Large Intestine Structure and Function Flashcards
What is the pathway of the junction between the small intestine and the large intestine
Chyme moves from Illieum through ileocaceal valve into the caesum (blind sac)
The caecum, then drains into the large intestine or can then drain down into the appendix and lymph nodes below,
What is the four colon parts of the Large intestine
Ascending
Transverse
Descending
Sigmoid
How is the muscularis externa composed in the large intestine
A complete layer of circular muscle
Surrounded by an incomplete layer of Longitudinal muscle
consisting of 3 narrow bands of smooth muscles called Tenia coli
What affect does the Tenia Coli have on the large intestine
The teniae coli contract lengthwise to produce the haustra, the bulges in the colon
Pouches from give a puckered appearance
What is the mucosa composed of in the large intestine
Simple columnar epithelium
What is present in the large straight crypts found in the submucosa layer of the large intestine
Goblet cells
What is the purpose of Goblet cells on the large intestine
Produce mucus, which allows lubrication for the movement of faeces
Where is the rectum located
Between sigmoid colon and anal canal
What is the structure of the rectum
Straight muscular tube composed of simple columnar epithelium
Where is the anal canal located
Distal to the rectum and anus (2-3cm)
What is the mucularis externia of the rectum and the anal canal compared to the remainder of the alimentary tract
Thicker
But anal canal is even thicker due to the presence of the internal anal spinchter
What is the change in the mucosa layer in the anal canal
Changes from simple columnar to stratified squamous epithelium
How is the colons of the large intestine involved in nutrient absorption
They aren’t involved
What is the function of the colon
Form solid faecal pellets
How is solid faecal pellets formed in the colon
Sodium is actively transported from the lumen and into the blood, so water follows osmotic gradient out into the blood, the removal of water dehydrates the chyme creating the solid formation of faeces
What is the benefit of the long residence time of chyme in the large intestine
Allows time for bacterial colonisation of colonic microflora
What is the function of colonic microflora in the colon
Bacterial fermentation of undigested carbohydrates
What is the major benefit of colonic microflora in the colon
Produce additional energy source in short chain fatty acids
Produces Vitamin K which is needed for blood clotting
Produces Flatus
What controls the internal and external anal spinchters
in the anus
Internal - smooth muscle under autonomic control
External - skeletal muscle under voluntary control
What is the pathway occurring in the large intestine before defaecation occurs
After a meal there is a Mass movement of contraction from colon to rectum - this moves faecel into the rectum and distends the rectal wall upon arrival
This is senses by mechanoreceptors creating the defeaecation reflex, giving you the urge to defaecate
What controls the defaecate reflex
Parasympathetic NS innervation the pelvic splanchnic
no sympathetic intervention
What is the steps of the defeacation reflex
The stretched wall recoils and the rectum contracts
This causes the relaxation of the internal spinchter and the contraction of the external anal spinchters
Increasing the peristaltic activity in the colon
The increased pressure of the external anal spinchter
Under voluntary control is then relaxed and allows the explosion of faeces
How does voluntary delay of defection occur
Voluntary contraction of external spinchter
What happens to the toxins during constipation
difficulty emptying bowels
They are not reabsorbed but remain in faecal bulk
What can voluntary delay of defecation cause
Constipation
due to delay faeces harden up due to continually water absorption so are then harder to expel
What is the symptoms associated with constipation
Headaches
Nausea
Loss of appetite
Abdominal distension
What directly causes the symptoms associated with constipation
The distension of the rectum due to the build up of material
What is the definition of Diarrhoea
Too frequent passage of faeces which are too liquid
What is the causes of Diarrhoea
Pathogenic bacteria Protozoans Viruses Toxins Foods Stress
What is examples of enterotoxigenic bacteria
Vibrio cholerae, Escherichia coli
How do enterotoxigenic bacteria cause detrimental diarrhoea
Produce protein enterotoxin bacteria that elevates intracellular secondary messengers that increase intestinal chloride secretion from crypt cells
Due to to increased osmotic gradient this increases H2O secretion that swamps absorptive capacity of villus cells therefore resulting in profuse watery diarrhoea
Why is death a possibility in diarrhoea
As your body cannot tolerate that much fluid loss
What are the secondary messengers that enterotoxigenic bacteria micmic their physiological mechanism to produce an exaggerated stimulation
cAMP
cGMP
Calcium
What affect does enterotoxins have on villus cells
No effect - no damage
What is the treatment for diarrhoea
Oral rehydration therapy (ORS)
which is a sodium/ glucose solution
What is the purpose of the diarrhoea treatment
Rehydrate - by driving H2O absorption
Wash away infection
What is flatulus composed of
Nitrogen CO2 Hydrogen Methane Hydrogen sulphide
