Test 1: Wk1: 3 Heart and Vascular Histology - Norton Flashcards
4 Tissues of the Heart and Vascular Walls
1. Endothelium 2. Smooth muscle 3. Cardiac muscle 4. Connective tissue
Endothelium
Lines the heart and blood vessels but more than just a lining, it is a sophisticated tissue with multiple functions
5 Endothelium Functions
1 Provides a nonthrombogenic surface
2 Has antithrombotic and prothrombotic properties
3 Regulates vascular tone and blood flow
4 Plays several roles in inflammation and local immune responses
5 Secretes growth factors
How does endothelium regulate vascular tone and blood flow
flow by secreting factors that
stimulate smooth muscle contraction (endothelin 1, ACE) and
relaxation (NO, prostacyclin)
How does endothelium play a role in inflammation and immune response
in
venules induces specific leukocytes to migrate out of the circulation into
injured or infected tissues
Smooth muscle found in
Found in the walls of all vessels larger than capillaries and in
the endocardium
Smooth Muscle arranged
Arranged helically in layers
Smooth Muscle BP regulation
Blood pressure regulation: in small arteries and arterioles,
SMCs are connected by gap junctions and permit
vasoconstriction and vasodilation
Connective tissue made of
collagen and elastic fibers
collagen location
subendothelial layer, between smooth muscle layers
and in the outer covering
Elastic Fibers (elastin) located in
in elastic arteries, layered between
smooth muscle cells
Heart
Three major layers
1. Endocardium 2. Myocardium 3. Epicardium
Endocardium
Surface endothelium supported by a layer of fibroelastic
connective tissue + few smooth muscle fibers
Subendocardium
deep to the surface endothelium, connective
tissue (continuous with connective tissue in the myocardium)
which surrounds variable numbers of modified cardiac muscle
fibers that comprise the heart’s impulse conducting system
Myocardium
Tightly knit, contractile cardiac muscle fibers arranged spirally
around each heart chamber
Myocardium is much thicker in — than —
ventricles than atria
myocardium of LV is — thicker than RV
3x
Epicardium
Outermost layer
Epicardium composed of — which —
adipose tissue; cushions the heart
Epicardium contains
Coronary Vessels
Nerves
Connective Tissue
Epicardium covered by
Covered by simple squamous mesothelium
simple squamous mesothelium composes
Composes visceral and parietal pericardium
— cells secrete lubricant which reduces friction when the
heart moves during contraction and relaxation
Mesothelial cells secrete lubricant which reduces friction when the
heart moves during contraction and relaxation
Cardiac skeleton
Masses of irregular, dense
connective tissue, primarily in the
endocardium
Cardiac skeleton function
Anchors valves
Provides insertions for cardiac
muscle
Cardiac Skeleton surrounds
the two atrioventricular canals
cardiac skeleton separates
atria from the ventricles
Conducting system
Initiates the electrical impulse
for contraction
Conduction System spreads impulse through the
myocardium
Modified cardiac muscle fibers
form: 5
•
Sinoatrial node
Atrioventricular nodes
Atrioventricular bundle of His
Bundle branches right and left
Purkinje fibers
Purkinje fibers branches of
right and left bundles
Purkinje fibers located
in subendocardium of both ventricles
Purkinje fibers stain
pale
– have greater diameter than contractile muscle fibers
Purkinje fibers
Purkinje fibers have abundant — and sparse bundles of —
glycogen; myofibrils
Purkinje fibers merge with
contractile muscle fibers
— trigger waves of contraction through ventricles
Purkinje fibers
Cardiac muscle fibers are — like skeletal muscle, but they consist of individual
— cells rather than fused cells like in skeletal muscle
Cardiac muscle fibers are striated like skeletal muscle, but they consist of individual
cylindrical cells rather than fused cells like in skeletal muscle
Cells contain one or two central nuclei and are linked by adherent and gap junctions at
prominent —
Cells contain one or two central nuclei and are linked by adherent and gap junctions at
prominent intercalated discs
Mitochondria occupy — of the cell volume
40%
Sarcomeres of cardiac muscle are organized and function similarly to those of —
Sarcomeres of cardiac muscle are organized and function similarly to those of skeletal muscle
Contraction of cardiac muscle is —
Contraction of cardiac muscle is all or none
Impulses for contraction are initiated, regulated and coordinated by the — and
— nodes
Impulses for contraction are initiated, regulated and coordinated by the sinoatrial and
atrioventricular nodes
— nerves regulate the rate of contraction
autonomic
Vessels
Three major layers (tunics)
Intima
Media
Adventitia
Intima
endothelium, thin subendothelial layer of connective
tissue +/ SMCs, and internal elastic lamina, in larger vessels.
In large and medium veins, the intima folds to form valves
Media
alternating layers of smooth muscle and collagen or
elastic lamellae
Adventitia
connective tissue (type I collagen and elastic fibers), small vessels (vasa vasorum) and nerves
Arteries
Grouped by size and wall composition
Elastic arteries - largest
Muscular - medium
Small
Elastic arteries diameter
> 10mm
Elastic A Intima
Intima: Endothelium, connective tissue with smooth muscle
Elastic A Media
Media: Many elastic lamellae alternating with smooth muscle
Elastic A Adventitia
Adventitia: Connective tissue, thinner than media, with vasa
vasorum
Elastic A Role in Circulation
Role in Circulation: Called conducting arteries because they conduct
blood from heart to smaller arteries.
Expand when heart contracts, reducing blood pressure
Elastic A
recoil during diastole helps move blood forward under steady pressure
Elastic A
Elastic A Ex
Examples: aorta, pulmonary arteries and their largest branches
Muscular A diameter
1-10mm
Muscular A Intima
Intima: Endothelium, connective tissue with smooth muscle,
internal elastic lamina is prominent
External elastic lamina present only in larger muscular arteries
External elastic lamina present only in larger muscular arteries
Muscular A Media
Media: Many (up to 40) smooth muscle layers with variable,
decreasing elastic material
Muscular A Adventitia
Adventitia: Connective tissue, thinner than media, vasa vasorum maybe present
Muscular A Role in Circulation
in circulation: Called distributing arteries because they
distribute blood to all organs and maintain steady blood
pressure and flow with vasodilation and constriction
Small A diameter
0.1-1 mm
Small A Intima
Intima: Endothelium, connective tissue with less smooth
muscle
Small A Media
Media: 3 to 10 layers of smooth muscle
Small A Adventitia
Adventitia: Connective tissue, thinner than media, NO vasa
vasorum
Small A Role in circulation
Role in circulation: Distribute blood to arterioles, adjusting flow
with vasodilation and constriction
Microvasculature permeates
most organs
why are Microvasculature vessels unnamed
and too small for surgical manipulation
Arterioles
one to three smooth muscle layers
Capillaries
consisting only of an intima endothelial layer
Venules
large lumens and thin walls, which drain capillaries
Terminal arterioles branch into —
metarterioles
metarterioles
smooth muscle
sphincters contract to resist blood flow and relax cyclically to allow
pulsatile flow of blood into an anastomosing capillary bed, where
metabolic exchange with surrounding cells occurs
Arterioles diameter
10-100 um
Arterioles Intima
Intima: Endothelium only, NO connective tissue, NO smooth
muscle
Arterioles Media
Media: 1 to 3 layers of circumferential smooth muscle cells
Arterioles Adventitia
Adventitia: Very thin connective tissue layer
Arterioles Role in Circulation
Role in circulation: Resist and control blood flow to capillaries;
major determinant of systemic blood pressure
First vessel in microvascular
Arterioles
Capillaries Diameter and length
4-10 um length < 50 um
Capillaries Intima
simple layer of endothelial cells rolled as a tube,
surrounded by basement membrane
Allow transit of blood one at a time
Capillaries
Capillaries Role in Circulation
in circulation: Exchange of metabolites by between blood
and tissues
Associated with pericytes
Capillaries
pericytes
perivascular contractile cells with a
variety of functions
Capillaries always function in networks called
capillary beds
Size, shape and density of capillary beds depends on t
Size, shape and density of capillary beds depends on the size
and metabolic activity of the tissue being perfused
what makes up 90% of vasculature
Capillaries
Capillary beds are supplied by
metarterioles
metarterioles
continuous with thoroughfare channels and postcapillary venules
Continuous capillaries
most common, many tight junctions so that all exchange must occur through the cells by
diffusion or transcytosis
Fenestrated capillaries
also have tight junctions but perforations (fenestrations) through the endothelial cells allow
greater exchange across the endothelium. Both continuous and fenestrated have continuous basement membrane.
Found in organs where molecular exchange with the blood is important (
Discontinuous capillaries or sinusoids
larger lumens, large spaces between the endothelial cells, discontinuous
basal lamina. Found in organs where exchange of macromolecules and cells occurs readily between tissue and blood
Fenestrated capillaries ex
kidneys, endocrine organs, intestinal walls,
choroid plexus)
Discontinuous capillaries or sinusoids ex
bone marrow, liver, spleen)
Venules Diameter
10-100um
Venules Intima
Endothelium; no valves
Venules Media
Media: Pericytes and scattered smooth muscle cells
Venules Adventitia
none
Venules Role in circulation
Role in circulation: Drain capillary beds; site of leukocyte exit
from vasculature into damaged or infected tissue
last segment of microvasculature
Venules
Veins size
small
med
large
Small (0.1 1 mm), medium (1 10mm) and large (>10 mm)
— that prevent backflow are found in medium and large veins
Intimal valves that prevent backflow are found in medium and large veins
Veins Intima
thin
Veins Media
small bundles of SMCs and Connective tissue
Veins Adventitia
collagenous, thick and well developed
— become increasingly well developed as vein increases in diameter
Tunics become increasingly well developed as vein increases in diameter
Small and medium veins usually travel with —
Small and medium veins usually travel with muscular arteries
Arteriovenous anastomoses (AV
Arteriovenous anastomoses (AV shunts) arterioles can bypass a capillary bed (skin)
Venous portal system
venules draining a capillary bed quickly branch again to form another capillary bed (anterior pituitary, liver)
Arterial portal system
afferent
arteriole → capillaries → efferent
arteriole (kidney glomerulus)
Carotid sinuses located
Located in the internal carotid arteries just after the bifurcations
of the common carotids
Carotid sinuses Act as — to monitor — blood pressure
Carotid sinuses Act as baroreceptors to monitor arterial blood pressure
— is thinner in carotid sinuses and allows for greater — when blood pressure rises
Tunica Media; distension
Carotid Sinuses Adventitia
Adventitia contains many sensory nerve endings from CN IX
(glossopharyngeal
— centers in the brain process impulses from the — and adjust vasoconstriction to maintain normal blood pressure
Vasomotor centers in the brain process impulses from the carotid sinuses and adjust vasoconstriction to maintain normal blood pressure
Carotid and aortic bodies (glomus bodies) are — that monitor —
Complex chemoreceptors that monitor CO 2 , O 2 and pH
Carotid bodies found in the
the walls of the carotid sinuses
Aortic bodies found in the arch of the aorta
arch of the aorta
Carotid and aortic bodies (glomus bodies) are part of the — known as —
Part of the autonomic nervous system known as paraganglia
paraganglia contain
Contain rich capillary networks
paraganglia capillaries are surrounded by
glomus cells
glomus cells contain
neurotransmitters
ACh and dopamine
paraganglia supported by
satellite cells
Glomus cell membranes respond to —, — and — by releasing neurotransmitters
Glomus cell membranes respond to hypoxia, hypercapnia and acidosis by releasing neurotransmitters
Sensory fibers from CN — synapse with glomus cells, signal brain centers to initiate cardiovascular and respiratory adjustments to correct the condition
Sensory fibers from CN IX synapse with glomus cells, signal brain centers to initiate cardiovascular and respiratory adjustments to correct the condition
Interstitial fluid that is not pulled into venules by colloidal osmotic
pressure drains as lymph into — — called lymphatics
Interstitial fluid that is not pulled into venules by colloidal osmotic
pressure drains as lymph into blind vessels called lymphatics
lymphatic capillaries have
very think endothelial cell walls with spaces between cells
Lymphatics converge into larger, thin walled lymphatic vessels in
which lymph is propelled by movements of surrounding muscles and organs, with — — keeping the flow unidirectional
Lymphatics converge into larger, thin walled lymphatic vessels in
which lymph is propelled by movements of surrounding muscles and organs, with intimal valves keeping the flow unidirectional
largest lymphatic vessel
thoracic duct and right lymphatic duct
The largest lymphatic vessels, the thoracic duct and right lymphatic
duct, both with walls having — return lymph to the circulatory system by joining veins near the —
The largest lymphatic vessels, the thoracic duct and right lymphatic
duct, both with walls having tunics return lymph to the circulatory system by joining veins near the heart
