20.3 Cardiovascular, Hematologic, Lymphatic & Respiratory Systems
Key Takeaways
- Blood flows from the venae cavae to the right atrium, tricuspid valve, right ventricle, pulmonary valve, lungs, pulmonary veins, left atrium, mitral valve, left ventricle, aortic valve, and out the aorta.
- Arteries carry blood away from the heart and veins carry it toward the heart; the pulmonary artery is the one artery carrying deoxygenated blood and the pulmonary veins the only veins carrying oxygenated blood.
- The lymphatic system returns interstitial fluid to circulation, absorbs dietary fat through intestinal lacteals, and houses the immune tissue of the nodes, spleen, thymus, and tonsils.
- External respiration exchanges oxygen and carbon dioxide across the alveolar-capillary membrane, while internal respiration exchanges them between systemic capillaries and tissue cells.
- Chronic obstructive pulmonary disease obstructs airflow out of the lungs and is largely irreversible, while asthma is characterized by reversible bronchoconstriction and inflammation.
Cardiovascular System
Normal structure and function
The heart has four chambers — two thin-walled atria that receive and two muscular ventricles that pump — separated by the interatrial and interventricular septa. Its wall has three layers: endocardium (inner lining), myocardium (contractile muscle), and epicardium, with the whole organ enclosed in the pericardium.
Four valves prevent backflow:
| Valve | Location | Also called |
|---|---|---|
| Tricuspid | Right atrium → right ventricle | Right atrioventricular |
| Pulmonary | Right ventricle → pulmonary artery | Pulmonic semilunar |
| Mitral | Left atrium → left ventricle | Bicuspid, left atrioventricular |
| Aortic | Left ventricle → aorta | Aortic semilunar |
The path of blood is a high-yield sequence: superior and inferior venae cavae → right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary arteries → lungs (gas exchange) → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → systemic circulation.
Vessels. Arteries carry blood away from the heart and have thick elastic muscular walls; arterioles regulate resistance; capillaries are one cell thick and are where exchange occurs; venules and veins carry blood toward the heart and contain valves that prevent backflow against gravity. The exception every exam tests: the pulmonary artery carries deoxygenated blood and the pulmonary veins carry oxygenated blood, because the naming follows direction relative to the heart, not oxygen content.
Conduction. The sinoatrial (SA) node in the right atrium is the natural pacemaker at 60 to 100 beats per minute, followed by the atrioventricular (AV) node (40 to 60), the bundle of His, the right and left bundle branches, and the Purkinje fibers (20 to 40). Coronary arteries — the right and left, the left dividing into the left anterior descending and circumflex — supply the myocardium itself and are the vessels occluded in myocardial infarction.
Blood and hematopoiesis
Blood is about 55 percent plasma (mostly water with albumin, globulins, fibrinogen, electrolytes, and nutrients) and 45 percent formed elements:
- Erythrocytes (RBCs): biconcave, anucleate, carry oxygen bound to hemoglobin; lifespan about 120 days
- Leukocytes (WBCs): immune defense — neutrophils, lymphocytes, monocytes, eosinophils, basophils
- Thrombocytes (platelets): cell fragments initiating hemostasis
All are produced by hematopoiesis in red bone marrow.
Blood typing. The ABO system is defined by antigens on the red cell surface: type A has A antigen and anti-B antibodies, type B has B antigen and anti-A antibodies, type AB has both antigens and no antibodies — the universal recipient, and type O has neither antigen and both antibodies — the universal donor. The Rh factor is a separate antigen; Rh-negative individuals form anti-Rh antibodies only after exposure, which is why an Rh-negative pregnant patient carrying an Rh-positive fetus receives Rh immune globulin to prevent hemolytic disease of the newborn.
Abnormal structure and function
| Condition | Description |
|---|---|
| Hypertension | Persistently elevated arterial pressure; largely asymptomatic; damages heart, brain, kidney, and retina |
| Atherosclerosis | Lipid plaque narrowing and stiffening arteries |
| Angina pectoris | Chest pain from transient myocardial ischemia; relieved by rest or nitroglycerin |
| Myocardial infarction | Coronary occlusion causing myocardial necrosis; crushing chest pain, diaphoresis, dyspnea, radiation to jaw or left arm; women and patients with diabetes present atypically more often |
| Heart failure | Impaired pumping; left-sided causes pulmonary congestion and dyspnea, right-sided causes peripheral edema and jugular distention |
| Arrhythmias | Atrial fibrillation, ventricular tachycardia, ventricular fibrillation, heart block |
| Anemia | Reduced hemoglobin or red cells — iron deficiency (microcytic), B12 or folate deficiency (macrocytic), sickle cell, aplastic |
| Leukemia | Malignant proliferation of leukocytes |
| Deep vein thrombosis | Clot in a deep vein; risk of pulmonary embolism |
| Varicose veins | Incompetent venous valves with dilation and tortuosity |
Lymphatic and Immune System
Lymphatic vessels collect interstitial fluid as lymph and return it to the venous circulation through the thoracic duct and right lymphatic duct. Lymph nodes filter lymph and house lymphocytes; major chains are cervical, axillary, and inguinal. The spleen filters blood and removes aged erythrocytes, the thymus matures T lymphocytes, and the tonsils guard the entrance to the respiratory and digestive tracts. Intestinal lacteals absorb dietary fat, giving the lymphatic system a nutritional as well as immune role.
Immunity is innate (nonspecific — skin, mucous membranes, inflammation, phagocytosis) or adaptive (specific — B lymphocytes producing antibodies for humoral immunity, T lymphocytes for cell-mediated immunity). Adaptive immunity is acquired actively (infection or vaccination, producing memory and lasting protection) or passively (preformed antibodies from maternal transfer or immune globulin, immediate but temporary).
Disorders include HIV/AIDS (destruction of CD4 T lymphocytes), autoimmune disease (lupus, rheumatoid arthritis, Hashimoto thyroiditis), hypersensitivity including anaphylaxis, lymphoma (Hodgkin and non-Hodgkin), and lymphedema, commonly following lymph node dissection — which is why blood pressure measurement and venipuncture are avoided in the affected arm after axillary node surgery.
A patient asks why the pulmonary artery is called an artery when the blood inside it has not yet been oxygenated. What is the correct explanation?
Respiratory System
Normal structure and function
Air travels through the upper respiratory tract — nose and nasal cavity (warming, humidifying, filtering), pharynx (naso-, oro-, and laryngopharynx), and larynx (voice box, containing the vocal cords and guarded by the epiglottis, which closes during swallowing) — into the lower respiratory tract: the trachea, which bifurcates at the carina into right and left primary bronchi, then bronchioles, and finally the alveoli, the roughly 300 million thin-walled sacs where gas exchange occurs across the alveolar-capillary membrane.
The right lung has three lobes and the left has two, the left being smaller to accommodate the cardiac notch. The right primary bronchus is wider, shorter, and more vertical, which is why aspirated material lodges there preferentially. The lungs are covered by the visceral pleura and the thoracic cavity by the parietal pleura, with a thin layer of pleural fluid between them.
Mechanics. Inspiration is active: the diaphragm contracts and flattens and the external intercostals elevate the ribs, expanding thoracic volume, lowering intrathoracic pressure, and drawing air in. Expiration is normally passive, driven by elastic recoil.
Gas exchange occurs in two places, and the distinction is a recurring exam item:
- External respiration — between the alveoli and the pulmonary capillaries; oxygen enters the blood and carbon dioxide leaves it.
- Internal respiration — between the systemic capillaries and the tissue cells; oxygen enters the cells and carbon dioxide enters the blood.
Control. The medulla oblongata houses the primary respiratory center, and the principal stimulus to breathe in healthy people is a rising arterial carbon dioxide level, not a falling oxygen level. Normal adult respiratory rate is 12 to 20 breaths per minute.
Abnormal structure and function
| Condition | Description |
|---|---|
| Asthma | Reversible bronchoconstriction, airway inflammation, and mucus; wheezing, cough, chest tightness; managed with rescue bronchodilators and controller corticosteroids |
| Chronic obstructive pulmonary disease (COPD) | Largely irreversible airflow obstruction — chronic bronchitis (productive cough) and emphysema (alveolar destruction, air trapping, barrel chest); smoking is the dominant cause |
| Pneumonia | Alveolar infection and consolidation; fever, productive cough, pleuritic pain, crackles |
| Tuberculosis | Mycobacterial infection spread by airborne droplet nuclei; requires an airborne infection isolation room and N95 respirator |
| Pulmonary embolism | Clot obstructing pulmonary arterial flow; sudden dyspnea, pleuritic pain, tachycardia, hypoxemia |
| Pneumothorax | Air in the pleural space causing lung collapse |
| Pleural effusion | Fluid accumulation in the pleural space |
| Cystic fibrosis | Inherited disorder producing thick secretions in lungs and pancreas |
| Sleep apnea | Repeated airflow cessation during sleep; daytime somnolence, cardiovascular risk |
| Upper respiratory infection / influenza / COVID-19 | Common viral illnesses; droplet precautions per current guidance |
Terminology to distinguish: dyspnea (difficult breathing), orthopnea (dyspnea when lying flat), apnea (absence of breathing), tachypnea (rapid rate), bradypnea (slow rate), hypoxia (inadequate tissue oxygen), hypoxemia (low arterial oxygen), cyanosis (bluish discoloration from deoxygenated hemoglobin), and hemoptysis (coughing blood).
The asthma-versus-COPD contrast — reversible versus largely irreversible obstruction — is the most heavily tested respiratory distinction, and it is what spirometry before and after a bronchodilator is performed to demonstrate.
A patient undergoing spirometry shows an obstructive pattern that improves substantially after administration of an inhaled bronchodilator. Which condition does this reversibility most support?
A patient had an axillary lymph node dissection on the right side following breast cancer surgery. What precaution applies during her office visit?