Ch. 12 The Circulatory System. The heart. The heart is a double pump. A quick note on arteries vs. veins. = the muscular pump of the CV system

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1 Ch. 12 The Circulatory System The heart A.k.a. the cardiovascular system Blood was discussed in Ch. 11 Focus of Ch. 12: heart and blood vessels = the muscular pump of the CV system ~ 100,000 heartbeats/day! ~ 9000 liters of blood/day!! The heart is a double pump Right heart: Powers pulmonary Pumps blood to and from lungs Receives blood from systemic Left heart: Powers systemic Pumps blood to and from rest of body Receives blood from pulmonary A quick note on arteries vs. veins Definitions: Arteries carry blood away from the heart Veins carry blood towards the heart About color: While most arteries are systemic and carry oxygen-rich blood (and thus are red), the pulmonary arteries are a notable exception While most veins are systemic and carry oxygen-poor blood (and thus are blue), the pulmonary veins are a notable exception Pulmonary artery Pulmonary vein (to systemic ) (from systemic ) 1

2 Heart location and pericardium Pericardium: fibrous, multilayered sac (with fluid between the layers) that surrounds, protects, anchors, and lubricates the heart Some cardiac anatomy Heart wall Surrounded by pericardium Lined by thin, smooth endocardium Middle, thickest layer is myocardium (cardiac muscle tissue) Thicker on left side why? (Intercalated disc) Intercalated discs are specialized junctions that electrically connect cells, allow rhythmic contraction A schematic heart Papillary muscles 2

3 Heart valves Coronary circulation One-way valves; prevent backflow Open when upstream pressure is higher Close when downstream pressure is higher Closing of valves creates heart sounds ( lub-dup ) Papillary muscles contract and tense chordae tendineae to prevent AV valves from opening the wrong way (back into atria) when ventricles contract Cardiac cycle Diastole = relaxation Feeds blood to the myocardium of the heart Cardiac conduction system = the events of one heartbeat Sinoatrial (SA) node ( pacemaker ) spontaneously generates electrical impulses sets basic heart rate No nervous or hormonal input needed for heart to beat However, autonomic nervous input and/or hormonal input needed to change heart rate or Systole = contraction Electrical impulses spread (like a wave) cell to cell via intercalated discs, causing cardiac muscle to contract rhythmically His (AV bundle) Bundle branches Purkinje fibers down septum 3

4 Electrocardiogram (ECG or EKG) = graphical recording of electrical activity in body fluids (conducted from heart) Does not directly record muscle contraction ECG waves record electrical changes from baseline (0 mv) P wave = electrical impulse spreads through atria QRS complex = electrical impulse spreads through ventricles (Return of atria to resting electrical state is hidden) T wave = ventricles return to resting electrical state Blood vessels and you! Some examples of major blood vessels Main types of BVs 4

5 Arteries Arteries carry blood away from the heart Higher pressure vessels Walls have lots of elastin (an elastic protein) to withstand pressure Pulse = stretch/recoil of arteries with each heartbeat Thick wall compared to lumen size Walls have lots of smooth muscle that may vasoconstrict ( vessel diameter) or vasodilate ( vessel diameter) to specifically direct blood flow to certain locations as needed Arterioles = really small arteries Capillaries Capillaries exchange gases, nutrients, wastes, etc. between blood and interstitial fluid Microscopic, extremely thinwalled, leaky Form networks called capillary beds to increase total surface area for exchange (see lower right picture) Capillary fluid exchange Slightly more fluid leaves the capillaries for the tissues than re-enters the capillaries from the tissues The excess is returned to the circulation by the lymphatic system Blood flow through capillary beds Precapillary sphincters may contract (vasoconstrict) or relax (vasodilate) to adjust blood flow in response to metabolic needs of different tissues/organs 5

6 Velocity of blood flow Veins carry blood towards the heart Veins Lower pressure vessels So need skeletal muscle contraction and one-way valves (in limbs) to aid venous return to heart (often against gravity) Flow slows down as blood spreads throughout capillary beds Thin wall compared to lumen size Venules = really small veins So more time for exchange Blood pressure (BP) A BV problem = the force exerted by blood against the wall of a vessel Atherosclerosis Some solutions? Systolic pressure = maximum BP generated during ventricular contraction Diastolic pressure = minimum BP at end of ventricular relaxation BP typically reported as: systolic pressure 120 mm Hg diastolic pressure 80 mm Hg Balloon angioplasty Coronary bypass surgery 6

7 Lymphatic system Components: Lymph = excess interstitial fluid that gets absorbed and transported by Lymphatic vessels = low pressure tubes that ultimately return lymph to bloodstream Lymphoid tissues and organs that contain lymphocytes and other supporting cells General functions: Return excess interstitial fluid to bloodstream Transport products of fat digestion from small intestine to bloodstream Help defend against pathogens (= disease-causing organisms) more detail in Ch. 13 Flow of lymph Lymphatic vessels ultimately return lymph to cardiovascular system at subclavian veins Lymphatic capillaries = tiny, low pressure tubes that drain excess interstitial fluid Larger and more permeable than blood capillaries Flaplike minivalves help ensure one-way flow Drain into larger lymphatic vessels Some lymphoid tissues and organs Thoracic duct drains lymph from most of body, empties into left subclavian vein Right lymphatic duct drains lymph from upper right quadrant of body, empties into right subclavian vein No pump, so lymph moves slowly, in same ways that venous blood moves (skeletal muscle contraction, one-way valves, breathing) Lymph passes through lymph nodes on the way (see next slide) Peyer s patches Keep bacteria from breaching the intestinal wall 7