Physiology Flashcards
(145 cards)
1
Q
What are the seven sphincters of the GI tract?
A
UES LES pyloric sphincter sphincter of Oddi ileocecal internal anal external anal
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
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
4
Q
What does the enteric nervous system control?
A
motility, exocrine and endocrine secretions, and microcirculation of the GIT
5
Q
How is the enteric nervous system connected to the autonomic neural network in CNS?
A
by parasympathetic and sympathetic nerves
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)
7
Q
Where are primary vagal afferent neuron cell bodies?
A
nodose ganglia
8
Q
Where are primary sympathetic afferent neuron cell bodies?
A
dorsal root ganglia
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
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
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)
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
13
Q
When the vagus nerves are activated, what happens?
A
mostly excitatory - increasing motility or secretion
14
Q
What two neurotransmitters are considered excitatory? What two neurotransmitters are considered inhibitors?
A
excitatory - ACh and SubP
inhibitory - VIP and NO
15
Q
Where do sympathetic post-g adrenergic fibers arise from?
A
prevertebral ganglia
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
17
Q
Pathways which influence the muscularis externa (____________) and muscularis mucosae (__________) act through the intramural plexuses.
A
inhibitory
stimulating
18
Q
Sympathetic fibers innervate blood vessels of the gut, directly causing what? through what mechanism?
A
causing vasoconstriction (alpha1 mediated) which reduces secretion
19
Q
Circular and longitudinal smooth muscle is arranged in ________, connected together via _______________ allowing ion movement
A
bundles
low resistance gap junctions
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
21
Q
What are slow waves?
A
oscillations in resting membrane potential (from ~-40 to -80 mV) that occur at a given rate
22
Q
What is the basic electrical rhythm?
A
the rate at which slow waves occur
23
Q
What are pacemaker cells called?
A
interstitial cells of Cajal
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
25
The BER of each segment is set by a group of faster cells called what?
pacemakers
26
What characteristic of slow waves can be modulated by intrinsic and extrinsic neural input? What increases or decreases this?
amplitude;
sympathetic input decreases amplitude,
parasympathetic increases amplitude
27
If _______________ exceeds threshold, action potentials may be triggered. The more APs that occur, the greater the contraction and force (tension) developed)
slow waves
28
What phase of AP is due primarily to Calcium entry into the cell through L-type Ca channels? Repolarization occurs coincident with increasing what?
initial rising phase
| Gk
29
What is a major source of calcium for concentration?
extracellular calcium entering visceral smooth muscle cells during an AP
30
Initial AP occurs near what part of the slow wave?
peak on the rising phase
31
What contracts only in response to APs?
intestine
32
What can contract in the absence of APs?
stomach
33
Mixing movements of the GIT that are local constrictive contractions are called what?
segmentation
34
What is the stimulus for peristalsis?
distention
35
What is the peristaltic reflex?
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
36
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?
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
37
What are four things that control contractile activities of the GI system?
1. CNS/ANS
2. ENS
3. electrical coupling between cells
4. humoral factors
38
Neuromuscular contractions- the circular layer of smooth muscle makes the gut __________________. the longitudinal layrer of smooth muscle makes ___________________.
circular layer - longer and thinner
| longitudinal layer - shorter and wider
39
What two transmitters excite smooth muscle contraction?
ACh and Sub P
40
What two transmitters relax GI smooth muscle?
NO and VIP (vasoactive intestinal polypeptide)
41
What transmitter is released by enteric interneurons?
serotonin (5-HT)
42
What hormone increases the force of stomach contractions?
gastrin
43
what hormone is responsible for MMC (migrating motor complex?
motilin
44
Where is CCK released and what does it cause?
secreted in the SI in response to acid chyme entering the duodenum;
decreases gastric motility
increases GB contractility
45
What does secretin do?
Decreases motility of most of GIT
46
What does Gastric Inhibitory Peptide (GIP) do?
mildly decreases gastric motility
47
What are the three phases of swallowing?
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)
48
Describe the pressure at the UES at rest and when swallowing.
at rest - about 40 mmHg
| when swallowing, pressure rapidly drops, bolus passes, pressure rapidly increases, prevents entry of air
49
Describe the LES pressure and tone at rest
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)
50
What is LES relaxation mediated by?
a vagovagal reflex that causes relaxation of the circular muscle layer
51
What is achalasia? What is it associated with?
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)
52
Describe the LES pressure in relation to gastric pressure
in normal person, the LES pressure is always higher than gastric pressure except during swallowing
53
What are three functions of the stomach and its associated motility?
1. large reservoir
2. fragment and mix food into chyme
3. control rate of emptying from antrum to duodenum
54
What are folds of the mucosal lining of the stomach called?
rugae
55
swallowing causes receptive relaxation of the orad portion of the stomach; what is this mediated by?
vagal efferents: VIP and NO are the transmitters
56
Where are the interstitial cells of Cajal located? What do they initiate?
centrally in the body of the stomach
| initiate the slow waves about 3/min
57
As pressure builds in the antrum, what will happen to chyme?
some is forced into the duodenum, most is forced back into the body of the stomach by retropulsion
58
The vagus does what two things in regard to emptying the stomach into the duodenum?
organizes both the peristaltic wave and influences force of the contractions
59
Describe the tone of the pyloric sphincter at rest.
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
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?
acidity, fat content, and osmotic pressure
61
What hormone is released in response to food in the stomach? What does this do?
gastrin - increases stomach motility and thereby promotes gastric emptying
62
What four factors tend to decrease gastric motility?
acids, fats, hypertonicity, and amino acids
63
What hormonally stimulates vomiting?
GI irritation causes paracrine release of serotonin 5-HT from enterochromaffin cells which stimulates vagal afferents to medullary vomiting center
64
What receptors mediate the "emetic trigger zone"? Where is this zone located?
dopamine, histamine, and serotonin receptors
| located in the fourth ventricle
65
What is the first step of vomiting? Where does this begin?
reverse peristalsis, starting as low as the mid SI, copious salivation begins
66
The feeling of nausea is the indication that what two things have begun?
pyloric sphincter and stomach relaxation have begun
67
What is the physiology behind retching?
stomach contents are being pushed up in the esophagus and the UES remains closed
68
What is segmentation in the SI?
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
What is the rate of segmentation determined by? What is the innervation of this?
that segment's BER; duodenum 12/min ileum 8-9/min, frequency decreasing along length;
the ENS - myenteric plexus
70
What is intestinointestinal reflex?
overdistention of one segment of the intestine will cause reflex relaxation in the rest of the intestine through extrinsic nerves
71
What is gastroileal reflex?
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
What is the gastrocolic reflex?
gastric distention will increase activity in the colon
73
What are the four phases of MMC?
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
Distention of the cecum causes the ileocecal valve to do what?
contraction
75
What three things relax the ileocecal valve?
1. distention in the terminal ileum
2. gastrin
3. gastroileal reflex
76
Circular muscle in the colon contracts in intervals and causes what to occur? What is this similar to in the SI?
haustra formation similar to segmentation in the SI
77
Three strips of longitudinal muscle in the colon that can contract are called what?
taenia coli
78
What are propulsive peristaltic waves in the colon called? How often do they occur?
mass movements, occur 1 to 3 times a day
79
What two reflexes increase mass movement activity?
gastrocolic and duodenocolic reflexes
80
Describe the resting state of the rectum and anal sphincters,
rectum is usually empty, the internal anal sphincter is tonically constricted while the external anal sphincter is relaxed at rest
81
What is the rectosphincteric reflex?
a mass movement from the sigmoid colon fills the rectum, which then contracts, while reflexively relaxing the IAS and contracting the EAS
82
How is the EAS innervated and controlled?
striated muscle under voluntary control via the pudendal nerve
83
What physiological changes can cause diarrhea?
increased osmotic load, inflammatory exudate, increased secretion, and/or decreased absorption time
84
Irritation of the lower GIT can cause release of what hormone causing increasing water and motility?
serotonin
85
What four other reflexes of the intestine and its pair reduce gastric motility?
1. peritoneointestinal reflex (peritoneum irritation)
2. renointestinal reflex (kidney irritation)
3. vesicointestinal reflex (bladder irritation)
4. somatointestinal reflex (irritation of skin over stomach)
86
What are the three sources of gas in the GIT?
swallowed air, formed by bacteria, diffusion from blood
87
What are three roles of secretion?
facilitate digestion - enzyme secretion
provide protection - mucous secretion
provide lubrication - serous secretion
88
What are three types of mucous cells?
goblet cells, neck mucous cells, and surface mucous cells
89
What are the two principle locations of acinus glands and what kind of secretions do they have?
salivary glands and pancreas
| produce watery secretions containing proteins such as digestive enzymes
90
What cells secrete a large volume of extracellular fluid into the GIT? Where are these located?
crypts of liberkuhn (water and electrolyte secretion)
| in mucosa of SI
91
What four receptive type things will stimulate secretion?
tactile, chemical, distention, motility
92
What does sympathetic stimulation due to secretion
decreases secretion by inhibiting parasympathetic ACh release and decreasing blood flow (alpha1)
93
What are the glycoproteins that lubricate food and where are they made?
mucins made in the submandibular and sublingual glands
94
At what pH does the function of salivary amylase stop?
<4
95
What three things in saliva have antibacterial action?
lysozyme, lactoferrin and peroxisomes
96
Parasympathetic stimulation of salivary glands causes what to happen?
vasodilation and increased blood flow
| ACh activates endothelial NO synthase, and NO causes relaxation of VSMC
97
Why is saliva hypotonic?
because sodium and chloride are readily reabsorbed in excretory ducts leaving water behind.
98
What are four characteristics unique to salivation?
1. saliva always hypotonic
2. almost totally under neural control
3. parasympathetic stimulation vasodilates
4. sympathetic stimulation causes secretion (initially)
99
Acinar cell secretion of amylase, fluid, and electrolytes is dependent on what?
second messengers including cAMP, IP3, and Ca
100
increased cAMP (from NE) means increased what? increased Ca2+ (from ACh, and SubP) means increased what?
amylase
| volume
101
What are six things in gastric juice?
salts, water, HCl, pepsins, intrinsic factor, and mucous
102
What can cause hypokalemia in regards to gastric acid? Why?
vomiting, because gastric acid contains more potassium than plasma does
103
What is the major anion in gastric acid?
Cl-
104
What is the tonicity of gastric acid in relation to plasma?
ranges from isotonic (high rates of secretion) to hypotonic
105
What converts pepsinogen to pepsin?
HCl
106
What are the morphological changes of parietal cells during acid secretion?
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
What is the alkaline tide?
When bicarb ion leaves the cell and Cl enters the cell against gradient. bicarb into blood, raising blood pH
108
Where is pepsin stored and how is it released?
stored in zymogen granules, released by exocytosis stimulated by histamine, ACh, gastrin, secretin, and CCK
109
What secretes insoluble mucous? soluble mucous?
insoluble mucous by surface epithelial cells (surface mucous cells) and insoluble mucous by pyloric glands
110
When cell damage leads to ulceration, what causes vasodilation?
histamine release
111
What increases mucosal blood flow, bicarb and mucus secretions, while stimulating mucosal cell repair and renewal?
prostaglandins
112
How does ACh stimulate HCl secretion? What blocks this?
from vagus, stimulates muscarinic receptors, opens calcium channels
atropine blocks
113
How does histamine stimulate HCl secretion? What blocks this?
from enterochromaffin-like cells (ECL) diffuses to parietal cells and stimulates H2 receptor (then activates cAMP); blocked by H2 receptor antagonists like cimetidine
114
Where is gastrin from that stimulates HCl secretion?
from G cells in the stomach antrum and duodenu; opens calcium channels
115
What are three phases of gastric acid secretion?
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
When is HCl secretion high? low?
high HCl secretion in the evening, low in the morning
117
Acid less than 3 pH in the antrum of the stomach stimulates what?
somatostatin release by D cells, which decrease gastrin release by G, INHIBITING gastric acid secretion
118
Acid in duodenum causes what?
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
Hyperosmotic solutions, fatty acids, and monoglycerides in the duodenum cause what?
GIP and CCK release, which inhibit acid secretion
120
Despite secretin and CCK inhibiting acid secretion, they stimulate what?
pepsinogen secretion
121
Someone losing gastric juices (vomiting or aspirating) can't get just NaCl and dextrose replacement because why?
it will result in hypokalemic metabolic alkalosis (fatal)
122
How are secretions of the pancreas different when stimulated by secretin and CCK?
secretin - aqueous pancreatic juice
| CCK - rich in pancreatic enzymes
123
What is in aqueous pancreatic juice?
Na, K similar to plasma
HCO3 and Cl major anions
initially hypertonic because of HCO3 but equilibriates with water to make it isotonic
124
What four proteases are released in the pancreas in inactive form?
trypsin, chymotrypsin, carboxypeptidase, ribonuclease and deoxyribonuclease
125
What prevents activation of proteases while in the pancreatic duct?
trypsin inhibitor
126
What are three lipases found in pancreatic juice?
pancreatic lipase, cholesterol ester hydrolase, phospholipase A2
127
What is the pancreas condition between meals in regard to neural control?
sympathetic stimulation, reducing enzyme secretion, secondary to reduced blood flow
128
How is parasympathetic neural regulation acting on the pancreas?
during cephalic and gastric phases of stomach secretions, accumulate enzymes, low secretion level
129
What causes pancreatic juices to be released?
chyme into duodenum triggers secretin to release pancreatic juice. CCK regulates proportion of enzymes in juice to chyme consistency
130
ACh, CCK, gastrin, and Sub P in the pancreas work on what?
Ca channels
131
Secretin and VIP in the pancreas work on what?
cAMP
132
What are Brunner's glands stimulated by?
tactile stimuli
133
How are crypts of Libekuhn stimulated?
mechanical stimuli
134
How is splanchnic circulation arranged?
both in parallel (intestines and pancreas) and series (hepatic artery and portal vein into liver)
135
Sympathetic stimulation causes what kind of control on circulation?
temporary expulsion of up to 1 L of blood into systemic circulation from capacitance veins - providing autotransfusion
136
Parasympathetic stimulation causes what kind of control on circulation?
(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
What protects capillaries in the gut from high systemic pressures and excess fluid filtration?
myogenic vasoconstriction
138
Low perfusion pressures result in what?
decreased blood flow, reduced substrates delivery and the accumulation of metabolic factors that cause vasodilation and increased blood flow
139
Control of local blood flow is closely linked to what in the hepatosplanchnic ciruclation?
metabolic activity of the tissue (secretory or muscular)
140
What is the escape phenomenon?
despite continued stimulation the splanchnic arterioles but not veins, will spontaneously vasodilate within minutes - protective mech to prevent consequences of countercurrent exchange - hypoxia
141
What are three reasons for biles secretion?
1. digest and absorb lipids
2. eliminate excess cholesterol and bile pigments
3. eliminate heavy metals or phenothiazines
142
How does bile remain isosmotic?
the large number of inorganic cations present in the GB are bound to bile acids
143
What causes contraction of the GB?
vagal stimulation and CCK cause contractions of the GB and relaxation of the sphincter of Oddi
144
What is the standing gradient osmotic mechanism?
```
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
What is absorbed in the ileum?
bile acids - in portal blood, bound to plasma proteins
