Physiology 1 Flashcards
(38 cards)
Describe the major daily inputs and outputs of fluid in the GI tract.
Inputs
- 1200mL ingested
- 1500mL salivary secretions
- 2000mL gastric secretions
- 500mL bile secretions
- 1500mL pancreatic secretions
- 1500mL intestinal secretions
Outputs
- 6700 mL small intestines
- 1400 mL large intestine
- 100mL in feces
What serves as the pacemaker/regulator of slow wave activity in GI muscle.
Interstitial cells of cajal, they are located near the enteric plexi, (meissners and auerbachs)
Describe slow wave activity.
occurs in four phases
only electrical activity in the stomach
not innervated by neural or hormonal input.
Aurbach vs Meissner plexi? Actions, locations.
Auerbach - Myenteric plexus, primarily controls GI motility
Meissner - Submucosal plexus, receives sensory info from chemo and mechanoreceptors in the GI and primarily regulates SECRETIONS and BLOOD FLOW
Three types of innervation to the GI tract?
Parasympathetic - excitatory, vagus/pelvic nerves
Sympathetic - inhibitory, adrenergic fibers from prevertebral ganglia, splanchnic nerves
Enteric nervous system (ENS) - primary control of GI motility and secretions, coordinates local reflex information
Where are the swallowing centers located?
medulla
What nerve carries afferent signals back to the medulla to begin the act of swallowing?
Glossopharyngeal- kicks off the action of
What is the mechanism behind slow wave action in the GI tract?
cyclic opening of Ca+ channels (depolarization) followed by opening of K+ channels (repolarization)
Describe the action of relaxation of the LES when a food bolus approaches.
Relaxation is vagally mediated via the NT VIP.
The term for when teh LES does not relax during swallowing, resulting in food accumulation in the esophagus.
Achalasia
Describe 5 major functions of digestion performed in the stomach.
Emulsification of fats (acid lipase)
Breakdown Proteins (pepsin)
Oxidize Iron (HCl)
Release of Intrinsic Factor for use in the duodenum (B12 abs.) (Parietal Cells)
What reflex is initiated by distention of the stomach causing stretching of the stomach with increased food intake?
Vagovagal reflex - causes “adaptive relaxation”
“Receptive relaxation” - causes relaxation of stomach tissue in response to swallowing, allowing room for food to enter.
What hormone acts on the antrum of the stomach to stimulate gastric emptying into the duodenum?
Gastrin (secreted by G cells) - initiated via vagal stimulation in response to gastric distention.
What disease is associated with increased action/secretion of gastrin?
Zollinger-Ellison syndrome
Name 4 major pathways of inhibiting gastric emptying
- Sympathetic stimulation
- Acid chemoreceptors in duodenum sensing acid relay neg. feedback via direct interneurons.
- Fat sensed in the duodenum/jejunum causes the release of CCK from I cells
- Hyper/Hypotonic meals cause slowed emptying via unidentified hormone.
What causes hunger pangs?
Migrating myoelectric complexes (MMCs): they are interdigestive electrical oscillations that fire spike potentials, leading to peristaltic waves.
They help prepare for next meal.
Describe the simple idea behind the “peristaltic reflex”
local distention causes wave to begin proximal to distention and inhibition distal (an enteric reflex)
Functions of saliva?
alpha amylase - carbs
lingual lipase - fats
Lubrication - mucins secreted in saliva, creates bolus
compare primary and secondary saliva during a meal and at rest.
Primary: isotonic, similar composition of Na/K/Cl/HCO3 as plasma (gets modified before secretion via duct cells on its way out)
Secondary: after modified by the duct cells the secondary secretion is hypotonic (Na/Cl resorbed, K/HCO3 added, water stays the same)
Describe ductal cells and how they modify acinar secretions.
At higher flow rates, the ductal cells act on the saliva less, leaving the saliva closer to isotonicity
Describe the autonomic control of salivary secretions
Both para and sympathetic innervations cause saliva production to increase. The only thing that causes decreased saliva is inhibition of the pathways
What causes dry mouth
Parasympathetics are much stronger saliva inducers than sympathetic, therefore sympathetic deactivation of parasympathetics can cause fry mouth, via vasoconstriction.
Atropine, fear, dehydration, sjogren syndrome (autoimmune damage to exocrine glands)
Describe the secretions of parietal cells.
HCl - activates pepsin to pepsinogen, kills bacteria, emulsifies fats, oxidizes iron
Intrinsic factor - absorption of Vit. B12 in duodenum
Discuss the regulation of gastric secretions
Activators: Histamine, Gastrin, Ach
Inhibitors: Somatostatin, Prostaglandins
