The Circulatory System: The Heart Flashcards
Two Divisions of the Cardiovascular System
1) Pulmonary Circuit - carries blood to the lungs for had exchange and returns it to the heart; supplied by the right half of the heart
2) Systemic Circuit - supplies blood to every organ of the body, including portions of the lung and the wall of the heart itself; supplies by the left half of the heart
Cardiovascular System
Heart and the blood vessels
Venous Blood
Deoxygenated blood
The Pericardium
- The outer wall of the pericardium is the pericardial sac which is also known as the parietal pericardium
- The visceral pericardium surrounds the heart and is separated from the pericardial sac by the pericardial cavity which is filled with serous fluid
The Heart Wall
Three Layers:
1) Epicardium
2) Myocardium (cardiac muscle)
3) Endocardium (lines the heart chambers)
- When the parietal pericardium is removed, the visceral pericardium is called the epicardium
Four Chambers of the Heart
- The two superior chambers of the heart are the right and left atria which receive blood returning to the heart by way of the great veins
- The two inferior chambers are the right and left ventricles which pump blood into the arteries to flow away from the heart and around the body
Three Sulci of the Heart Surface
- Coronary sulcus = separates the atria from the ventricles
- Anterior and posterior interventricular sulci extend obliquely down the heart
Interventricular Septum
Muscular internal wall of the heart that divides the right and left ventricles
Interatrial Septum
Internal wall separating the atria
Valves of the Heart
- There is a valve between each atrium and its ventricle (atrioventricular or AV valves) and a valve between each ventricle and its great artery (semilunar valves)
- Each valve consists of two or three fibrous flaps of tissue called cusps or leaflets
- Pushed open and closed by changes in blood pressure
Atrioventricular (AV) Valves
- The right AV valve (or the tricuspid valve) has three cusps
- The left AV valve (or the bicuspid/mitral valve) has two cusps
- AV valves are connected to the papillary muscles on the floor of the ventricle by tendinous cords
Coronary Sinus
Venous blood from the wall of the heart travels into the right atrium
Fossa Ovalis
- Hole during fetal development
- Before birth blood travels through the fossa ovalis to the left atrium where it bypasses the pulmonary trunk as blood does not need to be transported to the lungs at this time
Semilunar Valves
- Pulmonary valve controls the opening from the right ventricle to the pulmonary trunk
- Aortic valve controls the opening from the left ventricle into the aorta
- No tendinous cords
Coronary Circulation
- The myocardium has its own supply arteries and capillaries that deliver blood to every muscle cell
- The right and left coronary arteries arise from the ascending aorta and travel through the coronary sulcus -these are the only branches of the ascending aorta
Branches of the Left Coronary Artery
- Anterior Interventricular branch supplies blood to the anterior portion of both ventricles
- Circumflex branch supplies blood to the left side of the heart
Branches of the Right Coronary Artery
- Posterior Interventricular branch supplies blood to the posterior portion of both ventricles
- Marginal artery supplies blood to the right side
Myocardial Infarction (MI)
- Heart attack
- Sudden death of a patch of myocardium
- Caused by fatty deposits or blood clots in a coronary artery
- Angina pectoris = chest pain
- Ischemia = deficiency of blood flow to cardiac muscle
Venous Drainage
- The route by which blood leaves an organ
Capillaries –>Veins –>Coronary Sinus
- ex Great cardiac vein collects blood from the anterior portion of the heart which travels along the interventricular artery and drains into the coronary sinus
- ex Middle cardiac vein collects blood from the posterior portion of the heart and also drains into the coronary sinus
Five Characteristics of Myocytes/Cardiocytes
1) Striated muscle fibers
2) Uninucleated cells
3) Involuntary
4) Branched cells
5) Intercalated discs
- Desmosomes bind muscle fibers together
- Gap junctions allow quick transport of ions
Cardiocyte Internal Cell Structure
- Large, central nucleus surrounded. by glycogen
- Large mitochondria for enhanced aerobic respiration (to produce ATP)
- Rich in myoglobin (short-term O2 storage)
Cardiac Conduction System - Five Steps
1) SA node fires
2) Excitation travels through the atrial myocardium
3) AV node fires (after collecting impulses from the SA node)
4) Excitation spreads down the AV bundle
5) Purkinje fibers distribute excitation through the ventricular myocardium
6) Cardiocytes perpetuate the signal by transporting ions cell-to-cell through their gap junctions
Systole versus Diastole
Systole = contraction
Diastole = relaxation
Nerve Supply to the Heart
- While the ANS does not produce heartbeats, it does modify the heart rate and contraction strength
- Parasympathetic:
Vagus X fibers slow the heart (Craniosacral, Ach=Cholinergic) - Sympathetic:
Spinal nerves accelerate the heart
(Thoracolumbar, NE=Adrenergic) - Efferent nerve fibers also ascend from the heart to the brain to regulate cardiovascular reflexes and pain signals
Sinus Rhythm
The normal heartbeat triggered by the SA node (~70-80 bpm)
- Non-SA nodal rhythms are called an ectopic focus
Nodal Rhythm
Slower heartbeat produced by the AV node (~40-50 bpm)
- Most common ectopic focus
Ectopic Focus
- Any region of spontaneous firing other than the SA node
- Hypoxia, electrolyte imbalances, caffeine, nicotine, and other drugs can cause a premature ventricular contraction (PVC) or extrasystole
Electrocardiogram (ECG or EKG)
- Composite recording of all action potentials produced by nodal and myocardial cells (not a single action potential)
- P wave = atrial depolarization
- QRS complex = ventricular depolarization (and masked atrial repolarizarion)
- T wave = ventricular repolarizarion
Arrhythmia
Any abnormal cardiac rhythm
- One cause is heart block, the failure of any part of the cardiac conduction system
- Total heart block is damage to the AV node so that signals do not reach the ventricles
Pacemaker Potential
- Cells of the SA node do not have a stable resting membrane potential like skeletal muscle or neurons
- Starts at -60mV and moves upward, slow Na+/Ca++ inflow at -40mV, slower K+ outflow at 0mV
Cardiac Output (CO)
- Blood ejected from ventricle in 1 min
= HR x SV
Adrenergic versus Cholinergic
- Sympathetic postganglionic fibers as Adrenergic, meaning they release norepinephrine and increase HR
- Parasympathetic nerves have Cholinergic effects as they release ACh and slow down the heart
Cardiac Center in the Medulla Oblongata
- Propioceptors - in muscles/joints
- Baroreceptors - detect pressure changes in the aorta and carotid sinuses and arteries (CN IX)
- Chemoreceptors - detect blood pH, CO2 and O2 levels (CN IX and X)
Hypercapnia
High CO2 levels in the blood and CSF detected by chemoreceptors
Three Variables Affecting Stroke Volume
(1) Preload
- Frank-Starling law - the more ventricles are stretched, the harder they will contract
(2) Contractility
- Inotropic effects (effects on contractile strength)
- Hypercalcemia has positive Inotropic effects
- Hyperkalemia has negative Inotropic effects
(3) Afterload
- the pressure resulting from blood against the semilunar valves
- increased Afterload reduced SV
- Cor pulmonale = R ventricle failure due to pulmonary obstruction
