CH 3: DIGESTION AND ABSORPTION

Digestion

Process of breaking foods down into nutrients to prepare for absorption so the body can use them to build and nourish cells

Chemosenses

o   Olfactory Cells (smell)

o   Gustatory Cells (taste)

Contribute to flavor and Cephalic Phase Responses

Cephalic Phase Responses

• Sight, smell, taste, sound, and thought of food

• Causes reactions in the body before food enters mouth

GI TRACT

• Flexible muscular tube from mouth to anus

• Ingestion, Secretion, Digestion, Absorption, and Elimination

• Esophagus, stomach, small intestine, large intestine

• Accessory organs: Salivary glands, liver, pancreas, gallbladder

SEROSA

• Outer surface

• Under serosal layer, LONGITUDINAL MUSCLE and CIRCULAR MUSCLES help with the PHYSICAL BREAKDOWN of food

LUMEN

• Inner lumen lined with MUSCOSA

• Muscosa of mouth, stomach, and small intestines have tiny glands that secrete digestive juices CHEMICAL BREAKDOWN

SPHINCTERS

• gates or garage door that work with a motion sensor

• Muscular valves that control the passage of food

• ex. illial cecum valve -  prevents food from moving backwards (NO BACKFLOW

Physical Breakdown

• Peristalsis

  • longitudinal muscles relax, while circular muscles contract which breaks down food bolus, pushes digestive contents along

• Stomach Action

  • Circular, longitudinal, and diagonal muscle

• Segmentation

  • Contractions by circular muscles that breaks down foods and mixing with digestive juices

• Sphincter Contractions

  • Open and close passageways, prevents reflux and controls passage of contents

LIVER (ACESSORY)

• Secretes bile

• Detox & metabolic transformations, storage center

GALLBLADDER (ACESSORY)

• Stores and releases bile

• Sits under the liver

PANCREAS

• Secretes bicarbonate (neutralize acidic contents)

• Secretes digestive enzymes

UPPER esophageal sphincter

keeps food from going back into mouth

LOWER esophageal sphincter (cardiac sphincter)

• Keeps food from stomach going back up from stomach

  • Prevents reflux / heartburn

Pyloric sphincter

regulates flow of digested food into small intestine

SMALL INTESTINE

Chyme mixes with digestive juices from gallbladder and pancreas

o   3 SECTIONS = Duodenum, jejunum, ileum

o   SECRETIONS = Bicarbonate (neutralizes stomach acid) – from pancreas

o   Most nutrients are absorbed here

o   Has folds, vili, microvilli that allows efficient absorption

o   Fat soluble nutrients go into lymph

o   Other nutrients go directly into blood

LARGE INTESTINE

o   Ileocecal valve controls chyme flow

o   Absorption and elimination

o   Rectum, anus

ENTEROHEPATIC CIRCULATION

• Recycling process for bile

• First produced by liver, stored released by gallbladder into small intestine

• Bile salts are reabsorbed and sent back to liver for reuse

• Fiber binds with bile and prevents some of its reabsorption, non absorbed eliminated in fece

PASSIVE TRANSPORT

Nutrients and small fat molecules will move easily through the membrane

FACILITATED DIFFUSION

Some molecules (ex. water soluble vitamins) need assistance into cell

ACTIVE TRANSPORT

• Some molecules (ex. amino acids) need a lot of assistance into cells

• Requires energy to work

ENDOCYTOSIS

Cells use cell membrane to engulf cells

VASCULAR SYSTEM

• Portal vein = blood rich in absorbed water soluble nutrients from the GO tract to the liver

• Hepatic vein = takes blood from the liver to the heart

LYMPHATIC SYSTEM

• Lacteals = lymphatic vessels of the intestine that absorb fat soluble nutrients and pass them to the lymphatic system, muscular contractions

• Lymph = clear yellowish fluid without red blood cells or platelets  

GASTRIN

secreted by stomach, stimulates HCL, pepsinogen release, and INCREASE motility

SECRETIN

Secreted by duodenum

• Stimulates pancreatic juices release

• Signal pancreatic juices to release, changes based on content of diet

• Pancreas never damaged by enzymes it produced because it doesn’t get activated until released

CHOLECYSTOKININ (cck)

targets gal bladder to contract, target pancreas to secrete enzymes and slows gastric emptying

GASTRIC INHIBITORY PEPTIDE (gip)

• released by intestinal mucosal cells, slows gastric secretions and motility, increases emptying. Which increases insulin from pancreas used in glucose utilization

• INSULIN NOT USED IN GI TRACT, USED THROUGHOUT BODY

Diverticulosis

Pouches along colon; high fiber diet reduces formation

Heartburn / Gastroesophageal Reflux (GER)

• Backward flow of stomach into esophagus

• Antacids and acid controls

• Smaller meals, less fat, not lying down right after meals

• Improved with weight lose

Irritable Bowel Syndrome (IBS)

• Disorder, functional disorder because there is no structural abnormality

Ulcers

• Bacterial cause (Helicobacter pylori – H. pylori)

• Antibiotics / antacids, avoid caffeins and alcohol, minimize aspirin and ibuprofen (can damage stomach mucosa), no smoking