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Digestion part 1

Terms in this set (73)

Food has large molecules that
cannot be used by cells
food needs to be broken down into
molecules ----> digestion
the GI tract is a continuous tube from
mouth to anus
the GI tract consists of
mouth, pharynx, esophagus, stomach, small intestine, large intestine
Accessory GI tract organs include
Teeth, tongue, salivary glands, liver, gallbladder, pancreas
teeth and tongue help to
break down food
salivary glands, liver, gallbladder, pancreas help with
secretions into the GI tract such as enzymes and mucous
functions of the digestive system
ingestion, secretion, mixing and propulsion of food, digestion, absorption, and defecation
ingestion
taking food into the mouth
secretion
completed by cells in the GI tract and accessory organs
Release of water, acid, buffers, and enzymes into lumen
mixing and propulsion of food
Contraction and relaxation of smooth muscles in wall of GI tract
digestion
Mechanical digestion by churning food (muscle contraction)
Chemical digestion (enzymes) Hydrolysis of food producing smaller molecules
absorption
passing into blood or lymph
Vitamins, ions, cholesterol and water absorption without chemical digestion
defecation
Elimination of waste products from food in the feces
layers of the GI tract
Mucosal layer
Submucosal layer
Muscular layer (Muscularis)
Serosa
Mucosal layer
Made up of: Epithelium
For:
Protection
Secretion of mucus, enzymes and hormones
Absorption
Submucosal layer
Made up of:
Connective tissue
Nerves (submucosal plexus)
Blood and lymph vessels
Muscular layer (Muscularis)
Made up of:
Circular and longitudinal muscles
Myenteric plexus (neurons)
Serosa
Connective tissue
Peritoneal membrane
Enteric nervous system (ENS)
Made up of:
Motor neurons (esophagus to anus)
Myenteric (Auerbach's) plexus
Myenteric (Auerbach's) plexus
Located in the muscularis layer
Control motility
Submucosal (Meissner's) plexus
It is buried in the submucosa
It senses the environment in the lumen --->
Blood flow and cell function
Innervation of the GI System (1)
Interneurons
Innervation of the GI System (2)
Integrate information from sensory neurons to motor neurons in plexuses
Innervation of the GI System (3)
Sensory neurons receives information from sensory receptors in mucosa and muscles
Innervation of the GI System (4)
Chemoreceptors detect osmolarity and pH of the contents
Innervation of the GI System (5)
Mechanoreceptors lead to organ stretching
Autonomic Nervous System
Made up of:
Parasympathetic system
Sympathetic system
Parasympathetic system
Form connections with ENS
Increases GI secretion and motility by increasing activity of ENS
Sympathetic system
Synapse with ENS
Decreases GI secretions and motility by inhibiting ENS
Mechanical Digestion
food is manipulated by tongue, ground by teeth, mixed with saliva and dissolved in the water
mechanical digestion leads to
the formation of bolus
bolus
soft, flexible, easily swallowed mass
chemical digestion
done by enzymes known as salivary amylase and lingual lipase
salivary amylase
breaks disaccahrides and starches into monosaccharides
Breaks starch into maltose, maltotriose, alpha-dextrin
Its activity continues into the stomach
lingual lipase
breaks triglycerides into fatty acids and diglycerides
saliva
secreted by salivary glands
99.5% water, 0.5% ions
Dissolves foods to be tasted by gustatory cells
Allows digestion to begin
Buffers in saliva
Bicarbonate and phosphate ions
Mucus
lubricates food
Immunoglobulin A (IgA)
Prevents microbes from penetrating epithelium
Enzymes in saliva
Salivary amylase
Lysozyme
Salivary or lingual lipase
Lysozyme
Enzyme that kills bacteria
Protection of oral cavity from bacteria
functions of the stomach
Mixing chamber
Reservoir for food before releasing it into small intestine
Secretion
Bolus is converted into
chyme
chyme
mix of saliva, food, gastric juice
soupy liquid
gastric juice mixed with digested food
salivary amylase is inactivaed and lingual and gastric lipases are activated in the stomach
types of secretion in the stomach
Gastric acid (HCl)
Pepsin
Intrinsic factor
Gastric lipase
gastrin (hormone)
Gastric acid (HCl)
kills bacteria, denatures proteins
partially activates pepsinogen and gastric lipase
pepsin
digests proteins
secreted by chief cells as pepsinogen
breaks peptide bonds
active at ph 2
inactive pepsinogen is activated to pepsin by HCl and other pepsin molecules
Intrinsic factor
Vitamin B12 absorption
gastric lipase
triglycerides digestion
gastrin (hormone)
Causes release of gastric acid
Stimulates pancreas (enzymes), liver (bile), intestines (movement)
mechanical digestion in the stomach
mixing
several minutes after food enters the stomach mixing waves pass over the stomach ever 15-25 seconds
propulsion and retropulsion movements
results in chyme
gastric emptying
chyme passes through pyloric sphincter
3 ml at a time
chemical digestion in the stomach
parietal cells secrete gastric acid (HCl) by the proton pump
H+/K+ ATPase
gastric acid partially denatures proteins
HCl
Pepsin
Gastric and lingual lipases
Stomach cells are protected from acid by
alkaline mucus produced by surface and neck mucous cells
acid secretion by parietal cells (1)
Parietal cells secrete H+ and Cl- separately into the lumen of the stomach
acid secretion by parietal cells (2)
H+ are transported into the lumen of the stomach by the H+-K+ ATPase or proton pump
acid secretion by parietal cells (3)
Following secretion of H+ and Cl-, HCl is formed in the gastric lumen
Components for Acid Secretion by Parietal Cells
H+ (protons)
Cl-
K+
source of H+ (protons) for Acid Secretion by Parietal Cells
H+ comes from carbonic acid (H2CO3) and it is pumped into the lumen by the proton pump
H2CO3 is synthesized from CO2 and water
The reaction is catalyzed by carbonic anhydrase
Dissociation of H2CO3 originates H+ and bicarbonate (HCO3-)
HCO3- is transported out of the cell
source of Cl- for Acid Secretion by Parietal Cells
HCO3- is transported into the interstitial lumen in exchange for Cl- using the Cl--HCO3- antiporter
HCO3- diffuses into nearby capillaries
source of K+ for Acid Secretion by Parietal Cells
The K+ ions in the gastric lumen are used by the H+-K+ ATPase or proton pump in exchange for H+
K+ is transported inside the cell from the interstitial fluid by the Na+-K+ ATPase
K+ ions are transported to the gastric lumen by K+ channel
The excess K+ ions inside the cell moves outward by K+ channels on the basolateral membrane
Regulation of Gastric Acid Secretion
Parietal cell has receptors for
Acetylcholine (ACh)
Gastrin
Histamine
Acetylcholine (ACh)
Released by parasympathetic neurons
gastrin
Secreted from G cells
histamine
Released by ECL cells
direct regulation of gastric acid in parietal cells
^cAMP and CA2+ activate PKA
PKA phosphorylates and activates H+-K+-ATPase (proton pump)
production of gastric acid
indirect regulation of gastric acid secretion by histamine
gastrin-histamine main pathway
effect of histamine
histamine is released by ecl cells
activation of h2 receptors on parietal cells
simulation of the proton pump by PKA
enterochromaffin
like cells in the gastric gland of the gastric mucosa
close to the parietal cells
Indirect Regulation of Gastric Acid by ACh and Gastrin
Modulation via (ACh) in the cephalic phase (30% of the acid)
indirect effect of gastrin
gastrin activates CCK receptors on ECL cells
histamine released from ecl cells activated H2R on parietal cells which leads to acid secretion
indirect effect of ach
ach activates the release of histamine from ecl cells (M1R)
ach activates the release of gastrin from G cells in the antrum
gastrin activates histamine release from ECL Cells (CCK-R)
histamine activates acid secretion in parietal cells (H2-R)
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