Large intestine, constipation diarrhoea and lactose intolerance

what happens when longitudinal muscle contraction occurs?

lumen becomes shorter and fatter

what happens when circular muscle contraction occurs?

lumen becomes narrower and longer

what happens when the muscularis mucosae contraction occurs?

hange in absorptive and secretory area of mucosa

why does gastrointesintal motility take place?

It is mostly due to the activity of smooth muscle (circular, longitudinal layers and the muscularis mucosa)

where is the enteric nerbous system located?

• in the gut - in the G.I tissue 

• the cells are located in the ganglia, within the myenteric and submucuous plexus

how are the 2 plexus connected?

they are connected by interganglionic fibres

what does the enteric nervous system compromsise of?

sensory neurones

interneurons 

effector neurons

name examples of sensory neurones 

mechanoreceptors

chemoreceptors

thermoreceptors

name examples of effector neurones 

excitatory and inhibitory motor neurones

what is the function of interneurons  

co-ordinating reflexes and motor programs

where is the ICCs?

what does slow waves determine?

the basic electric rhythym - not all slow waves trigger contraction 

what does the ampitude of the slow wave depend on?

• neuronal stimuli

• hormonal stimuli

• mechanical stimuli

how many slow waves are there in the stomach per minute?

3 slow waves per minute

how many slow waves are there in the small intestine per minute?

1-12 waves per minute in the duodenum

8 waves per minute in the terminal ileum 

what do the slow waves do in the large intestine per minute?

favours retention of luminal contents, facilitating absorption of water and electrolytes

what type of process is the absorption of water?

its a passive process

what drives the process of absoprtion of water in the G.I tract?

driven by the transport of solutes (particularly Na⁺) from the lumen of the intestines to the bloodstream

what is diarrhoea?

the loss of fluid and solutes from the GI tract in excess of 500ml per day

what are the types of mechanisms of sodium/water absorption?

Na⁺/glucose co-transport 

Na⁺/amino acid co-transport 

Na⁺/H⁺ exchange 

Parallel Na⁺/H⁺ and Cl^-/HCO₃^- exchange

epithelial Na⁺ channels (ENaC)

what is the feature of Na⁺/glucose co-transport?

its electrogenic

what is th feature of Na⁺/amino acid co-transport?

its electrogenic

what is the feature of Na⁺/H⁺ exchange?

its electroneutral

its powered by the presence of bicarbonate

what is the feature of Parallel Na⁺/H⁺ and Cl^-/HCO₃^- exchange?

its electroneutral

its powered by the presence of cAMP/cGMP and calcium dependent

what is the feature of epithelial Na⁺ channels (ENaC)?

its electrogenic

regulated by aldosterone

what are the causes of diarrhoea?

Excessive secretion - Secretory diarrhoea

• most common cause: E. Coli (Traveller’s diarrhoea)

impaired absorption of NaCl

non-absorbable/poorly absorbable solutes of intestinal lumen 

hyper motility 

what does electrogenic mean?

changes the charge of the blood 

describe the mechanism of excessive diarrhoea:

• Cholera toxin enters the enterocyte and enzymatically inhibits the GTPase activity of the Gsa subunit 

• increased activity of adenylate cyclase

• increased concentration of cAMP

• cAMP stimulates CFTR

• Hypersecretion of Cl^-, with Na⁺ and water following

what is the consequences of diarrhoea?

• can result in dehydration (Na⁺ and H₂O loss)

• metabolic acidosis (HCO₃^- loss)

• hypokalaemia (K⁺ loss)

• may be fatal if severe (e.g cholera)

what are the types of treatments used to treat diarrhoea?

• Maintenance of fluid and electrolyte balance (first priority)

• use of antiinfective agents (if appropriate)

• Use of anti-motility agents

what happens in rehydration therapy?

it exploits Na⁺/glucose

describe the process of rehydration therapy:

1. Two Na⁺ bind

2. Affinity for glucose increases, and glucose binds

3. Na⁺ and glucose translocate from the extracellular to the intracellular

4. 2 Na⁺ dissociate, affinity for glucose falls

5. glucose dissociates

6. The cycle is repeated

how can lactose intolerance be caused?

• Primary lactase deficiency– due to lack of the lactase persistence

(LP) allele – most common cause world wide

• Secondary lactase deficiency – caused by damage to/ infection of/

the proximal small intestine

• Congenital lactase deficiency – rare autosomal recessive disease –

no ability to digest lactose from birth

how is lactose intolerance diagnosed?

diet observation:

• Association of symptoms with lactose consumption

• hydrogen breath test

• Lactose/milk tolerance test

what are the symptoms of lactose-intolerance?

• bloating

• abdominal pains

• dirrhoea

how is lactose intolerance treated?

• Reduction or elimination of consumption of milk products

• use of milk prodicts treated with lactase

• Use of milk lactose-free

What are the causes of constipation?

• neurological disorders of the large intestine

• Abdominal muscle weakness

• Diet poor of fibres

• Sedentary life style

• Constant suppression of the urge to empty

• Antidepressant drugs -anticholinergics

• Opiates

• Aging

treatment for constipation:

• More water and less alcohol should be consumed

• Some wheat bran can be added to the diet

• Increase your activity- exercise

• Improve your toilet routine - Keep to a regular time and give yourself plenty of time to use the toilet

• don’t delay

• feet can be rested on a low stool while going to the toilet

what are the types of laxatives to treat constipation?

purgatives:

• bulk laxatives

• osmotic laxatives 

• faecal softeners 

• stimulant laxatives

drugs which increase GI motility without purgation:

• antimetics