Ch.3 digestion, absorption, and metabolism

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Digestion, Absorption, and Metabolism," discusses how food is digested, how nutrients form foods are absorbed into the body and transported to the cells where they are broken down to provide energy or used to synthesize structural or regulatory molecules, and finally how wastes are removed. This chapter provides an overview of metabolism that serves as a launching pad for the more detailed metabolism information presented in subsequent chapters.

atom

the smallest unit of an element that still retains the properties of that element

element

a substance that cannot be broken down into products with different properties

chemical bond

the force that holds an atom together

molecule

a group of two or more atoms of the same or different elements bonded together

cells

the smallest unit of life
the basic structural and functional unit of plant and animal life

organ

discrete structures composed of more than one tissue that perform a specialized function.

organ system

a group of organs that work together

hormones

chemical messengers that are produced in one location, released into the blood, and elicit responses at other locations in the body.

digestion

the process of breaking food into components small enough to be absorbed into the body

absorption

the process of taking substances into the interior of the body

feces

body waste, including unabsorbed food residue, bacteria, mucus, and dead cells which is excreted from the gastrointestinal tract by passing through the anus.

gastrointestinal tract

a hollow tube consisting of the mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anus in which digestion and absorption of nutrients occurs

transit time

the time between ingestion of food and the elimination of the solid waste from that food

mucosa

the layer of tissue lining the GI tract and other body cavities

mucus

a viscous material produced by glands in the GI tract and other parts of the body. It acts to lubricate, moisten, and protect cells from harsh environments

enzyme

a protein molecule that accelerates the rate of a chemical reaction without itself being changed

saliva

a watery fluid produced and secreted into the mouth by the salivary glands. It contains lubricants, enzymes, and other substances.

salivary amylase

an enzyme secreted by the salivary glands that breaks down starch

iysozyme

an enzyme in saliva, tears, and sweat that is capable of destroying certain types of bacteria

pharynx

a funnel-shaped opening that connects the nasal passages and mouth to the respiratory passages and esophagus. It is a common passageway for food and air and is responsible for swallowing.

epiglottis

a piece of elastic connective tissue at the back of the throat that covers the opening of the passageway to the lungs during swallowing.

esophagus

a portion of the GI tract that extends from the pharynx to the stomach

peristalis

coordinated muscular contractions that move food through the GI tract

sphincter

a muscular valve that helps control the flow of materials in the GI tract

chyme

a mixture of partially digested food and stomach secretions

pepsinogen

an inactive protein digesting enzyme produced by gastric glands and activated to pepsin by acid in the stomach

pepsin

a protein digesting enzyme produced by the gastric glands. It is secreted in the gastric juice in an inactive form and activated by acid in the stomach

gastrin

a hormone secreted by the stomach mucosa that stimulates the secretion of gastric juice

villi(villus)

finger-like protrusions of the lining of the small intestine that participate in the digestion and absorption of nutrients

microvilli or brush border

minute brush-like projections on the mucosal cell membrane that increase the absorptive surface area in the small intestine

lacteal

a small lymph vessel in the intestine that absorbs and transports the products of fat digestion.

segmentation

rhythmic local constrictions of the intestine that mix food with digestive juices and speed absorption by repeatedly moving the food mass over the intestinal wall

pancreatic amylase

starch digesting enzyme produced in the pancreas and released into the small intestine

protease

a protein-digesting enzyme

liapese

a fat-digesting enzyme

bile

a substance made in the liver and stored in the gallbladder. It is released into the small intestine to aid in fat digestion and absorption

simple diffusion

the movement of substances from an area of higher concentration to an area of lower concentration. No energy is required.

osmosis

the passive movement of water across a semipermeable membrane in a direction that will equalize the concentration of dissolved substances on both sides.

facilitated diffusion

the movement of substances across a cell membrane from an area of lower concentration to an area of lower concentration with the aid of a carrier molecule. No energy is required.

antigen

a foreign substance (always a protein) that, when introduced into the body, stimulates an immune response

antibody

a protein produced by cells of the immune system that destroys or inactivates foreign substances in the body

allergen

a substance that causes an allergic reaction

gastroesophageal reflux disease (GERD)

a chronic condition in which acidic stomach contents leak back up into esophagus, causing pain and damaging the esophagus

peptic ulcer

an open sore in the lining of the stomach, esophagus, or small intenstine

enteral or tube-feeding

a method of feeding by providing a liquid diet directly to the stomach or intestine through a tube placed down the throat or through the wall of the GI tract

total parenteral nutrition (TPN)

a technique for nourishing an individual by providing all needed nutrients directly into the circulatory system.

atrophic gastritis

an inflammation of the stomach lining that causes a reduction in the stomach acid and allows bacterial overgrowth

hepatic portal circulation

the system of blood vessels that collects nutrient-laden blood from the digestive organs and delivers it to the liver.

lymphatic system

the system of vessels, organs, and tissues that drains excess fluid from the spaces between cells, transports fat-soluble substances from the digestive tract, and contributes to immune

capillary

a small, thin-walled blood vessel where the exchange of gases and nutrients between blood and body cells occurs.

veins

a vessel that carries blood toward the heart

artery

a vessel that carries blood away from the heart

hepatic portal vein

the vein that transports blood from the GI tract to the liver

cell membrane

the membrane that surrounds the cell contents

selectively permeable

describes a membrane or barrier that will allow some substances to pass freely but will restrict the passage of others

cytosol

the liquid found within cells

organelles

cellular organs that carry out specific metabolic functions

mitochondrion (mitochondria)

cellular organelle that is responsible for providing energy in the form of adenosine triphoshpate (ATP) for cellular activities.

metabolic pathway

a series of chemical rections inside a living organism that results in the transformation of one molecule into another

coenzyme

a small organic molecule (not a protein but sometimes a vitamin) that is necessary for the proper functioning of many enzymes

catabolic pathways

the biochemical reactions by which substances are broken down into simpler molecules releasing energy

ATP (adenosine triphosphate)

the high-energy molecule used by the body to perform energy requiring activities

anabolic pathways

energy-requiring biochemical reactions in which simpler molecules are combined to form more complex substances

cellular respiration

the reactions that break down glucose, fatty acids, and amino acids in the presence of oxygen to produce carbon dioxide, water, and energy in the form of ATP

acetyl-CoA

a metabolic intermediate formed during the breakdown of glucose, fatty acids, and amino acids. It is a two-carbon compound attached to a molecule of CoA

citric acid cycle

also known as the Krebs cycle or the tricarboxylic acid cycle, this the stage of cellular respiration in which two carbons from acetyl-CoA are oxidize, producing two molecules of carbon dioxide

electron

high-energy particle carrying a negative charge that orbits the nucleus of an atom

electron transport chain

the final stage of cellular respiration in which electrons are passsed down a chain of molecules to oxygen to form water and produce ATP

oxidized

refers to a compound that has lost an electron or undergone a chemical reaction with oxygen

reduced

refers to a substance that has gained an electron

nephron

the functional unit of the kidney that performs the job of filtering the blood and maintaining fluid balance

glomerulus

a ball of capillaries in the nephron that filters blood during urine formation

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