The pathway of food from the mouth to the anus. Mouth–>Pharynx and Esophagus–>Stomach–>Small Intestine–>Large Intestine–>Rectum and Anus. The mouth is to chew and bite your food. The pharynx and esophagus is used to transport the food. The stomach involves mechanical disruption and absorption of water and alcohol. The small intestine uses chemical and mechanical digestion and absorption. The large intestine absorbs electrolytes and vitamins (B & K). The rectum and anus are for defecation.
There are six basic processes of digestion. 1. Ingestion, which is taking food into the mouth. 2. Secretion, which is the release of water, acids, buffers, and enzymes into the GI tract. 3. Mixing and propulsion, which is churning and propulsion of food through the GI tract. 4. Digestion, mechanical and chemical. Mechanical digestion is the movement of the GI tract that aids chemical digestion. Chemical digestion is a catabolic (hydrolysis) reaction to break down large molecules into smaller, usable molecules. Both types breakdown food.
Mouth:
Mechanical digestion, also known as mastication or chewing, breaks food into pieces and mixes with saliva so it forms a bolus. Chemical digestion involves two enzymes, amylase and lingual lipase, that aid in breaking down food. Amylase begins starch digestion at pH of 6.5 or 7.0 found in the mouth. When the bolus and the enzymes hit the pH 2.5, gastric juices hydrolysis ceases. (Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water.) Lingual lipaseis secreted by glands in the tongue. It begins the breakdown of triglicerides into fatty acids and glycerol.
Saliva is made up of 99.5% water. and 0.5% solutes. The solutes are ions such as NA, K, Cl, bicarbonate and phosphate. The solutes also include, lingual lipase, salivary amylase and lysozome. Lysozomes are organelles that contain enzymes that break down bacteria.
Esophagus:
The esophagus secretes mucous and transports food to the stomach. It uses peristalsis to push the bolus towards the stomach. It is connected to the pharynx by the upper esophageal sphincter and to the stomach by the lower esophageal sphincter.
Stomach:
The stomach begins the breakdown of proteins and lipids. It is where the formation of chyme is made and delivered to the small intestine. The stomach acts as a reservoir by mixing and holding ingested food. There are many secretions in the gastric pit. Parietal cells secrete gastric acid(mainly HCl) and intrinsic factor for red blood cell production. Mucus cells secrete mucus. Chief cells secrete pepsinogen to degrade food proteins into peptides. G cells secretes gastrin. They work in conjunction with chief cells and parietal cells. D cells secrete somatosin .
Mechanical digestion involves gentle mixing waves, vigorous waves and intense waves near the pylorus. The gentle mixing waves occur every 15 to 25 seconds. The mix the bolus with 2 quarts per day of gastric juice to turn it into chyme. The more vigorous waves travel from the body of the stomach to the pyloric region. The intense waves open the pylorus and squirt 1-2 teaspoons full with each wave.
Chemical digestion is when protein digestion begins and fat digestion continues. HCl unfolds protein molecules and transforms pepsinogen into pepsin. It breaks the peptide bonds between certain amino acids. Gastric lipase splits triglycerides in milk fat. It is most effective at a pH of 5 to 6 (seen in an infant stomach). HCl kills microbes in food. The mucous cells protect the stomach walls from being digested with 1-3mm thick layer of mucous.
Pancreas:
The pancreas produces pancreatic juice. The juices contains water, salts, sodium bicarbonate and enzymes. The enzymes are pancreatic amylase and pancreatic lipase. Pancreatic proteases (degrades) trypsin, ribonuclease, or deoxyribonuclease. Pancreatic enzymes are involved with digestion of all nutrients.
Liver:
The liver is the heaviest gland in the body. It is also the second largest. It gives energy by gluconeogenesis (making of new glucose), breaks down amino acids and stores triglycerides and breakdown of fatty acids. The liver produces bile and stores glycogen and vitamins (A,B12, D, E,K). It is the synthesis of cholesterol and detoxification of drugs and alcohol. The liver and gall bladder create bile composition. The composition is made up of water, cholesterol, bile salts (Na & K), carbohydrates, lecithin and electrolytes (Na, bicarbonate and Cl). The composition also contains bile pigments. Bile’s function is to break down lipids and neutralize chyme. The gallbladder is used for the storage, concentration and delivery of bile into the duodendum.
Small Intestine:
The small intestine has three parts; duodendum, jejunum and ileum. The small intestine chemically digests carbohydrates, proteins, lipids and nucleic acids. It absorbs monosaccharides, amino acids, dipeptides, tripeptides, lipids, electrolytes, vitamins and water. The inner surface is formed into villi and crypts. Epithelial cells line the inside of the the GI tract.
Large Intestine:
The large intestine uses mechanical digestion where gastroileal reflex forces chyme from small intestine to the large intestine. Each haustrum remains relaxed while filling and then contract and send chyme to the next one. It is the final stage of digestion…bacteria fermentation–> final decomposition–> carbohydrates–> gases. Amino acids are also broken down. Chyme water absorption turns into feces after 3-10 hours. The distention of the walls stretch the receptors. Parasympathetics stimulates the descending colon, rectum and anus. The long muscles contract and pressure increases. The internal anal sphincter then opens. Next is the external sphincter which has voluntary control. The abdominal and diaphragm muscles aid in this event.
Disease:
A disease of digestion is gastroesophageal reflex disease. It is when the lower sphincter fails to open. The distension of the esophagus feels like chest pain or a heart attack. If the lower esophageal sphincter were to fail to close, stomach acids would enter the esophagus and cause heartburn (GERD). Smoking and alcohol make the sphincter relax which worsens the situation.
To help control these symptoms, avoid coffee, chocolate, tomatoes, fatty foods, onions and mints.
Tags: Education // Add Comment »
