GI Phys 1

• - continuous tube from mouth to anus

  - 7 sphincters of significance


  GI tract
• salivary glands, liver, gallbladder, and pancreas


  accessory organs
• UES

  upper esophageal sphincter
• LES

  lower esophageal sphincter
• mucosa

  - surface area

  - secretions

  - connective tissue

  - flux & agitation of surface

  
• submucosa

  - vascular & lymphatic interface

  - ENS control of secretions

  - lots of reabsorption

  - can innervate the secretions of exocrine cells

  
• muscularis externa (primary muscle)

  - changes diameter

  - ENS control of muscle

  - changes length

  - myenteric plexus communicates with submucosa

  - longitudinal muscle shortens and lengthens

  
• serosa

  - connective tissue

  - holding things in place

  - parasympathetic = increases motility/secretions

  - sympathetic = decreases motility/secretions

  - ENS = local controls

  - ANS = external overrides

  - ducts from external exocrine glands (liver, pancreas, salivary glands)

  
• ingestion of foods and liquids containing nutrients and ions


  a function of the digestive system
• digestion of large molecules in food and liquids into absorbable molecular forms. Then transport across the GI epithelium.


  a function of the digestive system
• absorption of nutrients from the gut lumen into the internal environment = ECF 


  a function of the digestive system
• metabolic transformation of fuel molecules and detoxification of foreign substances (delivered to liver via hepatic portal vein)


  a function of the digestive system
• elimination (=excretion) of small amounts of metabolic end products secreted by the liver, including Bilirubin from RBC breakdown (color of feces, urine, and bile)


  a function of the digestive system
• carrying out a variety of immune functions, including production of antibodies and fighting infectious microorganisms not destroyed by the acidity of the stomach, defense makes sense! (barrier)


  a function of the digestive system
• four major processes of the digestive system

  1.) motility

  2.) digestion

  3.) absorption

  4.) secretion
• not just propel contents along, but also mix and expose

  motility
• breakdown both mechanically and chemically

  digestion
• small intestine dominates here

  absorption
• mucus throughout, notable secretions throughout

  secretion
• entire tract lumen is OUTSIDE the body; blood from GI tract capillaries goes to liver first


  image:

  
• digestion of the major macronutrients

  image:

  
• amylase ->

  polysaccharides (starch and glycogen)
• sucrase ->

  sucrose
• lactase ->

  lactose
• maltase ->

  maltose
• basic building blocks (glucose, fructose, and galactose)

  monosaccharides
• pepsin, trypsin, chymotrypsin ->

  polypeptides
• carboxypeptidase + aminopeptidase ->

  peptide fragments
• how many types of amino acids?

  20
• lipase ->

  glycerol bound to 3 fatty acids
• monoglyceride plus ___ free fatty acids

  two
• why is the amount absorbed so much greater than the amount consumed?

  secretions
• where do all those secretions come from?

  exocrine glands
• how many liters of secretions are added into your stomach?

  7
• gastrointestinal fluid regulation

  - 1200 mL water/day; 500-800 g solids/day ingested

  - feces 100 mL water; 50-100 g solids excreted