Week 1 Flashcards
Diverticulitis
Multiple diverticulum (diverticulosis) which are pouches protruding from the alimentary tract that become impacted w/ feces, inflamed, painful, and if blood vessel is eroded hemorrhage.
True divertucula - all layers of bowel
False divertucla - includes only serosa and mucosal layer.
4 basic processes facilitating caloric uptake
Digestion
Absorption
Secretion
Motility
Absorption of amino acids
D and J through secondary active transport (sodium)
Absorption of monosaccharides
D and J through secondary active transport (sodium)
Fat absorption
Bile salts facilitate absorption which occurs primarily in the ileum.
B12 absorption
Ileum
Mesenteric Ischemia
Causes:
- Occlusive mechanisms including thrombi
- Non-occlusive mechanisms including prologed refelx vasoconstriction (hypovolemia, heart failure) or abnormal levels of circulating vasoconstrictors (epi, at II)
Effects:
- Posprandial pain and sitophobia (fear of eating)
- Necrosis of the tips of the villi
- Loss of barrier function of the wall of the gut –>uptake of the vasodilator toxins from the gut –> septic shock.
Osmotic diarrhea
Small bowel overgrowth of bacteria leads to increased production of organic acids sufficient to pull water from the blood streams by osomosis
I.e. lactose intolerance
Secretory diarrhea
Infection leads to excess secretion of chloride drawing water into the lumen.
I.e. cholera
Average Transit time
Esophagus 10 s
Stomach 4-5hrs
Small Intestine 2.5-3 hrs
Large Intestine 30-40 hrs.
Gi Smooth Muscle Contraction
- Rhythmic “phasic” (seconds) contractions (peristaltic waves) and long “tonic” contractions (minutes to hours –> sphincters)
- ) Basal resting tension or tone is maintained without elevation in intracellar Ca++ and without energy expenditure (sphincters)
- ) GI smooth muscle has a remarkable ability to shorten (to 50%)
- ) Can initialte depolarization in response to stretch –> contraction
Migrating motor complex
Relaxation of sphincters and contractions in stomach and si occurring during fasting (inter-digestive) controlled by hormone motilin.
Excitatory (contraction) Neurotransmitters
Ach
Neurokinin A
Substance P
Inhibitory (relaxation Neurotransmitters
Vasoactive Intestinal Peptide (VIP) and Nitric Oxide
Vago-vagal reflex
Vagal afferent info is transmitted to autonomic centers in the medulla
Vagal efferents coordinate excitatory and inhibitory activity within the Enteric Nervous System to mediate peristalsis.
Acetylcholine
Primary excitatory NT from sensory cells and from motor neurons to muscle, epithelium, secretory cells, and at intraneural junctions –> increases ic CA++
Gastrin Releasing Peptide
Released from vagal nerve endings to stimulate G cell secretion of gastrin
Substance P (tachykinin)
An excitatory transmitter generally coreleased w/ Ach
Vasoactive Intestinal Peptide
Promotes motility
Releases smooth muscle in esophagus and stomach
Stimulates fluid secretion and promotes dilation of the GI vasculature.
Increases cAMP
Nitric Oxide
Inhibitory transmitter co-released w/ VIP from inhibitory motor neurons, hydrophobic intracellular targets.
Gastrin
G cells in the antrum of stomach detect amino acids leading to pepsinogen and H+ release by parietal cells
Cholecystokinin (CCK)
I cells in D/J detect fat and amino acids, secretion of pancreatic enzymes and bile salts involved in fat uptakes
Secretin
S cells primarily in D/J detect acid stimulates secretion of pancreatic juice including bicarb and inhibits gastric motility
Gastric Inhibitory Peptide or Glucose-Dependent Insulinotropic Peptide (GIP)
K cells in D/J detect carbs and fat to inhibit gastric acid secretion and stimulate insulin release from pancreas
Motilin
Secreted by endocrine cells; released cyclically during fasting state to initiate Migrating Motor Complex
Small intestine bacterial overgrowth syndrome
Occurs due to delayed small intestine transit and diverticulum
Sx: Gas and bloating from fermentation;
Compete for B12 uptake leading to anemia;
deconjugate bile acids –> steatorrhea;
produce toxins altering epithelium
GI properties that limit colonization by microbes
Saliva contains lactoferrin, lysozyme, and secretory IgA
Acidic stomach
More lymphocytes in GI than in circulating immune system
Mucus -mucins, IgA, lysozyme, lactoferrin
Paneth cells secrete defensins (antimicrobial peptides)
Peyer’s patches contain M cells to transport antigens to B and T cells
Digestive enzymes cleave bacteria
Diarrhea & Vomiting
Microflora prevent colonization of pathogenic organisms (probiotics and prebiotics)
Peristalsis, Ileoceccal valve
