1 respiration intro 2011

7/30/2019 1 Respiration Intro 2011

1/36

Respiration

The process of taking up oxygen and removingcarbon dioxide from cells in the body

Howard Mass, Ph.D.

August 2011 1


2/36

Processes

Two processes:

Internal (cellular) Respiration

Mitochondrial respiration -

a series of complex metabolic reactions that break downmolecules of food, releasing carbon dioxide and energy.

oxygen is required in the final step of cellular respiration to serveas an electron acceptor in the process by which cells obtainenergy.

2


3/36

External Respiration (gas exchange)

Consists of two processes:

Transport of O2 from atmosphere to the mitochondria Transport of CO2 from the mitochondria to the

atmosphere

3


4/36

Diffusion

Most fundamental mechanism of O2/CO2transport

Driving force for diffusion is the ________

gradient In discussion of gases, we use Partial Pressure

(described later)

4


5/36

Described by Fick's Law:

Rate of diffusion of a gas through a tissue slice isproportional to the area but inversely proportional tothe thickness

Diffusion rate is proportional to the partial pressure

difference

Diffusion rate is proportional to solubility of the gas

in the tissue; inversely proportional to the square

root of the molecular weight

Flow = P x Area

5


6/36

Diffusion through a tissue sheet. The amount of gas transferred is proportional to thearea (A), a diffusion constant (D), and the difference in partial pressure (P1 - P2), and isinversely proportional to the thickness (T). The constant is proportional to the gassolubility (Sol) but inversely proportional to the square root of its molecular weight (MW).

6


7/36

Surface area increased by development of

Bronchi and alveoli

At rest, flow across the alveolar wall is about 3X

faster than what is necessary at a normal cardiac

output

Changes in Surface area: Surgical, disease (edema)

7


8/36

Simple Diffusion is the mechanism by which O2and CO2 move short distances in therespiratory system

Between the: Air and the blood in the alveoli

Mitochondria and the blood of the peripheral circulation

8


9/36

Diffusion is an adequate gas delivery system foronly very small organisms (~1 mm).

Another mechanism is necessary:

9


10/36

Convection

Adds to the process by bringing more gas to theexchange surface

In an organism such as a paramecium, the

mechanism of convection is the beating of the cilia

In fish, it is movement of water over the gills

In mammals, one part of the convection system isan air pump (lungs), the airways, and therespiratory muscles

10


11/36

Ventilation The process of moving air into and out of the lungs

Moves the air into contact with the gas-exchange barrier

thereby maintaining a high PO2 and low PCO2

An EXTERNAL CONVECTIVE SYSTEM

11


12/36

Internal Convection System the circulation

Maximizes the flow of O2 and CO2 across the gas-

exchange barrier

Delivers to the inner surface of the barrier blood

that has a low PO2 and a high PCO2

Perfusion The process of delivering blood to the lungs

12


13/36

13


14/36

Nomenclature

PAO2

CvO2

PaCO2

Partial PressureAlveolar

gas

Contentvenous

arterial

FIO2Fractioninhaled


15/36

15


16/36

Gas Laws

General gas law::

PV = nRT

where T is temperature, n is the number of moles of

a gas, and R is a constant.

16


17/36

Boyle's Law

is commonly used to predict the result ofintroducing a change, in volume and pressureonly, to the initial state of a fixed quantity of gas.

P1V1 = P2V2

Where P1, 2 are the pressures of the system; V1, 2 are

the volumes of the gas

17


18/36

Charles' Law

At constant pressure, the volume of a givenmass of an ideal gas increases or decreases bythe same factor as its temperature (in Kelvin)increases or decreases

18


19/36

Dalton's Law

The total pressure of a mixture of gases is the sumof the individual partial pressures.

PB = PN2 + PO2 + PH2O + PCO2

19


20/36

The partial pressures are the pressures that the individual gases would exert if each gas

were present alone in the volume occupied by the whole mixture at the same temperature.

Therefore, the partial pressure of oxygen (PO2), according to the Dalton law, is determinedas PO2 = PB FO2, where FO2 is the fractional concentration of oxygen. Because 21% of

air is made up of oxygen, the partial pressure (PO2) exerted by oxygen is 160 mm Hg (760

0.21) at sea level. If all of the other gases in a container of air were removed, the remaining

oxygen would still exert a pressure of 160 mm Hg. Partial pressure of a gas is often referred

to as gas tension, and partial pressure and gas tension are used synonymously.

20


21/36

21

H ' L


22/36

Henry's Law

Henry law states that at equilibrium, the amount

of gas dissolved in a liquid at a given

temperature is directly proportional to the partial

pressure and the solubility of the gas.

22


23/36

Henrys law only accounts for the gas that is physically dissolved and not for chemicallycombined gases (e.g., oxygen bound tohemoglobin).

Dissolved O2 (ml/dL) = solubility x PaO2

0.003 (ml/ dL/ mmHg) x PaO2

so, at a PaO2 of 100 mmHg,

dissolved O2 = 0.3 ml/dL

23


24/36

Dissolved O2 ~ 0.3 ml O2 / 100 ml blood

At a cardiac output of 5 L / min, the total amount

of O2 available is 15 ml / min.

A 70 kg person at rest consumes 250 ml O2 /

min

24


25/36

Other Mechanism for Increasing theCarrying Capacity of Blood for O2 - CO2:

Hemoglobin

Iron containing compound

Reversibly binds about 96% of the O2 that diffuses

Also carries CO2

Acts as a buffer

25


26/36

Organization of the Respiratory System

Two important characteristics:

Convection and Diffusion are used

Convection used for long distance transport ofO2 and CO2

Diffusion used for the short distance movementof these 2 gases

26


27/36

Key Components

Air Pump the external convective system

Delivers air to, and removes air from the alveoli

(alveolar ventilation) Inspiration an active process

Expiration - at rest a passive process

27


28/36

Mechanisms for O2, CO2 carriage in the blood

A surface for gas exchange

Internal convection system the circulation

Local regulation of Ventilation and Perfusion

Central regulation for Ventilation

28


29/36

29


30/36

30


31/36

Lung Volumes

Dead Space

Anatomic

31


32/36

Physiologic

32


33/36

33


34/36

34


35/36

35


36/36

36

1 respiration intro 2011

Documents