Body Fluids & Circulation – Cehensive Bullet-Pointes

Blood – General Overview

• Essential fluid connective tissue that transports nutrients, $\text{O}_2$, hormones, waste, and immune factors between every living cell and its environment.

• Two principal internal transport fluids in higher animals:

  • Blood – primary, present in all vertebrates and many invertebrates.

  • Lymph (tissue fluid) – auxiliary, drains interstitial spaces and participates in immunity & fat absorption.

Plasma (Fluid Matrix)

• Straw-coloured, viscous liquid ≈ 55 % of total blood volume.

• Water content: 90–92 % (solvent & temperature buffer).

• Proteins (6–8 %):

  • Fibrinogen – clotting precursor ➔ fibrin threads.

  • Globulins – immune defence (antibodies, complement, transport globulins).

  • Albumins – maintain osmotic/oncotic pressure; carrier of lipophilic molecules.

• Solutes/ions: $\text{Na}^+,\;\text{K}^+,\;\text{Ca}^{2+},\;\text{Mg}^{2+},\;\text{Cl}^-,\;\text{HCO}_3^-$ etc. – regulate pH, excitability, membrane potential.

• Nutrients in transit: glucose, amino acids, fatty acids, lipids, vitamins—link to digestive absorption and cellular respiration lectures.

• Waste metabolites: urea, uric acid, bilirubin – destined for kidneys/liver.

• Dissolved gases: $\text{O}<em>2,\;\text{CO}</em>2$.

• Plasma − clotting factors = Serum (used diagnostically).

Formed Elements (≈ 45 % of Blood)

• Produced mainly in red bone marrow (myeloid tissue).

Erythrocytes (RBCs)

• Count: $5{-}5.5\times10^6\;\text{mm}^{-3}$ (males), slightly less in females.

• Anucleate, biconcave discs – ↑ surface-area/volume ratio; flexible for capillary transit.

• Pigment: Haemoglobin (Hb) $12{-}16\,\text{g}\cdot100\,\text{mL}^{-1}$ ➔ reversible $\text{O}<em>2/\text{CO}</em>2$ carriage.

• Life span: ≈ 120 days; cleared by spleen (“graveyard of RBCs”) & liver macrophages.

• Significant link to iron metabolism and anaemia pathophysiology.

Leucocytes (WBCs)

• Count: $6{,}000{-}8{,}000\;\text{mm}^{-3}$; nucleated, motile, immunological.

• Short-lived (hours–days) but rapidly replaced.

• Two categories:

  1. Granulocytes (cytoplasmic granules, lobed nuclei)

  • Neutrophils (60–65 %) – phagocytosis of bacteria; first responders.

  • Eosinophils (2–3 %) – combat parasites; modulate allergic responses.

  • Basophils (0.5–1 %) – release histamine, heparin, serotonin → inflammation.

  1. Agranulocytes

  • Monocytes (6–8 %) – largest; differentiate into tissue macrophages.

  • Lymphocytes (20–25 %)
    • B-cells – humoral (antibody) immunity.
    • T-cells – cell-mediated immunity; helper, cytotoxic subsets.

Thrombocytes (Platelets)

• Fragments of megakaryocytes; count $1.5{-}3.5\times10^5\;\text{mm}^{-3}$.

• Contain clotting factor granules; aggregate at injury → release $\text{ADP}/\text{TXA}_2$ etc.

• Thrombocytopenia → bleeding disorders; thrombocytosis → thrombosis risk.

Blood Groups

ABO System

• Based on surface antigens A & B on RBC membrane glycolipids.

• Plasma naturally contains complementary antibodies (isoagglutinins):

  • Group A → anti-B; Group B → anti-A; Group AB → none; Group O → anti-A & anti-B.

• Transfusion compatibility (memorise as clinical essential):

  • O = Universal donor; AB = Universal recipient.

• Agglutination/haemolysis risk if mismatched (foundation for safe transfusion ethics).

Rh System

• Rh antigen (D) present in ≈ 80 % population → Rh$^{+}$; absent → Rh$^{-}$.

• Rh$^{-}$ recipients develop anti-D only after exposure (transfusion/pregnancy).

• Erythroblastosis foetalis (haemolytic disease of newborn): Rh$^{-}$ mother, Rh$^{+}$ fetus ➔ maternal anti-D IgG crosses placenta in subsequent pregnancies, lyses fetal RBCs.

  • Prevention: inject anti-D (Rho(D) immune globulin) within 72 h postpartum.

Coagulation (Clotting Cascade)

• Purpose: prevent exsanguination; maintain circulatory integrity.

• Key sequence (simplified):

  1. Injury activates platelets & tissue factors.

  2. Formation of Prothrombin activator (Thrombokinase) $\rightarrow$ converts $\text{Prothrombin} \xrightarrow{Ca^{2+}} \text{Thrombin}$.

  3. Thrombin catalyses $\text{Fibrinogen} \rightarrow \text{Fibrin threads}$.

  4. Fibrin network + trapped blood cells = clot (coagulum).

• $Ca^{2+}$ indispensable; Vitamin K dependent synthesis of several factors.

• Failure ➔ haemophilia, vitamin-K deficiency bleeding.

Lymph (Tissue Fluid)

• Formed via ultrafiltration at capillary beds; resembles plasma minus large proteins.

• Functions:

  • Medium of exchange between blood & cells.

  • Immune surveillance – contains lymphocytes.

  • Fat transport – chylomicrons absorbed via intestinal lacteals.

• Collected by lymphatic vessels ➔ thoracic duct/right lymph duct ➔ drains into major veins (connection to venous return concepts).

Circulatory Pathways in Animals (Comparative View)

• Open system – haemolymph bathes organs directly (arthropods, molluscs).

• Closed system – blood confined to vessels (annelids, chordates) → precise pressure control, higher metabolic rates.

• Heart chamber evolution:

  • Fish: 2-chambered (1 atrium, 1 ventricle) – single circulation.

  • Amphibians/Reptiles (except crocodile): 3 chambers – incomplete double circulation.

  • Birds, mammals, crocodiles: 4 chambers – complete double circulation.

Human Heart – Structure & Anatomy

• Location: mediastinum, thoracic cavity; size ≈ closed fist; tilted left.

• Pericardium: double-walled sac; pericardial fluid ↓ friction.

• Chambers:

  • Right/Left Atria – thin-walled receiving chambers.

  • Right/Left Ventricles – thick-walled pumping chambers (left > right thickness).

• Septa:

  • Inter-atrial septum, Inter-ventricular septum, Atrio-ventricular (A-V) septum.

• Valves:

  • Right A-V → Tricuspid (3 cusps).

  • Left A-V → Bicuspid/Mitral (2 cusps).

  • Semilunar → Pulmonary & Aortic valves at ventricular exits.

• One-way flow ensured; murmurs indicate valvular pathology.

Nodal (Conducting) Tissue – The Myogenic Pacemaker System

• Sino-atrial node (SAN) – wall of right atrium; generates $70{-}75\,\text{APs·min}^{-1}$ → sets heart rate (pacemaker).

• Atrio-ventricular node (AVN) – lower RA; delays impulse ≈ $0.1\,\text{s}$.

• A-V Bundle (Bundle of His) → right & left bundle branches ➔ Purkinje fibres – rapid conduction through ventricles.

• Auto-rhythmicity due to unstable resting membrane potential (funny current, $I_f$) explored in cellular electrophysiology topics.

Cardiac Cycle (0.8 s at HR = 72 bpm)

• Joint Diastole (0.4 s) – all chambers relaxed; passive ventricular filling.

• Atrial Systole (0.1 s) – SAN impulse; atria contract → additional 30 % ventricular filling.

• Ventricular Systole (0.3 s) – AV valves close (1st heart sound lub); semilunar valves open → ejection.

• Ventricular Diastole – pressure falls; semilunar valves snap shut (2nd sound dub); AV valves reopen.

• Stroke Volume (SV) ≈ $70\,\text{mL}$.

• Cardiac Output (CO): $\displaystyle CO = SV \times HR$ ⇒ $70\,\text{mL} \times 72\,\text{min}^{-1} \approx 5\,\text{L}\,\text{min}^{-1}$.

• Athletes: ↑ SV, sometimes lower HR, maintaining/raising CO.

Heart Sounds

• S_1 (lub) – closure of tricuspid & mitral; onset ventricular systole.

• S_2 (dub) – closure of semilunar; end ventricular systole.

• Abnormal additional sounds = gallops, murmurs (stenosis, regurgitation).

Electrocardiogram (ECG)

• Non-invasive recording of summed electrical potentials; standard limb leads (I, II, III).

• Wave components:

  • P-wave – atrial depolarisation.

  • QRS complex – ventricular depolarisation (atrial repolarisation hidden).

  • T-wave – ventricular repolarisation.

• Interval analysis (PR, QT, ST segments) diagnoses blocks, ischemia, electrolyte imbalance.

Blood Vessels – Histological Layers

• Tunica intima – endothelial lining (barrier, anti-thrombogenic).

• Tunica media – smooth muscle + elastic fibres (thicker in arteries) → regulates diameter & BP.

• Tunica externa (adventitia) – collagenous support, vasa vasorum.

• Veins: thinner media, larger lumen, valves to prevent backflow (important in lower limbs).

Double Circulation in Humans

• Pulmonary Circuit: RV → Pulmonary artery → Lungs (gas exchange) → Pulmonary veins → LA.

• Systemic Circuit: LV → Aorta → Body tissues → Vena cavae → RA.

• Ensures complete separation of oxygenated & deoxygenated blood, supporting high metabolic demands of endothermy.

• Hepatic portal system: Intestinal capillaries → Hepatic portal vein → Liver sinusoids → Hepatic veins → IVC.

• Coronary circulation: Coronary arteries (first aortic branches) nourish myocardium; blockage → myocardial infarction.

Regulation of Cardiac Activity

• Intrinsic (myogenic) – SAN pacemaking, Frank–Starling law (pre-load ↔ SV).

• Extrinsic (neuro-hormonal):

  • Sympathetic (\beta_1) stimulation → ↑ HR (chronotropy), ↑ contractility (inotropy), ↑ CO.

  • Parasympathetic (vagus) stimulation → ↓ HR, ↓ conduction velocity.

  • Adrenal medulla catecholamines (adrenaline, noradrenaline) mirror sympathetic effects.

• Integration centre: Cardiac control centre in medulla oblongata.

Common Cardiovascular Disorders

• Hypertension: BP persistently $\ge 140/90\,\text{mmHg}$; strains heart, damages vessels, kidneys, brain.

• Coronary Artery Disease (CAD/Atherosclerosis): lipid-calcium plaques narrow coronary lumen ➔ myocardial ischemia.

• Angina pectoris: transient chest pain due to inadequate myocardial $\text{O}_2$; warning of CAD.

• Heart Failure (Congestive HF): heart unable to pump sufficient CO; results in pulmonary/systemic congestion; distinct from cardiac arrest.

Numerical/Statistical Quick-Reference

• RBC count: $\approx 5\times10^6\;\text{mm}^{-3}$

• WBC count: $6{-}8\times10^3\;\text{mm}^{-3}$

• Platelets: $1.5{-}3.5\times10^5\;\text{mm}^{-3}$

• Hb concentration: $12{-}16\,\text{g} \cdot 100\,\text{mL}^{-1}$

• Cardiac cycle: $0.8\,\text{s}$ @ $72\,\text{bpm}$

• SV: $70\,\text{mL}$; CO: $5\,\text{L·min}^{-1}$

• Normal BP: $120/80\,\text{mmHg}$

Ethical & Practical Implications

• Safe transfusion protocols relying on ABO/Rh compatibility prevent fatal haemolysis – cornerstone of clinical ethics.

• Anti-D prophylaxis in Rh incompatibility exemplifies preventive medicine.

• Public health strategies targeting hypertension and CAD reduce morbidity & socioeconomic burden.

Connections & Real-World Relevance

• Membrane transport (previous physiology unit) underpins capillary exchange forming tissue fluid.

• Respiratory physiology: Hb–$\text{O}_2$ dissociation curve crucial for gas transport efficacy.

• Exercise physiology: adaptations (athlete’s heart) illustrate plasticity of SV and CO.

• Pharmacology: beta-blockers lower HR/contractility, nitrates relieve angina, anticoagulants modulate clotting – tie-ins for therapeutic application.

Concept Integration / Quick Mind-Map

• Blood & Lymph → Transport/Immunity.

• Heart (pump) → Myogenic rhythm ↔ Neural/Hormonal control → Cardiac cycle → CO.

• Vessels → Closed circuit → Double circulation (Pulmonary + Systemic) → Tissue exchange (capillaries).

• Disorders ↔ Lifestyle, genetics → Prevention & treatment.

Blood – General Overview

• Essential fluid connective tissue that transports nutrients, $\text{O}_2$, hormones, waste, and immune factors between every living cell and its environment.

• Two principal internal transport fluids in higher animals:

  • Blood – primary, present in all vertebrates and many invertebrates.

  • Lymph (tissue fluid) – auxiliary, drains interstitial spaces and participates in immunity & fat absorption.

Plasma (Fluid Matrix)

• Straw-coloured, viscous liquid ≈ 55 % of total blood volume.

• Water content: 90–92 % (solvent & temperature buffer).

• Proteins (6–8 %):

  • Fibrinogen – clotting precursor ➔ fibrin threads.

  • Globulins – immune defence (antibodies, complement, transport globulins).

  • Albumins – maintain osmotic/oncotic pressure; carrier of lipophilic molecules.

• Solutes/ions: $\text{Na}^+,\;\text{K}^+,\;\text{Ca}^{2+}, ext{Mg}^{2+}, ext{Cl}^-, ext{HCO}_3^-$ etc. – regulate pH, excitability, membrane potential.

• Nutrients in transit: glucose, amino acids, fatty acids, lipids, vitamins—link to digestive absorption and cellular respiration lectures.

• Waste metabolites: urea, uric acid, bilirubin – destined for kidneys/liver.

• Dissolved gases: $\text{O}_2, ext{CO}_2$.

• Plasma − clotting factors = Serum (used diagnostically).

Formed Elements (≈ 45 % of Blood)

• Produced mainly in red bone marrow (myeloid tissue).

Erythrocytes (RBCs)

• Count: $5{-}5.5\times10^6\;\text{mm}^{-3}$ (males), slightly less in females.

• Anucleate, biconcave discs – ↑ surface-area/volume ratio; flexible for capillary transit.

• Pigment: Haemoglobin (Hb) $12{-}16\,\text{g}\cdot100\,\text{mL}^{-1}$ ➔ reversible $\text{O}_2/\text{CO}_2$ carriage.

• Life span: ≈ 120 days; cleared by spleen (“graveyard of RBCs”) & liver macrophages.

• Significant link to iron metabolism and anaemia pathophysiology.

Leucocytes (WBCs)

• Count: $6{,}000{-}8{,}000\;\text{mm}^{-3}{;}$ nucleated, motile, immunological.

• Short-lived (hours–days) but rapidly replaced.

• Two categories:

1. Granulocytes (cytoplasmic granules, lobed nuclei)

   • Neutrophils (60–65 %) – phagocytosis of bacteria; first responders.

   • Eosinophils (2–3 %) – combat parasites; modulate allergic responses.

   • Basophils (0.5–1 %) – release histamine, heparin, serotonin → inflammation.

2. Agranulocytes

   • Monocytes (6–8 %) – largest; differentiate into tissue macrophages.

   • Lymphocytes (20–25 %)

   • B-cells – humoral (antibody) immunity.

   • T-cells – cell-mediated immunity; helper, cytotoxic subsets.

Thrombocytes (Platelets)

• Fragments of megakaryocytes; count $1.5{-}3.5\times10^5\;\text{mm}^{-3}$ .

• Contain clotting factor granules; aggregate at injury → release $\text{ADP}/\text{TXA}_2$ etc.

• Thrombocytopenia → bleeding disorders; thrombocytosis → thrombosis risk.

Blood Groups

ABO System

• Based on surface antigens A & B on RBC membrane glycolipids.

• Plasma naturally contains complementary antibodies (isoagglutinins):

  • Group A → anti-B; Group B → anti-A; Group AB → none; Group O → anti-A & anti-B.

• Transfusion compatibility (memorise as clinical essential):

  • O = Universal donor; AB = Universal recipient.

• Agglutination/haemolysis risk if mismatched (foundation for safe transfusion ethics).

Rh System

• Rh antigen (D) present in ≈ 80 % population → Rh$^{+}$; absent → Rh$^{-}$.

• Rh$^{-}$ recipients develop anti-D only after exposure (transfusion/pregnancy).

• Erythroblastosis foetalis (haemolytic disease of newborn): Rh$^{-}$ mother, Rh$^{+}$ fetus ➔ maternal anti-D IgG crosses placenta in subsequent pregnancies, lyses fetal RBCs.

• Prevention: inject anti-D (Rho(D) immune globulin) within 72 h postpartum.

Coagulation (Clotting Cascade)

• Purpose: prevent exsanguination; maintain circulatory integrity.

• Key sequence (simplified):

1. Injury activates platelets & tissue factors.

2. Formation of Prothrombin activator (Thrombokinase) $\rightarrow$ converts $\text{Prothrombin} \xrightarrow{Ca^{2+}} \text{Thrombin}$.

3. Thrombin catalyses $\text{Fibrinogen} \rightarrow \text{Fibrin threads}$.

4. Fibrin network + trapped blood cells = clot (coagulum).

• $\text{Ca}^{2+}$ indispensable; Vitamin K dependent synthesis of several factors.

• Failure ➔ haemophilia, vitamin-K deficiency bleeding.

Lymph (Tissue Fluid)

• Formed via ultrafiltration at capillary beds; resembles plasma minus large proteins.

• Functions:

  • Medium of exchange between blood & cells.

  • Immune surveillance – contains lymphocytes.

  • Fat transport – chylomicrons absorbed via intestinal lacteals.

• Collected by lymphatic vessels ➔ thoracic duct/right lymph duct ➔ drains into major veins (connection to venous return concepts).

Circulatory Pathways in Animals (Comparative View)

• Open system – haemolymph bathes organs directly (arthropods, molluscs).

• Closed system – blood confined to vessels (annelids, chordates) → precise pressure control, higher metabolic rates.

• Heart chamber evolution:

  • Fish: 2-chambered (1 atrium, 1 ventricle) – single circulation.

  • Amphibians/Reptiles (except crocodile): 3 chambers – incomplete double circulation.

  • Birds, mammals, crocodiles: 4 chambers – complete double circulation.

Human Heart – Structure & Anatomy

• Location: mediastinum, thoracic cavity; size ≈ closed fist; tilted left.

• Pericardium: double-walled sac; pericardial fluid ↓ friction.

• Chambers:

  • Right/Left Atria – thin-walled receiving chambers.

  • Right/Left Ventricles – thick-walled pumping chambers (left > right thickness).

• Septa:

  • Inter-atrial septum, Inter-ventricular septum, Atrio-ventricular (A-V) septum.

• Valves:

  • Right A-V → Tricuspid (3 cusps).

  • Left A-V → Bicuspid/Mitral (2 cusps).

  • Semilunar → Pulmonary & Aortic valves at ventricular exits.

• One-way flow ensured; murmurs indicate valvular pathology.

Nodal (Conducting) Tissue – The Myogenic Pacemaker System

• Sino-atrial node (SAN) – wall of right atrium; generates $70{-}75\,\text{APs·min}^{-1}$ → sets heart rate (pacemaker).

• Atrio-ventricular node (AVN) – lower RA; delays impulse ≈ $0.1\,\text{s}$.

• A-V Bundle (Bundle of His) → right & left bundle branches ➔ Purkinje fibres – rapid conduction through ventricles.

• Auto-rhythmicity due to unstable resting membrane potential (funny current, $I_f$) explored in cellular electrophysiology topics.

Cardiac Cycle (0.8 s at HR = 72 bpm)

• Joint Diastole (0.4 s) – all chambers relaxed; passive ventricular filling.

• Atrial Systole (0.1 s) – SAN impulse; atria contract → additional 30 % ventricular filling.

• Ventricular Systole (0.3 s) – AV valves close (1st heart sound lub); semilunar valves open → ejection.

• Ventricular Diastole – pressure falls; semilunar valves snap shut (2nd sound dub); AV valves reopen.

• Stroke Volume (SV) ≈ $70\,\text{mL}$.

• Cardiac Output (CO): $\displaystyle CO = SV \times HR$ ⇒ $70\,\text{mL} \times 72\,\text{min}^{-1} \approx 5\,\text{L}\,\text{min}^{-1}$.

• Athletes: ↑ SV, sometimes lower HR, maintaining/raising CO.

Heart Sounds

• S_1 (lub) – closure of tricuspid & mitral; onset ventricular systole.

• S_2 (dub) – closure of semilunar; end ventricular systole.

• Abnormal additional sounds = gallops, murmurs (stenosis, regurgitation).

Electrocardiogram (ECG)

• Non-invasive recording of summed electrical potentials; standard limb leads (I, II, III).

• Wave components:

  • P-wave – atrial depolarisation.

  • QRS complex – ventricular depolarisation (atrial repolarisation hidden).

  • T-wave – ventricular repolarisation.

• Interval analysis (PR, QT, ST segments) diagnoses blocks, ischemia, electrolyte imbalance.

Blood Vessels – Histological Layers

• Tunica intima – endothelial lining (barrier, anti-thrombogenic).

• Tunica media – smooth muscle + elastic fibres (thicker in arteries) → regulates diameter & BP.

• Tunica externa (adventitia) – collagenous support, vasa vasorum.

• Veins: thinner media, larger lumen, valves to prevent backflow (important in lower limbs).

Double Circulation in Humans

• Pulmonary Circuit: RV → Pulmonary artery → Lungs (gas exchange) → Pulmonary veins → LA.

• Systemic Circuit: LV → Aorta → Body tissues → Vena cavae → RA.

• Ensures complete separation of oxygenated & deoxygenated blood, supporting high metabolic demands of endothermy.

• Hepatic portal system: Intestinal capillaries → Hepatic portal vein → Liver sinusoids → Hepatic veins → IVC.

• Coronary circulation: Coronary arteries (first aortic branches) nourish myocardium; blockage → myocardial infarction.

Regulation of Cardiac Activity

• Intrinsic (myogenic) – SAN pacemaking, Frank–Starling law (pre-load ↔ SV).

• Extrinsic (neuro-hormonal):

  • Sympathetic ($\beta_1$) stimulation → ↑ HR (chronotropy), ↑ contractility (inotropy), ↑ CO.

  • Parasympathetic (vagus) stimulation → ↓ HR, ↓ conduction velocity.

  • Adrenal medulla catecholamines (adrenaline, noradrenaline) mirror sympathetic effects.

• Integration centre: Cardiac control centre in medulla oblongata.

Common Cardiovascular Disorders

• Hypertension: BP persistently $\ge 140/90\,\text{mmHg}$; strains heart, damages vessels, kidneys, brain.

• Coronary Artery Disease (CAD/Atherosclerosis): lipid-calcium plaques narrow coronary lumen ➔ myocardial ischemia.

• Angina pectoris: transient chest pain due to inadequate myocardial $\text{O}_2$; warning of CAD.

• Heart Failure (Congestive HF): heart unable to pump sufficient CO; results in pulmonary/systemic congestion; distinct from cardiac arrest.

Numerical/Statistical Quick-Reference

• RBC count: $\approx 5\times10^6\;\text{mm}^{-3}$

• WBC count: $6{-}8\times10^3\;\text{mm}^{-3}$

• Platelets: $1.5{-}3.5\times10^5\;\text{mm}^{-3}$

• Hb concentration: $12{-}16\,\text{g} \cdot 100\,\text{mL}^{-1}$

• Cardiac cycle: $0.8\,\text{s}$ @ $72\,\text{bpm}$

• SV: $70\,\text{mL}$; CO: $5\,\text{L·min}^{-1}$

• Normal BP: $120/80\,\text{mmHg}$

Ethical & Practical Implications

• Safe transfusion protocols relying on ABO/Rh compatibility prevent fatal haemolysis – cornerstone of clinical ethics.

• Anti-D prophylaxis in Rh incompatibility exemplifies preventive medicine.

• Public health strategies targeting hypertension and CAD reduce morbidity & socioeconomic burden.

Connections & Real-World Relevance

• Membrane transport (previous physiology unit) underpins capillary exchange forming tissue fluid.

• Respiratory physiology: Hb–$\text{O}_2$ dissociation curve crucial for gas transport efficacy.

• Exercise physiology: adaptations (athlete’s