2nd year · Cardiorespiratory apparatus

The rib cage has 12 pairs of ribs: 7 pairs of true ribs (vertebro-sternal), 3 pairs of false ribs (vertebro-chondral) and 2 pairs of floating ribs.

The sternum is the flat, odd, median bone located in the anterior part of the thorax; it articulates with the clavicles and the first seven costal cartilages.

Laterally, the mediastinum is limited by the two mediastinal pleurae. The sternum limits it in front, the dorsal spine behind, and the diaphragm below.

The septum primum then the septum secundum partition the primitive atrium, providing the foramen ovale which ensures the right-left fetal shunt.

The aorticopulmonary septum, with a spiral arrangement, divides the common arterial trunk into the aorta and the pulmonary trunk.

The heart is shaped like a triangular pyramid with the base looking backwards and the top (apex) looking forward, down and to the left.

The mitral (left atrioventricular) valve is bicuspid; the tricuspid valve (right) has three cusps.

The sinus node is located in the wall of the right atrium, at the junction with the superior vena cava; it is the physiological pacemaker of the heart.

The myocardium is the thickest muscular layer responsible for contraction. The endocardium lines the interior and the epicardium (visceral pericardium) covers the surface.

The aorta arises from the left ventricle: ascending aorta, then arch (aortic arch), then descending thoracic aorta.

The right and left coronaries arise from the aortic sinuses (of Valsalva) located at the origin of the ascending aorta, just above the aortic valve.

Cardiac venous drainage occurs mainly through the coronary sinus, located in the posterior coronary sulcus, which empties into the right atrium.

The larynx is considered the transition: above are the upper airways (nasal passages, pharynx) and below are the lower airways (trachea, bronchi).

The turbinates (upper, middle, lower) are bony reliefs of the lateral wall of the nasal cavity, delimiting the meatus.

The thyroid cartilage, forming the 'Adam's apple', is the largest of the laryngeal cartilages; the cricoid is ring-shaped and the epiglottis closes the vestibule during swallowing.

The right main bronchus is wider, shorter and more vertical than the left; inhaled foreign bodies lodge there more readily.

The tracheal bifurcation (carina) gives rise to the two main right and left bronchi.

The diaphragm is the main inspiratory muscle; its contraction lowers the phrenic center and increases thoracic volume. The abdominals are accessory expirators.

The pulmonary trunk emerges from the right ventricle and carries deoxygenated blood to the lungs via the pulmonary arteries.

A, C, and D are correct: the mediastinum contains the heart, great vessels, trachea, main bronchi, esophagus, nerves, and thoracic duct. B is false: the lungs occupy the lateral pleuropulmonary compartments, outside the mediastinum.

A, B and D are correct: the coronary groove separates the atria and ventricles, the interventricular grooves house the interventricular arteries, and all of the grooves house the coronary vessels surrounded by fat. This is false: the ascending aorta arises from the left ventricle and is not located in the coronary groove.

A, B and C are correct: the right ventricle receives the tricuspid valve, the cusps of which are connected to the pillars by the chordae tendineae. D is false: the mitral valve belongs to the left heart.

A, B and C are correct: the external fibrous pericardium surrounds a serous pericardium with two layers delimiting a virtual cavity with lubricating liquid. D is false: it is the visceral layer of the serous (epicardium) which is attached to the myocardium, not the fibrous pericardium.

A, B and C are correct: the aortic arch gives, from right to left, the brachiocephalic trunk, the left common carotid and the left subclavian. D is false: the coronaries arise from the ascending aorta (sinus of Valsalva), not from the arch.

A, B and C are correct: the left coronary artery arises from the left sinus and divides into the anterior descending (IVA) and circumflex, mainly supplying the left ventricle. D is false: the sinus node artery most often arises from the right coronary artery.

A, B, and D are correct: the SVC drains the upper territory, the IVC the lower territory, and the azygos system drains the chest walls by emptying into the SVC. This is false: the venae cavae end in the right atrium, not the left.

A, B and C are correct: the right lung has 3 lobes (upper, middle, lower), the left 2 lobes (upper, lower), the left upper lobe presenting the lingula (equivalent to the middle lobe). D is wrong: it is the right lung which has 3 lobes.

A, B and C are correct: the pleura is a serosa with two layers; the visceral adheres to the lung, and the virtual pleural cavity is the seat of negative pressure favoring pulmonary expansion. D is false: it is the visceral layer, and not the parietal, which covers the parenchyma.

The heart derives from the splanchnic mesoderm. Cardiogenic cells first form two endocardial tubes which fuse in the midline to form the primitive heart tube. This tube has several downstream segments upstream: the sinus venosus, the primary atrium, the primary ventricle, the cardiac bulb and the truncus arteriosus. It then undergoes plication (cardiac loop or bulbo-ventricular loop) to the right, then partitioning of the atrium (septum primum and secundum), ventricles (interventricular septum) and truncus arteriosus (spiral aortico-pulmonary septum) resulting in a four-chambered heart.

The heart, contained in the pericardial sac within the middle mediastinum, presents as follows: in front the sternum and the anterior chest wall (with the pleural recesses and the lungs); posteriorly the esophagus, the descending aorta and the dorsal spine; laterally the mediastinal pleura, lungs and phrenic nerves; below the diaphragm (on which the underside of the heart rests); at the top the large vessels (ascending aorta, pulmonary trunk, vena cavae).

The heart wall is made, from the lumen outwards, of the endocardium, the myocardium then the epicardium (visceral layer of the serous pericardium).

The intercalary discs (scalariform striae) provide mechanical anchoring (desmosomes, fascia adherens) and electrical coupling (communicating junctions/gap) between cardiomyocytes.

For comparable caliber, the vein has a thinner wall (underdeveloped media) and a wider lumen than the artery; some veins have valves.

The endocardium, lining the interior of the cardiac cavities, is continuous with the endothelium which borders the lumen of the vessels.

The microcirculation brings together the arterioles, the capillary network and the post-capillary venules, the place of exchanges and local regulation of flow.

The respiratory epithelium is ciliated columnar pseudostratified comprising mucus goblet cells, ensuring muco-ciliary clearance.

The bronchiole is distinguished by the absence of cartilage and glands; its wall contains smooth muscle and a thinning epithelium, with Clara (club) cells.

Like any serosa, the pleura is covered with a simple squamous mesothelium resting on submesothelial connective tissue.

The lower respiratory system derives from a ventral diverticulum of the foregut (endodermis); the endoderm gives the epithelium, the splanchnic mesoderm the connective tissue, the muscle and the cartilage.

Arteriovenous anastomoses cause arteriole and venule to communicate directly by short-circuiting the capillary bed; they are involved in particular in thermoregulation.

The nodal tissue is made of modified cardiomyocytes (nodal cells and conduction fibers) specialized in the genesis and propagation of the impulse.

A, B and C are correct: the vascular wall includes intima, media and adventitia; the large elastic arteries (aorta) have a media rich in elastin, the muscular arteries a media rich in smooth muscle. D is false: the intima is the innermost tunic, the outermost adventitia.

A, B and C are correct: the capillary is made of an endothelium resting on a basal lamina (sometimes with pericytes), available in continuous, fenestrated and discontinuous types, and represents the site of exchanges. D is false: capillaries do not have a thick muscular media.

A, B and C are correct: the trachea has incomplete cartilaginous rings closed posteriorly by the tracheal muscle; the bronchi retain cartilage in plates. D is false: bronchioles are precisely defined by the absence of cartilage.

A, B and C are correct: type I pneumocytes, very flattened, form the exchange surface; type II pneumocytes produce surfactant and serve as stem cells regenerating type I. D is false: it is pneumocytes II, not I, which secrete surfactant.

The alveolar-capillary barrier (air-blood barrier) is extremely thin to facilitate the diffusion of gases. It is made up, from the alveolus towards the capillary, of: the surfactant film; type I pneumocyte (flattened cytoplasm); the basal lamina of the pneumocyte; possibly a fine connective interstice (fused in places); the basal lamina of the capillary endothelium; and the capillary endothelial cell. It is through this barrier that O2 and CO2 diffuse between the alveolar air and the blood.

The sinus node has the highest automatic frequency and imposes its rhythm on the entire heart: it is the dominant pacemaker.

The P wave reflects the depolarization of the atria; the QRS complex ventricular depolarization and the T wave ventricular repolarization.

Ventricular filling occurs during ventricular diastole (relaxation), supplemented by atrial systole at end of diastole.

Cardiac output (L/min) is the product of heart rate (bpm) and stroke volume (mL).

As diastole lasts longer, MAP is estimated by PAd + 1/3 of the pulse pressure (PAs − PAd).

During systole, intramyocardial compression interferes with left coronary flow; perfusion of the left ventricle is therefore mainly diastolic.

The low pressure system (veins, atria, pulmonary circulation) contains most of the blood volume and acts as a capacitive reservoir modulating venous return.

Venous return is favored by the muscular pump (contractions of skeletal muscles with anti-reflux valves), the respiratory pump and venous tone.

Inspiration is active: contraction of the diaphragm increases thoracic volume, lowering alveolar pressure below atmospheric, which creates the incoming air gradient.

Only the fraction of air which reaches the alveoli participates in the exchanges: alveolar ventilation = minute ventilation − ventilation of the dead space.

The gases cross the alveolar-capillary barrier by passive diffusion, from the zone of high partial pressure towards the zone of lower pressure (O2: alveolus → blood; CO2: blood → alveolus).

At rest, alveolar ventilation (~4 L/min) and perfusion (~5 L/min) give an average VA/Q ratio close to 0.8, with regional peak/base variations.

Hemoglobin, contained in red blood cells, reversibly fixes oxygen and ensures its transport; each molecule can bind up to four O2.

The pulmonary circulation operates at low pressure and low resistance, while receiving the full right cardiac output (equal to systemic flow).

A, B and C are correct: phase 0 by incoming sodium current, plateau (phase 2) by incoming calcium current balancing the potassium output, repolarization (phase 3) by K+ output. D is wrong: the plateau depends on calcium, not chlorine.

A, B and C are correct: B1 (mitral and tricuspid closure) opens systole, B2 (aortic and pulmonary closure) marks the start of diastole. D is false: B2 corresponds to sigmoid closure, not to the opening of the A-V valves.

A, B and C are correct: the baroreflex, starting from the carotid and aortic baro-receptors, quickly (seconds) corrects the pressure by sympathetic/parasympathetic modulation. D is false: the renin-angiotensin-aldosterone system is involved in medium and long-term regulation, not immediate.

A, B and C are correct: the tidal volume is mobilized at rest; vital capacity = VC + VRI + ERV; the residual volume cannot be expelled and escapes simple spirometry. D is false: vital capacity does not include residual volume (total lung capacity includes it).

A, B and C are correct: O2 is mainly fixed on hemoglobin (oxyhemoglobin), the HbO2 curve is sigmoidal, and CO2 travels mainly in the form of bicarbonates (and carbamine). D is false: the fraction of O2 dissolved in the plasma is very low.

A, B and C are correct: primary hemostasis (vessel + platelets) forms the white thrombus, coagulation transforms fibrinogen into fibrin consolidating the clot, and fibrinolysis dissolves it secondarily. D is false: fibrin is produced by coagulation, not primary hemostasis.

The stroke volume depends on three major determinants: preload (ventricular filling, end-diastolic volume, according to the Frank-Starling law: the more the ventricle is filled, the more the ejection force increases), contractility (inotropism, state of the myocardial fiber, increased by sympathetic stimulation) and afterload (resistance to ejection, essentially aortic pressure and peripheral resistance; its increase tends to reduce the ejected volume).

PaCO2 is the main stimulus for respiratory regulation. An increase in PaCO2 (hypercapnia) increases the production of H+, particularly in the cerebrospinal fluid after diffusion of CO2 and hydration with carbonic acid. The central chemoreceptors (spinal bulb) are sensitive to this variation in pH/CO2, and the peripheral chemoreceptors (carotid and aortic corpuscles) contribute to it. The response is stimulation of the bulbo-protuberantial respiratory centers, increasing ventilatory frequency and amplitude to eliminate CO2 and return PaCO2 to normal. Conversely, hypocapnia reduces ventilation.

By analogy with Ohm's law, the flow rate Q = ΔP / R: the flow rate is proportional to the pressure difference and inversely proportional to the resistance.

The Reynolds number characterizes the flow regime: low, the flow is laminar; beyond a critical value, it becomes turbulent (source of blasts).

Blood is a non-Newtonian fluid: its viscosity depends in particular on the hematocrit and the shear rate; it is greater than that of water.

The surfactant lowers the surface tension at the air-liquid interface, reduces the work of breathing and prevents the collapse of small alveoli (effect on the Laplace equation).

Compliance C = ΔV/ΔP measures distensibility: high compliance means that a small variation in pressure results in a large variation in volume.

The hydrostatic pressure increases linearly with depth according to P = ρgh; this explains in particular the effect of gravity on venous pressures depending on position.

A, B and C are exact: R = 8ηL / (πr⁴), so the resistance increases with length and viscosity and decreases very strongly with radius (power 4). D is false: color has no physical effect.

A, B and C are exact: Laplace's law (P = 2T/r for a sphere) links pressure, tension and radius; it explains the constraint of the ventricular wall and the tendency of the small alveoli to collapse, stabilized by the surfactant. D is false: the pressure depends precisely on the radius.

A, B and C are correct: Fick's law states that diffusive flux increases with surface area and partial pressure gradient, and decreases with membrane thickness. D is false: the flow depends on the exchange surface.

Poiseuille's law expresses the flow rate Q = ΔP·π·r⁴ / (8·η·L). The radius intervenes to the power of 4, unlike the other factors which are linear. Therefore, if the radius is divided by 2, the flow rate (at constant pressure) is divided by 2⁴ = 16; if it doubles, the flow rate is multiplied by 16. This is why vasomotion (vasoconstriction/vasodilation of the arterioles, which hardly changes the radius) constitutes the most powerful mechanism for adjusting the flow rate and peripheral resistance, much more effective than a variation in pressure or viscosity.

Water movements through the capillary wall result from the balance between hydrostatic and oncotic pressures (Starling's law). At the arteriolar tip, high capillary hydrostatic pressure exceeds the oncotic pressure of plasma proteins, which pushes fluid toward the interstitium (filtration). At the venular end, hydrostatic pressure has fallen and plasma oncotic pressure prevails, drawing fluid toward the capillary (reabsorption). The slight excess filtration is drained by the lymphatic system. An imbalance (hydrostatic hyperpressure or drop in oncotics) promotes edema.

Protection aims to eliminate or remove the danger to avoid further accidents, by ensuring the safety of the rescuer, the victim and witnesses, before any other action.

An effective alert message indicates the exact location, the nature of the situation, the number and condition of victims, and must not be interrupted before the regulator's agreement.

Faced with an unconscious person who is not breathing normally (absence of breathing or gasps), we make the diagnosis of cardio-respiratory arrest and we begin resuscitation.

The AED automatically analyzes the rhythm and indicates/delivers an electric shock in the event of a shockable rhythm (ventricular fibrillation, pulseless ventricular tachycardia), increasing the chance of survival.

During the analysis and delivery of the shock, no one must touch the victim so as not to distort the analysis or risk being electrified.

As long as the cough is effective (partial obstruction), we do not intervene mechanically: we encourage the cough and we monitor closely, ready to act if the obstruction becomes complete.

A, B and C are correct: the action to be taken follows the sequence Protect – Examine – Alert – Rescue. D is false: leaving the scene without taking action is contrary to the role of the first aider.

A, B and C are correct: the center of the thorax is compressed, at 100-120/min, in a 30:2 cycle in adults. D is wrong: compressions must be deep (5-6 cm) and forceful, not superficial.

A, B and C are correct: faced with a total obstruction, alternate 5 back slaps and 5 abdominal compressions (Heimlich) until the obstruction is cleared. D is false: inaction exposes you to asphyxiation.

Respiratory distress is manifested by: difficulty breathing (dyspnea), an abnormal increase or slowdown in respiratory rate, noisy or wheezing breathing, the inability to speak in complete sentences, the use of accessory respiratory muscles (drawing), sweating, agitation or anxiety, and signs of poor oxygenation such as cyanosis (bluish discoloration of the lips and extremities). Faced with these signs, the rescuer places the victim in the position where they breathe best (often sitting), reassures them, loosens their clothing and alerts the emergency services.