13 CH Heart and Circulation
Functions and Components of the Circulatory System: REVIEW Composition of the Blood: IN LAB Structure of the Heart Cardiac Cycle and Heart Sounds Electrical Activity of the Heart & the EKG
Pulmonary & Systemic Circulations Heart Valves
The EKG Blood Vessels Atherosclerosis and Cardiac Arrhythmias (NOT THIS) Lymphatic System (NOT THIS)
Pacemaker Potential Myocardial Action Potential Conducting Tissues of the Heart Conduction of the Impulse ExcitationContraction Coupling in Heart Muscle
Functions of Circulatory System
Transportation of respiratory gases, delivery of nutrients & hormones, waste removal, temperature regulation, clotting, & immune function. Includes cardiovascular & lymphatic systems Heart pumps blood thru cardiovascular system Includes arteries, arterioles, capillaries, venules, veins Blood vessels carry blood from heart to cells & back Lymphatic system picks up excess fluid filtered out in capillary beds & returns it to veins. Lymph nodes are part of immune system.
Structure of the Heart
The heart has 4 chambers 2 atria receive blood from venous system 2 ventricles pump blood to arteries 2 sides of heart are 2 pumps separated by muscular septum
Fig 13.10
Fibrous Skeleton of the Heart
Atria & ventricles separated by dense connective tissue the fibrous skeleton. Atrial cells attach to top of fibrous skeleton & form a myocardial unit. Ventricle cells attach to bottom of fibrous skeleton & form another myocardial unit. Fibrous skeleton also forms rings (annuli fibrosi) that hold the heart valves.
Blood from tissues enters superior & inferior vena cavae which empty into right atrium. Blood then goes to right ventricle which pumps it through pulmonary arteries to lungs.
Pulmonary Circulation
Fig 13.10
Systemic Circulation
Oxygenated blood from lungs passes thruough pulmonary veins to left atrium, then to left ventricle which pumps it through aorta to the body.
Fig 13.10
Pulmonary & Systemic Circulations
Pulmonary circulation is p a th o f b lo o d fro m rig h t ve ntric le th ro u g h lung s & b a c k to h e a rt. Systemic circulation: b lo o d fro m le ft ve ntric le to b o d y & b a c k to h e a rt. Rate of flow through systemic circulation = flow rate through pulmonary Fig 13.10 A diagram of the circuit. circulatory system
Pulmonary & Systemic Circulations
Resistance in systemic circuit > resistance in pulmonary circuit. Therefore the amount of work done by the left ventricle pumping to systemic is 57X greater than right ventricle, causing the left ventricle to be more muscular (34X thicker) than the right.
Fig 13.11: Heart
2 Atrioventricular (AV) Valves
Blood flows from atria to ventricles through oneway AV valves. RIGHT. Tricuspid valve: b e twe e n rig h t a trium & rig h t ve ntric le LEFT. Bicuspid (mitral) valve: b e twe e n le ft a trium & le ft ve ntric le . AV valves open and close by pressure changes in heart. Papillary muscles c o nne c te d to AV va lve s b y chordae tendineae. P re ve nt h ig h p re s s ure d e ve lo p e d b y ve ntric ula r c o ntra c tio n fro m e ve rting AV va lve s .
Fig 13.11 The Heart Valves
Two Semilunar (SL) Valves
Pressure rise during ventricular contraction (systole) pumps blood through aortic & pulmonary semilunar valves. Pressure drop during ventricular relaxation (diastole) closes SL valves.
Fig 13.11 The Heart Valves
Cardiac Cycle
A repeating pattern of contraction & relaxation of the heart. Systole re fe rs to c o ntra c tio n p h a s e Diastole re fe rs to re la xa tio n p h a s e Both atria contract simultaneously; both ventricles contract 0.1 0.2 sec later. Stroke volume is a m o unt o f b lo o d e je c te d fro m ve ntric le s d uring s y s to le . End-diastolic volume is vo lum e o f b lo o d in ve ntric le s a t e nd o f d ia s to le . End-systolic volume is a m o unt o f b lo o d le ft in ve ntric le s a t e nd o f s y s to le .
One cycle 0.8 secs (at 75 bpm)
Fig 13.13 The cardiac cycle of ventricular systole and diastole
SYSTOLE
SL closed SL open AV closed AV closed
Ventricles contract, ventricular pressure rises, AV valves close. Isovolumetric Contraction: ve ntric u la r p re s s u re is to o lo w to o p e n S L va lve s ; s o a ll va lve s a re c lo s e d .
Ventricular Ejection: b e g ins wh e n ve ntric u la r p re s s u re e xc e e d s a o rtic p re s s u re ; th is o p e ns s e m ilun a r va lve s .
DIASTOLE
SL closed AV open AV closed
SL closed
DIASTOLE: Ve ntric le s re la x a nd ve ntric u la r p re s s ure fa lls . Wh e n ve n tric ula r p re s s ure fa lls b e lo w a tria l p re s s ure th e n AV va lve s o p e n a nd atrial systole s e nd s a tria l b lo o d into ve ntric le s .
Cardiac Cycle: Pressure Changes
1. Ve ntric le s b e g in c o ntra c tio n , p re s s ure ris e s , AV va lve s c lo s e (LUB) : p o int wh e re a ll va lve s a re c lo s e d c a lle d isovolumetric contraction. 2. Wh e n p re s s ure in ve n tric le s e xc e e d s th a t in th e a o rta & p ulm o na trunk, ry S L va lve s o p e n & e je c tio n b e g ins . 3. Wh e n p re s s ure in ve n tric le s fa lls b e lo w th a t in a o rta & p ulm o na ry trunk, b a c k p re s s ure c lo s e s S L va lve s (DUB) . 4. Wh e n a ll va lve s a re c lo s e d ve ntric le s und e rg o isovolumetric relaxation. 5. Wh e n p re s s ure in ve n tric le s fa lls b e lo w p re s s ure in a tria , th e n AVs o p e n. 6. Atrial systole s e nd s a tria l b lo o d into ve ntric le s .
Fig 13.14 The relationship between heart sounds and the intraventricular pressure and volume.
Closing of AV and semilunar valves produces sounds that can be heard through the stethoscope. Lub (1st sound) produced by closing of AV valves. Dub (2nd sound) produced by closing of semilunar valves.
Heart Sounds
Electrical Activity of Heart
Myocardial cells are short, branched, & interconnected by gap junctions. Entire muscle mass forming heart chamber is called myocardium or functional syncytium because APs originating in any cell are transmitted to all others. The chambers are separated by nonconductive tissue.
Fig 12.31
SA Node The Pacemaker
Sinoatrial node functions as the pacemaker. Depolarizes spontaneously to threshold (= pacemaker potential).
Fig 13.20 The conduction system of the heart
SAN has slow spontaneous depolarization (pacemaker potential) ; h a s no R e s ting Me m b ra ne P o te ntia l. Cardiac pacemaker channels: HCN (Hyperpolarization Cyclic Nucleotide) channel o p e n in re s p o ns e to a h y p e rp o la riza tio n s tim ulus th a t a p p ro a c h e s 6 0 m V. Once the HCN channels are open, a depolarization is caused by inflowing Na+. When the depolarization reaches threshold (40mV) it causes the opening of voltagegated Ca+ channels in the plasma membrane of the cardiac cells, creating upstroke & contraction. Repolarization is via opening of voltagegated K+ channels.
Pacemaker Potentials (SAN)
action potential
Fig 13.18: Pacemaker potentials and action potentials in the SA node.
Fig 7.13: Normal Action Potentials in Nerves
Myocardial cells have RMP of 90 mV. Depolarized to threshold by APs originating in SA node. Upstroke occurs as voltagegated Na+ channels open. MP rapidly declines to 15 mV & stays there for 200300 msec (plateau phase). Plateau results from balance between slow Ca2+ influx & K+ efflux. Repolarization due to opening of extra K+ channels.
Myocardial APs
Fig 13.19: An action potential in a myocardial cell from the ventricles
Conducting Tissues of Heart
APs spread through atrial myocardium via gap junctions. APs need special pathway (AVN and bundle of His) to re a c h ve ntric le s b e c a us e b lo c ke d b y no n c o n d uc tin g fib ro u s tis s ue a t b a s e o f rig h t a trium . Bundle of His in s e p tu m o f ve ntric le s d ivid e s into right & left bundle branches. T h e s e g ive ris e to Purkinje fibers in th e wa lls o f th e ve ntric le s a nd s tim ula te c o ntra c tio n o f ve n tric le s .
Fig 13.20 The conduction system of the heart
Conduction of APs
APs from SAN spread at rate of 0.8 1 m/sec. Time delay occurs as APs pass through AVN which has a slow conduction of 0.03 0.05 m/sec. AP speed increases in Purkinje fibers to 5 m/sec. Ventricular contraction begins 0.10.2 sec after contraction of atria.
Excitation-Contraction Coupling
Depolarization of myocardial cells opens voltagegated Ca2+ channels in sarcolemma. This depolarization opens voltagegated Ca2+ release channels in SR (calcium-stimulated-calciumrelease). Ca2+ binds to troponin & stimulates contraction (as in skeletal muscle). During repolarization Ca2+ pumped out of cell & back into SR.
Refractory Periods
Heart contracts as syncytium & thus cannot sustain force. Its AP lasts about 250 msec. Has a refractory period almost as long as AP. Cannot be stimulated to contract again until it has relaxed.
Fig 13.21: Correlation of the myocardial action potential with myocardial contraction.
Cardiac muscle lacks tetanus
Electrocardiogram (ECG/EKG)
Recording of electrical activity of heart conducted through ions in body and picked up on skin surface.
Fig 13.22a. The ECG.
Correlation of ECG with Heart Sounds
1st heart sound (lub) comes immediately after QRS wave as AV valves close 2nd heart sound (dub) comes as T wave begins & semilunar valves close.
Fig 13.25
Structure of Blood Vessels
The innermost layer of all blood vessels is the endothelium. Capillaries are made of only endothelial cells. Arteries & veins have 3 layers called: Tunica Externa: connective tissue Tunica Media: mostly smooth muscle Tunica Interna: made of endothelium, basement membrane, & elastin. Although arteries & veins have same basic layers, they are functionally quite different.
Fig 13.26
Fig 14.15
Fig 13.27
Veins: Skeletal muscle pumps
Blood is moved toward heart by contraction of surrounding skeletal muscles (skeletal muscle pumps) . Pressure drops in chest during breathing. 1way venous valves ensure that blood moves only toward heart.
Fig 13.30: The action of the oneway venous valves