Gastrointestinal System Flashcards
four stages of activity as food moves along the alimentary canal
- cephalic phase
- ingestion
- digestion
- absorption
- egestion (elimination)
fundamental actions of the organs of the alimentary canal and their accessories
- motility
- secretion
- absorption
- control (hormones)
the alimentary canal: mouth (4 fundamental actions)
- motility: chewing, sucking, swallowing
- secretion; saliva is produced by the three pairs of salivary glands
- the primary function of saliva is lubrication
- amylase is an enzyme that begins to digest starch and glycogen - absorption: none
- control: a central pattern generator involving the trigeminal nerve and nucleus controls chewing
- sucking and swallowing are under reflex control
- secretion of saliva is controlled by the parasympathetic
the alimentary canal: esophagus
- motility: peristalsis
- secretion: mucus
- absorption: none
- control: the peristalsis is controlled by the enteric nervous system (two layers of nerve plexus located within the walls of the alimentary canal)
the alimentary canal: stomach
- motility: grinding action, esophageal and pyloric sphincters
- secretion: pepsinogen and HCl are secreted by the gastric glands
- absorption: very little
- control: parasympathetic and enteric NS, paracrine and endocrine secretions
stomach secretion
- chief cells secrete pepsinogen
- pepsin is a proteolytic enzyme
- parietal cells make H+ with carbonic anhydrase and transport it into the lumen of the gland with H+/K+-ATPase
- bicarbonate formed in the process is transported into the blood
stomach: control
- motility is controlled by enteric and parasympathetic NS
- secretion is controlled by synergistic actions of three chemical messages:
1. acetylecholine from parasympathetic nerves opens calcium channels in secreting cells
2. histamine, a paracrine secretion, activates the Gs protein in secreting cells
3. Gastrin, a hormone from the stomach, activates the Gp protein in secreting cells
small intestine
- motility: segmentation
- secretion: the small intestine secretes enzymes. It also receives secretions from the pancreas and gall bladder
- absorption: absorbs everything nutritional
- control: the small intestine releases several hormones in response to stretch, low pH and nutrients in its lumen. Enteric NS and parasympathetic NS are also important
small intestine: secretion enzymes
- intestinal: peptidases, disaccharidases, lipases, nucleases
- pancreatic: peptidases, amylase, lipases, nucleases, bicarbonate
- gall bladder: bile and bicarbonate
small intestine: control hormones
Secretin:
-it is small intestine hormone that is released when the pH of the duodenum drops.
-it stimulates bicarbonate secretion by the pancreas and gall bladder
-it inhibits HCl secretion by the stomach
-its receptors are linked to Gs protein
Cholecystokinin:
-it is a small intestine hormone that is released when the fat and amino acid concentration of the duodenum increases
-it causes contraction of the gall bladder to squirt bile into the small intestine
-it causes secretion of pancreatic enzymes
-it causes satiety and drowsiness when it reaches the brain
-its receptors are linked to Gp protein
colon
- motility: segementation, mass movement (3-4x per day), defecation
- secretion: small amounts of potassium and chloride
- absorption: water
- control: motility is controlled by the enteric and parasympathetic NS (gastrocolic reflex). defecation is a spinal reflex
Livers involvement in GI
- blood from the small intestinal capillaries, carrying most of the absorbed nutrients goes directly to the liver via the hepatic portal veins
- the liver organizes the conversion and storage of the nutrients
- nutrients are taken in by the GI system, converted to glucose or fats by the liver, then either stored for later use or consumed by tissues
endocrine system maintains balance of what
-balance between storage and consumption
2 phases of metabolic life
- the absorptive phase is during and immediately following meals
- the postabsorptive phase is between meals
what hormone regulates the absorptive phase
Insulin
- sythesized by beta-cells in the isles of langerhans, the endocrine pancreas in response to increased glucose in the blood
- insulin causes increased glucose uptake by adipose cells and consumer cells. also stimulates by glycogen synthesis and glycolysis
- -has effect of lowering blood glucose concentration, completes a negative feedback loop
- -glucose uptake is enhanced by installation of glucose transport proteins in the plasma membrane by exocytosis
- insulin inhibits fat mobilization by inhibiting hormone-sensitive lipase in adipose tissue. it also stimulates the synthesis of triglycerids.
- -this prevents breakdown of previously stored adipose fat and results in the storage of any newly ingested fat
