Constipation Flashcards
Does the GI tract store energy?
No!
What are the roles of the GI tract?
Transportation of food
Digestion of food
Absorption of nutrients
Excretion of waste products
What are the functions of the large intestine?
Reabsorb water and compact material into faeces - major role
- Absorb vitamins produced by bacteria – this is not a significant role
- Store faecal matter prior to defecation – major role
What are the six areas of the colon?
Ascending
Transverse
Descending
Sigmoid
Rectum
Anal canal
What is the difference between the proximal and distal half of the colon?
The proximal half of the colon is concerned with absorption and the distal half is concerned with storage.
What are the two movements of the colon?
Mixing movements (Haustrations)
Propulsive movements (Mass Movements)
Causes of Chronic Constipation?
Intrinsic factors:
–Abnormal intrinsic motility
–Lack of luminal factors that sense stretching, chemical changes and tactile stimuli
–Lack of extrinsic innervation (in paraplegia – the innovation that controls the movement of the gut has been lost)
–Hormones (very rarely, e.g., in pheochromocytoma)
- Medications
- Impaired defecation
- Fluid handling & faecal impaction
What is Iatrogenic constipation?
Constipation caused by medical treatment
What medicines cause constipation?
Pain medications,
Iron
Calcium
Blood pressure medications, etc
• Opioid-induced constipation in palliative care is the most common.
How do Opioids cause constipation?
• Increasing smooth muscle tone, which suppresses peristalsis, that moves matter forward, through the GI tract
–Increases the tone in the anal sphincters
–Increases transit time and the amount of water absorption, per time, in the large intestine
• Reduces sensitivity to anal distension. This reduces the urge to defecate.
Explain Laxative Misuse?
When a patient takes too many laxatives, there is a longer interval needed to refill the colon – the patient may interpret this as further constipation, leading to further laxative use.
If this happens then the body loses water and salts and potassium in the faeces, which causes release of aldosterone. Aldosterone stimulates the reabsorption in intestine, but increases renal excretion of K+.
So you lose potassium (double loss of K+), through the faeces and renal excretion (from the gut and the kidney). This causes hypokalaemia (low levels of potassium in the blood), which reduces peristalsis.
The patient can misinterpret this as constipation causing further laxative use.
So they get into a cycle.
Explain the Defecation Reflex?
Step 1: Distension of the rectum, as it fills with feceal matter, descending through the large intestine.
This distension is picked up from two feedback loops.
1:
There are stimulation of stretch receptors, in the wall of the rectum.
That can lead to the stimulation of smooth muscle in rectal wall.
This causes increased local peristalsis throughout large intestine (increased movement, within the rectum itself).
Which then leads to distension of the rectum (so back to step 1).
2:
There are stimulation of stretch receptors, in the wall of the rectum.
This leads to a spinal reflex. You get the stimulation of the parasympathetic motor neurons in sacral spinal cord.
This leads to increased local peristalsis throughout the large intestine, moving further foetal matter down towards the rectum. This leads to further distension of the rectum (back to step 1).
Eventually the stimulation of the stretch receptors in the rectum triggers the stimulation of somatic motor neurons in the brain.
This sends signals down to the sphincter in the anus.
This leads to relaxation of the internal anal sphincter and leads to the contraction of the external sphincter.
Internal sphincter relaxes and the external sphincter contacts.
What happens during defaecation?
You voluntarily relax the external sphincter.
Puborectalis are also relaxed for defaecation.
Explain Faecal Impacation?
If you reabsorb too much fluid, the fetal matter can become quite hard and dry and difficult to pass.
That can lead to a build-up of this dry and hard matter.
This forms a blockage, transit time is decreased and more matter becomes dry and hard.
How can you avoid Faecal Impaction?
Drink lots of water and eat more fibre.
Is constipation a disease?
No, it is a symptom!
Name some treatments for Constipation?
Treatment involves diet, hydration and exercise.
And if these fail, medication and other possible solutions.
What are some treatments of constipation after dietary?
–Bulk-forming laxatives
–Osmotic laxatives
–Stimulant laxatives –Stool softeners
–Other agents
Explain the mechanism of Bulk-forming laxatives?
Increases the amount of fibre in the diet. This cannot be digested and cannot be absorbed. So the amount of matter entering the large intestine is increased.
It is good at holding fluids so you get a large bulk of ‘wet’ matter in the large intestine. This helps us to move things through the intestine at a sensible rate.
Explain the mechanism of Osmotic Laxatives?
Increases the amount of fluid content that is drawn into the large intestine - increases fluid content of stools, making it easier to pass. This also increases the volume and allows peristalsis to work on them in a better manner.
