The Digestive SystemChapter 48

Digestion is the mechanical and chemical breakdown of food into forms that cells can absorb.

The FUNCTIONs of the Digestive System include1. Breakdown food 2. Convert it into a usable form3. Form and expel solid wastes

INTRODUCTION

HUMAN DIGESTIVE

SYSTEM

If stretched out, the alimentary canal is about 8 meters long. That’s 26 feet!

THE ALIMENTARY CANAL

OVERVIEW• https://www.youtube.com/watch?v=nM5kMSjBrmw

THE MOUTH (ORAL CAVITY)• The mouth:

• Receives food• Mechanically breaks up solid particles using TEETH &

TONGUE• Chemically digest food using saliva.

• This action is called mastication

• Makes a BOLUS (wet ball of food)

• The mouth also functions as an organ of speech, and sensory reception.

TEETH & TONGUE

TEETHIncisors- bite or cut offCanines- grasp and tearPremolars – grinding foodMolars – grinding food

TONGUE• Position food between

teeth• Push food back to pharynx

• Secrete salivaSaliva moistens the food, and

begins the digestion of carbohydrates

SALIVARY GLANDS

Three pairs of major salivary glands.

THE PALATE AND UVULA

During swallowing, muscles draw the soft palate and the uvula upward preventing food from entering the nasal cavity.

PHARYNX• The back of the

throat.

• Deglutition (swallowing)

SWALLOWING

• Epiglottis • flap of cartilage• closes trachea (windpipe) when swallowing• food travels down esophagus

ESOPHAGUS

• Moves food down to stomach by PERISTALSIS • involuntary

muscle contractions to move food along

STOMACH• 2 sphincters (valves)

• 3 layers of muscle

• Secretes gastric juices

(enzymes + HCl)

• Mechanically and chemically breaks down food

GASTRIC JUICE• Acidic (pH 1.5-2.5)

(HCl)

• Pepsin- an enzyme that breaks down large proteins into amino acids.

• HCl activates pepsin

• BOLUS + GASTRIC JUICE = chyme.

• Heartburn

• Acid Reflux

ACCESSORY ORGANS

ACCESSORY ORGANS

•Pancreas•Gall Bladder•Liver

PANCREAS

Secretes PANCREATIC JUICE which contains enzymes to digest all major nutrient types.

• Alkaline (base) neutralizes acidic chyme coming from stomach.

LIVER

LIVER • Function: produces bile

• BILE breaks up fats

GALL BLADDER

• It stores bile between meals

• Bile duct – • Connects the liver, pancreas, and gall bladder to the

duodenum (small intestine)

GALLSTONES

• GALLSTONES – an accumulation of hardened cholesterol and/or calcium deposits in the gallbladder• Can either be “passed” (OUCH!!) or surgically

removed

SMALL INTESTINE• Function• Digestion & absorption• over 6 meters! • small intestine has huge

surface area ~size of tennis court

• Structure• 3 sections• duodenum = most

digestion• jejunum = absorption of

nutrients & water• ileum = absorption of

nutrients & water

ABSORPTION IN THE SI

• Much absorption is thought to occur directly through the wall without the need for special adaptations

• Almost 90% of our daily fluid intake is absorbed in the small intestine.

• Villi - increase the surface area of the small intestines, thus providing better absorption of materials

Villi increase surface area. More surface area = More absorption

LARGE INTESTINES (COLON)

• Function

• re-absorb water• use ~9 liters of water every

day in digestive juices• > 90% of water reabsorbed

LARGE INTESTINE• Solid materials pass

through the large intestine.• These are undigestible

solids (fibers).• Water is absorbed.• Vitamins K and B are

reabsorbed with the water.• Rectum- solid wastes exit the

body.

BACTERIAL FLORA

• Living in the large intestine is a community of helpful bacteria

• Escherichia coli (E. coli)• produce vitamins • vitamin K; B vitamins

• generate gases• by-product of bacterial

metabolism • methane, hydrogen

sulfide

FECES

• Poop, excrement, solid waste, etc…

• Feces is composed of materials not digested or absorbed, and include: Water, Electrolytes, Mucus, Bacteria, and Bile pigments

• Approximately 1/3 of the dry weight of feces is bacteria.

• The color of feces is provided by bile pigments altered by bacteria

.

DIARRHEA• a gastrointestinal

disturbance characterized by decreased water absorption and increased peristaltic activity of the large intestine.

• This results in increased, multiple, watery feces.

• This condition may result in severe dehydration, especially in infants

• a condition in which the large intestine is emptied with difficulty

• Too much water is reabsorbed

• Solid waste hardens

CONSTIPATION

RECTUM • Last section of colon

(large intestines)• eliminate feces

• undigested materials• extracellular

waste• mainly

cellulose from plants

• roughage or fiber

• masses of bacteria

ANAL CANAL / ANUS… LAST STOP

• Exit or opening for solid wastes• Regulated by anal

sphincter (valve)• Anal sphincter surrounded

by muscles• Elimination aided by

abdominal muscles

HEMORRHOIDS

Symptoms• Anal itching • Anal ache or pain, especially while

sitting • Bright red blood on toilet tissue, stool, or in the toilet bowl

•Very common, especially during pregnancy and after childbirth. •Result from increased pressure in the veins of the anus. The pressure causes the veins to bulge and expand, making them painful, particularly when you are sitting..

Pain during bowel movements One or more hard tender lumps near the anus