The Cardiovascular System: Structure, Function, and Circulation

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The Cardiovascular System

Heart Structure and Location

The heart is a muscular organ about the size of your fist, located in the mediastinum (the space between the lungs, backbone, and sternum). It is central to the circulatory system, pumping blood throughout the body. - Size: Approximately 9x14 cm. - Location: Mediastinum, between the lungs. - Function: Pumps blood to supply oxygen and nutrients to tissues and remove waste products. Heart location in chest Anatomical location of the heart and its coverings

Heart Coverings: The Pericardium

The heart is enclosed by the pericardium, a double-walled sac that protects and anchors the heart, preventing overfilling and reducing friction during contractions. - Parietal layer: Outermost covering. - Visceral layer: Lines the surface of the heart. - Pericardial fluid: Lubricates and protects the heart. Pericardium and pericardial fluid Layers of the heart wall and pericardium

Parts and Chambers of the Heart

The heart consists of four chambers and several key structures that ensure efficient blood flow. - Atria: Receiving chambers where blood enters the heart. - Ventricles: Pumping chambers where blood leaves the heart. - Valves: Prevent backflow and ensure one-way blood flow. - Chordae tendineae: Cord-like tendons anchoring the AV valves, resisting blood pressure during ventricular contraction. - Septum: Myocardial wall separating right and left ventricles. Normal heart showing chambers and blood flow

Heart Valves

Valves ensure blood flows in one direction only, preventing backflow between contractions. - Atrioventricular (AV) valves: Between atrium and ventricle (Tricuspid on right, Bicuspid/Mitral on left). - Semilunar valves: Between ventricle and outbound artery (Pulmonary on right, Aortic on left). - Function: AV valves close during ventricular contraction; semilunar valves close during ventricular relaxation. Valves of the heart Structure of heart valves and chordae tendineae Cross-section of heart valves

Blood Vessels Attached to the Heart

Several major blood vessels are directly connected to the heart, facilitating circulation. - Aorta: Largest artery, carries oxygenated blood from heart to body. - Pulmonary veins: Carry oxygenated blood from lungs to heart. - Pulmonary artery: Carries deoxygenated blood from heart to lungs. - Vena cavas: Veins carrying deoxygenated blood from body to heart.

Heart Circuits

Pulmonary and Systemic Circulation

The heart acts as two pumps: one for the lungs (pulmonary circulation) and one for the body (systemic circulation). - Pulmonary circuit: Right ventricle → pulmonary arteries → lung capillaries → pulmonary veins → left atrium. - Systemic circuit: Left ventricle → arteries → body capillaries → veins → right atrium. Difference between pulmonary and systemic circulation Pulmonary and systemic circuits with blood flow

Blood Vessels

Types of Blood Vessels

Blood vessels are classified into arteries, veins, and capillaries, each with distinct structure and function. - Arteries: Strong, elastic vessels carrying blood away from the heart; thick walls of smooth muscle and elastic fibers; smaller lumen. - Veins: Thinner, less muscular vessels carrying blood toward the heart; larger lumen; contain valves to prevent backflow. - Capillaries: Smallest vessels; walls made of a single layer of squamous cells; site of gas and nutrient exchange. Three types of blood vessels: artery, vein, capillary Structure of artery, vein, and capillary Vein valves and skeletal muscle contraction Capillary structure and function

Capillary Function

Capillaries penetrate nearly all tissues, allowing exchange of gases (O2 and CO2) and nutrients between blood and tissues. - Wall composition: Single layer of squamous cells for rapid diffusion. - Critical function: Exchange of materials between blood and tissues. Capillary network and exchange Capillary beds and blood flow External and internal respiration in capillaries

Cardiac Conduction System

Electrical Impulse Generation

The cardiac conduction system (nodal system) is a group of specialized cardiac muscle cells that send signals to the heart muscle, causing it to contract. - Components: SA node, AV node, bundle of His, bundle branches, Purkinje fibers. - Function: Initiates and coordinates heart contractions independently of the nervous system. Cardiac conduction system pathways

Regulation of Cardiac Cycle

Heart rate is controlled by the cardiac center within the medulla oblongata, adjusting in response to changes in the body's state (homeostasis). Heart anatomy with conduction system Medulla oblongata location in brain

Electrocardiograms (ECG)

Measuring Heart Activity

Electrocardiograms (ECGs) measure electrical impulses from the heart, creating a graph of the output. - P wave: Atria contract. - QRS wave: Ventricles contract. - T wave: Ventricles relax and reset.

Heart Rate

- Normal resting heart rate: 60-100 beats per minute. - Bradycardia: Heart rate below 60 bpm. - Tachycardia: Heart rate above 100 bpm.

Coronary Circulation

Supplying the Heart Muscle

Coronary circulation is the specialized vascular network supplying oxygenated blood to the myocardium (heart muscle). - Coronary arteries: Supply oxygenated blood to heart muscle. - Coronary veins: Carry away deoxygenated blood.

Heart Sounds

Normal Heart Sounds

- S1 (Lub): Closure of atrioventricular (mitral and tricuspid) valves at the beginning of systole. - S2 (Dub): Closure of semilunar (aortic and pulmonic) valves at the beginning of diastole.

Blood Pressure

Definition and Measurement

Blood pressure is the force of blood pushing against the walls of arteries as the heart pumps it throughout the body. - Systolic pressure: Peak pressure during ventricular contraction. - Diastolic pressure: Low pressure during ventricular refilling. - Normal range: 120-140 / 80-90 mmHg.

Cardiovascular Disorders

Atherosclerosis

Atherosclerosis is a buildup of lipids, calcium, or cell debris that restricts blood flow, causing higher blood pressure and potentially leading to heart attacks if a blockage occurs in a coronary artery.

Aneurysm

An aneurysm is a weakening of a blood vessel wall, causing it to bulge and potentially burst or form a thrombus. Risk factors include high blood pressure, atherosclerosis, and smoking.

Heart Attack

A heart attack is caused by a blockage in a coronary artery, disrupting the flow of oxygenated blood to the heart muscle.

Coronary Bypass and Angioplasty

- Coronary bypass: Transplants a vein to reroute blood around a blockage. - Angioplasty: Balloon inserted and inflated to expand a blocked vessel; a stent may be used to keep it open.

Hypertrophic Cardiomyopathy

Abnormal thickening of the heart muscle wall, decreasing the heart’s ability to pump blood. Usually inherited or occurs with age.

Hemostasis and Blood Clotting

Stages of Hemostasis

Hemostasis is the stoppage of bleeding from a break in a blood vessel. - Stage 1: Platelets attach to the vessel wall, forming a platelet plug. - Stage 2: Platelets activate thrombin, which activates fibrin strands that stick to the plug. - Stage 3: Fibrin proteins cause red blood cells to stick to the clot, sealing the vessel until it heals.

Blood Clotting Disorders

- Hemophilia: Hereditary disorder impairing blood clotting; platelet plug forms but fibrin does not. - Thrombus: Blood clot in an unbroken vessel. - Embolus: Thrombus that breaks away and clogs a vessel elsewhere (e.g., stroke). - Hematoma: Swelling of clotted blood within tissue; bruise colors result from hemoglobin breakdown.

Fetal Circulation

Unique Features of Fetal Circulation

In a fetus, the lungs are nonfunctional and are bypassed by the foramen ovale, a hole allowing blood to pass directly from the right atrium to the left atrium. The foramen ovale closes at birth. - Umbilical cord: Contains one vein (oxygenated blood to fetus) and two arteries (deoxygenated blood from fetus to mother). - Fetal hemoglobin: Greater affinity for oxygen than maternal hemoglobin.

Summary Table: Heart Valves and Circuits

Valve	Location	Circuit	Function
Tricuspid (AV)	Right atrium & ventricle	Pulmonary	Prevents backflow to atrium
Bicuspid/Mitral (AV)	Left atrium & ventricle	Systemic	Prevents backflow to atrium
Pulmonary Semilunar	Right ventricle & pulmonary artery	Pulmonary	Prevents backflow to ventricle
Aortic Semilunar	Left ventricle & aorta	Systemic	Prevents backflow to ventricle

Key Equations

Blood Pressure

Cardiac Output

Summary Table: Blood Vessel Structure

Type	Lumen Size	Wall Structure	Function
Artery	Small	Thick muscle & elastic fibers	Carry blood away from heart
Vein	Large	Thin muscle & elastic fibers, valves	Carry blood toward heart
Capillary	Very small	Single layer of squamous cells	Exchange of gases & nutrients