BIO271 Lecture 6 - Respiratory System 1

what are animals?

-they are heterotrophs that evolved from colonial protists

when do biologists hypothesize that the first animals evolved?

-they hypothesize that the first animals evolved around 600 million years ago

-had to evolve to produce oxygen for larger organisms

what are all terrestrial vertebrates?

-they are all tetrapods

tetrapods

-animals with four limbs

who were the first tetrapods?

-amphibians were the first tetrapods

→ followed by the evolution of reptiles (including birds)

**first to occupy land

where does most of our knowledge on our heart and lungs come from?

-most of what we know about our heart and lungs was figured out using an animal models

why do we use animal models to gain knowledge on human hearts and lungs?

-because it is not ethical to do a lot of these studies on humans

comparative physiology

-is the study of how physiological functions vary across species

what does comparative physiology (research) help scientists understand? (4)

1. how evolution shaped physiological functions

2. adaptations to specialized environments

3. survival strategies

4. provides models for human physiology and disease

what can we learn about by examining how different organisms solve common biological problems?

we can learn about the:

→ diversity of physiological solutions

→ the unifying principles that govern them

respiration

-the entire sequence of events that results in the exchange of oxygen and carbon dioxide between the external environment of an animal and the mitochondria

-there are different phases of this

what are the steps to respiration?

1. mitochondria consume O2 to produce ATP for our systems (oxygen moves down its conc. gradient) → its a sync - lot of oxygen outside the mitochondria and little inside

2. produces CO2 in the process

what must organisms have?

-they must have mechanisms to obtain O2 from the environment and get rid of CO2

(ex. external respiration)

what are the 5 respiratory strategies of animals?

1. diffusion through water or air

2. bulk flow of water

3. bulk flow of air

4. diffusion/gas transport

5. ventilation/gas transport

what respiratory strategy do unicellular and small multicellular organisms rely on?

-they rely on diffusion for gas exchange into their tissues

what respiratory strategy do larger organisms rely on?

-they rely on a combination of bulk flow and diffusion for gas exchange (they need a respiratory system)

what do many animals have?

-they have specialized respiratory organ with a larger surface area (gills or lungs) for gas exchange and a circulatory system which transport oxygen by bulk floe through the body

how is respiration divided in animals?

-in animals, respiration is divided into 4 steps

what are the 4 steps of respiration in animals?

1. ventilation

2. external respiration

3. gas transport

4. internal respiration

ventilation (step 1 of respiration)

-bulk flow of the medium across the the respiratory surface/gas exchange at the respiratory surface

external respiration (step 2 of respiration)

-diffusion across the respiratory surface/gas exchange at the respiratory surface

gas transport (step 3 of respiration)

-bulk flow in the circulatory system

internal respiration (step 4 of respiration)

-diffusion across the surface/gas exchange at the tissues

-cellular respiration/Mitochondrial respiration

-production of ATP via oxidation of carbohydrates, amino acids, or fatty acids.

-oxygen is consumed and carbon dioxide is produced

where is the concentration of O2 highest and lowest?

highest: in the alveoli of the lungs (exchange 1)

lowest: cells (exchange 3)

where is the concentration of CO2 highest and lowest?

highest: in the blood and cells (exchange 3)

lowest: in the alveoli of the lungs (exchange 1)

what is exchange 1?

-between atmosphere and lung

what is exchange 2?

between lung and blood

what is exchange 3?

-between blood and cells

where is transport of gases in the blood located?

-in the heart (veins/arteries/capillaries area) → pulmonary and systemic circulation

what are the 7 equations involved in the physics of the respiratory system?

1. the fick equation

2. the ideal gas law

3. dalton’s law

4. henry’s law

5. graham’s law

6. boyle’s law

7. resistance opposes flow

**know relationship of these

what does resistance oppose?

-it opposes flow

fick equation

-rate of diffusion

→ dQ/dt= DA(dC/dx)

-rate of diffusion will be greatest when the diffusion coefficient (D), area of membrane (A), and energy gradients (dC/dx) are large AND the diffusion distance is small

-larger conc. gradient = higher drive

-*tells us the diffusion

what are gas exchange surfaces like?

-they are typically thin, with a large surface area

diffusion

-is the movement of molecules from an area of higher concentration to a lower concentration

→ slow over long distances

→ fast over short distances

what do respiratory membranes need to be?

-they need to be very thin

what do we use for gases in the fick equation?

-we use partial pressure rather than concentration

the ideal gas law

-gases exert pressure

→ PV = nRT

-total pressure exerted by a gas is related to the number of moles of the gas and the volume of the chamber

what is air a mixture of?

-it is a mixture of gases: nitrogen (78%), oxygen (21%), argon (0.9%) and carbon dioxide (0.03%)

dalton’s law

-in a gas mixture each gas exerts each its own partial pressure

-the sum of the partial pressures of the gases in a gas mixture yields the total pressure of the gas mixture

why do we usually use partial pressure rather than concentration for gases?

-because gases have special properties such as they dissolve, diffuse, and react according to their pressure

henry’s law

-gases dissolve in liquids

→ [G] = P_gas x S_gas

-the amount of gas that will dissolve in a liquid is determined by the partial pressure of the gas and the solubility of the gas in the liquid

-gas molecules in air must first dissolve in liquid (water or extra-cellular fluid) in order to diffuse into a cell

which is more soluble CO2 or O2?

-CO2 is much more soluble in water than is O2

what happens when CO2 and O2 are at the same partial pressure ?

-more CO2 will be dissolved in a solution than will oxygen

what does low O2 solubility mean?

-it means concentrations are not equal (in air and water)

what happens when CO2 is at equilibrium at the same partial pressure as O2?

-this means that CO2 dissolves more because it has a higher solubility than O2

graham’s law

-gases diffuse at different rates

→ Diffusion rate ~ solubility/√MW

-when gases are dissolved in liquids, the relative rate of diffusion of a given gas is proportional to its solubility in the liquid and inversely proportional to the square root of its molecular weight

-O2 is lighter (32 amu) than CO2 (44 amu)

in air, what are the solubilities of CO2 and O2?

-their solubilities are the same (100 ml/L at 20 degrees celsius)

which diffuses faster: O2 or CO2?

-Oxygen diffuses about 1.2 times faster than CO2 (since it is a physically smaller molecule)

-however, CO2 is about 24 times more soluble in aqueous solutions than O2, therefore CO2 diffuses about 20 times faster than O2 in water

what is the combined equation with the fick equation + henry & graham’s laws?

-Diffusion rate ~ D x P_gasx A x S_gas/ X * √(MW)

in the combined F+H+G equation, at a constant temperature, what is the rate of diffusion proportional to?

-diffusion coefficient of the gas (an index of the ease of diffusion of a particular substance through a given medium)

-partial pressure gradient (P_gas)

-cross-sectional area (A)

-solubility of the gas in the fluid (S_gas)

in the combined F+H+G equation, at a constant temperature, what is the rate of diffusion inversely proportional to?

-diffusion distance (X)

-molecular weight of the gas (MW)

boyles’s law

-fluids flow from areas of high pressure to low pressure

→P1V1 = P2V2

-P1 and V1 are the initial pressure and volume

-P2 and V2 are the final pressure and volume

-describes the effects of changes in volume on changes in pressure

**temperature and the number of gas molecules remain constant

what happens when you apply pressure?

-it decreases the volume and increases pressure (forcing air out)

bulk flow

-mass movement of liquids or air as the result of pressure gradients

how do fluids and gases flow?

-they flow from areas of high to low pressures in bulk flow

gases

-don’t have a fixed volume or shape

-so it responds to pressure changes by changing their volume

-are compressible

liquids and solids

-are incompressible

-their volume does not change in response to changing pressure

what do respiratory systems use?

-they use changes in volume to cause changes in pressure

resistance opposes flow

→ Q = deltaP/R (where Q = flow, deltaP = pressure gradient, R = resistance)

-frictional resistance opposes the bulk flow of fluids

in tubes, how does resistance increase?

-resistance increases in direct proportion to the length of the tube and with the viscosity of the fluid

in tubes, how does resistance decrease?

-resistance decreases in inverse proportion to the radius to the fourth power

what happens as an organism grows larger?

-as it gets larger, their ratio of surface area to volume decreases

-can't use diffusion because it will take too long for the gas to reach the rest of the organs

-this limits the area available for diffusion and increases the diffusion distance (dQ/dt= DA(dC/dx))

what are the 3 respiratory strategies that animals more than a few millimeters thick choose from to use?

1. circulating the external medium through the body

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

3. diffusion of gases across the body surface accompanied by circulatory transport

circulating the external medium through the body (respiratory strategies)

-sponges, cnidarians, and insects use this strategy

diffusion of gases across a specialized respiratory surface accompanied by circulatory transport (respiratory strategies)

-gills (evaginations) or lungs (invaginations)

-vertebrates

**use this strategy

diffusion of gases across the body surface accompanied by circulatory transport (respiratory strategies)

-cutaneous respiration

-most aquatic invertebrates, some amphibians, eggs of birds use this strategy

Telmatobius culeus

-this frog lives in high altitudes in Peru, which increased is surface area

-so it has evolved this extensive external skin

-never leaves water and never breathes air (gets all the oxygen from its skin and when it needs O2 it does pushups)

what is ventilation?

-the active movement of the respiratory medium (air or water) across the respiratory surface

-this reduces the formation of static boundary layers (ex. improves efficiency of gas exchange)

what are the 3 types of ventilation?

1. nondirectional

2. tidal

3. unidirectional

nondirectional ventilation

-medium flows past the respiratory surface in an unpredictable pattern

-fully mixed medium and thin respiratory surface (example)

-poorly mixed medium or thick respiratory surface (example)

(ex. amphibian skin)

what is the process of nondirectional ventilation?

1. partial pressure of oxygen (PO2) in the blood leaving the gas exchanger can approach the PO2 in the medium (but it will not surpass it because it can’t, it will eventually plateau)

what happens if ventilation is inefficient?

-then an oxygen depleted boundary layer will form at the respiratory surface

(ex. if frog is ill and has barrier such as slime on skin, less O2 can be picked up across skin)

what can anything that increases diffusion distance do?

-it will decrease oxygen exchange efficiency and reduce the PO2 in the blood leaving the gas exchanger

tidal ventilation

-external medium moves in and out of respiratory system in a back and forth movement

(ex. mammalian lungs)

what is the process of tidal ventilation?

1. respiratory cavities do not fully empty

2. fresh air mixes with oxygen-depleted residual air

3. in animals that tidally ventilate, PO2 in the respiratory cavity is lower than the outside medium

4. PO2 of blood equilibrates with the PO2 of the respiratory cavity

unidirectional ventilation

-respiratory medium enters the chamber at one point and exits at another

-the blood can flow in 3 ways relative to the flow of the medium

the boundary layer

-is the region of a solution that is in direct contact with the animal's body surface

-layer depleted of oxygen

what are the 3 ways blood can flow relative to the flow of the medium in unidirectional ventilation?

1. concurrent flow

2. countercurrent flow

3. crosscurrent flow

concurrent flow

-medium and blood flow in same direction

countercurrent flow

-medium and blood flow in opposite direction

crosscurrent flow

-medium and blood flow at an angle

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