Week 9 - Blood & Introduction to the Respiratory System

Week 9 - Blood & Introduction to the Respiratory System

Overview

• Date: March 15th, 2025

• Instructor: Dr. Phil Medeiros

• Course: KP222/HN220 Human Physiology

• Readings: Chapters 15.1-15.3 & 16.1-16.3

Functions of Blood

• Transportation:

• Transports dissolved gases such as oxygen (O2) from the lungs to body tissues and carbon dioxide (CO2) from tissues back to the lungs.

• Carries nutrients absorbed from the digestive tract, hormones secreted by glands, and waste products from cellular metabolism to excretory organs (e.g., kidneys).

• Regulation:

• Regulates body temperature by absorbing and distributing heat throughout the body.

• Maintains pH balance through buffer systems, ensuring that body fluids remain within a narrow pH range critical for enzyme function.

• Controls electrolyte levels in interstitial fluids (e.g., calcium ions (Ca²⁺), sodium ions (Na⁺), potassium ions (K⁺)), helping to maintain osmotic balance.

• Clotting and Repair:

• Prevents excessive fluid loss through mechanisms involving plasma proteins and platelets in response to vascular injury.

• Initiates clot formation via a series of complex biochemical reactions, leading to the formation of a stable clot to seal wounds and promote healing.

• Defense Mechanisms:

• White blood cells (WBCs), including various types such as neutrophils, lymphocytes, monocytes, eosinophils, and basophils, play key roles in the immune response, combating pathogens and foreign substances.

• Antibodies produced by B cells neutralize toxins and mark pathogens for destruction by other immune cells.

• Temperature Regulation:

• Acts as a medium for heat exchange, enabling mechanisms like sweating and shivering to maintain optimal body temperature under varying environmental conditions.

Major Components of Whole Blood

• Density Order:

1. Plasma

2. Buffy Coat (containing white blood cells and platelets)

3. Erythrocytes (red blood cells)

Composition of Plasma

• Composed of approximately 90% water, serving as a solvent for various substances.

• Electrolytes (ions): Such as sodium, potassium, calcium, magnesium, chloride, bicarbonate, and phosphate, critical for muscle function, nerve impulses, and maintaining osmotic pressure.

• Proteins:

• Albumins: Maintain osmotic pressure and transport molecules.

• Globulins: Function in immunity (e.g., antibodies).

• Fibrinogen: Essential for blood coagulation when activated during injury.

• Organic molecules: Such as amino acids, glucose, and lipids required for cellular functions and energy production.

• Nitrogenous waste products: For example, CO₂, urea, and creatinine, eliminated through the kidneys.

Blood-Formed Components

• Erythrocytes (RBCs):

• Primary function revolves around gas exchange; they are anucleate once matured, allowing more room for hemoglobin.

• They possess a lifespan of about 120 days and are recycled in the spleen and liver.

• White Blood Cells (WBCs):

• Vital for the immune response, capable of independent movement and capable of responding to infection or inflammation.

• Different types of WBCs have specialized roles (e.g., defending against bacteria, viruses, and parasites).

• Platelets:

• Cell fragments that play a crucial role in hemostasis (the process of blood clotting).

• They aggregate at injury sites to form a plug and release chemicals that promote clotting and healing.

Red Blood Cells

• Structure:

• Biconcave shape increases surface area for gas exchange and allows flexibility to squeeze through narrow capillaries.

• Contains approximately 270 million hemoglobin molecules per cell, each capable of binding to four O2 molecules.

• Function:

• Effectively pick up O2 in the lungs, where the partial pressure of O2 is high, and release it to tissues, where the partial pressure is low.

• Transports around 20% of CO₂ produced in tissues back to the lungs, primarily bound to hemoglobin as carbaminohemoglobin.

Hemoglobin Function

• Composed of four polypeptide chains (2 alpha and 2 beta), with heme groups containing iron that binds to O2.

• Types of Hemoglobin:

• Oxyhemoglobin: Bright red color when bound to O2.

• Deoxyhemoglobin: Dark red color when not bound to O2.

• Carbaminohemoglobin: Formed when CO2 binds to hemoglobin, important for CO2 transport.

• The affinity of hemoglobin for O2 is influenced by factors such as pH, temperature, and CO2 levels (Bohr effect).

Erythropoiesis Regulation

• Stimulated by conditions such as low RBC count (anemia) or increased oxygen demand (high altitude, physical activity).

• Erythropoietin (EPO), a hormone primarily produced by the kidneys, acts on bone marrow to enhance the production and maturation of RBCs.

• Hematocrit: The proportion of blood volume that is occupied by red blood cells; elevated levels can cause increased blood viscosity and circulation issues, particularly in states of dehydration or intense exercise.

Introduction to the Respiratory System

• Core Functions:

• Internal Respiration: Involves the utilization of oxygen at the cellular level for ATP production and releasing CO2 as a metabolic byproduct.

• External Respiration: Encompasses gas exchange in the lungs, involving the intake of O2 and the expulsion of CO2, followed by transportation to and from tissues.

Anatomy of the Respiratory System

Major Structures

• Upper Airways:

• Consist of the nasal cavity (moistens and filters air), oral cavity, pharynx (passage for air and food), and larynx (voice box that prevents food from entering the trachea).

• Lower Airways:

• Include the trachea (windpipe), which branches into primary, secondary, and tertiary bronchi, leading to the bronchioles and lungs.

• Alveoli:

• The primary site of gas exchange containing approximately 300 million tiny air sacs with extensive surface area and rich capillary networks for efficient diffusion of gases.

Conducting Zone

• Function:

• Serves as an air passageway that warms, humidifies, and filters inhaled air (approximately 150 mL designated as dead space where no gas exchange occurs).

• Components:

• Comprises the bronchi, bronchioles, and terminal bronchioles.

Respiratory Zone

• Forms part of the lower respiratory tract, consisting of respiratory bronchioles, alveolar ducts, and alveolar sacs.

• Function:

• Facilitates gas exchange through diffusion across the thin alveolar and capillary membranes due to differences in partial pressures.

Alveolar Structures

• Contains around 300 million alveoli, providing a vast interface for gas exchange with extensive vascularity to enhance efficiency.

• Cell Types:

• Type I Alveolar Cells: Form the thin wall of the alveoli, crucial for gas exchange.

• Type II Alveolar Cells: Secrete surfactant to reduce surface tension and prevent alveolar collapse.

• Macrophages: Help clear debris and pathogens from the alveolar space, maintaining lung health.

Respiratory Membrane

• Composed of the alveolar epithelium (1 layer of cells thick) and the capillary endothelium (0.2 µm thick).

• The thinness of the respiratory membrane is essential for effective gas diffusion between alveolar air and blood, allowing for rapid equilibration of O2 and CO2.

Thoracic Cavity Structures

• Components:

• Enclosed by the chest wall (rib cage, sternum) and diaphragm which separates the thoracic cavity from the abdominal cavity.

• The pleura (serous membranes) encasing the lungs provide lubrication and reduce friction during respiration.

• Functionality:

• Protects lung structures while playing a critical role in ventilation mechanics, allowing for proper lung expansion and contraction during breathing.

Pulmonary Ventilation

• Refers to the mechanical process of air movement into and out of the lungs, driven by the differences in intra-alveolar pressure and atmospheric pressure.

• Inspiration: Occurs when lung pressure drops below atmospheric pressure, allowing air to flow in; primarily involves contraction of the diaphragm and intercostal muscles.

• Expiration: Activated when lung pressure exceeds atmospheric pressure, air is expelled from the lungs due to the elastic recoil of lung tissues and relaxation of respiratory muscles.

Relevant Pressures

• Atmospheric Pressure: Standard pressure at sea level is 760 mm Hg; it varies with altitude affecting respiratory function and gas exchange.

• Intra-alveolar Pressure (Palv): Varies during breathing; plays a critical role in airflow dynamics—becomes negative during inspiration and positive during expiration, essential for effective ventilation.

Conclusion of Lecture

• Learning Objectives:

• Identify the various components and their specific functions related to blood physiology.

• Describe in detail the functions and production of red blood cells, including mechanisms influencing erythropoiesis.

• Differentiate between internal and external respiration, recognizing the physiological processes involved.

• Outline the anatomical structures of the respiratory system and their specific roles in ventilation.

• Explain the anatomy of the respiratory membrane and its significance in facilitating efficient gas exchange.

Contact Information

• Email: pmedeiros@wlu.ca