Digestive System & Nutrition - 1

Digestion of protein does not start with chewing of food in the mouth. It begins in the stomach.

Epiglottis is a flap of cartilage located in the throat behind the tongue and in front of the larynx. 

The esophagus which is also known as the Gullet, is an organ in vertebrates which consists of a muscular tube through which food passes from the pharynx to the stomach. During swallowing food passes from the mouth through the pharynx into the esophagus and travels to the stomach.

The primary function of the digestive system is to break down the food we eat into smaller parts so the body can use them to build and nourish cells and provide energy.

The epiglottis is flap of cartilage located in the throat behind the tongue and in front of the larynx. The epiglottis is usually upright at rest allowing air to pass into the larynx and lungs. When a person swallows the epiglottis folds backward to cover the entrance of the larynx so food and liquid do not enter the windpipe and lungs. After swallowing the epiglottis returns to its original upright position.

It is chief function of buccal cavity to break down huge macromolecules (proteins, fats and starch), which cannot be absorbed intact, into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed across the wall of the tube, and into the circulatory system for dissemination throughout the body.

Bile is a bitter, alkaline, brownish-yellow or greenish-yellow fluid that is secreted by the liver, stored in the gallbladder, and discharged into the duodenum and aids in the emulsification, digestion, and absorption of fats.

The saliva in the moth, besides helping to masticate the food, carries an enzyme called ptyalin which begins the chemical action of digestion. It initiates the catabolism  of carbohydrates by converting starches into simple sugars.

Rennin, plays an important role in the stomach of the infant. It curdles milk and allows the pepsin to work upon it.

Chyme undergoes chemical changes initiated by gastric juices secreted by the walls of the stomach. These juices include mucus for lubricating the stomach, hydrochloric acid and gastric juice. The enzyme or active principle of the gastric juice is pepsin. This enzyme in combination with hydrochloric acid starts the breakdown of proteins into absorbable amino acids called polypeptides. The gastric juice has no effect upon starches or fats.
 

The inner surface of the intestine is made of mucosal folds, or folds covered in mucus, like the stomach. These folds mix food and crimp the intestine to provide large surface area. The surface of these folds are covered with villi, or small hairs that contains cells that will extract nutrients. The surface of villi is covered with epithelial cells, and the surface of these is covered in microvilli. Together, these elements allow the intestine to be capable to ingesting huge amounts of food.

Mastication or chewing is the process by which food is crushed and grinedd by teeth. It is the first step of digestion and it increases the surface area of foods to allow more efficient break down by enzymes.It takes place in the mouth.

The liver is the largest gland of the human body, with a weight of about 3 to 3½ lb (1.4 to 1.6 kg). It is an accessory digestive organ.It secretes bile, a greenish, bitter juice which breaks up the fatty part of the food into tiny drops. Bile from the liver is collected in the gall-bladder from which it flows into the intestine.

The milk or deciduous or temporary teeth are 20 in numbers; 10 each in the upper jaw and in the lower jaw. The milk teeth begin to erupt when the child is about 6 months old and should all be present by the end of 24 months.

The mouth, or oral cavity, is the first part of the digestive tract. It is adapted to receive food by ingestion, break it into small particles by mastication, and mix it with saliva. The lips, cheeks, and palate form the boundaries. The oral cavity contains the teeth and tongue and receives the secretions from the salivary glands.

From the stomach, the partially digested food passes into the duodenum, the upper part of the small intestine. Food that has been thoroughly digested should have a thin liquid consistency when it leaves the stomach.

The kidneys perform the essential function of removing waste products from the blood and regulating the water fluid levels. It does not produce digestive juices.

Saliva is a clear liquid .It is made up mostly of water, with a few other chemicals. It is produced by the salivary glands. Saliva wets food and makes it easier to swallow. It also helps the tongue to taste. It helps begin the process of digestion Saliva also cleans the inside mouth and rinses the teeth to keep them clean.

Amylase is an enzyme that breaks down starch, converting it into sugar. There are two major types of amylase, alpha and beta. Alpha-amylase is found in human saliva, where it begins a chemical process in digestion with the hydrolysis of starch. It is also found in the pancreas. Beta-amylase is found in the seeds of some plants, as well as bacteria, yeast, and molds. Amylase is also found in other animals that use it to aid the digestive process.

The pancreas secretes digestive enzymes into the duodenum, the first segment of the small intestine. These enzymes break down protein, fats, and carbohydrates. The pancreas also makes insulin, secreting it directly into the bloodstream. Insulin is the chief hormone for metabolizing sugar.

It is made up of three segments — the duodenum, jejunum, and ileum .It is a 22-foot long muscular tube that breaks down food using enzymes released by the pancreas and bile from the liver. Peristalsis also is at work in this organ, moving food through and mixing it with digestive secretions from the pancreas and liver. The duodenum is largely responsible for the continuous breaking-down process , with the jejunum and ileum mainly responsible for absorption of nutrients into the bloodstream.

Canine teeth are 4 in number.They are very strong, pointed corner teeth for tearing and shredding, placed laterally to each lateral incisor. They are larger and stronger than the incisors. The canine tooth morphology is characterized by the large, conical crown which projects beyond the level of the other teeth and one single root, longer than all other human teeth types.The upper canine teeth are sometimes called eyeteeth.

All the above three are enzymes.

Pepsinogen is the inactive version or precursor of pepsin, a protease (protein-digesting enzyme), secreted in the stomach. The active site of the pepsin enzyme is obscured by a section of polypeptide (propeptide) chain - 44 amino acid residues long - and this is removed by the action of hydrochloric acid and pepsin already in the stomach. This means that the enzyme is inactive when first secreted from chief cells in the stomach wall, which prevents damage to the cells of the stomach wall itself. Pepsinogen is converted by autocatalysis into the active form of the enzyme pepsin.

The anus is the last part of the digestive tract. It is a 2-inch long canal consisting of the pelvic floor muscles and the two anal sphincters (internal and external). The anus is surrounded by sphincter muscles that are important in allowing control of stool. The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The internal sphincter is always tight, except when stool enters the rectum.