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)