Chapter 63: General Principles of GI Function

The intestinal wall is composed of the following layers, from out to in: (1) _____, (2) _____, (3) _____, (4) _____, and (5) _____.

Serosa, longitudinal smooth muscle, circular smooth muscle, submucosa, mucosa

Motor functions of the gut are performed by layers of _____ which are electrically connected in a _____.

Smooth muscle, syncytium

The rhythm of most GI contractions is determined by the frequency of _____ in the smooth muscle _____ potential.

Slow waves, membrane

Slow waves in smooth muscle membrane potential may result from slow undulation of the activity of the _____ or rhythmic changes is _____.

Sodium-potassium pump, sodium permeability

_____ are true action potentials in the gut that cause muscle contraction, and they occur when the resting membrane potential of smooth muscle cells becomes more positive than _____ mV (the normal membrane potential is _____ to _____ mV).

Spike potentials, -40, -50, -60

Channels responsible for spike potentials are the _____ channels.

Calcium-sodium

Factors that shift the resting membrane potential of GI smooth muscle cells to a less negative value (depolarization) include (1) _____ of muscle, (2) _____ stimulation, (3) _____ nerve stimulation, or (4) stimulation by _____.

Stretching, acetylcholine, parasympathetic, hormones

Factors that hyperpolarize resting membrane potential of GI smooth muscle cells include (1) _____ or _____ in the blood, and (2) _____ nerve stimulation.

Norepinephrine, epinephrine, sympathetic (via norepinephrine)

The GI tract possesses its own nervous system, the _____ nervous system.

Enteric

The enteric nervous system is composed mainly of two plexuses: the _____ between smooth muscle layers and the _____ in the submucosa.

Myenteric plexus of Auerbach, submucosal plexus of Meissner

Stimulation of the myenteric plexus of Auerbach causes (1) increased _____ of gut wall, (2) increased _____ of rhythmical contractions, (3) increased _____ of conduction, and (4) increased _____ of conduction.

Tone, intensity, rate, velocity

The myenteric plexus of Auerbach _____ three sphincters in the GI tract: the _____ sphincter, which empties the stomach; the sphincter of the _____, which empties the small intestine; and the _____ sphincter, which allows food into the stomach.

Inhibits, pyloric, ileocecal valve, lower esophageal

Many _____ signals originating from GI epithelium are integrated in the submucosal plexus of Meissner to help control local intestinal _____, local intestinal _____, and local _____ of submucosal muscle.

Secretion, absorption, contraction

Parasympathetic nerves _____ the activity of the enteric nervous system, and thus must GI functions.

Increase

Sympathetic nerves _____ the activity of the enteric nervous system, and thus, most GI functions.

Decrease

Parasympathetic supply to the gut comes through a _____ division, by way of the _____ nerves, which supply the esophagus, stomach, pancreas, small intestine, and first half of the large intestine; and through a _____ division, by way of the _____ nerves, to the distal half of the large intestine.

Cranial, vagus, sacral, pelvic

Sacral parasympathetics travelling by way of the _____ nerves to the sigmoidal, rectal, and anal regions function in _____ reflexes.

Pelvic, defecation

Sympathetic nerves innervate _____ portions of the GI tract, unlike parasympathetic nerves.

All

Sympathetic nerve endings in the GI tract secrete _____, which acts directly to inhibit _____ (in a slight way) and indirectly, to inhibit the _____ (in a major way).

Norepinephrine, smooth muscle, enteric nervous system

There are three types of reflex essential for GI control: (1) reflexes occurring entirely within the _____, (2) reflexes traveling from the gut to _____ and back, and (3) reflexes traveling from the gut to the _____ or _____ and back.

Enteric nervous system, sympathetic ganglia, spinal cord, brainstem

In the _____ reflex, signals from the stomach cause evacuation of the colon.

Gastrocolic

In the _____ reflexes, signals from the colon and small intestine inhibit stomach motility and secretions.

Enterogastric

In the _____ reflex, signals from the colon inhibit emptying of ileal contents into the colon.

Coloileal

GI reflexes occurring entirely within the _____ control GI secretion, peristalsis, mixing contractions, local inhibitory effects, etc.

Enteric nervous system

GI reflexes involving _____ include the gastrocolic, enterogastric, and coloileal reflexes (in which signals are transmitted very long distances).

Sympathetic ganglia

GI reflexes involving the _____ or _____ include signals from the stomach/duodenum controlling gastric motor/secretory activity, pain reflexes which _____ the entire GI tract, and defecation reflexes.

Spinal cord, brainstem, inhibit

There are two types of movement in the GI tract: _____ movements and _____ movements.

Propulsive, mixing

_____ is the basic propulsive movement of the GI tract.

Peristalsis

_____ is the term used to describe when, at the same time a contractile ring moves anal-ward, the gut relaxes several centimeters downstream, allowing food to be propelled more easily.

Receptive relaxation

The contractile ring and receptive relaxation pattern of propulsion in the GI tract does not occur in the absence of the _____, and thus this reflex is known as the _____ or _____ reflex.

Myenteric plexus of Auerbach, myenteric, peristaltic

The _____ is the term combining the phenomena of the peristaltic reflex plus the direction of movement toward the anus.

Law of the gut

_____ contractions, by themselves or in combination with _____ contractions, can mix the contents of the intestines.

Peristaltic, segmental

Blood vessels of the GI tract are part of the _____ circulation.

Splanchnic

The _____ circulation includes blood flow through the gut, spleen, pancreas, and liver.

Splanchnic

During active absorption of nutrients, blood flow in the villi and submucosal regions are _____.

Increased

One reason for increased blood flow during increased GI activity is the release of _____ from mucosa during digestion.

Vasodilator substances (e.g. cholecystokinin, gastrin, secretin)

One reason for increased blood flow during increased GI activity is the release of _____ from GI glands.

Kinins (kallidin, bradykinin)

Perhaps the most important reason for increased blood flow during increased GI activity is the _____ of the gut wall due to greater gut metabolic activity.

Hypoxia

Parasympathetic stimulation of the stomach and lower colon _____ local blood flow and glandular secretion. The change in _____ might be secondary to the change in _____.

Increases, blood flow, secretion

Sympathetic stimulation of the gut _____ blood flow, but it soon restores to normal by means of _____.

Decreases, autoregulatory escape

_____ vasoconstriction in the GI tract is important when other parts of the body need extra blood flow (e.g., during heavy exercise, or when in circulatory shock).

Sympathetic