Week 1 (For realsies) Flashcards
Amino acids and monosaccharides are absorbed in
the duodenum and jejunum through secondary active transport
absorbed primarily in ileum?
Cobalamine (B12) and bile salts/acids
All blood leaving the small intestine is directed through…
All blood leaving the small intestine is directed through the portal vein to the liver.
How are Chylomicrons absorbed?
Chylomicrons are too large to pass through capillary cells so lipids are absorbed through lacteals which empty into the bloodstream via the thoracic duct
Metabolic vasodilators?
CO2, H+, K+, adenosine
Mesenteric Ischemia
Causes:
Occlusive mechanisms including thrombi (mesenteric infarction)
Non-occlusive mechanisms including prolonged reflex vasoconstriction (due to hypovolemia, heart failure) or abnormal levels of circulating vasoconstrictors (e.g, epinephrine, angiotensin II)
Effects
Postprandial Pain, Sitophobia
Necrosis of the tips of the villi
Loss of barrier function of the wall of the gut and uptake of vasodilator toxins (endotoxin) from the gut resulting in Septic Shock
bile salts
Bile salts are synthesized from cholesterol in the liver
Bile salts are stored in the gallbladder before entering duodenum
Bile salts are transported back to the liver through hepatic portal vein
Osmotic diarrhea
Small bowel overgrowth of bacteria leads to increased production of organic acids sufficient to pull water from the blood stream by osmosis
Secretory diarrhea
Infection leads to excess secretion of chloride
drawing water into lumen
GI Smooth Muscle - Contractile characteristics:
Rhythmic “phasic” (seconds) contractions and long “tonic” contractions (minutes to hours).
Basal resting tension or “tone” is maintained without elevation in intracellular Ca++ and without energy expenditure. (sphincters)
GI smooth muscle has a remarkable ability to shorten (e.g., to 50% of resting length!!!)
Can initiate depolarization in response to stretch leading to contraction
GI Smooth Muscle - Excitation-Contraction Coupling
Slow waves generated due to increase in calcium followed by repolarization by K+ channels
Amplitude, but not frequency, of slow waves can be altered by signals releasing calcium from internal stores or opening Ca++ channels on plasma membrane
Muscle contraction accompanies action potential.
Migrating Motor Complex
relaxation of sphincters and contractions in stomach and small intestine occurring during fasting(interdigestive) controlled by hormone motilin
Submucosal nerve plexus
within small and large intestine, sensory and blood flow, Meissner’s
Myenteric nerve plexus
between circular and longitudinal muscle layer from esophagus to internal anus
Auerbach’s
Enteric Nervous System – afferent sensory neurons
- excited by fast distension of the gut wall or chemical signals from the lumen of the gut transmitted to sensory neurons.
- many of the sensory neurons are stimulated by serotonin (5-HT) released from mucosal enterochromaffin cells (ECL)
- respond with a few action potentials followed by hyperpolarization (adaptation).- transfer information about gut environment to interneurons in myenteric plexus which relay signals up and down the gut.
Enteric Nervous System –efferent motorneurons
- found primarily in the myenteric plexus- usually unipolar in structure
- excited by fast EPSPs- respond with sustained trains of action potentials
- carry “efferent” information to GI smooth muscle, vascular smooth muscle, GI exocrine secretory cells and GI endocrine secretory cells
- excitatory fibers release acetylcholine, neurokinin A and substance P
- inhibitory fibers release vasoactive intestinal peptide (VIP) and nitric oxide (NO) on smooth muscle cells.
-Parasympathetic and sympathetic systems
- Parasympathetic: mostly cholinergic of vagus nerve; stimulates activity of the enteric plexuses, increases GI motility and secretory activity.
- Sympathetic: mostly adrenergic, generally inhibits activity of the enteric plexuses, decreases GI motility, contracts GI sphincters, constricts GI microvasculature
In general,
- parasympathetic increases activity, cholinergic, vagus “rest and digest”
- sympathetic stimulation decreases activity. noradrenaline,
dopamine, neuropeptide Y
Vago-vagal reflex
Vagal afferent info is transmitted to autonomic centers in the medullaVagal efferents coordinate excitatory and inhibitory activity within the Enteric Nervous System to mediate peristalsis
Acetylcholine
primary excitatory transmitter from sensory cells and from motoneurons to muscle, epithelium, secretory cells and at interneuronal junctions. increases intracellular Ca++
Gastrin releasing peptide
released from vagal nerve endings to stimulate G cell secretion of gastrin.
Substance P
(tachykinin) - an excitatory transmitter generally co-released with acetylcholine.
Vasoactive Intestinal Peptide
(VIP) – Promotes motility
Relaxes smooth muscle in esophagus and stomach
Stimulates fluid secretion and promotes dilation of the GI vasculature. increases cAMP
Nitric Oxide
(NO) - an inhibitory transmitter co-release with VIP from inhibitory motoneurons, hydrophobic- intracellular targets.
Gastrin
G cells in 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 uptake
Secretin
S cells primarily in D/J detect acid stimulates secretion of pancreatic juice including bicarbonate and inhibits gastric motility.
Gastric Inhibitory Peptide or Glucose-Dependent Insulinotropic Peptide (GIP
K cells in D/J detect carbohydrates 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
What happens to fiber?
Fiber is converted into short chain fatty acids by bacteria in the colon
Borborygmi
rumbling noise created by movement of gas in bowels
small intestine bacterial overgrowth syndrome
can occur due to delayed small intestine transit and diverticulum.
Gas and bloating fromfermentation
Compete for B12 uptake leading to anemia
Deconjugate bile acids leading to steatorrhea
Produce toxins altering epithelium
Diagnose with hydrogen breath test
