Physiology of Digestion and Absorption Flashcards
What are the three sections of the small intestine
Duodenum, jejunum, Ilium
What does the small intestine receive
Chyme from stomach (via pyloric sphincter)
Pancreatic juice from pancreas
Bile from gall bladder (both from spinster of Oddi)
Valve between small and large intestine
iliocaecal valve
Adaptations of the small intestine to increase absorption
Circular folds (of kerckringn) Villi micro villi (the brush border)
What cells secret gastrin and where do you find them
G cells in the gastric antrum (bottom of stomach) and duodenum
Secreted by I cells of the duodenum and jejunum
CKK (cholecystokinin)
what cells secrete motilin and from where
M cells in the duodenum and jejunum
What is an incretin
Incretins act upon b-cells in the pancreas to stimulate insulin release
What causes incretin from K cells of the duodenum and jejunum to be released
Glucagon-like insulinotropic peptide
Glucagon-like peptide 1 (GLP-1)
incretin from L cells
Ghrelin
from Gr cells of the gastric antrum, small intestine and elsewhere
What receptors do secretions of the small intestine act on
G-protein receptors
Succus entericus meaning
Juice of the intestine, 2 litres secreted a day
Control mechanisms for succus entericus
Digestion/irritation. gastrin, CCK, secretin, parasympathetic nerve activity, sympathetic nerve activity
What does succus entericus contain
mucus- for protection/lubrication (from goblet cells)
aqueous salt - for enzymatic digestion
no digestive enzymes
Segmentation
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
What initiates segmentation
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
What triggers segmentation in the empty ilium
Gastrin from stomach (gastroilial reflex)
Rate of contractions in the duodenum
12 per min
Rate of contractions in the ileum
9 per min
Net movement of segmentation is in which direction
Aboral - away from mouth towards anus
How long does movement through the small intestine take
3-5 hours to allow time for absorption
What enhances strength of segmentation
parasympathetic activity
What decreases strength of segmentation
sympathetic activity
Two activities which occur in the inderdigestive or fasting state (peristalsis)
few localised contractions
The migrating motor complex (MMC)
What does the Migrating Motor Complex involve
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)
What inhibits MMC
feeding and vagal activity
What triggers/inhibits MMC
Motilin triggers
gastrin and CCK inhibit
Endocrine pancreatic secretions
insulin and glucagon- secreted to blood
Exocrine pancreatic secretions
digestive enzymes (acing cells) aqueous NaHCO3- solution ( (duct cells) Secreted into the duodenum collectively and PANCREATIC JUICE
Purpose of pancreatic duct cell secretions
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
Pancreatic enzymes
Can completely digest food in the absence of all other enzymes
Produced in response to elivated calcium
Of the three pancreatic enzymes (proteases, amylases and lipases), only proteases are secreted in an inactive form true or falsee?
True
They only become activated when they reach the duodenum as if they were activate in the pancreas they’d disintegrate the pancreas
Three phases of control of pancreatic secretion
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
What are the main constituents of food
carbohydrates - starch, cellulose, glycogen, disaccharides
lipids - triglycerols, phospholipids, cholesterol, free fatty acids, lipid vitamins
Proteins - approx 70-100 g per day
what is digestion
enzymatic conversion of complex dietary substances to a form that can be absorbed
where do most digestion processed occur
small intestine as:
Luminal digestion - mediated by pancreatic enzymes
membrane digestion- mediated by enzymes situated at brush epithelial cells
What is absorption
The process by which the absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes
What is the name for the overall process of absorption and digestion
Assimilation
