Cardiovascular System Overview

Cardiovascular System Overview

• The cardiovascular system comprises the heart and blood vessels.
• It's responsible for transporting blood throughout the body.

Parts of the Circulatory System

• Heart: A fist-sized muscular pump (250-300 grams).
  • Located in the mediastinum, between the lungs.
  • Rests on the superior surface of the diaphragm.
  • Two-thirds of the heart lies to the left of the midsternal line.
  • Anterior to the vertebral column, posterior to the sternum.
• Blood vessels:
  • Arteries: Distribute blood away from the heart.
  • Veins: Return blood to the heart.
  • Lymphatic vessels: Part of the lymphatic system; involved in fluid balance.

Heart: Pericardium

• Pericardium: A double-walled sac surrounding the heart.
  • Superficial fibrous pericardium: Outer layer of the sac.
  • Deep two-layer serous pericardium: Inner layer.
    • Parietal layer: lines the internal surface of the pericardium.
    • Visceral layer (epicardium): lines the surface of the heart.
  • The space between the layers is the pericardial cavity, filled with fluid.
• Functions: Protect, anchor, and prevent overfilling of the heart. Allows for friction-free movement during contractions.

Layers of Heart Wall

• Epicardium (visceral pericardium): Outermost layer.
• Myocardium: Thick middle layer of cardiac muscle.
• Endocardium: Innermost layer, a thin endothelial layer.

External Markings of the Heart

• Apex: Pointed inferior region.
• Base: Upper region.
• Coronary sulcus: Separates atria from ventricles.
• Anterior and posterior interventricular sulcus: Separates the right and left ventricles.

Heart Chambers

• The heart has four chambers:
  • Right atrium: Receives blood from the body.
  • Left atrium: Receives blood from the lungs.
  • Right ventricle: Pumps blood to the lungs.
  • Left ventricle: Pumps blood to the body.

Heart Valves

• Atrioventricular valves: Control blood flow between atria and ventricles.
  • Tricuspid valve: Between right atrium and right ventricle.
  • Mitral (bicuspid) valve: Between left atrium and left ventricle.
• Semilunar valves: Control blood flow out of the ventricles.
  • Pulmonary valve: Between right ventricle and pulmonary artery.
  • Aortic valve: Between left ventricle and aorta.

Conduction System of the Heart

• Specialized myocardial cells coordinate the heart's rhythmic contractions.
• Sinu-atrial (SA) node: Pacemaker of the heart.
• Atrioventricular (AV) node: Delays impulse transmission.
• Atrioventricular (AV) bundle: Conducts impulses to the ventricles.
• Bundle branches: Distribute impulses through the ventricles.
• Purkinje fibers: Rapidly spread the impulse through the ventricular walls.

Coronary Circulation

• Functional blood supply to the heart muscle itself.
• Coronary arteries: Branches off the ascending aorta.
• Coronary sinus (vein): Empties into the right atrium.

Blood Vessels

• Arteries: Distribute blood.
• Arterioles: Resistance vessels.
• Capillaries: Exchange vessels (microscopic tubes).
• Venules: Collect blood from capillaries.
• Veins: Conduct blood back to the heart.
• Anastomosis: Communication between neighboring vessels.

Histology of Blood Vessels

• Tunica intima: Innermost layer (endothelium).
• Tunica media: Middle layer (smooth muscle and elastic fibers).
• Tunica adventitia/externa: Outer layer (connective tissue).

Types of Arteries

• Large (elastic) arteries: Thick walls with elastic fibers for expansion.
• Medium (muscular) arteries: Distribute blood to various parts.
• Small arteries and arterioles: Control blood flow into capillaries.

Types of Veins

• Small to medium veins

  • Tunica intima: Thin, contains endothelium, subendothelial layer, may have valves.

  • Tunica media: Thin, contains smooth muscle, collagen, and some elastic fibers.

  • Tunica adventitia: Well-developed. -Large veins

  • Tunica intima: Thicker, prominent internal elastic lamina.

  • Tunica media: Thinner, sparse smooth muscle, and connective tissue abundant.

  • Tunica adventitia: Thick, contains longitudinal bundles of smooth muscle, spirally arranged collagen fibers and laminated elastic fibers.

Types of Capillaries

• Continuous: Uninterrupted endothelial layer, most organs.
• Fenestrated: Pores (fenestrations) in the endothelial layer, kidney/endocrine glands.
• Sinusoidal: Wider spaces between endothelial cells, spleen/liver/bone marrow.

Venules

• Postcapillary venules similar to capillaries, but more contractile cells.
• Become muscular venules with a thicker tunica media and larger lumen compared to the overall thinness of the wall.

Systemic Circulation

• Blood flow from the left ventricle, throughout the body, then returns to the right atrium.
• Keeps tissues alive by supplying continuous blood supply.

Pulmonary Circulation

• Blood flow from the right ventricle to the lungs and back to the left atrium.
• Oxygenates blood.

Portal Circulation

• Part of systemic circulation; Blood passes through two sets of capillaries before draining into a systemic vein.
• Example: Hepatic portal circulation.

Physiology of Cardiovascular System

Objectives: Understand properties of cardiac muscle, the heart's pacemaker mechanism, cardiac output, arterial blood pressure, and vascular system/capillary circulation.

The Heart: Cardiac Muscle

• The heart is more than a pump; it secretes hormones (oxytocin, atrial natriuretic factor), contains 40,000+ ganglia, has an electromagnetic field, and has a connection to the brain.
• Cardiac muscle characteristics:
  • Interconnected by gap junctions (syncytium) in the atria and ventricles. Physiologically, these act as a single unit.
  • Properties: Rhythmicity (automaticity), conductivity, excitability, and contractility.
  • The sino-atrial (SA) node acts as a pacemaker.

Myocardial Contractility

• Defined by the ability of the cardiac muscle to contract as a response to stimulus.
• +ve inotropy: Increases cardiac muscle contraction.
• -ve inotropy: Decreases cardiac muscle contraction.
• Frank-Starling Law: Within limits, myocardial contraction force is directly proportional to myocardial fiber length.

Factors Affecting Cardiac Rhythmicity

Heart Sounds and Murmurs

• Heart Sounds (Lup-Dup): Sounds caused by valve closure.
  • Lup: Atrioventricular valve closure.
  • Dup: Semilunar valve closure.
• Murmurs: Abnormal heart sounds.

Heart Rate

• Autorhythmicity: Heart's inherent ability to beat regularly.
• ANS Regulation: Sympathetic increases heart rate, parasympathetic slows it down.
• Normal Range: 60-90 beats per minute (average 75 bpm).
• Factors affecting Heart Rate: Age, sex, physical activity, and emotions.

Regulation of Heart Rate

Cardiac Output (COP)

• The volume of blood pumped by each ventricle per minute.
• It is controlled to maintain an adequate supply to tissues.
• COP = Stroke Volume × Heart Rate (factors that affect stroke volume: venous return, myocardial strength).

Arterial Blood Pressure (ABP)

• Definition: The pressure of blood against the arterial walls.
• Systolic BP: The pressure during ventricular contraction.
• Diastolic BP: The pressure during ventricular relaxation.
• Normal Range: 120/80 mmHg.
• Pulse pressure: Difference between systolic and diastolic.
• Factors affecting ABP: Blood volume, cardiac output, vessel elasticity, vasoconstriction, blood viscosity.

Regulation of Arteriolar Diameter

• Vasoconstriction (sympathetic): Reduces vascular capacity (increase ABP).
• Vasodilation (parasympathetic): Increases vascular capacity (decrease ABP).

Edema

• Definition: Abnormal fluid accumulation in the extracellular spaces.
• Causes: Increased capillary blood pressure, decreased colloid osmotic pressure, lymphatic obstruction.

Factors Maintaining Normal Arterial Blood Pressure

Explore the components and functions of the cardiovascular system, including the heart and blood vessels. This quiz covers the anatomy of the heart, the structure of blood vessels, and the role of the pericardium. Test your knowledge on this essential body system!