Respiratory System (HAP 2) - Handwritten Notes
Download handwritten notes for Human Anatomy and Physiology 2, providing an in-depth look at the Respiratory System. These notes cover the blood-gas interface, conducting airways, lung inflation, inspiration and expiration, respiratory pressures, pulmonary compliance, elastic recoil, surface tension, pulmonary surfactant, airway resistance, lung volumes and capacities, ventilation, gas exchange, ventilation-perfusion matching, oxygen and carbon dioxide transport, and respiratory control mechanisms. Suitable for B.Pharm students. Available in PDF format.
Keywords: Respiratory System, Blood-Gas Interface, Conducting Airways, Lung Inflation, Inspiration, Expiration, Pulmonary Compliance, Elastic Recoil, Surface Tension, Pulmonary Surfactant, Airway Resistance, Lung Volumes, Ventilation, Gas Exchange, V/Q Ratio, Oxygen Transport, Carbon Dioxide Transport, Respiratory Control, Human Anatomy and Physiology, Handwritten Notes, PDF, Download, B.Pharm.
Respiratory System - Detailed Explanation
17.1 Introduction
The cells of the body require a continuous supply of oxygen to produce energy and carry out their metabolic functions. Furthermore, these aerobic metabolic processes produce carbon dioxide, which must be continuously eliminated. The primary functions of the respiratory system include:
- Obtaining oxygen from the external environment and supplying it to the body’s cells
- Eliminating carbon dioxide produced by cellular metabolism from the body
The process by which oxygen is taken up by the lungs and carbon dioxide is eliminated from the lungs is referred to as gas exchange.
17.2 Blood–Gas Interface
Gas exchange takes place at the blood–gas interface, which exists where the alveoli and the pulmonary capillaries come together. The alveoli are the smallest airways in the lungs; the pulmonary capillaries are found in the walls of the alveoli. Inspired oxygen moves from the alveoli into the capillaries for eventual transport to tissues. Entering the lungs by way of the pulmonary circulation, carbon dioxide moves from the capillaries into the alveoli for elimination by expiration. Oxygen and carbon dioxide move across the blood–gas interface by way of simple diffusion from an area of high concentration to an area of low concentration.
According to Fick’s law of diffusion, the amount of gas that moves across the blood–gas interface is proportional to the surface area of the interface and inversely proportional to the thickness of the interface. In other words, gas exchange in the lungs is promoted when the surface area for diffusion is large and the thickness of the interface is small. The lungs are ideally suited for gas exchange because of their large surface area and thin blood-gas interface.
Conducting Airways
The conducting airways include the nose, pharynx, larynx, trachea, bronchi, and bronchioles. Their functions include warming, humidifying, and filtering inspired air. They do *not* participate in gas exchange.
Airway Types (Epithelium and Cartilage)
The epithelium and cartilage change as you move down the respiratory tract:
- Trachea and Bronchi: Pseudostratified ciliated columnar epithelium with goblet cells (produce mucus). C-shaped cartilage rings provide support.
- Bronchioles: Transition to cuboidal epithelium. Cartilage is absent. Smooth muscle is present, allowing for bronchoconstriction and bronchodilation.
Lung Inflation
The lungs are maintained in an inflated state due to several forces and factors:
- Transpulmonary Pressure: The difference between the alveolar pressure (pressure inside the alveoli) and the intrapleural pressure (pressure in the pleural cavity). This pressure difference keeps the lungs expanded.
- Negative Intrapleural Pressure: The pressure in the pleural cavity is normally slightly negative (subatmospheric), which helps to "pull" the lungs outward.
- Elastic Recoil of the Lungs: The lungs have a natural tendency to collapse due to the elastic fibers in their tissues.
- Surface Tension: The force created by the attraction of water molecules at the air-liquid interface in the alveoli, which tends to collapse the alveoli.
- Pulmonary Surfactant: A substance produced by Type II alveolar cells that reduces surface tension, preventing alveolar collapse.
Inspiration and Expiration
- Inspiration (Inhalation): An active process. The diaphragm contracts and flattens, and the external intercostal muscles contract, lifting the rib cage. This increases the volume of the thoracic cavity, decreasing the alveolar pressure below atmospheric pressure. Air flows into the lungs.
- Expiration (Exhalation): Normally a passive process at rest. The diaphragm and external intercostal muscles relax. The elastic recoil of the lungs and chest wall decreases the volume of the thoracic cavity, increasing the alveolar pressure above atmospheric pressure. Air flows out of the lungs. Forced expiration involves contraction of the internal intercostal muscles and abdominal muscles.
Respiratory Pressures
- Atmospheric Pressure: The pressure of the air surrounding the body (around 760 mmHg at sea level).
- Alveolar Pressure (Intrapulmonary Pressure): The pressure inside the alveoli. It fluctuates during breathing, becoming slightly below atmospheric pressure during inspiration and slightly above during expiration.
- Intrapleural Pressure: The pressure in the pleural cavity (the space between the visceral and parietal pleura). It's normally negative (subatmospheric), which helps keep the lungs inflated.
- Transpulmonary Pressure: The difference between the alveolar pressure and the intrapleural pressure. It represents the force that keeps the lungs inflated.
Pulmonary Compliance
Pulmonary compliance is a measure of the lung's ability to stretch and expand. It's defined as the change in lung volume for a given change in transpulmonary pressure. High compliance means the lungs can expand easily; low compliance means the lungs are stiff and resist expansion.
Elastic Recoil and Compliance
The elastic connective tissues in the lungs contribute to both elastic recoil (the tendency of the lungs to return to their resting size after being stretched) and lung compliance. Elastic recoil is due to the elastic fibers and surface tension. Compliance is affected by both the elastic fibers and surface tension.
Surface Tension and Surfactant
Surface tension is the force created by the attraction of water molecules at the air-liquid interface in the alveoli. This force tends to collapse the alveoli. Pulmonary surfactant, produced by Type II alveolar cells, is a mixture of phospholipids and proteins that reduces surface tension. This prevents alveolar collapse, increases lung compliance, and reduces the work of breathing.
Alveolar Interdependence
Alveolar interdependence refers to the mechanical interaction between adjacent alveoli. If one alveolus starts to collapse, the surrounding alveoli are stretched, which helps to pull the collapsing alveolus open. This helps to stabilize alveoli and prevent widespread collapse.
Airway Resistance
Airway resistance is the opposition to airflow in the respiratory tract. Factors that determine airway resistance include:
- Airway Diameter: The most important factor. Smaller diameter = higher resistance. Bronchoconstriction (narrowing of airways) increases resistance; bronchodilation (widening of airways) decreases resistance.
- Lung Volume: At higher lung volumes, airways are wider, reducing resistance.
- Viscosity of Air: Increased viscosity (e.g., due to mucus) increases resistance.
Lung Volumes and Capacities
- Tidal Volume (TV): The amount of air inhaled or exhaled during normal breathing (around 500 mL).
- Residual Volume (RV): The amount of air remaining in the lungs after a maximal exhalation.
- Expiratory Reserve Volume (ERV): The additional amount of air that can be exhaled after a normal expiration.
- Inspiratory Reserve Volume (IRV): The additional amount of air that can be inhaled after a normal inspiration.
- Functional Residual Capacity (FRC): The volume of air remaining in the lungs after a normal expiration (FRC = ERV + RV).
- Inspiratory Capacity (IC): The maximum amount of air that can be inhaled after a normal expiration (IC = TV + IRV).
- Total Lung Capacity (TLC): The total amount of air the lungs can hold (TLC = VC + RV).
- Vital Capacity (VC): The maximum amount of air that can be exhaled after a maximal inhalation (VC = TV + IRV + ERV).
Ventilation
- Total Ventilation (Minute Ventilation): The total volume of air moved in and out of the lungs per minute (TV x respiratory rate).
- Alveolar Ventilation: The volume of air that reaches the alveoli per minute and participates in gas exchange. It's more relevant than total ventilation.
Dead Space
- Anatomical Dead Space: The volume of air in the conducting airways (nose, pharynx, trachea, bronchi, bronchioles) that does *not* participate in gas exchange (around 150 mL).
- Alveolar Dead Space: The volume of air in alveoli that are ventilated but *not* perfused (no blood flow). Normally very small.
- Physiological Dead Space: The sum of the anatomical dead space and the alveolar dead space. It represents the total volume of air that does not participate in gas exchange.
Fick's Law of Diffusion and Gas Exchange
Fick's law of diffusion states that the rate of gas transfer across a membrane is:
- Proportional to the surface area of the membrane.
- Proportional to the partial pressure difference of the gas across the membrane.
- Inversely proportional to the thickness of the membrane.
- Proportional to the diffusion coefficient of the gas.
Partial Pressures of Oxygen and Carbon Dioxide
The partial pressure of a gas is the pressure exerted by that gas in a mixture of gases.
- Alveolar Air: PO2 ≈ 100 mmHg, PCO2 ≈ 40 mmHg.
- Pulmonary Arteries (Deoxygenated Blood): PO2 ≈ 40 mmHg, PCO2 ≈ 46 mmHg.
- Pulmonary Veins (Oxygenated Blood): PO2 ≈ 100 mmHg, PCO2 ≈ 40 mmHg.
- Systemic Arteries (Oxygenated Blood): PO2 ≈ 100 mmHg, PCO2 ≈ 40 mmHg.
- Systemic Veins (Deoxygenated Blood): PO2 ≈ 40 mmHg, PCO2 ≈ 46 mmHg.
- Tissues: PO2 < 40 mmHg, PCO2 > 46 mmHg (due to cellular respiration).
Determinants of Alveolar PO2 and PCO2
- Alveolar PO2: Determined by the PO2 of inspired air, the rate of alveolar ventilation, and the rate of oxygen consumption by the tissues.
- Alveolar PCO2: Determined by the rate of alveolar ventilation and the rate of carbon dioxide production by the tissues.
Ventilation-Perfusion Matching (V/Q Ratio)
For efficient gas exchange, ventilation (airflow) and perfusion (blood flow) in the lungs must be matched. The ideal ventilation-perfusion ratio (V/Q) is close to 1.
- Airway Obstruction: Leads to decreased ventilation (low V/Q).
- Obstructed Blood Flow (e.g., pulmonary embolism): Leads to decreased perfusion (high V/Q).
Local Control Mechanisms to Restore V/Q Ratio
- Low Alveolar PO2 (Hypoxia): Causes vasoconstriction of pulmonary arterioles in that area, diverting blood flow to better-ventilated areas.
- High Alveolar PCO2: Causes bronchodilation, increasing airflow to that area.
Oxygen Transport in the Blood
Oxygen is transported in the blood in two ways:
- Dissolved in Plasma (about 1.5%): A small amount of oxygen is dissolved directly in the plasma.
- Bound to Hemoglobin (about 98.5%): Most oxygen is transported bound to hemoglobin in red blood cells. Each hemoglobin molecule can bind up to four oxygen molecules.
Oxyhemoglobin Dissociation Curve
The oxyhemoglobin dissociation curve shows the relationship between the partial pressure of oxygen (PO2) and the saturation of hemoglobin with oxygen.
- Plateau Portion: At high PO2 levels (e.g., in the lungs), hemoglobin is almost fully saturated with oxygen. This ensures adequate oxygen loading even with small fluctuations in alveolar PO2.
- Steep Portion: At lower PO2 levels (e.g., in the tissues), a small decrease in PO2 results in a large release of oxygen from hemoglobin. This facilitates oxygen delivery to tissues with high metabolic demands.
Factors Affecting Oxygen Transport
- Carbon Dioxide (Bohr Effect): Increased PCO2 shifts the oxyhemoglobin dissociation curve to the right, decreasing hemoglobin's affinity for oxygen and promoting oxygen release to tissues.
- pH (Bohr Effect): Decreased pH (increased acidity) shifts the curve to the right, promoting oxygen release.
- Temperature: Increased temperature shifts the curve to the right, promoting oxygen release.
- 2,3-Bisphosphoglycerate (2,3-BPG): Increased levels of 2,3-BPG (produced during anaerobic metabolism) shift the curve to the right, promoting oxygen release.
- Anemia: Reduces the total amount of hemoglobin available to carry oxygen, decreasing oxygen-carrying capacity.
- Carbon Monoxide (CO) Poisoning: CO binds to hemoglobin with much higher affinity than oxygen, preventing oxygen binding and reducing oxygen delivery.
Carbon Dioxide Transport in the Blood
Carbon dioxide is transported in the blood in three ways:
- Dissolved in Plasma (about 7%): A small amount dissolves directly in the plasma.
- Bound to Hemoglobin (about 23%): CO2 binds to the globin portion of hemoglobin (not the heme group where oxygen binds).
- As Bicarbonate Ions (HCO3-) (about 70%): Most CO2 is transported as bicarbonate ions. CO2 reacts with water in red blood cells (catalyzed by carbonic anhydrase) to form carbonic acid (H2CO3), which dissociates into H+ and HCO3-. The HCO3- diffuses out of the red blood cells into the plasma (in exchange for chloride ions – the "chloride shift").
Respiratory Control Mechanisms
Breathing is controlled by respiratory centers in the brainstem (medulla oblongata and pons).
- Medullary Respiratory Center:
- Dorsal Respiratory Group (DRG): Primarily involved in inspiration. Contains inspiratory neurons that send signals to the diaphragm and external intercostal muscles.
- Ventral Respiratory Group (VRG): Involved in both inspiration and expiration, especially during forceful breathing. Contains both inspiratory and expiratory neurons.
- Pontine Respiratory Centers: Influence the activity of the medullary centers, helping to smooth the transition between inspiration and expiration.
Input to the Medullary Respiratory Center
The medullary respiratory center receives input from various sources, including:
- Chemoreceptors: Detect changes in blood levels of oxygen, carbon dioxide, and pH.
- Stretch Receptors in the Lungs: Provide information about lung inflation.
- Proprioceptors: Provide information about body position and movement.
- Higher Brain Centers: Can influence breathing (e.g., voluntary control, emotional responses).
Chemoreceptors
- Peripheral Chemoreceptors: Located in the carotid bodies and aortic bodies. Primarily sensitive to decreased arterial PO2 (hypoxia), but also respond to increased PCO2 and decreased pH.
- Central Chemoreceptors: Located in the medulla oblongata. Most sensitive to increased arterial PCO2 (which leads to decreased pH in the cerebrospinal fluid).
Additional Content: Digestive System and Energetics
Note:- Given content mix with respiratory system data, the below content seperate from respiratory system.
Digestive System
Anatomy of GI Tract with special reference to anatomy and functions of stomach, ( Acid production in the stomach, regulation of acid production through parasympathetic nervous system, pepsin role in protein digestion) small intestine and large intestine, anatomy and functions of salivary glands, pancreas and liver, movements of GIT, digestion and absorption of nutrients and disorders of GIT.
Energetics
Formation and role of ATP, Creatinine Phosphate and BMR.
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