4. Physiology of Gastrointestinal Physiology Flashcards
Function of the stomach and it’s exocrine secretions
Stomach: Store, mix, dissolve and continue digestion of food.
Function of the stomach and it’s exocrine secretions
Stomach: Store, mix, dissolve and continue digestion of foo. Regulates 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 liver and its exocrine secretions
Liver: Secretion of bile
Exocrine secretions:
Bile salts: Solubilise water-insoluble fats
Bicarbonate: Neutralize HCl entering small intestine from stomach
Organic water products and trace metals: Elimination in faeces
Gall bladder function:
Store and concentrate bile between meals
Function of small intestine and it’s exocrine secretions
SI: Digestion and absorption of most substances; mixing and propulsion of contents.
Function of small intestine and it’s exocrine secretions
SI: 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 large intestine and its exocrine secretions
LI: Storage and concentration of undigested matter, absorption of salt and water, mixing and propulsion of contents, defecation
Exocrine secretion: Mucus for lubrication
Function of large intestine and its exocrine secretions
LI: Storage and concentration of undigested matter, absorption of salt and water, mixing and propulsion of contents, defecation
Exocrine secretion: Mucus for lubrication
List the 5 major physiological processes of the GI system
Motility Secretion Digestion Absorption Excretion
What are the 5 major physiological processes of the GI system
MOTILITY
Propulsion of ingested food from mouth to rectum, mixing and reducing in size to optimise time for absorption and digestion
SECRETION
Salivary glands, stomach, small intestine, pancreas and liver all add fluid, electrolytes, enzymes and mucus
DIGESTION
Ingested food is digested into absorbable molecules
ABSORPTION
Nutrients, electrolytes and water are absorbed from the intestinal lumen into the bloodstream
EXCRETION
What are the major immunological and non-immunological defence mechanisms of the GI?
Immunological mechanisms: Mucosal immune system (gut-associated lymphoid tissue, GALT).
These are aggregate of lymphoid tissue i.e. Peyer’s patches and diffuse populations of immune cells.
Provides: Protection against microbial pathogens, mediates immunological tolerance to dietary substance sea gut bacteria
Non-immunologic mechanisms: Gastric acid, mucin, peristalsis and the epithelial cell layer barrier
What are the layers of the GI wall?
- Muscular mucosal, epithelium, lamina propria
- Submucosa
- Submucosal nerve plexus
- Circular muscle (muscular externa)
- Myenteric plexus
- Longitudinal muscle
- Serosa
What is the lamina propria?
Underlying loose connective tissue with capillaries, enteric neurones and immune cells
What is the muscular mucosal?
Thin smooth muscle layer of the mucosa
What is contained within the submucosa?
Loose connective tissue Larger blood vessels Lymphatics Secretory glands Enteric neurones in the submucosa
What is the muscular externa?
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
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?
ENTERIC NERVOUS SYSTEM
- The submucosal plexus (Meissner’s plexus). In the LI and SI. Primarily regulates glandular, endocrine and epithelial secretions
- The myenteric plexus (Auerbach’s plexus). Between the circular and longitudinal muscle layers throughout he GI tracts. Primarily consists of motor neurones.
Describe where the extrinsic nervous system secretes neurotransmitters within the GI
PS from Vagus or pelvic nerve: Synapses of ACh in myenteric and submuscosal plexus. Released into circular and longitudinal muscle and mucosa.
Symp from sympathetic ganglia: NE synapse in myenteric and submucosal plexuses. Released into the circular muscle and mucosa
Which GI reflexes are integrated within the enteric nervous system?
Reflexes controlled 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?
(1) Reflexes from stomach and duodenum to brain stem and back to stomach to control gastric motor and secretory activity
(2) Pain reflexes causing general inhibition of entire GI tract
(3) Defecation reflexes from the colon and rectum that travel via the spinal cord back to produce powerful colonic, rectal and abdominal contractions
What is the
(1) Source
(2) Target
(3) Action
of the following GI hormone: Gastrin
(1) Source
G cells in the atrium of stomach
(2) Target
Parietal cells in body of stomach
(3) 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)
(1) Source
I cells in duodenum and jejunum; neurones in ileum and colon
(2) Target
Pancreas and gall bladder
(3) Action
Increases enzyme secretion
Increases contraction
