Summary Cardiorespiratory — 2nd year medicine

Anatomy of the heart

Hollow muscular organ located in the mediastinum, between the two lungs.

Internal configuration

4 cavities : 2 atria (top), 2 ventricles (bottom).
Right heart (deoxygenated blood) / left heart (oxygenated blood), separated by the septa.
Atrioventricular valves : tricuspid (right), mitral (left).
Sigmoid valves : pulmonary and aortic.

External configuration & envelopes

Pyramidal shape: base (top), apex (tip, bottom left).
Pericardium : fibro-serous sac surrounding the heart.
Wall: endocardium (internal), myocardium (muscle), epicardium (external).

The LV myocardium is the thickest because it must propel the blood throughout the great circulation at high pressure.

Large vessels & vascularization

The main routes of entry and exit of the blood.

Large ships

Vessel	Origin/endpoint	Blood
Aorta	VG → body	Oxygenated
Pulmonary artery	RV → lungs	Deoxygenated
Pulmonary veins	Lungs → OG	Oxygenated
Vena cava (sup. + inf.)	Body → OD	Deoxygenated

Vascularization of the heart

Coronary arteries (right and left), born from the aorta, irrigate the myocardium.
Venous return through the coronary sinus towards the OD.
Cava system and azygos system for thoracic venous return.

Cardiovascular & lymphoid histology

Microscopic structure of vessels and associated organs.

Wall of vessels (3 tunics)

Intima : internal endothelium.
Media : smooth muscle + elastic fibers (thick in the arteries).
Adventitia : external connective tissue.

Arteries = thick wall, elastic (high pressure); veins = thin wall with valves ; capillaries = simple endothelium (exchanges).

Hematopoietic & lymphoid organs

Bone marrow : hematopoiesis (production of blood cells).
Thymus : maturation of T lymphocytes.
Nodes, spleen, MALT : secondary lymphoid organs (immune response).

Electrophysiology & ECG

The electrical activity that controls contraction.

The nodal tissue (conduction system)

Sinus node

Pacemaker, in the OD (~70/min).

AV node

Relay with conduction delay.

His bundle

Crosses the septum, 2 branches.

Purkinje

Distribution to the ventricles.

Properties of the heart: automatism, excitability, conductivity, contractility. The heart beats alone (automatism), modulated by the autonomic nervous system.

ECG

P wave : atrial depolarization.
QRS complex : ventricular depolarization.
T wave : ventricular repolarization.

Cardiac cycle & flow

The pump in action: ~0.8 s per cycle at 75 bpm.

Cycle phases

Atrial systole : contraction of the atria (final filling).
Ventricular systole : contraction + ejection (sigmoid valves open).
Diastole : release + filling (AV valves open).

Heart sounds: B1 (closing of the AV valves, start of systole) and B2 (closure of the sigmoid, end of systole).

Cardiac output

Qc = VES × Fc

VES : stroke volume (~70 mL).
FC : heart rate (~70/min).
Flow ≈ 5 L/min at rest.

Blood pressure & its regulation

Force exerted by blood on the artery wall.

Concepts & regulation

PA = Qc × RPT

Systolic BP (~120 mmHg) / diastolic (~80 mmHg).
RPT = total peripheral resistance (arteriole caliber).
Nervous regulation rapid: baroreceptors → autonomic nervous system.
Hormonal regulation slow: renin-angiotensin-aldosterone system, ADH.

The coronary circulation nourishes the myocardium especially during diastole (the contracted muscle compresses its own vessels in systole).

Respiratory anatomy

Airways and organs of hematosis.

Tracheobronchial tree

Trachea → 2 stem bronchi (keel).
Right bronchus more vertical and wide (foreign bodies).
Bronchi → bronchioles → alveoli.

Lungs & pleura

Right lung : 3 lobes; left : 2 lobes (cardiac incision).
Pleura : double layer (visceral + parietal), virtual cavity.
Muscles: diaphragm + intercostals.

Respiratory physiology

Ventilatory mechanics, gas exchange and transport.

Ventilatory mechanics

Inspiration : active (diaphragm lowers), volume ↑, pressure ↓ → air enters.
Expiration : mainly passive (pulmonary elasticity).
Volumes: current, reserve, residual; capacities (CV, CPT).

Gas exchanges & transport

Broadcast alveolo-capillary according to pressure gradients.
O₂ : transported especially linked tohemoglobin (Barcroft curve).
CO₂ : especially in the form of bicarbonates.
Ventilation/perfusion ratio (V/Q) : optimizes exchanges.

The breathing is regulated by the bulbopontine centers, sensitive especially to PaCO₂ (via CSF pH) and, incidentally, to PaO₂ (chemoreceptors).