DIGESTIVE SYSTEM

ORGANS

DIGESTIVE SYSTEM BROKEN DOWN INTO 2 PARTS

1. Alimentary Canal – gastrointestinal (GI Tract) – Path that food travels

2. Accessory Organs

GI Tracts Oral Cavity

Pharynx

Esophagus

Stomach

Duodenum

Jejunum

Ileum

Cecum

Accessory Organs

Tongue

Liver

Parotid Gland

Sublingual Gland

Submandibular Gland

Uvula

Lingual Frenulum

Ascending Colon

Transverse Colon

Descending Colon

Sigmoid Colon

Rectum

Anus

Pancreas

Gallbladder

Appendix

MOUTH

Palate:HardSoftUvula

Tongue

SALIVARY GLANDS

Cleanses Mouth Important for Taste Moistens food Contains Enzymes

MAJOR SALIVARY GLANDS

•Parotid gland •Submandibular gland•Sublingual gland

The average person produces 1000-1500 ml a day

TEETH

Masticate = to chew

Baby teeth (deciduous)Full set = 20 teeth

Permanent teeth = 32 teethIncisorsCaninesPremolars/molars

PHARYNX

Longitudinal & Circular layers of Muscles Peristalsis

Peristalsis - is a radially symmetrical contraction and relaxation of muscles that propagates in a wave down a tube

ESOPHAGUS

Propels food using muscles (Peristalsis)

STOMACH

Mostly Protein DigestionNo Absorption***Mechanically & Chemically Digested Into ChymeGastric glands produce gastric juice: acidicWalls of Stomach lined with mucus so the acid doesn’t “digest itself”

CHYME

Substance in the stomach that is formed from food and enzymes

PROBLEMS OF THE STOMACH

Ulcers: a hole in the mucus lining of the stomach

Heartburn (acid reflux): contents of stomach move into esophagus

SMALL INTESTINE

SM. INTESTINE

Chemical digestion of carbohydrates, proteins, nucleic acids, & fatsDone with enzymes from pancreas and bile (formed in liver)Pancreatic duct and bile duct empty into duodenum – where enzymes empty into.

LARGE INTESTINE Function:To absorb waterEliminate residue as fecesAbsorb vitamins produced by bacteria

Role of Bacteria:Digest some nutrientsProduce vitaminsProduce gas

ACTION OF L. INTESTINE Peristalsis Mass Peristalsis: a strong wave that pushes contents towards rectum

Problems:DiarrheaConstipation

ACCESSORY ORGANS - PANCREAS

Releases enzymes into duodenum

Has an endocrine function

ACCESSORY ORGANS - LIVER

Produces bile; leaves through common hepatic duct Bile: part waste produce, part digestive secretion (mechanical digestion of lipids)

OTHER LIVER FUNCTIONS

Metabolism of carbs, lipids, and proteins Processing of drugs and hormones Excretion of bilirubin (from hemoglobin of old RBCs)

ACCESSORY ORGANS - GALLBLADDER

Releases bile in response to fatty food entering duodenum Location: underside of liver Gallstones

STEPS OF DIGESTION

DIGESTION

Major functions of the digestive tract are digestion and absorption

ESSENTIAL ACTIVITIES OF THE GI TRACTIngestionPropulsionFood Breakdown – mechanical digestionFood Breakdown – chemical digestionAbsorptionDefecation

1. INGESTION

•Food must be placed into the mouth before it can be acted on.

•Active, voluntary process

2. PROPULSION

•In order for food to be processed by different organs, they must be propelled from one organ to the next.

•Example:•Swallowing – depends on the propulsive process called peristalsis•Peristalsis – involuntary and involves alternating waves of contraction and relaxation of the muscles in the organ walls

3. FOOD BREAKDOWN – MECHANICAL DIGESTION•Mixing of food in the mouth by the tongue•Churning food in stomach•Segmentation – propels foodstuffs through the small intestine

•Prepares food for further degradation by enzymes

4. FOOD BREAKDOWN – CHEMICAL DIGESTION

•Sequence of steps which large food molecules are broken down to their building blocks by enzymes

5. ABSORPTION

•Transport of digested end products from the lumen of the GI tract to the blood or lymph

•For absorption to occur, digested foods must first enter the mucosal cells by active or passive transport processes

•Small intestine is major site of absorption

6. DEFECATION

•Elimination of indigestible residues from the GI tract via the anus to form feces

NEURAL & HORMONAL CONTROL

CEPHALIC PHASE•Occurs before food enters the stomach, especially while it is being eaten

•Brain is activated by smell, sight, thought, and taste of food

•Neurons to salivary glands and gastric glands/stomach muscles

•Autonomic Nervous System

GASTRIC PHASESTIMULUS: FOOD IN STOMACH•Neural:•Stretch receptors activated. Impulse to neurons in submucosa

•Triggers:•Gastric gland production and causes peristalsis

•Hormonal:•Food triggers release of gastrin. Goes in the blood.•Triggers:•Gastric gland juices•Sphincter to prevent acid-reflux

•Stomach muscles•Relaxes lower stomach sphincter

INTESTINAL PHASESTIMULUS: FOOD IN INTESTINE•Neural:•Stretch receptors to medulla oblongata

•Sympathetic nerves to stomach cause:•Decreased stomach movement & increase contraction of pyloric – bottom – sphincter (delays stomach emptying)

•Hormonal:•Cholecytokinin (CCK): stimulates pancreatic juice/squeezes gallbladder