Respiration I

Gas Exchange Systems

The tracheal gas exchange system of insects

Spiracles in the abdomen open to allow gas exchange and close to limit water loss.

Spiracles open into tracheae, that branch to tracheoles, that end in air capillaries.

Diffusion distance only a few uM

The tracheal gas exchange system of insects

Tracheae branch intotracheole and endin air capillaries

Insects are forced to be small

• Since there is no circulatory system ininsects, insects are forced to be small.

• It they are too big, it would take foreverto diffuse O2 to mitochondria insidecells.

Bulk flow is done in bigger tubes

Bulk flow is done in bigger tubes

Diffusion only takes place in destination (Alveolus)

Diffusion only takes place in destination (Capillaries)

• Perform the ultimate function of the cardiovascular system• Permeate almost every tissue (most cells < 0.1 mm from capillary wall)• Very thin wall consists of porous endothelial cells.• Nutrients and gases move in and out via diffusion.

cellcytoplasm

cell in tissue glucose

O2

CO2

blood

interstitial fluid

Flow is influenced by flow mechanics

Flow between two points is proportional topressure difference between two points

Keep radius as big as possible

Resistance is themeasure of the frictionthat impedes flow

Design of the system

To maintain flow, you need to have a systemwith low and and high konductance,

You don’t want to generate larger pressure,then you need to have large muscle

Design of system

An analogy: fire hydrant

Why big tubes in bulk flow?

Diffusion takes in terminal bronchiole

Geometry of the blood vessels in the mesentery of the dog

Kind of vessel Diameter Number Total cross-sectional (mm) area (cm2)

Aorta 10 1 0.8Large arteries 3 40 3Arterial branches 1 2,400 5Arterioles 0.02 40,000,000 125

Capillaries 0.008 1,200,000,000 600

Venules 0.03 80,000,000 570Veins 2 2,400 30Large Veins 6 40 11Vena cava 12.5 1 1.2

From: “Animal Physiology”, 5th Edition, Schmidt-Nielsen

Blood pressure, velocity and total cross area

The Respiratory System of a bird

How birds breath

Anteriorair sacs

Posteriorair sacs Lungs

Air

Lungs

Air

1 mm

Trachea

Air tubes(parabronchi)in lung

EXHALATIONAir sacs empty; lungs fill

INHALATIONAir sacs fill

Fick’s law of diffusion applies to all gasexchange systems.

Some sample calculations

Relationship between gas content in liquid,partial pressure and gas solubility in liquid

Henry’s law for concentrations of dissolved gas in solutionCx= Px X solubility

–Px = partial pressure of gas (mmHg) –Solubility: solubility of gas in blood (mL gas/100mL blood/mmHg)

Oxygen transport in blood

Oxygen transport in blood• Forms of O2 in blood: Dissolved and bound

• Dissolved O2: accounts for around 2% of the total O2 content of blood– The dissolved form is the only form that produces a partial pressure

which in turn drives O2 diffusion.• The concentration of dissolved O2 is proportional to the partial

pressure of O2 and its solubility in blood

• O2 bound to hemoglobin: the remaining 98% of the total O2 content ofblood is reversibly bound to hemoglobin in red blood cell.

Oxygen content

Causes of shift to the right and to the left

O2 movement in the lungs and tissues

O2 binding capacity,O2 content and O2 delivery• O2 binding capacity: the maximum amount of O2 that can be

bound to hemoglobin per volume of blood, assuming that hemoglobin is100% saturated ( all four heme group on each molecule of hemoglobinare bound to O2)– Exposing blood to air with very high PO2 so hemoglobin will be 100%

saturated, 1g of hemoglobin A can bind 1.34ml O2 and the normalconcentration of hemoglobin A in blood is 15g/100mL. The O2 bindingcapacity of blood is therefore 20.1mLO2/100mLbood (15g/10mL x1.34mLO2/ghemoglobin =20.1mLO2/100mL blood)

• O2 content= bound + dissolved– O2 content = (O2 binding capacity x % saturation) +

dissolved O2

• O2 delivery to tissues:– O2 delivery= cardiac output x O2 content of blood =

cardiac output x( dissolved O2 + O2 bound tohemoglobin)