Chapter 3: Body Fluids and Circulation

Introduction

Overview

• Living cells require nutrients, oxygen, and waste removal for healthy function.
• Complex organisms use body fluids for transport of substances.
• Blood is the primary transport fluid in higher organisms including humans.
• Lymph also aids in transport of certain substances.

Memory Aids

• Blood = main transport fluid in humans.
• Lymph = secondary transport fluid.

Quick Checkpoints

• What are the main transport fluids in humans?
• Why is a transport system essential?

Blood

Composition and Properties

• Blood is a mobile connective tissue with plasma (fluid matrix) and formed elements.
• Adult human blood volume: 5-5.5 litres, 30-35% of extracellular fluid.
• Blood is slightly alkaline with pH 7.4.

Memory Aids

• Blood volume ~5 litres in adults.
• pH ~7.4 (alkaline).

Quick Checkpoints

• What is the pH of blood?
• What percentage of extracellular fluid does blood constitute?

Plasma

Composition and Functions

• Plasma is a pale yellow, viscous, non-living intercellular fluid making up 55% of blood.
• 90-92% water; 6-8% plasma proteins including albumin, globulin, immunoglobulin, prothrombin, fibrinogen.
• Fibrinogen aids blood clotting; globulins aid defense; albumins maintain osmotic balance.
• Contains minerals (Na⁺, Ca²⁺, Mg²⁺, HCO₃^-, Cl^-), glucose, amino acids, lipids in transit.
• Clotting factors are inactive in plasma; plasma without clotting factors is called serum.

Memory Aids

• Plasma = 55% blood, mostly water.
• Serum = plasma minus clotting factors.

Quick Checkpoints

• What is plasma made of?
• What is serum?

Formed Elements (Blood Corpuscles)

Types and Functions

• Formed elements: erythrocytes (RBCs), leucocytes (WBCs), platelets.
• They constitute about 45% of blood volume.
• 
• Erythrocytes carry oxygen; biconcave, enucleated, formed in red bone marrow.
• Haemoglobin gives red color; lifespan ~120 days; formation called erythropoiesis.
• Iron, proteins, vitamin B12, folic acid essential for RBC formation.
• Spleen destroys RBCs; called graveyard of RBCs.
• Polycythemia = high RBC count; erythrocytopenia = low RBC count causing oxygen shortage; anemia = low haemoglobin.
• People in hills have more RBCs to adapt to low oxygen.
• Leucocytes (WBCs) are nucleated, colorless, 6000-8000 per cubic mm, short-lived.
• Two types: granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes, monocytes).
• 
• Neutrophils most numerous; monocytes largest.
• Leucocyte formation called leucopoiesis; decrease called leukopenia; increase in leukemia.
• Platelets (thrombocytes) are cell fragments from megakaryocytes; 1.5-3.5 lakh per cubic mm.
• Platelets aid blood clotting; lifespan ~1 week; low count causes clotting disorders.

Memory Aids

• RBCs = oxygen carriers, biconcave, no nucleus.
• WBCs = immune defense, nucleated.
• Platelets = clotting, cell fragments.

Quick Checkpoints

• What are the three formed elements of blood?
• Where are RBCs formed?
• What causes anemia?
• Types of leucocytes?
• Role of platelets?

Blood Groups

ABO Blood Grouping

• Discovered by Karl Landsteiner (1900); AB group by Dacastello and Sturli (1902).
• Controlled by gene I with alleles Iᴬ, Iᴮ, Iᴼ.
• Iᴬ and Iᴮ produce A and B antigens on RBC surface; antibodies present in plasma.
• Donor and recipient blood groups must match to avoid RBC clumping.
• 
• Group O = universal donor; Group AB = universal recipient.

Rh Grouping

• Rh antigen discovered by Landsteiner and Wiener (1940) in Rhesus monkey.
• Present in ~80% humans; Rh+ve have antigen, Rh-ve lack it.
• Rh-ve exposed to Rh+ve blood form antibodies; matching needed before transfusion.
• Rh incompatibility in pregnancy causes erythroblastosis fetalis (fetal RBC destruction, anemia, jaundice).
• Prevented by anti-Rh antibodies given to mother after first delivery.

Memory Aids

• ABO: A and B antigens; O no antigen.
• Rh+: antigen present; Rh-: antigen absent.
• O = universal donor; AB = universal recipient.

Quick Checkpoints

• What alleles control ABO blood groups?
• Who is universal donor and recipient?
• What causes erythroblastosis fetalis?

Coagulation of Blood

Process and Importance

• Blood clotting stops bleeding after injury to blood vessels.
• Clot is a fibrin network trapping blood cells, forming a seal.
• 
• Steps: injury releases thromboplastin; platelets release platelet factor 3.
• Thromboplastin + platelet factor 3 + Ca²⁺ form prothrombinase.
• Prothrombinase converts prothrombin to thrombin.
• Thrombin converts fibrinogen to fibrin, forming clot.
• Clotting time: 3-8 minutes.
• Vitamin K needed for prothrombin synthesis.
• Anticoagulants (heparin, oxalates) prevent clotting.

Memory Aids

• Clotting = thromboplastin → prothrombinase → thrombin → fibrin.
• Vitamin K essential for clotting.
• Heparin = anticoagulant.

Quick Checkpoints

• What triggers blood clotting?
• Role of thrombin?
• Why is vitamin K important?

Lymph (Tissue Fluid)

Composition and Characteristics

• Mobile connective tissue with lymph plasma and lymph corpuscles.
• Lymph plasma: Similar to blood plasma but with fewer proteins, less calcium and phosphorus, and higher glucose.
• Collected and drained by the lymphatic system into major veins.

Cellular Components and Functions

• Lymph corpuscles: Amoeboid leucocytes, mainly lymphocytes; no erythrocytes or platelets.
• Transports nutrients, hormones, and fats (absorbed via lacteals in intestinal villi).
• Acts as a transporter between body cells and blood, carrying wastes like carbon dioxide to blood.
• Destroys microorganisms and foreign particles in lymph nodes.

Memory Aids

• Lymph = Plasma + Corpuscles (mostly lymphocytes).
• Fats absorbed via lacteals → transported by lymph.
• Lymphatic system drains fluid back to veins.

Quick Checkpoints

• What are the main components of lymph?
• How does lymph plasma differ from blood plasma?
• Which cells are present and absent in lymph?
• What is the role of lymph in fat absorption?
• How does lymph contribute to immune defense?

Circular Pathways

Types of Circulatory Systems

• Open system: Blood leaves vessels, fills sinuses; found in arthropods, mollusks.
• Closed system: Blood stays in vessels, circulates continuously; found in annelids, chordates.
• Closed system allows precise regulation of fluid flow.
• Evolution of vertebrate hearts:
  • 2-chambered: 1 atrium, 1 ventricle; single circulation in fishes; pumps deoxygenated blood to gills.
  • 3-chambered: 2 atria, 1 ventricle; incomplete double circulation in amphibians, reptiles; mixed blood pumped.
  • 4-chambered: 2 atria, 2 ventricles; double circulation in crocodiles, birds, mammals; no blood mixing.

Memory Aids

• Open = blood leaves vessels; Closed = blood stays in vessels.
• 2-chambered = fish, single loop; 3-chambered = amphibians/reptiles, mixed blood; 4-chambered = birds/mammals, separate loops.

Quick Checkpoints

• What distinguishes open from closed circulatory systems?
• How does blood flow differ in 2, 3, and 4-chambered hearts?
• Why is closed circulation more efficient?

Human Circulatory System

Components and Heart Structure

• Also called blood vascular system: muscular heart, closed vessels (arteries, veins), blood.
• Heart: four-chambered, mesodermal, in thoracic cavity, left tilted, fist-sized.
• Enclosed in pericardium with pericardial cavity and fluid.
• Right and left atria separated by interatrial septum; ventricles by interventricular septum.
• Right atrium receives deoxygenated blood via superior and inferior vena cava.
• Left atrium receives oxygenated blood from lungs via pulmonary veins.
• Left ventricle thicker to pump blood at higher pressure.
• Atrioventricular septum separates atrium and ventricle on same side with valves:
  • Bicuspid (mitral) valve on left side.
  • Tricuspid valve on right side.
• Chordae tendineae connect valve flaps to papillary muscles.
• Semilunar valves at pulmonary artery and aorta openings prevent backflow.
• Heart muscle includes nodal tissue: sino-atrial node (SAN) as pacemaker, atrioventricular node (AVN) as pacesetter.
• AV bundle (bundle of His) and Purkinje fibers conduct impulses for rhythmic contraction.
• Heartbeat types:
  • Neurogenic: nerve impulse initiated (annelids, arthropods).
  • Myogenic: muscle initiated (molluscs, vertebrates including humans).

Memory Aids

• SAN = pacemaker; AVN = pacesetter.
• Left ventricle thicker = higher pressure pump.
• Bicuspid = 2 cusps; Tricuspid = 3 cusps.

Quick Checkpoints

• What separates atria and ventricles?
• Which valves prevent backflow into atria?
• What is the role of nodal tissue?
• Difference between neurogenic and myogenic heartbeat?

Cardiac Cycle

Stages and Events

• Cardiac cycle = systole (contraction) + diastole (relaxation) of atria and ventricles.
• Stages:
  • Joint diastole: all chambers relaxed, AV valves open, semilunar valves closed, ventricles fill.
  • Atrial systole: atria contract, increase ventricular filling by 30%.
  • Ventricular systole: ventricles contract, AV valves close (first heart sound 'lub'), semilunar valves closed initially.
  • Ventricular diastole: semilunar valves open, blood ejected, ventricles relax, semilunar valves close (second heart sound 'dub').
  • Complete ventricular diastole: ventricles relax, AV valves open, cycle repeats.
• Cardiac output = heart rate × stroke volume (~5.5 L/min in humans).
• Duration of cardiac cycle = 0.8 seconds.
• Heart sounds: 'lub' (0.15 s, 25-45 Hz), 'dub' (0.12 s, 50 Hz).

Memory Aids

• Lub = AV valves closing; Dub = semilunar valves closing.
• Atrial systole = 0.1 s; Ventricular systole = 0.3 s; Joint diastole = 0.4 s.
• Cardiac output depends on heart rate and stroke volume.

Quick Checkpoints

• What happens during atrial systole?
• Which valves produce the first and second heart sounds?
• How is cardiac output calculated?
• Duration of one cardiac cycle?

Electrocardiogram (ECG)

Basics and Components

• ECG records electrical activity of cardiac muscles using electrocardiograph.
• Standard ECG uses three leads: two wrists, one left ankle.
• Normal ECG waves:
  • P wave: atrial depolarisation (contraction), caused by SA node.
  • QRS complex: ventricular depolarisation (contraction), starts with Q (down), R (up), S (down).
  • T wave: ventricular repolarisation (relaxation), dome-shaped.
• End of T wave marks end of systole.
• Heart rate can be determined by counting QRS complexes per time.
• Abnormal ECG shapes indicate heart diseases.

Memory Aids

• P wave = atrial contraction.
• QRS complex = ventricular contraction.
• T wave = ventricular relaxation.

Quick Checkpoints

• What does the P wave represent?
• Which wave indicates ventricular contraction?
• How is heart rate measured from ECG?
• What does an abnormal ECG indicate?

Double Circulation

Blood Vessels

• Three types: arteries, veins, capillaries.
• Arteries: Elastic vessels carrying oxygenated blood from heart to tissues; pulmonary artery carries deoxygenated blood.
• Veins: Carry deoxygenated blood to heart; pulmonary vein carries oxygenated blood from lungs to left atrium; veins have valves to prevent backflow.
• Capillaries: Connect arteries and veins in tissues.
• Walls of arteries and veins have three layers:
  • Tunica intima: Innermost, squamous endothelium + elastic membrane.
  • Tunica media: Middle, smooth muscle + elastic fibers; thinner in veins.
  • Tunica externa: Outer fibrous connective tissue with collagen.

Double Circulation Pathways

• Blood passes twice through heart in separate routes per cycle.
• Consists of pulmonary circulation and systemic circulation.

Pulmonary Circulation

• Deoxygenated blood pumped from right ventricle to lungs via pulmonary trunk and arteries.
• Blood gets oxygenated in lungs.
• Oxygenated blood returns to left atrium via pulmonary veins.

Systemic Circulation

• Oxygenated blood pumped from left ventricle to body through arteries, arterioles, capillaries.
• Deoxygenated blood collected by venules, veins, vena cava, returns to right atrium.
• Delivers O₂, nutrients; removes CO₂, wastes.

Special Circulations

• Hepatic portal system: Connects digestive tract to liver.
• Coronary circulation: Supplies blood to cardiac muscle.

Memory Aids

• Arteries away, veins to heart (except pulmonary vessels).
• Pulmonary artery = deoxygenated; pulmonary vein = oxygenated.
• Double circulation = two heart passes per blood cycle.
• Hepatic portal = digestive tract to liver.
• Coronary = heart muscle blood supply.

Quick Checkpoints

• What are the three types of blood vessels and their functions?
• Which artery carries deoxygenated blood?
• Describe the layers of artery and vein walls.
• Explain pulmonary circulation steps.
• Explain systemic circulation steps.
• What is the hepatic portal system?
• What is coronary circulation?

Regulation of Cardiac Activity

Autoregulation by Nodal Tissue

• Heart's normal activity controlled by specialized muscles called nodal tissue.
• Heart is myogenic: it generates its own impulses without external stimuli.
• Medulla oblongata contains a neural center that modulates heart function via the autonomic nervous system (ANS).

Neural and Hormonal Control

• Sympathetic nerves (ANS) increase heart rate, ventricular contraction strength, and cardiac output.
• Parasympathetic nerves (ANS) decrease heart rate, slow action potential conduction, and reduce cardiac output.
• Adrenal medullary hormones also enhance cardiac output.

Memory Aids

• Myogenic = Heart beats by itself.
• Sympathetic = Speed up heart.
• Parasympathetic = Slow down heart.
• Medulla oblongata = Cardiac control center.

Quick Checkpoints

• What does myogenic mean in cardiac activity?
• How does the sympathetic nervous system affect the heart?
• Role of parasympathetic nerves in heart regulation?
• Which hormones increase cardiac output?

Disorders of Circulatory System

Hypertension and Blood Pressure

• Hypertension is high blood pressure above 140/90 mmHg, harming heart, brain, kidneys, and eyes.
• Blood pressure is the force exerted by blood on artery walls.
• Systolic pressure (120 mmHg) is pressure when left ventricle contracts.
• Diastolic pressure (80 mmHg) is pressure when heart rests during diastole.
• Blood pressure is expressed as BP = 120/80 mmHg.
• Difference between systolic and diastolic pressure is pulse pressure.
• Measured using a sphygmomanometer.

Memory Aids

• Normal BP: 120/80 (Systolic/Diastolic)
• Hypertension if BP > 140/90
• Pulse pressure = Systolic - Diastolic

Quick Checkpoints

• What defines hypertension?
• Difference between systolic and diastolic pressure?
• Device used to measure blood pressure?

Atherosclerosis and Coronary Artery Disease

Causes and Effects

• Atherosclerosis/CAD is lipid, fat, calcium, and fibrous tissue buildup forming atheromatous plaques in arteries.
• Plaques can block arteries, reducing blood supply to heart muscle, causing heart attack or stroke.
• Arteriosclerosis is hardening and thickening of arteries due to calcium and cholesterol deposits.
• Hardened arteries lose elasticity and may rupture, leading to heart attack or death.

Memory Aids

• Atherosclerosis = Plaque buildup in arteries
• Arteriosclerosis = Artery hardening
• CAD affects coronary arteries causing heart issues

Quick Checkpoints

• What forms atheromatous plaques?
• Difference between atherosclerosis and arteriosclerosis?
• Consequences of artery blockage?

Angina

Definition and Symptoms

• Angina pectoris is acute chest pain due to insufficient oxygen to heart muscle.
• Affects all ages, more common in middle-aged and elderly.
• Caused by reduced blood flow to heart.

Memory Aids

• Angina = Chest pain from low oxygen
• Occurs due to blood flow issues

Quick Checkpoints

• What causes angina?
• Who is commonly affected?

Heart Failure

Definition and Symptoms

• Heart failure or congestive heart failure is when heart pumps blood ineffectively.
• Leads to lung congestion as a main symptom.

Memory Aids

• Heart failure = weak heart pump
• Causes lung congestion

Quick Checkpoints

• What is congestive heart failure?
• Main symptom of heart failure?

Cardiac Arrest

Definition

• Cardiac arrest is the complete stop of heart beating.

Memory Aids

• Cardiac arrest = Heart stops beating

Quick Checkpoints

• What happens in cardiac arrest?

Heart Attack

Definition

• Heart attack occurs when heart muscle is damaged due to inadequate blood supply.

Memory Aids

• Heart attack = Sudden heart muscle damage

Quick Checkpoints

• Cause of heart attack?

Human Heart Structure

Key Features

• Four chambers: left atrium, left ventricle, right atrium, right ventricle.
• Blood enters via superior and inferior vena cava.
• Right atrium receives oxygen-poor blood, sends to right ventricle.
• Right ventricle pumps blood to lungs via pulmonary artery.
• Oxygen-rich blood returns to left atrium via pulmonary veins.
• Left ventricle pumps blood to body through aorta.
• Heart supplied by coronary arteries and veins on surface.
• Smaller vessels circulate blood within heart muscle.
• Apex is the pointed end directed downwards.

Memory Aids

• Right side: deoxygenated blood; Left side: oxygenated blood
• Coronary arteries supply heart muscle
• Apex points downwards

Quick Checkpoints

• Name the four chambers of the heart.
• Path of oxygen-poor blood through the heart?
• Function of coronary arteries?