Cardiovascular System Notes

Venous Return

  • Venous return is the flow of blood back to the heart, specifically into the right atrium, from the veins.
  • Veins operate under low pressure, so the body uses several mechanisms to assist in this return.
  • Mechanisms:
    • Skeletal Muscle Pump: When contracting, skeletal muscles squeeze nearby veins, pushing blood forward. Valves in the veins prevent backflow. Found in limbs, especially in the legs.
    • Respiratory Pump: During inhalation, pressure in the chest decreases, while abdominal pressure increases. This draws blood from abdominal veins into the thoracic veins and toward the heart.
    • Venous Valves: One-way valves inside medium and large veins prevent blood from flowing backward, especially when upright. Important for counteracting gravity in the legs.
    • Cardiac Suction: During ventricular diastole, the atria expand, slightly lowering the pressure and "sucking" blood in from the veins.
    • Sympathetic Nervous System: Constricts smooth muscles in the vein walls, reducing their diameter and pushing more blood toward the heart. Happens during exercise or stress.

Capillaries

  • Continuous Capillaries: The most common type, found in skin, muscles, and the central nervous system. They have tight junctions, making them the least permeable type of capillary.
  • Fenestrated Capillaries: Found in the kidneys, small intestine, and endocrine glands. They have pores that allow for filtration and absorption.
  • Sinusoidal Capillaries: Found in the liver, spleen, and bone marrow. They have large gaps that allow the passage of large molecules and cells.

Heart Structure and Function

  • Right Side of the Heart
    • Sends blood that needs oxygen to the lungs.
    • Doesn’t need to push very hard, so its walls are thinner.
    • Includes:
      • Right atrium (receives blood from the body).
      • Right ventricle (pumps blood to the lungs).
      • Tricuspid valve (keeps blood moving the right way).
  • Left Side of the Heart
    • Sends oxygen-rich blood to the rest of the body.
    • Has to push much harder, so its walls, especially the left ventricle, are thicker.
    • Includes:
      • Left atrium (receives blood from the lungs).
      • Left ventricle (pumps blood to the body).
      • Bicuspid (mitral) valve.
  • Each side of the heart is built to do its job; the right side sends blood a short distance to the lungs, while the left side is strong enough to send blood all around the body.

Functions of Blood

  • Transports essential substances such as gases, nutrients, and hormones throughout the body.
  • Regulates various physiological processes, including maintaining a stable body temperature, pH, and fluid volume.
  • Acts as a protective mechanism, supporting the immune response and facilitating blood clotting.

Red Blood Cells (Erythrocytes)

  • Specialized blood cells that lack a nucleus.
  • Packed with hemoglobin, a protein molecule that contains iron.
  • Hemoglobin’s primary function is to bind to oxygen, enabling red blood cells to transport oxygen throughout the body.
  • Lifespan is approximately 120 days, after which they are destroyed in the spleen.
  • The liver processes the breakdown products of red blood cells, such as bilirubin.
  • Produced in the bone marrow through a process called erythropoiesis.

White Blood Cells (Leukocytes)

  • Crucial component of the immune system, responsible for defending against pathogens.
  • Types:
    • Neutrophils: First responders to infections, destroying bacteria and fungi through phagocytosis. Lifespan: 6–8 hours in blood, 1–2 days in tissues.
    • Lymphocytes: Including T cells, B cells, and Natural Killer (NK) cells. Defend against viruses, bacteria, and other invaders. Lifespan varies widely, from a few weeks to years/decades (memory lymphocytes).
    • Monocytes: Become macrophages in tissues and digest pathogens and dead cells. Lifespan: 1–3 days in blood, months as macrophages.
    • Eosinophils: Fight parasites and play a role in allergic reactions. Lifespan: 8–12 hours in blood, up to 1 week in tissues.
    • Basophils: Release histamine during allergic reactions and are involved in inflammation. Lifespan: a few hours to a few days.

Thick Blood

  • Difficult for it to circulate effectively throughout the body.
  • The heart has to exert additional effort to pump thick blood, which can lead to fatigue or health complications.
  • Can form clumps called clots, which can block blood flow and cause severe consequences such as strokes or heart attacks.
  • Poor circulation prevents adequate oxygen delivery, resulting in feelings of tiredness, dizziness, or blurred vision.

Blood Proteins

  • Albumin: Maintains the right balance of water in the bloodstream. Its absence leads to water leakage and swelling.
  • Globulins: Act as the body’s immune system, fighting infections and transporting essential substances like vitamins and hormones.
  • Fibrinogen: Plays a crucial role in blood clotting, preventing excessive bleeding from minor injuries.
  • The primary site of protein production in the body is the liver.

Plasma Osmolarity

  • A way of measuring how concentrated a solution is.
  • Tells us how many particles (like salts, sugars, or proteins) are dissolved in a certain amount of liquid.

Blood Clotting Process

  1. When you cut yourself, blood starts leaking out.
  2. Platelets rush to the cut. These are tiny cells in your blood that stick to the cut and clump together to plug the hole.
  3. Platelets send out chemical signals that start a chain reaction in your blood, calling for backup.
  4. A special protein called fibrin forms a net. This net is made of long sticky strands that weave through the platelet plug, making the plug strong.
  5. The clot hardens, stopping the bleeding and giving your skin time to heal underneath.
  6. Once healing is done, the clot goes away. Your body breaks down the clot once it’s no longer needed.
  • Mnemonic: Prothrombin converts to thrombin, which then converts to fibrinogen. Fibrinogen forms fibrin, insoluble threads that form a stable clot to stop bleeding.

Hormones and Anemia

  • Erythropoietin (EPO): A kidney hormone that triggers the production of red blood cells (RBCs).
  • Thrombopoietin: A hormone that stimulates the production of platelets from megakaryocytes.
  • Pernicious Anemia: Caused by a deficiency of vitamin B12.
  • Hemorrhagic Anemia: Caused by blood loss.
  • Sickle Cell Anemia: A genetic disorder in which the hemoglobin molecule in red blood cells becomes abnormal and forms sickle-shaped cells.

Blood Typing

  • Determining your blood type, which is one of four main types: A, B, AB, and O.
  • Types are determined by the presence of specific markers (antigens) on your red blood cells.
    • Type A: Has A antigens on red blood cells and B antibodies in the plasma.
    • Type B: Has B antigens and A antibodies.
    • Type AB: Has both A and B antigens but lacks antibodies (making it a universal recipient).
    • Type O: Has no antigens but possesses both A and B antibodies (making it a universal donor).
  • The Rh factor is a second component of your blood type.
    • If you have the Rh factor, you’re Rh-positive (e.g., A+).
    • If you don’t have it, you’re Rh-negative (e.g., A-).
  • For instance, if your blood type is B+, it indicates the presence of B antigens, the Rh factor, and A antibodies in your plasma.

Miscellaneous Terms

  • Megakaryocyte: Bone marrow cell that produces platelets.
  • Pulmonary Embolism: Clot in the lung vessels.
  • Heart Murmur: Abnormal heart sound due to valve issues.
  • Pericarditis: Inflammation of the heart’s outer lining.
  • Hemolytic Disease of the Newborn: Rh– mother + Rh+ baby = immune response in 2nd pregnancy. RhoGAM prevents antibody formation.

Cardiac Muscle Characteristics

  • Location: Only in the heart.
  • Control: Involuntary (automatic).
  • Appearance: Striated (light and dark stripes).
  • Cell Shape: Branched (Y-shaped) cells that connect like a web.
  • Nuclei: One nucleus per cell.
  • Intercalated Discs: Special connections between cells that:
    • Help the heart cells stick together.
    • Allow signals to pass quickly so the heart beats smoothly.
  • Fatigue: Never gets tired; it keeps working your whole life without stopping!

Gap Junctions

  • Connect heart cells like small bridges.
  • Let messages (electric signals) pass quickly from one heart cell to another.
  • Help the heart beat in a smooth rhythm.
  • Part of the intercalated discs, which hold heart cells together.

Heart Function and Oxygen Supply

  • The heart works continuously (24/7) and requires a substantial amount of oxygen.
  • The heart obtains oxygen from its coronary arteries, not from the blood within its chambers.
  • Heart Attack: Occurs when blood flow to the heart muscle is obstructed, leading to damage.
  • Blockage = coronary thrombosis → myocardial infarction (heart attack).

Pericardial Membranes

  • Like a double-layered water balloon around the heart.
  • Protect, anchor, and lubricate the heart so it can beat smoothly without rubbing too much against other organs.
  • Pericarditis occurs when the pericardium becomes swollen or inflamed.

Heart Wall Layers

  • Epicardium: Outer layer; provides protection and reduces friction.
  • Myocardium: Middle, thickest layer; responsible for contraction and pumping blood.
  • Endocardium: Inner layer; provides smooth blood flow and prevents clots.

Pulmonary and Systemic Circuits

  • Pulmonary Circuit
    • The right ventricle pumps blood to the lungs, where gas exchange occurs in the alveoli.
    • The left atrium receives the oxygenated blood.
  • Systemic Circuit
    • The left ventricle pumps blood to the body, where oxygen is delivered to tissues and organs.
    • The right atrium collects the deoxygenated blood.

Cardiac Conduction System

  • SA Node (Sinoatrial Node): The “Pacemaker,” located in the right atrium, initiates the electrical signal. It instructs the atria to contract and pump blood into the ventricles.
  • AV Node (Atrioventricular Node): The “Gatekeeper,” situated between the atria and ventricles. It introduces a slight delay in the signal, allowing the ventricles to fill before passing it on.
  • Bundle of His: Transmits the signal from the AV node down the septum, preparing the ventricles for contraction.
  • Purkinje Fibers: Spread the signal throughout the walls of the ventricles, causing them to contract and pump blood to the lungs and the rest of the body.

Cardiac Output

  • CO=HeartRate×StrokeVolumeCO = Heart Rate \times Stroke Volume
  • If the heart rate is too fast, stroke volume decreases → reduced output.

Heart Rhythms

  • Pacemaker: Device or natural SA node that controls rhythm.

ECG Waves

  • P wave: Represents atrial depolarization.
  • QRS complex: Signifies ventricular depolarization.
  • T wave: Indicates ventricular repolarization.

Blood Vessel Types

  • Elastic Arteries: Stretch during systole and recoil during diastole.
  • Muscular Arteries: Distribute blood to organs.
  • Arterioles: Major regulators of blood pressure, controlling the flow of blood into capillaries.
  • Capillaries: Exchange vessels.
  • Veins: Return blood to the heart and contain valves.

Blood Pressure Regulation

  • Baroreceptors: Detect pressure changes and send signals to the medulla oblongata to maintain blood pressure.
  • Resistance: Primarily occurs in arterioles and capillaries.

Artery Wall Structure

  • Tunica Intima: The innermost layer, lined with endothelium.
  • Tunica Media: The middle layer, composed of smooth muscle that controls vasoconstriction and dilation.
  • Tunica Externa: The outermost layer, made of connective tissue, providing protection and support.

Blood Pressure Measurements

  • Systolic: Pressure after ventricular contraction.
  • Diastolic: Pressure between heartbeats.

Chemoreceptors and Blood pH

  • Specialized sensors in your neck and brain that detect changes in blood pH.
  • When blood pH becomes too acidic (low pH), these sensors signal your body to increase breathing rate, which helps eliminate excess carbon dioxide.
  • This process helps restore blood pH to its normal range.