Cardiovascular and Blood System Study Guide

Cardiovascular System

Overview

The cardiovascular system generates its own electrical impulses and coordinates rhythmic contractions through the Intrinsic Cardiac Conduction System (ICCS). This system ensures the atria contract first, followed by the ventricles, creating efficient blood flow through the heart.

Intrinsic Cardiac Conduction System (ICCS)

• Function:

  • Generates action potentials (APs) independently of the nervous system.

  • Gap junctions between cardiac cells allow rapid spread of APs.

  • Conducting fibers transmit impulses efficiently with fewer myofibrils.

  • Ensures proper timing: atria contract first, then ventricles.

Key Structures

Structure	Location	Function
SA Node	Superior wall of right atrium	Primary pacemaker; initiates AP
Internodal Pathways	Between SA and AV nodes	Conducts impulses through atria
AV Node	Inferior wall of right atrium	Delays AP ~0.1 sec; backup pacemaker
Bundle of His (AV Bundle)	Superior interventricular septum	Conducts AP from atria → ventricles
Right & Left Bundle Branches	Along interventricular septum	Carry impulses to ventricles
Purkinje Fibers	Subendocardial layer	Spread AP through ventricles for contraction

Flow of Impulse: SA Node → Internodal Pathways → AV Node → Bundle of His → R/L Bundle Branches → Purkinje Fibers

Pacemaker & Contractile Cells

• Pacemaker Cells: Found in SA and AV nodes; depolarize spontaneously via automaticity.

  • Slow depolarization: Na+ influx & K+ efflux.

  • Depolarization: Ca2+ influx via voltage-gated channels.

  • Repolarization: K+ efflux restores resting potential.

  • Intrinsic rate ≈ 100 bpm (modified by ANS).

• Contractile Cells: Make up most of myocardium (pumping cells).

  • Rapid depolarization: Na+ influx.

  • Plateau phase: Ca2+ influx + K+ efflux = sustained depolarization.

  • Repolarization: K+ out.

  • Prolonged refractory period prevents tetany and ensures relaxation.

ECG Correlation

Wave/Interval	Represents
P Wave	Atrial depolarization (SA node)
QRS	Ventricular depolarization, atrial repolarization
T Wave	Ventricular repolarization
PR Interval	SA → AV conduction
ST Segment	Plateau phase of ventricular AP

Cardiac Cycle

The cardiac cycle consists of a series of mechanical and electrical events that result in the coordinated contraction and relaxation of the heart chambers.

Phase	Mechanical Event	Valves Open	Valves Closed	Notes
Ventricular Filling	Blood flows atria → ventricles	AV	SL	Diastole
Isovolumetric Contraction	Ventricles contract, no volume change	--	AV & SL	Start systole
Ventricular Ejection	Blood flows ventricles → arteries	SL	AV	Peak systole
Isovolumetric Relaxation	Ventricles relax, no blood flow	--	AV & SL	Early diastole

• AV Valves: Tricuspid (right), Bicuspid/Mitral (left)

• SL Valves: Pulmonary (right), Aortic (left)

Heart Sounds

Sound	Event	Phase
S1 (Lub)	AV valves close	Isovolumetric contraction (start systole)
S2 (Dub)	SL valves close	Isovolumetric relaxation (start diastole)
S3	Rapid ventricular filling	Mid-diastole

Cardiac Output & Regulation

• Cardiac Output (CO) Formula:

  • $CO = SV \times HR$

  • Average CO ≈ 5 L/min (70 mL × 75 bpm)

• Stroke Volume Influences:

  • Preload: Degree of stretch before contraction

  • Contractility: Strength of contraction

  • Afterload: Resistance ventricles must overcome

• Nervous System Control:

  • Medulla Oblongata: Controls HR via two centers:

    • Cardioacceleratory (Sympathetic): Increases HR & contractility via SA/AV nodes

    • Cardioinhibitory (Parasympathetic): Decreases HR via vagus nerve

  • SNS: ↑ HR, ↑ force of contraction

  • PNS: ↓ HR (no effect on contractility)

Blood Vessels & Circulation

Functions

• Transport blood, deliver nutrients & oxygen, remove waste.

• Arteries → Arterioles → Capillaries → Venules → Veins → Heart

Vessel Wall Structure

Layer	Description	Components
Tunica Intima	Innermost; contact with blood	Endothelium (simple squamous), basement membrane
Tunica Media	Middle; maintains BP & flow	Smooth muscle, elastic fibers
Tunica Externa	Outer; structural support	Collagen & CT, vasa vasorum

Vessel Types

Type	Description	Function
Elastic Arteries	Large (e.g., aorta); stretch/recoil	Conducting vessels
Muscular Arteries	Medium; thick smooth muscle	Distribute blood to organs
Arterioles	Smallest arteries	Regulate blood flow & pressure
Capillaries	Thin walls; one cell layer	Site of exchange
Venules/Veins	Thin walls, valves	Return blood to heart

Capillary Types

Type	Description	Example
Continuous	Uninterrupted endothelium	Skin, muscle
Fenestrated	Pores for exchange	Kidneys, intestines
Sinusoid	Large openings	Liver, spleen, marrow

• Capillary Beds: Terminal arteriole → Capillary network → Postcapillary venule

• Precapillary sphincters: Regulate flow.

• Metarteriole-throughfare channel: Bypasses capillaries when closed (vascular shunt).

• Microcirculation: Local blood distribution based on tissue demand.

Quick Reference Tables

• Intrinsic Conduction Flow: SA Node → Atria → AV Node → Bundle of His → R/L Bundle Branches → Purkinje Fibers → Ventricular contraction

• Cardiac Cycle Timing: See table above for phase timing and valve status.

Key Takeaways

• ICCS controls the timing and coordination of contractions.

• Pacemaker cells depolarize slowly; contractile cells have plateau phases.

• CO = SV × HR defines heart efficiency.

• Sympathetic ↑ HR/force. Parasympathetic ↓ HR.

• Arteries carry blood away; veins return it.

• Capillaries are the exchange site of gases and nutrients.

Blood System

Overview of Blood

• Only liquid connective tissue in the body.

• Bright red = high O2; dark red = low O2.

Functions of Blood

1. Transport

   • O2 from lungs → tissues.

   • CO2 and wastes → lungs and kidneys.

   • Transports nutrients, hormones, and heat.

2. Regulation

   • Maintains temperature (vasoconstriction/dilation).

   • Regulates pH via buffers.

   • Maintains fluid volume via plasma proteins.

3. Protection

   • Prevents blood loss (clotting proteins & platelets).

   • Prevents infection (WBCs, antibodies, complement proteins).

Composition of Blood

Component	Description	% of Total
Plasma	Non-living fluid matrix (90% water; 10% solutes like proteins, ions, gases, nutrients, hormones, waste)	55%
Buffy Coat	Thin middle layer: leukocytes (WBCs) + platelets (thrombocytes)	<1%
Erythrocytes (RBCs)	Formed elements, carry gases	45% (hematocrit)

• Hematocrit: % of RBCs in total blood volume: Men 42–52%, Women 36–48%.

• Indicates oxygen-carrying capacity.

Erythrocytes (Red Blood Cells)

• Biconcave discs, flexible shape for gas diffusion.

• Anucleate, lack organelles.

• Contain structural protein spectrin for shape integrity.

• Packed with hemoglobin (Hb) (~97% of RBC mass).

• Specialized for gas transport of O2 and CO2.

• Use hemoglobin to bind and release gases reversibly.

• Life span ≈ 120 days; recycled in spleen and liver.

Hemoglobin (Hb)

• Structure:

  • 4 globin subunits (2 alpha + 2 beta chains).

  • Each subunit contains a heme group with a Fe2+ ion that binds 1 O2 molecule.

  • Each Hb molecule binds up to 4 O2 molecules — oxyhemoglobin.

  • Hb can also bind CO2 — deoxyhemoglobin (via amino groups).

• Function:

  • Oxygen transport: lungs → tissues.

  • Carbon dioxide transport: tissues → lungs.

  • Reversible binding maintains efficient gas exchange.

Summary Equations: $Hb + O_2 \rightarrow HbO_2$ (oxyhemoglobin) $Hb + CO_2 \rightarrow HbCO_2$ (carbaminohemoglobin)

Leukocytes (White Blood Cells)

• Defend against pathogens and abnormal cells.

• Migrate through blood and tissues (diapedesis).

• Two main groups: granulocytes and agranulocytes.

A. Granulocytes

Type	Appearance	Function
Neutrophils	Nucleus 3–5 lobes; fine granules	Most abundant (70%); 1st responders; phagocytosis; release enzymes & antimicrobial proteins
Eosinophils	Bilobed nucleus; red/orange granules	Defend against parasitic worms (helminths); involved in allergies
Basophils	Bilobed nucleus; deep blue/purple granules	Release histamine (inflammation); increase capillary permeability

• Mast cells: tissue-resident cousins of basophils; release histamine during allergic reactions.

B. Agranulocytes

Type	Function
Monocytes	Circulate → become macrophages or dendritic cells. Macrophages: phagocytic "sentinels"; dendritic cells: activate adaptive immunity.
Lymphocytes	T-cells (cell-mediated immunity), B-cells (antibody production), NK cells (innate killing of abnormal cells).

Platelets (Thrombocytes)

• Fragments of megakaryocytes; anucleate.

• Contain granules with clotting factors (ADP, serotonin, thromboxane).

• Circulate in inactive state; activate upon vessel injury → become spiky & sticky.

Process: Megakaryocyte → Platelet (inactive) → Activated platelet → Platelet plug

Hemostasis (Stopping Bleeding)

A fast, local, and controlled process with three main steps:

1. Vascular Spasm

   • Immediate vasoconstriction of damaged vessels.

   • Triggered by endothelin release from endothelium & platelets.

   • Lasts 20 min–few hours; buys time for next steps.

2. Platelet Plug Formation

   1. Adhesion: Platelets bind exposed collagen using von Willebrand factor (vWF).

   2. Activation/Degranulation: Platelets release ADP, serotonin, thromboxane A2 to attract more platelets.

   3. Aggregation: Platelets stick together → temporary plug forms (positive feedback).

   Summary: Adhesion → Activation → Aggregation → Plug

3. Coagulation (Clotting Cascade)

   • Reinforces platelet plug with fibrin mesh (molecular glue).

   • Requires 30+ reactions, Ca2+, and vitamin K.

   Phases:

   1. Prothrombin Activator Formation

      • Intrinsic pathway: slow, within blood; initiated by negatively charged surfaces.

      • Extrinsic pathway: fast, tissue factor (TF) from damaged tissue.

      • Both lead to Factor X → Prothrombin activator.

   2. Prothrombin → Thrombin (enzyme activation).

   3. Fibrinogen → Fibrin via thrombin.

      • Fibrin forms mesh that stabilizes clot.

   Memory Tricks: "Extrinsic = X & Field" = Extrinsic (Tissue Factor III); "In Half a Fame" = Intrinsic (Hageman Factor XII) PPTF Sequence: Prothrombin activator → Prothrombin → Thrombin → Fibrinogen → Fibrin

Clot Retraction & Fibrinolysis

• Clot Retraction: Platelet-induced contraction using actin & myosin. Pulls wound edges together for repair. Releases Platelet-Derived Growth Factor (PDGF) → stimulates vessel healing.

• Fibrinolysis (Clot Breakdown): Restores normal blood flow after repair. Plasminogen → Plasmin (via tPA) → dissolves fibrin mesh. Occurs once vessel is healed.

Quick Reference Table: Blood Composition

Component	Function	% of Blood
Plasma	Nutrient & waste transport, osmotic	55%
Buffy Coat	Immunity & clotting	<1%
RBCs	Gas exchange	45%