Human Respiration Overview

Human Respiration

• The respiratory system enables oxygen intake and carbon dioxide removal.
• Breathing involves two phases: inspiration (inhaling) and expiration (exhaling).

Respiration Processes

• Breathing (ventilation) is the process of air moving in and out of the lungs.
• External respiration is the exchange of gases between the air and blood.
• Internal respiration is the exchange of gases between the blood and tissues.

Respiratory System Functions

• Gas exchange: Oxygen enters the blood, and carbon dioxide leaves the blood.
• Thermoregulation and fluid balance: The respiratory system helps regulate body temperature and fluid levels.
• Maintaining blood pH: The respiratory system helps control blood acidity by regulating carbon dioxide levels.
• Protection: Mucous and hairs in the respiratory system filter and trap foreign particles.
• Voice production: The vocal cords generate sound.

Structure of the Respiratory System

• The respiratory system is divided into upper and lower tracts.
• The upper respiratory tract includes the nasal cavity and pharynx (throat).
• The larynx (voice box), trachea, primary bronchi, and lungs make up the lower respiratory tract.
• Alveoli are tiny air sacs in the lungs where gas exchange occurs.

Blood and Lungs Interaction

• Blood flow through capillaries in the lungs is low-pressure (~70 ml/second).
• The surface area for gas exchange (in the alveoli) in lungs is about 80 square meters.
• The ventilation-perfusion ratio relates the amount of air reaching alveoli to the amount of blood reaching alveoli per minute.
• A ratio of 0.8 typically indicates good ventilation-perfusion matching.

Gas Exchange Process

• The primary function of breathing is gas exchange.
• Dalton's law states that total pressure is the sum of partial pressures of each gas.
• Diffusion is the movement of gases from higher to lower concentration.
• Henry's Law states that gas dissolving is proportional to partial pressure and solubility.

Physics of Breathing (Ventilation)

• Pressure in liquids: Pressure (P) = density (ρ) × acceleration due to gravity (g) × height of liquid (h).
• Standard atmospheric pressure is 760 mmHg or 76 cm of mercury.
• Boyle's Law: For a fixed quantity of gas at constant temperature, pressure and volume are inversely related (P₁V₁ = P₂V₂).
• This law explains how changes in lung volume create pressure differences, driving air flow.

Pressures Differences

• Transrespiratory pressure: controls overall air flow.
• Transpulmonary pressure: defines the degree of alveolar inflation.
• Transthoracic pressure: controls the expansion or contraction of lungs and chest wall.

Pressure-Air flow-Volume Relationship of the Lungs

• Changes in lung volume, pressures, and air flow during breathing are cyclical.
• Alveolar pressure, intrapleural pressure, and airflow have distinct and related wave patterns over time.

Lung Compliance

• Emphysema is a condition where alveoli break down, increasing lung compliance (making them more expandable).

Airways Resistance

• Airways resistance is related to properties like diameter and mucous.
• Increased resistance can be caused by swelling or contraction of airways. (e.g. in asthma).

Measurement of Lung Capacity

• Lung capacity measurements can differ between healthy and diseased lungs. This can be observed by differences in curves/graphs