Section 7: Hormonal and Neural Regulation of the gastrointestinal tract and smooth muscle Flashcards
Function of gastrointestinal tract;
exchange with external environment required for single cell metabolism
Layers of the lumen of gastrointestinal tract:
mucosa, submucosa, muscularis externa, and serosa
Layers within mucosa:
epithelium, lamina propria muscularis mucosa
Layers within submucosa:
major blood and lymphatic vessels and submucosal plexus
Layers within muscularis external:
circular muscle, myenteric plexus and longitudinal muscle
True or False? Exocrine cells line the lumen of the gastrointestinal tract, while endocrine cells do not.
F. they both do
Primary gastrointestinal processes:
Chemical and mechanical break down, mixing and movement by smooth muscle
Which is expensive and which efficient, chemical and mechanical break down vs. mixing and movement by smooth muscle
expensive: chemical and mechanical break down, efficient: mixing and movement by smooth muscle
Gastrointestinal processes are controlled by:
hormones and nerves
Speed of chemical regulators, fastest to slowest:
neurocrine, endocrine, paracrine
A stimulus can act on either __ or __ to elicit a change in a target cell.
nervous system or endocrine cell
“True hormones”:
produced in response to a meal AND at physiological tissue concentrations
Hormone is aka:
endocrine
Two structurally similar families of true hormones:
Gastrin and CCK, Secretin and Gastric Inhibitory Peptide
Which portion of the “extrinsic” Autonomic nervous system is the most significant regulator?
Parasympathetic
Major extrinsic nerves of the autonomic nervous system:
vagus and pelvic nerves
The sympathetic branch of the autonomic nervous system is (excitatory/ inhibitory) in the gastrointestinal tract.
inhibitory
What is the “enteric” nervous system?
“Brain of the gut”
Enteric means:
internal
The myenteric plexus is found between:
the longitudinal and circular muscle
The submucosal plexus is found between:
the circular muscle and the muscularis mucosae
Neurotransmitter released form inhibitory motor neurons of the myenteric and submucosal nerve plexus:
VIP and NO
Neurotransmitter released form excitatory motor neurons of the myenteric and submucosal nerve plexus:
ACh and/or Substance P
The gastrointestinal system is involved in the transport of:
fluid and organic matter
In which body system does smooth muscle provide the driving force?
gastrointestinal tract
In which body system does smooth muscle provide the resistance to flow?
cardiovascular system
Smooth muscle is involved in the transport of:
materials in bulk quantities
What kind of muscle is smooth muscle?
unitary muscle
What permit coordinated contraction of unitary muscle?
Gap junctions
Synaptic contacts are aka:
varicosities
True or False? In multiunit smooth muscle each cell is innervated.
T. e.g., iris of the eye
These propagate slow wave activity to and between smooth muscle cells:
Gap junctions
How many subunits is a connexon made of?
6
What forms an open channel between adjacent cells?
two connections in register
Cells act as a ____.
synctium (can act as a unit), a single cell containing several nuclei, formed by fusion of cells or by division of nuclei.
These will pass through gap junctions:
inorganic ions (Na+, Ca2+), monosaccharides (glucose), amino acids, vitamins, nucleotides (ATP, cAMP)
These will not pass through gap junctions:
proteins, nucleic acids, polysaccharides
These are the current carriers through gap junctions:
inorganic ions
Signalling components of the gap junctions:
nucleotides (ATP, cAMP)
Metabolic components of gap junctions:
monosaccharides and amino acids
ion driving forces in smooth muscles:
K out, Ca2+ in
What causes depolarization in nerve cells?
opening of voltage-gated Na+ channels
What does a rise in cell Ca2+ initiate?
Cross-bridge cycling and contraction
This complex is needed to activate myosin:
active calmodulin/ MLCK complex
What is the most important source of Ca2+ in visceral smooth muscle?
extracellular Ca2+
Why is visceral smooth muscle slow?
because diffusion of Ca2+ from the outside is slow
From where does the Ca2+ needed form contraction of skeletal smooth muscle come?
intracellular stores
Why is skeletal smooth muscle fast?
Because the calcium comes from intracellular stores
What forms transverse tubules in skeletal smooth muscle?
Invaginations of plasma membrane
What makes up the triad?
2 sarcoplasmic reticulum cisterna and a transverse tubule
What is contained within the sarcoplasmic reticulum cisterna?
calcium stores
Why do special properties of visceral smooth muscle occur?
because smooth muscle cells have an unstable membranes potential that can be affected by enteric neurotransmitter
What causes greater tone?
greater number of AP’s
What generatest spontaneous slow wave activity?
pacemaker cells of the interstitial cells of cajal
ICCs are interconnected into:
networks
What do ICC’s contact?
gastrointestinal musculature
What connect the ICCs to the circular muscle?
gap junctions
Tubes of kidney are made of what type of cells?
epithelial cells
True or False? All of the digestive tract is lined with epithelial cells.
T
True or False? Feces is metabolic waste.
F. What we can not digest and can’t absorb
Where is metabolic waste eliminated?
Lungs or kidney
True or False? There is communication between the submucosal and myenteric plexuses.
T
Secretion:
Out of blood or interstitial space
% of body water secreted each day into the lumen
20%, must be reabsorbed
Function of outer layer:
shortening, to help the outer layer in peristalsis
True or False? Endocrine cells are innervated by the nervous system.
T
True or False? Paracrine signals can be sent to target tissue via the blood stream.
F
Salivary secretion is regulated by:
nerves
Small and large intestines are controlled via this type of regulation:
paracrine regulation
Affect of opiates in the gastrointestinal tract:
slows motility in the gastrointestinal tract
True or False? There are many hormonal receptors in the salivary gland.
F.
Drugs largely effect:
receptors
Gastin;
gastric secretion
Effects gall bladder, bile release and fat processing:
CCK
Produces secretions by the pancreas:
secretin
GIP:
metabolic effects, not many on food processing
external nerves
external to gastrointestinal tract
Nerve that controls secretory functions of the stomach:
vagus nerve
Nerve that stimulates motility in the distal end of the gastrointestinal tract:
pelvic nerve
What extrinsic innervation is required for the enteric nervous system to function?
none
submucosal plexus interprets:
what happens in the lumen, then signals the myenteric plexus
NO:
gas, neurotransmitter, inhibitory
GRP:
Gastrin releasing peptide, released onto G cells, which release endocrine (gastrin) into circulation that stimulates more acid secretion from parietal cell (this is in addition to acetylcholine stimulating acid release from parietal cells via the vagus nerve/ bags nucleus)
smooth muscle cells:
lots of nuclei, not striated, smallest of muscle type cells, connect to each other in units
Unitary:
What happens in one cell can be transmitted total he adjacent cells
True or False? smooth muscle cell action potentials are activated by Na rushing in.
F. calcium
Visceral smooth muscle resting potential:
-60 to -40 mV (30 mV less negative than skeletal muscle)
How can smooth muscle be self excitatory?
due to spontaneous slow wave action
What causes the upstroke of the action potential in visceral smooth muscle?
activation of voltage-gated Ca2+ channels that bring Ca2+ into the cells
What causes basal tone?
slow waves and APs (causes spontaneous activity too)
Basal resting tone =
tension in the absence of external stimuli (e.g., intestines are much longer after death)
True or False? Spontaneous activity happens without innervation or circulation.
T
True or False? Visceral smooth muscle contract in the absence of neural or endocrine influences.
T
T or F? visceral smooth muscle contracts in response to stretch.
T
How do enteric nerves regulate smooth muscle?
release neurotransmitters, acetylcholine contracts smooth muscle
How does the release of acetylcholine by enteric nerves affect Ca2+ levels?
Ca2+ increases and initiates contraction
What type of neurotransmitters activate calmodulin/ MLCK complex?
those that raise Ca2+
What type of neurotransmitters interfere with phosphorylation by calmodulin/MLCK complex?
those that raise cAMP/cGMP
What do puringenic enteric nerves release?
VIP or NO, causing a rise in cAMP/cGMP and relaxation
What does the release of VIP or NO from enteric nerves cause?
a rise in cAMP/cGMP and relaxation
Factors that control overall regulation of smooth muscle:
action potentials can be elicited by electrical stimulation, hormones, neurotransmitter, or stretch . intracellular Ca2+ can be altered by hormones and neurotransmitter without action potentials/ local tissue factors, hormones and neurotransmitter can cause smooth muscle contraction without action potentials
How are unitary muscle cells connected?
gap junctions, allow passage
MLCK:
Myosin light chain kinase
What does Calicium bind in visceral smooth muscle once it enters?
calmodulin
True or False? There are intracellular stores of calcium released in visceral smooth muscle.
T. Not substantial amounts
True or False? skeletal muscle has tension when at rest.
F
What can lead to longer activation and more action potentials?
Acetylcholine release that makes potential less negative.
True or False? Parasympathetic neurotransmitter input is required for resting tone.
F
True or False? Oscillation of smooth muscle is a property of smooth muscle.
F. (?)
Where are the pacemaker cells connected to the visceral smooth muscle cells?
varicosities
What type of potential does visceral smooth muscle have?
ocilating potential
True or False? Resting tone will continue without innervation or circulation.
T
Neurotransmitter released by the plexus:
acetylcholine, excitatory (contraction)
What nerves supply input to the plexuses?
vagus and pelvic
Purinergic nerves control:
positive control of relaxation, blocks phosphorylation, leads to relaxation
Purinergic:
mediated by purine nucleotides and nucleosides such as adenosine and ATP
