Bio241_chapter13_blood_lecture
Overview
- Chapter focuses on Blood, Heart, and Circulation (BIOL 241 – Ch. 13)
- Sub-topics: Blood • Pulmonary & Systemic Circulations • Heart Valves • Cardiac Cycle • Electrical Activity • Structure of Vessels
Functions of the Circulatory System
- Transport
- \mathrm{O_2}, nutrients, enzymes, hormones ⟶ tissues
- \mathrm{CO_2} & metabolic wastes ⟶ excretory organs
- Heat distribution → regulation of body temperature
- Fluid, electrolyte & pH homeostasis
- Protection
- Immune surveillance (microbes, foreign Ag, tumors)
- Hemostasis → prevents blood loss
Components of the Circulatory System
- Cardiovascular system: heart + blood vessels (arteries, arterioles, capillaries, venules, veins)
- Lymphatic system: returns excess interstitial fluid to venous blood; lymph nodes = immune organs
Composition of Whole Blood
- Total volume ≈ 5 L
- Two compartments:
- Plasma (≈ 55 %)
- 92 % H₂O, 8 % proteins + solutes (ions, nutrients, gases, wastes)
- Serum = Plasma – clotting factors
- Formed Elements (≈ 45 %)
- \approx 95\% RBCs (erythrocytes) – anucleate
- <1\% WBCs (leukocytes) – nucleated
- \approx 5\% Platelets (thrombocytes) – anucleate
Hematocrit (Hct)
- % RBCs in whole blood
- Women: 36\text{–}46\%
- Men: 41\text{–}53\%
- Example: 80 mL sample → 30 mL RBCs ⇒ \text{Hct}=\frac{30}{80}\times100=37.5\% (within female range)
Plasma Proteins (7–9 % of plasma)
- Albumin (60–80 %)
- Creates colloid osmotic pressure → draws \mathrm{H_2O} into capillaries, maintains BP & volume
- Globulins
- Alpha/Beta: lipid carriers
- Gamma: antibodies (immunoglobulins)
- Fibrinogen → Fibrin (clotting)
Erythrocytes (RBCs)
- Flattened biconcave discs → large SA for diffusion
- Lack nuclei & mitochondria; contain ~280 million Hb molecules/RBC
- Production rate: \approx 3\times10^{11}\ \text{day}^{-1}
Leukocytes (WBCs)
- Have nucleus, mitochondria, amoeboid motility, diapedesis capability
- Granular (detox + heparin): neutrophils, eosinophils, basophils
- Agranular (phagocytosis/antibodies): lymphocytes, monocytes
Platelets (Thrombocytes)
- Smallest, anucleate fragments of megakaryocytes
- Majority of clot mass; live 5–9 days
- Release serotonin (vasoconstriction) & growth factors for vessel repair
Hematopoiesis
- Occurs in myeloid (red marrow) & lymphoid tissue
- Output: \approx5\times10^{11} cells/day
- Fetal site = liver
- Erythropoiesis
- Stimulus: renal \mathrm{EPO}
- Rate: 2.5\times10^{6}\ \text{sec}^{-1}; lifespan 120 days; old cells removed by liver, spleen, marrow; Fe recycled
- Leukopoiesis
- Regulated by cytokines (autocrine factors)
Blood Groups & Typing
- ABO antigens on RBC membrane
- Agglutination / Transfusion Reactions
- Type A → anti-B Abs; Type B → anti-A; Type AB → none; Type O → both
- Universal donor = O (no antigens); universal recipient = AB (no anti-A/B Abs)
- Rh Factor
- Rh⁺: D antigen; Rh⁻: none
- Erythroblastosis fetalis: Rh⁻ mother sensitized by Rh⁺ fetus → anti-D Abs hemolyze next Rh⁺ fetus
Hemostasis (Bleeding Cessation)
- Platelet Plug (small tears)
- Intact endothelium secretes prostacyclin (PGI₂) & NO → inhibit platelet stickiness & vasodilate
- Damage exposes collagen; von Willebrand factor bridges collagen ↔ platelets
- Platelet Release Reaction: ADP, serotonin, thromboxane A₂ (TxA₂)
- Serotonin & TxA₂: vasoconstriction; ADP & TxA₂: recruit more platelets → positive feedback until plug forms
- Aspirin inhibits TxA₂ synthesis ⇒ antiplatelet effect
- Coagulation (Fibrin Clot) (large tears)
- Intrinsic Pathway (contact activation)
- Negatively charged surface → activates factor XII ⇒ cascade ⇒ factor X (prothrombin activator)
- Extrinsic Pathway (tissue factor)
- Tissue thromboplastin (factor III) from damaged tissue directly activates factor X (shortcut)
- Common Pathway: \mathrm{Prothrombin\ (II) \xrightarrow{Xa+Ca^{2+}+PL} Thrombin}
\mathrm{Fibrinogen\ (I) \xrightarrow{Thrombin} Fibrin \rightarrow polymer}
- Hemophilia: absence of factor VIII (intrinsic)
- Vitamin K–dependent factors; Heparin blocks thrombin
- Dissolution: Factor XII → kallikrein → plasminogen → plasmin → digests fibrin
- Anticoagulants: Ca²⁺ chelators (citrate, EDTA), Heparin (activates antithrombin III), Coumarins (vit K antagonism ↓ Ca²⁺ availability)
Heart Anatomy & Circulations
- Four chambers: 2 atria (receive) • 2 ventricles (pump)
- Two pumps separated by muscular septum
- Fibrous skeleton (dense CT between atria & ventricles): electrical insulation + valve rings (annuli fibrosi)
- Pulmonary circuit: RV → pulmonary arteries → lungs → pulmonary veins → LA
- Systemic circuit: LV → aorta → tissues → veins → RA
- Systemic resistance > pulmonary; LV workload ≈ 5–7× RV ⇒ LV wall 3–4× thicker
- Flow rates through both circuits must be equal
Heart Valves
- Atrioventricular (AV): Right = tricuspid; Left = bicuspid/mitral
- Chordae tendineae + papillary muscles prevent prolapse during systole
- Semilunar: Aortic & Pulmonary; open in ventricular systole, close in diastole
Cardiac Cycle (Repeat every heartbeat)
- Systole = contraction; Diastole = relaxation
- Sequence
- Isovolumetric Contraction: ventricles contract, all valves closed, pressure ↑
- Ejection: when P{vent}>P{aorta/pulmon} → semilunars open → stroke volume ejected
- Isovolumetric Relaxation: ventricles relax, semilunars shut (dub), all valves closed
- Ventricular Filling: when P{atria}>P{vent} → AV valves open; final filling by atrial systole
- Pressures: Systemic ≈ 120/80\ \text{mmHg}; Pulmonary ≈ 25/10
- Volumes
- End-diastolic (EDV) ("preload")
- End-systolic (ESV)
- Stroke Volume \mathrm{SV = EDV - ESV}; Example: \mathrm{SV}=80-20=60\,mL; \mathrm{EDV>ESV}
Heart Sounds & Murmurs
- "Lub" (S₁): AV closure just after QRS
- "Dub" (S₂): Semilunar closure at T-wave onset
- Murmurs = turbulent flow (valve defects or septal defects)
- Mitral stenosis → pulmonary hypertension
- Incompetent valves → regurgitation
- Septal defects (e.g., patent foramen ovale) ⇒ left→right shunt due to higher LV pressure
Electrical Activity & Conduction
Myocardium
- Cardiac muscle cells connected by gap junctions → functional syncytium (atria & ventricles separate via fibrous skeleton)
Pacemaker (SA Node)
- Resting V_m=-60\,mV → slow depolarization (pacemaker potential) via HCN Na⁺ channels (open on hyperpolarization)
- Threshold -40\,mV → \mathrm{Ca^{2+}} influx (L-type) → AP upstroke; repolarization via \mathrm{K^{+}} efflux
- Autonomic modulation alters slope of pacemaker potential
Ectopic Pacemakers
- AV node, Purkinje, etc., have slower intrinsic rates; suppressed by SA overdrive; take over if SA blocked
Contractile Myocardial AP
- RMP -90\,mV; rapid Na⁺ upstroke
- Plateau (200–300 ms): balance of slow Ca²⁺ influx vs K⁺ efflux → prolonged refractory period (prevents tetany)
Conduction Pathway
- SA node → atrial myocardium → AV node (delay 0.1 s) → Bundle of His → R/L bundle branches → Purkinje fibers (5 m/s) → ventricular myocardium (contr. starts 0.1–0.2 s after atria)
Excitation–Contraction Coupling
- Extracellular Ca²⁺ via L-type channels triggers SR Ca²⁺ release (Ca²⁺-induced Ca²⁺-release); Ca²⁺ binds troponin; relaxation via uptake/outflow pumps
Refractory Period
- ≈ 300 ms (≈ duration of AP) → heart cannot summate contractions
Electrocardiogram (ECG/EKG)
- Surface recording of electrical events (not mechanical)
- P wave: atrial depolarization
- QRS complex: ventricular depolarization (+ atrial repolarization)
- T wave: ventricular repolarization
- Correlation with sounds: S₁ just after QRS; S₂ at start of T
Structure of Blood Vessels
- Tunica interna: endothelium + basement membrane + elastin
- Tunica media: smooth muscle (thicker in arteries)
- Tunica externa: CT
- Only capillaries = endothelium only → site of exchange
Arteries
- Elastic (conducting): elastin; expand (systole) & recoil (diastole) → dampen pulse pressure
- Muscular & arterioles: resistance vessels; greatest pressure drop; precapillary sphincters regulate flow; some arteriovenous anastomoses bypass capillaries
Capillary Types
- Continuous: tight; small pores; muscle, lung, adipose
- Fenestrated: wide pores; kidneys, endocrine, intestines
- Discontinuous (sinusoids): large gaps; liver, spleen, marrow
Veins