Pharmacology and physiology of the Small Intestine Flashcards
What are the 3 parts of the small intestine?
Jejunum
Ileum
Duodenum
What products does the small intestine receive?
chyme from the stomach
pancreatic juice from pancreas
bile from the gall bladder
Which sphincter does the pancreatic juices and bile come from?
Sphincter of Oddi
What does the small intestine secrete?
Succus entericus (intestinal juice)
What types of stimuli influence the small intestine?
Mechanical
Neuronal
Hormonal
How is the surface area of the small intestine increased?
Circular folds
Villi
Microvilli
What is the villi made of?
Epithelial cells
Endothelial cells
Exocrine cells
Mucous secreting cells
What are the villi?
The circular folds which have an associated epithelium
the folded epithelium is the villi
Describe the villi vascular supply
Each villi has it’s own vascular supply in capillaries
In the lumen, there is a central lacteal vessel which drains into the lymph vessels then into the systemic circulation
What are the microvilli?
The apical membrane of the epithelial cells are folded into microvilli
Gives a brush border appearance
What are the small intestine hormones?
Gastrin Cholecystokinin (CCK) Secretin Motilin Glucagon like insulinotropic peptide (GIP) Glucagon-like peptide 1 (GLP1) Ghrelin
Where is gastrin made?
G cells in the gastric antrum and duodenum
Where is CCK made?
From I cells of duodenum and jejunum
Where is secretin made?
From S cells of duodenum
where is the motilin made?
From M cells of duodenum and jejunum
Where is GIP made?
K cells of the duodenum and jejunum
Where is GLP-1 made?
L cells of the gut
What are GIP and GLP-1?
Incretins
What is the function of GIP and GLP-1?
Acts on the beta cells and makes them release insulin and makes them more sensitive to insulin - feed forward mechanism - happens before blood glucose levels begin to rise
Where is ghrelin made?
Gr cells of the gastric antrum, small intestine and elsewhere
What does the succus entericus contain?
Mucus - for protection/ lubrication
Aqueous salt - for enzymatic digestion
No digestive enzymes
Where is the mucus from?
The goblet cells
Where is the aqueous salt from?
Crypts of Lieberkuhn
What mediates brush border digestion?
Digestive enzymes at the surface of the epithelial cells
What is the process of succus entericus formation similar to?
primary secretion formation in salivary glands
What initiates small intestine segmentation?
The small intestine pacemaker cells
What activates segmentation of the duodenum?
distension
What activates segmentation of the empty ileum?
Gastrin from the stomach
Why is segmentation slow?
For nutrient absorption
What two ways is chyme mixed in the small intestine?
peristalsis and segmentation
What are the two types of peristalsis?
A few localisation contractions
Migrating motor complex (MMC)
Function of MMC
Strong peristaltic contractions passing length of the intestine
clears the small intestine of debris, mucus and sloughed epithelial cells between meals
What inhibits MMC?
Feeding and vagal activity
What triggers MMC?
Motillin
What hormones suppress MMC?
gastrin
CCK
What are the endocrine pancreatic secretions?
insulin and glucagon
Where are the endocrine pancreatic secretions secreted into?
The blood
What are the exocrine pancreatic secretions?
Digestive enzymes (acinar cells) aqueous NaHCO3- solution (duct cells)
where are the exocrine pancreatic secretions secreted into?
Duodenum collectively as pancreatic juice
What is the function of secretions from the pancreatic duct cells?
Neutralises acidic chyme entering the duodenum
Why is neutralisation of acidic chyme important?
provides optimum pH for pancreatic enzyme function
protects the mucosa from erosion by acid
What are protein enzymes made as?
pro-proteases
Name the three pro-proteases
trypsinogen
chymotrypsinogen
procarboxypeptidase A and B
What enzymes is used in the conversion of trypsinogen?
enterokinase
Where are the pro-proteases converted into proteases?
Duodenum - on the surface of the mucosal cells
What do tyrpsin do?
Autocatalysis it’s self
Catalyses the conversion of chymotrypsinogen to chymotrypsin
What is trypsinogen converted to?
Trypsin
What does chymotrypsin do?
converts procarboxypeptidase A and B to carboxypeptidase A and B
What are the three phases of controlling pancreatic secretions?
Cephalic
Gastric
Intestinal
What mediates the cephalic phase?
Vagal stimulation of acinar cells
What mediates the gastric phase?
Gastric distension evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells
What is digestion?
The enzymatic conversion of complex dietary substances into a form which can be absorbed
What is absorption?
The process by which absorbable products of digestion are transferred across both the apical and basolateral membranes of enterocytes
What is the vagovagal reflex?
A stimulus which is detected by the sensory elements of the vagus, this is then relayed into motor elements of the vagus and causing a feedback response
What are the two types of digestion in the small intestine?
Luminal digestion
Membrane digestion
Describe luminal digestion
mediated by pancreatic enzymes secreted from the duodenum
Describe membrane digestion
mediated by enzymes situated at the brush border epithelial
What are enterocytes?
The epithelial cells which control membrane digestion
Which compound can enter the epithelial cell without being broken down but then has to broken down to enter the interstitial space?
Peptide
What compound is broken down in the lumen and then reformed in the epithelium?
Triacylglycerol
