Heart and Blood Vessel Anatomy & Physiology: Study Guide

Heart Anatomy and Circulation

External Anatomy of the Heart

The heart's external features are important for understanding its function and the flow of blood. The apex and base, chambers, grooves, and great vessels are all visible externally.

• Apex: Pointed inferior tip, formed mostly by the left ventricle, points down and to the left.

• Base: Broad superior portion, where great vessels attach, mostly formed by the atria.

• Chambers: 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

Internally, the heart is divided into four chambers, separated by septa, and contains valves to ensure one-way blood flow.

• Chambers:

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

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

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

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

• Septa:

  • Interatrial Septum: Separates right & left atria.

  • Interventricular Septum: Separates right & left ventricles.

  Purpose: Prevents mixing of oxygenated and deoxygenated blood.

• Heart Valves:

  • Atrioventricular (AV) Valves:

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

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

  • Semilunar Valves:

    • Pulmonary Semilunar Valve: RV → pulmonary trunk.

    • Aortic Semilunar Valve: LV → 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

Blood enters the right atrium from the body (via superior/inferior vena cava and coronary sinus) and the left atrium from the lungs (via pulmonary veins).

• Memory Trick: "Atria Accept" (Atria = Accept blood, Ventricles = Venture out).

Pulmonary and Systemic Circulation

The heart pumps blood through two main circuits: pulmonary (to the lungs) and systemic (to the body).

• Pulmonary Circulation: Right ventricle → pulmonary semilunar valve → pulmonary trunk → pulmonary arteries → lungs (gas exchange) → pulmonary veins → left atrium.

• Systemic Circulation: Left ventricle → aortic semilunar valve → aorta → systemic arteries → arterioles → capillaries (exchange) → venules → veins → superior/inferior vena cava → right atrium.

• Key Difference: Pulmonary circulation moves blood between heart and lungs; systemic circulation moves blood between heart and body.

Systole vs. Diastole

The cardiac cycle alternates between contraction (systole) and relaxation (diastole).

• Systole: Heart muscle contracts, blood is pushed out (ventricles pump). Systolic pressure is the "top number" in blood pressure.

• Diastole: Heart muscle relaxes, chambers fill with blood. Diastolic pressure is the "bottom number" in blood pressure.

• Heart Sounds: "Lub" = AV valves close (start of systole); "Dub" = semilunar valves close (start of diastole).

Cardiac Conduction System

The heart's electrical system coordinates contraction. The action potential starts in the SA node and travels through a specific pathway.

• SA Node (Sinoatrial Node): Pacemaker, initiates action potential, sets heart rate (~60–100 bpm).

• Electrical Pathway: SA node → atria → AV node (delay) → bundle of His → bundle branches → Purkinje fibers → ventricles contract.

• AV Node Delay: Allows atria to empty before ventricles contract.

Phases of the Cardiac Cycle

The cardiac cycle consists of five main phases, each with distinct events.

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

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

3. Isovolumetric Contraction: Ventricles contract, all valves closed, pressure rises.

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

5. Isovolumetric Relaxation: Ventricles relax, all valves closed, pressure drops.

Blood Vessel Structure and Function

Layers of a Blood Vessel

Blood vessels have three main layers, each with specific functions and features.

• Tunica Intima: Innermost layer, endothelium (simple squamous), smooth surface, may form valves in veins.

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

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

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

Types of Blood Vessels

Arteries, veins, and capillaries have distinct roles in circulation.

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

• Vein: Carries blood toward the heart, usually deoxygenated (except pulmonary veins), thin walls, wider lumen, valves, low pressure.

• Capillary: Smallest vessel, connects arteries to veins, one cell layer thick, site of gas/nutrient/waste exchange.

Blood Flow Through Capillaries

Capillary blood flow is governed by hydrostatic and osmotic pressures, allowing exchange of substances.

• Step-by-step:

  1. Blood enters capillary from arteriole (high pressure).

  2. Arterial end: Fluid pushed out (filtration).

  3. Middle: Exchange of gases/nutrients/wastes.

  4. Venous end: Fluid pulled back in (reabsorption).

  5. Blood leaves through venule.

• Starling Forces:

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

  • Blood Colloid Osmotic Pressure (BCOP): Pulls fluid in, strongest at venous end.

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)

True Veins and Blood Reservoirs

True veins are standard systemic veins returning blood to the heart. Veins serve as the body's main blood reservoirs.

• True Veins: Carry blood toward the heart, low pressure, thin walls, large lumens, often contain valves.

• Blood Reservoirs: Systemic veins hold most blood volume at rest (~60–70%), can expand or constrict to store/release blood.

Blood Pressure and Regulation

Blood Pressure

Blood pressure is the force of blood against arterial walls, measured as systolic/diastolic values.

• Systolic Pressure: Pressure during ventricular contraction.

• Diastolic Pressure: Pressure during ventricular relaxation.

• Example: 120/80 mmHg.

Factors Influencing Blood Pressure

• Cardiac Output (CO): Amount of blood pumped per minute.

  • Formula: $CO = HR \times SV$

• Peripheral Resistance: Resistance in vessels, especially arterioles.

• Blood Volume: Total blood in system; more volume increases BP.

• Blood Viscosity: Thickness; more cells/proteins increases BP.

• Elasticity of Arteries: Stiff arteries increase BP.

• Nervous System & Hormones: Sympathetic increases BP; hormones (epinephrine, norepinephrine, ADH, aldosterone) increase BP.

Major Arteries and Blood Flow

Neck, Arm, and Lower Limb Arteries

Major arteries supply the head, neck, upper and lower limbs.

• Neck: Common carotid artery splits into internal (brain) and external (face/scalp/neck) carotid arteries.

• Arm: Subclavian → axillary → brachial → radial (thumb side) & ulnar (pinky side) arteries.

• Lower Limb: Femoral → popliteal (behind knee) → anterior tibial (front, dorsalis pedis) & posterior tibial (back, sole of foot) arteries.

Regulation of Blood Pressure

Autonomic Nervous System 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

Specialized receptors monitor blood pressure and blood chemistry to regulate cardiovascular and respiratory responses.

• Baroreceptors: Detect vessel stretch, found in carotid sinus and aortic arch, help maintain stable BP by adjusting heart rate and vessel diameter.

• Chemoreceptors: Monitor O2, CO2, and pH, found in carotid and aortic bodies, regulate respiration and circulation.

Receptor	Location	Function
Baroreceptor	Carotid sinus, aortic arch	Detect BP changes, regulate HR & vessel diameter
Chemoreceptor	Carotid bodies, aortic bodies	Detect O2, CO2, pH; regulate respiration & circulation

Summary Table: Circulation Pathways

Pathway	Start	End	Main Function
Pulmonary	Right ventricle	Left atrium	Oxygenate blood
Systemic	Left ventricle	Right atrium	Deliver O2 & nutrients

Key Equations

• Cardiac Output: $CO = HR \times SV$

• Blood Pressure: $BP = CO \times PR$ (where PR = peripheral resistance)

• Mean Arterial Pressure: $MAP = \frac{1}{3} (SP - DP) + DP$ (SP = systolic, DP = diastolic pressure)

Additional info:

• Some memory tricks and mnemonics were expanded for clarity.

• Tables were recreated and summarized for comparison and classification.

• Equations were added for academic completeness.