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DIGESTIVE SYSTEM
GENERAL
1st System to Develop
“Tube” Within a Tube
Contents Remain External Until
Absorbed Through Walls
Humans are (Anatomical) Omnivores
Consists of Alimentary Canal/Digestive
Tract and Accessory Organs
DIGESTIVE SYSTEM
FUNCTIONS
Ingestion – Food Enters Through Mouth
Digestion – Breaking Large Molecules
into Smaller, Absorbable Molecules
- Mechanical (Physical)
- Chemical (Enzymatic)
Absorption – Passage of Molecules
Through GI Tract Wall into Blood or
Lymph
Egestion – Elimination of Non-digestible
Substances Through Anal End
DIGESTIVE SYSTEM
ORGANIZATION
Alimentary Canal (Gastrointestinal or
Digestive Tract)
- Mouth, Pharynx, Esophagus, Stomach,
Small Intestine, Large Intestine
- Lumen is part of External Environment
Accessory Organs
-
Salivary Glands
Liver
Gall Bladder
Pancreas
26-5
ALIMENTARY CANAL
HISTOLOGY
Mucosa
- Innermost, Surrounds Lumen
- Mucous Membrane
- Secretes, Absorbs, Protects
Submucosa
- Below Mucosa
- C.T., Blood Vessels, Lymphatics, Nervous
Tissue
ALIMENTARY CANAL
HISTOLOGY continued
 Muscularis (Externa)
- Smooth Muscle
- Inner, Circular,  Diameter of Lumen
- Outer, Longitudinal,  Diameter of Lumen
- Propels Substances
 Serosa (Visceral Peritoneum)
- Outermost
- Serous Membrane, Lubricates
- Adventitia outside of Ventral Body Cavity
ALIMENTARY CANAL
ORGANIZATION
MOUTH
- Oral (Buccal) Cavity Functions in
Ingestion
- Digestion:
*Mechanical (Teeth, Tongue)
*Chemical (Saliva Begins
Carbohydrate Digestion)
- Cheeks
- Hard Palate (Bony)
MOUTH continued
- Soft Palate (Muscular)
* Blocks Nasopharynx During Swallowing
* Uvula - Dangling end
- Tongue
* Frenulum Anchors to Floor of Mouth
* Skeletal Muscle Tissue covered with
Mucosa
* Papillae with Taste Buds
* Lingual Tonsil & Sublingual Gland
MOUTH continued
- Teeth
* Vestibule – Space between Teeth & Lips
* Two Sets: Deciduous (20) & Permanent
(32)
* Four Types:
Incisors – Biting
Canines – Tearing & Grasping
Bicuspids & Molars - Grinding
ALIMENTARY CANAL
ORGANIZATION continued
PHARYNX
- Connects Oral Cavity, Nasal Cavity,
Larynx & Esophagus
- Passageway for Food, Water, Air
- Muscular Walls (Swallowing)
- 3 Regions: Nasopharynx, Oropharynx,
Laryngopharynx
ALIMENTARY CANAL
ORGANIZATION continued
ESOPHAGUS
-
Collapsible, 10” Tube
Connects Pharynx & Stomach
Lies Posterior to Trachea
Lower Esophageal Sphincter Prevents
Stomach Contents from Re-entering
Esophagus
- Passes Through Neck  Thoracic Cavity 
Esophageal Hiatus  Abdominal Cavity
26-18
ALIMENTARY CANAL
ORGANIZATION continued
STOMACH
- J-Shaped Organ, Inferior to
Diaphragm
- Functions:
*Storage
*Digestion (Mechanical & Chemical)
*Protein Digestion Begins here
*Absorption of Water, Alcohol,
Drugs
STOMACH continued
- Enters as Bolus – Mixture of Food &
Saliva
- Leaves as Chyme – Milky Mixture of
Partially Digested Food & Gastric
Juices
STOMACH continued
- 4 Regions:
* Cardia – Connects with Esophagus
* Body – Principal, Main Part
* Fundus – Superior, Bulge, Food Storage
* Pylorus – Terminal Part, Pyloric
Sphincter
- 2 Curves:
* Greater Curvature
* Lesser Curvature
STOMACH continued
- Wall Modifications:
* Rugae –Expandable Folds,
Accommodate More Food
* Oblique Muscle in Muscularis
* Gastric Glands in Mucosa
Mucus Cells (Protective Coating)
Parietal Cells (HCl, pH = 2)
Chief Cells (Pepsinogen + HCl 
Pepsin (Proteolytic)
ALIMENTARY CANAL
ORGANIZATION continued
SMALL INTESTINE
- Site of Most Chemical Digestion
- Site of 90% of Absorption
* Monosaccharides  Blood
* Amino Acids  Blood
* Fatty Acids & Glycerol  Lymph
* Nitrogenous Bases, Phosphates  Blood
SMALL INTESTINE
continued
- 3 Subdivisions:
* Duodenum
First 10-12”
Receives Secretions from Liver &
Pancreas
* Jejunum –Middle Length
* Ileum – Last, Joins with Large Intestine
at Ileocecal Valve
Small Intestine
SMALL INTESTINE
continued
- Wall Modifications:
* All Increase Surface Area for Maximum
Absorption
* Plicae Circulares – Transverse Folds of
Mucosa & Submucosa
* Villi – Finger-like Projections of Mucosa,
contain Capillaries & Lacteal
* Microvilli – Microscopic Folds of
Epithelial Cell Membrane
ALIMENTARY CANAL
ORGANIZATION continued
LARGE INTESTINE
- Functions:
* Secretes Mucus
* Absorbs Water, Ions, Vitamins (From
Bacterial Metabolism)
* Forms & Compacts Feces (Undigested
Food, Bacteria, Water)
26-36
LARGE INTESTINE
continued
- 3 Divisions:
* Cecum
Blind Pouch
Appendix Attached
* Colon - Divided into Ascending,
Transverse, Descending, Sigmoid
* Rectum – Anal Canal
 Internal Anal Sphincter (Smooth)
 External Anal Sphincter (Skeletal)
LARGE INTESTINE
continued
- Wall Modifications:
* Taenia Coli – 3 Bands of Longitudinal
Muscle from Muscularis of Colon
* Haustra – Pouches in Wall of Colon
* No Villi
ALIMENTARY CANAL
MOVEMENTS
Most stimulated by Parasympathetic &
inhibited by Sympathetic
Peristalsis - Wave-like Contraction of
Circular & Longitudinal Smooth Muscle
for Propulsion
Segmentation – Mixes & Pushes Chyme
Against Wall of Small Intestine
Haustral Churning – Pouch-to-Pouch
Movement in Large Intestine
Reverse Peristalsis
Movements
ACCESSORY ORGANS
 SALIVARY GLANDS
- Exocrine Glands
- Ducts Carry Secretions (Saliva) into Mouth
- Saliva: Amylase, Mucous, Water,
Antibodies, Lysozyme
- 3 Pairs:
* Parotid (Most Salivary Amylase)
* Submandibular
* Sublingual
ACCESSORY ORGANS
continued
LIVER
- Largest Gland in Body (Exocrine)
- Produces & Secretes Bile (Fat
Emulsifier)
- Nutrient Storage & Conversion
- Synthesizes Blood Proteins
- Detoxification
ACCESSORY ORGANS
continued
GALL BLADDER
- Muscular Sac
- Stores & Concentrates Bile
- Receives Bile from Liver via Common
Hepatic Duct  Cystic Duct
- Releases into Duodenum via Cystic Duct 
Common Bile Duct  Ampulla of Vater
(Sphincter of Oddi)
ACCESSORY ORGANS
continued
Bile Release:
*Chyme Enters Duodenum
*Cholecystokinin (CCK) & Secretin
Secreted by Duodenum, Enters
Blood
*Secretin stimulates liver to produce
bile
*CCK Stimulates Contractions in
Gall Bladder & Relaxation of
Sphincter
ACCESSORY ORGANS
continued
 PANCREAS
- Exocrine (& Endocrine) Gland
- Secretes Pancreatic Juice (Digestive Enzymes
& Buffers)
- Leaves Pancreas Through Pancreatic Duct(s),
Enters Duodenum Through Ampulla of Vater
(hepatopancreatic ampulla)
- Raises pH of Duodenum (pH 8) via
bicarbonate ions