DIGESTIVE SYSTEM

GENERAL

1st System to Develop“Tube” Within a TubeContents Remain External Until

Absorbed Through WallsHumans are (Anatomical) OmnivoresConsists 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

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

MOVEMENT OF FOOD

Peristalsis - Wave-like Contraction of Circular & Longitudinal Smooth Muscle for Propulsion

ANS

- Stimulated by Parasympathetic

- Inhibited by Sympathetic

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 – BitingCanines – Tearing & GraspingBicuspids & 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 Entering Esophagus

- Passes Through Neck Thoracic Cavity Esophageal Hiatus Abdominal Cavity

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

SMALL INTESTINE continued

- 3 Subdivisions:* Duodenum

First 10-12”Ampulla of Vater Receives Secretions from

Liver & Pancreas» Bile through Common Bile Duct» Pancreatic Juice through Pancreatic Duct

* Jejunum –Middle Length* Ileum – Last, Joins with Large Intestine at

Ileocecal Valve

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 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)

LARGE INTESTINE continued

- 3 Divisions:* Cecum

Blind PouchAppendix 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

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

- Raises pH of Duodenum (pH 8, “Natural Antacid”) via bicarbonate ions