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027:130 Human Physiology
Chapter 15: Digestion and Absorption of Food
30
Physiology
Undergraduate 2
12/11/2011

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Term
GI system
Definition
  • transfers organic nutrients, minerals, and water from the external environment to the internal environment
  • critical for absorption of nutrients
  • tube open to the external environment
Term

GI system

-order of structures-

Definition
  • mouth
  • pharynx
  • esophagus
  • stomach
  • small intestine
    • duodenum
    • jejunum
    • ileum
  • large intestine¬†
    • ascending colon
    • transverse colon
    • descending colon
    • sigmoid colon
  • rectum
Term
where majority of absorption takes place:
Definition
duodenum
Term
Glandular organs in the GI system (and what they secrete):
Definition
salivary glands (amylase)

liver (bile salts)

gallbladder (bile)

pancreas (bicarbonate & enzymes)
Term
digestion
Definition
  • the dissolving and breaking down process of food so it can be more easily absorbed
  • starts in the stomach region
  • occurs via:
    • HCl (secreted by parietal cells in the stomach)
    • bile (secreted by the liver)
    • digestive enzymes (secreted from exocrine glands)
Term
body of the stomach
Definition
middle portion of the stomach

secretes mucus, pepsinogen, & HCl
Term
chyme
Definition
solution of partially digested food in stomach & intestinal lumen
Term
mass movement
Definition
contraction of large segments of colon

propels fecal matter into the rectum
Term
segmentation
Definition
series of stationary rhythmical contractions & relaxations of rings intestinal smooth muscle

- mixes intestinal contents
Term
parietal cells
Definition
secrete HCl & intrinsic factor
Term
amylase
Definition
enzyme secreted by salivary glands & pancreas

- digests carbs (partially breaks down polysaccharides
Term
fundus
Definition
upper portion of the stomach

- secretes mucus, pepsinogen, & HCl
Term
pepsinogen
Definition
inactive precursor of pepsin

- secreted by chief cells of gastric mucosa
Term
micelle
Definition
soluble cluster of amphipathic molecules

- formed from fatty acids, 2 monoglycerides, & bile salts (during fat digestion in small intestine)
Term
migrating myoelectric complex
Definition
pattern of peristaltic waves that pass over small segments of intestine after absorption of a meal
Term
chief cell
Definition
gastric gland cell that secretes pepsinogen
Term
sphincter
Definition
smooth-muscle ring that surrounds a tube, closing the tube as muscle contracts
Term
sphincter of Oddi
Definition
sphincter surrounding common bile duct at its entrance into the duodenum
Term
epiglottis
Definition
thin cartilage flap that folds down, covering the trachea during swallowing
Term
large intestine
Definition
absorbs salts & water
Term
secretion
Definition
various substances are released by organs & exocrine glands into the GI system

- aid in digestion & breakdown
Term
absorption
Definition
movement of products created by digestion from the lumen --> across epithelial cell layer --> into the blood (carbs, AA's, nutrients, water, salts) or lymph (fats, fat-soluble vitamins)
Term
motility
Definition
contractions of smooth-muscles in GI tract that mix contents & move them through the tract

- at a rate that ensures maximal digestion & absorption of nutrients
Term
the GI system is not designed to be selective --> it is designed to maximize the absorption of most nutrients

* everything you put in will be digested & absorbed

- regulation is dictated by volume & composition of luminal contents
Definition
Term
the GI tract secretes more fluid into the lumen than is ingested

- fluid is constantly being recycled & reabsorbed

- only about 1% of luminal contents is excreted in the feces
Definition
Term
GI system has many components:
Definition
neural
muscular
cardiovascular
Term
Structure of the GI tract wall
Definition
- 1 single epithelial cell layer separates the lumen from rest of body

- has neural innervation (motor, sympathetic, parasympathetic,afferent)

-has capillaries, arterioles, venules

- different types of muscles work in concert (longitudinal & circular)

- take away neural/muscular components --> food will just sit there (no processing or motility)
Term
longitudinal muscles
Definition
help with motility (move material through the GI system)

- contraction shortens the length of the tube
Term
circular muscles
Definition
help squeeze tube down (help with processing & moving food products through)
Term
endocrine cells
Definition
secrete hormones into blood

monitor intestinal content (are responsive to the luminal environment --> trigger hormonal secretion into circulation --> responses eventually come back to GI system)
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