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
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