Physiology and Pharmaxology of the small and large intestine Flashcards
Describe the length of the different parts of the small intestine
Duodenum - 25cm
Jejunum - 2.5m
Ileum - 3m
What happens in the small intestine
Major site for digestion and absoprtion
Receives chyme from the stomach, pancreatic juice from pancreas and bile form the gall bladder
How does the small intestine move remaining residues to the large intestine
Through the ileocaecal valve
In which part of the small intestine does most of the absorption and digestion occur?
Duodenum
How do pancreatic secretions and bile secretions enter the small intestine?
Through the sphincter of Oddi
What moves into the large intestine?
Unabsorbed electrolytes, water and indigestible residue (cellulose)
What is the sphincter between the small intestine and the large intestine
Ileocaecal valve
What controls the opening of the ileocaecal valve
The hormone Gastrin
In what 3 ways is the surface area of the small intestine increased?
Circular folds of Kerckring
Villi
Microvilli
What is the name of the absorptive cells?
Enterocytes
What 7 peptide hormones are secreted from endocrine cells within the mucosa
Gastrin Cholexystokinin (CKK) Secretin Motilin Glucaogon-like insulinotropic peptide (GIP) Glucagon like peptide 1 Ghrelin
Where is gastrin secreted from
From G cells of gastric antrum and duodenum
Where is CCK secreted from?
From I cells of duodenum and jejunum
Where is secretin secreted from?
S cells of duodenum
WHere is motilin secreted?
From M cells of duodenum and jejunum
It has a special purpose in migrating the motor complex
Where is GIP secreted
an incretin from K cells of duodenum and jejunum
It causes an increase in gastric motility and serves as an incretin (feedforward signal)
Where is GLP-1 secreted
an incretin from L cells of the gut
Where is Ghrelin secreted
from Gr cells of the gastric antrum, small intestine and elsewhere (pancreas)
Where do all peptide hormones act on
G protein couple receptors
What is the role of Ghrelin
To release a hunger signal as a feedforward mechanism to prepare the body for food
What is the name given to the jucie of the small intestine
Succus entericus
What will cause the release off the intestinal juice
Any stimulatory act on the GI tract
What are some of the control mechanisms related to the secretions of the small intestine
Distension / irritation if acid is present
Parasympathetic activity - change in ACh
Secretions of the small intestine include:
Mucus - for protection/ lubrication
Aqueous salt - for enzymatic digestion
No digestive enzymes
What does excessive activity cause?
Secretory diarrhoea (cholera)
What is the function of the ATPase in the basolateral membrane
To maintain a low intracellular concentration of sodium
Cysitic fibrosis patients may suffer from what in GI
a decrease in secretion of succus entericus
Segmentation in the duodenum is primarily due to what?
distension due to Chyme entering
What is triggered by gastrin from the stomach
What is the alternative name for this?
Segmentation in the empty ileum
Gastroileal reflex
How many segmentation contraction are there in the duodenum?
In the ileium
Duodenum: 12/min
Ileum: 9/min
What enhances the strength of segmentation
Parasympathetic nervous system
What decreases the strength of segmentation
Sympathetic system
Describe the 2 main activities which occur in the interdigestive or fasting state
A few localised contractions
The mirgrating motor complex (MMC)
What happens to the small intestine when chyme enters
therefore it is inhibited by feeding, vagal activity, gastrin and motility and poylystic kinin. ]
What are the 2 main types of pancreatic secretions
Endocrine and Exocrine
Give two examples of endocrine hormones
Insulin and Glucagon
Give 2 examples of exocrine cells
acquous NaHCO3, dyct cells)
What do acini cells eventually form? and where dies it join?
Pancreatic duct which joins the common bile duct.
What are the 3 main types of pancreatic enzyme
Proteases, amylases and lipases
Name the 3 phases of pancreatic secretion control
Cephalic
Gastrin
Intestinal
What is cephalic control
The feedforward mechanism which is stimulated by vagal sitmulation of acinar cells
What is gastric control
Evokes a vagovagal reflex resulting in parasympathetic stimulation of acinar and duct cells
What is intestinal control
Chyme enterinf the stomach is acidic which triggers the release of secretin
What is secreten
It is carried in the blood and effects the pancreatic duct cels causing an increased in the secretion of aqueous NaHCO3 solution into duodenal lumen . This results in the neutralisation of acid in the duodenual lumen
Name the different parts of the large intestine
Appendix Caecum Ascending Colon Transverse Colon Descending Colon Sigmoid colon Rectum
How much does the large intestine receive of ileocaecal material
1L per day
What are the four primary functions of the large intestine
Absorption of H20, Na and Cl with secretion of K, HCO3 and mucus - proximal colon
Absorption of short chain fatty acids
Reservoir - distal colon
Periodic elimination of faeces
What is faeces composed of
H20, 50g solid, including cellulose, bacteria, bilirubin and a small amount of salt
What is the only product which is truly excretory
Bilirubin
What occurs in the first 2rds of the large intestine
Fluid reabsorption and bacterial fermentation
What occurs in the last part of the large intestine
Final drying and storage
What are the 3 patterns of motility in the large intestine
Haustration
Peristaltic propulsive movements
Defaecation
How does haustration occur?
It is caused by contraction of the circular muscle - similar to segmentation in function, but much lower frequency
It occurs in the proximal colon
Generated by slow wave activity and mixes content allowing time for fluid and electrolyte reabsorption
What is the outer longtitudinal muscle layer comprised of?
3 bands - the taenia coli
What is mass movement
Simultaneous contraction of large section of the circular muscle of the ascending and transverse colon
When is mass movement triggered?
triggered by a meal
It can also occur in the distal colon, propelling faeces in to the rectum
Where else does mass momvemtn occur?
Int he distal colon, propelling faeces in to the rectum triggering the defaecation reflex
What happens when it IS convenient to defaecate
The anal sphincter which turns to the rectum causing contraction assisted by abdominal muscles. These cause an increase in pressure in the abdomen so the diaphragm moves down
What is Hirschsprung disease
A condition in which rectal filling does not cause internal anal sphincter to relax
What happens if it is safe and convenient to defaecate?
Afferent signals are sent back tot he spinal cord and cause relaxation
What happens if it is not safe and convenient to defaecate?
The skeletal muscle of the external anal sphincter contracts strongly until there is another mass movement
What do the bacteria in the colon do?
increase intestinal immunity by competition with pathogenic microbes
promote motility and help maintain mucosal integrity
synthesise vitamin K and free fatty acids that are absorbed
activate some drugs (used in treatment of IBD)
What does the anus permit
Expulsion of intestinal gas (flatus) as well as faeces
Where do gasses arise from
swallowed air
bacteria in the colon which attack forms of carbs that are indigestible to humans
gas that is not absorbed in the large intestine
What happens when we want to expel gas
The abdominal muscles contract to cause pressure but both the external and internal anal sphincters contract strongly to produce a slit like exit to prevent liquid material escaping and only gas is expelled
Why is turbulence produced?
Gas escapes at a high pressure
