Digestion of Carb,Pro,Fat

7/25/2019 Digestion of Carb,Pro,Fat

1/3

DIGESTION OF CARBOHYDRATES

Digestion of carbohydrate begins in the mouth, with the secretion of the enzyme salivary amylase from

the serous cells of the salivary gland. This enzyme breaks starch and glycogen into disaccharides. The mucous

cells of the salivary gland secrete a mucus, which causes the food to stick together, and acts as a lubricant to aid

in swallowing. The salivary glands are grouped into three categories: the parotid gland, submandibular glands,

and sublingual, all located near the mouth. The food (bolus) is forced into the pharyn by the tongue. !s the

food is swallowed, it moves into the esophagus (a straight collapsible tube), which essentially provides a

passageway from the pharyn to the stomach. The mucous glands of the esophagus secrete mucus to aid in

moistening and lubricating the bolus. The bolus passes through the cardiac sphincter, into the first section of the

stomach. The stomach is divided into several regions: the cardiac region, body region, fundic region, and

pyloric region. The stomach works to mi and churn the food, which aids in further digestion of carbohydrates.

!t this point, the bolus is converted into a semifluid paste of bolus and gastric "uices called chyme.

The chyme then travels through the pyloric sphincter into the first section of the small intestines. The

small intestines is divided into three sections: the duodenum, "e"unum, and ileum. The ma"ority of digestion of

carbohydrates takes place in the small intestines. !s the chyme moves into the duodenum, an enzyme called

pancreatic amylase is released through the pancreatic duct. This enzyme splits molecules of starch and glycogen

into disaccharides.

The liver plays an important role in the several metabolic activities. #t is responsible for changing

glycogen to glucose to increase blood glucose or converting glucose to glycogen, thereby decreasing blood

glucose. The liver also converts other noncarbohydrates into glucose, if needed.

The interior wall of the small intestines is covered with tiny pro"ections called the villi. These

pro"ections increase the surface area of the intestines and play an important part in the process of absorption of

the nutrients. The epithelial cells of the villi contain even smaller etensions, called microvilli. $mbedded in

the microvilli are digestive enzymes which are needed to further break down carbohydrates. The include

sucrase, maltase, and lactase, which break down the disaccharides into monosaccharide. These monosaccharide

are then absorbed by the villi and enter the blood capillaries to be transported to other parts of the body.


2/3

DIGESTION OF LIPIDS

!s food containing fat travels through the digestive tract, digestion takes place in different locations.

The food containing fats essentially follow the same pathway as carbohydrate foods, with chemical digestion

primarily beginning in the stomach.

The surface of the inner lining of the stomach contains openings called gastric glands, which are made

up of three types of cells: mucous cells, chief cells, and parietal cells. ! hormone called gastrin stimulates the

gastric glands to secrete their fluids. %astric enzymes are secreted by the chief cells, while hydrochloric acid is

secreted by the parietal cells. The combination of mucus, hydrochloric acid and enzymes is referred to as gastric

"uices. The gastric "uices contain small amounts of gastric lipase, which begin the breaking down of specific

lipids. ! hormone called somatostatin inhibits the release of acid. !s the stomach churns, it mies the bolus and

converts it into a semifluid referred to as chyme.

The liver also plays an important role in lipid metabolism by oidizing fatty acids, synthesizing

lipoproteins, phospholipids, and cholesterol& and converting portions of carbohydrates and protein molecules

into fat molecules.

#f fats are not being digested well enough in the stomach the hormone cholecystokinin slows gastric

motility. !s the chyme passes into the duodenum, cholecystokinin stimulates the gallbladder to release a

substance called bile through the common bile duct. The function of bile is to emulsify fats, or break them into

smaller droplets. This allows the small droplets of fat to be digested more effectively. 'holecystokinin also

stimulates the release of pancreatic "uices, which contains pancreatic lipase. This enzyme initiates the breaking

down of lipids. The cells of the small intestines release intestinal gastrin, which increases gastric secretions. The

mucosal cells release an enzyme called intestinal lipase, which splits fats into fatty acids and glycerol. The fatty

acids are then dissolved in the epithelial cell membranes of the villi and diffuse into them. ome fatty acids may

be absorbed directly into the blood capillary, without being converted back into fat, while others are

incorporated into chylomicrons (large molecules of lipoprotein) for transport.


3/3

DIGESTION OF PROTEIN

!s food containing protein enters the mouth, mucus is secreted to bind the particles together. The food

then travels down the esophagus and more mucus is secreted by the wall of the esophagus.

The chief cells located in the stomach secrete gastric "uices containing an enzyme precursor called

pepsinogen. !s it comes in contact with hydrochloric acid, it is converted into an active form referred to as

pepsin. This begins the process of chemical digestion of dietary protein. ! hormone called gastrin is

responsible for stimulating the secretion of gastric "uices. !fter the food is mied and churned in the stomach, it

is converted into chyme.

The liver plays a vital role in protein metabolism by deaminating amino acids and forming urea

nitrogen. #t also is responsible for synthesizing certain blood proteins and converting certain amino acids to

other amino acids.

The chyme moves into the duodenum and enzymes begin to work on the protein. The hormone called

intestinal gastrin stimulates the gastric glands to increase secretion. hen protein reaches the duodenum, a

hormone called cholecystokinin is released from the intestinal walls, which stimulates the release of pancreatic

"uice. The pancreatic "uice contains three protein splitting enzymes in inactive formscalled trypsinogen,

chymotrypsinogen, and procarboypeptidase. *nce trypsinogen comes in contact with an enzyme called

enterokinase, which is secreted by the mucosal cells of the small intestines, then trypsin is activated. The

presence of trypsin then activates the inactive procarboypeptidase and chymotrypsinogen, and they are

converted into chymotrypsin and carboypeptidase. The enzymes are then able to work on the protein. The

mucosal cells secrete an enzyme called peptidase, which splits peptide bonds into amino acids to allow for

digestion. +rotein digestion is completed in the small intestines. maller particles of amino acids are absorbed

into the villi, and are carried away by the blood.

Documents

Digestion of Carb,Pro,Fat