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Physiology Flashcards

1
Q

What are the seven sphincters of the GI tract?

A 
UES
LES
pyloric sphincter
sphincter of Oddi
ileocecal
internal anal
external anal
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2
Q

What area of the GIT is Meissner’s plexus best developed in? What does it control?

A

best developed in the SI and controls GI secretions

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3
Q

Where is Auerbach’s plexus found? What does it control?

A

it is between circular and longitudinal layers of muscle in muscularis externa and is well developed throughout the GIT; controls GI movements

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4
Q

What does the enteric nervous system control?

A

motility, exocrine and endocrine secretions, and microcirculation of the GIT

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5
Q

How is the enteric nervous system connected to the autonomic neural network in CNS?

A

by parasympathetic and sympathetic nerves

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6
Q

What are examples of intermediate cells which the ENS is able to indirectly influence effector systems?

A

endocrine, interstitial cells of Cajal, cells of immune system (mast cells)

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7
Q

Where are primary vagal afferent neuron cell bodies?

A

nodose ganglia

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8
Q

Where are primary sympathetic afferent neuron cell bodies?

A

dorsal root ganglia

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9
Q

The presence of extrinsic nerves from the autonomic nervous system is not necessary for may of the functional characteristics of GIT, but is needed for ____________

A

coordination of most GI functions

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10
Q

Afferent fibers come from what, within the gut wall and then run to the CNS, which then influence central and neural control

A

chemoreceptors and mechanoreceptors

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11
Q

What nerves contribute the parasympathetic innervation of the GIT and what area do they go to?

A 
vagus nerves (above and first 2/3 of the transverse colon)
pelvic (sacral) nerves (below and distal of the transverse colon)
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12
Q

Where do parasympathetic, pre-g fibers terminate? what do they share their post-g fibers with?

A

ganglia of the intramural plexuses and share their post-g with the ENS

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13
Q

When the vagus nerves are activated, what happens?

A

mostly excitatory - increasing motility or secretion

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14
Q

What two neurotransmitters are considered excitatory? What two neurotransmitters are considered inhibitors?

A

excitatory - ACh and SubP

inhibitory - VIP and NO

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15
Q

Where do sympathetic post-g adrenergic fibers arise from?

A

prevertebral ganglia

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16
Q

Most sympathetic fibers synapse where? This releases norepinepherine that does what?

A

intramural plexuses
NE inhibits parasympathetic ACh release by activating alpha2 presynaptic receptors
ultimately decreasing motility and secretion

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17
Q

Pathways which influence the muscularis externa (____________) and muscularis mucosae (__________) act through the intramural plexuses.

A

inhibitory

stimulating

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18
Q

Sympathetic fibers innervate blood vessels of the gut, directly causing what? through what mechanism?

A

causing vasoconstriction (alpha1 mediated) which reduces secretion

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19
Q

Circular and longitudinal smooth muscle is arranged in ________, connected together via _______________ allowing ion movement

A

bundles

low resistance gap junctions

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20
Q

What is a major determinant of how far the electrical signal is transmitted in smooth muscle down the GI tract?

A

excitability of cells in adjacent muscle bundles

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21
Q

What are slow waves?

A

oscillations in resting membrane potential (from ~-40 to -80 mV) that occur at a given rate

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22
Q

What is the basic electrical rhythm?

A

the rate at which slow waves occur

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23
Q

What are pacemaker cells called?

A

interstitial cells of Cajal

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24
Q

What is the BER in the stomach? in the duodenum? ileum?

A

3/min in stomach, 12/min in duodenum, slows on way to ileum

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25
Q

The BER of each segment is set by a group of faster cells called what?

A

pacemakers

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26
Q

What characteristic of slow waves can be modulated by intrinsic and extrinsic neural input? What increases or decreases this?

A

amplitude;
sympathetic input decreases amplitude,
parasympathetic increases amplitude

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27
Q

If _______________ exceeds threshold, action potentials may be triggered. The more APs that occur, the greater the contraction and force (tension) developed)

A

slow waves

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28
Q

What phase of AP is due primarily to Calcium entry into the cell through L-type Ca channels? Repolarization occurs coincident with increasing what?

A

initial rising phase

Gk

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29
Q

What is a major source of calcium for concentration?

A

extracellular calcium entering visceral smooth muscle cells during an AP

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30
Q

Initial AP occurs near what part of the slow wave?

A

peak on the rising phase

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31
Q

What contracts only in response to APs?

A

intestine

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32
Q

What can contract in the absence of APs?

A

stomach

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33
Q

Mixing movements of the GIT that are local constrictive contractions are called what?

A

segmentation

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34
Q

What is the stimulus for peristalsis?

A

distention

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35
Q

What is the peristaltic reflex?

A

The law of the gut - segment on the orad side of a distention contracts first and moves sequentially caudad. simultaneous reflex relaxation of the smooth muscle in front of the distention through ENS

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36
Q

What is the strong wave of contractile activity that spreads down through the GIT between meals called? When does this occur? What is its purpose?

A

Migrating Motor Complex (MMC); occurs once every two hours during the interdigestive (fasted) period; sweep clean the GI lumen between meals, moving undigested contents >2mm in diameter to move out of stomach and into SI

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37
Q

What are four things that control contractile activities of the GI system?

A
  1. CNS/ANS
  2. ENS
  3. electrical coupling between cells
  4. humoral factors
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38
Q

Neuromuscular contractions- the circular layer of smooth muscle makes the gut __________________. the longitudinal layrer of smooth muscle makes ___________________.

A

circular layer - longer and thinner

longitudinal layer - shorter and wider

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39
Q

What two transmitters excite smooth muscle contraction?

A

ACh and Sub P

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40
Q

What two transmitters relax GI smooth muscle?

A

NO and VIP (vasoactive intestinal polypeptide)

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41
Q

What transmitter is released by enteric interneurons?

A

serotonin (5-HT)

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42
Q

What hormone increases the force of stomach contractions?

A

gastrin

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43
Q

what hormone is responsible for MMC (migrating motor complex?

A

motilin

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44
Q

Where is CCK released and what does it cause?

A

secreted in the SI in response to acid chyme entering the duodenum;
decreases gastric motility
increases GB contractility

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45
Q

What does secretin do?

A

Decreases motility of most of GIT

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46
Q

What does Gastric Inhibitory Peptide (GIP) do?

A

mildly decreases gastric motility

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47
Q

What are the three phases of swallowing?

A
  1. oral or voluntary phase
    food bolus to back and tactile receptors initiate swallowing reflex at pharyngeal level
  2. pharyngeal phase
    prevention of food going into nasopharynx and trachea; UES relaxes, superior constrictor initiates peristalsis (coordinated by swallowing center in reticular formation)
  3. esophageal phase
    UES constricts, primary peristalsis continues down and then secondary peristalsis is a second wave occurring d/t continued distention if the primary wave did not completely clear (regulated by swallowing center)
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48
Q

Describe the pressure at the UES at rest and when swallowing.

A

at rest - about 40 mmHg

when swallowing, pressure rapidly drops, bolus passes, pressure rapidly increases, prevents entry of air

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49
Q

Describe the LES pressure and tone at rest

A

resting pressure about 30 mmHg
sphincter is tonically contracted by extrinsic and intrinsic nerves, hormones, and neuromodulators
ENS alone can maintain constriction (extrinsic nerves can be cut and maintained tone)

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50
Q

What is LES relaxation mediated by?

A

a vagovagal reflex that causes relaxation of the circular muscle layer

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51
Q

What is achalasia? What is it associated with?

A

a condition where the LES does not fully relax during swallowing. associated with degeneration of nerve ganglion cells within the myenteric plexus (often a result of an autoimmune attack)

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52
Q

Describe the LES pressure in relation to gastric pressure

A

in normal person, the LES pressure is always higher than gastric pressure except during swallowing

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53
Q

What are three functions of the stomach and its associated motility?

A
  1. large reservoir
  2. fragment and mix food into chyme
  3. control rate of emptying from antrum to duodenum
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54
Q

What are folds of the mucosal lining of the stomach called?

A

rugae

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55
Q

swallowing causes receptive relaxation of the orad portion of the stomach; what is this mediated by?

A

vagal efferents: VIP and NO are the transmitters

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56
Q

Where are the interstitial cells of Cajal located? What do they initiate?

A

centrally in the body of the stomach

initiate the slow waves about 3/min

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57
Q

As pressure builds in the antrum, what will happen to chyme?

A

some is forced into the duodenum, most is forced back into the body of the stomach by retropulsion

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58
Q

The vagus does what two things in regard to emptying the stomach into the duodenum?

A

organizes both the peristaltic wave and influences force of the contractions

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59
Q

Describe the tone of the pyloric sphincter at rest.

A

tonically constricted, allows fluid and small particles to pass but prevents most of the chyme from entering the duodenum even when there are strong antral contractions

60
Q

emptying of the stomach is regulated by bother neural and humoral mechanisms, with receptors in the SI that can sense and respond to what three things?

A

acidity, fat content, and osmotic pressure

61
Q

What hormone is released in response to food in the stomach? What does this do?

A

gastrin - increases stomach motility and thereby promotes gastric emptying

62
Q

What four factors tend to decrease gastric motility?

A

acids, fats, hypertonicity, and amino acids

63
Q

What hormonally stimulates vomiting?

A

GI irritation causes paracrine release of serotonin 5-HT from enterochromaffin cells which stimulates vagal afferents to medullary vomiting center

64
Q

What receptors mediate the “emetic trigger zone”? Where is this zone located?

A

dopamine, histamine, and serotonin receptors

located in the fourth ventricle

65
Q

What is the first step of vomiting? Where does this begin?

A

reverse peristalsis, starting as low as the mid SI, copious salivation begins

66
Q

The feeling of nausea is the indication that what two things have begun?

A

pyloric sphincter and stomach relaxation have begun

67
Q

What is the physiology behind retching?

A

stomach contents are being pushed up in the esophagus and the UES remains closed

68
Q

What is segmentation in the SI?

A

mixing contractions (chopping) and stretch (distention) by chyme initiating localized contraction of circular muscle layer at spaced intervals; muscle relaxes and it starts over at a location a segment away

69
Q

What is the rate of segmentation determined by? What is the innervation of this?

A

that segment’s BER; duodenum 12/min ileum 8-9/min, frequency decreasing along length;

the ENS - myenteric plexus

70
Q

What is intestinointestinal reflex?

A

overdistention of one segment of the intestine will cause reflex relaxation in the rest of the intestine through extrinsic nerves

71
Q

What is gastroileal reflex?

A

stomach and ileum interact reflexly; increases activity in the stomach will increase motility of the ileum and accelerate the movement of chyme through the ileocecal sphincter

72
Q

What is the gastrocolic reflex?

A

gastric distention will increase activity in the colon

73
Q

What are the four phases of MMC?

A
  1. quiescence; slow waves, minimal mechanical activity
  2. irregular APs and contractions increase frequency and intensity
  3. intense electrical and mechanical activity lasting 3-6 minutes
  4. rapid decline in electrical and mechanical activity
74
Q

Distention of the cecum causes the ileocecal valve to do what?

A

contraction

75
Q

What three things relax the ileocecal valve?

A
  1. distention in the terminal ileum
  2. gastrin
  3. gastroileal reflex
76
Q

Circular muscle in the colon contracts in intervals and causes what to occur? What is this similar to in the SI?

A

haustra formation similar to segmentation in the SI

77
Q

Three strips of longitudinal muscle in the colon that can contract are called what?

A

taenia coli

78
Q

What are propulsive peristaltic waves in the colon called? How often do they occur?

A

mass movements, occur 1 to 3 times a day

79
Q

What two reflexes increase mass movement activity?

A

gastrocolic and duodenocolic reflexes

80
Q

Describe the resting state of the rectum and anal sphincters,

A

rectum is usually empty, the internal anal sphincter is tonically constricted while the external anal sphincter is relaxed at rest

81
Q

What is the rectosphincteric reflex?

A

a mass movement from the sigmoid colon fills the rectum, which then contracts, while reflexively relaxing the IAS and contracting the EAS

82
Q

How is the EAS innervated and controlled?

A

striated muscle under voluntary control via the pudendal nerve

83
Q

What physiological changes can cause diarrhea?

A

increased osmotic load, inflammatory exudate, increased secretion, and/or decreased absorption time

84
Q

Irritation of the lower GIT can cause release of what hormone causing increasing water and motility?

A

serotonin

85
Q

What four other reflexes of the intestine and its pair reduce gastric motility?

A
  1. peritoneointestinal reflex (peritoneum irritation)
  2. renointestinal reflex (kidney irritation)
  3. vesicointestinal reflex (bladder irritation)
  4. somatointestinal reflex (irritation of skin over stomach)
86
Q

What are the three sources of gas in the GIT?

A

swallowed air, formed by bacteria, diffusion from blood

87
Q

What are three roles of secretion?

A

facilitate digestion - enzyme secretion
provide protection - mucous secretion
provide lubrication - serous secretion

88
Q

What are three types of mucous cells?

A

goblet cells, neck mucous cells, and surface mucous cells

89
Q

What are the two principle locations of acinus glands and what kind of secretions do they have?

A

salivary glands and pancreas

produce watery secretions containing proteins such as digestive enzymes

90
Q

What cells secrete a large volume of extracellular fluid into the GIT? Where are these located?

A

crypts of liberkuhn (water and electrolyte secretion)

in mucosa of SI

91
Q

What four receptive type things will stimulate secretion?

A

tactile, chemical, distention, motility

92
Q

What does sympathetic stimulation due to secretion

A

decreases secretion by inhibiting parasympathetic ACh release and decreasing blood flow (alpha1)

93
Q

What are the glycoproteins that lubricate food and where are they made?

A

mucins made in the submandibular and sublingual glands

94
Q

At what pH does the function of salivary amylase stop?

A

<4

95
Q

What three things in saliva have antibacterial action?

A

lysozyme, lactoferrin and peroxisomes

96
Q

Parasympathetic stimulation of salivary glands causes what to happen?

A

vasodilation and increased blood flow

ACh activates endothelial NO synthase, and NO causes relaxation of VSMC

97
Q

Why is saliva hypotonic?

A

because sodium and chloride are readily reabsorbed in excretory ducts leaving water behind.

98
Q

What are four characteristics unique to salivation?

A
  1. saliva always hypotonic
  2. almost totally under neural control
  3. parasympathetic stimulation vasodilates
  4. sympathetic stimulation causes secretion (initially)
99
Q

Acinar cell secretion of amylase, fluid, and electrolytes is dependent on what?

A

second messengers including cAMP, IP3, and Ca

100
Q

increased cAMP (from NE) means increased what? increased Ca2+ (from ACh, and SubP) means increased what?

A

amylase

volume

101
Q

What are six things in gastric juice?

A

salts, water, HCl, pepsins, intrinsic factor, and mucous

102
Q

What can cause hypokalemia in regards to gastric acid? Why?

A

vomiting, because gastric acid contains more potassium than plasma does

103
Q

What is the major anion in gastric acid?

A

Cl-

104
Q

What is the tonicity of gastric acid in relation to plasma?

A

ranges from isotonic (high rates of secretion) to hypotonic

105
Q

What converts pepsinogen to pepsin?

A

HCl

106
Q

What are the morphological changes of parietal cells during acid secretion?

A

At rest, internalized intracellular canaliculi with tubovesicles in cytoplasm. Active cells have tubulovesicular system fused with intracellular canaliculi to open the lumen of the gland, exposing HCl-pumps

107
Q

What is the alkaline tide?

A

When bicarb ion leaves the cell and Cl enters the cell against gradient. bicarb into blood, raising blood pH

108
Q

Where is pepsin stored and how is it released?

A

stored in zymogen granules, released by exocytosis stimulated by histamine, ACh, gastrin, secretin, and CCK

109
Q

What secretes insoluble mucous? soluble mucous?

A

insoluble mucous by surface epithelial cells (surface mucous cells) and insoluble mucous by pyloric glands

110
Q

When cell damage leads to ulceration, what causes vasodilation?

A

histamine release

111
Q

What increases mucosal blood flow, bicarb and mucus secretions, while stimulating mucosal cell repair and renewal?

A

prostaglandins

112
Q

How does ACh stimulate HCl secretion? What blocks this?

A

from vagus, stimulates muscarinic receptors, opens calcium channels
atropine blocks

113
Q

How does histamine stimulate HCl secretion? What blocks this?

A

from enterochromaffin-like cells (ECL) diffuses to parietal cells and stimulates H2 receptor (then activates cAMP); blocked by H2 receptor antagonists like cimetidine

114
Q

Where is gastrin from that stimulates HCl secretion?

A

from G cells in the stomach antrum and duodenu; opens calcium channels

115
Q

What are three phases of gastric acid secretion?

A
  1. cephalic - vagal reflexes to parietal and G cells (ACh and gastrin released)
  2. gastric - distention causes local and vagovagal reflexes to parietal and G cells (ACh and gastrin released)
  3. intestinal - protein digestion products in duodenum lead to stimulation of intestinal G cells and release of gastrin
116
Q

When is HCl secretion high? low?

A

high HCl secretion in the evening, low in the morning

117
Q

Acid less than 3 pH in the antrum of the stomach stimulates what?

A

somatostatin release by D cells, which decrease gastrin release by G, INHIBITING gastric acid secretion

118
Q

Acid in duodenum causes what?

A

enterogastric reflex which inhibits acid secretion
stimulates release of both secretin and bulbogastrone which inhibit gastrin release as well as directly inhibiting parietal cells

119
Q

Hyperosmotic solutions, fatty acids, and monoglycerides in the duodenum cause what?

A

GIP and CCK release, which inhibit acid secretion

120
Q

Despite secretin and CCK inhibiting acid secretion, they stimulate what?

A

pepsinogen secretion

121
Q

Someone losing gastric juices (vomiting or aspirating) can’t get just NaCl and dextrose replacement because why?

A

it will result in hypokalemic metabolic alkalosis (fatal)

122
Q

How are secretions of the pancreas different when stimulated by secretin and CCK?

A

secretin - aqueous pancreatic juice

CCK - rich in pancreatic enzymes

123
Q

What is in aqueous pancreatic juice?

A

Na, K similar to plasma
HCO3 and Cl major anions
initially hypertonic because of HCO3 but equilibriates with water to make it isotonic

124
Q

What four proteases are released in the pancreas in inactive form?

A

trypsin, chymotrypsin, carboxypeptidase, ribonuclease and deoxyribonuclease

125
Q

What prevents activation of proteases while in the pancreatic duct?

A

trypsin inhibitor

126
Q

What are three lipases found in pancreatic juice?

A

pancreatic lipase, cholesterol ester hydrolase, phospholipase A2

127
Q

What is the pancreas condition between meals in regard to neural control?

A

sympathetic stimulation, reducing enzyme secretion, secondary to reduced blood flow

128
Q

How is parasympathetic neural regulation acting on the pancreas?

A

during cephalic and gastric phases of stomach secretions, accumulate enzymes, low secretion level

129
Q

What causes pancreatic juices to be released?

A

chyme into duodenum triggers secretin to release pancreatic juice. CCK regulates proportion of enzymes in juice to chyme consistency

130
Q

ACh, CCK, gastrin, and Sub P in the pancreas work on what?

A

Ca channels

131
Q

Secretin and VIP in the pancreas work on what?

A

cAMP

132
Q

What are Brunner’s glands stimulated by?

A

tactile stimuli

133
Q

How are crypts of Libekuhn stimulated?

A

mechanical stimuli

134
Q

How is splanchnic circulation arranged?

A

both in parallel (intestines and pancreas) and series (hepatic artery and portal vein into liver)

135
Q

Sympathetic stimulation causes what kind of control on circulation?

A

temporary expulsion of up to 1 L of blood into systemic circulation from capacitance veins - providing autotransfusion

136
Q

Parasympathetic stimulation causes what kind of control on circulation?

A

(PRIMARY)increases both the secretory and contractile activities of the gut - most are vasoactive and cause dilation(SECONDARY) - increasing metabolic activity and increases the production of vasoactive metabolites - causing increased blood flow

137
Q

What protects capillaries in the gut from high systemic pressures and excess fluid filtration?

A

myogenic vasoconstriction

138
Q

Low perfusion pressures result in what?

A

decreased blood flow, reduced substrates delivery and the accumulation of metabolic factors that cause vasodilation and increased blood flow

139
Q

Control of local blood flow is closely linked to what in the hepatosplanchnic ciruclation?

A

metabolic activity of the tissue (secretory or muscular)

140
Q

What is the escape phenomenon?

A

despite continued stimulation the splanchnic arterioles but not veins, will spontaneously vasodilate within minutes - protective mech to prevent consequences of countercurrent exchange - hypoxia

141
Q

What are three reasons for biles secretion?

A
  1. digest and absorb lipids
  2. eliminate excess cholesterol and bile pigments
  3. eliminate heavy metals or phenothiazines
142
Q

How does bile remain isosmotic?

A

the large number of inorganic cations present in the GB are bound to bile acids

143
Q

What causes contraction of the GB?

A

vagal stimulation and CCK cause contractions of the GB and relaxation of the sphincter of Oddi

144
Q

What is the standing gradient osmotic mechanism?

A 
Na/K pump moves Na out of cell
Cl follows
outside cell is hypertonic
water goes out of cell
hydrostatic pressure moves water and electrolytes into capillaries
145
Q

What is absorbed in the ileum?

A

bile acids - in portal blood, bound to plasma proteins

GI (6 decks)

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