Download Digestion - UBC Zoology

Digestive System Anatomy
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Digestive tract
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Accessory organs
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Alimentary tract or
canal
GI tract
Primarily glands
Regions
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Mouth or oral cavity
Pharynx
Esophagus
Stomach
Small intestine
Large intestine
Anus
Functions
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Ingestion: Introduction of food into stomach
Mastication: Chewing
Propulsion
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Deglutition: Swallowing
Peristalsis: Moves material through digestive tract
Digestive Tract Histology
Digestive System Regulation
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Nervous regulation
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Involves enteric nervous
system
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Types of neurons: sensory,
motor, interneurons
Coordinates peristalsis
and regulates local
reflexes
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Chemical regulation
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Production of hormones
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Gastrin, secretin
Production of paracrine
chemicals
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Histamine
Help local reflexes in ENS
control digestive
environments as pH levels
Peritoneum and Mesenteries
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Peritoneum
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Visceral: Covers organs
Parietal: Covers interior
surface of body wall
Retroperitoneal: Behind
peritoneum as kidneys,
pancreas, duodenum
Mesenteries
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Routes which vessels and
nerves pass from body wall to
organs
Greater omentum
Lesser omentum
Oral Cavity
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Mouth or oral cavity
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Lips (labia) and
cheeks
Palate: Oral cavity
roof
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Vestibule: Space
between lips or cheeks
and alveolar processes
Oral cavity proper
Hard and soft
Palatine tonsils
Tongue: Involved in
speech, taste,
mastication,
swallowing
Teeth
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Two sets
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Primary, deciduous,
milk: Childhood
Permanent or
secondary: Adult (32)
Types
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Incisors, canine,
premolar and molars
Tooth structure:
Salivary Glands
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Produce saliva
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Prevents bacterial
infection
Lubrication
Contains salivary
amylase
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Breaks down starch
Three pairs
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Parotid: Largest
Submandibular
Sublingual: Smallest
Pharynx and Esophagus
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Pharynx
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Nasopharynx
Oropharynx: Transmits
food normally
Laryngopharynx:
Transmits food
normally
Esophagus
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Transports food from
pharynx to stomach
Passes through esophageal
hiatus (opening) of
diaphragm and ends at
stomach
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Hiatal hernia
Sphincters
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Upper
Lower
Deglutition (Swallowing)
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Three phases
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Voluntary
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Bolus of food moved by tongue from oral cavity to
pharynx
Pharyngeal
Reflex: Upper esophageal sphincter relaxes, elevated
pharynx opens the esophagus, food pushed into
esophagus
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Esophageal
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Reflex: Epiglottis is tipped posteriorly, larynx elevated
to prevent food from passing into larynx
Phases of Deglutition
(Swallowing)
Stomach Anatomy:
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Openings
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Gastroesophageal:
To esophagus
Pyloric: To
duodenum
Regions
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Cardiac
Fundus
Body
Pyloric
Stomach Histology:
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Layers
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Serosa or visceral
peritoneum:
Outermost
Muscularis: Three
layers
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Outer longitudinal
Middle circular
Inner oblique
Submucosa
Mucosa
Stomach Histology
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Rugae: Folds in
stomach when empty
Gastric pits: Openings
for gastric glands
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Contain cells
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Surface mucous: Mucus
Mucous neck: Mucus
Parietal: Hydrochloric
acid and intrinsic factor
Chief: Pepsinogen
Endocrine: Regulatory
hormones
Hydrochloric Acid Production
Movements in Stomach
Phases of Gastric
Secretion
Small Intestine
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Site of greatest amount of
digestion and absorption
Divisions
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Modifications
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Duodenum
Jejunum
Ileum: Peyer’s patches or
lymph nodules
Circular folds or plicae
circulares, villi, lacteal,
microvilli
Cells of mucosa
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Absorptive, goblet, granular,
endocrine
Small Intestine Secretions
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Mucus
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Digestive enzymes
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Protects against digestive enzymes and stomach acids
Disaccharidases: Break down disaccharides to
monosaccharides
Peptidases: Hydrolyze peptide bonds
Nucleases: Break down nucleic acids
Duodenal glands
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Stimulated by vagus nerve, secretin, chemical or tactile
irritation of duodenal mucosa
Duodenum and Pancreas
Duodenum Anatomy and
Histology
Liver
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Lobes
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Major: Left and right
Minor: Caudate and
quadrate
Ducts
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Common hepatic
Cystic
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From gallbladder
Common bile
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Joins pancreatic duct at
hepatopancreatic ampulla
Functions of the Liver
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Bile production
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Storage
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Hepatocytes remove ammonia and convert to urea
Phagocytosis
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Glycogen, fat, vitamins, copper and iron
Nutrient interconversion
Detoxification
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Salts emulsify fats, contain pigments as bilirubin
Kupffer cells phagocytize worn-out and dying red and white blood cells,
some bacteria
Synthesis
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Albumins, fibrinogen, globulins, heparin, clotting factors
Blood and Bile Flow
Duct System
Gallbladder
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Bile is stored and concentrated
Stimulated by cholecystokinin and vegal
stimulation
Dumps into small intestine
Production of gallstones possible
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Drastic dieting with rapid weight loss
Pancreas
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Anatomy
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Endocrine
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Exocrine
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Pancreatic islets produce
insulin and glucagon
Acini produce digestive
enzymes
Regions: Head, body, tail
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Secretions
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Pancreatic juice (exocrine)
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Trypsin
Chymotrypsin
Carboxypeptidase
Pancreatic amylase
Pancreatic lipases
Enzymes that reduce DNA
and ribonucleic acid
Bicarbonate Ion Production
Gastric hormones:
Movement in small intestine:
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Mixing: Segmental contraction that occurs in small intestine
Secretion: Lubricate, liquefy, digest
Digestion: Mechanical and chemical
Absorption: Movement from tract into circulation or lymph
Elimination: Waste products removed from body
Large Intestine:
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Extends from ileocecal junction to anus
Consists of cecum, colon, rectum, anal canal
Movements sluggish (18-24 hours)
Large Intestine
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Cecum
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Colon
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Ascending, transverse, descending, sigmoid
Rectum
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Blind sac, vermiform appendix attached
Straight muscular tube
Anal canal
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Internal anal sphincter (smooth muscle)
External anal sphincter (skeletal muscle)
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Hemorrhoids: Vein enlargement or inflammation
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Secretions of Large Intestine
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Mucus provides protection
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Parasympathetic stimulation increases rate of goblet
cell secretion
Pumps
Exchange of bicarbonate ions for chloride ions
 Exchange of sodium ions for hydrogen ions
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Bacterial actions produce gases called flatus
Histology of Large Intestine
Movement in Large Intestine
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Mass movements
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Local reflexes in enteric plexus
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Gastrocolic: Initiated by stomach
Duodenocolic: Initiated by duodenum
Defecation reflex
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Common after meals
Distension of the rectal wall by feces
Defecation
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Usually accompanied by voluntary movements to expel feces
through abdominal cavity pressure caused by inspiration
Reflexes in
Colon and
Rectum:
Digestion, Absorption,
Transport
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Digestion
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Breakdown of food molecules for absorption into
circulation
Mechanical: Breaks large food particles to small
 Chemical: Breaking of covalent bonds by digestive
enzymes
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Absorption and transport
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Molecules are moved out of digestive tract and
into circulation for distribution throughout body
Lipoproteins
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Types
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Chylomicrons
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VLDL
LDL
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Enter lymph
Transports cholesterol to
cells
HDL
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Transports cholesterol
from cells to liver
Water and Ions:
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Water
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Can move in either direction
across wall of small intestine
depending on osmotic
gradients
Ions
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Sodium, potassium, calcium,
magnesium, phosphate are
actively transported
Effects of Aging
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Decrease in mucus layer, connective tissue,
muscles and secretions
Increased susceptibility to infections and toxic
agents
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Ulcerations and cancers