Applied Physiology Flashcards
How do laxatives work?
e. g. Epsom salts
- Poorly absorbed so add osmotic pressure in lumen so drag water out to help liquify stool
What do bacterial agents target to cause diarrhoea?
Loosen tight junctions in intestinal epithelial
Where is Na absorbed and how?
- Jejunum
- Co-transport with glucose via SLGT-1
- Exchange with H+
Where is K absorbed and how?
- Paracellular absorption throughout small intestine - via solvent drag as Na pulled in…
- Secreted in colon - aldosterone
How is Ca absorbed and how?
- Passive (paracellular) in jejunum + ileum
- Active transport (transcellular) in duodenum via TRPV channels
= regulated by calcitriol + requires intracellular buffer calbindin
How is Fe absorbed?
- Ferric (Fe3+) = dietary form reduced to ferrous (Fe2+)
- Fe2+ either
1. Sequestered as ferritin
2. Transported out + complexed as transferrin
Which is absorbed and secreted between Cl- and HCO3-?
Cl- absorbed
HCO3- secreted
What stimulates enteric (NANC) neurons and EC cells?
Cl- secretion
What sitmulates D cells and enteric neurons?
Na+ and Cl- absorption
What influences motility in the small and large intestine?
- Enteric NS
- Myenteric plexus - motor
- Submucosal plexus - sensory, affects secretary activity - Autonomic NS
- PSNS increases motility
- SNS decreases motility
Which are the excitatory NT’s in gut motility?
ACh
Sub P
Which are the inhibitory NT’s in gut motility?
VIP
NO
What are the basic types of postprandial movement in the SI?
- Individual villi
- Pendular
- Segmentation
- Peristaltic
- Migrating motility complex during fasting
What is motility in intestines enhanced and inhibited by?
- Enhances by gastrin
- Inhibited by secretin
What is the role of interstitial cells of cajal (ICC)?
- Form part of SIP syncytium = Smooth muscle cells
Interstitial cells of Cajal
Platelet-derived growth factor receptor alpha-positive cells - ICC’s display pacemaker activity due to IC release of Ca
- Depolarisations transmitted to smooth muscle cells via gap junctions = slow waves = propagate in antral direction
Which motility influencing mediators are released from cells in gut wall?
- NANC: VIP` relaxes smooth muscle
- Enteric neurons: enkephalins regulate peristaltic reflex
- EC cells: serotonin activates local motor reflex
- N cells in ileum: release neurotensin in response to fat = decreases motility
- L cells in distal ileum: release GLP-1 in response to glucose + fat
- M cells in duodenum: release motilin in response to fat + acid = increases sensitivity of SM to intrinsic nervous activity, stimulates gastric emptying + migrating motility complex
What is entry at ileocecal junction regulated by?
- Relaxes by ileal distension
- Increases in tone by colon distension
What electrolyte and water absorption is their in the colon?
Na actively transported
(aldosterone)
Cl- exchanged with HCO3-
Summarise the movements in the colon
- Segmental mixing - circular SM, haustrations
- Propulsive - initiated by intrinsic reflex pathways, enhances by vagal neurons, gastrin + CCK increase colon excitability
What muscles make up the anal canal?
- Internal sphincter - smooth muscle
- External sphincter - skeletal muscle
What control causes walls of sigmoid colon and rectum to contract?
PS
What allow rectum to straighten?
Pelvic floor muscles