Physiology of Digestion and Absorption

Question 1

What are the three sections of the small intestine

Answer 1

Duodenum, jejunum, Ilium

Question 2

What does the small intestine receive

Answer 2

Chyme from stomach (via pyloric sphincter)
Pancreatic juice from pancreas
Bile from gall bladder (both from spinster of Oddi)

Question 3

Valve between small and large intestine

Answer 3

iliocaecal valve

Question 4

Adaptations of the small intestine to increase absorption

Answer 4

Circular folds (of kerckringn) 
Villi 
micro villi (the brush border)

Question 5

What cells secret gastrin and where do you find them

Answer 5

G cells in the gastric antrum (bottom of stomach) and duodenum

Question 6

Secreted by I cells of the duodenum and jejunum

Answer 6

CKK (cholecystokinin)

Question 7

what cells secrete motilin and from where

Answer 7

M cells in the duodenum and jejunum

Question 8

What is an incretin

Answer 8

Incretins act upon b-cells in the pancreas to stimulate insulin release

Question 9

What causes incretin from K cells of the duodenum and jejunum to be released

Answer 9

Glucagon-like insulinotropic peptide

Question 10

Glucagon-like peptide 1 (GLP-1)

Answer 10

incretin from L cells

Question 11

Ghrelin

Answer 11

from Gr cells of the gastric antrum, small intestine and elsewhere

Question 12

What receptors do secretions of the small intestine act on

Answer 12

G-protein receptors

Question 13

Succus entericus meaning

Answer 13

Juice of the intestine, 2 litres secreted a day

Question 14

Control mechanisms for succus entericus

Answer 14

Digestion/irritation. gastrin, CCK, secretin, parasympathetic nerve activity, sympathetic nerve activity

Question 15

What does succus entericus contain

Answer 15

mucus- for protection/lubrication (from goblet cells)
aqueous salt - for enzymatic digestion
no digestive enzymes

Question 16

Segmentation

Answer 16

Mixing of chyme, ‘chopping’ moves chyme back and forth - very vigorous after a meal, little between meals
Alternating contraction and relaxation of segments of circular muscle

Question 17

What initiates segmentation

Answer 17

Small intestine pace maker cells causing the BER (basal electronic rhythm) which is continuous
At threshold stimulates segmentation which in the duodenum is due to dimension by entering chyme

Question 18

What triggers segmentation in the empty ilium

Answer 18

Gastrin from stomach (gastroilial reflex)

Question 19

Rate of contractions in the duodenum

Answer 19

12 per min

Question 20

Rate of contractions in the ileum

Answer 20

9 per min

Question 21

Net movement of segmentation is in which direction

Answer 21

Aboral - away from mouth towards anus

Question 22

How long does movement through the small intestine take

Answer 22

3-5 hours to allow time for absorption

Question 23

What enhances strength of segmentation

Answer 23

parasympathetic activity

Question 24

What decreases strength of segmentation

Answer 24

sympathetic activity

Question 25

Two activities which occur in the inderdigestive or fasting state (peristalsis)

Answer 25

few localised contractions

The migrating motor complex (MMC)

Question 26

What does the Migrating Motor Complex involve

Answer 26

occurs every 90-20 mins between meals
strong peristaltic contraction passes the length of the intestine (stomach - iliocaecal valve)
clears small intestine of debris, mucus and sloughed epithelial cells between meals (housekeeper function)

Question 27

What inhibits MMC

Answer 27

feeding and vagal activity

Question 28

What triggers/inhibits MMC

Answer 28

Motilin triggers

gastrin and CCK inhibit

Question 29

Endocrine pancreatic secretions

Answer 29

insulin and glucagon- secreted to blood

Question 30

Exocrine pancreatic secretions

Answer 30

digestive enzymes (acing cells)
aqueous NaHCO3- solution ( (duct cells) 
Secreted into the duodenum collectively and PANCREATIC JUICE

Question 31

Purpose of pancreatic duct cell secretions

Answer 31

Secrete 1-2 litres of alkaline fluid in duodenum per day to neutralise acidic chyme entering the duodenum
provides optimum pH for pancreatic enzyme function
protects mucosa from mucosa from erosion by acid

Question 32

Pancreatic enzymes

Answer 32

Can completely digest food in the absence of all other enzymes

Produced in response to elivated calcium

Question 33

Of the three pancreatic enzymes (proteases, amylases and lipases), only proteases are secreted in an inactive form true or falsee?

Answer 33

True
They only become activated when they reach the duodenum as if they were activate in the pancreas they’d disintegrate the pancreas

Question 34

Three phases of control of pancreatic secretion

Answer 34

cephalic - mediated by the vagal stimulation of mainly the acing cells
gastric - gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells
Intestinal - increase secretion of aqueous NaHCO3 solution into duodenal lumen

Question 35

What are the main constituents of food

Answer 35

carbohydrates - starch, cellulose, glycogen, disaccharides
lipids - triglycerols, phospholipids, cholesterol, free fatty acids, lipid vitamins
Proteins - approx 70-100 g per day

Question 36

what is digestion

Answer 36

enzymatic conversion of complex dietary substances to a form that can be absorbed

Question 37

where do most digestion processed occur

Answer 37

small intestine as:
Luminal digestion - mediated by pancreatic enzymes
membrane digestion- mediated by enzymes situated at brush epithelial cells

Question 38

What is absorption

Answer 38

The process by which the absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes

Question 39

What is the name for the overall process of absorption and digestion

Answer 39

Assimilation