Causes of constipation
After explaining epidemiology of constipation in previous post here we will discuss causes of constipation.
As we know constipation is just a symptom rather than a disease, it has underlying cause. The underlying cause may have symptoms other than constipation along with constipation. The other symptoms and pattern of constipation helps for the diagnosis of the underlying cause.
It is important to know the causes of constipation as it helps in diagnosis and treatment of the condition, also helping to know the prognosis of the individual case.
Before going into the causes of the constipation we will first see the mechanism of defecation as it is important in understanding the causes of the constipation.
Mechanism of the defecation:
Anatomic and physiological understanding of the mechanism of the defecation helps us in understanding the causes and correct diagnosis and treatment of constipation. In the mechanism of the defecation, There is rectum and anus, the sensory part which carries signals to brain and motor part which carries orders from the brain. This mechanism is important to hold the stool at will and avoid the embarrassment in the public places.
· Rectum and anus:
Rectum is structure situated at the distal end of the large intestine and proximal to the anal opening. Rectum is sac like in the structure. It can store the stool for some time at the will of the person. The stool is hold in the rectum till person finds suitable place to pass it. This rectum, a sac can contract when it is needed. When it contracts the stool is passed out. It is closed by the anal sphincters. Anal canal is the most distal opening which has sphincters.
· Sensory mechanism:
The anal canal from the inside is covered with squamous cell that is stratified. This layer is very richly supplied by the neurons. It is very sensitive to touch, pressure, pain and temperature. The senses from this place are carried to the brain in central nervous system by the pudendal nerves. When stool is in the anal canal the sensation produced by it are carried to the brain. Rectum is sensitive to pressure. Rectum is not sensitive to touch. When stool is stored to a capacity in the rectum the pressure senses are carried to the brain. It produces strong urge to defecate.
· Central nervous system:
The role of central nervous system is controlling the mechanism. The main role of central nervous system is establishing the co-ordination in sensory and motor mechanism to hold the stool of pass it at the will of the person. Central nervous system plays an important role in social inhibition.
Rectum serves as storage compartment and anal canal with pelvic floor muscles and sphincters serve as holding mechanism. In the colon that is large intestine the contents are rather mixed and fluids are absorbed rather than pushing it distally.
Following factors help to maintain the continence:
– Colon compliance.
– Flap valve at the flexures and rectal valves.
– Reverse motility gradient in the rectosigmoid area.
– Smooth muscles of the internal anal sphincters.
– Skeletal muscles of the external anal sphincters.
– Anorectal angle produced by the muscles of the pelvic floor.
– The internal anal sphincter is made up of smooth muscle. That smooth muscle is thickened in the region of the internal sphincter. This smooth muscle of internal anal sphincter is in continuation of smooth muscle of the rectal muscle.
Rectum is a distensible sac like structure. It stores stool but it is sensitive to the pressure. It can recognize the pressure built inside it because of stool or gas. When this pressure increases to a limit the rectum starts contracting and inner smooth muscle sphincter at anus starts relaxing. This reflex is called as recto-sphincteric reflex. This leads to movement of stool towards the anus and it gives sensation of impending motion. It produces urge to defecate. The smooth muscle inner sphincter of anus relaxes involuntarily.
The external anal sphincter is made up of skeletal muscles. It is innervated by somatic nerve from the pudendal nerve from sacral plexus at S4-level. External anal sphincter and internal anal sphincter overlap each other. Additionally external anal muscle is surrounded by the levator ani muscle of the pelvic floor. These muscles have their inherent contraction at the resting stage. This inherent tone produces high pressure zone at the opening of the rectum.
At the resting stage the continence is maintained by the inherent contraction of the sphincter. External anal muscles can contract voluntarily with additional force creating more pressure. The external anal sphincter being a skeletal muscle it can contract for a very short period of some seconds then it shows fatigue. This intermittent contraction prolongs the period of contraction to some extent and helps to hold the stool.
At resting stage liquid and gas accumulated in rectum is hold by the contraction of the internal anal sphincter. It is further hold by the external anal sphincter if it bypasses the pressure of the internal anal sphincter, the primary mechanism of continence.
Angle of rectosigmoid junction plays a role in blocking the propulsion of the stool. This angle is maintained by striated puborectalis muscles. The striated puborectalis muscle works with levator ani muscle. This puborectalis muscle forms a u shaped sling at recto-anal junction. The angle at rectosigmoid junction is such that rectum remains at 90 degree angle to anus. The sling at recto-anal junction helps to maintain this angle in position all the time. This angle is decreased only when the hip joint is flexed by 90 degrees or more. This position is produced in squatting position ideally.
Process of defecation:
So to summarize the process of defecation, the stool and other liquid and gaseous contents are carried from the colon to the rectum The intrarectal pressure is increased with accumulation. When the pressure is reached the contraction of rectal wall starts along with the relaxation of then internal sphincter. The intrarectal pressure can be felt and person feels the urge to defecate. Still the person can hold the urge by contracting the external anal sphincter. When the person squats in the toilet the recto-anal angle is reduced. The rectum and anus is brought in a line so the stool can move easily. The person also increases the intra-abdominal pressure by valsalva maneuver. With this pressure stool cannot go backwards. The pelvic floor muscles are contracting so that the pelvic floor is held in place while defecating and it does not come out while defecating.
Now we will see the the list of causes of constipation and explaining how do they cause constipation.
1. Functional constipation.
Functional constipation is defined as constipation in which person does not have any anatomical, physiological or hormonal cause of constipation but still suffers from constipation that is difficulty in passing stool. Many factors associated with this type of constipation are diet poor in fibers, unwillingness to pass stool, poor bowel habits, deep psychosomatic disorder. In some population this is commonest type of constipation.
2. Dietary causes
– Malnutrition: Malnourished children which include both spectrum underweight and overweight are more prone for constipation. This generally due to changes in intestinal mucosa and also because of poor dietary habits, in some cases neglect by parents.
– Excessive intake of cow milk: Excessive intake of cow/animal milk is one of the common cause of constipation. Along with constipation these children are more prone for obesity and iron deficiency anaemia. The calcium in milk combines with iron in food preventing its absorption from the intestine. Additionally animal milk proteins alter the the structure of internal layer of the mucosa of the intestine. Cow and animal milk cause accumulation of inflammatory cells in the mucosa of the gut altering its fuction.
– Lack of dietary fibers: Lack of dietary fibers is main cause of constipation. Dietary fibers are necessary in food for good gut health. The dietary fibers do not get digested but the hold water in lumen of the gut with osmotic effect softening the stool. They help in digestion of the other food and reducing the blood cholesterol.
– Protracted vomiting: Protracted vomiting is the condition in which person has vomiting that does not decrease with medicines. This condition also sometimes associated with constipation.
– Iron preparation: Iron preparations routinely used to treat anaemia or used for prevention for anaemia may cause constipation in some patient, though lose motions are more frequent side effect of iron preparation. Iron preparations should be taken with medical advice.
– Aluminium hydroxide: Aluminium hydroxide preparations readily available over the counter used as antacids are widely used without medical advice and they frequently cause constipation. Many patients use these drugs chronically and they suffer. Aluminium hydroxide cause constipation by altering the motility of the gut and causing increasing the transit time of contents in guts. More the transit time more are the chances of the constipation.
– Antihistaminic: Antihistaminics widely available and used as anti allergics and cough-cold medications can alter the gut motility and cause constipation.
– Anti-depressant: Anti depressants have anti-cholinergic effects which alters the gut motility can cause retention of the stool in the intestine and can suppress the ability to pass stool and urine. Those on antidepressants should seek medical advice and report the side effects to their psychiatrist as these side effects are treatable.
– Anti-cholinergic: Anti-cholinergic medicines as we discussed earlier can alter the gut motility and increase the chances of the constipation.
– Opiates: Opiates have inherent property to suppress the gut motility. They also reduce the secretion of different digestive hormones and fluids in to the gut lumen from the gut wall, the result is constipation. Opiates are used as pain killer medicines and in cough preparations.
– Chronic laxative abuse; Laxatives many available over the counter, people use them without using with medical advice. This in turn leads to abuse of drug and if used in this style they cause injury and changes to the inner layer of the intestinal mucosa. The person may become dependent on them and after some period they may lose their effect leading to increase in constipation.
– Codeine: Codeine now a days banned in many countries is used in cough preparations can lead to changes in gut similar to the opiates leading to the constipation.
– Bismuth: Bismuth also used in antacid preparations can cause constipation.
– Calcium channel blockers: Calcium channel blockers are used as anti-hypertensives. Calcium is important for the smooth muscles of the gut in process of contraction and relaxation. Use of these calcium channel blockers in some patients can cause constipation.
– Terbutalin: Terbutalin is smooth muscle relaxants which is used as broncho-spam relieving drug in asthma also causes relaxation of smooth muscle in gut though to the lesser extent can cause altered motility of the gut causing constipation.
– Dicyclomine: Dicyclomine is used to relieve the abdominal pain. It also causes constipation in some patients.
4. Motility disorders
– Hirschsprung’s disease: Hirschprung’s disease is a congenital disease and it causes malformation or absesnse of neuronal plexus in the distal intestine. This causes chronic constriction of the distal intestine. Patient characteristically has constipation followed by lose motions. Patients of this disease need surgical intervention.
– Neuronal dysplasia: Neuronal dysplasia is incorrect formation of the neurons in gut. This condition can present as constipation.
– Pseudo-intestinal obstruction: Pseudo-intestinal obstruction manifests as intestinal obstruction without actual presence of obstruction. This condition can occur because of electrolyte imbalance and sometimes the cause is unknown.
5. Structural defects of GIT
– Anorectal malformation: This is congenital defect in which anus and rectum is not formed or incompletely formed. This condition needs surgical intervention.
– Anal fissures: Chronic constipation causing frequent local injury while passing stool can cause fibrous tissue formation at the local area causing the constriction. This condition needs combination of medical and surgical intervention.
– Tumours of anus, rectum, small bowel, colon: Tumours in anus, rectum and colon can present as constipation.
– Solitary rectal ulcer: Solitary rectal ulcer can present as constipation.
6 Neurological problem
– Mental retardation: Condition leading to mental impairment at any age can cause constipation in children and adults too.
– Spina bifida: Spina bifida is condition in which spinal cord is defective at birth, As the spinal cord carries important neuronal mechanism that controls the defecation the defect in this region can cause stool retention and constipation.
– Meningomyelocele: Meningomyeolocele can cause constipation.
– Cerebral palsy: Cerebral palsy is disorder of cerebrum, it is caused by the injury to the developing brain. It is commonly associated with the constipation.
– Neuropathies: Neuropathy can be of many types and it is disorder of the neurons. It can present as constipation.
– Diastematomyelia: It is type of spina bifida can cause constipation.
– Paraplegia: Paraplegia is paralysis of the both lower limbs. It can be caused by injury to the spinal cord or higher in the brain. The neuronal mechanism involved in process of defecation may be affected in such conditions along with motility of gut. This can cause constipation.
– Quada-equina tumour: Quada equina is distal part of the spinal cord. This condition can cause constipation.
7 Muscle disorder
– Myopathies; Myopathies are of different types of disorders of the muscles. They can present with constipation.
– Myotonia dystrophica:This is disorder of the muscle tone.
8 Collagen disorders
– Scleroderma: Scleroderma is a chronic inflammatory disorder can affect any organ including the gut. The ongoing inflammation and sclerosis in the gut wall leads to altered motility of the gut leading to constipation.
– Dermatomyositis: Dermatomyositis is the inflammation of the skin and the muscles. In some cases this disorder can present as constipation.
– SLE: SLE is chronic inflammatory autoimmune disease and has capability to affect any organ in the body. It can directly affect the gut or indirectly the disease process can cause changes in gu leading to constipation in some patients.
9 Metabolic disorders
– Diabetes mallitus: Diabetes mallitus is chronic illness it can present with symptoms of constipation.
– Hypothyroidism: Hypothyroidism is reduced secretion of thyroid hormones. This condition has reduced motility of the intestine leading to constipation.
– Hypoparathyroidism: Hypoparathyroidism is reduced function of the parathyroid gland and it can cause constipation by altering calcium and phosphate levels in blood.
– Hyperparathyroidism: Hyperparathyroidism is excessive function of the parathyroid gland and it can present as constipation.
– Idiopathic hypercalcaemia: Hypercalcaemia of unknown cause can present as constipation in a similar way of hyperparathyroidism.
– Hypervitaminosis D: Hypervitaminosis D can lead to hypercalcaemia which can present as constipation.
– Hypokalaemia: Hypokalaemia causes reduced capacity of smooth muscles to contract causing decreased motility of the gut causing constipation
– Renal tubular acidosis: Renal tubular acidosis is the disorder of kidneys that causes electrolytes and calcium imbalance leading to constipation.