Study Human Physiology for MH-CET 2014


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Study Human Physiology for MH-CET 2014

  1. 1. HUMAN PHYSIOLOGY Digestion and absorption Digestion - The process by which large food particles are broken down into nutrients through mechanical and chemical degradation Absorption - The stage of digestion during which nutrients are transported into the blood stream. Alimentary canal and digestive glands : The digestive tract is a muscular tube, approximately 18-27 feet in length that extends from the mouth to the anus. It is composed of seven compartments and four accessory
  2. 2. organs. The compartments carry the food as it passes through the digestive tract while the accessory organs secrete enzymes or produce molecules that aid indigestion. The accessory organs are connected to the main digestive tract by a series of ducts. The compartments occur in the following order: mouth, pharynx, esophagus, stomach, small intestine, large intestine and anus. The accessory organs consist of the paired salivary glands, the pancreas, the liver, and the biliary system. GI system breaks down particles of ingested food into molecular forms by enzymes (digestion) that are then transferred to the internal environment (absorption). Compartments of alimentary canal: 1. Mouth The process of digestion begins in the mouth. Within the mouth lie the teeth, tongue and jaws. Through a chewing motion, the food is mechanically broken down between the teeth and mixed with saliva, which aids in chemical digestion. Upon stimulation, saliva is produced in the salivary glands and brought into the mouth. It contains salivary amylase, an enzyme that digests starch. Once the digestion in the mouth is completed, the first phase of swallowing is initiated. This stage is voluntary and is characterized by contraction of the muscles of the floor of the mouth and tongue that propel the food bolus into the pharynx. 2. Pharynx The buccal cavity leads into a short pharynx which serves as a common passage for food and air. The oesophagus and the trachea (wind pipe) open into the pharynx. A cartilaginous flap called epiglottis prevents the entry of food into the glottis (opening of wind pipe) during swallowing. 3. Oesophagus The oesophagus is a thin, long tube which extends posterior passing through the neck, thorax and diaphragm and leads to a ‗J‘shaped bag like structure called
  3. 3. stomach. A muscular sphincter (gastro-oesophageal) regulates the opening of oesophagus into the stomach. The food moves through the oesophagus due to rhythmic contraction or longitudinal and circular muscle. This wave of contraction and relaxation is called peristalsis. Mucous secreted by epithelial cells in the inner lining helps in the smooth passage of food. 4. Stomach The stomach is a C-shaped pouch that receives the food bolus from the esophagus. It aids both in mechanical and chemical digestion. Acting like a churn, the stomach mixes the food with gastric acid and breaks down the food into a milky substance known as chyme. The acid reduces the pH of the stomach, in the process allowing activation of an enzyme called pepsin. This starts the chemical digestive process. 5. Small Intestine The majority of digestion occurs in the small intestine. This compartment has three distinct portions, each of which is highly specialized for different digestive functions. The first third is the duodenum. This part is responsible for signaling the distal digestive tract that food is arriving and that the stomach should stop sending food. Chemical digestion is very active at this stage, and food is broken down into basic proteins, carbohydrates, and fats. Digestive enzymes are released from the pancreas to enable the degradation process. Bile is released from the gall bladder and mixes with the chyme to aid in fat digestion and absorption. The second portion of the small intestine is the jejunum. It is composed of many folds that increase the surface area for absorption, known as the brush border membrane. As the digestive products move through the small intestine, different parts of the brush border membrane selectively allow the absorption of different nutrients. The third portion of the small intestine is the ileum. It is responsible for the very selective absorption of some significant nutrients, including vitamin B-12 and
  4. 4. vitamin C. By the end of the small intestine, the majority of the nutrients have been absorbed. The material is now mostly waste products and water, and is referred to as liquid stool. 6. Large Intestine It is broader than the small intestine. It consists of caecum, colon and rectum. Caecum is a small blind sac which hosts some symbiotic micro-organisms. A narrow finger-like tubular projection, the vermiform appendix which is a vestigial organ, arises from the caecum. The caecum opens into the colon. The colon is divided into three parts - an ascending, a transverse and a descending part. The colon is lined internally by mucosal cells secreting mucous that makes the passage of undigested material easy. The descending part opens into the rectum, which is the posterior region of large intestine. Undigested material called faecal matter is stored in the rectum temporarily before it is expelled through the anus. 7. Anus Rectum opens to the outside by the opening called anus which is guarded by a sphincter. It removes undigested matter outside by the process known as defecation or egestion. Keep on visiting for more study material about MH-CET. Feel free to ask your doubts in comments, or call 9011041155 for any help. - Team Ednexa