Cardio and Smooth Muscle Histology Flashcards
how do nuclei appear in cardiac muscle?
1 or 2 centrally located nuclei
in a cross section of cardiac vs skeleton muscle, how do cells appear histologically?
cross-section of cardiac muscle shows cell profiles in a variety of shapes, while skeletal muscle is much more uniform
also the CT between cells is more abundant and less organized in cardiac muscle
what are 2 features of cardiac muscle that can differentiate it histologically from skeletal muscle?
cardiac muscle has branching fibers, while skeletal does not
cardiac muscle contains intercalated discs at the Z line (T-tubules also found here)
*note cardiac muscle also has a higher abundance of mitochondria
what are the 3 components of intercalated discs in cardiac muscle?
cell-cell junction found at Z line
- fascia adherens: actin filaments, transverse component
- spot desmosomes: intermediate filaments, lateral component
- gap junction: lateral component
how can you identify Purkinje fibers of the heart histologically?
Purkinje fibers are larger and paler than ordinary myocytes
pale cytoplasm due to high glycogen content
they are found between endocardium and myocardium
what are the basic steps of contraction of cardiac muscle?
- action potential via pacemaker cells in SA node or AV node
- depolarization spreads over plasma membrane of cardiomyocytes to T tubules, causing extracellular Ca2+ to enter (via L/long-type calcium channel for sustained contraction)
- rise in cytoplasmic Ca2+ opens Ca2+ channels in SER
- Ca2+ is released from SER and it enters sarcoplasma (calcium-induced calcium release)
- contraction follows similar to skeletal muscle
- Ca2+ returns to SER and binds calsequestrin
how does smooth muscle appear histologically?
spindle-shaped, tapering cell without striations
1 centrally located nuclei
very little CT between cells (cell borders indistinguishable)
caveolae invaginations of plasma membrane - stimulate ion channels and receptors
alpha-actinin cytoplasmic dense bodies - actin filament attachment sites
which type of muscle cells can divide and secrete proteins of the extracellular matrix?
smooth muscle
how does smooth muscle contraction occur?
- depolarization or hormonal stimulation causes increase in cytosol Ca2+ (underdeveloped SR, so Ca2+ must come form extracellular source)
- Ca2+ binds calmodulin, complex binds myosin light chain kinase (MLCK)
- myosin changes from inactive/folded to active/unfolded state and phosphorylation allows it to attach to actin (slower cross-bridge than skeletal muscle)
*does not contain troponin, but does contain tropomyosin which binds/stabilizes actin filaments
*no sarcomeres
in smooth muscle, actin and associated myosin attach to dense bodies, which are attached to the plasma membrane through ___ and ___ intermediate filaments
desmin and vimentin intermediate filaments attach dense bodies of smooth muscle to plasma membrane
when actin-myosin complex contracts, their attachment to the dense bodies determines cell shortening
which side of the heart is a higher pressure system?
systemic (left) side is higher pressure than pulmonary (right) side
this makes sense because the left side has to pump blood with enough force for it to circulate the entire body!
what are the 3 tissue layers of the heart?
outermost: epicardium, contains coronary blood vessels embedded in adipose
middle: myocardium, with communicating/gap junctions/ nexus between myocytes
innermost: endocardium, simple squamous epithelium with thin layer of CT
cardiac muscle is attached to a fibrous _____ which reinforces the bases of valves and insulates the ventricles from electrical activity in the atria
cardiac skeleton
what are the 2 hormones secreted from myocytes, which myocytes secrete them, and what do they do?
myocytes secrete hypotensive hormones that promote natriuresis (secretion of salt, water follows) by kidneys
atrial myocytes secrete ANP (atrial natriuretic peptide) from granules in response to volume expansion
ventricle myocytes produce BNP (B-type natriuretic peptide), which causes a more slow effect because it must be unregulated first (not in granules)
contrast the natriuretic hormones secreted by atrial and ventricle myocytes
natriuresis = excretion of salt (and water follows) by kidneys
atrial: ANP (atrial natriuretic peptide), in response to volume expansion, secreted from pre-formed cytoplasmic granules
ventricle: in response to volume expansion and pressure overload, secrete proBNP (B-type natriuretic peptide) which is cleaved in blood to active BNP - not stored in granules, so production must be up regulated first —> slower response
blood levels of what cardiac hormone can be used as an important diagnostic sign of congestive heart failure?
congestive heart failure: heart is unable to maintain sufficient output for metabolic requirements
BNP (B-type natriuretic peptide) produced by ventricle myocytes (as opposed to ANP by atrial myocytes) is a key diagnostic sign…
…produced in response to volume expansion and pressure overload as proBNP, cleaved in blood to active BNP
not in granules, must be up-regulated first
what is the function of cardiac C-type natriuretic peptide hormone, and where is it released from?
vascular endothelium release C-type natriuretic peptide hormone
promotes clearance of types A (ANP, atrial myocytes) and B (BNP, ventricle myocytes)
remember that ANP and BNP are hypotensive hormones that promote natriuresis (salt excretion) - definitely don’t want too much of that
how does pressure/speed of flow, permeability, elasticity, and total area compare between large arteries, capillaries, and veins?
large arteries: HIGH pressure/speed of flow, low permeability, high elasticity, low total area
*makes sense because arteries have to pump blood through the whole body
capillaries: low pressure/speed of flow, low elasticity (none), HIGH permeability, HIGH total area
*makes sense because capillary beds are large and function in exchange
veins: low pressure/speed of flow, low permeability, mid-elasticity, mid-total area
what are the 3 layes (tunica) of blood vessels?
innermost: tunica intima - simple squamous endothelium, basement membrane, connective tissue, internal elastic lamina
middle: tunica media - smooth muscle, external elastic lamina, well developed in arteries
outermost: tunica adventitia - connective tissue, vaso vasorum/nervi vasorum (supply vessels themselves), well developed in large veins
*note that inner part of blood vessels is avascular because blood flow would damage small vessels (nutrients by diffusion), while outer layer is vascular zone
what makes up the perivascular/periarteriolar plexus of blood vessels?
vaso vasorum and nervi vascularis/vasorum - the vessels and nerves of the vessels
note the nervi vasorum innervate smooth muscle cells of vessels AND travel to destinations on internal organs
this plexus is found in the tunica adventitia (outermost layer)
how is the elastic tissue and smooth muscle arranged in arterial walls?
circular pattern
where does the elastic tissue in large elastic arteries come from?
smooth muscle cells in the tunica media produce the elastic tissue (secretory function)
the elastic tissue is arranged in both fibers and sheets (lamina) in the intima and media, and the elastic lamina has holes to allow diffusion of substances
as arteries get smaller the have more ____ and less _____ in the tunica media
as arteries get smaller the have more SMOOTH MUSCLE and less ELASTIC TISSUE in the tunica media
this is to help direct blood flow
describe the transition from arteries to capillaries
arteries decrease in size to arterioles, which have relatively thick walls compared to lumen size - this confers high resistance to blood flow, which is responsible for drop in arterial pressure before blood enters capillary bed
metarterioles serve as transition between arterioles and capillary bed, with incomplete layer of smooth muscle, and smooth muscle cells arranged longitudinally
*metartioles can also continue as preferential/thoroughfare channels through a vascular bed that allow capillaries to be bypassed
_____ of smooth muscle cells controls the entrance to the capillary bed and regulates the amount of blood that enters
pre-capillary sphincter
what allows endothelial cells to regulate capillary diameter?
actin and myosin in their cytoplasm
pericytes are contractile cells (also stem cells) found at intervals along capillaries
what are the 3 types of capillaries?
- continuous: least permeable (zona occludens) - blood-brain barrier, blood-thymus barrier, blood-testis barrier
- fenestrated: may be covered by a diaphragm - viscera, endocrine glands, renal glomerulus
- sinusoid (discontinuous): most permeable, lined by fixed macrophages - liver, spleen, bone marrow
what are 2 forms of transportation in/out of capillaries?
- hydrostatic pressure forces plasma out of capillaries and into interstitial tissues… at venous end osmotic pressure (from large proteins that can’t escape) draws fluid back in
- transcytosis via pinocytotic vesicles: transports larger molecules
what determines blood flow in veins?
blood flow in veins is independent of blood pressure in arteries
muscular activity in the lower limb and movement of abdominal/thoracic organs is responsible for squeezing veins to propel blood, and valves in veins inferior to the heart prevent back-flow
T/F: venules are as permeable as capillaries
true!
leukocytes often leave circulation via diapedisis from venules to enter tissues
[recall that in lymph nodes, HEV/high endothelial venules facilitate migration of T cells into lymph nodes]
how could you distinguish a large vein inferior to the heart from an artery histologically?
large veins inferior to the heart will have large bundles of smooth muscle, like arteries have
however, arteries will have an internal elastic lamina while veins will not! Veins are low-pressure vessels, no need for elasticity
what determines the capacitance of veins?
capacitance = ability to store blood
most circulating blood volume is within venous system
distensibility of the walls of veins allows veins to store large amounts of blood with little change in pressure (low pressure system)
what is the function of atriovenous (AV) shunts of capillary beds?
allow blood to bypass a capillary bed, such as in the skin to conserve heat
shunts have thick muscular walls and are innervated by the automatic nervous system
what is structurally different about lymphatic capillaries compared to blood capillaries?
lymphatic capillaries pick up tissue fluid not taken up by venous end of capillaries (~10%) and deliver to lymph nodes for filtration
lymphatic capillaries have discontinuous basement membranes or are missing altogether so that large proteins and particulates can easily enter
most numbers in CT of skin, mucous membranes, respiratory tract, GI, and UG tract
describe what is meant by the “metabolic blood brain barrier”
some endothelial cells have metabolic properties that allow them to activate/inactivate materials before they pass through
the metabolic blood brain barrier modifies some substances to make them less available to the CNS
ex: anti-Parkinson drug L-dopa is decarboxylated in endothelial cells
what is the function of acetyl cholinesterase (AChE) and monoamine oxidase (MAO), enzymes found within endothelial cells?
AChE and MAO inactivate neurotransmitters
example of how endothelial cells act as metabolic as well as physical barrier
most endothelial cells contain ________, which converts vaso-inactive angiotensin I to angiotensin II, a potent vasoconstrictor which also inactivates the vasodilator ______
most endothelial cells contain ACE (angiotensin converting enzyme), which converts vaso-inactive angiotensin I to angiotensin II, a potent vasoconstrictor which also inactivates the vasodilator BRADYKININ
how does the anti-angina drug nitroglycerin work?
nitroglycerin is metabolized by endothelial cells to nitric oxide (NO) and acts as a vasodilator on the coronary arteries
how do endothelial cells allow platelets to aggregate, which don’t normally stick to EC due to heparin sulfate (polyanionic)?
damaged EC produce Factor VIII (Von Willebrand’s Factor), which is needed for platelets to adhere to sub-endothelial CT
Factor VIII is stored in Weibel-Palade bodies
recall that Factor VIII deficiency (von Willebrand’s disease) leads to excessive bleeding
what do tissue cells deprived of oxygen secrete to increase the transcription of VEGF and induce angiogenesis?
hypoxia-inducible factor I (HIF-1): gene regulatory protein which increases transcription of VEGF (vascular endothelial growth factor)
—> proteases dissolve basement membrane and endothelial cells proliferate and mature
claudication
claudication: pain in muscles on exertion due to lack of oxygen
symptom of atherosclerosis
