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Cardiovascular System: Heart and Blood Vessels Study Guide

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External Anatomy of the Heart

Major External Features

  • Apex: The pointed inferior tip of the heart, formed mostly by the left ventricle. It points downward and to the left.

  • Base: The broad superior portion of the heart, where the great vessels attach. Mostly formed by the atria.

  • Chambers (Visible Externally): Right atrium, left atrium (mostly posterior), right ventricle, left ventricle.

  • Grooves (Sulci): Contain coronary blood vessels.

    • Coronary (Atrioventricular) Sulcus: Separates atria from ventricles.

    • Anterior Interventricular Sulcus: Separates right and left ventricles on the front.

    • Posterior Interventricular Sulcus: Separates ventricles on the back.

  • Great Vessels: Superior vena cava, inferior vena cava, pulmonary trunk, pulmonary arteries, pulmonary veins, ascending aorta.

  • Auricles: Small, ear-like extensions of the atria.

  • Coronary Arteries & Cardiac Veins: Supply blood to the heart muscle itself.

Internal Anatomy of the Heart

Heart Chambers and Septa

  • Right Atrium (RA): Receives deoxygenated blood from the body.

  • Right Ventricle (RV): Pumps blood to the lungs.

  • Left Atrium (LA): Receives oxygenated blood from the lungs.

  • Left Ventricle (LV): Pumps blood to the body (thickest wall).

  • Interatrial Septum: Separates right and left atria.

  • Interventricular Septum: Separates right and left ventricles.

  • Purpose: Prevents mixing of oxygenated and deoxygenated blood.

Heart Valves and Support Structures

  • Atrioventricular (AV) Valves:

    • Tricuspid Valve: Between RA and RV (3 cusps).

    • Bicuspid (Mitral) Valve: Between LA and LV (2 cusps).

  • Semilunar Valves:

    • Pulmonary Semilunar Valve: RV to pulmonary trunk.

    • Aortic Semilunar Valve: LV to aorta.

  • Valve Support Structures:

    • Chordae Tendineae: Tendon-like cords attached to AV valves.

    • Papillary Muscles: Anchor chordae tendineae to ventricular walls.

  • Internal Surface Features:

    • Trabeculae Carneae: Irregular ridges inside ventricles.

    • Pectinate Muscles: Ridges in atrial walls (especially right atrium).

  • Major Openings: For superior/inferior vena cava, pulmonary veins, aorta, and pulmonary trunk.

Blood Flow Through the Heart

Receiving Chambers

  • Right Atrium: Receives deoxygenated blood from the body via superior vena cava, inferior vena cava, and coronary sinus.

  • Left Atrium: Receives oxygenated blood from the lungs via pulmonary veins.

Memory Trick: "Atria Accept" (Atria = Accept blood, Ventricles = Venture out/pump blood)

Pulmonary Circulation

  • Definition: Pathway carrying blood from the heart to the lungs and back for gas exchange.

  • Steps:

    1. Right ventricle pumps deoxygenated blood.

    2. Blood exits through pulmonary semilunar valve.

    3. Enters pulmonary trunk, then pulmonary arteries.

    4. Reaches lungs (CO2 released, O2 picked up).

    5. Oxygenated blood returns via pulmonary veins to left atrium.

Systemic Circulation

  • Definition: Pathway of blood from the heart to the body and back, delivering oxygen and nutrients.

  • Steps:

    1. Left ventricle pumps oxygenated blood.

    2. Blood leaves through aortic semilunar valve into aorta.

    3. Travels through systemic arteries, arterioles, capillaries.

    4. O2 and nutrients delivered to tissues; CO2 and wastes picked up.

    5. Blood returns via venules, veins, superior/inferior vena cava to right atrium.

Tracing Blood Flow Through the Heart

  • Superior vena cava → Right atrium → Tricuspid valve → Right ventricle → Pulmonary semilunar valve → Pulmonary trunk → Pulmonary arteries → Lungs → Pulmonary veins → Left atrium → Bicuspid (mitral) valve → Left ventricle → Aortic semilunar valve → Aorta → Body → Back to right atrium via vena cavae.

Comparison Table: Pulmonary vs. Systemic Circulation

Circulation

Pathway

Main Function

Pulmonary

Heart → Lungs → Heart

Gas exchange (O2 in, CO2 out)

Systemic

Heart → Body → Heart

Deliver O2/nutrients, remove wastes

Cardiac Cycle and Heart Sounds

Systole vs. Diastole

  • Systole: Contraction phase; heart muscle contracts, blood is pushed out (ventricles pump). Systolic pressure is the "top number" in BP.

  • Diastole: Relaxation phase; heart muscle relaxes, chambers fill with blood. Diastolic pressure is the "bottom number" in BP.

Memory Tricks: "SYSTOLE = Squeeze", "DIASTOLE = Dwell (fill time)"

Heart Sounds

  • "Lub": Closing of AV valves at start of systole.

  • "Dub": Closing of semilunar valves at start of diastole.

Phases of the Cardiac Cycle

  1. Ventricular Filling (Diastole): AV valves open, blood flows from atria to ventricles (mostly passive).

  2. Atrial Systole: Atria contract, push final blood into ventricles.

  3. Isovolumetric Contraction: Ventricles contract, all valves closed, pressure rises, no blood leaves yet.

  4. Ventricular Ejection: Semilunar valves open, blood pumped into aorta/pulmonary trunk.

  5. Isovolumetric Relaxation: Ventricles relax, all valves closed, pressure drops, prepares for next filling.

Cardiac Conduction System

Electrical Pathway

  • SA Node (Sinoatrial Node): Located in right atrium near superior vena cava; pacemaker of the heart; initiates action potential (~60–100 bpm).

  • AV Node: Delays signal, allowing ventricles to fill.

  • Bundle of His (AV Bundle): Carries impulse to bundle branches.

  • Right & Left Bundle Branches: Conduct impulses through interventricular septum.

  • Purkinje Fibers: Distribute impulse through ventricles, causing contraction from bottom up.

AV Node Delay: Ensures atria empty fully before ventricles contract.

Blood Vessels: Structure and Function

Layers of a Blood Vessel

Layer

Main Composition

Key Function

Tunica Intima

Endothelium

Smooth blood flow

Tunica Media

Smooth muscle + elastic fibers

Controls diameter & BP

Tunica Externa

Connective tissue

Protection & anchoring

  • Tunica Intima: Innermost, smooth endothelial lining, may form valves in veins.

  • Tunica Media: Middle, smooth muscle and elastic fibers, thickest in arteries, controls vasoconstriction/dilation.

  • Tunica Externa (Adventitia): Outermost, connective tissue, anchors and protects vessel, contains vasa vasorum in large vessels.

Types of Blood Vessels

  • Arteries: Carry blood away from heart, usually oxygenated (except pulmonary artery), thick muscular walls, high pressure.

  • Veins: Carry blood toward heart, usually deoxygenated (except pulmonary veins), thin walls, valves, low pressure.

  • Capillaries: Connect arteries to veins, one cell layer thick, site of gas/nutrient/waste exchange.

Capillary Exchange and Starling Forces

Blood Flow Through Capillaries

  • Blood enters capillary from arteriole (high pressure).

  • At arterial end, fluid is pushed out (filtration).

  • Oxygen and nutrients diffuse into tissues; CO2 and wastes enter blood.

  • At venous end, fluid is pulled back in (reabsorption).

  • Blood leaves through venule.

Forces Acting on Capillary Blood Flow (Starling Forces)

Location

Main Force

Movement

Arterial end

Hydrostatic pressure > osmotic pressure

Fluid OUT (filtration)

Middle

Balanced forces

Exchange occurs

Venous end

Osmotic pressure > hydrostatic pressure

Fluid IN (reabsorption)

  • Capillary Hydrostatic Pressure (CHP): Pushes fluid out (strongest at arterial end).

  • Blood Colloid Osmotic Pressure (BCOP): Pulls fluid back in (strongest at venous end, due to plasma proteins).

Veins and Blood Reservoirs

True Veins

  • Standard systemic veins returning blood to the heart.

  • Thin walls, large lumens, often contain valves.

  • Examples: Superior/inferior vena cava, femoral veins, jugular veins.

Blood Reservoirs

  • Veins (especially systemic veins): Store most of the blood volume at rest (~60–70%).

  • Can expand or constrict to store or release blood as needed (e.g., during exercise or blood loss).

Blood Pressure and Its Regulation

Definition and Measurement

  • Blood Pressure (BP): Force of blood against arterial walls.

  • Measured as systolic/diastolic (e.g., 120/80 mmHg).

Factors Influencing Blood Pressure

  • Cardiac Output (CO):

  • Peripheral Resistance: Resistance in blood vessels (narrower vessels = higher BP).

  • Blood Volume: More blood increases BP; less blood decreases BP.

  • Blood Viscosity: Thicker blood increases BP.

  • Elasticity of Arteries: Stiff arteries increase BP.

  • Nervous System & Hormones: Sympathetic stimulation and hormones (epinephrine, norepinephrine, ADH, aldosterone) can increase BP.

Major Arteries of the Body

Neck (Head & Neck Supply)

  • Common Carotid Artery: Main artery of the neck, splits into:

    • Internal Carotid Artery: Supplies brain.

    • External Carotid Artery: Supplies face, scalp, neck.

Arm (Upper Limb)

  • Blood flows: Subclavian artery → Axillary artery (armpit) → Brachial artery (upper arm) → splits into:

    • Radial artery: Thumb side (lateral forearm).

    • Ulnar artery: Pinky side (medial forearm).

Lower Limb

  • Femoral artery: Main artery of thigh → becomes popliteal artery (behind knee) → splits into:

    • Anterior tibial artery: Front of lower leg (becomes dorsalis pedis in foot).

    • Posterior tibial artery: Back of lower leg (supplies sole of foot).

Autonomic Regulation of Blood Pressure

Sympathetic vs. Parasympathetic Effects

  • Sympathetic Nervous System: Increases BP by raising heart rate, contractility, and causing vasoconstriction.

  • Parasympathetic Nervous System: Decreases BP by lowering heart rate and promoting relaxation.

Baroreceptors and Chemoreceptors

Baroreceptors

  • Detect changes in blood pressure by sensing vessel stretch.

  • Locations: Carotid sinus (neck), aortic arch.

  • Function: Help maintain stable BP by adjusting heart rate and vessel diameter.

Chemoreceptors

  • Monitor blood chemistry (O2, CO2, pH).

  • Locations: Carotid bodies, aortic bodies.

  • Function: Regulate respiration and cardiovascular responses (increase breathing/heart rate if O2 low or CO2 high).

Summary Table: Blood Vessel Types

Vessel Type

Direction of Blood Flow

Wall Structure

Key Features

Artery

Away from heart

Thick, muscular, elastic

High pressure, no valves (except pulmonary artery is deoxygenated)

Vein

Toward heart

Thin, wide lumen, valves

Low pressure, blood reservoir

Capillary

Connect arteries to veins

One cell layer (endothelium)

Exchange of gases/nutrients/wastes

Key Equations

  • Cardiac Output:

  • Blood Pressure:

Additional info:

  • Some memory tricks and mnemonics were included to aid recall.

  • Tables were inferred and expanded for clarity and completeness.

  • All major concepts from the study guide were expanded with academic context for exam preparation.

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