Respiratory Physiology Quiz

Respiratory Physiology

• Respiratory system exchanges O₂ and CO₂
• Body cells need 200 ml O₂/min
• Gas exchange: O₂ enters blood, CO₂ leaves
• Regulation of blood pH: Altered by blood CO₂ levels
• Voice production: Air movement through vocal folds creates sound
• Olfaction: Airborne molecules detected in nasal cavity
• Protection: Prevents and removes microorganisms

Respiratory System

• Upper respiratory system: Nose, nasal cavity, oral cavity, pharynx, larynx, paranasal sinuses
• Conducting zone: Nose, pharynx, larynx, trachea, bronchi, bronchioles, terminal bronchioles
• Respiratory zone: Respiratory bronchioles, alveolar ducts, alveolar sacs, alveoli (300 million)
• Conducting zone function: Filter, warm, and moisten air; conduct into lungs. Volume is 150 ml
• Respiratory zone function: Main sites for gas exchange between blood and air. Increased surface area (70 m²). Volume is 5-6 liters
• Non-respiratory functions: route for water loss and heat, enhance venous return, maintenance of acid-base balance, enables vocalization, defense against foreign matter

Functional Parts of Respiratory System

• The respiratory zone: tissues within the lungs for gas exchange
• The conducting zone: Series of interconnected tubes and cavities that bring inhaled air into the lungs.
  • Nose
  • Pharynx
  • Larynx
  • Trachea
  • Bronchi
  • Bronchioles
  • Terminal bronchioles
• Alveoli: Cup shaped outpouching. The walls are lined with simple squamous epithelium
  • 300 million alveoli, providing surface area of 70 m²
  • Alveolar sacs are groups of alveoli that share a common opening
  • Type I alveolar cells: continuous lining for gas exchange
  • Type II alveolar cells: Septal cells that secrete alveolar fluid (surfactant)
  • Alveolar macrophages (dust cells)
• The respiratory membrane: 4 layers. simple squamous epithelium, epithelial basement membrane, capillary basement membrane, capillary endothelium. The gas exchange takes place across the respiratory membrane.

Alveoli

• Alveolus: Cup shaped outpocket lined by simple squamous epithelium, with an elastic basement membrane. 300 million alveoli providing a large surface area of 70 m².
• Alveolar Sac: Consists of two or more alveoli that share a common opening.
• Two types of alveolar cells: Type I (lining for gas exchange), and Type II (septal cells that secrete surfactant)
• Surfactant: Mixture of phospholipids and lipoproteins to reduce surface tension, preventing alveoli collapse
• Alveolar macrophages (dust cells): Engulf foreign particles.

Three Basic Steps of Respiration

• Pulmonary ventilation: Movement of air in and out of lungs (inspiration and expiration)
• External respiration: Gas exchange between the lungs and blood
• Internal respiration: Gas exchange between blood and tissues

Pulmonary Ventilation

• Mechanical process with volume change in the thoracic cavity leading to pressure change; pressure and volume have inverse relationship
• Volume change leads to pressure change, and forces gases to move from area of higher pressure to area of lower pressure.
• Inhalation: Increased lung volume, decreased pressure, causing air to flow into the lungs.
• Expiration: Decreased lung volume, increased pressure, causing air to flow out of the lungs.
• Muscles involved in ventilation: Diaphragm and external intercostals muscles during inspiration, and internal intercostals and abdominal muscles during expiration.

Inhalation and Exhalation (Mechanics)

• Lungs expand and contract in two ways:
• Downward/upward diaphragm movement to lengthen/shorten chest cavity
• Elevation/depression of ribs to increase/decrease anteroposterior diameter

Muscles involved in ventilation

• Inspiration: Diaphragm contracts, external intercostals contract

• Expiration: Diaphragm relaxes, internal intercostals contract, abdominals contract (active exhalation)

Inhalation

• Expansion of the lungs increases lung volume, creating lower pressure than the atmosphere which leads to air in the lungs
• Diaphragm (innervated by phrenic nerves): Pulls lower lung surfaces downward
• External intercostals: Elevate ribs and sternum
• Increase in volume in thoracic cavity

Exhalation

• Passive process due to the elastic recoil of the chest wall and lungs.
• Recoil of elastic fibers stretched during inhalation
• Inward pull of surface tension in alveoli fluid
• Pressure in lungs is higher than atmospheric pressure, causing air to leave the lungs

Pulmonary Pressure

• Atmospheric pressure: 760 mmHg.
• Intrapleural pressure: Pressure in the space between the lung pleura and chest wall. Normally ~754 mm Hg (negative pressure)
• Alveolar pressure: Pressure inside the alveoli. At rest, it's equal to atmospheric pressure (760 mm Hg). During inspiration, it's slightly lower than atmospheric pressure; during expiration, it's slightly higher than atmospheric.
• Transpulmonary pressure: Difference between alveolar pressure and intrapleural pressure. keeps the lungs inflated

Pressure Changes in Pulmonary Inhalation

• At rest, alveolar pressure = 760 mmHg and intrapleural pressure = 756 mmHg
• During inhalation, alveolar pressure decreases slightly to about 758 mmHg while the intrapleural pressure also decreases to about 754 mmHg - creating a negative pressure.

Pressure Changes During Pulmonary Exhalation

• During exhalation, alveolar pressure increases slightly to 762 mmHg and intrapleural pressure increases very slightly to 756 mmHg

Three types of breathing

• Eupnea (Quiet breathing): Diaphragm and internal/external intercostals
• Hyperpnea (Forced breathing): Involvement of accessory muscles
• Apnea (No breathing)

Factors Affecting Pulmonary Ventilation

• Surface tension of alveolar fluid.
• Compliance of lungs.
• Airway resistance

Role of Surfactant

• Reduces surface tension & prevents alveolar collapse
• Secreted by Type II alveolar cells
• Composed of phospholipids, surfactant apoproteins, and calcium ions

Role of Alveoli Diameter

• Blocked airway increases surface tension, leading to lung collapse
• Pressure generated in an alveolus is proportional to surface tension divided by radius

Effect of Alveolar Radius

• Smaller alveolar radius increases alveolar pressure due to surface tension
• Small premature babies show surfactant deficiency causing lung collapse; called Respiratory distress syndrome of the newborn

Spirometry

• Records changes in pulmonary volume; rises and falls of a drum create a recording on a moving sheet; lung has 4 volumes and 4 capacities.

Pulmonary Volumes

• Tidal volume: Amount of air inspired or expired during normal breathing
• Inspiratory reserve volume: Extra air inspired above tidal volume
• Expiratory reserve volume: Extra air expired by forceful exhalation after normal exhalation
• Residual volume: Amount of air remaining in lungs after forceful exhalation.
• Other important measurements: Inspiratory capacity, functional residual capacity, vital capacity, total lung capacity

Lung Volumes

• Minute Ventilation: Total volume of air inhaled and exhaled per minute.
• Alveolar Ventilation Rate: Volume of fresh air reaching the alveoli per minute.

Pulmonary Capacities

• Inspiratory capacity: Maximum amount of air that can be inhaled after a normal exhalation
• Functional residual capacity: Maximum amount of air that can remain in lungs after a normal exhalation
• Vital Capacity: Maximum amount of air that can be exhaled after maximum inhalation
• Total lung capacity: Maximum amount of air the lungs can hold.

Restrictive vs. Obstructive Lung Disease

• Restrictive: Reduced lung expansion; decreased total and inspiratory lung capacity, and decreased RV (residual volume).
• Obstructive: Decreased expiratory flow in lungs; increased total lung capacity, increased residual volume.

FVC vs. FEV

• FVC (Forced Vital Capacity): Total volume of air exhaled with forceful effort.
• FEV1 (Forced Expiratory Volume in 1 second): Volume of air exhaled in the first second of forceful exhalation.

Dead Space Air

• Air in the conducting zone is called dead space air.
• Volume of dead space air is about 150 ml in young adults.

Nervous Stimulation

• Bronchial tree is responsive to norepinephrine and epinephrine.
• Sympathetic stimulation leads to bronchodilation.
• Parasympathetic stimulation leads to bronchoconstriction.
• Acetylcholine (parasympathetic) leads to vasoconstriction
• Atropine blocks release of acetylcholine to relieve the obstruction.

Airway Resistance

• Sympathetic motor neurons cause bronchodilation to decrease airway resistance, and increase air flow.
• Parasympathetic motor neurons cause bronchoconstriction to increase airway resistance, and decrease air flow.
• Substances like histamine and nicotine released by mast cells cause bronchoconstriction and airway obstruction.

Gas Exchange

• Gas exchange across respiratory membrane is efficient due to:
• Difference in partial pressure
• Small diffusion distance
• Lipid-soluble gases
• Large surface area of alveoli
• Coordination of blood flow and air flow

Basic Laws of Gas Exchange

• Dalton's law: The partial pressure of each gas in a mixture is directly proportional to its percentage in the mixture.
• Henry's law: When a mixture of gases is in contact with a liquid, each gas will dissolve in the liquid in proportion to its partial pressure and its solubility coefficient.
• Gases in air have different solubility in blood; carbon dioxide is most soluble, followed by oxygen, and nitrogen is the least soluble

Alveolar Gas Exchange

• Partial pressures of gases (e.g., O₂ and CO₂) drive gas movement.
• Gas diffuses from a region of high partial pressure to a region of low partial pressure.

Gas Exchange in the Body

• External respiration (pulmonary): O₂ absorbed from alveoli into blood and CO₂ expelled from blood into alveoli.
• Internal respiration (systemic): O₂ moves from blood into tissue cells and CO₂ moves from tissue cells into blood.

Transport of Oxygen

• In resting humans, 250 ml of O₂ is utilized per minute; 100 ml of oxygenated blood contains 20 ml of O₂.
• 1.5% O₂ dissolved in plasma.
• 98.5% O₂ bound to hemoglobin (Hb) within red blood cells.

Transport of Carbon Dioxide

• In resting humans, 200 ml of CO₂ is produced per minute.
• 100 ml of deoxygenated blood contains 53 ml of CO₂.
• 7% dissolved in plasma
• 23% bound to hemoglobin
• 70% transported as bicarbonate ions (HCO₃⁻)

Factors Affecting Oxygen Dissociation

• Acidity (pH)
• Partial pressure of CO₂
• Temperature
• 2,3-Biphosphoglycerate (BPG)

CO Poisoning

• CO binds to hemoglobin with a higher affinity than oxygen.
• Disrupts oxygen transport and can lead to death if not treated.

Respiratory Acidosis and Alkalosis

• Acidosis: Low blood pH due to increased CO₂ or other acids.
• Alkalosis: High blood pH due to decreased CO₂ or other acids.

Metabolic Acidosis and Alkalosis

• Metabolic acidosis: Low blood pH due to metabolic factors (e.g., kidney failure).
• Metabolic alkalosis: High blood pH due to metabolic factors (e.g., excessive vomiting).

Regulation of Respiration

• Involuntary control: Chemoreceptors (central and peripheral) and inflation reflex.
• Voluntary control: Cerebral cortex.

Chemoreceptors

• Central chemoreceptors: Located in the medulla oblongata, sensitive to changes in H+ concentration or pCO2 in the cerebrospinal fluid.
• Peripheral chemoreceptors: Located in the carotid and aortic bodies, sensitive to changes in arterial pO2, pCO2, and H+ ion concentration.

Chemical Control of Respiration

• Excess CO₂ or H+ ions in the blood stimulate chemoreceptors that trigger an increase/decrease in respiratory rate.
• Oxygen does not directly stimulate the central respiratory center.

Central Chemoreceptors in the Medulla Oblongata

• Sensitive to pH changes in cerebrospinal fluid (CSF)
• CO₂ diffuses into CSF, converts to carbonic acid (H₂CO₃), and dissociates into H⁺ ions and bicarbonate ions (HCO₃⁻).
• Increased pCO₂ leads to increased H⁺, stimulating hyperventilation.
• Decreased pCO₂ leads to decreased H⁺, stimulating hypoventilation.

Direct Chemical Control of Respiratory Center

• A chemosensitive area in the medulla oblongata, detects changes in H⁺ ions and pCO₂
• H⁺ ions directly stimulate the medullary respiratory center.
• Changes in H⁺ concentration have less effect than changes in blood pCO₂

Ventilatory Response to CO₂

• Normal arterial pCO₂ is 40 mmHg.
• Increased pCO₂ (hypercapnia) stimulates both central & peripheral chemoreceptors, leading to an increase in respiratory rate.
• Decreased pCO₂ (hypocapnia) reduces stimulation of chemoreceptors, potentially leading to a decrease in respiratory rate.

Peripheral Chemoreceptors

• Located in carotid and aortic bodies, and respond to changes in arterial pO2, pCO2, and H+.
• pO₂: Sensitive to low pO₂ (hypoxia), leading to increased respiration. Relatively rapid response.
• pCO₂ and H⁺: Sensitive, but less than pO₂

Factors stimulating Peripheral Chemoreceptors

• Decreased arterial pO2 (hypoxia)
• Increased arterial pCO2
• Increased arterial H+ concentration

Ventilatory Response to CO

• Increasing arterial pCO2 elevates acidity, leading to hyperventilation.
• Decreased arterial pCO2 leads to hypoventilation.

Inflation Reflex

• Stretch receptors in the lungs, activated by excessive lung inflation.
• Inhibitory impulses sent to the inspiratory and apneustic areas in the medulla oblongata.
• Prevents over-inflation of the lungs, and helps maintain normal respiration.

Resuscitator

• Used to force air into lungs through a mask or endotracheal tube.
• Modern ones have adjustable positive pressure limits.

Tank Respirator ("Iron Lung")

• Positive pressure valve inflates a diaphragm, causing expiration.
• Negative pressure valve causes air to enter and move the diaphragm outward, causing inspiration.

Ageing and Respiratory System

• Respiratory system efficiency decreases with age due to:
• Rigid chest wall
• Deterioration of elastic tissue in lungs
• Reduced lung compliance
• Reduced alveolar and cilia activity

Test your knowledge on the principles of respiratory physiology, focusing on inhalation and exhalation processes. This quiz covers key concepts such as pressure differences, muscle involvement, and definitions related to breathing. Perfect for students in human biology or physiology classes.