Lecture 6: Secretions of the Small Intestine and Accessory Organs

Question 1

what are the secretions of the small intestine and what do they contain

Answer 1

• intestinal juice (HCO3- and mucus)
• pancreatic juice (digestive enzymes)
• bile (bile salts)

Question 2

what are the hormones secreted by the small intestine

Answer 2

• secretin
• cholecystokinin
• glucose dependent insulinotrophic peptide (GIP)

Question 3

what are the secretory cells in the villi

Answer 3

• absorptive enterocytes

- goblet cells

Question 4

what are the secretory cells in the intestinal glands

Answer 4

• enterocytes secreting isotonic fluid
• entero-endocrine cells
• paneth cells

Question 5

what are the secretory cells in the duodenum only

Answer 5

Brunner’s glands, which secrete mucus and HCO3-

Question 6

how quick is epithelial cell turnover

Answer 6

3-6 days

Question 7

CCK secretion and effect

Answer 7

• I cells

- stimulate pancreatic and gallbladder secretion

Question 8

secretin secretion and effect

Answer 8

• S cells

- stimulate pancreatic and biliary bicarbonate secretion

Question 9

GIP secretion and effect

Answer 9

• K cells

- may inhibit acid secretion / stimulate insulin release

Question 10

what clusters does the pancreas consist of

Answer 10

• 99% exocrine acinar clusters

- 1% endocrine pancreatic islets (islets of langerhans)

Question 11

what do the exocrine acinar clusters secrete

Answer 11

pancreatic juice containing:

• water
• electrolytes
• sodium bicarbonate
• proenzymes

Question 12

what do the endocrine pancreatic islets secrete

Answer 12

• glucagon
• insulin
• somatostatin
• pancreatic polypeptide

Question 13

what do the acinar cells secrete and what do the ducts secrete

Answer 13

acinar:
- enzymes
- NaCl
- fluid
duct:
- NaHCO3
- fluid

Question 14

what are the acinar secretions regulated by

Answer 14

• acetylcholine

- cholecystokinin triggered by chyme containing fat and protein products

Question 15

what are the ductal secretions regulated by

Answer 15

secretin triggered by H+ in highly acidic chyme

Question 16

what enzyme activates proteolytic enzymes and where is it found

Answer 16

• enterokinase enzyme

- in small intestinal brush border

Question 17

how is Cl- recycled out of the pancreatic cell

Answer 17

• CTFR chloride channel
• under secretin stimulation
• via cAMP

Question 18

what is the composition of pancreatic juice with a low secretion rate

Answer 18

electrolyte content similar to that of plasma

Question 19

what is the composition of pancreatic juice with a high secretion rate

Answer 19

• high in HCO3-

- low Cl-

Question 20

what happens in cystic fibrosis

Answer 20

• dysfunctional CFTR channel
• ducts become blocked with precipitated enzymes and mucus
• pancreas undergoes fibrosis
• impaired secretion of digestive enzymes
• malabsorption
• patients given oral pancreatic enzyme supplements during meals

Question 21

what happens in pancreatitis

Answer 21

• pancreatic enzymes are activated within the pancreas
• autodigestion
• most common causes are gallstones and alcohol abuse

Question 22

which waste products does bile eliminate

Answer 22

• bilirubin
• cholesterol
• drugs

Question 23

where is bile produced and stored

Answer 23

• produced by hepatocytes

- stored in gallbladder

Question 24

what are the 3 overall causes of jaundice

Answer 24

• prehepatic
• hepatocellular / congenital
• posthepatic

Question 25

what happens in pre-hepatic jaundice

Answer 25

- excessive rbc breakdown - buildup of unconjugated bilirubin - eg due to haemolytic anaemia

Question 26

what happens in hepatocellular jaundice

Answer 26

- altered hepatocyte function - eg Crigler-Najjar syndrome - absence of enzyme glucoronyl transferase, which normally conjugates bilirubin - results in increased unconjugated bilirubin

Question 27

what happens in post-hepatic jaundice

Answer 27

- obstruction to normal bile drainage - eg due to gallstones - build up of conjugated bilirubin

Question 28

what is involved in regulation of bile secretion

Answer 28

- cholecystokinin - secretin - minor role of acetylcholine

Question 29

when is cholecystokinin released and what effect does it have on bile secretion

Answer 29

- released in response to fat content of duodenum - results in gall bladder contraction - sphincter of oddi relaxation

Question 30

when is secretin released and what effect does it have on bile secretion

Answer 30

- released in response to acidic chyme | - results in liver duct secretion of bicarbonate rich watery secretions

Question 31

what effect does acetylcholine have on bile secretion

Answer 31

- increased bile flow | - increased gallbladder contraction

Question 32

what are the common causes of gallstones

Answer 32

- excessive water and bile salt reabsorption from bile - excessive cholesterol in bile (due to high fat diet) - inflammation of the epithelium