Digestive System Flashcards
Digestive System Overview
Includes:
1) Gastrointestinal (GI) Tract
- Tube from mouth to anus
2) Accessory Organs
- Teeth, tongue, salivary glands
- Pancreas
- Liver, gallbladder
- Know quadrants
Ingestion
Food into oral cavity
Digestion
- Large molecules broken down into smaller molecules
- 2 Types:
a) mechanical - Motility e.g. chewing
b) chemical - enzymes + acid secretions
Absorption
- End products of digestion enter blood or lymph
Defecation
Elimination of waste + indigestion material
Gastrointestinal Tract Layers
1) Mucosa
2) Submucosa
3) Muscular Externa
4) Serosa
5) Enteric Nervous System
Mucosa (Inner most layer)
- 3 layers
1) Epithelium with numerous goblet cells - Stratified squamous: mouth, pharynx, esophagus, anal canal
- Simple columnar: stomach, small + large intestine
2) Lamina Propria = areolar CT - Contains blood, lymph vessels, lymph nodules/ tissues (immune)
3) Muscular Mucosa (just in the GI tract, not found anywhere else) - Smooth muscle -allows movement of mucosa
Submucosa
- Areolar CT
- Contains: blood + lymphatic vessels, submucosa nerve plexus
Muscular Externa
- Smooth muscle
- Inner circular layer
- Outer longitudinal Layer
- Myenteric nerve plexus between layers
- Contractions cause motility (mixing + movement)
Serosa (or adventitia)
- Cavity = lumen
Enteric Nervous System
- Nervous system of GI tract
- Myenteric system of GI tract - controls muscular external
- Submucous plexus- controls activity of mucosal glands and muscle
Oral Cavity (Digestive System)
Includes
1) Lips
2) Cheeks
3) Palate
i) Hard plate - 2 maxillae + 2 palatine bones
ii) Soft - posterior to hard palate
- Skeletal muscle
- Posterior projection = uvula
- Rises to close the nasopharynx when swallowing
4) Tongue
- attached to hyoid bone
- skeletal muscle
- projections of mucosa = papillae (taste buds)
Salivary Glands
- 3 pairs
1) Parotid - inferior and anterior to ears
- mumps = inflammation of 1 or both parotids
2) Submandibular - floor of mouth
3) Sublingual - below tongue on floor of mouth
- Saliva
- 99.5% H20
- 0.5% solutes (e.g. enzymes)
Dentition (Teeth)
-in maxillae and mandible
- Child dentition
Primary dentition - deciduous (“baby”) teeth
- Adult dentition
Secondary dentition - permanent teeth
- LOOK AT DIAGRAM
Tooth Structure
1) Crown
-above the gum
- dentin = majority of tooth
- enamel overlay = acellular, highly calcified (HARD)
2) Root
- Dentin with cementum overlay
3) Neck
- Enamel + cementum boundary (gums)
4) Periodontal Ligaments
- Attach root to bones
5) Root canal extends to pulp cavity
- Contains CT, blood/lymph vessels, and nerves
NOTE: dentin, enamel + cementum = similar to bone, but avascular
Oropharynx and Laryngopharynx
- Only muscular externa (skeletal muscle) and mucosa (stratified squamous epithelium)
Esophagus
- Posterior to trachea
- Passes through diaphragm to the abdominal cavity
- All 4 histological layers in GI tract from this point on - exceptions in esophagus
1) Muscular Externa - Upper 1/3 -skeletal muscle
- Middle 1/3 - skeletal + smooth muscle (transition zone)
- Lower 1/3 - smooth muscle
2) Has adventitia in mediastinum (outermost layer) = fibrous CT (no epithelium)
Stomach
- Has 4 regions:
1) Cardiac region (cardia) - attached to esophagus
2) Fundus - above esophageal entrance
3) Body
4) Pyloric Region (Pylorus) - has pyloric sphincter - Greater and lesser curvatures
- Converts food into chime
Stomach Mucosa
- Invaginations of epithelium form gastric glands (exocrine) - Secretes gastric juice to lumen
Gastric Glands Contain (Stomach)
1) Chief Cells
- Secrete pepsinogen + gastric lipase (enzymes)
2) Parietal Cells
- Secrete HCI + intrinsic factor (for vit B12 abs in lieu)
3) Goblet Cells
- Mucus (surface epithelium also contains many goblet cells)
4) G cells (enteroendocrine cells)
- Secrete gastrin (hormone; to blood)
Rugae (Stomach)
- Folds of the mucosa + submucosa due to contraction of muscular mucosa
- Allows expansion without tearing mucosa
Muscular Externa (Stomach)
- Function = churning
- 3 layers:
1) Inner oblique
2) Middle circular
3) Outer longitudinal
Small Intestine
- End of pyloric Sphincter to ileocaecal valve
- 3 segments:
1) Duodenum - first fold (short) - retroperitoneal - Extra glands here secrete alkaline mucus to protect against stomach acid
2) Jejunum - middle section
3) Ileum - Has groups of lymph nodules = Peyer’s patches
- Prevent infection of small intestine and bacteria from entering blood
Segments specialized to increase absorption surface area: (Small intestine)
1) Plicae circulares
- Submucosa thrown into folds
2) Villi
- Projections of mucosa into lumen
- Contains:
Blood capillaries
Lacteals (= lymph capillaries that absorb e.g. fats)
3) Microvilli
- Brush border on enterocytes (simple columnar)
- Extend into lumen
Microvilli - villus - Enterocyte
