The Digestive SystemChapter 23

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

• Mechanical Digestion – breaks down food into smaller pieces

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

INTRODUCTION

• Chemical Digestion – decomposes food into smaller molecules

Add these terms to vocabulary list…

The digestive system consists of:• The alimentary canal – extends from mouth to anus

• Accessory glands –secrete chemicals into the alimentary canal.

HUMAN DIGESTIVE

SYSTEM

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

THE ALIMENTARY CANAL

STRUCTURE OF THE WALLMucosa – mucous membrane• Epithelial tissues on a bed of connective tissue• This layer absorb nutrients, secrete chemicals, and

protect the underlying layers.Submucosa – Beneath the mucosa• Loose connective tissue• Blood vessels, nerves, and lymphatic vessels• This layer nourishes the surrounding tissues, and

carries away nutrients.Muscular – • Decrease and increase the diameter of the

A.C. to push food throughSerosa – serous membrane• Secretes serous fluid, which lubricates the A.C.

MOVEMENTS OF THE ALIMENTARY CANALMuscles of the A.C. provide two basic

movements:

Segmentation – mixing movement• Smooth muscles contract

and relax, mixing foods with digestive juices

Peristalsis – propelling movement• Smooth muscles contract in a

wave-like motion pushing food through the alimentary canal

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.

• Secrete salivaSaliva moistens the food, and

begins the digestion of carbohydrates

SALIVARY GLANDS

Three pairs of major salivary glands, include:

• Parotid glands • Submandibular

• Sublingual

SALIVA = water + mucus + amylase

Parotid glands • Secrete clear watery fluid• Rich in salivary amylase – begins the chemical digestion of

carbohydrates

Submandibular glands• Secretes a mixed saliva with both watery fluid

and mucus

Sublingual glands• Secrete primarily mucus

SALIVARY GLANDS

THE PALATE AND UVULA• The palate forms the roof of the oral cavityHard Palate - bony roof of the mouth• Formed by the palatine bones and portions of the maxilla

Soft Palate - Muscular arch

Uvula – cone-shaped projection

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

Teeth are the hardest structures in the body

THE TEETH

•primary (deciduous) teeth numbering 20• Usually erupt through the

gums from age of 6 months to 2 years

•secondary (permanent) teeth numbering 32• Usually begin to erupt at 6

years• 3rd molars = wisdom teeth,

which may erupt between 17-25 years of age

TYPES OF TEETHIncisors- blade shaped teeth that bite or cut off large pieces of food

Canines- cone shaped teeth that grasp and tear food

Adult – 8 Child – 8

Adult – 4Child – 4

Premolars – flattened surface for grinding food

Adult – 8 Child – 0

Molars – flattened surface for grinding food

Adult – 12 Child – 8

THE TONGUE• Thick, muscular organ• Manipulate foods and aids in swallowing

Mucous Membrane

Frenulum

Root• Anchored to the hyoid bone.• Covered with lingual tonsils

Papillae – projections on the surface of the tongue.• Some provide friction, others house taste buds.

PHARYNX• The back of the

throat.

• Deglutition (swallowing)

• 3 parts

SWALLOWING

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

ESOPHAGUS• Peristalsis • involuntary muscle

contractions to move food along

• Esophageal Hiatus – opening in the diaphragm, passage for esophagus

• Hiatal hernia – part of the stomach protrudes through the hiatus.

STOMACH• 2 sphincters (valves)

• 3 layers of muscle

• Secretes gastric juices

(enzymes + HCl)

• Mechanically and chemically breaks down food

STOMACH

• Fundus = top portion

• Pyloris = funnel-shaped lower portion

• Rugae – gastric folds line the stomach

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.

ACCESSORY ORGANS

•Pancreas•Gall Bladder•Liver

PANCREAS

• An organ which secretes both digestive enzymes (exocrine) and hormones (endocrine)

• Pancreatic juice digests all major nutrient types. • “ENZYME COCKTAIL” includes enzymes top break down all

compounds: proteins, lipids and carbohydrates• Alkaline (base) neutralizes acidic chyme coming from stomach.

PANCREAS

LIVER

LIVER FUNCTIONS• The liver carries on many important metabolic activities, including:

• Glycogenesis: producing glycogen from glucose

• Glycolysis: breakdown of glycogen into glucose

• Gluconeogenesis: converts non-carbohydrates to glucose

• Oxidizes fatty acids

• Synthesizes phospholipids and cholesterol

• Forms urea

• Synthesizes plasma proteins

• Stores glycogen, iron, and vitamins A, D, and B12

• Phagocytosis of worn out RBCs and foreign substances

• Removes toxins such as alcohol and certain drugs from the blood

LIVER • Function: produces bile

• BILE breaks up fats

GALL BLADDER

• It stores bile between meals• It concentrates bile by reabsorbing water• The gall bladder itself does not produce bile

• Bile duct – • a long tube that carries BILE • 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• chemical digestion• major organ of digestion &

absorption• absorption through lining• over 6 meters! • small intestine has huge

surface area = 300m2

(~size of tennis court) • Structure• 3 sections• duodenum = most

digestion• jejunum = absorption of

nutrients & water• ileum = absorption of

nutrients & water

DUODENUM

• 1st section of small intestines• acid food from stomach • mixes with digestive juices from:

pancreas liver gall

bladder

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

APPENDIX

Vestigial organVestigial organ

APPENDICITIS

• inflammation of the appendix due to infection• Common treatment is removal of the appendix

via surgery

THE LARGE INTESTINE The large intestine is named because of its diameter

It has four parts:

1. Cecum – blind pouch• Ileocecal sphincter • The appendix projects from the cecum.

2. Colon (ascending, transverse, descending, sigmoid)

3. Rectum - straight

4. Anal canal• The anus – is guarded by two sphincter muscles• external anal sphincter – composed of skeletal muscle• internal anal sphincter – composed of smooth muscle

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.

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

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

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

EPISIOTOMY

This…

NOTEBOOKS

Due Monday, April 14

Must include:• RESPIRATORY SYSTEM• DIGESTIVE SYSTEM• URINARY SYSTEM

See website for DIGESTIVE SYSTEM powerpoint to help finish notes on chart.