Physiology of Respiration

Physiology of Respiration

• Respiration is the exchange of gases between the body and the environment. It has two main parts, external and internal respiration.
• External respiration involves gas exchange with the atmosphere and is characterized by ventilation, diffusion of gases, transport, and diffusion.
• Internal respiration is the use of oxygen by mitochondria to produce energy and create carbon dioxide.

Lecture Objectives

• Students will be able to describe the functional anatomy of the respiratory system.
• Students will be able to recognize the functions of the respiratory system.
• Students will be able to discuss alveolar ventilation.
• Students will be able to discuss the mechanics of breathing.
• Students will be able to discuss the transport of gases and oxygen-hemoglobin dissociation curves.
• Students will be able to define hypoxia and compare its types.
• Students will be able to define cyanosis.
• Students will be able to discuss the regulation of respiration.

Components of the Respiratory System - Air Passages

• The respiratory system is divided into upper and lower air passages.
• Upper air passages include the nose, pharynx, and larynx.
• Lower air passages include the conducting zone and respiratory zone.
• The conducting zone is the tracheobronchial tree, extending from the trachea to the terminal bronchioles.
• The respiratory zone includes respiratory bronchioles and alveoli. These sites are responsible for gas exchange.

Lower Air Passages

• The conducting zone has progressively smaller branching tubes (trachea, bronchi, bronchioles, terminal bronchioles).
• Bronchial tree branching increases progressively in number, which dramatically increases surface area for gas exchange in alveoli.
• The respiratory zone includes the respiratory bronchioles, alveolar ducts, and alveolar sacs, forming the primary site for gas exchange.

Conducting vs. Respiratory Zones

• The conducting zone's function is to warm, humidify, and filter inhaled air.
• The respiratory zone's function is gas exchange.

Functions of the Respiratory System

• Gas exchange: Extract oxygen and eliminate carbon dioxide from metabolic processes.
• Venous Return: Lung surfactant synthesis and conversion of angiotensin-I to angiotensin-II helps venous return, with the fibrinolytic system dissolving blood clots.
• Metabolic function: Synthesis of surfactant, converting angiotensin-I to angiotensin-II, and containing the fibrinolytic system.

Thoracic Cage and Respiratory Centre

• The thoracic cage protects the lungs.
• The ribs, muscles, and pleura are components of the thoracic cage.
• The respiratory center initiates and regulates respiration.

Pleural Sac

• The pleural sac is a double-layered membrane surrounding the lungs.
• The pleural cavity is filled with intrapleural fluid.
• Intrapleural pressure is always negative, which helps keep the lungs inflated and prevents lung collapse.

Functions of Respiration

• External Respiration: The process of exchanging gases between the body and the atmosphere.
  • Ventilation: Movement of air between the atmosphere and alveoli.
  • Diffusion of gases: Exchange between alveolar air and blood and blood and tissues.
  • Transport: Transport of gases by the blood.
  • Diffusion: Exchange of gases between blood and tissues.
• Internal Respiration: The use of oxygen by mitochondria to create energy and the generation of carbon dioxide as a byproduct.

What is Ventilation?

• Bringing fresh air to the alveoli and removing stale air.
• Alveolar air is oxygen-poor and carbon dioxide-rich since oxygen diffuses into the blood and carbon dioxide out of the blood into the alveolar air.
• Ventilation is essential to maintain the partial pressure gradients, necessary for gas diffusion.
• Lack of ventilation will prevent oxygen replacement and carbon dioxide removal from alveoli.

Mechanics of Breathing

• Inspiration: Muscles contract, increasing lung volume and decreasing pressure, drawing air from the atmosphere into the lungs.
• Expiration: Muscles relax, decreasing lung volume and increasing pressure, forcing air out of the lungs.
• Normal resting expiration is a passive process, but with increased effort during exercise or exertion it's active via muscle contraction.

Why the Lung is Elastic?

• Lungs are elastic due to elastic fibers.
• Fluid film lining in alveoli also contribute to lung elasticity, via surface tension.
• Surfactant is a moderator of surface tension preventing lung collapse.

Lung Surfactant Function

• Surfactant is critical in reducing surface tension in the alveoli to improve lung expansion and prevent collapse.
• It is produced by type II alveolar cells to minimize surface tension.

Transport of Gases

• Oxygen transport is mostly via hemoglobin in red blood cells. This is because a small amount of dissolved oxygen is not sufficient to meet the entire body's needs.
• Carbon dioxide is transported in the blood primarily as bicarbonate ions (HCO3-).

Oxygen Transport

• Oxygen delivery relies on the lungs and the cardiovascular system.
• Oxygen moves into alveoli, crosses the alveolocapillary membrane, binds to hemoglobin, circulates in the blood, and dissociates to be taken by tissues.
• Obstacles in this process result in oxygen deficiency (hypoxia).

Oxygen Transport in Blood

• Oxygen is transported in two primary ways: dissolved in the plasma and bound to hemoglobin.
• Hemoglobin is the most significant carrier and facilitates efficient oxygen transport throughout the body.

Hypoxia

• Hypoxia is reduced oxygen tension in tissues.
• Decreased oxygen tension in the blood is called hypoxemia.
• Various forms of hypoxia, including hypoxic, anemic, stagnant, and histotoxic hypoxia, exist.
• Specific causes of each form are discussed separately.

Cyanosis

• Cyanosis is a bluish discoloration of skin and mucous membranes.
• It occurs when the amount of reduced hemoglobin exceeds 5 gm/100 ml of blood.
• Hypoxia and stagnant hypoxia cause cyanosis.

Regulation of Respiration

• Respiration is primarily involuntary.
• The medullary respiratory center controls rhythmic breathing.
• Other centers, the pontine respiratory groups, switch between inhalation and exhalation.
• Chemical regulation and other signals from the brain and the lungs play roles.
• Peripheral and central chemoreceptors are in the arterial blood and cerebrospinal fluid, providing feedback to respiratory control centers on levels of O2, CO2, and pH.

Non-Chemical Regulation

• The cerebral cortex can voluntarily alter breathing rate and depth.
• Lung receptors, such as stretch receptors, can also influence respiratory function.

This quiz evaluates your understanding of respiration, covering both external and internal processes. You will explore the anatomy and function of the respiratory system, mechanisms of breathing, and gas transport. Gain insights into key concepts such as hypoxia and the oxygen-hemoglobin dissociation curve.