Digestion is the breakdown of large, complex organic molecules into smaller components that can be used by the body.Molecules need to be small enough to diffuse across plasma membranes.
Steps of digestion Ingestion – this is the consumption of or taking in of nutrients. Digestion – the chemical breakdown of large organic molecules into smaller components by enzymes. Absorption – the transport or delivery of digested nutrients to body tissues. Assimilation-the conversion of absorbed food into the substance of the body. Egestion – the elimination of food waste materials from the body.
EsophagusApproximately 10” longFunctions include:1.Secrete mucus2.Moves food from the throat tothe stomach using musclemovement called peristalsisIf acid from the stomach gets inhere that’s heartburn.
STOMACHJ-shaped muscular bag that stores thefood you eat, breaks it down into tinypieces.Mixes food with digestive juices thatcontain enzymes to break downproteins and lipids.Acid in the stomach kills bacteria.Food found in the stomach is calledchyme.
Small intestines are roughly7 meters longLining of intestine walls hasfinger-like projectionscalled villi, to increasesurface area.The villi are covered inmicrovilli which furtherincreases surface area forabsorption.
SMALL INTESTINEThe majority of chemicaldigestion occurs in the firstof three sections of thesmall intestine known as theduodenum.This section also contains anopening from the bile ductand pancreatic duct throughwhich bile and pancreaticenzymes enter the smallintestine
Small Intestine Food enters the small intestine as a semi- solid mixture known as chyme. The chyme is acidic due to the HCl in the stomach so it needs to be neutralized. The presence of chyme in the small intestine triggers the conversion of prosecretin into secretin which is absorbed into the blood stream and carried to the pancreas
Large intestineAbout 5 feet longAccepts what smallintestines don’t absorbRectum (short termstorage which holdsfeces before it isexpelled).
ANUS Thehuman anus is the external opening of the rectum.Its closure is controlled by sphincter muscles. Feces are expelled from the body through the anus during the act of defecation, the primary function of the anus.
Accessory Organs• Salivary gland• Liver• gall bladder• pancreas
Salivary glands parotid glands - produce a serous, watery secretion. submaxillary (mandibular) glands - produce a mixed serous and mucous secretion. sublingual glands - secrete a saliva that is predominantly mucous in character.
Liver The liver is a large accessory organ of the digestive system that is constantly producing a fluid known as bile. Bile is stored in the gall bladder until it is needed in the small intestine.
Liver and Gall Bladder The presence of lipids in the small intestine trigger the release of the hormone cholecystokinin (CCK) which triggers the release of bile from the gall bladder. Bile contains bile salts that emulsifies fats which means it breaks them into smaller droplets so they can be digested.
Pancreas The pancreas is an accessory organ of the digestive system. It releases chemicals to aid in digestion. Secretin will stimulate the pancreas to release a solution containing bicarbonate ion into the small intestine where it will neutralize the acidic chyme and raise the pH from 2.5 to 9.0. This inactivates the pepsin.
Pancreas and Carbohydrates Amylase enzymes are released from the pancreas that break large carbohydrate chains into small chains called disaccharides. Then the small intestine releases disaccharide enzymes which break those small chains into individual sugars.
Pancreas & Proteins Trypsinogen, a protein- digesting enzyme is released into the small intestine where it is convertes into trypsin and it breaks down large protein chains into smaller chains. The final step in protein digestion occurs with the release of erepsins from the pancreas and they break the smaller chains into individual amino acids.
ABSORPTION OF MATERIALThe passage of digested food from the digestive tract intothe tissue or into the blood and lymph is calledabosrption.
Structure of the Villus Each villus contains a capillary network along with a lacteal. End products of protein and carbohydrate digestion enter the capillary network. End products of fat digestion are absorbed into the lacteal. The lacteal is a vessel of the lymphatic system.