GI 2 and 3 Flashcards
Digestion
Chemical and mechanical breakdown of food into absorbable units
Secretion
Movement of material from cells of the lumen or ECF
Absorbtion
Movement of material from GI lumen to ECF
mobility
Movement of material through the GI tract as a result of muscle contraction
Challenges of the digestive system
Avoiding autodigestion
Defense
Maintaining mass balance
Avoiding Autodigestion
Breaking food down into small enough molecules to be absorbed without digesting the cell of the GI tract
Defense
Absorbing water and nutrients while preventing bacteria, viruses and other pathogens from entering the body.
mechanisms of defense
Mucus, digestive enzymes, acid and the largest collection of lymphoid tissue
Fluid secretions
Water, Digestive Enzymes and Mucus
Water
Ions are transported from ECF into the Lumen
Creates osmotic gradient for water movement
Digestive Enzymes
- Exocrine glands (Salivary and pancreas)
- Epithelial cells in stomach and small intestine
Zymogen
Inactive enzymes
Mucus
Viscous glycoprotein (mucins) secretions that protect GI cells and lubricate the contents
Most fluid secretion fascilitates
Digestion
Two purposes of motility
- Moves food from mouth to anus
- Mechanically mixing food breaks it into uniformly small particles
Muscles involved in motility
Skeletal and Smooth Muscle
How are smooth muscles of motility modifies
Chemical and mechanical input from nerves
Hormones and paracrine signals
Phasic smooth muscle
Cycle of contraction and relaxation
In esophagus, stomach and large intestile
Slow wave
Modified by chemical input from neurons, hormones and paracrine signals
Where do slow waves likely orginate from
Interstitial cells of cajal (icc)
ICC
Modified smooth muscle cells serving as the pacemaker for slow wave activity
Migrating Motor Complex
Starts in stomach and passes from section to section terminating at the ilum (Through the small intestine)
Inbetween meals.
Sweeps food remnants and bacteria out of the upper GI tract and into the large intestine
Peristaltic Contractions
During or following a meal
Circular layer of smooth muscle: Contracts responsible for forward movement
Segmental Contractions
Are responsible for mixing
Circular and longitudinal contractions
Primarily Regulated functions of GI system
Motility and secretion
Neural regulation
Submucosal and myenteric plexuses from the ENS
Neurons synapse with each other. Smooth muscles, glands and epithelial cells
Short reflexes integrated entirely within the ENS
Long reflexes integrated within the CNS
GI peptides
Hormones, neuropeptides and cytokines
Similarities of ENS and CNS
intrinsic neurons: Entirely within the GI tract
Neurotransmitters and neuromodulators
Has glial support cells: Similar to astrocytes
Diffusion barrier
Integrating center
Short reflexes
Original in the ENS, and carried out entirely within the wall of the gut
Mycentric plexus control
Motility
Submucosal plexus control
Secretion from GI secretory cells
Long reflexes
Integrated in the CNS
When a long reflex begins in the brain
Cephalic reflex
PNS
Enhances GI functioning
Which region of the GI tract has a large amount of bacteria
Large Intestine
Movement from lumen of the GI tract into the ECF
Absorption
Two families of HOEMONES
Gastrin Family
secretion Family
3 Phases within the digestive system
Cephalic/oral phase
Gastric Phase
intestinal phase
How is cephalic phase increased
From parasympathethietic output from medulla
Cephalic phase
Digestive processes can actually start before food enters the mouth and are reinforced once food enters the GI tract
In a feedforward fashion
once food enters the mouth
Mastification (Increased Parasympathethetic output)
3 main salivary glands
Parotid Gland
Sublingual Gland
Submandibular Gland
4 functions of the salivary glands
Softens and moisten food
Digestion of Carbohydrates (Amylase)
Dissolve foods (Taste)
Defence (Lysozome)
Where are secretory cells of saliva found
Acini
All glands are not
Identical
Parotid
Watery solution with amylase (Just serous cells)
Submandibular
Similar to parotid plus some mucus. Many serous, some mucus cells
Sublingual
Mainly mucus cells
Degutition
Reflex that pushes the bolus of good into the esophagus
What stares swallowing
Tongue pushing up
swallowing centre
medulla
