Nutrition 2114 Ch. 3 (Digestion, Absorption and Transport)

Digestion in the Large Intestine

(Chemical) Some remaining food residues are digested by bacteria. (Absorption) Salts, water and some vitamins reabsorbed. (Propulsion) compacts waste into feces.

Digestion in the Rectum

(Elimination) Feces are temporarily stored before voluntary release through the anus.

Digestion in the Small Intestine

(Mechanical and Propulsion) Segmentation mixes chime with digestive juices: peristaltic waves move it along the tract. (Chemical) Digestive enzymes from pancreas and brush border digest most classes of food. (Absorption) Nutrients are absorbed into blood and lymph through enterocytes.

Digestion in the Stomach

(Mechanical) This process mixes and churns the bolus with acid, enzymes, and gastric fluid into a liquid called chime. (Chemical) Pepsin begins digestion of proteins. (Absorption) A few fat-soluble substances are absorbed through the stomach wall.

Digestion in Pharynx and Esophagus

(Propulsion) swallowing and peristalsis move the bolus from the mouth to the stomach.

Mechanical Digestion

Breaking down food by chewing, grinding, squeezing and moving food through the GI tract by peristalsis and segmentation.

Chemical Digestion

Breaking down food through enzymatic reactions

Epiglottis

Cartilage at the back of the tongue that closes off the trachea during swallowing (so food doesn't go down "the wrong pipe")

Goblet Cells

Cells throughout the GI tract that secrete mucus.

Mastication

Chewing food

Salivary Glands

Cluster of glands located underneath and behind the tongue that release saliva in response to the sight, smell and taste of food.

Substrate

Enzymes are compatible only with a specific compound or nutrient - referred to as a substrate. Each enzyme have a binding site that only fits certain substrates. *A substrate is a substance or compound that is altered by an enzyme.

Elimination

Excretion of undigested and unabsorbed food through the feces.

Extrinsic vs. Intrinsic Nerves

Extrinsic nerves originate in the brain/spinal cord. Intrinsic nerves are woven into the linings of the esophagus, stomach and small and large intestines.

Rectum

Final 8-inch portion of the large intestine.

What are accessory organs?

Food does not pass through them during digestion, but they are still very important to digestive processes - contribute digestive secretions (saliva, bile and enzymes) that help with breakdown/transport of nutrients.

Digestion in the Mouth

Food enters the GI tract via the mouth. (Mechanical) Mastication tears, shreds, and mixes food with saliva to form a bolus. (Chemical) Salivary amylase begins carbohydrate breakdown.

Celiac Disease

Genetic disease that causes damage to the small intestine when gluten containing foods are eaten.

Crypts

Glands at the base of the villi: they contain stem cells that manufacture young cells to replace the cells of the villi when they die. They secrete intestinal juice.

Gastric Pits

Indentations or small pits in the stomach lining where the gastric glands are located: gastric glands produce gastric juices.

Gastroenteritis

Inflammation of the lining of the stomach and intestines; also known as stomach flu. Due to the lower esophageal sphincter (LES) not closing properly and HCI flows back into the esophagus, irritating the lining.

What makes the large intestine different from the small intestine?

It is much shorter, does not have villi or microvilli, does not produce digestive enzymes and is not tightly coiled.

First organ to receive water soluble nutrients absorbed through the intestines

Liver

Where are most digestive enzymes secreted?

Most are produced in the pancreas - although they are also secreted all along the GI tract.

Segmentation

Muscular contractions of the small intestine that move food back and forth, breaking the mixture into smaller and smaller pieces and combining it with digestive juices. (occurs in the small and large intestines)

Salivary Glands (helping in digestion)

Produce saliva, a mixture of water, mucus, enzymes and other chemicals.

Digestion in the Liver

Produces bile to digest fats

Pancreas in Digestion

Produces digestive enzymes and bicarbonate ions that are released into the small intestine through the pancreatic duct.

Flatulence

Production of excessive gas in the stomach of the intestines.

What does the GI barrier regulate?

Regulates which nutrients enter the body based on need and which nutrients pass through the GI tract unabsorbed.

Function of the endocrine glands in the GI tract

Secrete hormones when a stimulus is present and stop secreting the hormones when the stimulus is gone.

Secretion pathway and action of Mucus

Secreted by gastric glands into stomach. Action to lubricate and coat the internal mucosa to protect it from chemical or mechanical damage.

Secretion pathway and action of Mucus

Secreted by intestinal glands into small intestine. Action to protect the intestinal cells.

Secretion pathway and action of Bicarbonate Ions

Secreted by pancreas through the pancreatic duct into the small intestine. Action to raise pH and neutralize stomach acid.

Secretion pathway and action of Hydrochloric acid (HCI)

Secreted by parietal cells into stomach. Action includes denaturing proteins, activates pepsinogen -- pepsin.

Secretion pathway and action of Intrinsic factor

Secreted by parietal cells into stomach. Action includes needed for vitamin B12 absorption.

Secretion pathway and action of saliva

Secreted by salivary glands into mouth. Action includes moistening food, eases swallowing and contains the enzyme salivary amylase.

Describe salivary amylase (including organ/gland secreted from, action and nutrient affected)

Secreted by salivary glands, begins the digestions of starch and affects carbohydrates

Describe Procarboxypeptidase -- Carboxypeptidase (including organ/gland secreted from, action and nutrient affected)

Secreted by the Pancreas, Hydrolyzes the carboxyl end of the peptide, releasing the last amino acid in the peptide chain and affects proteins.

Describe Chymotrypsinogen -- Chymotrypsin (including organ/gland secreted from, action and nutrient affected)

Secreted by the Pancreas, catalyzes the hydrolysis of proteins in the small intestine into polypeptides and amino acids and affects proteins.

Secretion pathway and action of Intestinal juice

Secreted by the crypts into small intestine. Action to contain enzymes that digest carbohydrate, protein and lipid.

Secretion pathway and action of Bile

Secreted by the liver into the gallbladder for storage; released from gallbladder into the small intestine through the common bile duct. Action to emulsify large globules of lipid into smaller droplets.

Describe Trypsinogen -- trypsin (including organ/gland secreted from, action and nutrient affected)

Secreted by the pancreas, catalyzes the hydrolysis of proteins in the small intestine to form small polypeptides, affects proteins

Describe Pancreatic Amylase (including organ/gland secreted from, action and nutrient affected)

Secreted by the pancreas, digests starch and affects carbohydrates

Describe Pancreatic Lipase (including organ/gland secreted from, action and nutrient affected)

Secreted by the pancreas, digests triglycerides and affects lipids (fats)

Describe Depeptidase (including organ/gland secreted from, action and nutrient affected)

Secreted by the small intestine, digests dipeptides, affects proteins

Describe Lactase (including organ/gland secreted from, action and nutrient affected)

Secreted by the small intestine, digests lactose, affects carbohydrates

Describe Maltase (including organ/gland secreted from, action and nutrient affected)

Secreted by the small intestine, digests maltose, affects carbohydrates

Describe Lipase (including organ/gland secreted from, action and nutrient affected)

Secreted by the small intestine, digests monoglycerides, affects lipids (fats)

Describe sucrase (including organ/gland secreted from, action and nutrient affected)

Secreted by the small intestine, digests sucrose, affects carbohydrates

Describe Tripeptidase (including organ/gland secreted from, action and nutrient affected)

Secreted by the small intestine, digests tripeptides, affects proteins

Describe Gastric lipase (including organ/gland secreted from, action and nutrient affected)

Secreted by the stomach, begins digestion of lipids (fats) and affects lipids

Describe Pepsinogen -- Pepsin (including organ/gland secreted from, action and nutrient affected)

Secreted by the stomach, begins the hydrolysis of polypeptides and affects proteins.

Saliva

Secretion from the salivary glands that softens and lubricates food, and begins the chemical breakdown of starch.

Mucus

Secretion produced throughout the GI tract that moistens and lubricates food and protects membranes

Villi

Small, fingerlike projections that line the interior of the small intestine. Increase surface area to maximize absorption and help mix partially digested chyme with intestinal secretions.

Chief Cells

Specialized cells in the stomach that secrete an inactive protein-digesting enzyme called pepsinogen.

Parietal Cells

Specialized cells in the stomach that secrete the gastric juices hydrochloric acid and intrinsic factor.

Pyloric Sphincter

Sphincter between the stomach and small intestine, it relaxes and chyme gradually enters the small intestine. Prevents chyme from exiting the stomach too soon, and blocks the intestinal contents from returning to the stomach.

Gallstones

Stones formed from the cholesterol in the gallbladder or bile duct.

Gallbladder in Digestion

Stores bile before releases into the small intestine through the bile duct.

Enzymes

Substances, mostly proteins, that increase the rate of chemical changes or catalyze chemical reactions; also called biological catalysts.

Hemorrhoid

Swelling in the veins of the rectum and anus.

Diarrhea

The abnormally frequent passage of watery stools.

Pepsin

The active protease that begins the digestion of proteins in the stomach.

Pharynx

The area of the GI tract between the mouth and the esophagus; also called the throat.

Gastroesophageal Reflus Disease (GERD)

The backward flow of stomach contents into the esophagus due to improper functioning of the LES, resulting in heartburn.

Lumen

The channel of inside space of a vessel such as the intestine of artery. The circular folds cause chyme to spiral forward through the small intestine (increasing exposure to the villi).

Peristalsis

The forward, rhythmic motion that moves food through the digestive system. Peristalsis is a form of mechanical digestion because it influences motion, but it does not add chemical secretions. (Occurs in the esophagus, stomach and small intestine)

Pepsinogen

The inactive protease secreted by the chief cells in the stomach: this enzyme is converted to the active form called pepsin in the presence of HCI.

Constipation

The infrequent passage of dry, hardened stools.

Liver

The largest organ in the body, located in the upper abdomen. Plays an essential role in carbohydrate metabolism, produces proteins and manufactures bile salts used to digest fats. This organ aids in digestion by secreting biles. Also removes/degrades toxins and excess hormones from circulation.

Describe the circular folds in the small intestine?

The lining of the small intestine is heavily folded, resulting in increased surface area for the absorption of nutrients.

Small Intestine

The long coiled chamber that is the major site of food digestion and nutrient absorption.

Large Intestine

The lowest portion of the GI tract, where water and electrolytes are absorbed and waste is eliminated.

Upper Esophageal Sphincter

The muscular ring located at the top of the esophagus.

Lower Esophageal Sphincter (LES)

The muscular ring located between the base of the esophagus and the stomach.

Anus

The opening of the rectum, or the end of the GI tract

Passive diffusion

The process of absorbing nutrients freely across the cell membrane from an area of high to low concentration. (water, small lipids, few minerals and vitamin C are absorbed through passive diffusion)

Active Transport

The process of absorbing nutrients with the help of a carrier molecule and energy expenditure; from an area of low TO high concentration. (glucose and amino acids use active transport)

Facilitated Diffusion

The process of absorbing nutrients with the help of a carrier molecule. Does not require energy and transport is from high to low concentration. (fructose is a nutrient that needs carrier to move across membrane)

Transport

The process of moving absorbed nutrients throughout the body through the circulatory and lymph systems.

Absorption

The process of moving nutrients from the GI tract into the circulatory system.

Enterohepatic Circulation

The process of recycling bile from the large intestine back to the liver to be reused during fat digestion.

Propulsion

The process that moves food along the gastrointestinal tract during digestion.

Chyme

The semiliquid, partially digested food mass that leaves the stomach and enters the small intestine.

Ileocecal Valve

The sphincter that separates the small intestine from the large intestine.

Hepatic Vein

The vein that carries the blood received from the hepatic portal vein away from the liver.

Emulsify

To break large fat globules into smaller droplets.

Ferment

To metabolize sugar into carbon dioxide and other gases. Bacteria ferment some of the undigested and unabsorbed carbohydrates into simpler compounds (methane gas, carbon dioxide and Hydrogen)

Esophagus

Tube that connects the mouth to the stomach.

Stool

Waste that is produced in the large intestine, also called feces.

3 segments of the large intestine

cecum, colon and rectum

6 Organs that make up the digestive tract

mouth, pharynx, esophagus, stomach, small intestine and large intestine

4 accessory organs of digestion

salivary glands, liver, gallbladder and pancreas

3 segments of the small intestine

the duodenum, jejunum and ileum

Ulcer

A sore or erosion of the stomach or intestinal lining.

Hydrochloric Acid (HCI)

A strong acid produced in the stomach that aids in digestion. Has the ability to change the acidity of digestive fluids to a pH close to 1.5 and this acidic pH denatures protein. Mucus acts as a barrier between stomach lining and HCI

Lymphatic System

A system of interconnected spaces and vessels between the tissues and organs that contains lymph and circulates fat-soluble nutrients throughout the body.

Endocytosis

A type of active transport in which the cell membrane forms an indentation, engulfing the substance to be absorbed.

Colon

Another name for the large intestine. Chyme comes here after the cecum.

What are the three conditions that must be present for enzymes to catalyze hydrolytic reactions?

1) The compatible enzyme and nutrient are both present. 2) The pH of the surrounding environment falls in the correct range. 3) The temperature of the environment is optimal.

Stomach

A J-Shaped muscular organ that mixes and churns food with digestive juices and acid to form chyme.

Hydrolysis

A chemical reaction that breaks the bond between two molecules (all digestible carbs, fats, proteins and alcohol) with water. A hydroxyl group is added to one molecule and a hydrogen ion is added to the other molecule. Produces single molecules small enough to be absorbed by the intestines.

Ulcerative Colitis

A chronic inflammation of the colon or large intestine that results in ulcers forming in the lining of the colon.

Sphincter

A circular ring of muscle that opens and closes in response to nerve input.

Proteases

A classification of enzymes that catalyze the hydrolysis of protein

Crohn's Disease

A form of ulcerative colitis in which ulcers form throughout the GI tract and not just in the colon.

Enterogastrones

A group of GI tract hormones, produced in the stomach and small intestine, that controls gastric motility and secretions.

Gastric Inhibitory Peptide (GIP)

A hormone produced by the small intestine that slows the release of chyme from the stomach.

Peptide YY

A hormone produced in the small intestine that reduces hunger.

Ghrelin

A hormone produced in the stomach that stimulate hunger.

Cholecystokinin (CCK)

A hormone released by the duodenum that stimulates the gallbladder to release bile and the pancreas to release lipase.

Gastrin

A hormone released from the stomach that stimulates the release of acid.

Secretin

A hormone secreted from the duodenum that stimulates the stomach to release pepsin, the liver to make bile and the pancreas to release digestive juices.

Pancreas

A large gland located behind the stomach that releases digestive enzymes after a meal. The pancreas also secretes the hormones insulin and glucagon, which control blood glucose. Also produces and secretes digestive enzymes into the small intestine.

Hepatic Portal Vein

A large vein that connects the intestinal tract to the liver and transports newly absorbed, water soluble nutrients (including carbohydrates, amino acids and water soluble vitamins) .

Gastrointestinal (GI) Tract

A long tube comprised of the organs of the digestive tract. It extends from the mouth through the esophagus, stomach, and small and large intestines to the anus.

pH

A measure of the acidity or alkalinity of a solution. Scale is from 0 to 14, 7 is considered neutral. pH lower than 7 is considered acidic and one higher than 7 is basic. (lower number on scale = greater concentration of hydrogen ions).

Bicarbonate

A negatively charged alkali ion produced from biocarbonate salts; during digestion, bicarbonate ions are released from the pancreas to neutralize HCI in the duodenum.

Gallbladder

A pear-shaped organ located behind the liver. The gallbladder stores bile produced by the liver and secretes the bile through the common bile duct into the small intestine.

Cecum

A pouch at the beginning of the large intestine that receives waste from the small intestine. Marks the beginning of the large intestine.

Digestion

A process that breaks down food into individual molecules small enough to be absorbed through the intestinal wall.

Bile

A secretion produced in the liver and stored in the gallbladder. It is released through the common bile duct into the duodenum to digest dietary fat.

Bolus

A soft mass of chewed food.

Enterocytes

Absorptive epithelial cells that line the walls of the small intestine. They have microvilli on them.

Microvilli

Also known as "brush border," are tiny projections on the end of the villi in the small intestine. They trap and absorb nutrients into the cells to be transported throughout the body.

Irratable bowel Syndrome (IBS)

An intestinal disorder resulting in abdominal discomfort, pain, diarrhea, constipation and bloating; the cause is unknown.