The Respiratory System

Major Function of the Respiratory System

The primary function of the respiratory system is to supply the body with oxygen and remove carbon dioxide, a waste product of metabolism. This process is essential for cellular respiration and energy production.

• Oxygen Intake: Delivers oxygen to the blood for distribution to body cells.

• Carbon Dioxide Removal: Eliminates CO2 produced by cellular metabolism.

Processes of Respiration

Respiration involves four main processes that collectively ensure gas exchange between the atmosphere and body tissues:

1. Pulmonary Ventilation: Movement of air into and out of the lungs (breathing).

2. External Respiration: Exchange of gases between the lungs and the blood.

3. Transport of Gases: Movement of oxygen and carbon dioxide between the lungs and tissues via the blood.

4. Internal Respiration: Exchange of gases between systemic blood vessels and tissues.

Upper and Lower Respiratory Organs

• Upper Respiratory Tract: Nose, pharynx (naso-, oro-, and laryngo-), larynx

Larynx: Voice box, houses vocal folds, and is surrounded by cartilage

• Provides an open airway, routes food and air into proper channels, and handles voice production.

  • Epiglottis is made of elastic cartilage and covers laryngeal inlet during swallowing

  • Vocal folds contain vocal ligaments (true vocal cords) and elastic fibers. The glottis is the opening between vocal folds

  • Vestibular folds (false vocal cords) are superior to vocal folds and help close glottis

Voice Production

• Speech: intermittent release of air during opening and closing of glottis

• Pitch: determined by length and tension of vocal cords

• Loudness: determined by force of air

• Lower Respiratory Tract: Trachea, bronchial tree, lungs

Trachea: extends from larynx to behind the heart

• Walls are composed of;

  • Mucosa: epithelial tissue with goblet cells

  • Submucosa: connective tissue with seromucous glands with cartilage rings to prevent collapse

  • Adventitia: Outermost layer, made of connective tissue

Bronchial Tree: Consists of branching airways that conduct air to the alveoli. Major branches include:

• Primary Bronchus (divides trachea into left and right) → Secondary Bronchus (Splits into three on the right and two on the left) → Segmental Bronchus (divides repeatedly) → Bronchioles → Terminal Bronchioles (Smallest of branches) → Respiratory Bronchioles → Alveolar Ducts → Alveoli

Conducting Zone vs. Respiratory Zone

• Conducting Zone (Bronchi to Bronchioles) : Includes all respiratory passageways that provide conduits for air to reach the sites of gas exchange. No gas exchange occurs here. Support structures, Epithelium, and the amount of smooth muscle change here

• Respiratory Zone: Site of gas exchange; includes respiratory bronchioles, alveolar ducts, and alveoli.

Alveoli: Tiny air sacs with thin walls and extensive capillary networks, site of gas exchange, respiratory membrane with blood air barrier made of alveolar and capillary walls.

• Alveolar walls are made of type 1 alveolar cells (squamous epithelium) and type 2 alveolar cells (scattered cuboidal) that secrete antimicrobial protiens

• Contain alveolar macrophages

Lungs

• Cardiac notch is the concavity for the heart to fit on left side

• Mostly composed of alveoli; the rest is made of stroma and elastic connective tissue

  • makes lungs elastic to allow for expasion and recoil

• Pulmonary Circulation

  • Pulmonary arteries deliver de-oxygenated blood from the heart to lungs

  • Pulmonary veins carry oxygenated blood from lungs back to the heart

• Bronchial Circulation

  • Bronchial arteries provide oxygenated blood to lung tissue

  • pulmonary veins carry most de-oxygenated blood back to the heart

The Pleurae

• Visceral Pleura: Covers the lungs.

• Parietal Pleura: Lines the thoracic cavity.

• Pleural Cavity: Space between pleurae containing lubricating fluid to reduce friction during breathing.

Homeostatic Imbalances

• Laryngitis: Inflammation of the larynx, often causing voice loss.

• Rhinitis: Inflammation of the nasal mucosa.

• Pleurisy: Inflammation of the pleurae, causing painful breathing.

Respiratory Physiology

Pulmonary Ventilation

Pulmonary ventilation consists of inspiration (air in) and expiration (air out). It is driven by pressure changes in the thoracic cavity.

• Inspiration: Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing intrapulmonary pressure, drawing air in. Active Process

• Expiration: Muscles relax, thoracic volume decreases, pressure increases, pushing air out. Normally a passive process

Relevant Gas Law:

Boyle's Law: The pressure of a gas varies inversely with its volume at constant temperature.

• If the amount of gas stays the same and the size of the container is reduced, the pressure will increase

Volume-Pressure Relationship: As lung volume increases, pressure decreases, and vice versa.

Gas Exchange

• Dalton’s Law: The total pressure exerted by a mixture of gases is equal to the sum of the pressures exerted by each gas independently. Partial Pressure, pressure exerted by each gas

  • at high altitude partial pressure declines, at lower altitudes, the partial pressure increases

• Henry’s Law: The amount of gas that dissolves in a liquid is proportional to its partial pressure and solubility.

External Respiration: Gas exchange across respiratory membranes.

• Influenced by partial pressure gradients and gas solubility

  • Steep partial pressure gradient for oxygen between blood and lungs, drives oxygen flow into blood

  • Carbon monoxide diffuses in equal amount with oxygen because carbon monoxide is more soluble in plasma and alveolar fluid

• Influenced by thickness and surface area of respiratory membrane

  • Thickness of walls can affect the amount of oxygen that is able to pass through

  • Reduction of surface area, such as the breakdown of alveoli or tumors, can block effective gas flow

Internal Respiration: Gas exchange between blood and tissues, driven by partial pressure gradients.

• Influenced by partial pressure gradients

  • Pressure gradients are reversed, oxygen moves from blood to tissues and carbon dioxide moves from tissues to blood

Gas Transport

Oxygen Transport

• Transport Mechanisms:

  • 98.5% bound to hemoglobin (as oxyhemoglobin) in red blood cells

  • 1.5% dissolved in plasma

• Partial Pressure of Oxygen: High amount of pressure in alveoli and arterial blood; low in tissues and venous blood. The higher the partial pressure, the more oxygen will bind to hemoglobin. In low pressure areas, the hemoglobin will release the oxygen.

  • Higher temperature, higher partial pressure of carbon dioxide, higher level of acidity, and BPG denature hemoglobin, causing it to release oxygen.

• Types of Hypoxia: Anemic (low RBC), ischemic (impaired circulation), histotoxic (cells unable to use oxygen), hypoxemic (abnormal ventilation)

Carbon Dioxide Transport

• Transport Mechanisms:

  • 7-10% dissolved in plasma

  • 20% bound to hemoglobin (as carbaminohemoglobin)

  • 70% as bicarbonate ions (HCO3-) in plasma

• Partial Pressure of CO2: High in tissues and venous blood; low in alveoli and arterial blood.

• Imbalances: Excess CO2 leads to respiratory acidosis; too little leads to alkalosis. Affects pH

  • The rate of your breathing is a major factor in the carbon dioxide level in your blood.

Lung Diseases (General Descriptions)

• Obstructive Diseases: Asthma, chronic bronchitis, emphysema, Chronic Obstructive Pulmonary Disease (COPD)

  • Asthma is characterized by coughing, wheezing, chest tightness, and gasping. Is the acute inflammation of airway passages

  • Chronic Bronchitis is characterized by excessive mucus that can cause inflammation and obstructed airways. Caused by inhaled irritants

  • Emphysema is characterized by the enlargement of alveoli and destruction of alveolar walls that decreases lung elasticity. Reduces ventilation efficiancy.

  • COPD is characterized by the irreversible decrease in ability to force air out of the lungs. Often caused from smoking, can cause labored breathing (dyspnea), coughing, or hypoventilation

• Infectious Diseases: tuberculosis

  • Tuberculosis is caused by bacterium and can cause fever, night sweats, weight loss, racking cough, and coughing up blood

• Lung Cancer: Leading cause of cancer deaths in North America. 90% of cases resulted from smoking

  • Adenocarcinoma originates in peripheral lungs; develops from bronchial glands and alveolar cells (~40% of cases)

  • Squamous cell carcinoma arises in bronchial epithelium and tends to form masses that may hollow out and bleed (~20-40% of cases)

  • Small cell carcinoma contains lymphocyte-like cells that originate in primary bronchi forming small clusters that sperad throughout the body (~20%)

Blood

General Functions of Blood

• Transport of gases, nutrients, hormones, and wastes

• Regulation of pH, temperature, and fluid volume

• Protection against blood loss (clotting) and infection (immune response)

Components of Blood

• Plasma: Liquid matrix (about 55% of blood volume), contains water, proteins, nutrients, hormones, and waste products.

• Formed Elements:

  • Erythrocytes (Red Blood Cells): Transport oxygen and carbon dioxide; regulated by erythropoietin in response to hypoxia.

  • Leukocytes (White Blood Cells): Defend against pathogens; types include neutrophils, lymphocytes, monocytes, eosinophils, basophils.

  • Platelets (Thrombocytes): Cell fragments involved in clotting.

Phases of Hemostasis

1. Vascular Spasm: Vasoconstriction to reduce blood flow.

2. Platelet Plug Formation: Platelets adhere to exposed collagen and aggregate.

3. Coagulation: Fibrin mesh forms, stabilizing the clot.

Blood Grouping (Types)

• Agglutinogens: Antigens on the surface of RBCs (determine blood type).

• Agglutinins: Antibodies in plasma that react with foreign agglutinogens.

• ABO Types: A, B, AB, O (based on presence/absence of A and B agglutinogens).

• Transfusions: Incompatible transfusions cause agglutination and hemolysis.

• Rh Factor: Presence (+) or absence (−) of D antigen; Rh− individuals can develop anti-Rh antibodies after exposure.

• Pregnancy: Rh incompatibility can cause hemolytic disease of the newborn if mother is Rh− and fetus is Rh+.

The Heart

Pulmonary and Systemic Circuits

• Pulmonary Circuit: Right side of heart pumps deoxygenated blood to lungs for oxygenation.

• Systemic Circuit: Left side pumps oxygenated blood to body tissues.

General Structure of the Heart

• Coverings: Pericardium (fibrous and serous layers)

• Chambers: 2 atria (receiving), 2 ventricles (pumping)

• Valves: Atrioventricular (tricuspid, mitral) and semilunar (pulmonary, aortic)

Pathway of Blood Through the Heart

1. Right atrium → tricuspid valve → right ventricle → pulmonary valve → pulmonary arteries → lungs

2. Lungs → pulmonary veins → left atrium → mitral valve → left ventricle → aortic valve → aorta → body

Cardiac Muscle Fibers

• Striated, branched, interconnected by intercalated discs

• Supplied by coronary arteries; rely on aerobic metabolism

Electrical Events of the Heart

• Sequence of Excitation: SA node → AV node → AV bundle (bundle of His) → bundle branches → Purkinje fibers

• Electrocardiogram (ECG): Records electrical activity; main features are P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization)

Mechanical Events of the Heart (Cardiac Cycle)

• Phases: Atrial systole, ventricular systole, diastole

• Heart Rate Regulation: Autonomic nervous system, hormones, ions, fitness level, age

Homeostatic Imbalances

• Myocardial Infarction: Heart attack due to blocked coronary artery

• Fibrillation: Uncoordinated contraction of heart muscle

Blood Vessels

Tunics of Blood Vessels

• Tunica Intima: Endothelial layer lining the lumen

• Tunica Media: Smooth muscle and elastic fibers (controls vasoconstriction/dilation)

• Tunica Externa: Connective tissue for support and protection

Types of Blood Vessels

• Arteries:

  • Elastic Arteries: Large, near the heart, withstand pressure fluctuations

  • Muscular Arteries: Distribute blood to organs, more smooth muscle

  • Arterioles: Smallest arteries, control blood flow into capillaries

• Capillaries:

  • Continuous: Most common, uninterrupted lining

  • Fenestrated: Pores for increased permeability (kidneys, intestines)

  • Sinusoidal: Large gaps, allow passage of large molecules (liver, spleen)

• Veins: Thin walls, large lumens, valves to prevent backflow

Capillary Exchange and Pressures

• Exchange occurs via diffusion, filtration, and osmosis

• Driven by hydrostatic and osmotic pressures

Pulse and Blood Pressure

• Pulse: Rhythmic expansion of arteries due to heartbeats

• Blood Pressure: Force exerted by blood on vessel walls; measured as systolic/diastolic (e.g., 120/80 mmHg)

• Factors Influencing Blood Pressure: Cardiac output, blood volume, resistance, vessel elasticity

Example: During exercise, increased CO2 production leads to increased breathing rate (respiratory system), increased heart rate (cardiovascular system), and increased oxygen delivery to muscles (blood system).

Additional info: Academic context and explanations have been expanded for clarity and completeness based on standard Anatomy & Physiology textbooks.