GI

Question 1

What are the organs of the GI tract and what are their specific function?

Answer 1

Mouth: chewing, hydrolysis to create a bolus of food
Oesophagus: propel bolus to stomach
Stomach: churning, hydrolysis of bolus to create chyme
Small intestine (duodenum: digestion, jejunum:absorption, ileum: absorption of lipids)
Large intestine: absorption of water/salts/ions
Rectum: storage of waste
Anus: expulsion of waste

Question 2

What are the organs of the biliary tree and their specific function?

Answer 2

Liver: makes bile, stores nutrients
Pancreas: produces most of the enzymes for digestion
Gallbladder: stores bile

Biliary tree: produces mixture (neutralising salts + enzymes) that meets chyme from the stomach in the duodenum for digestion

Question 3

What is the lining of the GI tract made of?

Answer 3

Mucosa (epithelium, lamina propria, muscularis mucosae)

Sub-mucosa (connective tissue with glands, vessels, nerves)

Muscularis externae (inner circular layer of smooth muscle, outer longitudinal layer of smooth muscle)

Serosa (connective tissue connected to mesothelium of the peritoneum - serous membrane)

Question 4

Define digestion

Answer 4

Conversion of large molecules of food by physical and chemical disruption into a solution that is sterile, neutral and isotonic for absorption of our nutrients

Question 5

What is the function of saliva?

Answer 5

Contains lipase/amylase (breakdown of lipids and sugars)
Assists swallowing
Protects the mouth and teeth (high in Ca)
Bacteriostatic (IgA antibody prevents growth of bacteria)

Question 6

Describe the features of the oesophagus

Answer 6

Skeletal muscle moving down and becoming smooth muscle though neither is under voluntary control

Question 7

How does the stomach aid digestion?

Answer 7

Acts as food store (eat quicker than we digest)
Secretes enzymes and acid for chemical disruption
Contracts to mix food with enzymes and acid + has longitudinal ridges called rugae for physical disruption

Question 8

What is the product after stomach has digested food?

Answer 8

Chyme - hypertonic, acidic solution of partially digested lipids, proteins, sugars that is delivered to the duodenum in a controlled manner

Question 9

What is gastrin?

Answer 9

Peptide hormone secreted by G-cells that stimulates the release of HCl from parietal cells and pepsinogen from chief cells and gastric motility

Question 10

What is GERD and what are the symptoms?

Answer 10

Gastroesophageal Reflux Disease:
Caused when the lower sphincter of the oesophagus does not work to prevent HCl from entering the oesophagus

Symptoms:
Heart-burn/Chest pain
Difficulty swallowing

Question 11

Describe the composition of a gastric gland and what cells are found there

Answer 11

Pit - mucous secreting cells
Isthmus - stem cells that differentiate and migrate up/down
Neck - parietal and chief cells
Base - enteroendocrine cells (G-cells)

Question 12

What do each of the gastric cells do?

Answer 12

Parietal cells: secrete HCl into the gastric gland and HCO3- into capillaries that release them at the surface
Chief cells: secrete pepsinogen, activated by HCl —> pepsin (which hydrolyses proteins partially)
Neck cells: secrete mucous to protect its mucosa layer
G-cells: secrete gastrin

Question 13

What happens to chyme once it leaves the stomach?

Answer 13

Enters the duodenum:
Brunners glands secrete HCO3- to neutralise chyme
Extracellular water is used to dilute the hypertonic solution
Liver/gallbladder secrete bile (emulsifies fats for increased SA for digestion)
Liver/pancreas/duodenum produce enzymes for final digestion of food

Question 14

After digestion of food in the duodenum what remains?

Answer 14

Proteins —> amino acids
Lipids —> fatty acids and glycerol
Sugars —> monosaccharides
Nucleotides —> ribose sugars and bases

Question 15

How are nutrients absorbed?

Answer 15

In the jejunum:
Amino acids: primary active transport
Monosaccharides: secondary active transport (Na+ co-transporter)
Ribose sugars and bases: primary active transport
In the ileum:
Fatty acids and glycerol: diffusion

Question 16

What happens to nutrients in enterocytes?

Answer 16

Amino acids, monosaccharides, ribose sugars and bases diffuse into the capillaries where they join the hepatic portal vein and pass through the liver
Fatty acids and glycerol enter the ER of the enterocytes to be reformed into lipids, packaged into chylomicrons and diffuse into the lacteals of the lymphatic system

Question 17

What are the segments of the colon?

Answer 17

Caecum
Ascending colon
Transverse colon
Descending colon
Sigmoid colon

Question 18

What is the function of the colon?

Answer 18

Contents await expulsion in the colon
Contains bacteria that:
Synthesise vitamins K, B12, thiamine, riboflavin (absorbed)
Breakdown of bile acids (absorbed)
Conversion of bilirubin to non-pigmented metabolites (absorbed)

Question 19

How much water is added to 1kg of food?

How much faeces is produced from 1kg of food?

Answer 19

13 Litres

0.15 Kg

Question 20

What are the networks of nerves that innervates the GI system and where are they found?

Answer 20

Sub-mucosal plexus (submucosa)
Myenteric plexus (outer longitudinal smooth muscle wall - muscularis externae)

Question 21

What are the hormones involved with hunger?

Answer 21

Gherlin: stimulates hunger (appetite stimulator)
Lepton: inhibits hunger (appetite suppressor)

Question 22

What vessels drain into the hepatic portal vein?

Answer 22

Superior mesenteric vein (small intestine, caecum, ascending colon, transverse colon)
Inferior mesenteric vein (descending colon, sigmoid colon, rectum)
Splenic vein (spleen, pancreas, stomach)

Question 23

What happens at the capillaries of the hepatic portal vein?

Answer 23

Stomach and intestines: nutrients and toxins absorbed

Liver hepatocytes: nutrients and toxins leave

Question 24

What vessels enter and leave the liver?

Answer 24

Enter:
Hepatic portal vein (nutrient rich)
Proper hepatic artery (oxygen rich)

Leave:
Hepatic vein (nutrient + oxygen poor) joins inferior vena cava
Common hepatic duct (bile —> gallbladder)

Question 25

What are the functions of the liver?

Answer 25

Storage of sugars as glycogen, vitamins A, B, D, K and Iron
Anabolism of albumin
Catabolism of drugs, Hb, hormones
Detoxification (cytochrome P450)
Produces and modifies hormones
Bile production

Question 26

What role do kupffer cells take in the liver?

Answer 26

Type of macrophage: Break down red blood cells and pathogens (complement pathway)

Question 27

Describe the function and structure of hepatic lobules

Answer 27

Six-sided structure with:
Sinusoids (mixing of blood from hepatic portal vein and proper hepatic artery) with kupffer cells and stellate cells
Hepatocytes
Portal triad (hepatic portal vein, proper hepatic artery and bile duct)
Central vein (drains into the hepatic vein)

Question 28

What condition is associated with stellate cells?

Answer 28

Liver fibrosis:
In liver cirrhosis (scarring); stellate cells lose the ability to hold vitamin A
They differentiate into myofibroblasts, secrete collagen which causes fibrosis
The fibres can also constrict the central vein causing portal hypertension

Question 29

What cells are the hormones of the liver secreted from?

Answer 29

Glucagon: alpha-islet cells (release of glucose)
Insulin: beta-islet cells (storage of glycogen)
Somatostatin: delta-islet cells (inhibits other hormones)