Respiration

Overview of Gas Exchange

Every organism must exchange materials with its environment, ultimately at the cellular level.

  • Unicellular organisms exchange materials directly with their environment.

  • Multicellular organisms have specialized systems for gas exchange as direct exchange is not feasible.

Specialized Exchange Systems

Gills in Animals

  • Gills are specialized structures for gas exchange in aquatic animals.

  • Internal transport systems and gas exchange are interrelated in most multicellular organisms.

Gas Exchange Mechanism

  • Gas exchange occurs across specialized respiratory surfaces, supplying oxygen for cellular respiration and removing carbon dioxide.

  • Gases diffuse down partial pressure gradients in the lungs and other organs due to pressure differences.

Definition of Partial Pressure

  • Partial pressure is the pressure exerted by a particular gas in a mixture.

  • Gases move from areas of higher partial pressure to areas of lower partial pressure.

Respiratory Media

  • Animals can utilize air or water as sources of oxygen (O2) for respiration.

  • Water holds less O2 than air, making it more challenging for aquatic organisms to extract necessary oxygen efficiently.

Respiratory Surfaces

  • Effective gas exchange requires large, moist respiratory surfaces.

  • Types of respiratory surfaces include skin, gills, tracheae, and lungs, all facilitating gas exchange by diffusion.

Gills in Aquatic Animals

  • Gills are outfoldings of the body, increasing surface area for efficient gas exchange.

  • Various structures function in gas exchange, illustrating diversity among aquatic animals.

Ventilation Principles

  • Ventilation moves the respiratory medium over the exchange surfaces; aquatic animals may swim or push water over gills.

  • Fish utilize a countercurrent exchange system where blood flows opposite to water, maximizing oxygen uptake.

Anatomy of Gills

  • Gill arches support gill filaments, through which water flows and gas exchange occurs via capillary blood vessels in lamellae.

  • Partial pressure gradients ensure net diffusion of O2 from water to blood throughout the gills.

Tracheal Systems in Insects

  • Insects possess a tracheal system of tiny tubes delivering O2 directly to body cells.

  • The respiratory and circulatory systems function independently, necessitating ventilation in larger insects for adequate oxygen supply.

Lungs in Animals

  • Lungs, an infolding of body surfaces, serve to exchange gases, with the circulatory system transporting gases throughout the body.

  • The lung's size and complexity typically correlate with an animal’s metabolic demands.

Human Respiratory System

  • Air follows a specific pathway: nostrils → pharynx → larynx → trachea → bronchi → bronchioles → alveoli (site of gas exchange).

  • Exhaled air passes over vocal cords, aiding in sound production.

  • Alveoli are coated with surfactants, preventing collapse and optimizing gas exchange.

Breathing Mechanisms

Amphibian Breathing

  • Amphibians like frogs use positive pressure breathing to ventilate lungs, pushing air down the trachea.

Mammalian Breathing

  • Mammals utilize negative pressure breathing, drawing air into lungs through rib and diaphragm muscle movement.

  • Tidal volume is the amount of air per breath, while vital capacity is the maximum tidal volume.

Bird Breathing

  • Birds possess air sacs that maintain unidirectional airflow through lungs, ensuring complete air renewal with each breath.

Control of Breathing in Humans

  • Controlled by brain regions: medulla oblongata (rate/depth regulation) and pons (breath tempo).

  • Sensors in the aorta and carotid arteries monitor blood gas concentrations, providing secondary regulation.

Adaptations for Gas Exchange

  • Respiratory pigments enhance oxygen and carbon dioxide transport capacity in blood.

  • Organisms with high metabolic demands rely on effective transport mechanisms for O2 and CO2.

Coordination of Circulation and Gas Exchange

  • Blood arriving in lungs has low O2 and high CO2 partial pressures, facilitating diffusion of gases between blood and alveoli.

  • In tissues, O2 diffuses into interstitial fluids while CO2 moves into the blood due to partial pressure gradients.

Respiratory Pigments

  • Respiratory pigments like hemocyanin (found in some invertebrates) and hemoglobin (most vertebrates) enhance oxygen transport.

  • Hemoglobin's structure allows it to carry four O2 molecules, responding dynamically to changes in oxygen demand (Bohr shift).

Adaptations of Elite Animal Athletes

Endurance Runners

  • Animals like pronghorn antelope exhibit extreme O2 consumption aiding long-distance speed.

Diving Mammals

  • Diving species, e.g., Weddell seals, can store O2 effectively in muscles, supporting extended diving via specialized adaptations.

Learning Objectives

  • Understand the pros and cons of water vs. air as respiratory media.

  • Describe gas exchange in human lungs and tissues.

  • Grasp and illustrate the hemoglobin-oxygen dissociation curve.