Overview of GIT, Lower GIT Physiology

Question 1

Pancreatic Enzymes

Answer 1

Zymogen granules of secretory cells contain digestive enzymes:

– Proteolytic enzymes:break certain proteins apart
• Trypsinogen (inactive)
• Chemo-trypsinogen
• Pro-carboxypeptidase

– Alpha-amylase:similar to salivary amylase, breaks down carbohydrates

– Lipase: breaks down complex lipids (triglycerides)

– Nucleases: breakdown nucleic acids

Question 2

duct cells

Answer 2

(secrete aqueous NaHCO3– solution)

- exocrine portion of solution

Question 3

Duodenum =

Answer 3

need an alkaline solution because stomach has pH of 2 > 2.5

Question 4

Acinar cells

Answer 4

(secrete digestive enzymes)

- exocrine portion of solution

Question 5

control of pancreatic aqueous NaHCO-3 secretion cycle

Answer 5

acid in duodenal lumen > inc. secretion release from duodenal mucosa >(secretin carried by blood) inc. stimulation of pancreatic duct cells > inc. secretion of aqueous NaHCO3 solution into duodenal lumen
> neutralises >

Question 6

control of pancreatic digestive enzyme secretion

Answer 6

fat and protein priducts in duodenal lumen > (CCK carried by blood) inc. CCK release from duodenal mucose > pancreatic acinar cells > incrs. secretion of pancreatic digestive enzymes into duodenal lumen > digests (cholecystokinin) >

Question 7

External features of Liver and Gallbladder

Answer 7

1. MetabolicFunctions
2. Bile Production
3. Blood circulation and filtration

Question 8

Portal triad:

Answer 8

hepatic artery, hepatic vein and bile duct.

Bile salt functions

Question 9

bile

Answer 9

One function of liver is to produce & secrete bile (600-1200ml/day)
– An alkaline solution containing bile salts, bile pigments, cholesterol, neutral fats, phospholipids, and electrolytes
– Stored in gallbladder and discharged into duodenum.

Question 10

bile salt functions

Answer 10

• Bile functions:
– Lipid digestion & absorption; absorption of cholesterol and fat soluble vit; A, D, E, & K.
– Major route for cholesterol synthesis & degradation

• Bile salts - emulsify large fat particles into tiny particles that can be attacked by lipases

Question 11

bile cycle

Answer 11

Secreted bile salts consist of 95% old, recycled bile salts and 5% newly synthesized bile salts.
>
95%of bile salts are reabsorbed by terminal ileum.
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Reabsorbed bile salts are recycled by enterohepatic circulation.

Question 12

Small Intestine (SI)

Answer 12

• Plays key role in digestion and absorption of nutrients
– Most digestion and 90% of nutrient absorption occurs in the SI

• Runs from pyloric sphincter to the ileocecal valve.

Question 13

Small Intestine (SI) segments

Answer 13

Three segments:
– Duodenum is 25 cm long segment closest to stomach;
– Jejunum is 2.5 meter long, middle segment, and is the location of most chemical digestion & nutrient absorption!
– Ileum is 3.5 meter long segment, joins large intestine at ileocecal valve

Question 14

The lining of the small intestine

Answer 14

is made up of numerous features
• Villi: finger like projections of the mucosa
• Microvilli: tiny structures that increases intestinal surface area 600-fold

Question 15

Transverse colon

Answer 15

Storage of Waste & Water reabsorption & Defecation

Question 16

large intestine

Answer 16

Large intestine mucousa: Lacks villi, produces mucous to lubricate faeces, secrete HCO3

1. Cecum
2. Colon
3. Rectum & Anus

Question 17

defecation

Answer 17

Impulses from cerebral cortex (conscious control) > Voluntary motor nerve to external anal sphincter > External anal sphincter (skeletal muscle)

Question 18

defeaction 2

Answer 18

Feces move into
and distend the rectum, stimulating stretch receptors there. The receptors transmit signals along afferent fibers to spinal cord neurons.
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A spinal reflex is initiated in which parasympathetic motor (efferent) fibers stimulate contraction of the rectum and sigmoid colon, and relaxation of the internal anal sphincter.
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If it is convenient to defecate, voluntary motor neurons are inhibited, allowing the external anal sphincter to relax so feces may pass.