Gas exchange and circulation

Gill

Outgrowths of the body surface used for gas exchange

Operculum

Flap of tissue covering the gill

Ram ventilation

water is forced through gills when swimming fast

Gill lamellae

Thin sheet structure which water is pumped over

Trachea in insects

Series of tubes which carry gases to directly to and from tissues

Trachea in vertebrates

Carries inhaled air to the bronchi

Spiracle

Openings of trachea in insects

Hemolymph

Fluid medium in an open circulatory system

Lung

Organ connecting to the trachea specialized for gas exchange

Bronchi

Branching tubes which carry oxygen from the trachea to the lungs

Bronchioles

Branching passages in the lungs which connect bronchi to alveoli

Alveoli

Air sacs at the end of bronchioles for gas exchange between the lungs and blood

Tidal Flow Ventilation

Bidirectional Flow

Flow-through Ventilation

Uni-directional flow

Pulmonary Circuit

Blood exits the heart and travels to the lungs/gills to pick up oxygen and dispose of carbon dioxide

Systemic Circuit

Oxygenated blood leaves the lungs and returns to the heart before being pumped to the tissues

Sinoatrial Node

Pacemaker causing electrical signals in the heart

Artery

Carries blood away from the heart. Has larger diameter, thick walls, highest flow rate and highest pressure

Vein

Carries blood to the heart. Has high flow rates, lowest pressure, and thinner walls

Capillary

Vessels with one-cell-thick walls which carry one blood cell at a time, are narrowest, have slowest flow, and are under very little pressure

Systole

Contraction of the heart

Diastole

Relaxed stage between heart contractions

Atrium

Receives blood to fill the ventricles

Ventricle

Generates the main pressure for circulation

Atrioventricular valve

Allows blood to flow from atria to ventricles

Semilunar Valve

Allows blood to flow from ventricles to arteries

Ventilation

Movement of air or water through a specialized gas exchange organ (lungs or gills)

Diffusion

Oxygen movement from air or water into the blood or carbon dioxide moving from the blood into the air or water

Circulation

The transport of oxygen and carbon dioxide throughout the entire body via the circulatory system

How do ventilation, diffusion, and circulation work together in gas exchange?

Ventilation leads air or water into the organism’s body where it is diffused into the blood, and then circulated through the body before carbon dioxide is diffused back into the air or water and undergoes ventilation to get back into the air or water

Pressure

Force exerted over unit area

Partial Pressure

Pressure of a particular gas in a mixture of gases

How is partial pressure of a component gas calculated?

P_x = P_total * F_x

P_x = Pressure of the component gas

P_total = Total pressure of the gas

F_x = Fraction of the component gas over total gas

Air and water as respiratory media

Air has a high oxygen content with low density and viscosity

Water has a low oxygen content with high density and viscosity

Bulk Flow

The movement of fluids driven by hydrostatic pressure

What does rate of flow depend on?

Pressure differential (+)

Viscosity (-)

Diameter of biological “tubes” (+)

What factors determine the rate of gas diffusion?

Surface Area (+)

Distance of diffusion (-)

Temperature (+)

Solubility (+)

Partial Pressure Gradient (+)

What factors affect gas solubility?

Pressure in contact with the solvent (+)

Nature of gas

Nature of solvent

Temperature of water (-)

Presence of other solutes (-)

Carrier Affinity (+)

How does dissolved oxygen vary among aquatic habitats?

More photosynthetic organisms (+)

Surface (+) vs depth of same water (-)

Shallow (+) vs deep (-)

Rough water (+) vs still water (-)

Freshwater (+) vs seawater (-)

Gills advantage

Easier to move water over evaginated structures, no opportunity for water loss from an external structure, water supports structures with neutral bouyancy

Lungs advantage

Invagination reduces water loss, air is cheaper than water to move into internal spaces

What structures do insects use to transport respiratory gases?

Trachea

Spiracles

Lung morphology and function

Trachea carries air to bronchi

Bronchi carries blood to bronchioles

Bronchioles carry air to alveoli

Alveoli carry oxygen into blood

Positive-pressure ventilation

Throat opening increases volume and draws in air which is forced into the lungs during throat contractions (amphibians)

Negative-pressure ventilation

Expansion of the thoracic cavity generates a drop in pressure which pulls air into the lungs (vertebrates besides amphibians)

Explain the role of countercurrent exchange in gills

Oxygen poor water runs next to oxygen poor blood, but due to higher water pressure, oxygen diffuses into blood. As blood picks up more oxygen, it runs next to water with a higher oxygen content which results in more diffusion.

Diaphragm

Muscular sheet across the bottom of the thoracic cavity

How does the diaphragm assist mammalian ventilation?

When drawn downward the ribcage expands, increasing thoracic volume of the chest cavity, dropping pressure which expands the lungs and pulls air inward. This processes is reversed as the diaphragm relaxes, resulting in exhalation

How do gills function in gas exchange?

Through either the opening of mouth and operculum to cause a pressure gradient or ram ventilation, water is pumped across the gill lamellar which causes oxygen to enter the blood from the water due to a concentration gradient established by countercurrent exchange

Ideal gas law

PV=nRT

How does the ideal gas law apply to ventilation?

As volume around the lungs increases, pressure drops. The negative pressure on the lungs increases their size

How does avian ventilation work?

Inhale: Air flows through the trachea and enters posterior air sacs

Exhale: Air leaves the posterior air sacs and enters the posterior parabronchi

Inhale: Air flows into the anterior parabronchi and into anterior air sacs (inhale)

Exhale: Air leaves the anterior air sacs and exits through the trachea

Why is avian gas exchange more efficient than mammalian?

Gas exchange occurs during both inhale and exhale

Birds must be able to extract oxygen at higher elevations

Function of hemoglobin

Carries up to 4 oxygen molecules, using iron molecules to bond inside of red blood cells

Cooperative Binding

Each oxygen molecule bound to Hb increases the likelihood other oxygen molecules will bond

Each oxygen molecule released from Hb increases the likelihood other oxygen molecules will be released

Importance of cooperative binding in oxygen transport

Allows oxygen to be loaded/ unloaded more fully based on small changes in tissues

Interpret an oxygen equilibrium curve

Relationship between pressure of oxygen and amount of oxygen bound to hemoglobin is nonlinear. At rest, saturation is about 75% and tissues have about 25% of bound oxygen unloaded into them. As tissues use more oxygen, pressure drops and more oxygen is unloaded.

CO₂ + H₂O <=> HCO₃^- + H⁺

More CO₂ triggers a decrease in pH, so hemoglobin is more likely to unload oxygen into tissues. CO₂ is converted to bicarbonate in blood

Negative feedback relationship between CO₂ levels, blood pH, and ventilation

CO₂ increases → pH decreases → ventilation increases → CO₂ decreases → pH incrases

Open vs Closed Circulatory Systems

Open- vessels empty in sinus, then hemolymph reenters vessel/heart system (most invertebrates) Lower pressure, flow rate, and diffusion distance, limited control

Closed- blood stays in vessels throughout transit, allowing more precise delivery to needy tissues (all vertebrates) Higher pressure, flow rate, and diffusion distance, significant control

Peristaltic pump

part of blood vessel, limited to lower pressures

Chambered pump

Specialized with one way valves to generate higher pressure

Path of blood through the mammalian heart

Blood is oxygenated in the lungs/gills, travels to the right atrium which supplies the right ventricle, is pumped through the body (systemic circuit), becomes deoxygenated and returns to the left atrium which supplies the left ventricle and pumps the blood back to the lungs/gills (pulmonary circuit)

Cardiac Cycle

SA nose generated a signal which spreads over the atria which causes them to contract. Then the signal is delayed by the AV node, before the signal spreads to ventricles which contract as atria relax, before the ventricles relax as well