Blood Pressure, Respiratory System, & Gas Exchange (Chapter 48)

Learning Objectives

• Relate blood pressure and blood flow to physiological events in the body

  • Distinguish between vasoconstriction and vasodilation effects on blood flow

• Understand partial pressure and its role in gas exchange

• Know anatomy of the mammalian respiratory system and importance of alveoli

• Describe the process of ventilation in mammals

• Explain Boyle’s Law as it relates to ventilation

Velocity of Blood Flow

• Blood velocity is highest in arteries

• Blood flow slows down in veins

• Blood flow is slowest in capillaries

Blood Flow and Blood Pressure

• Blood flow is highest in arteries and slowest in capillaries

  • Understanding why capillaries withstand high pressure despite slower flow is critical

Blood Flow Dynamics

• Normal blood flow measurements:

  • Systolic <120 mmHg

  • Diastolic <80 mmHg

• Flow resumes at high velocity after stoppage

Homeostasis and Blood Pressure

• Homeostasis maintains blood pressure (BP) through:

  • Increased vascular resistance results in increased arterial BP and heart rate

  • Vasodilation: Decreases BP

  • Vasoconstriction: Increases BP

• Homeostatic mechanisms ensure adequate blood flow to meet body demands

Blood Flow Regulation in Capillaries

1. Vasoconstriction or vasodilation of the arteriole supplying the capillary bed

2. Precapillary sphincters regulate blood passage

• Blood pressure drives fluid out of capillaries

Exchange in a Capillary Bed

• Mid-capillary: Blood pressure equals osmotic pressure - NO net fluid movement

• Arterial End: Higher blood pressure compared to osmotic pressure - NET pressure OUT

• Venous End: Osmotic pressure exceeds blood pressure - NET pressure IN

• Net movement of fluid is controlled by the difference between blood pressure and osmotic pressure

Air Composition and Gas Exchange

• Air consists of:

  • 21% Oxygen

  • 78% Nitrogen

  • 1% Carbon Dioxide among others

• Atmospheric pressure = 760 mmHg

• Gas exchange depends on solubility in water and diffusion rate

Respiratory Surfaces for Gas Exchange

• Oxygen sources: Air and water

  • Air: Plentiful and easier to breathe

  • Water: Requires more energy for extraction of O2

• Key features of respiratory surfaces:

  • Large surface area

  • Thin walls

  • Moist inner surfaces

  • Rich blood supply

  • Passive diffusion occurs for gas exchange

  • Variations in respiratory surfaces across animal types

Continues on Respiratory Surfaces

• Gas exchange occurs by passive diffusion across respiratory surfaces

• Surface types vary by animal species

Reiteration of Oxygen Sources

• O2 can source from air or water

Anatomy of Lungs

• Lungs: Internal, paired structures, infolded body surface

• Continuous with external environment, attached only to trachea and circulatory system

• Circulation transports gases between lungs and body tissues

Overview of the Respiratory System

• Primary functions:

  • Bring atmospheric O2 into the body and deliver it to tissues

  • Remove CO2 produced during cellular respiration

Respiratory System Anatomy

• Air entrance through nose/mouth

• Inhaled air converges in the pharynx

• Passes through larynx into trachea

• Trachea branches into bronchi, then into bronchioles

• Alveoli are located at bronchiole tips

Gas Exchange at Alveoli

• Gas exchange occurs at alveoli (air sacs in bronchioles)

• Two major alveoli cell types:

  • Type I: Facilitate gas diffusion

  • Type II: Secretory cells

Gas Exchange Mechanism

• O2 diffuses through moist epithelium into capillaries

• CO2 diffuses from capillaries into air spaces

• Branching: Pulmonary vein carries oxygen-rich blood to left atrium; pulmonary artery carries oxygen-poor blood from right ventricle

Lung Function and Boyle’s Law

• Lungs utilize negative pressure filling

• Boyle’s Law: Pressure inversely related to volume

  • Example: Increasing volume decreases pressure

• Pressure gradients generated by changing lung volume facilitate air movement

Understanding Partial Pressure

• Partial pressure: Pressure exerted by a specific gas in a mixture

• Atmospheric pressure = 760 mmHg

Impact of Partial Pressure on Gas Diffusion

• Partial pressure values guide predictions of gas movement

• Net diffusion occurs from higher to lower partial pressure regions

• Atmospheric pressure reference remains 760 mmHg

Phases of Breathing

• Breathing consists of two phases: inhalation and exhalation

• Mammals ventilate lungs through negative pressure breathing, pulling air into lungs

Inhalation Process

• Lung volume increases as rib muscles and diaphragm contract

• Volume increase leads to decreased pressure in lungs, becoming negative relative to outside air

Exhalation Dynamics

• Lung volume decreases as rib muscles and diaphragm relax

• Decreased volume raises pressure within lungs, expelling air

Inhalation vs Exhalation

• Inhalation: Active process bringing air into lungs

• Exhalation: Typically passive, expelling air from lungs

Boyle’s Law in Ventilation

• Ventilation adheres to Boyle’s Law principles

• Constant temperature: Pressure inversely proportional to gas volume

Tidal Volume and Gas Exchange

• Tidal volume: Air volume inhaled per breath

• Each inhalation mixes fresh air with oxygen-depleted residual air

• Maximum PO2 in alveoli is lower than atmospheric levels

Residual Air in the Lungs

• Type II alveolar cells secrete surfactant, keeping alveoli open

• Premature infants, lacking surfactant, face respiratory distress syndrome (RDS)

• Treatment involves artificial surfactants

Respiratory Pigments

• Respiratory pigments: Oxygen-binding proteins evolved in many animals

• Hemoglobin: Present inside erythrocytes (RBCs), binds up to 4 O2 molecules

Alternative Respiratory Pigments

• Hemocyanin: Another respiratory pigment in arthropods, utilizes copper for binding

• Characterized by blue pigmentation

CO2 Transport in Blood

• Limited CO2 dissolves in blood

• Some CO2 binds to hemoglobin

• Majority converted into bicarbonate ions; impacts pH and enzyme activities