DSA- Introduction to GI physiology Flashcards
Main functions of GI tract
digestion and absorption of nutrients
Main properties of GI tract
- motility
- secretions
GI tract sphincter function
restrict passage of intestinal content to optimize digestion and absorption
List the GI tract sphincters (7)
1) upper esophageal sphincter (UES)
2) lower esophageal sphincter (LES)
3) Pylorus
4) sphincter of Oddi
5) Ileocecal valve
6) Internal anal sphincter
7) External anal sphincter
Intestinal Wall Structure
- layers and what they contain
4 layers
1) Mucosal Layer
- epithelium
- lamina propria
- muscularis mucosae
2) Submucosa
3) Muscle layers
- circular
- longitudinal
- myenteric plexus
4) Serosa
Enteric nervous system of GI
- nicknames
- what they consist of
- innervation
“nervous system of GI tract”
“the second brain or little brain in gut”
- sensory neuron
1) submucosal plexus
2) myenteric plexus
Innervated by extrinsic autonomic nervous system
ENS functions
functions:
1) integrating center
2) can exert its functions without CNS input
3) control contraction, secretion, and endocrine function of GI tract
4) receive information from parasympathetic and sympathetic nervous system and CNS
5) receive sensory information from mechanoreceptor and chemoreceptors in mucosa
Role fo CNS in GI regulation
- pathway
vago-vagal reflex ( gastric receptive relaxation reflex)
modulate ENS responses
centers that control food intake are located in brain
**vagal afferents-> sensory ganglion of vagal nerve (Nodose ganglion)-> Nucleus of tractus solitarius (NTS)-> vagal efferents
Parasympathetic innervation of GI
- nerves
- location (2)
- type of receptors
- vagus & pelvic nerve
- Preganglionic nerve cell bodies: at brainstem or sacral spinal cord
- Postganglionic neurons: wall of organ (ENS in gut wall)
- synapse between pre and post ganglionic cell is NICOTINIC (nAChRs)
Sympathetic innervation of GI
- nerves
- location (2)
- type of hormones released
- via nerves running between spinal cord and prevertebral ganglia
- via nerves running between ganglia and GI organs
- Preganglionic efferent fibers: at spinal cord and end of prevertebral ganglia (OUTSIDE GI tract)
- Postganglionic fibers: innervate myenteric and submucosal plexus
- Preganglionic efferent fibers release ACh
- Post ganglionic nerve release NE
Cell Communication in GI tract: paracrine regulation
Paracrine regulation (locally) 2 hormones: histamine and somatostatin - peptide (somatostatin) - messenger molecule (histamine) - reach their target cells by diffusion over short distance
Somatostatin
- location
- stimuli
- action
PARACRINE
secreted by
- D cells of GI mucosa
- hypothalamus
- delta cells of exocrine pancreas
stimuli: low luminal pH
Action:
- inhibit gastric H+ secretion
- inhibit secretion of other GI hormones
Histamine
- location
- target
- action
PARACRINE
stomach
- stored and secrceted by enterochromaffin-like cells (ECL) in gastric glands
target: parietal cells
action: stimulate acid production
Cell Communication in GI tract: Endocrine regulation
- hormones
- action of hormones
- enteroendocrine cells contain secretary granules filled with hormones that are released upon stimulation
- hormones are secreted into circulation
4 hormones
1) Gastrin
2) Cholecystokinin (CCK)
3) Secretin
4) Glucose-dependent insulinotropic peptide (GIP)
Gastrin
- actions
ENDOCRINE
- increase gastric H+ secretion
- stimulate growth of gastric mucosa
CCK
- actions (6)
ENDOCRINE
1) increase pancreatic enzyme secretion
2) increase pancreatic HCO3- secretion (not direct effect- potentiates effects of secretin)
3) stimulates contraction of gallbladder and relaxation of sphincter of Oddi
4) stimulates growth of exocrine pancreas and gallbladder (trophic effect)
5) inhibit gastric emptying
6) act as paracrine signal
Secretin
- actions (5)
ENDOCRINE
1) increase pancreatic HCO3- secretion
2) increase biliary HCO3- secretion
3) decrease gastric H+ secretion
4) inhibit trophic effect of gastrin on gastric mucosa
5) act as paracrine signal
GIP
- actions
- best method of administration
ENDOCRINE
1) increase insulin secretion form pancreatic B cells (incretin effect)
2) decrease gastric H+ secretion
ORAL glucose administration more effective than IV glucose in increasing insulin secretion
Cell Communication in GI tract: Neural regulation
- hormones
- action of neurotransmitters
- AP needed for NT release
- NT molecules diffuse across synapse and bind to their specific receptors in postsynaptic cell
Hormones (8)
1) Ach
2) NE
3) Vasoactive intestinal peptide (VIP)
4) Nitric Oxide
5) Gastrin- releasing peptide (GRP)
6) Enkephalins
7) Neuropeptide Y
8) Substance P
Acetylcholine
- source
- actions (5)
NEURAL
Source: cholinergic neurons
Actions
1) contraction of smooth muscle in wall
2) relaxation of sphincters
3) increase salivary secretion
4) increase gastric secretion
5) increase pancreatic secretion
Norepinephrine (NE)
- source
- actions
NEURAL
Source: adrenergic neurons
Actions
1) relaxation of smooth muscle in wall
2) contraction of sphincters
3) increase salivary secretion
Vasoactive Intestinal Peptide (VIP)
- source
- actions
NEURAL
Source: neurons of ENS
Actions
1) relaxation of smooth muscle
2) increase intestinal secretion
3) increase pancreatic secretion
Nitric Oxide
- source
- actions
NEURAL
Source: neurons of ENS
Action
- relaxation of smooth muscle
Gastrin- releasing peptide (GRP)
- source
- actions
NEURAL
Source: vagal neurons of gastric mucosa
Action
- increase gastrin secretion
Enkephalins
- source
- actions
NEURAL
Source: Neurons of ENS
Action
1) contraction of smooth muscle
2) decrease intestinal secretion
Neuropeptide Y
- source
- actions
Neural
Source: neurons of ENS
Action
1) relaxation of smooth muscle
2) decrease intestinal secretion
Substance P
- source
- actions
NEURAL
Source: co-secreted with ACh by neurons of ENS
Action
1) contraction of smooth muscle
2) increase salivary secretion
