Cardiovascular System: Heart Anatomy

• The cardiovascular system consists of the heart, blood vessels, and blood
• The heart pumps blood into blood vessels, which distribute it throughout the cardiovascular system

Location and Structure of the Heart

• The heart is a cone-shaped organ located slightly to the left in the thoracic cavity, posterior to the sternum, resting on the diaphragm
• The apex of the heart points toward the left hip, while the base faces the posterior rib cage
• The heart in general weighs between 250 to 350 grams

Chambers and Anatomical Features of the Heart

• The chambers include the superior right and left atria and the inferior right and left ventricles
• The atrioventricular sulcus separates the atria and ventricles
• The interventricular sulcus is an external depression located between the right and left ventricles

Blood Flow and Great Vessels

• Both atria receive blood from veins
• Blood drains from the atria to ventricles, where it is pumped into blood vessels called arteries
• The main veins and arteries that bring blood to and from the heart are known as great vessels

Pulmonary and Systemic Circuits

• The heart pumps blood through two separate circuits
• The right side of the heart pumps blood into a series of blood vessels in the lungs, known as the pulmonary circuit
• Pulmonary arteries deliver deoxygenated blood to the lungs, where gas exchange occurs in the pulmonary capillaries within the alveoli
• Oxygen diffuses into the blood and carbon dioxide diffuses out
• Oxygenated blood returns to the left side of the heart via the pulmonary veins
• The vessels and organs that transport oxygenated blood are red in diagrams, while those carrying deoxygenated blood are blue
• The left side of the heart is the systemic pump, receiving oxygenated blood from pulmonary veins and pumping it into the systemic circuit
• Arteries in the systemic circuit deliver oxygenated blood to the smallest vessels, called systemic capillaries
• Oxygen diffuses from the blood into tissues, and carbon dioxide diffuses into the blood
• Blood also delivers nutrients, picks up wastes, and distributes hormones
• Deoxygenated blood returns to the right side of the heart via veins
• The pulmonary circuit is a low-pressure circuit, while the systemic circuit is a high-pressure circuit

The Pericardium

• The pericardium is a membranous structure that surrounds the heart
• It is made of the fibrous and serous pericardium
• The fibrous pericardium is a tough, outer layer that prevents overfilling
• The serous pericardium has 2 layers: Parietal fused to inner fibrous pericardium; Visceral epicardium directly adheres to heart
• The pericardial cavity sits between the parietal and visceral pericardial layers and contains serous fluid for lubricant purposes

Heart Wall and Cardiac Tamponade

• Myocardium is cardiac muscle tissue that consists of cardiac muscle cells
• The heart lumen is lined by the endocardium
• Endocardium is the deepest layer of the heart wall
• Endothelial cells of the endocardium are continuous with those lining blood vessels
• In cardiac tamponade, excess fluid in pericardial cavity squeezes heart
• As a result, it limits the ventricles to fill completely

Coronary Circulation and the Consequences of CAD

• The myocardium is too thick for oxygen and nutrients to diffuse from inside the chambers, so it is supplied by coronary circulation
• The coronary circulation consists of coronary arteries and veins
• The first two branches of the aorta are the right and left coronary arteries
• Blood flows through the vessels of coronary circulation
• Coronary sinus receives blood from great, small, and middle cardiac veins
• A buildup of fatty material called plaques in coronary arteries can lead to coronary artery disease (CAD)
• CAD decreases blood flow to the myocardium, resulting in myocardial ischemia
• Myocardial ischemia causes chest pain known as angina pectoris
• The most dangerous consequence of CAD can result in a myocardial infarction (MI), or heart attack
• An MI occurs when plaques rupture, obstructing blood flow causing tissue to infarct, or die

Surviving Myocardial Infarction

• Survival after an MI depends on the extent and location of the damage
• Cardiac muscle cells do not generally undergo mitosis, so dead cells are replaced with noncontractile scar tissue
• The death of part of the myocardium increases the workload of the remaining heart muscle
• Survival may be affected by lifestyle modifications and medical treatment
• Angioplasty is commonly preformed where a balloon is inserted into a blocked artery along with a wire-mesh stent to keep the artery open
• Coronary artery bypass grafting can also be done, which grafts other vessels to the diseased coronary artery

The Heart's Great Vessels, Chambers and Valves

• The heart consists of four chambers: two atria and two ventricles
• Atria receive blood from veins and pump blood into ventricles through valves
• Valves have flaps that close when ventricles contract, keeping blood from moving backward

Atria and Ventricles

• They are not symmetrical in size, shape, or location where each atrium has a muscular pouch called an auricle
• The interatrial septum is a thin wall that separates the atria and ventricles
• The fossa ovalis sits inside of the interatrial septum
• Ventricles are asymmetrical, so the right ventricle is wider
• A thick, muscular intervenricular septum separates the right and left ventricles
• Papillary muscles are finger-like projections of muscle that attach to chordae tendineae

Preventing Backflow

• AV valves consist of flaps that are called cusps
• Named for the number of cusps it contains: Tricuspid and Bicuspid on the right and left side respectively.

Semilunar Valve

• Blood is stopped from flowing back into ventricles by two valves known as semilunar valves
• There are 3 cusps located near the endocardium
• Located near the pulmonary and aortic arteries
• The pulmonary artery is located between the right ventricle and pulmonary trunk
• The aortic valve is posterior to it, between the left ventrical and aorta

Valvular Heart Diseases and Treatment

• Valvular heart diseases impair function of one or more valves which are either present at birth or acquired from disease
• Insufficient valve fails to close and stenotic valve causes inflexibility
• Both cause heart murmur, fatigue, dizzniness
• Are all commonly affect the mitral and aortic valves

Understanding Cardiac Muscle Tissue

• Contains myoglobin for carrying oxygen and large number of mitochondria
• Intercalated discs join muscle cells and gap junctions allow for communication
• Heart contracts as a whole

The Rhythm of Electrophysiology

• Heart contracts by itself, it can set it's own rhythm
• It contains pacemaker cells, who have spontaneous, rhythmic depolarization
• The signal spreads to the body through the cardiac conduction system
• Order of events: The SA node generates an electrical current into the AV node, after a delay
• Electrical signal is then sent to the AV bundle and then to the left/right bundle branches

Conduction System

• SA node depolarizes about 60x per minute
• AV node sits near the tricuspid valve
• The signal spreads to body through the purkinje fibers
• The SA is the natural pacemaker
• Rhythmically, electrical signals generated from the SA node are called sinus rhythms

ECG

• Clinical tool to examine heart health
• Measures electrical activity and its spread
• Small P wave
• Large QRS complex
• Small T wave

Dysrhythmias

• Disturbances in the rate of the heart
• Bradycardia - Rate is under 60 beats/min
• Tachycardia - Rate is above 100 beats/min
• Often found at AV node because of additional delays

Fibrillation

• Electrical signals go haywire, causing parts of the heart to repolarize and depolarize all over the place
• Often compared to a bag of earthworms

Mechanical Physiology and Pressure

• Muscle cells produce coordinated contractions known at heartbeats
• Pressure changes drive blood flow through heart and valves prevent it from flowing backward
• This takes place within the cardiac cycle

The Cardiac Cycle

• Each cardiac cycle has time for relaxation, called diastole, and contraction which is systole
• Atrial and ventricular diastoles and systoles occur at different times due to AV node delay
• Each side of the heart is working in synchronization
• There are 4 main phases that are defined by actions of the heart (filling, contraction, ejection, relaxation)

Ventricular Filling Phases

• Period where blood drains from atria to ventricles
• High pressures in pulmonary trunk and aorta cause valves to stay closed
• AV valves are open because of higher atrial pressures

Volume in Each Ventricle

• About 80 percent of total blood volume drains passively
• With a variable amount entering the bloodstream
• Ventricle holds 120 ml of blood: Known as end-Diastolic Volume

Cardiac Contraction Phase

• 1-5 milisecond cycle where cardiac muscle contracts
• Ventricles begin to contract: Increases pressures
• As pressures rise, valves close (S1 = Sound 1)
• Ventricular pressure isn't high enough to open lunar valves which close and keep the ventricular volume the same

Ventricular Ejection Phase

• Pressures rise to a higher level in the pulmonary trunk
• Blood from each area flows: About 70 ml from each ventricle
• This is the highest point of the cardiac cycle
• In this phase, about 50 ml of blood remains

Final Phase, called Isovolumetric Relaxation

• A brief period where there is ventricular diastole
• As diastole begins, pressure declines
• Lunar valves snap shut: Point S2 is observed/heard at this moment
• Pressure in ventricles stay a little higher so AV valves remain shut

Volume Remaining and Phases of Volume Change

• Neither being added or subtracted for just a moment
• Briefly volume isn't constant: Called Isovolumetric

Cardiac Output

• Heart averages 60-80 cycles/min = this measure is know as heart rate
• Important for evaluating the amount of blood/time
• One determinant of CO = How much blood pumped by the heart at one cycle/min

Stroke and Blood Volume

• To calculate CO, measure each heartbeat that occurs through 1 heartbeat
• Stroke Volume (SV) = By subtracting the amount from the heart at the end of a contraction (end-Systolic Volume)
• Subtracted from the amount of blood in the heart during diastole (end-Diastolic Volume)
• So, the average for a person, resting, where the heart has a stroke volume of about 70 ml = SV
• 120 ml (EDV) - 50 ml (ESV) =70 ml (SV)

To Find the Cardiac Output: Multiply Heart Rate by Stroke Volume

• CO output would look something like this = Beats/min HR is 72 x 70 ml volume (SV) = 5040 ml/min, or 5 liters

Volume During Systole

• Right and left ventricles pump = Systolic
• Normal blood volume in adults is 5 liters + goes through minute

What Impacts Stroke Volume?

• Preload
• Contractility
• Afterload
• Preload: Stretch in heart before contract
• Contracility: forcefulness of heart
• Afterload: pressures that heart has to pump/fight against

Contractions Based on Preload And Afterload

• Increases in pre and afterload cause ventricular hypertrophy
• High blood pressure in pulmonary causes same

Endocrine Regulation

• Primarily: Nervous and Endocrine Systems
• Two Branches: Autonomic nervous system (ANS)
• Sympathetic nerves increases heart rate = From Spinal Cord
• parasympathetic NS slows heart rate: releases Acetylcholine
• These NS affect SA node rate

Hormonal & Electrolytes Regulators

• Hormonal Regulation: Adrenal Medulla gets stimulated, secretes certain hormones
• The stimulation is: Epinephrine and Norepinephrine from Medulla
• Release effects and affect body in similar ways: Although Effect is longer lasting
• Water Volume helps determine pressure by its power
• Some chemicals help stimulate increase in pressure: Aldosterone, Anti-Dieretic and cardiac outputs to compensate, in response

Other Volume/Pressure Influences

• Some Chemicals are also a big influence. Depending on length of cardiac cycle.
• Heartrate in relation to physical fitness can depend on age / exercise
• This can alter blood flow needed

Heart Failure Occurs When there is an issue Pumping

• As a result of electrolytes balance
• Decrease in Heart Rate in return leads to decrease in Cardiac output

Symtoms of HF occur when blood pressure gets too low

• Blood backs up in body's organs
• Left/Right ventricular failure can cause fluid build up in lungs
• This results in: Swelling due to Kidneys over producing liquid and the cycle continues.

The Best way to treat HF = Increase Output

• This can mean changes to the life style: Less weight, restricted diets
• Other treatments include: transplant , Pacemakers, medicine

Explore the cardiovascular system, focusing on the heart's location, structure, chambers, and blood flow. Understand the atria, ventricles, and their functions in circulating blood. Learn about the great vessels and how blood moves through the heart.