Digestive SystemDigestive System

2 types:

Mechanical:Organs physically break food into smaller pieces

Chemical:Enzymes break large molecules into smaller molecules that can be absorbed into the cells

Leftovers = feces

Alimentary Canal / Gastrointestinal Tract

29 foot tube in adults

Extends from mouth to anus

Alimentary Canal / Gastrointestinal Tract

Wall anatomy:

Mucosa:- secretes mucus

into lumen- absorbs small nutrient

moleculesSubmucosa:

- anchors mucosa by C.T.

- contains blood vessels and nerves

Muscularis:- 2 layers

- longitudinal and circular- smooth muscles that produce

peristalsis- wavelike contractions- 2 functions:

- move food through tract- mix food with digestive juice

Serosa- secretes serous fluid- anchored to mesentary

- double fold of peritoneal tissue

Processes• Ingestion

– Taking in food

• Move Food– Passing food along GI tract

• Digestion– Breaking food down

• Absorption– Passing nutrients from GI tract to cardiovascular and

lymphatic systems then to cells

• Defecation– Eliminating undigestible material from tract

Mastication

First process of digestionPerformed by teethCreates bolus

Teeth •2 main parts:•Crown

•Exposed ; junction @ gingivae

•Enamel: hardest substance in body- Protects against acid and abrasions•Dentin: calcified C.T. - Gives teeth shape and rigidity

Teeth •2 main parts:•Root

•Embedded parts•Cementum: covers dentin in root•Pulp Cavity: hollow internal section•Pulp: C.T. with nerves, blood vessels, lymph vessels•Root Canal: passageway for nerves, etc.

Dentitions •Deciduous:

(6 months – 6/12 yrs)•20 total

•8 incisors-4 central-4 lateral•8 molars•4 cuspids (canines)

Dentitions •Permanent:

(6/12 yrs - loss)•32 total

•8 incisors-4 central-4 lateral•12 molars•8 premolars/bicuspids•4 cuspids (canines)

Salivary Glands• Parotid

• Submandibular

• Sublingual

Salivary Glands

• Secrete 1000-1500 mL/day of saliva– 99.5% H2O, .5% solutes

• Mucin– Protein forming mucus

lubricates mouth and throat

• Lysozyme– Bacteria killing enzyme

• Salivary amylase– Breaks starches into maltose

Tongue

• Most coordinated muscle – Partially controlled by lingual frenulum

Ankyloglossia:lingual frenulum is too short and restricts tongueimpedes speech- treated by cutting

Papillae• Filiform

– Cone shaped– Anterior 2/3 of tongue– Lack taste buds

• Fungiform– Mushroom shaped– Near tip of tongue, along

sides and at back– Most have taste buds

• Circumvallate– Large and round– Located on an inverted “V” at posterior of the tongue– All have taste buds

Swallowing/Deglutition

• Tongue pushes food back

• Bolus passes through pharynx– Respiratory passages close

• Soft palate and uvula move up to block nasal passage

• Larynx rises and is pulled forward• Epiglottis is forced down – seals

off trachea

– Breathing temporarily pauses

Swallowing/Deglutition

• Bolus passes through upper esophageal sphincter

• Peristalsis propels bolus further down esphagus

• Bolus passes through lower esophageal sphincter into stomach

Achalasia:lower esophageal sphincter fails to relax as food approaches- esophagus bulges causing chest pain

Stomach4 Areas:• Fundus:

– Area away from lower opening

• Cardia:– Surrounds lower

esophageal sphincter

• Body:– Center portion

• Pyloris:– Lower section

2 curvatures:Lesser = inside curveGreater = outer curve

Stomach

Internal Structure

• Rugae:– Folds of mucosa

• Gastric Pits– Narrow openings between rugae– Gastric glands secrete gastric juice at bottom

StomachStomach Digestion• Mechanical:

– Mixing Waves• Occur in body• 15-25 sec. apart• Break bolus up and combine it with liquid to form chyme

• Chemical:– Pepsinogen/Pepsin:– HCl:– Mucus– Gastric lipase:– Pancreatic lipase:– Rennin (in infants):

StomachEmpties contents within 2-6 hours

– Carbs– Proteins– Lipids

Vomiting (Reverse peristalsis/Emesis):

Physical Process:– Stimuli

• Irritation, sights, sounds, drugs

– Squeezing between diaphragm and abdominal muscles forces esophageal sphincters to open

Small Intestines3 Areas:

• Duodenum– 1st section; 10”

• Jejunum– Next 8’

• Ileum– Next 12’

Villi:fingerlike projections

of mucosalined with microvilli

Ileocecal Valve: controls opening into large intestines

Small IntestinesDigestion• Mechanical:

– Segmentation• Mixes small chunks of chyme• 12-16 contractions/min

– Peristalsis• Moves chyme forward 1cm/min• Chyme stays in small intestines 3-5 hrs

• Chemical:– Maltase:– Sucrase:– Lactase:– Peptidases:

Pancreas

• 1200 – 1500 mL of pancreatic juice/day– Pancreatic Juice

• Alkaline pH– Neutralizes pepsin

• Consists of

– H2O

– Salts– Enzymes– Sodium bicarbonate

Pancreas• Enzymes:

– Pancreatic amylase:– Trypsinogen (Trypsin):– Chymotrypsingogen (Chymotrypsin):– Procarboxypeptidase (Carboxypeptidase):– Pancreatic lipase;– Ribonuclease:– Deoxyribonuclease:Protein digesting enzymes are secreted in inactive

forms to prevent digestion of organs

- Trypsin activates enzymes

- Trypsin is activated by enteropeptidase/enterokinase

Liver

• 3 lbs

• 2 primary lobes– Right and left

• 2 inferior lobes– Quadrate and caudate– According to internal morphology, inferior

lobes are part of left lobe

Liver

• Functions:– Excretion of bile– Carbohydrate metabolism– Lipid metabolism– Protein metabolism– Filters blood of drugs and hormones– Synthesis of bile salts– Phagocytosis of blood cells and bacteria

Liver

• Functions (cont.):– Activates Vitamin D– Storage:

• Glucogen– Stimulates breakdown of glycogen and release of

sugar into bloodstream

• Vitamins– A, B12, D, E, K

• Minerals– Iron, copper

Liver

• Bile Secretion:– 800 -1000 mL daily

• From l. and r. hepatic duct

• Hepatic duct• Cystic duct

(connects with gallbladder)

• Common bile duct

Bile Composition:– H2O

– Bile Salts• Break fats into micelles for absorption = Emulsification

– Cholesterol– Ions – Pigments

• Give bile yellow-brown-olive green color• Mainly bilirubin (created from heme unit of worn-out red

blood cells)– Coloring occurs as bilirubin breaks down in intestines

Jaundice:

– Build up of bilirubin in body– Symptoms

• Yellow color of sclera and skin

– 3 main causes:• Obstruction of bilirubin• Overproduction of bilirubin• Dysfunctioning liver cells

Gallbladder:

– Stores and concentrates bile– Gallstones

• Crystallized cholesterol in ducts• Blocks bile from emptying• Treatment:

– Surgery– Lithotripsy (shock wave treatment)– Cholesterol dissolving drugs (methyl tert-butyl ether)

Large Intestines• 5’ long• 2 1/2” in diameter• Lack villi• Cecum

– 2.5” pouch – Vermiform appendix is attached

• Colon – ascending, transverse, descending

• Rectum– 8”

• Anus– Final sphincter

Large Intestines

Digestion• Mechanical:

– Mass Peristalsis• Stimulated by food entering stomach • Wave contraction pushes contents of

transverse colon into rectum

• Chemical:– Bacteria ferment amino acids

• Produces gas (flatulence)

– Water absorption– Takes 3-10 hours

Large IntestinesFeces

• H2O, epithelial cells, bacteria, inorganic salts, undigested material

Defecation

• Emptying of rectum

• Diarrhea = chyme passes too quickly through intestines– H2O doesn’t get absorbed = dehydration

– Caused by stress, microbes

Large Intestines

Defecation

• Constipation = passage is too slow– Too much H2O is absorbed

– Caused by insufficient bulk in diet, stress, no exercise

Digestive System Disorders

• Tooth Decay (dental caries)– Demineralization – Softens enamel and dentin– Allows microorganisms to infect pulp– Begins with dental plaque (mixture of

decomposing sugars and bacteria wastes)

Digestive System Disorders

• Ulcers:– Craterlike lesions in a membrane– Caused by tissue destruction due to:

• Hyposecretion of mucus– Due to bacterial infection

• Hypersecretion of acids– Due to emotions, smoking, certain foods

– Can lead to hemorrhage, bleeding, anemia

Digestive System Disorders

• Appendicitis:– Bacterial infection

• Caused by obstruction due to fecal matter, tumor, inflammation, etc.

• Rupturing spills infection into body cavity • Spreading infection = peritonitis

Digestive System Disorders

• Cirrhosis:– Distorted or scarred liver due to chronic

inflammation• Symptoms:

– Jaundice– Bleeding– Hypersensitivity to drugs

• Causes:– Hepatitis (virus infection of liver)– Inflammation– Cell destroying chemicals (alcohol)– Parasites

Digestive System Disorders

• Polyps:– Small growths of colon’s epithelial lining

• May be benign or cancerous• Removed by surgery• Dietary fat increases risk• Dietary fiber decreases risk