4 Overview of GI physiology Flashcards
Function of the mouth and pharynx
- Chewing begins
* Initiation of swallowing reflex
Function of the salivary glands’ exocrine secretions
- Salt + water - moisten food
- Mucus - lubrication
- Amylase - polysaccharide-digesting enzyme
Function of the oesophagus and its exocrine secretions
- Oesophagus function:
• Move food to stomach by peristaltic waves - Exocrine secretion:
• Mucus - lubrication
Function of the stomach and its exocrine secretions
- Stomach function:
• Store, mix, dissolve and continue digestion of food
• Regulate emptying of dissolved food into small intestine - Exocrine secretions:
• HCl - solubilisation of food particles; kill microbes
• Pepsin - protein-digesting enzyme
• Mucus - lubricate and protect epithelial surface
Function of the small intestine and its exocrine secretions
- Small intestine function:
• Digestion and absorption of most substances
• Mixing and propulsion of contents - Exocrine secretions:
• Enzymes - food digestion
• Salt and water - maintain fluidity of luminal contents
• Mucus - lubrication
Function of the large intestine and its exocrine secretions
1. Large intestine function: • Storage and concentration of undigested matter • Absorption of salt and water • Mixing and propulsion of contents • Defecation
- Exocrine secretions:
• Mucus - lubrication
Function of the pancreas and its exocrine secretions
- Pancreas function:
• Secretion of enzymes and bicarbonate
• Nondigestive endocrine functions - Exocrine secretions:
• Enzymes - digest carbohydrates, fats, proteins, and nucleic acids
• Bicarbonate - neutralise HCl entering small intestine from stomach
Function of liver and its exocrine functions
- Liver function:
• Secretion of bile; many other nondigestive functions - Exocrine secretions:
• Bile salts - neutralise water-insoluble fats
• Bicarbonate - neutralise HCl entering small intestine from stomach
• Organic water products and trace metals - elimination in faeces
Function of gallbladder
Store and concentrate bile in between meals
List the 5 major physiological processes of the GI system
- Motility
- Secretion
- Digestion
- Absorption
- Excretion
What is motility?
Propulsion of ingested food from mouth to rectum mixing and reduction in particle size to optimise time for digestion and absorption
What is secretion?
Salivary glands, stomach, small intestine, pancreas, liver
- add fluid, electrolytes, enzymes and mucus
What is digestion?
Ingested food is digested into absorbable molecules
What is absorption?
Nutrients, electrolytes and water are absorbed from the intestinal lumen into the blood stream
Example of activity: 1200 ml water/day; 800 g solids/day:
- Saliva secretion?
- Gastric secretion?
- Bile secretion?
- Pancreatic secretion?
- Intestinal secretion?
- Absorption by small intestine
- Absorption by large intestine?
- Water in faeces? Gram of solids?
Secretions: • Saliva - 1500 ml • Gastric - 2000 ml • Bile - 500 ml • Pancreatic - 1500 ml • Intestinal - 1500 ml
Absorption:
• Small intestine - 6700 ml
• Large intestine - 1400 ml
Faeces:
• Water - 100 ml
• 50 g solids
List the major defence mechanisms of GI
- Immunological mechanisms - mucosal immune system (GALT)
2. Non-immunologic mechanisms
What are the immunological defence mechanisms of GI?
Mucosal immune system (gut-associated lymphoid tissue, GALT):
• Organised aggregate of lymphoid tissue - Peyer’s patches
• Diffuse populations of immune cells (lymphocytes and mast cells)
Provides:
• Protection against microbial pathogens
• Mediates immunological tolerance to dietary substance and gut bacteria
What are the non-immunologic defence mechanisms to GI?
- Gastric acid
- Mucin
- Peristalsis
- Epithelial cell layer barrier
What are the layers of the GI wall?
- Mucosa - epithelium, lamina propria, muscularis mucosae
- Submucosa
- Submucosal nerve plexus
- Circular muscle
- Myenteric plexus
- Longitudinal muscle
- Serosa
What is the lamina propria?
• In mucosa
• Underlying loose connective tissue with capillaries, enteric
neurones and immune cells
What is the muscular mucosae
Thin smooth muscle layer of mucosa
What is contained within the submucosa?
- Loose connective tissue
- Larger blood vessels
- Lymphatics
- Secretory glands
- Enteric neurones in the submucosa - submucosal plexus
What is the muscular externa (muscle layer)?
- Inner layer of circular muscle
- Outer layer of longitudinal muscle
- Enteric neurones between the muscle layers- myenteric plexus
What is the serosa?
Outer layer of connective tissue covered with squamous epithelial cells
List the innervations of the GI tract
Autonomic nervous system:
- Extrinsic component:
• Sympathetic
• Parasympathetic - Intrinsic component (Enteric nervous system):
• Submucosal plexus (Meissner’s plexus)
• Myenteric plexus (Auerbach’s plexus)
What is the intrinsic component of the innervation of the GI tract?
What are the two plexuses? Where are they found and what do they do?
Intrinsic component (Enteric Nervous System):
- Submucosal plexus (Meissner’s plexus)
– small and large intestine (primarily regulate glandular, endocrine and epithelial secretions) - Myenteric plexus (Auerbach’s plexus)
– between the circular and longitudinal muscle layers throughout the GI tract (primarily motor neurons)
Describe where the extrinsic nervous system secretes neurotransmitters within the GI
?
Which GI reflexes are integrated within the enteric nervous system?
Reflexes controlling secretion, peristalsis, mixing, local inhibitory actions
Which GI reflexes are from the GI tract to prevertebral sympathetic ganglia and then back to the GI tract?
Reflexes that transmit signals to other areas of the GI tract:
- Gastrocolic reflex (stomach-colon)
- Enterogastric reflexes (stomach and colon inhibiting gastric motility)
- Colonoileal reflexes (inhibition of ileal emptying)
Which GI reflexes from the GI tract to the brain stem or spinal cord and then back to the GI tract?
- Reflexes from stomach and duodenum to brain stem and back to stomach to control gastric motor and secretory activity
- Pain reflexes causing general inhibition of entire GI tract
- Defecation reflexes from the colon and rectum that travel via spinal cord back to produce powerful colonic, rectal and abdominal contractions
Which GI reflexes are from the GI tract to prevertebral sympathetic ganglia and then back to the GI tract?
Reflexes that transmit signals to other areas of the GI tract:
- Gastrocolic reflex (stomach-colon)
- Enterogastric reflexes (stomach and colon inhibiting gastric motility)
- Colonoileal reflexes (inhibition of ileal emptying)
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone: Gastrin
- Source:
• G cells in antrum of stomach - Target:
• Parietal cells in body of stomach - Action:
• Increases H+ secretion
• Stimulates growth of gastric mucosa
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Cholecystokinin (CKK)
- Source:
• I cells in duodenum and jejunum
• Neurones in ileum and colon - Target:
• Pancreas
• Gall bladder - Actions:
• Pancreas - increases enzyme secretion
• Gall bladder - increases contraction
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Secretin
- Source:
• S cells in small intestine - Target:
• Pancreas
Stomach - Action:
• Pancreas - increases HCO-3 and fluid secretion by pancreatic ducts
• Stomach - decreases gastric acid secretion
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Gastric inhibitory peptide
- Source:
• K cells in duodenum and jejunum - Target:
• Pancreas
• Stomach
3. Action: • Pancreas - exocrine: decreases fluid absorption -endocrine: increases insulin release • Stomach - decreases gastrin release
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Gastric inhibitory peptide
- Source:
• K cells in duodenum and jejunum - Target:
• Pancreas
• Stomach
3. Action: • Pancreas - exocrine: decreases fluid absorption -endocrine: increases insulin release • Stomach - decreases gastrin release
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Glucagon
- Source:
• alpha cells of pancreatic islets of Langerhans - Target:
• Liver - Action:
• Increases glycogenolysis and gluconeogenesis
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Guanylin
- Source:
• Ileum and colon - Target:
• Intestine - Action:
• Increases fluid absorption
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Motillin
- Source:
• Endocrine cells in upper GI tract - Target:
• Oesophageal sphincter
• Stomach
• Duodenum - Action:
• Increases smooth muscle contraction
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone:
Neurotension
- Source:
• N cells of ileum - Target:
• Smooth muscle
• Vagus - Action:
• Relaxes smooth muscle (LES)
• Decreases gastric acid secretion
What is the
(1) Source
(2) Target
(3) Action
of the following GI paracrine:
Somatostatin
- Source:
• D cells of stomach and duodenum
• Beta cells of pancreatic islets
2. Target: • Stomach • Intestine • Pancreas • Liver
3. Action: • Stomach -decrease gastric release • Intestine -increase fluid absorption -decrease fluid secretion • Pancreas - decrease endocrine and exocrine secretions • Liver - decrease bile flow
What is the
(1) Source
(2) Target
(3) Action
of the following GI paracrine:
Histamine
- Source:
• Endocrine cells of gastric mucosa (esp. H+ secreting region of stomach) - Target:
• Stomach - Action:
• Stimulates H+ secretion from parietal cells in the stomach
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine:
ACh
- Source:
• Cholinergic neurons
2. Target: • Smooth muscle • Salivary glands • Stomach • Pancreas
3. Action: • Smooth muscle - contraction in GI wall -relaxation of sphincters • Salivary glands - increases secretion • Stomach - increases secretion • Pancreas - increases secretion
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine: NA (NE)
- Source:
• Adrenergic neurons - Target:
• Smooth muscle
• Salivary glands - Action:
• Smooth muscle - relaxation in GI wall
• Salivary glands - increases secretion
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine:
Vasoactive intestine peptide
- Source:
• Enteric nervous system - Target:
• Smooth muscle
• Pancreas
• Intestine - Action:
• Smooth muscle - relaxation
• Pancreas - increases secretion
• Intestine - increases secretion
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine:
Gastrin released peptide (GRP)
- Source:
• Neurones of the gastric mucosa
• Vagal nerve endings - target:
• G cells in the antrum of the stomach - Action:
• Increases gastrin secretion
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine:
Enkephalins (opiates)
- Source:
• Neurones of mucosa and smooth muscle - Target:
• Smooth muscle
• Intestinal secretion - Action:
• Smooth muscle - contraction
• Intestinal secretion - decreases
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine:
Neuropeptide Y
- Source:
• Neurons of the mucosa and smooth muscle - target:
• Smooth muscle
• Intestinal secretion - Action:
• Smooth muscle - relaxation
• Intestinal secretion - decreases
What is the
(1) Source
(2) Target
(3) Action
of the following GI neurocrine:
Substance P
- Source:
• Co-secreted with Each - Target:
• Smooth muscle
• Salivary glands - Action:
• Smooth muscle - contraction
• Salivary glands - increases secretion
