ENDOCRINE SYSTEM

 

Fewa Med

Cardiovascular System

1. Heart Anatomy – In-Depth

1.1 External Anatomy

  • Located in the middle mediastinum, apex pointing to 5th intercostal space midclavicular line

  • Surfaces:

    • Sternocostal: RA & RV predominantly

    • Diaphragmatic: LV and some RV

    • Pulmonary (left): LV impression on left lung

  • Borders:

    • Right: RA

    • Left: LV and auricle

    • Superior: Base – LA and great vessels

Pericardium:

  • Fibrous pericardium: tough outer layer, attached to diaphragm and sternum

  • Serous pericardium:

    • Parietal layer: lines fibrous pericardium

    • Visceral layer (epicardium): on heart surface

  • Pericardial cavity: 15–50 mL of lubricating fluid

Clinical correlation: Pericardial effusion → cardiac tamponade; auscultation changes



1.2 Internal Anatomy

  • Chambers & Wall Thickness:| Chamber | Wall Thickness (mm) | Relative Function ||---------|-------------------|-----------------||


    RA | 2–3 | Low pressure reservoir ||

    RV | 3–5 | Pumps to pulmonary circulation ||

    LA | 2–4 | Receives pulmonary venous blood ||

    LV | 8–12 | Pumps to systemic circulation |


  • Atrioventricular valves:

    • Tricuspid: 3 cusps, chordae tendineae attached to papillary muscles

    • Mitral: 2 cusps

    • Function: Prevent regurgitation during systole

  • Semilunar valves:

    • Pulmonary and Aortic, 3 cusps each

    • Nodules of Arantius: ensure closure

    • Sinuses of Valsalva: origin of coronary arteries (aortic)



1.3 Conduction System

  • SA Node: Junction of RA and superior vena cava, intrinsic rate 60–100 bpm

  • AV Node: Located in interatrial septum, delays impulse 0.1 s

  • Bundle of His → Left/Right bundle branches → Purkinje fibers

  • Special features:

    • AV bundle passes fibrous skeleton, isolates atrial from ventricular conduction

    • Purkinje fibers conduct rapidly (2–4 m/s)

Clinical: SA node dysfunction → sinus arrest; AV block → varying degrees of heart block


1.4 Cardiac Cycle Physiology

Pressure-Volume Relationship:

  • Isovolumetric contraction:

    • Ventricular pressure rises, all valves closed

  • Ejection phase:

    • Semilunar valves open, stroke volume ejected

  • Isovolumetric relaxation:

    • Ventricles relax, valves closed

  • Ventricular filling:

    • Passive and active (atrial systole)

Pressure-volume loop:

  • X-axis: Volume, Y-axis: Pressure

  • End-diastolic volume (EDV), end-systolic volume (ESV)

  • Stroke Volume (SV) = EDV – ESV

Regulation:

  • Frank-Starling law: SV ↑ with ↑ EDV

  • Autonomic control: Sympathetic ↑ HR, contractility; Parasympathetic ↓ HR

  • Hormonal: Epinephrine, thyroxine



2. Blood Vessels – Detailed

2.1 Arteries

  • Elastic arteries: Aorta, Pulmonary artery – buffer systolic pressure

  • Muscular arteries: Coronary, brachial – distribute blood

  • Arterioles: Regulate peripheral resistance

2.2 Veins

  • Thin-walled, valves to prevent backflow

  • Capacitance vessels, contain ~70% blood at rest

  • Clinical: Varicose veins, DVT

2.3 Capillaries

  • Types: Continuous, Fenestrated, Sinusoidal

  • Exchange mechanisms: Diffusion, filtration (Starling forces), pinocytosis

Starling Forces:

  • Filtration = Capillary hydrostatic pressure – Interstitial hydrostatic + Oncotic forces


3. Coronary Circulation

  • RCA: SA node, AV node, RV, RA

  • LCA: LAD → anterior LV, septum; Circumflex → lateral LV

  • Dominance: Right, Left, Co-dominant

  • Venous: Coronary sinus → RA

Clinical: LAD occlusion → Anterior MI; RCA occlusion → Inferior MI

4. Lymphatics

  • Subendocardial, subepicardial plexus → Trunks → Thoracic duct & right lymphatic duct

  • Clinical: Lymphatic obstruction → edema; important in cardiac surgery

5. Hemodynamics

  • Flow (Q) = ΔP / R, Resistance ∝ viscosity × length / radius⁴

  • MAP = CO × TPR

  • Pulmonary circulation: Low pressure, high compliance

Regulation: Preload, afterload, contractility, venous return



6. ECG & Electrophysiology

  • P: atrial depol

  • QRS: ventricular depol

  • T: ventricular repol

  • Intervals: PR (0.12–0.2 s), QT, RR

  • Vectors: Lead orientation, axis determination

  • Clinical: STEMI changes, bundle branch blocks

7. Common Clinical Correlations

  • Angina/MI, heart failure, valvular diseases, arrhythmias, pericardial effusion

8. MCQs

  1. SA node location? → Right atrium

  2. Frank-Starling law? → Ventricular filling vs SV

  3. Most common MI site? → LAD

  4. Phase with semilunar valves open? → Ejection



Please give your opinions.


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Cardiovascular System

  1. Heart Anatomy – In-Depth 1.1 External Anatomy Located in the middle mediastinum , apex pointing to 5th intercostal space midclavicular line Surfaces: Sternocostal : RA & RV predominantly Diaphragmatic : LV and some RV Pulmonary (left) : LV impression on left lung Borders: Right: RA Left: LV and auricle Superior: Base – LA and great vessels Pericardium: Fibrous pericardium : tough outer layer, attached to diaphragm and sternum Serous pericardium: Parietal layer: lines fibrous pericardium Visceral layer (epicardium): on heart surface Pericardial cavity:  15–50 mL of lubricating fluid Clinical correlation:  Pericardial effusion → cardiac tamponade; auscultation changes 1.2 Internal Anatomy Chambers & Wall Thickness: | Chamber | Wall Thickness (mm) | Relative Function ||---------|-------------------|-----------------|| RA | 2–3 | Low pressure reservoir || RV | 3–5 | Pumps to pulmonary circulation || LA | 2–4 | Receives pulmonary venous blood || LV | 8–12 | Pump...
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