Cardiovascular System: Anatomy & Physiology Study Guide

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Cardiac Anatomy

Heart Structure and Location

The heart is a muscular organ located in the thoracic cavity, slightly left of the midline. It is responsible for pumping blood throughout the body.

Base: The broad, superior portion of the heart where major blood vessels attach.
Apex: The pointed, inferior tip of the heart, directed downward and to the left.
Pericardium: The double-walled sac that encloses the heart, providing protection and reducing friction.

Membrane Layers Around the Heart

The heart is surrounded by several layers that protect and anchor it.

Fibrous Pericardium: The tough, outermost layer that prevents overstretching and anchors the heart.
Serous Pericardium: A thinner, double-layered membrane consisting of:
- Outer layer: Parietal pericardium, lines the internal surface of the fibrous pericardium.
- Inner layer: Visceral pericardium (epicardium), covers the heart surface.
- Pericardial cavity: The space between the two layers, filled with serous fluid to reduce friction.

Heart Wall Layers

The heart wall consists of three distinct layers:

Epicardium: Outer layer, also known as the visceral pericardium.
Myocardium: Middle, muscular layer responsible for contraction.
Endocardium: Inner layer lining the heart chambers and valves.

Heart Chambers

The heart contains four chambers that receive and pump blood.

Right Atrium: Receives deoxygenated blood from the body.
Right Ventricle: Pumps deoxygenated blood to the lungs.
Left Atrium: Receives oxygenated blood from the lungs.
Left Ventricle: Pumps oxygenated blood to the body.

Features of the Atria and Ventricles

Atria: Thin-walled chambers; act as receiving areas for blood.
Ventricles: Thick-walled chambers; act as pumping areas for blood.

Chordae Tendineae

Chordae tendineae are tendon-like cords that anchor the heart valves to papillary muscles, preventing valve prolapse during contraction.

Blood Flow Pathway

Blood flows through the heart in a specific sequence:

Body (systemic veins)
Right atrium
Right ventricle
Pulmonary arteries
Lungs
Pulmonary veins
Left atrium
Left ventricle
Aorta
Body (systemic arteries)

Major Coronary Vessels

Coronary vessels supply blood to the heart muscle itself.

Right and left coronary arteries: Branch from the aorta to supply the heart.
Cardiac veins: Drain deoxygenated blood from the myocardium into the coronary sinus.

Cardiac Muscle and Physiology

Skeletal vs. Cardiac Muscle Cells

Cardiac muscle cells differ from skeletal muscle cells in several ways:

Cardiac muscle cells: Branched, interconnected, have intercalated discs, and are involuntary.
Skeletal muscle cells: Long, cylindrical, multinucleated, voluntary, and lack intercalated discs.

Intercalated Discs

Intercalated discs are specialized connections between cardiac muscle cells that allow rapid transmission of electrical impulses and mechanical force.

Cardiac Pacemaker Cells

Pacemaker cells in the sinoatrial (SA) node generate spontaneous action potentials, initiating the heartbeat.

Sequence of Cardiac Excitation

The electrical impulse travels through five main parts:

SA node: Initiates impulse (right atrium).
AV node: Delays impulse (interatrial septum).
AV bundle (Bundle of His): Conducts impulse to ventricles.
Right and left bundle branches: Carry impulse through interventricular septum.
Purkinje fibers: Distribute impulse to ventricular muscle.

Electrocardiogram (ECG)

An ECG records the electrical activity of the heart. The three main parts are:

P wave: Atrial depolarization.
QRS complex: Ventricular depolarization.
T wave: Ventricular repolarization.

Systole and Diastole

Systole: Contraction phase of the heart.
Diastole: Relaxation phase of the heart.

Cardiac Output

Cardiac output is the volume of blood pumped by the heart per minute.

Formula:

Heart Rate Regulation

Sympathetic stimulation: Increases heart rate.
Parasympathetic stimulation: Decreases heart rate.

Heart Sounds

Heart sounds are produced by valve closures:

"Lub" (S1): Closure of AV valves.
"Dub" (S2): Closure of semilunar valves.

Common Heart Problems

Coronary Blockage: Caused by atherosclerosis; leads to reduced blood flow and possible heart attack.
Heart Murmurs: Abnormal sounds due to valve defects.
Pacemaker Problems: Arrhythmias due to SA or AV node dysfunction.
Tachycardia: Fast heart rate; Bradycardia: Slow heart rate.
Congestive Heart Failure: Inability of the heart to pump effectively.

Blood Vessels

Types of Blood Vessels

Arteries: Carry blood away from the heart; high pressure.
Veins: Carry blood toward the heart; low pressure.
Capillaries: Microscopic vessels for exchange of gases, nutrients, and wastes.

Blood Pressure

Blood pressure is the force exerted by blood on vessel walls, measured in mmHg.

Highest pressure: Arteries (especially aorta).
Lowest pressure: Veins (especially vena cava).

Types of Arteries

Elastic arteries: Large, close to the heart; stretch and recoil.
Muscular arteries: Medium-sized; distribute blood to organs.
Arterioles: Smallest arteries; regulate blood flow into capillaries.

Structure of Capillaries

Capillaries consist of a single layer of endothelial cells, allowing efficient exchange.

Types of Capillaries

Continuous capillaries: Most common; uninterrupted lining.
Fenestrated capillaries: Have pores for increased permeability.
Sinusoidal capillaries: Large gaps; found in liver, spleen.

Structure of Veins

Veins have thinner walls and larger lumens than arteries. They contain valves to prevent backflow, a feature not found in arteries.

Blood Pressure Measurement and Factors

Measurement: Sphygmomanometer; systolic/diastolic values.
Peripheral resistance: Resistance to blood flow due to vessel diameter, blood viscosity, and vessel length.

Determinants of Arterial Blood Pressure

Cardiac output
Peripheral resistance
Blood volume

Arterial Pressure Maintenance

Arteries maintain pressure between heartbeats via elastic recoil.

Pulse

Pulse is the rhythmic expansion of an artery due to heartbeat.

Veins vs. Arteries

Veins: Thinner walls, valves, lower pressure.
Arteries: Thicker walls, no valves, higher pressure.

Nervous System Control of Blood Pressure

Medulla oblongata: Regulates neural control via baroreceptors, chemoreceptors, and higher brain centers.
Stimuli: Blood pressure changes, blood chemistry, emotional states.

Kidney Regulation of Blood Pressure

Renin-angiotensin-aldosterone system: Adjusts blood volume and vessel constriction.
Direct filtration: Alters blood volume by excreting or retaining water.

Blood Vessel Disorders

Atherosclerosis

Causes: High cholesterol, hypertension, smoking.
Effects: Plaque buildup, vessel narrowing, risk of heart attack.
Prevention/Treatment: Lifestyle changes, medications, surgery.

Hypertension and Hypotension

Hypertension: High blood pressure; risk factors include obesity, genetics, stress.
Hypotension: Low blood pressure; may cause dizziness, fainting.

Shock

Hypovolemic shock: Due to blood loss or dehydration.
Cardiogenic shock: Due to heart failure.

Type	Main Feature	Example
Elastic Artery	Large, stretchable	Aorta
Muscular Artery	Medium, distributes blood	Radial artery
Arteriole	Small, regulates flow	Precapillary arteriole

Capillary Type	Structure	Location
Continuous	No pores	Muscle, skin
Fenestrated	Pores	Kidney, intestine
Sinusoidal	Large gaps	Liver, spleen

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