The Cardiovascular System I: The Heart

General Function of the Cardiovascular System

The cardiovascular system is responsible for transporting blood, nutrients, gases, hormones, and wastes throughout the body, ensuring homeostasis and tissue viability.

• Primary function: Deliver oxygen and nutrients to tissues and remove carbon dioxide and metabolic wastes.

• Components: Heart, blood vessels (arteries, veins, capillaries), and blood.

Major Function and Location of the Heart

• Function: Acts as a muscular pump to propel blood through the circulatory system.

• Location: Situated in the mediastinum of the thoracic cavity, between the lungs, posterior to the sternum, and superior to the diaphragm. The heart is slightly left of the midline and tilted so the apex points to the left hip.

Double Pump Function: Pulmonary and Systemic Circuits

• Pulmonary Circuit: Right side of the heart pumps deoxygenated blood to the lungs for gas exchange.

• Systemic Circuit: Left side of the heart pumps oxygenated blood to the rest of the body.

• Differences:

  • Location: Pulmonary (right heart), Systemic (left heart)

  • Blood type: Pulmonary (deoxygenated to lungs, returns oxygenated), Systemic (oxygenated to body, returns deoxygenated)

  • Function: Pulmonary (gas exchange), Systemic (nutrient/waste exchange)

Pericardium and Heart Wall

• Pericardium: Double-walled sac surrounding the heart, consisting of:

  • Fibrous pericardium: Outer tough layer for protection and anchoring.

  • Serous pericardium: Inner layer with parietal and visceral (epicardium) layers.

• Pericardial cavity: Space between serous layers containing serous fluid to reduce friction.

• Heart wall layers:

  • Epicardium: Outer layer (visceral pericardium)

  • Myocardium: Middle, muscular layer (cardiac muscle tissue)

  • Endocardium: Inner endothelial lining

Heart Anatomy: Chambers, Valves, and Great Vessels

• Chambers: Right atrium, right ventricle, left atrium, left ventricle

• Blood type: Right chambers (deoxygenated), left chambers (oxygenated)

• Great vessels:

  • Veins: Superior/inferior vena cava, pulmonary veins

  • Arteries: Pulmonary trunk, aorta

• Valves: Atrioventricular (tricuspid, bicuspid/mitral), semilunar (pulmonary, aortic)

Key Internal Structures of the Heart

• Right Atrium:

  • Fossa ovalis/foramen ovale: Remnant of fetal circulation

  • Coronary sinus: Drains deoxygenated blood from myocardium

  • Tricuspid valve: Prevents backflow to right atrium

• Right Ventricle:

  • Trabeculae carneae: Muscular ridges

  • Papillary muscles & chordae tendineae: Anchor AV valves

  • Pulmonary trunk & pulmonary semilunar valve: Direct blood to lungs

• Left Atrium:

  • Pulmonary veins: Bring oxygenated blood from lungs

  • Bicuspid (mitral) valve: Prevents backflow to left atrium

• Left Ventricle:

  • Aorta & aortic semilunar valve: Direct blood to systemic circuit

Coronary Circulation

• Function: Supplies blood to the heart muscle (myocardium)

• Coronary arteries: Right and left coronary arteries branch from ascending aorta

• Major branches:

  • Right: Marginal artery, posterior interventricular artery

  • Left: Anterior interventricular (LAD), circumflex artery

• Major veins: Great cardiac vein, middle cardiac vein, small cardiac vein

• Coronary sinus: Large vein draining into right atrium

Cardiac Muscle and Electrophysiology

• Cardiac muscle: Striated, branched, single nucleus, involuntary

• Differences from skeletal muscle: Intercalated discs, more mitochondria, autorhythmicity

• Structures for aerobic respiration: Abundant mitochondria, myoglobin, rich capillary supply

• Intercalated discs: Contain desmosomes (mechanical connection) and gap junctions (electrical connection)

• Action potential phases (contractile cells):

  1. Rapid depolarization (Na+ influx)

  2. Plateau (Ca2+ influx, K+ efflux)

  3. Repolarization (K+ efflux)

• Extended refractory period: Prevents tetanus, ensures rhythmic contractions

• Pacemaker potential (autorhythmic cells):

  1. Slow depolarization (Na+ influx)

  2. Threshold reached, rapid depolarization (Ca2+ influx)

  3. Repolarization (K+ efflux)

Cardiac Conduction System

• Function: Coordinates heart contractions

• Order of structures: Sinoatrial (SA) node → Atrioventricular (AV) node → AV bundle (Bundle of His) → Right and left bundle branches → Purkinje fibers

• SA node: Pacemaker due to fastest rate of spontaneous depolarization

Electrocardiogram (ECG) Waves and Segments

• P wave: Atrial depolarization

• QRS complex: Ventricular depolarization (and atrial repolarization)

• T wave: Ventricular repolarization

• ST segment: Ventricles depolarized

• PR interval: Atrial depolarization to ventricular depolarization

Cardiac Cycle: Systole and Diastole

• Systole: Contraction phase (chamber ejects blood)

• Diastole: Relaxation phase (chamber fills with blood)

• Heart sounds: 'Lub' (AV valves close), 'Dub' (semilunar valves close)

• Pressure and flow: Blood flows from high to low pressure; valve function ensures unidirectional flow

Pressure and Volume Changes in the Cardiac Cycle

• Left ventricle generates higher pressure than right (systemic vs. pulmonary)

• Volume changes correspond to phases of filling and ejection

Cardiac Output and Related Terms

• Cardiac Output (CO): Volume of blood pumped by each ventricle per minute

• Stroke Volume (SV): Volume of blood ejected per beat

• End Diastolic Volume (EDV): Volume in ventricle at end of filling

• End Systolic Volume (ESV): Volume in ventricle after contraction

• Formulas:

Factors Influencing Stroke Volume and Heart Rate

• Preload: Degree of stretch before contraction (Frank-Starling Law: increased preload increases SV)

• Contractility: Force of contraction at a given preload (increased by positive inotropic agents, decreased by negative agents)

• Afterload: Resistance ventricles must overcome to eject blood

• Chronotropic agents: Affect heart rate (sympathetic = positive, parasympathetic = negative)

The Cardiovascular System II: The Blood Vessels

Structure and Function of Blood Vessels

• Arteries: Carry blood away from heart; thick muscular walls

• Veins: Return blood to heart; thinner walls, larger lumen, valves

• Capillaries: Microscopic vessels for exchange between blood and tissues

Blood Vessel Wall Structure

• Tunica intima: Inner endothelial layer

• Tunica media: Middle smooth muscle layer

• Tunica externa (adventitia): Outer connective tissue

Types of Arteries

• Elastic arteries: Largest, near heart, stretch and recoil (e.g., aorta)

• Muscular arteries: Distribute blood to organs, more smooth muscle

• Arterioles: Smallest, regulate flow into capillaries

Veins and Venous Return

• Function: Return blood to heart, serve as blood reservoirs

• Venous valves: Prevent backflow, especially in limbs

• Venules: Smallest veins, collect blood from capillaries

Anastomoses and Angiogenesis

• Anastomosis: Connection between blood vessels

• Types: Arterial, venous, arteriovenous

• Angiogenesis: Formation of new blood vessels

Blood Pressure, Flow, and Resistance

• Blood pressure: Force exerted by blood on vessel walls

• Pressure gradient: Drives blood flow from high to low pressure

• Peripheral resistance: Opposition to flow, mainly in arterioles

• Factors affecting resistance: Vessel diameter (most important), blood viscosity, vessel length

• Relationship: (Flow = Pressure difference / Resistance)

Blood Pressure Measurements

• Systolic pressure: Peak during ventricular contraction

• Diastolic pressure: Lowest during ventricular relaxation

• Pulse pressure: Difference between systolic and diastolic

• Mean Arterial Pressure (MAP): Average pressure in arteries

Venous Return Mechanisms

• Venous return: Blood flow back to heart

• Skeletal muscle pump: Muscle contractions squeeze veins

• Respiratory pump: Pressure changes during breathing assist return

Regulation of Blood Pressure

• Arterioles: Regulate tissue blood flow and systemic pressure

• Short-term regulation: Sympathetic (increases BP), parasympathetic (decreases BP)

• Baroreceptor reflex: Detects pressure changes, adjusts heart and vessel activity

• Chemoreceptor reflex: Responds to blood O2, CO2, pH

• Hormonal regulation: Angiotensin II, aldosterone, ADH (increase BP); atrial natriuretic peptide (decreases BP)

• Long-term regulation: Endocrine and urinary systems adjust blood volume

Capillaries and Tissue Perfusion

• Capillary types:

  • Continuous: Least permeable, most common (muscle, skin)

  • Fenestrated: Pores for increased permeability (kidneys, intestines)

  • Sinusoidal: Large gaps, most permeable (liver, bone marrow)

• Exchange processes: Diffusion, transcytosis, bulk flow

• Tissue perfusion: Blood flow through tissues

• Autoregulation: Myogenic (vessel response to pressure), metabolic (local chemical signals)

Bulk Flow and Fluid Exchange

• Blood hydrostatic pressure (BHP): Pushes fluid out of capillaries

• Interstitial hydrostatic pressure (IHP): Pushes fluid into capillaries

• Blood colloid osmotic pressure (BCOP): Pulls fluid into capillaries

• Interstitial fluid colloid osmotic pressure (IFCOP): Pulls fluid out of capillaries

• Net Hydrostatic Pressure (NHP):

• Net Colloid Osmotic Pressure (COP):

• Net Filtration Pressure (NFP):

• Filtration: Occurs at arterial end; Reabsorption: Occurs at venous end

• Lymphatic system: Returns excess fluid to blood

Systemic Circulation: Major Vessels

• Arteries: Trace from left ventricle to subclavian arteries, upper and lower limbs

• Veins: Trace from limbs, trunk, head, and neck back to heart

• Hepatic portal system: Veins from digestive organs drain into hepatic portal vein, delivering nutrients to liver

Example Table: Types of Capillaries

Additional info: Some details, such as specific figure references and certain vessel names, were inferred or generalized for completeness and clarity.