GI 7 Flashcards
Defecation
Two reflexes initiated by distension of the rectum
Short and long reflex
Short reflex of defecation
Local peristaltic waves
Long reflex of defecation
Relaxation of internal sphincter (smooth muscle)
Contraction of external (skeletal)
More forceful peristaltic contractions form parasympathetic input
What is the defecation reflex completed by
Voluntary relaxation of external sphincter (skeletal) and aided by increased abdominal pressure
Diarrhea
An increase in frequency, volume, and fluid content of feces due to increased secretion, reduced absorption or increased motility
What is diarrhea induced by
Osmotic, secretory, inflammatory or motility
Osmotic diarrhea
Excess solute stays within lumen of GI which prevents normal amt of H20 absorption
Water stays and leaves
Inflammatory diarrhea
Due to infection
Breaks barrier and causes damage to int preventing proper absorption
What can secretory be caused by
Immune cells (flush out GI)
Bacteria
How does cholera cause secretory diarrhea
Cholera toxin causes persistent opening of Cl leak channels
Cl draws Na, water into lumen
Creates watery secretion
Use of penicillin based antibiotics can alter
Normal bacterial flora
Remaining bacteria have reduced competition for space and nutrients
What does reduced competition of bacteria leave you prone to
Infection by C.difficile
What does c. Difficile cause
Colitis: watery diarrhea, fever, nausea, abdominal pain
What is cure for C. difficile infection
Fecal transplant from healthy individual
Rapid addition of good bacteria
Vomiting
Contents of stomach and occasionally small int are forcefully expelled through mouth
- associated with nausea
Vomiting center is where
Medulla
Vomiting center in medulla causes 3 responses
- Retrograde contractions in small int and stomach (towards stomach +lower esophageal)
- Contraction of abdominal inspiratory muscles (diaphragm) increases gastric pressure
- Relaxation of esophageal sphincters
What is outside BBB and communicated with vomiting center
Chemoreceptor trigger zone
Causes of vomiting
Abnormal vestibular input (motion sickness, spinning)
Input from sensory receptors in stomach and intestines
Direct input from drugs, toxins in chemoreceptor trigger zone
Where is immune function in GI tract
Gut -Associated lymphoid tissue (GALT)
80% of lymphocytes located in gut
What cells play big role in immune responses
M cells
How do M cells work in immune responses
Receptor mediated endocytosis
- transport antigens to macrophages, lymphocytes, and dendritic cells
- release cytokines to attract more immune cells
What do cytokines do in gut
- attract more immune cells to attack invaders
- trigger increased Cl secretion (diarrhea) to flush out pathogens
What do we rely on to regulate intake
Behavioural mechanisms
Appetite and satiety
During feeding state and 3-6 hours following what state is body in
Anabolism
Body will store nutrients
During fasting state body is in
Catabolism
High levels of breakdown
What is the hunger center
LH- Lateral hypothalamus
Communication between 2 areas for satiety
ARC - Arcuate nucleus
PVN- paraventricular nucleus
What in medulla plays role in appetite and satiety
NTS- nucleus tractus solitarii
What maintains body weight at a relatively stable value
Behavioural mechanisms
Theories of long term regulation of feeding behaviour
- Glucostatic theory
- Lipostatic theory
Glucostatic theory
Glucose metabolism in the hypothalamus regulates food intake (proved to be short term)
Lipostatic theory
Signals from the bodies fat stores regulate food intake (long term regulator)
If weight is lost during starvation
Weight is rapidly gained when food is freely available
What is ob/ob gene
Encodes a protein that tell brain fat reserves are normal
What was ob/ob mouse
Obese
Leptin
Released from adipocytes and regulates body mass by acting on neurons of hypothalamus that decrease appetite and increase energy expenditure
In most obese individuals what does leptin do
Brain doesnt respond to it
Elevated leptin
Decrease energy intake
Increase energy output
What does leptin act on
Arcuate nucleus
Response to elevated leptin
- Inhibition of lateral feeding center
- Activation of paraventricular nucleus (PVN)
What are 2 responses of activation of PVN from increased leptin
Humoral response
Visceromotor response
Humoral response
Increase TSH, ACTH from pituitary
- increased metabolic rate throughout body
Visceromotor response
Increased sympathetic output
- increase body temp to increase metabolism
What do anorectic peptide do when increased leptin
Reduce food intake
Response to decreased leptin
- Reduced activation of a-MSH and CART neurons
- Activation of NPY and AgRP containing neurons
Reduced activation of a-MSH and CART neurons
Reduced activation of PVN (decreased TSH and ACTH)
- Decreased metabolic rate
Activation of parasympathetic output
Activation of NPY and AgRP containing neurons
-stimulation of feeding center
- further inhibition PVN
Orexigenic peptides
From NPY/AgRP neurons of Arcuate nucleus
- facilitate eating
When is aMSH/CART neuron activity high
High leptin level
Why did leptin supplementation fail to treat obesity
Have to have OB/OB mutation (rare)
