Respiratory Systems

ZOO 250

External Respiration

sequence of events that result in the exchange of oxygen and carbon dioxide between the external environment and the mitochondria

Mitochondrial (Cellular) Respiration

production of ATP by oxidation of carbohydrates, amino acids, or fatty acids; oxygen is consumed and carbon dioxide is produced

What organisms rely on diffusion for gas exchange?

unicellular and small multicellular

What organisms must rely on a combination of bulk flow and diffusion for gas exchange?

larger organisms

Bulk Flow Components

1. Ventilation

2. Circulation

3. Diffusion into the tissues 

What is Ventilation entail in Bulk Flow?

moving medium (air or water) over respiratory surface (lung or gill) to allow for diffusion

What does Circulation entail in Bulk Flow?

transport of gases in the circulatory system

How many times does Bulk Flow occur?

twice

Bulk Flow in Single Celled Organisms, Simple Ones

diffusion

Bulk Flow in Insects

bulk flow through tracheal system

Spiracles

holes on animals where air moves in and out 

Tracheae

tubes that allow flow of air into the animal

Bulk Flow in Worms and Leeches

diffusion through skin then bulk flow

Bulk Flow in Mammals

bulk flow, gas dissolved at the respiratory surface and diffuses into circulatory system, then bulk flow to the tissues 

Problem of Solubility

gases must dissolve into an aqueous solution to be uses in the body

Solubility of a gas depends on:

• pressure

• temperature

• concentration of other solutes 

(must also traverse a cell layer)

Henry’s Law

amount of gas that will dissolve into a liquid is determined by partial pressure and solubility

Graham’s Law

when gases are dissolved in a liquid, how fast they move through the liquid (diffusion rate) is determined by solubility and molecular weight. Bigger stuff moves more slowly, especially with lower solubility

Boyle’s Law 

pressure/volume relationship, increasing volume of a chamber decreases pressure (and vice versa)

Bulk Flow

pressure and resistance affect flow

Oxygen Characteristics

• abundant in air (20%) but not very soluble in water

• keep gradient steep by taking up in respiratory pigments 

Carbon Dioxide Characteristics

• not abundant in air (0.05%) but very soluble in water

Nitrogen Characteristics 

• 70%

• not relevant physiologically under most circumstances 

• the only exception is during deep diving; dissolved into the blood under high pressures and can cause issues 

Animals more than a few millimeters thick use one of Three Respiratory Strategies 

1. circulating the external medium through the body

2. diffusion of gases across the body surface accompanies by circulatory transport

3. diffusion of gases across a specialized respiratory surface accompanied by circulatory transport 

Respiratory Strategy: Circulating the External Medium Through the Body

sponges, cnidarians, and insects 

sponges/cnidarians-gas exchange with the sea water 

insects-air, however aquatic insects can use gills or air bubbles 

Respiratory Strategy: Diffusion of Gases Across the Body Surface Accompanies by Circulatory Transport 

• cutaneous respiration

• skin must be thin and moist

• most aquatic invertebrates, some amphibians, eggs of birds

Respiratory Strategy: Diffusion of gases across a specialized respiratory surface accompanied by circulatory transport

• gills (evaginations) or lungs (invaginations)

• vertebrates

Nondirectional Ventilation

medium flows past the respiratory surface in an unpredictable pattern

Tidal Ventilation

medium moves in and out of the chamber

PO2 in blood increases, but PO2 in air decreases because of confined space

Unidirectional Ventilation 

medium enters the chamber at one point and exits at another 

Thin Respiratory Surface 

greater surface area, greater gas exchange

PO2 almost reaches the level in the medium, the medium does not change 

Gases enter the blood at….

the respiratory surface

Movement of blood through the respiratory surface can affect…

efficiency of gas exchange

Since the Gases have to diffuse from air/water to blood/hemolymph…

movement of blood through the tissue can affect how efficiently diffusion will take place

Concurrent Flow

once the medium and blood approach each other (equilibrium) gas exchange discontinues

Countercurrent Flow

low O2 blood encounters lowest O2 medium, which is still higher than blood

Crosscurrent

a capillary bed splits up and flows across the respiratory surface, first capillaries get highest PO2 medium but all other caps still lower than medium, so actually end up with blood higher than medium