CV-Overview & Anatomy Flashcards
Functions of CV system
o distributes dissolved gases & nutrients.
o removes metabolic waste
o contributes to systemic homeostasis by controlling temp, O2 supply, pH, ionic composition, nutrient supply o quickly adapts to changes in conditions and metabolic demands
Heart is a dual pump
o left side of heart pumps blood to the systemic circulation
o rightsidepumpsbloodtothepulmonarycirculation
o right&leftheartarranged“inseries”
- no direct connection between right & left
- output of left and right sides of heart must be closely matched
Pulmonary circulation
o low pressure
o single pathway between heart and lungs
Systemic circulation
o higher pressure
o multiple pathways from heart to different systemic vascular beds.
o Systemic circulation is primarily arranged “in parallel.” This is important because
- oxygenated blood visits only one organ system beforere turning to pulmonary circulation
- Changes in metabolic demand or blood flow in one organ do not significantly affect other organs
- Blood flow to different organs can be individually varied to match demand
- At rest, most blood directed to brain (~14%), skeletal muscle (~15%), GI system (~221%), and kidney (~22%). During exercise up to 80% to exercising muscle.
- major exception = hepaticcirculation large fraction of hepatic blood supply is via intestinal circulation
Walls of the heart & membranes
Walls have three major layers:
- epicardium (outer membrane = connective tissue & fat)
- myocardium (thick muscle layer)
- endocardium (inner membrane = endothelial cells, as in vessels).
Pericardium encloses entire heart
- fluid-filledmembranoussac,notconnected to walls of heart
- Stiff&non-compliant,resistssudden distension of chambers. Inflammation = Pericarditis – restricts filling of heart.
Chambers of the heart
4 chambers
- Ventricles (left & right) = main pumping chambers. Left ventricle supplies higher pressure systemic circulation, so is bigger and has thicker walls than right ventricle. Left ventricle does more work, uses more O2 than right.
- Atria (left & right) = small “primer” chambers, supply the ventricles with blood. Thinner walls than ventricles.
Vessles of the heart
4 vessels
- Vena cavae (superior vena cava & inferior vena cava)–inlet vessel(s) into right atrium
- Pulmonary Artery – outlet vessel from right ventricle [Arteries go Away from heart]
- Pulmonary Vein – inlet vessel into left atrium
- Aorta – outlet from left ventricle – main blood supply to body, size of garden hose ~1” in diameter
Valves of the heart
4 valves
- o Tricuspid valve – between right atrium & right ventricle
- o Pulmonic valve – between right ventricle & pulmonary artery o Mitral valve – between left atrium & left ventricle
- o Aortic valve – between left ventricle & aorta
Valves are arranged in 2 sets
- o Atrioventricular = Tricuspid & mitral valve
- between atria & ventricles
- attached to papillary muscles in ventricles by chordae tendonae = tendon-like attachments that prevent valves from prolapsing into atria during ventricular contraction.
- Semilunar valves = Pulmonic & aortic valves
- between ventricles and great arteries
- Valves = thin flaps (“cusps”) of fibrous tissue covered by endothelium.
- o Mitral has two cusps (bicuspid), others have three
- o One-way, pressure-operated (= passive) -> direct forward blood flow, prevent back ward blood flow
- All located in the same horizontal plane in heart
- Heart sounds generated by opening and closing of valves.
- Defective valves make unusual sounds = murmurs. Regurgitation = minor leakage, Prolapse = major failure, where valve gets pushed backward.
Cardiac conduction system
Specialized cells initiate the heart beat and coordinate contraction by conducting electrical impulses.
- Sinoatrial (SA) node ->in wall of right atrium, spontaneously depolarizes to initiate the heart beat. It’s intrinsic activity is ~100 bpm and highly regulated by autonomic nervous system and many humoral factors
- Impulse spreads through atria via gap junctions — not clear whether there is preferential conduction pathway through atria
- Atrioventricular (AV) node is between atria and ventricles, slows conduction to allow atrial contraction to precede ventricular contraction
- His-Purkinje system = specialized cells that rapidly conduct depolarization to trigger coordinated ventricular contraction.
Coronary blood flow
- Most coronary blood flow occurs during diastole because of compression of microvasculature during systole. Flow thus depends on heart rate — less time for perfusion at higher heart rates.
- Heart has high oxygen consumption. Supply must closely match demand or hypoxia results (angina).
Right & left coronary arteries
- o arise from root of aorta
- o Major coronary arteries course along epicardial surface of heart. Smaller branches enter myocardium
- o some variation in anatomy between individuals
- o left main coronary artery is short ~ 1 cm, bifurcates to left anterior descending (LAD) artery and circumflex artery, primarily supply blood to left atrium and left ventricle
- right coronary artery is in groove between right atrium and right ventricle, primarily supply blood to right atrium and right ventricle, as well as posterior part of left ventricle
Coronary capillaries
very dense — each myocyte is associated with several capillaries
Coronary veins
- located adjacent to corresponding coronary arteries
- drain into coronary sinus, which opens into right atrium near inferior vena cava
BLOOD FLOW PATHWAY
- Deoxygenated blood returns from systemic circulation via superior & inferior venae cavae, passively enters right atrium (no valve). Right atrium contracts, increased pressure pushes open tricuspid valve, blood enters right ventricle. Right ventricle contracts, pushes open pulmonic valve, blood enters pulmonary circulation via pulmonary arteries.
- Oyxgenated blood returning from lungs enters left atrium via pulmonary veins. Left atrium contracts, pushes open mitral valve, blood enters left ventricle. Left ventricle contracts, pushes open aortic valve, blood enters systemic circulation via aorta.
Vascular system has three parts
- Arterial system = distribution of oxygenated blood and nutrients
- Microcirculation and lymphatic system = diffusion & filtration system
- Venous system = collection of deoxygenate blood and wastes
Types of vessels aorta, arteries, arterioles, capillaries
Aorta
- single outlet from left side of heart, diameter ~25 mm (garden hose), dampens pulsatile pressure
Arteries
- thick walled, resist expansion, diameter ~ 0.2-6.0 mm, distribute blood to different organs
Arterioles
- relatively thicker walls (more vascular smooth muscle), diameter ~ 10-70 μm, highly innervated by autonomic nerves, circulating hormones, and local metabolites, primary site of regulation of vascular resistance, via changes in diameter
Capillaries
- smallest vessels – walls just single layer of epithelial cells, no smooth muscle; approx same size as RBCs, which travel through single-file, diameter <10 μm; huge total surface area, primary site of gas & nutrient exchange with interstitial fluid
Types of vessles: Venules, veins, vena cavae
Venules, veins
- thin walls relative to diameter compared to equivalent-sized arteries (but still some smooth muscle), not much elasticity, diameter ~ 20 μm – 0.5 cm, primary capacitance vessels of the body (most of blood volume)
- one-way valves compensate for lower pressure in venous system to ensure blood flows only in the correct direction
Vena cavae
- superior & inferior
- diameter ~ 25-30 mm
Anatomy of resistance vessels - Arterioles
Arterial walls have three layers:
1) Tunica adventitia: outer layer, mostly connective tissue = collagen and elastin
2) Tunica media: middlelayer, mostly innervated vasculars mooth muscle, controls diameter of vessels, particularly resistance arteries, not present in capillaries
3) Tunica intima inner layer of vessel lined with vascular endothelium, single continuous layer of endothelial cells, very important in regulation of blood flow, site of atherosclerotic plaque formation.
