromised swallowing be alleviated when drinking liquids and why does this technique work?

Answer 19

Liquids may be thickened

This is helpful because swallowing liquids is more difficult than swallowing solids

Question 20

What occurs in the stomach

Answer 20

Preliminary physical and chemical disruption brought about by secretion of acid and enzymes

Question 21

Why does the acid in the stomach not affect the stomach itself?

Answer 21

There is a mucous layer and the cells of the stomach secrete hydrogen carbonate to defend against the acid

Question 22

What may care the stomach’s acid defences to fail and what may this cause?

Answer 22

Drugs which affect prostoglandin secretion, infection by Helicobacter pylori and excess acid secretion
Failure of defences may lead to peptic ulceration

Question 23

Where else may stomach acid cause problems?

Answer 23

In the oesophagus if the lower oesophageal sphincter is weak, acid may reflux back to cause heartburn and possibly worse epithelial damage
Also in the 1st part of the duodenum before alkaline secretions are mixed, ulceration may occur

Question 24

What could happen as a result of peptic ulcers?

Answer 24

The ulcers may bleed or occasionally perforate

Question 25

What leaves the stomach?

Answer 25

Acid, hypertonic, partly digested material known as chyme

Question 26

What happens to the contents of the stomach after they enter the duodenum?

Answer 26

At the 2nd part of the duodenum, the bile duct merges from the pancreas, gall bladder and liver through which bile is secreted. This bile is alkaline and rich in enzymes to neutralise and digest the chyme
Water flows down its concentration gradient until the hypertonic solution becomes isotonic

Question 27

Describe bile?

Answer 27

Secreted into the 2nd part of the duodenum via the bile duct
Its function is mainly fat digestion and neutralisation of chyme
Re absorbed in the terminal ileum
Recycled to the liver and stored in the gall bladder

Question 28

What is the excretory function of bile?

Answer 28

Bilirubin, a breakdown product of haemoglobin, is a component of bile

Question 29

What happens when bilirubin excretion goes wrong?

Answer 29

Jaundice - not enough bilirubin is excreted so builds up in the blood, causing the patient to gain a yellow tinge to the skin and eyes

Question 30

How may jaundice occur?

Answer 30

Excess breakdown of haemoglobin saturates the liver’s ability to excrete all bilirubin, leading to pre-hepatic jaundice
The liver may be damaged by disease so unable to excrete normal levels of bilirubin, leading to hepatic jaundice
The bile duct may become obstructed, causing a backup of bile and hepatic damage, leading to post-hepatic jaundice

Question 31

Describe liver damage due to alcohol

Answer 31

Fibrotic changes known as cirrhosis causes loss of liver function and may cause impaired hepatic portal vein flow. This causes portal hypertension, which may lead to ascites and increased bloodflow through the abdominal collateral venous pathways

Question 32

How may the bile duct become obstructed?

Answer 32

Gallstones from the gall bladder may move into the bile duct and obstruct.
Pancreatic tumours may cause obstruction

Question 33

Describe gallstones’ clinical relevance

Answer 33

Usually asymptomatic
If they move within the gall bladder they can cause biliary colic, which is very painful
If they move into the bile duct they can obstruct it, causing a backup of bile, which causes liver damage and post hepatic jaundice

Question 34

Describe pancreatitis

Answer 34

Inflammation of the pancreas
Considerable pain
Characterised by the release of amylases into the blood

Question 35

What is the main function of the small intestine?

Answer 35

Absorption

Question 36

What may cause malabsorption in the small intestine?

Answer 36

Paralytic ileum - the motility of the ileum may be compromised
There may be an obstruction (by either internal obstruction or external compression)

Question 37

What are other common ailments of the midgut?

Answer 37

Appendicitis - the appendix is particularly at risk of inflammation.
Peritonitis - inflammation of the sac containing the major parts of the gut, the peritoneum. Will usually follow any perforation of the gut.

Question 38

What is the main function of the large intestine?

Answer 38

Absorption of the remaining water and electrolytes from the chyme as it leaves the small intestine. Faeces are periodically formed and pushed into the rectum prior to defecation.

Question 39

How do inflammatory bowel diseases affect the bowel?

Answer 39

Symptoms are diarrhoea, pain, blood loss and problems with absorption

Question 40

Give and describe examples of inflammatory bowel diseases

Answer 40

Ulcerative colitis affects the large intestine and does not extend through the full thickness of the wall
Crohn’s disease may affect any part of the intestines and spans the full thickness of the wall

Question 41

What else can go wrong with the large intestine?

Answer 41

Colorectal cancer is a common cancer
Infections in the colon can cause disruption to normal micro fauna, leading to diarrhoea and so water and electrolyte imbalances