DIGESTIVE SYSTEM

Nutrition and digestion  All organisms need energy for their metabolism. They get this energy by nutrition.  Digestion is the breaking down the food into monomers, making easy the diffusion of molecules through the membrane.

Mechanical and chemical digestion.  Mechanical or physical digestion: It is the breaking down the polymers physically. In that way the surface area of the substrate is increased. This enables the digestive enzyme activity.  Chemical digestion: It is the breaking down the polymers into monomers by the help of the digestive enzymes.

 Intracellular digestion  Intracellular digestion takes part in cell. To do intracellular digestion, food molecules should be taken from outside by phagocytosis. Lysosome takes part in this kind of digestion. Unicellular organisms, some primitive multicellular animals or specialized cells like liver and white blood cells do intracellular digestion.  Extracellular digestion  Extracellular digestion takes part out of the cell. To do extracellular digestion, digestive enzymes are secreted out of the cells. Then digested monomers are taken to the cells by transport mechanisms. Most of the multicellular animals, fungi, both autotroph heterotroph plants do extracellular digestion. In that way organisms can use many kinds of polymers

Digestion in unicellular organisms  Digestion is intracellular in unicellular organisms. Food is taken by phagocytosis. Food vacuole then unites with the primary lysosome to form secondary lysososme. Food molecules are broken down by hydrolytic enzymes. Undigested materials are thrown out of the cell by exocytosis.

Digestion in Invertebrates  Digestive systems of the invertebrates are adapted according to their nutritional types.  Sponges make intracellular digestion. Hydra can do both intra and extracellular digestion.  Parasites like don’t have developed digestive systems because they their food readily. Planaria has a primitive digestive system with one opening.

 From the beginning of the phylum Annelids 2 openings (mouth and anus) can be seen. In the earthworm digestive system consists of mouth, pharynx, esophagus, crop, gizzard, intestine, anus.  Snail has a teeth-like structure called radula.  Arthropoda has a developed digestive system.  Filter feeders, such as clams and blue whales, prey on small organisms by filtering them from the aquatic environment

Digestive system in Vertebrates  Herbivores, Carnivores and omnivores have different adaptations according to their nutrition.

 the teeth of herbivorous vertebrates have been shaped by selection to process plant. The digestive processes of herbivores can also be quite specialized.  Digestive system is very long in herbivores but short in carnivores. Nonruminant herbivores(rabbit) have developed cecum which has microorganisms to digest cellulose in plant tissues.  The digestive tracts of ruminants (cud chewers) such as cattle, goats, and sheep are specialized to maximize the benefits of their endosymbiotic microorganisms. They have a large, four-chambered stomach. The first two chambers, the rumen and the reticulum, are packed with anaerobic microorganisms that break down cellulose by fermentation. The ruminant periodically regurgitates the contents of the rumen (the cud) into the mouth for rechewing. When the more thor­oughly ground-up vegetable fibers are swallowed again, they present more surface area to the microorganisms for their digestive actions.

(işkembe, börkenek, kırkbayır, şirden)

 Birds don’t have teeth, instead their beaks(bill) help gathering food.  esophagus - narrow tube that carries food to the crop  crop - a sack-like widening of the digestive tract where food can be stored temporarily  proventriculus - the first chamber of a bird's stomach where food is broken down by digestive enzymes  gizzard - the second chamber of a bird's stomach where food is ground up by muscular action and small stones or grit (ingested by the birds)  intestines -

Human Digestive System The human digestive system is a coiled, muscular tube (6-9 meters long when fully extended) stretching from the mouth to the anus. Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. Accessory digestive organs are connected to the main system by a series of ducts: salivary glands, exocrine part of the pancreas, liver and gall bladder The human digestive system is a coiled, muscular tube (6-9 meters long when fully extended) stretching from the mouth to the anus. Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus. Accessory digestive organs are connected to the main system by a series of ducts: salivary glands, exocrine part of the pancreas, liver and gall bladder

 There are 32 permanent teeth  From the midline of one side of each jaw consists of 2 incisors, 1 canine, 2 premolars and 3 molars

 Mechanical breakdown begins in the mouth by chewing (teeth) and actions of the tongue. Chemical breakdown of starch by production of salivary amylase from the salivary glands. This mixture of food and saliva is then pushed into the pharynx and esophagus. The esophagus is a muscular tube whose muscular contractions (peristalsis) propel food to the stomach.

 Muscles in the esophagus propel the bolus by waves of involuntary muscular contractions (peristalsis) of smooth muscle lining the esophagus  Stomach is lined with epithelial layer which secrete Gastric juice. Gastric juice contains hydrochloric acid, pepsinogen, lipase and mucus. Secretions are controlled by nervous (smells, thoughts, and caffeine) and endocrine signals. Mucus covers the inner layer of stomach and prevents the damage of HCl. HCl activates inactive enzyme pepsinogen and form pepsin which digests proteins. Small amount of lipase digests lipids.

 The small intestine is where final digestion and absorption occur. The small intestine is a coiled tube about 6 meters long. The surface area of the small intestine is increased by villi(fingerlike projections).  The upper part, the duodenum, is the most active in digestion. Secretions from the liver and pancreas are used for digestion in the duodenum. Epithelial cells of the duodenum secrete a watery mucus. The pancreas secretes digestive enzymes and stomach acid-neutralizing bicarbonate. The liver produces bile, which is stored in the gall bladder before entering the bile duct into the duodenum.

The liver produces and sends bile to the small intestine via the hepatic duct and vater point. Bile contains bile salts, which emulsify fats, making them susceptible to enzymatic breakdown. In addition to digestive functions, the liver plays several other roles: In addition to digestive functions, the liver plays several other roles: 1) detoxification of blood; 2) synthesis of blood proteins; 3) destruction of old erythrocytes and conversion of hemoglobin into a component of bile; 4) production of bile; 5) storage of glucose as glycogen, and its release when blood sugar levels drop; (stores ADEK vit.) 6) production of urea from amino groups and ammonia.

 Liver recieves blood from 2 different supplies. Blood rich in digested monomers comes from the vein from the intestine. (hepatic portal vein) Blood rich in digested monomers comes from the vein from the intestine. (hepatic portal vein) Blood rich in oxygen comes from the AORT(hepatic artery) Blood rich in oxygen comes from the AORT(hepatic artery)  The pancreas contains exocrine cells that secrete digestive enzymes(trypsinogen, amylase, lipase) into the small intestine and clusters of endocrine cells. The Langerhans islets secrete the hormones insulin and glucagon, which regulate blood glucose. Hepatic portal system, has capillary, vein capillary, vein structure

Mouth: mechanical and chemical digestion Stomach: mechanical and chemical digestion pepsinogen HCl pepsin pepsinogen HCl pepsin Duodenum: mechanical and chemical digestion Gall bladder: Fat bile fat droplet pancreas: fat droplet Lipase glycerol+fatty acid starch amylase maltose peptons Chymotrypsin peptides+ aa peptons Chymotrypsin peptides+ aa trypsin trypsin Intestine: Chemical digestion and absorption dipeptid erepsin aa Maltose maltase glucose sucrose sucrase glucose+fruc

Digestion of polymers Don’t forget vitamins, minerals, water can’t be digested and can’t give energy. They are absorbed without any change

Digestion of carbohydrates mouth duodenum Small intestine

Digestion of proteins stomach duodenum Small intestine

Digestion of fat duodenum

Absorption  Villi and micro villi increases absorption rate. Under the epithelial layer there are blood and lymph vessels in mucosa.

 Monosaccharides, aminoacids, minerals, water soluble vitamins pass to the blood vessels. They are carried to the liver by portal vein.  But fatty acid, glycerol and fat soluble vitamins pass to the lymphatic vessels from the epithelium. Lymphatic vessels mix with the circulatory system just before the heart.  Water is absorbed all the way through the digestive system. Minerals and vitamins are mainly absorbed from large intestine.  Undigested matter is thrown out by feces.

Pathway of the monomers glucose, fructose, galactose, minerals, water soluble vitamins, aminoacids glucose, fructose, galactose, minerals, water soluble vitamins, aminoacids  Mesenteric vein from intestine  Hepatic portal vein  Liver  Hepatic vein  İnferior vena cava  Right atrium Fatty acid, glycerol, fat soluble vitamins Fatty acid, glycerol, fat soluble vitamins  Lymphatic vessels  Thoracic duct  Left subclavian vein  Superior vena cava  Right atrium

Salivation is stimulated by the sight or smell of food. That response is an autonomic reflex, as is the act of swallowing following tactile stimulation at the back of the mouth. Many such autonomic reflexes coordinate activity in different regions of the digestive tract. Stretching the stomach with food, for example, stimulates increased activity in the colon, which can lead to the expulsion of feces. The stomach secretes a hormone called gastrin into the blood. Gastrin circulates in the blood until it reaches cells in the upper areas of the stomach wall, where it stimulates the secretions and movements of the stomach. secretin is one of several hormones that con­trol pancreatic secretion; specifically, secretin stimulates the pancreas to secrete a solution rich in bicarbonate ions. In response to the presence of fats and proteins in the chyme, the mucosa of the small intestine secretes cholecystokinin, a hormone that stimulates the gallbladder to release bile and the pancreas to release digestive enzymes.