digestion

Vocabulary terms and definitions focusing on the biological and chemical processes of human digestion, nutrient absorption, and metabolism according to the Fundamentals of Nutrition curriculum.

what is metabolism?

the use of the food by the body after digestion, which results in energy; it involves both building up (anabolism) and breaking down (catabolism) substances in the body.

what is digestion?

the breakdown of food in the body in preparation for absorption, occurring through two types of action—mechanical and chemical.

what is the gastrointestinal (gi) tract?

the body structures that participate in digestion, starting at the mouth and ending at the anus.

what is mechanical digestion?

the part of digestion that requires certain mechanical movements, such as chewing by the teeth, swallowing, and peristalsis.

what is peristalsis?

the rhythmic contraction of the muscular walls of the gastrointestinal tract that moves chyme along.

what is chemical digestion?

process where the composition of carbohydrates, proteins, and fats is changed through hydrolysis into nutrients that tissues can absorb and use.

what is hydrolysis?

the addition of water, resulting in the splitting or breaking down of food molecules into simpler compounds.

what is an enzyme?

organic substances that cause changes in other substances and act as catalysts to speed up chemical reactions without being changed themselves.

what is a catalyst?

a substance that causes another substance to react or speeds up a chemical reaction without itself being changed in the process.

what is saliva?

a secretion of the salivary glands that moistens food and begins chemical digestion.

what is salivary amylase?

also called ptyalin; the enzyme secreted by the salivary glands to act on complex carbohydrates (starch).

what is a bolus?

each mouthful of food that has been mixed with saliva and is ready to be swallowed.

what is the esophagus?

a $10 ext{in}$ muscular tube through which a bolus of food travels from the mouth to the stomach via peristalsis and gravity.

what is the cardiac sphincter?

also known as the lower esophageal sphincter, this muscle at the base of the esophagus prevents gastric reflux from moving back into the esophagus.

what is the fundus?

the upper part of the stomach where food enters before moving to the body of the stomach.

what is the pylorus?

the end of the stomach nearest the intestine where food mass is propelled forward in slow, controlled movements.

what is chyme?

the semiliquid food mass as it has been mixed with gastric juices in the stomach.

what is gastrin?

a hormone released by the stomach that increases the release of gastric juices when chyme causes distention in the pylorus.

what are gastric juices?

digestive secretions of the stomach containing hydrochloric acid, pepsin, and mucus.

what is pepsin?

an enzyme secreted by the stomach that is essential for the initial digestion of proteins; it is activated by hydrochloric acid.

what is rennin?

an enzyme present in children that acts on milk protein and casein.

what is gastric lipase?

a stomach enzyme in children that breaks the butterfat molecules of milk into smaller molecules.

what is the duodenum?

the first and smallest section of the small intestine where chyme first enters from the stomach.

what is the jejunum?

the middle section comprising about two-fifths of the small intestine.

what is the ileum?

the last part of the small intestine which connects to the large intestine.

what is secretin?

a hormone triggered by food in the small intestine that causes the pancreas to release sodium bicarbonate to neutralize the acidity of the chyme.

what is cholecystokinin (cck)?

a hormone produced by intestinal mucosal glands when fat enters, triggering the gallbladder to release bile.

what is bile?

a secretion produced by the liver and stored in the gallbladder that is essential for the emulsification of fats.

what is the pancreas?

a gland that secretes enzymes essential for digestion as well as insulin for glucose metabolism.

what are pancreatic proteases?

protein-splitting enzymes produced by the pancreas, including trypsin, chymotrypsin, and carboxypeptidases.

what is pancreatic amylase?

the enzyme secreted by the pancreas that is essential for converting starches (polysaccharides) into simple sugars.

what is pancreatic lipase?

also called steapsin; the enzyme secreted by the pancreas that reduces fats to fatty acids and glycerol.

what is lactase?

an enzyme secreted by the small intestine for the digestion of lactose into simple sugars.

what is maltase?

an enzyme secreted by the small intestine that is essential for the digestion of maltose.

what is sucrase?

an enzyme secreted by the small intestine to aid in the digestion of sucrose.

what are peptidases?

enzymes secreted by the small intestine that break down proteins into amino acids.

what is the colon?

the large intestine, measuring roughly $5 ext{ft}$ long and $3 ext{in}$ in diameter, whose primary function is to absorb water and salts.

what is absorption?

the passage of nutrients into the blood or lymphatic system after digestion is complete.

what is the lymphatic system?

a transport system where lymphatic vessels carry fat-soluble particles and large molecules into the bloodstream.

what are villi?

tiny fingerlike projections on the mucosal folds of the small intestine that increase surface area for maximum nutrient absorption.

what are capillaries?

tiny blood vessels within the villi that absorb glucose, fructose, galactose, amino acids, minerals, and water-soluble vitamins.

what are lacteals?

lymphatic vessels located in the villi of the small intestine that absorb glycerol, fatty acids, and fat-soluble vitamins.

what are feces?

solid waste from the large intestine comprising undigested fibers, bacteria, pigments, mucus, and water, stored in the rectum prior to elimination.

what is aerobic metabolism?

the process within cells where nutrients are combined with oxygen, also known as oxidation.

what is anaerobic metabolism?

the metabolic process that reduces fats without the use of oxygen.

what is the krebs cycle?

a series of enzymatic reactions that serve as the main source of cellular energy through the complete oxidation of carbohydrates, proteins, and fats.

what is anabolism?

the part of metabolism where released energy is used to build new substances from simpler ones, such as the formation of new body tissues.

what is catabolism?

the part of metabolism where released energy is used to reduce substances to simpler ones.

what is a kilocalorie (kcal)?

the unit used to measure the fuel value of foods; one kcal yields $4.184 ext{kilojoules}$.

what is a calorie?

the amount of heat needed to raise the temperature of $1 ext{kg}$ of water by $1 ^{\circ}\text{C}$.