The Cardiovascular System: Heart and Blood Vessels – Comprehensive Study Notes

Chapter 17 – The Cardiovascular System I: The Heart

General Function of the Cardiovascular System

• Cardiovascular System: A network consisting of the heart, blood, and blood vessels that transports nutrients, gases, hormones, and wastes throughout the body.

• Main Function: To maintain homeostasis by ensuring adequate tissue perfusion and removal of metabolic wastes.

Major Function and Location of the Heart

• Heart: A muscular organ that pumps blood through two major circuits: pulmonary and systemic.

• Location: Situated in the mediastinum of the thoracic cavity, between the lungs, posterior to the sternum, and superior to the diaphragm.

Double Pump Function: Pulmonary vs. Systemic Circuits

• Pulmonary Circuit: Right side of the heart; carries deoxygenated blood to the lungs and returns oxygenated blood to the left atrium.

• Systemic Circuit: Left side of the heart; pumps oxygenated blood to the body and returns deoxygenated blood to the right atrium.

• Key Differences:

  • Location: Pulmonary (right heart/lungs), Systemic (left heart/body)

  • Blood Type: Pulmonary (deoxygenated to lungs, oxygenated to heart), Systemic (oxygenated to body, deoxygenated to heart)

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

Pericardium and Heart Wall

• Pericardium: Double-walled sac surrounding the heart; consists of fibrous and serous layers.

• Serous Fluid: Found in the pericardial cavity; reduces friction during heartbeats.

• 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

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

• Blood Type in Chambers: Right (deoxygenated), Left (oxygenated)

• Great Vessels: Superior/inferior vena cava, pulmonary trunk, pulmonary veins, aorta

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

Significant Heart Structures and Functions

• Right Atrium:

  • Fossa Ovalis/Foramen Ovale: Remnant of fetal circulation

  • Coronary Sinus: Drains deoxygenated blood from myocardium

  • Tricuspid Valve: Prevents backflow into right atrium

• Right Ventricle:

  • Trabeculae Carneae: Muscular ridges

  • Papillary Muscles & Chordae Tendineae: Anchor AV valves

  • Pulmonary Trunk & Valve: Directs blood to lungs

• Left Atrium:

  • Pulmonary Veins: Bring oxygenated blood from lungs

  • Bicuspid (Mitral) Valve: Prevents backflow into left atrium

• Left Ventricle:

  • Aorta & Aortic Valve: Distributes oxygenated blood to body

Coronary Circulation

• Function: Supplies blood to heart muscle (myocardium)

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

• Major Branches: Right (marginal, posterior interventricular), Left (circumflex, anterior interventricular)

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

• Coronary Sinus: Collects deoxygenated blood, drains into right atrium

Cardiac Muscle and Electrophysiology

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

• Differences from Skeletal Muscle: Intercalated discs, autorhythmicity, longer refractory period

• Structures for Aerobic Respiration: Numerous 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): Slow Na+ influx, Ca2+ influx, K+ efflux

Cardiac Conduction System

• Function: Coordinates heart contractions

• Components (in order): SA node → AV node → AV bundle (Bundle of His) → Right/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: Plateau phase of ventricular action potential

• PR interval: Time from atrial to ventricular depolarization

Cardiac Cycle: Systole and Diastole

• Systole: Contraction phase (blood ejected)

• Diastole: Relaxation phase (chambers fill)

• Heart Sounds: "Lub" (AV valves close), "Dub" (semilunar valves close)

• Pressure, Blood Flow, and Valve Function: Blood flows from high to low pressure; valves prevent backflow

Pressure and Volume Changes in Cardiac Cycle

• Left vs. Right Ventricle: Left generates higher pressure; both eject similar volumes

• Aorta: Receives blood during left ventricular systole

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 remaining after contraction

• Formula:

  • $CO = SV \times HR$

  • $SV = EDV - ESV$

Regulation of Stroke Volume

• 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, e.g., sympathetic stimulation, Ca2+; decreased by negative agents, e.g., acidosis)

• Afterload: Resistance ventricles must overcome (increased afterload decreases SV)

• Inotropic Agents: Substances that alter contractility (positive: epinephrine; negative: beta-blockers)

Regulation of Heart Rate

• Chronotropic Agents: Affect heart rate (positive: sympathetic nerves, negative: parasympathetic nerves)

Chapter 18 – The Cardiovascular System II: The Blood Vessels

Structure and Function of Blood Vessels

• Arteries: Carry blood away from heart; thick, elastic walls

• Veins: Carry blood toward heart; thinner walls, larger lumens, valves

• Capillaries: Microscopic vessels for exchange between blood and tissues

Blood Vessel Wall Structure

• Three Tunics:

  • Tunica intima: Endothelial lining

  • Tunica media: Smooth muscle and elastic fibers

  • Tunica externa: Connective tissue

Types of Arteries

• Elastic (Conducting) Arteries: Largest, near heart, withstand high pressure

• Muscular (Distributing) Arteries: Medium-sized, distribute blood to organs

• Arterioles: Smallest, regulate blood flow into capillaries

Veins and Venous Return

• Function: Return blood to heart; act 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

• Blood Flow: Volume of blood moving through a vessel per unit time

• Peripheral Resistance: Opposition to flow; affected by vessel diameter, blood viscosity, vessel length

• Key Relationships:

  • $F = \frac{\Delta P}{R}$ (Flow = Pressure difference / Resistance)

Factors Affecting Blood Pressure and Flow

• Three Main Factors: Cardiac output, blood volume, peripheral resistance

• Most Important for Resistance: Vessel radius (small changes greatly affect resistance)

Capillaries and Tissue Perfusion

• Types of Capillaries:

  • Continuous: Least permeable; muscle, skin, CNS

  • Fenestrated: Pores; kidneys, intestines, endocrine glands

  • Sinusoidal: Large gaps; liver, spleen, bone marrow

• Exchange Processes: Diffusion, transcytosis, bulk flow

• Tissue Perfusion: Blood flow through tissues; regulated by autoregulation (myogenic and metabolic mechanisms)

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

• Key Equations:

  • $NHP = BHP - IHP$

  • $NCOP = BCOP - IFCOP$

  • $NFP = NHP - NCOP$

• Filtration: Occurs at arterial end (NFP positive)

• Reabsorption: Occurs at venous end (NFP negative)

• Lymphatic System: Returns excess interstitial fluid to blood

Systemic Circulation: Major Vessels

• Arteries: Trace from left ventricle → aorta → subclavian arteries → upper/lower limbs

• Veins: Trace from limbs/trunk/head/neck → superior/inferior vena cava → right atrium

• Hepatic Portal System: Veins from digestive organs drain into hepatic portal vein; blood processed by liver before returning to systemic circulation

Table: Comparison of Arteries, Veins, and Capillaries

Vessel Type	Wall Structure	Function	Valves
Artery	Thick tunica media, elastic fibers	Carry blood away from heart	No
Vein	Thin tunica media, large lumen	Carry blood to heart	Yes (especially in limbs)
Capillary	Single endothelial layer	Exchange of substances	No

Table: Types of Capillaries

Type	Structure	Location	Permeability
Continuous	No pores, tight junctions	Muscle, skin, CNS	Low
Fenestrated	Pores in endothelium	Kidneys, intestines	Medium
Sinusoidal	Large gaps, incomplete basement membrane	Liver, spleen, bone marrow	High

Additional info:

• Short-term regulation of blood pressure involves neural (baroreceptor and chemoreceptor reflexes) and hormonal mechanisms (e.g., angiotensin II, ADH, aldosterone, ANP).

• Long-term regulation involves renal mechanisms adjusting blood volume.

• Venous return is aided by the skeletal muscle pump and respiratory pump.

• Mean Arterial Pressure (MAP) can be estimated as $MAP = \text{Diastolic Pressure} + \frac{1}{3}(\text{Systolic} - \text{Diastolic})$.