Comprehensive Notes on Body Fluids and Circulation

Body Fluids and Circulation

Introduction

• Function of Body Fluids: Transport nutrients, gases, and wastes.
• Types:
  • Blood
  • Lymph

Blood

• Nature: Specialized connective tissue.
• Components:
  • Plasma (Fluid)
  • Formed Elements (Cells)

Plasma

• Composition:
  • Water: 90-92%
  • Proteins:
    • Fibrinogen: For clotting.
    • Albumins: For osmotic balance.
    • Globulins: Defense.
  • Minerals: $Na^+, Ca^{2+}, Mg^{2+}, HCO_3^-, Cl^-$
  • Nutrients: Glucose, amino acids, lipids

Formed Elements (45%)

• Types:
  • Red Blood Cells (RBCs) / Erythrocytes
  • White Blood Cells (WBCs) / Leucocytes
  • Platelets / Thrombocytes

Red Blood Cells (RBCs) / Erythrocytes

• Count: 5-5.5 million/$mm^3$
• Lifespan: 120 days
• Characteristics:
  • Biconcave
  • Enucleated
• Function: Transport of gases
• Grave yard: Spleen

White Blood Cells (WBCs) / Leucocytes

• Count: 6000-8000/$mm^3$
• Lifespan: Generally short-lived
• Types:
  • Granulocytes:
    • Neutrophils: 60-65%, phagocytic.
    • Eosinophils: 2-3%, resist infections, associated with allergic reactions.
    • Basophils: 0.5-1%, involved in inflammatory reactions.
  • Agranulocytes:
    • Lymphocytes: 20-25%, immune response.
    • Monocytes: 6-8%, phagocytic.

Platelets / Thrombocytes

• Count: 150,000-350,000/$mm^3$
• Lifespan: Short-lived
• Origin: Cell fragments of megakaryocytes
• Function: Coagulation of blood; if the number drops, it can lead to loss of blood from the body.

Blood Groups

ABO Blood Grouping

• Based on: Presence or absence of A and B antigens on RBCs.
• Blood Types and Antibodies:
  • A: Anti-B antibodies.
  • B: Anti-A antibodies.
  • AB: No antibodies; universal recipient.
  • O: Anti-A and Anti-B antibodies; universal donor.

Rh Grouping

• Rh Factor: Present (Rh +ve) or absent (Rh -ve) on RBCs identified in Rhesus monkeys.
• Prevalence: 80% of humans have Rh antigen.

Special Case: Rh Incompatibility

• Scenario: Rh-ve mother and Rh+ve foetus.
• First Pregnancy: Baby normal due to placental separation.
• During Delivery: Mixing of blood can occur.
• Subsequent Pregnancy:
  • Rh-ve mother develops antibodies against Rh antigen.
  • Antibodies cross the placenta.
  • Causes severe anemia and jaundice in baby (Erythroblastosis foetalis).
• Prevention: Administer anti-Rh antibodies to the mother immediately after the first delivery.

Coagulation of Blood

• Process:
  • Injury or removal of blood from vessels.
  • Cascade of events involving clotting factors.
  • $Ca^{2+}$ is essential.
• Steps:
  • Prothrombin $xrightarrow{Thrombokinase + Ca^{2+}}$ Thrombin
  • Fibrinogen $xrightarrow{Thrombin}$ Fibrin threads
  • Blood cells + Fibrin threads = Clot

Lymph (Tissue Fluid)

• Formation:
  • As blood passes through capillaries, water and small soluble substances move into spaces between tissue cells.
  • Larger proteins and formed elements remain in blood vessels.
  • Fluid released out is called interstitial fluid or tissue fluid.
• Lymphatic System: An elaborate network of vessels collects this fluid and drains it back to major veins.
• Lymph: Fluid present in the lymphatic system.
• Function:
  • Contains specialized lymphocytes for immune responses.
  • Carrier for nutrients and hormones.
  • Fats are absorbed through lymph in lacteals present in intestinal villi.

Circulatory Pathways

• Open Circulatory System: Blood flows in open spaces called sinuses without vessels (e.g., arthropods and molluscs).
• Closed Circulatory System: Blood flows in vessels (e.g., annelids and chordates).

Circulation Based on Vertebrate Groups

• Fishes:
  • Heart: 1 auricle, 1 ventricle
  • Circulation: Single
• Amphibians and Reptiles:
  • Heart: 2 auricles, 1 ventricle (incomplete separation)
  • Circulation: Incomplete double
• Crocodiles, Birds, and Mammals:
  • Heart: 2 auricles, 2 ventricles
  • Circulation: Double

Single-Loop Circulatory System

• Example: Fishes
• Pathway: Heart → Gills capillaries → Body capillaries → Heart

Double Circulation

• Pulmonary Circulation:
  • Deoxygenated blood goes from the right ventricle to the lungs for oxygenation and returns to the left atrium.
• Systemic Circulation:
  • Oxygenated blood goes from the left ventricle to the body tissues and returns deoxygenated to the right auricle.

Human Circulatory System

Components

• Heart
• Blood vessels
• Blood

Heart

• Origin: Mesodermally derived.
• Location: Between the lungs in the thoracic cavity, tilted to the left.
• Protection: Double-walled membranous bag – Pericardium with pericardial fluid.
• Chambers: Four chambers – two auricles (atria) and two ventricles.
  • Inter-atrial septum: Separates the atria (thin, muscular).
  • Inter-ventricular septum: Separates the ventricles (thick-walled muscular).
  • Atrio-ventricular septum: Separates auricles and ventricles (thick fibrous).
• Valves:
  • Atrio-ventricular valves:
    • Tricuspid valve: Between right auricle and right ventricle (3 cusps).
    • Bicuspid/Mitral valve: Between left auricle and left ventricle (2 cusps).
  • Semilunar valves:
    • At the base of the pulmonary artery.
    • At the base of the aorta.

Cardiac Muscle

• Specialized Muscle Tissue: Contractile.
• Nodal Tissue: Auto-excitable.
  • Sino-atrial node (SAN/pacemaker): Right upper corner of the right atrium. Initiates and maintains the rhythmic contractile activity of the heart.
  • Atrioventricular node (AV node): Left lower corner of the right atrium.
  • AV bundle/Bundle of His: Passes the impulse from the AV node to the ventricles, divides into right and left bundles.
  • Purkinje fibers: Divides at apex of ventricle, spread throughout ventricular musculature.

Blood Vessels

• Arteries:
  • Thick walls, carry blood away from the heart, oxygenated blood (except pulmonary artery).
• Veins:
  • Thin walls, carry blood towards the heart, deoxygenated blood (except pulmonary vein), have valves to prevent backflow.
• Capillaries:
  • Smallest vessels, thin walls (one-cell thick), facilitate exchange of materials between blood and tissues.

Types of Circulation

• Pulmonary Circulation: Deoxygenated blood from the right ventricle goes to the lungs (via the pulmonary artery), gets oxygenated, and returns to the left atrium (via the pulmonary vein).
• Systemic Circulation: Oxygenated blood from the left ventricle goes to the body tissues (via the aorta), delivers oxygen, and returns deoxygenated to the right auricle (via the vena cava).
• Hepatic Portal Circulation: Blood from the digestive tract goes to the liver before returning to the heart.
• Coronary Circulation: Blood flow to and from the cardiac musculature.
  • Mostly deoxygenated blood transported by arteries, arterioles, capillaries to tissues. Returned by veins, venules, capillaries.

Cardiac Cycle

• Definition: The sequential event in the heart which is cyclically repeated.
• Duration: 0.8 seconds.
• Phases:
  • Atrial systole (0.1 sec): Atria contract.
  • Ventricular systole (0.3 sec): Ventricles contract.
  • Joint diastole (0.4 sec): Atria and ventricles are relaxed.

Events in Cardiac Cycle

• Atrial Systole:
  • Atria contract, increasing the flow of blood into ventricles by 30%.
• Ventricular Systole:
  • Ventricles contract, throwing out 70ml of blood/ventricle – Stroke volume.
• Valve Action:
  • Tricuspid and bicuspid valves:
    • Open during atrial systole.
    • Closed during ventricular systole (1st heart sound Lub).
  • Semilunar valves:
    • Closed during atrial systole.
    • Open during ventricular systole (2nd heart sound Dub).

Cardiac Output

• Definition: Volume of blood pumped out by each ventricle per minute.
• $CO = SV \, x \, HR$
  • SV = Stroke Volume ( volume of blood out of ventricles).
  • HR = Heart Rate (number of heart beats per minute).
• Typical Values:
  • SV = 70 ml/beat.
  • HR = 72 beats/minute.
  • CO = 70 ml/beat x 72 beats/minute = 5040 ml/minute ≈ 5L
• Factors Affecting Cardiac Output: The body's ability to alter SV or HR allows it to adjust cardiac output.

Heart Sounds

• Lub: Closure of tricuspid and bicuspid valves.
• Dub: Closure of semilunar valves.
• Clinical Significance: Sounds have clinical significance and can be heard using a stethoscope.

Electrocardiogram (ECG)

• Definition: Graphical representation of the electrical activities of the heart during a cardiac cycle.
• Procedure: 3 leads are connected to monitor heart activity (right wrist, left wrist, and left ankle).
• Interpretation:
  • The number of QRS complexes in a given time period determines the heart beat rate.
  • The end of the T-wave marks the end of systole.

ECG Waves

• P Wave: Depolarization of atria leading to contraction of atria.
• QRS Complex: Depolarization of ventricles leading to contraction of ventricles.
• T Wave: Repolarization of ventricles leading to relaxation of ventricles.

Regulation of Heart Activity

• Cardiac Centre: Medulla Oblongata modifies cardiac function through autonomic nerves.
  • Cardiac accelerator (sympathetic nerves): Increases heart rate, heart beat, ventricular contraction strength, and cardiac output.
  • Cardiac inhibitor (parasympathetic nerves): Decreases heart rate, heart beat, ventricular contraction strength, and cardiac output.

Disorders

• Cardiac Arrest: Heart stops beating.
• Heart Failure: Heart is not pumping blood effectively enough to meet the needs of the body; congestion is one of the main symptoms.
• Atherosclerosis/Coronary Artery Disease (CAD): Deposit of calcium, fats, and cholesterol in blood vessels that makes the arterial lumen narrower.
• High Blood Pressure/Hypertension:
  • Repeated checks of blood pressure of an individual ≥ 140/90 lead to heart diseases and also affect vital organs like the brain and kidneys.
  • Normal: 120/80 mm Hg.
• Angina Pectoris/Acute Chest Pain: Not enough oxygen reaching heart muscles due to conditions that affect the blood flow.
• Heart Attack: Heart muscle is suddenly damaged by an inadequate blood supply.