Week 1 (For realsies)

Question 1

Amino acids and monosaccharides are absorbed in

Answer 1

the duodenum and jejunum through secondary active transport

Question 2

absorbed primarily in ileum?

Answer 2

Cobalamine (B12) and bile salts/acids

Question 3

All blood leaving the small intestine is directed through…

Answer 3

All blood leaving the small intestine is directed through the portal vein to the liver.

Question 4

How are Chylomicrons absorbed?

Answer 4

Chylomicrons are too large to pass through capillary cells so lipids are absorbed through lacteals which empty into the bloodstream via the thoracic duct

Question 5

Metabolic vasodilators?

Answer 5

CO2, H+, K+, adenosine

Question 6

Mesenteric Ischemia

Answer 6

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

Question 7

bile salts

Answer 7

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

Question 8

Osmotic diarrhea

Answer 8

Small bowel overgrowth of bacteria leads to increased production of organic acids sufficient to pull water from the blood stream by osmosis

Question 9

Secretory diarrhea

Answer 9

Infection leads to excess secretion of chloride

drawing water into lumen

Question 10

GI Smooth Muscle - Contractile characteristics:

Answer 10

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

Question 11

GI Smooth Muscle - Excitation-Contraction Coupling

Answer 11

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.

Question 12

Migrating Motor Complex

Answer 12

relaxation of sphincters and contractions in stomach and small intestine occurring during fasting(interdigestive) controlled by hormone motilin

Question 13

Submucosal nerve plexus

Answer 13

within small and large intestine, sensory and blood flow, Meissner’s

Question 14

Myenteric nerve plexus

Answer 14

between circular and longitudinal muscle layer from esophagus to internal anus
Auerbach’s

Question 15

Enteric Nervous System – afferent sensory neurons

Answer 15

• 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.

Question 16

Enteric Nervous System –efferent motorneurons

Answer 16

• 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.

Question 17

-Parasympathetic and sympathetic systems

Answer 17

• 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

Question 18

Vago-vagal reflex

Answer 18

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

Question 19

Acetylcholine

Answer 19

primary excitatory transmitter from sensory cells and from motoneurons to muscle, epithelium, secretory cells and at interneuronal junctions. increases intracellular Ca++

Question 20

Gastrin releasing peptide

Answer 20

released from vagal nerve endings to stimulate G cell secretion of gastrin.

Question 21

Substance P

Answer 21

(tachykinin) - an excitatory transmitter generally co-released with acetylcholine.

Question 22

Vasoactive Intestinal Peptide

Answer 22

(VIP) – Promotes motility
Relaxes smooth muscle in esophagus and stomach
Stimulates fluid secretion and promotes dilation of the GI vasculature. increases cAMP

Question 23

Nitric Oxide

Answer 23

(NO) - an inhibitory transmitter co-release with VIP from inhibitory motoneurons, hydrophobic- intracellular targets.

Question 24

Gastrin

Answer 24

G cells in antrum of stomach detect amino acids leading to pepsinogen and H+ release by parietal cells.

Question 25

Cholecystokinin (CCK

Answer 25

I cells in D/J detect fat and amino acids, secretion of pancreatic enzymes and bile salts involved in fat uptake

Question 26

Secretin

Answer 26

S cells primarily in D/J detect acid stimulates secretion of pancreatic juice including bicarbonate and inhibits gastric motility.

Question 27

Gastric Inhibitory Peptide or Glucose-Dependent Insulinotropic Peptide (GIP

Answer 27

K cells in D/J detect carbohydrates and fat to inhibit gastric acid secretion and stimulate insulin release from pancreas.

Question 28

Motilin

Answer 28

secreted by endocrine cells; released cyclically during fasting state to initiate Migrating Motor Complex

Question 29

What happens to fiber?

Answer 29

Fiber is converted into short chain fatty acids by bacteria in the colon

Question 30

Borborygmi

Answer 30

rumbling noise created by movement of gas in bowels

Question 31

small intestine bacterial overgrowth syndrome

Answer 31

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