Gastrointestinal Tract (GI Tract):

• A tube within a tube, open system
• Continuous tube running from mouth to anus for food

Mucosa:

• Mucous Membrane:
  Produces mucus for reduction of friction and Protections
  -Epithelium
• varies in location
• Nonkeratinized stratified squamous in mouth, esophagus and anus, protection against friction
  
  • Simple columnar in intestine for absorption and secretion
    -Lamina Propria:
  • Areolar connective tissue
  • Contains blood and lymphatic vessels and lymph nodes
    -Muscularis mucosa: - 2 thing layers of smooth muscle

Submucosa:

• Areolar connective tissue containing major blood vessels
  
  • many elastic fiber
  • submucosal supply
  • glands and lymphatic tissue

Muscularis Layer:

• 2 layers of smooth muscles to allow peristalsis and segmentation
  
  • Inner circular:
    layer - squeeze, decrease size of lumen; in some areas act as sphincter or valves
    -Outer longitudinal layer: -Shortens intestine
• mouth, pharynx, superior esophagus, and anal
  -Sphincter- Voluntary muscle
• External anal sphincter is skeletal muscle
  -Myenteric plexus - nerves

Digestive accessory organs:
-Aid in digestion but not a pathway for food
-Involved in mechanical and chemical digestion
-found in mouth, stomach, and the intestine; also includes liver, pancreas, and gallbladder

Mouth:

• Opening into Oral cavity
  
  • Oral cavity:
    Area enclosed by the teeth and lips
• Contains salivary glands, tonsils, and tonsils
  -Mechanical digestion, by teeth bu mastication -
  Mixing of food with saliva by the tongue to make bolus
  -Chemical digestion by saliva produced by salivary glands, digestion of starch begins
  
  • Mucosa produces mucus to coat bolus for easier transports - Initiates deglutition
    -Tongue allows sense of taste -Immune function by palatine tonsils

Pharynx:
-Oropharynx:
located posteriorly to mouth; passage for food, water, and air

• Laryngopharynx:
  -Inferior to oropharynx
  
  • Involved in deglutition, forcing bolus from mouth to esophagus

Esophagus:

• collapsible tube runs from the pharynx to stomach pass through diaphragm
  -Located posteriorly to the trachea
  
  • food transported by peristalsis
• No digestive function, only a passage for food and water

Stomach:
Food enters at cardioesophagal sphincter
-Food empties into duodenum of small intestine at the pyloric sphincter
-Rugae:
Internal folds of stomach mucosa

• J-shaped, acts as storage tank for food
• food mixes with gastric juice to make chyme
  -Mechanical digestion by churning of stomach
• Chemical digestion
• break down of proteins begins
• Regions of stomach :
  -Cardiac region- near heart
  -Fundus dome shaped, filled with gas
• Body-main portion
  -Pylorus-funnels shaped end
  -Pyloric sphincter -controls food leaving stomach and entering small intestine
  
  • Only absorption occurs is water, alcohol, some vitamins, and aspirin

Small intestine:
-muscular tube extending from the pyloric sphincter to the ileocecal valve
- Chemical digestion of fat begins

• most chemical digestion takes place of all foods by enzymes produced by accessory organs
  
  • Site of absorption into blood and lymphatic vessels
• Peristalsis and segmental movement mix chyme with digestive enzymes
• Regions of SI:
• Duodenum 1st portion attached to stomach; chemical digestion
  -Jejunum - end portion, connected to cecum, some absorption
  
  • Villi of SI- finger like structures that increase surface area of absorption

-Large Intestine:
-site of absorption of water and electrolytes; produces vitamins.
-Eliminates indigestible food from body as feces.
-Doesn't participate in digestion but resident bacteria digest remaining nutrients; causes gas or flatuation (farts).
- Regions of Li:
Cecum 1st out pocketing of the LI, attached to small intestine; site of appendix attachment.

• colon ascending, transverse, descending, and sigmoid colon.
• Rectum stores feces until it's defecated
  - Features of LI:
  
  • contains tenia coli
    -Haustra-bulges or pockets along LI
    -Movement is slow and sluggish in the LI except for 3-4 mass peristaltic movement per day toward rectum

Teeth:
-Hardest substance in body; functions to mechanically break down food into smaller pieces
Anatomy:
-Enamel-hardest outer layer
-Dentin-middle layer of bone-like living tissue under enamel
-pulp-softer inside structure; contains nerves and blood vessel
-Supporting ligament:
connective tissue that attaches teeth to jaw bone
-Gingivi-gums

Salivary glands:

• Produces saliva(mix of 99% water and mucus0 to moisten food into bolus
  -Contains salivary amylase-digest starch
  
  • 3 pairs of glands: Parotid, submandibular, sublingual

Gastric Glands:
-Goblet cells- produces mucus(provides protective lining against stomach acid)

• Chief cells produce pepsinogen
  -Pepsinogen in presence of Hydrochloric acid, converts pepsinogen to pepsin
• Pepsin-protein digesting protein enzyme in stomach
  - Parietal cells-produce HCL and Intrinsic factor
  -Intrinsic factor
  -Needed for absorption of vitamin B12 in stomach

Intestinal Glands:

• Secrete intestinal juice
  - Duodenal glands:
  -Alkaline mucus to neutralize stomach acid
  
  • Enzymes in duodenum digest all food groups but requires neutral PH to work

Pancreas:

• Produces digestive enzymes:
  -Lipase(digest fats)
  -Pancreatic amylase(digest carbs)
• Trypsin and chymotrypsin (Digest proteins)
• Releases enzymes into duodenum
• Regulated blood sugar by producing insulin

Liver:

• Largest gland; made of 4 lobes
  
  • Falciform ligament holds lobes to abdominal wall
  • Functions for storage for glycogen, fat soluble vitamins and iron
  • Produces bile(emulsifies fat)
  • Removal of drugs, alcohol, and hormones