Cardio Histology Flashcards
arteries
-carry blood away from the heart
-thick, multi-layered walls which form the lumen for blood to flow
what are the three main layers of arteries?
- tunica interna (endothelium)
- tunica media
- tunica externa
what is the function of the arteries?
-carries blood away from the heart
-systemic arteries provide blood rich in oxygen to the body’s tissues
-pulmonary arteries carry blood low in oxygen exclusively to the lungs for gas exchange
what is the structure of the arteries?
-arterial walls: thick structures that are generally round in appearance, and experience higher blood pressure than other types of blood vessels
-lumen: inner passage where blood flows and small lumen maintain higher pressure
tunica interna structure
-endothelium usually appears wavy due to the constriction of smooth muscle
-internal elastic membrane present in larger vessels
tunica media structure
-normally the thickest layer in the arteries
-smooth muscle cells and elastic fibers predominate (the proportions of these vary with distance from the heart)
-external elastic membrane present in larger vessels
tunica externa (adventitia) structure
-normally thinner than the tunica media in all but the largest arteries
-collagenous and elastic fibers
-nervi vasorum and vasa vasorum present
tunica interna (media)
-composed of epithelial and connective tissue layers
-simple squamous endothelial lining
-basement membrane: provides strength and flexibility and binds the endothelium to connective tissue
-internal elastic membrane: present in large arteries, thick elastic fibers, and provides structure while allowing the artery to stretch
tunica media
-normally the thickest layer in the arteries
-smooth muscle cells and elastic fibers predominate (the proportions of these vary with distance from the heart)
-external elastic membrane present in larger vessels
-composes the middle layer of the artery wall
-consists of layers of smooth muscle and connective tissues arranged in circular sheets
-contraction and relaxation of these muscles lead to changes in blood flow and pressure
tunica externa
-normally thinner than the tunica media in all but the largest arteries
-sheath of connective tissue, primarily collagenous fibers
-edges are interlaced with surrounding connective tissue, maintaining vessel in the same relative position
elastic arteries
-vessels larger than 10 mm
-closest to the heart with the thickest walls
-contain the largest percentage of elastic fibers —> allows them to expand with the increased pressure as blood is pumped and rushes through them
-without the elastic fibers, these walls would be rigid and the blood pressure would greatly increase to very high levels and the heart would not pump efficiently
-elastic recoil helps maintain the pressure gradient that drives blood flow through the body
what happens to the amount of elastic fibers in the arteries as you move further from the heart?
decreases
tunica media of the elastic arteries
-middle layer composed of alternating layers of circumferentially arranged smooth muscle and sheets of elastic tissue
-thickest of the three layers in elastic arteries
muscular arteries
-distribute blood to various parts of organs and tissues like radial and femoral arteries
-well-defined elastic lamina- layer of undulating elastic fibers separating tunica intima from the tunica media
-tunica intima is thinner compared to elastic arteries
-walls have a greater number of smooth muscles
-has a companion vein, medium vein: thinner tunica media than muscular artery and adventitia is the thickest layer compared to tunica media
veins structure
-same three layers of arteries
-differences: lacks elastic lamina, thinner tunica media, larger lumens, and smooth muscle is more loosely arranged
-contains one-way valves that are outfoldings of the tunica intima
what is the function of veins
-return blood to the heart —> carry oxygen-poor blood from body to heart and carry oxygen-rich blood from lung to the heart
-venous system is low pressure —> one-way valves prevent backflow and muscle contractions in leg aid blood flow from lower extremities
what is the structure of capillaries?
-one layer of endothelial cells
-epithelial cells form a protective layer (basal lamina)
-three types of capillaries: continuous, fenestrated, and discontinuous
what is the function of capillaries?
-exchange materials between blood and tissue —> provides nutrients and oxygen to surrounding tissue and removes CO2 and other waste
-there are multiple mechanisms for exchange: simple diffusion, membrane transport carriers, and transcytosis through large molecules and endocytosis/exocytosis
continuous capillaries
-most common type
-found in brain, muscle, connective tissue
-endothelial cells are joined by a tight junction to form a continuous tube
-basal lamina is continuous
-less permeable —> only allows small molecules to pass through and can have a barrier function
fenestrated capillaries
-found in kidney, choroid plexus, endocrine organs, and gut
-endothelial cells contain pores (fenestrae) that are covered by thin layer of diaphragm
-basal lamina is continuous
-more permeable —> fenestrae allow larger molecules to pass through like proteins and facilitate absorption
discontinuous (sinusoidal) capillaries
-found in liver, bone marrow, and spleen
-endothelium has large openings which lack diaphragms
-basal lamina is thin and discontinuous over openings
-most permeable —> allow large proteins and cells can pass through these openings to allow trafficking of blood cells
properties of endothelial cells
-single cell layer
-line entire vascular system from the heart to the smallest capillary
-component of tunica intima
-selectively permeable
-phenotypically heterogeneous depending on localization so varying permeability
what are the functions of endothelial cells?
-regulate gas and nutrient exchanges between the bloodstream and surrounding tissues
-regulate immune responses and inflammation through the BBB, platelet adhesion, and leukocyte activation
-angiogenesis to form new vessels and capillaries
-vascular homeostasis- enable the blood vessel to adapt diameter and wall thickness plus release endogenous vasodilators like nitric oxide
arteriosclerosis
blood vessels that carry oxygen from heart to other parts of the body become thick and stiff —> restricts blood flow to organs and tissues
what causes atherosclerosis?
-buildup of fats, cholesterol, and other substances in and on artery walls called plaque
-plaque narrows the arteries, blocks blood flow, bursts, and blood clots
epidemiology of atherosclerosis
-less prevalent in central and south america, africa, and asia
-more prevalent in US and japan
-in the US, coronary artery disease causes approx. 1 of every 6 deaths
-account for more than 400,000 deaths annually
what are some risk factors of atherosclerosis plaque buildup?
-high blood pressure
-high cholesterol (high LDL cholesterol)
-irritant like tobacco or nicotine
-diseases like obesity and diabetes
-elderly people
-lack of physical activity
what are treatments for atherosclerosis plaques?
-lifestyle changes
-medications
-surgeries for severe blockages or high-risk complications
what are some symptoms of atherosclerosis plaques?
-most symptoms do not show until a blockage occurs
-chest pain or pressure (angina)
-pain in the leg or arm
-shortness of breath
-fatigue
-confusion, dementia (if blood flow is blocked to the brain)
-muscle weakness
-high blood pressure or kidney failure (if blood flow is blocked)
how does atherosclerosis develop?
-high LDL proteins enter the arterial intima
-if there are high levels, the LDL accumulate
-oxidation of the LDL into pro-inflammatory particle invokes an inflammatory response in the intima —> causes damage to the endothelium
-accumulation of macrophages form cells that cause cell necrosis (fatty streak)
-dead foam cells and other debris widen the fatty streak into a large piece of plaque
-fibrous tissue from the smooth muscle cells form a fibrous cap over the plaque and prevent it from breaking off
-prevents blood flow and eventually the plaque ruptures and leads to formation of a blood clot
angiogenesis
-formation of new blood vessels from pre-existing ones induced by angiogenesis factors (vascular endothelial growth factor or VEGF)
-endothelial cells differentiate, divide, and migrate within the lining of blood vessel walls
-occurs during embryonic development, postnatal growth, and wound repair
angiogenesis —> tumorigenesis
-tumorigenesis involves a multistep process in which the normal cells progress into cancerous cells through oncogenic mutations and clonal expansion
-initial solid tumors remain in an avascular state and absorb oxygen and nutrients from surrounding tissue
-blood vessel expression and movement to tumor increases its ability to access oxygen as well as nutrients
myocardial infarction (heart attack)
-decrease/cessation of blood flow to the myocardium (coronal arteries) results in ischemia and cell death
-ischemia initially presents as retrosternal chest/upper extremity pain (quick or gradual)
-often the result of plaque buildup/rupture or artery occlusion
-trigger cell death in cardiomyocytes through apoptosis and necrosis —> cardiomyocytes are thought not to proliferate so damage will be permanent and leads to scarring
how is a heart attack diagnosed?
-EKG
-imaging through MRI
-cardiac troponins in serum samples —> cardiac troponin T (cTnT) and cardiac troponin I (cTnI) and can differentiate between acute and chronic MI
how is a heart attack treated?
-less than 2 hours —> PCI (balloon angioplasty + stent placement)
-more than 2 hours —> fibrinolysis
histopathology of myocardial infarction
necrosis will trigger pro-inflammation signals and macrophages —> you will see lots of cell nuclei/cell waste as well as immune cells like neutrophils and macophrages plus scar tissue
pericardium
fibrous encasement of the heart and vessels
functions of the pericardium
- positions heart in the mediastinum and separates it from other organs
- allows for movement of the heart
- restricts the movements o the heart
- protects by providing cushioning
what are the layers of the pericardium?
fibrous and serous (subdivides to parietal and visceral layers)
fibrous pericardium
-strong connective tissue of collagen fibers and elastic lamellae
-restricts movement of the heart
-runs from the great vessels to diaphragm
serous pericardium
-parietal layer is attached to the fibrous layer and is composd of a serosal lining as well as a fibrous sac
-visceral layer is attached to the surface of the heart and forms the epicardium
epicardium
-innermost layer of the pericardium formed by mesothelial cells
-attached to the surface of the heart
-release a lubricating fluid
-contains blood vessels and is thicker in the ventricles but thinner in the atria
myocardium
-layer of muscle cells connected through intercalated discs
-they are near capillaries
-their helical arrangement allows for blood release upon contractions
-thicker in ventricle and thinner in atria
-cells can separate during the histo staining
endocardium
-layer of epithelial cells lining the heart and blood vessels
-connected to loose connective tissue (subendocardial layer)
-prevent blood from clotting (antithrombotic)
-thinner in ventricle and thicker in atria
-large purkinje cells are found in the subendocardial space below connective tissue
purkinje fibers
-specialized nerve cells that relay electrical signals between ventricles
-located in the subendocardial wall of ventricles
-3D mesh-like network
-paler cytoplasm than cardiomyocytes
intercalated disks or unique junction
-hold adjacent cells together and mediate intercellular signalling
-located between adjacent cardiac muscle cells at ends
-composed of gap junctions (allow propagation of action potentials) and desmosomes (anchor cardiac muscle fibers together so the cells do not move apart during individual contraction)
cardiomyocyte
-singular cardiac muscle cell
-rhythmic contractility
-located in the myocardium
-rectangular branching cells with central nucleus
-within the cardiomyocytes are myofibrils that contain myosin-actin filaments that cause the heart to contract
cardiac muscle
-located in the heart, specifically the myocardium
-involuntary contractions to pump blood
-structures are branched, striated (sarcomeres), mainly one central nucleus but sometimes two nuclei, and intercalated discs that join cells with adherent and gap junctions
skeletal muscle
-attached to skeleton
-voluntary movements like moving limbs
-large, elongated
-striated
-mutinucleated, on periphery
-sarcomeres
smooth muscle
-located in blood vessels and internal organs
-involuntary movements like blood pressure in vessels and moves food in digestive tract
-fibers are grouped fusiform cells, closely packed
-not striated
-central nucleus and the widest part of the cell
-contains gap junctions
