PROPERTIES OF GASES
 

Biologically important gasses in the atmosphere

• nitrogen (N₂) - ~ 79%
• oxygen (O₂) - ~ 21%
• carbon dioxide (CO₂) - ~ 0.03%
• other gasses - trace

Question: Why are oxygen, nitrogen, and carbon so important biologically? Give examples for each.
 
 
 
 
 
 
 
 
 
 
 
 
 

Pressure and diffusion of gases

pressure - movement of molecules of gas exerts physical pressure on container, solution, other molecules
 

partial pressure (pp) - pressure exerted by a particular gas within a mixture of gases

diffusion - pressure gradient required for net diffusion to occur

• each gas diffuses down its own gradient from high pp to low pp

 

Question: If the pO₂ inside an animal cell is 30 torr, what is the pressure gradient for oxygen?
 
 
 
 
 

Question: What is the pp of carbon dioxide?
 
 
 
 
 

Question: If the pCO₂ inside an animal cell is 20 torr, what is the pressure gradient for carbon dioxide?
 

Question: Why should we be sympathetic to plants for the hard life they lead?
 
 
 
 
 
 
 

Movement of gases in animals
 

Diffusion - molecule by molecule along the gas's partial pressure gradient

• diffusion across body surface sufficient for very small animals, single cells
• specialized respiratory organ needed for larger animals (low surface area : volume ratio)
• diffusion alone still inadequate

Convection - mass movement or bulk flow of many molecules at once

ventilation - convection of respiratory medium (water or air) over respiratory organs
circulation - convection of blood from respiratory organ to body tissues

Convection moves large quantities of gases but gases still are exchanged via diffusion at level of cells and tissues!!!!
 

RESPIRATORY ORGANS AND VENTILATION

Water-breathers - Oxygen has low solubility in water; low oxygen availability in water

Sponges - water circulates through pores of body

Molluscs - internal or external gills, cilia sweep water by

Crustaceans - gills move through water

Fish - pump water in through mouth, out gill slits; one-way, nearly continuous flow

• gills finely subdivided
• highly efficient - great surface area for diffusion
• still, little oxygen available; oxygen-limited in activity and metabolism

Air-breathers - Oxygen easy to get; more oxygen in air than in water

Insects - tracheal system

• air delivered directly to tissues via tiny tubules throughout body
• blood has no respiratory function

Amphibians -> reptile -> mammals --> birds

• greater and greater subdivisions in lungs
• more surface area
• greater efficiency, supports higher metabolism and activity

• continuous, one-way flow through lungs
• extremely high surface area
• details in text for those interested in how they do it

• trachea & bronchi - cartilage rings in wall
• lined with ciliated columnar epithelium
• many macrophages present

• smaller bronchioles - no cartilage present, smooth muscle in wall instead
• lined with mucus-producing epithelium also

• alveoli - simple squamous epithelium only
• 99% or more of gas exchange here
• associated with cells that produce surfactant which reduces the surface tension of the alveoli

Question: Some premature infants are born before their lungs are capable of producing surfactant. What effect would this have?
 

Mechanics of breathing

• contract diaphragm = lower it
• creates negative pressure - air flows in
• relax diaphragm = raises up
• creates positive pressure (pushing) - air pushed out

• inhibits and can kill macrophages
• inhibits cilia activity for several hours
• stimulates mucus secretion
• alveolar cells - destroyed by enzymes released in response to irritants, replaced with scar (connective) tissue

GAS TRANSPORT

Blood transports dissolved gasses in many animals (verts, crustaceans, molluscs, annelids)

Oxygen

• low solubility in water - need other way to carry in adequate amounts in blood
• respiratory pigment - metal-containing protein with high affinity for O₂  (hemoglobin and others)
• binds reversibly, depending on partial pressure

Question: Draw a diagram showing the pressure gradient for pick up and delivery of oxygen.
 
 
 
 
 
 
 
 
 

Carbon dioxide

• very soluble in water
• no special respiratory pigment, but some carried on hemoglobin
• 10% as dissolved CO₂ in water
• 30% bound to Hb in red blood cells
• 60% as bicarbonate ion

bicarbonate formation

CO₂ + H₂O <-----------> H₂CO₃ <-------------> H+ + CO₃-

At tissue - reaction forward: As CO₂ reacts with water, more CO₂ can be carried in blood

At lung - reaction backward: CO₂ removed by diffusion along its gradient

Question: How would respiration affect the acid-base balance of the body?