THE DIGESTIVE SYSTEM

OBJECTIVE

SC.912.L.14.46 - Describe the physiology of the digestive system, including mechanical digestion, chemical digestion, absorption and the neural and hormonal mechanisms of control.

6 FUNCTIONS

1. Ingestion

2. Mechanical Processing

3. Digestion

4. Secretion

5. Absorption

6. Excretion

INGESTION

Materials enter via the mouth

MECHANICAL PROCESSING

Crushing and shearing of materials

makes it easier to propel along digestive tract

DIGESTION

Chemical breakdown of foods

SECRETION

Release of water, acids, enzymes, buffers, and salts

ABSORPTION

Movement of organic substrates, electrolytes, vitamins, and water

EXCRETION

Removal of waste products from body fluids

ALIMENTARY CANAL

Muscular tube

Extends from mouth to anus

1-way tract

pharynx

esophagus

stomach

small intestine

large intestine

anus

ORAL CAVITY

Sensory analysis

of material before swallowing

Mechanical processing

teeth, tongue, palatal surfaces

Lubrication

saliva, mucus

Digestion

carbohydrates, lipids

PHARYNX

A common passageway for solid foods, liquid, and air

ESOPHAGUS

A hollow, muscular tube

~25 cm long, 2 cm wide

Conveys solid foods and liquids to the stomach

PERISTALSIS

Wave-like contractions that move food along the digestive tract

STOMACH

4 functions:

store ingested food

mechanical breakdown of ingested food

acids/enzymes disrupt chemical bonds in food

production of intrinsic factor

glycoprotein required for absorption of B12

REGIONS OF STOMACH

Cardia

Fundus

Body

Pylorus

DIGESTION IN THE STOMACH

Pepsin

aids in preliminary digestion of proteins

Salivary amylase

digests carbohydrates

Lingual lipase

digests lipids

pH ~2.0

SMALL INTESTINE

Where 90% of absorption occurs

microvilli increase surface area

3 segments:

duodenum

jejunum

Ileum

DUODENUM

~25 cm long

“Mixing bowl” receives:

chyme from stomach

digestive secretions from pancreas and liver

JEJUNUM

Middle segment

~2.5 m long

Location of most:

chemical digestion

nutrient absorption

ILEUM

Final segment

~3.5 m long

LARGE INTESTINE

Has a larger diameter than the small intestine

4 main segments:

ascending colon

transverse colon

descending colon

sigmoid colon

LARGE INTESTINE

Functions:

reabsorbs water

compaction of intestinal contents into feces

loaded with bacteria

feed on indigestible carbohydrates

produce flatus

RECTUM

Last 15 cm of digestive tract

An expandable organ for temporary storage of feces

Anal canal

last portion of rectum

ends in the anus

ACCESSORY ORGANS

Pancreas

secrete insulin & glucagon into the bloodstream

secrete digestive enzymes

Liver

secretes bile

aids in the

digestion of lipids

Gall Bladder

stores bile

AGING

Smooth muscle tone decreases

peristalsis contractions becomes weaker

Cumulative damage from toxins are transported to liver for processing

alcohol, other chemicals

Rates of stomach/colon cancer rise

Decline in olfactory/gustatory senses

dietary changes that affect entire body