Week 1

Question 1

aa’s & monosaccharides are absorbed in

Answer 1

duodenum & jejunum thru secondary active transport

 Na/K ATPases keep Na levels within enterocytes low; coupled transport w/Na often drives uptake of nutrients

Question 2

Cobalamin (B12) & bile salts/acids are absorbed in

Answer 2

the ileum

Question 3

All blood leaving the small intestine is directed thru the

Answer 3

portal vein to the liver

Question 4

Metabolic vasodilators

Answer 4

CO2, H+, K+, adenosine

Question 5

Chylomicrons

Answer 5

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

Question 6

Mesenteric Ischemia

Answer 6

Causes:
 Occlusive mechanisms including thrombi (mesenteric infarction)
 Non‐occlusive mechanisms: prolonged reflex vasoconstriction (due to hypovolemia, heart
failure) or abnormal levels of circulating vasoconstrictors (e.g, epinephrine, angiotensin II)
o Effects:
 Postprandial Pain, Sitophobia
 Necrosis of the tips of the villi
 Loss of barrier function of the wall of the gutuptake of vasodilator toxins (endotoxin) from
the gutresults in Septic Shock

Question 7

Secretory diarrhea

Answer 7

Infection leads to excess secretion of chloride (occurring in the crypts) drawing water into lumen

Question 8

GI Smooth Muscle – Contractile Characteristics

Answer 8

o Rhythmic “phasic” (seconds) contractions and long “tonic” contractions (minutes to hours).
o Basal resting tension or “tone” is maintained without elevation in intracellular Ca++ and without
energy expenditure. (Ex: sphincters are tonically contracted; don’t use energy, just general tone) o GI smooth muscle has a remarkable ability to shorten (e.g., to 50% of resting length!!!)
o Can initiate depolarization in response to stretch leading to contraction.

Question 9

GI Smooth Muscle – Excitation‐Contraction Coupling

Answer 9

o Slow wave electrical activity (3‐12/min, 5‐15 mV) initiated by interstitial cells of Cajal are phasic and propagated over a few centimeters to neighboring cells
o Slow waves generated by increase in Ca followed by repol. by K+ channels o Amplitude, but not frequency, of slow waves can be altered by signals
releasing calcium from internal stores or opening Ca++ channels on plasma
membrane
o Muscle contraction accompanies action potential.

o Excitation‐contraction coupling initiated by increases in intracellular calcium ion concentration
 Binding of ACh to muscarinic Rincreased influx of Ca into cellactivation of calmodulin‐
dependent myosin light chain kinasephosphorylation of myosinincreased myosin ATPase activity & binding of myosin to actincontractiondephosphorylation of myosin by myosin light chain phosphataserelaxation or sustained contraction due to the latch bridge & other mechanisms

Question 10

Migrating Motor Complex

Answer 10

relaxation of sphincters (fully opens all sphincters) and contractions in stomach
and small intestine occurring during fasting (interdigestive) controlled by hormone motilinrepeated giant
waves that sweep from stomach to large intestine to empty everythingwhy gum doesn’t stay for 7 years

Question 11

Submucosal nerve plexus

Answer 11

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

Question 12

Myenteric nerve plexus

Answer 12

bw circular & longitudinal muscle layer from esophagus to internal anus; Auerbach’s

Question 13

Afferent Sensory Neurons

Answer 13

o Excited by fast distension of the gut wall or chemical signals from the lumen of the gut transmitted to sensory neurons.
o Many of the sensory neurons are stimulated by serotonin (5‐HT) released from mucosal enterochromaffin cells (ECL)
 Sensory neurons respond w/ a few AP’s followed by hyperpolarization (adaptation)
o Transfer information about gut environment to interneurons in myenteric plexus which relay signals
up and down the gut.

Question 14

Efferent Motorneurons

Answer 14

o found primarily in the myenteric plexus
o usually unipolar in structure
o excited by fast EPSPsrespond with sustained trains of action potentials
o carry “efferent” information to GI smooth muscle, vascular smooth muscle, GI exocrine secretory
cells and GI endocrine secretory cells
o excitatory fibers release acetylcholine, neurokinin A and substance P
o inhibitory fibers release vasoactive intestinal peptide (VIP) and nitric oxide (NO) on smooth muscle
cellsrelaxation

Question 15

Neural Reflexes influencing GI Function

Answer 15

o “Short” = involve only nerves of the enteric plexes; occur right in your GI wall
o “Long” = both CNS and ANS are involved

Question 16

Extrinsic Autonomic Nervous System

Answer 16

o Afferent information leaving GI tract is carried by autonomic nerves
o Parasympathetic: mostly cholinergic of vagus nerve; stimulates activity of the enteric plexuses,
increases GI motility and secretory activity.
o Sympathetic: mostly adrenergic, generally inhibits activity of the enteric plexuses, decreases GI
motility, contracts GI sphincters, constricts GI microvasculature

Question 17

Parasympathetic …

 Sympathetic…

Answer 17

Parasympathetic increases activity: cholinergic, vagus“rest and digest”
 Sympathetic stimulation decreases activity: noradrenaline, dopamine, neuropeptide Y

Question 18

In general:
Parasympathetic …
 Sympathetic…

Answer 18

Parasympathetic increases activity: cholinergic, vagus“rest and digest”
 Sympathetic stimulation decreases activity: noradrenaline, dopamine, neuropeptide Y

Question 19

Vago‐vagal Reflex

Answer 19

o Vagal afferent info is transmitted to autonomic centers in the medulla
o Vagal efferents coordinate excitatory (ACh) & inhibitory (NO) activity within the Enteric Nervous System to mediate peristalsis:

Question 20

Acetylcholine

Answer 20

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

Question 21

Gastrin releasing peptide

Answer 21

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

Question 22

Substance P

Answer 22

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

Question 23

Vasoactive Intestinal Peptide

Answer 23

(VIP) – Promotes motility
 Relaxes smooth muscle in esophagus and stomach (“inhibitory”)
 Stimulates fluid secretion and promotes dilation of the GI vasculature increase cAMP

Question 24

Nitric Oxide

Answer 24

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

Question 25

Hormone:Cholecystokinin CCK

Cell:

Cell detects:

Hormone release stimulates secretion of:

Answer 25

Hormone:
Cholecystokinin CCK

Cell:
I cells (D/J)

Cell detects:
Fat
Amino acids

Hormone release stimulates secretion of:
Pancreatic enzymes Bile salts for fat uptake

Question 26

Hormone: Gastrin

Cell:

Cell detects:

Hormone release stimulates secretion of:

Answer 26

Hormone:
Gastrin

Cell:
G cell (stomach antrum)

Cell detects:
Amino acids
Pepsinogen

Hormone release stimulates secretion of:
H+ (from parietal cells)

Question 27

Hormone:
Secretin

Cell:

Cell detects:

Hormone release stimulates secretion of:

Answer 27

Hormone:
Secretin

Cell:
S cells (D/J)

Cell detects:
Acid

Hormone release stimulates secretion of:
Pancreatic juice (bicarbonate)

Question 28

Hormone:
Gastric Inhibitory Peptide or Glucose‐Dependent Insulinotropic Peptide (GIP)

Cell:

Cell detects:

Hormone release stimulates secretion of:

Answer 28

Hormone:
Gastric Inhibitory Peptide or Glucose‐Dependent Insulinotropic Peptide (GIP)

Cell:
K cells (D/J)

Cell detects:
Carbohydrates Fat

Hormone release stimulates secretion of:
Inhibits gastric acid secretion
Stimulates insulin release from pancreas

Question 29

Hormone:
Motilin

Cell:

Cell detects:

Hormone release stimulates secretion of:

Answer 29

Hormone:
Motilin

Cell:
Endocrine cells

Cell detects:
Fasting state (released cyclically thoughout)

Hormone release stimulates secretion of:
Initiates Migrating Motor Complex

Question 30

Paracrine Regulators

Answer 30

further modulate the response

 Histamine (ECL cells) and somatostatin (D cells) = paracrine regulators

Question 31

Borborygmi

Answer 31

rumbling noise created by movement of gas in bowels

Question 32

Sympathetic

Answer 32

associated with T1‐L2 spinal cord segments = Fight or Flight
 Function: inhibit peristalsis and vasoconstrict
 Preganglionic: cell bodies lie in thoracolumbar lateral horn; relatively short
 Single sympathetic preganglionic axon has many collateral branchesmay synapse with ≥ 20 postganglionic neuronssynapse with several visceral effectors
 Terminate in paravertebral or prevertebral ganglia; ACh is neurotransmitter
 Postganglionic: highly branched; long; release NE as neurotransmitter (except for sweat glands)

Question 33

Parasympathetic

Answer 33

associated with brain stem (cranial nerves) and spinal cord segments S2‐S4 = Rest, Read, and Digest  Function: stimulate peristalsis, relax sphincters, stimulate glandular secretion
 Preganglionic: fibers originate in cranial and sacral regions; relatively long; use ACh
 Postganglionic: short; release ACh

Question 34

Esophagus innervation

Answer 34

fibromuscular tube extending from cricoid cartilage to stomach (11th thoracic vertebra) o Upper 1/3: parasympathetics from recurrent laryngeal nerve
o Esophageal plexus: below bifurcation of trachea
 Parasympathetics: from vagus (CN X) – supply smooth muscle and glands
 Post‐ganglionic sympathetics: from ~T1‐4 – directly or via cardiac or pulmonary plexuses innervate vascular
smooth muscle
 Vagus provides VA from esophagus; thoracic splanchnic branches carry visceral pain from esophagus