BIOL 1030 / Topic 5: Circulation and Gas Exchange

Each cell needs a supply of two reactants. What are these two reactants?

Each cell needs a supply of two reactants. What are these two reactants?

O₂ and sugar.

Each cell needs a waste removal system for two toxins. What are these two toxins?

CO₂ and n-waste.

Solubility

The ability of a substance to dissolve in a solvent to form a homogeneous solution.

What’s the difference between respiration and cellular respiration?

Respiration is a broader term encompassing multiple processes involved in gas exchange, typically involving oxygen and carbon dioxide, either between organism and environment (external respiration) or between capillaries, tissues, and cells (internal respiration). Meanwhile, cellular respiration is the process by which cells convert glucose and oxygen into energy, carbon dioxide, and water.

How are respiration and cellular respiration connected?

The oxygen acquired through external respiration is used in cellular respiration.

What’s the difference between arteries, veins, and capillaries?

They’re all different blood vessels.

• Arteries transport blood away from the heart.

• Veins return blood back to the heart.

• Capillaries surround tissues to deliver and absorb oxygen, nutrients, and other substances, also often connecting branches of arteries to branches of veins.

Bulk flow

The mass movement of fluids, such as blood or air, in response to pressure differences within a system.

What is a respiratory medium, and what are our primary respiratory media?

The fluid from which O₂ is absorbed and to which CO₂ is released. Our primary respiratory media are air and water.

What is partial pressure, and what is the partial pressure of O₂ and CO₂ in air?

The pressure exerted by a specific gas in a mixture. The PO₂ and PCO₂ are 160 mmHg and 30mmHg, respectively.

Approximately, how much are O₂ and CO₂ in air?

~21% of O₂ in air, and ~0.04% in CO₂

What is the degree of solubility of O₂ and CO₂ in water?

O₂ is poorly soluble, while CO₂ is highly soluble.

Does warm water hold less or more O₂, and why? How about salt water?

• Warm water holds less O₂ because of the movement of the water molecules, causing the O₂ to be “pushed” into the atmosphere by the water molecules.

• Salt water holds less O₂ because the volume that water occupies already has Na⁺ and Cl^- ions around them, causing there to be no available space for O₂.

Why is oxygen consumed? Why do we need it?

Oxygen is consumed for there to be a final e^- acceptor.

Gas exchange

The process by which gases diffuse across a surface.

Give examples of which animals can perform diffusion somewhat easily, and why?

• Phylum Porifera, whose non-true tissue cells have direct consumption with water.

• Phylum Cnidaria, whose true tissue epithelial cells have direct consumption with water.

• Phylum Platyhelminthes, whose body is super flat, with diffusive distance less than 1mm.

• Phylum Nematoda.

Recall, what is diffusion, and what are is two types? Define these two types as well.

The movement of hydrophobic molecules and very small uncharged polar molecules through the lipid bilayer of a cell.

There are two types of diffusion:

• Simple diffusion, which doesn’t need transport proteins.

• Facilitated diffusion, which needs transport proteins.

What are the three requirements for simple diffusion?

• A concentration gradient.

• A moist surface.

• A large surface.

What is the “supply and demand” proportionality between volume, surface area, and respiratory media? When does this proportionality break down?

• The more the volume given or supplied, the more demand for respiratory media.

• The more the surface area given or supplied, the less demand for respiratory media.

The proportionality breaks down when performing activities akin to exercising.

What is the maximum efficient distance of diffusion? If any animal has thicker or longer diffusion distance, how do they survive?

The maximum efficient diffusion distance is 1mm. Bigger, thicker animals need diffusion and circulation.

In total, what are the sites of possible gas exchange in animals? Which are specialized?

Skin, gills, and lungs, with the latter two are specialized for gas exchange.

Regardless of the type, what are the requirements for gas exchange and gas diffusion for all respiratory surfaces?

• It must be highly vascularized, allowing for rapid transport of these gases to and from the respiratory surface.

• It must have a moist surface area, because a moist surface provides a thin film of water allowing gases to dissolve.

• It must have a large surface area, because the greater the surface area, more diffusion of gases.

There are three types of respiration based on the three possible sites of gas exchange. What are they?

Cutaneous respiration, water ventilation, and air ventilation.

What’s cutaneous respiration, and what are examples of animals that use this typa respiration?

Gas exchange through skin, in animals dependent upon water that have thin, vascularized skin and a large SA:V ratio. E.g. roundworms, flatworms, sponges, cnidarians, and amphibians.

Ventilation

The process of breathing in and out, allowing fresh oxygen to enter the respiratory surface and removal of carbon dioxide.

What’s water breathing, and what are examples of animals that use this typa respiration?

Gas exchange through gills made of thin, vascularized epithelia, used when cutaneous respiration isn’t sufficient for the environment or physiological requirements of the animal, e.g. larger aquatic organisms.

What are the two types of elaborate gills in water breathing animals?

• External gills, exposed to water currents.

• Internal gills, covered by a protective structure.

For animals with internal gills, how do they breathe or take in their respiratory medium, water?

The animal must actively create its own currents, e.g.

• Ciliated epithelia covering gills or lophophore.

• Appendages such as gill bailers.

• Active swimming or gulping.

Expanding on water ventilation via active swimming or gulping, what are these formally known as?

• “Active swimming” is formally known as ram-jet ventilation, wherein they swim with their mouth open.

• “Gulping” is formally known as buccal pumping, wherein the mouth closes and opens, appearing as the gulping action.

What’s the mechanism of buccal pumping?

Mouth opens, pressure decreases in the oral cavity. Water intake then occurs. Mouth closes, pressure increases in the oral cavity, pushing that gas exchange to occur in their gills.

What are the two types of extraction of oxygen from water? Which is more efficient?

• Concurrent exchange, wherein blood flows with the direction of oxygen in water.

• Countercurrent exchange, wherein blood flows against the direction of oxygen in water.

Countercurrent exchange is more efficient because the concentration gradient is maintained over time, while concurrent exchange has a concentration gradient diminishing over time.

What’s air ventilation, and what are examples of animals that use this typa respiration?

Gas exchange through lungs with more complex ventilation and respiration, present in terrestrial animals.

In mammals, what are the series of branching tubes that oxygen from air passes through?

1. Trachea.

2. Bronchi.

3. Bronchioles.

A couple of terms to know before discussing air breathing. Define the following: Alveoli, intercostal muscles, and diaphragm.

• Alveoli are air sacs where gas exchange occurs with a large surface area of ~100m² in humans.

• Intercostal muscles are muscles between the ribs, helping expansion and contraction of chest cavity.

• The diaphragm is a muscle underneath lungs, separating chest cavity from abdomen.

What does Boyle’s gas law posit?

Pressure is inversely proportional to volume, i.e. P ∝ 1/V.

When you breath, what do the intercostal muscles and diaphragm do? What happens to the lungs and ventilation?

Intercostal muscles lift rib cage, and the diaphragm moves down. Lungs expand, increasing volume. Pressure in lungs is now less than the pressure outside, i.e. atmospheric pressure. Air moves in.

When you exhale, what do the intercostal muscles and diaphragm do? What happens to the lungs and ventilation?

Intercostal muscles relax and lower the rib cage, and the diaphragm moves up. Chest volume, i.e. thoracic volume decreases, with the pressure increasing. Pressure inside is now more than the atmospheric pressure. Air moves out.

In regards to ventilation in birds, breathing doesn’t end in alveoli. Explain the breathing of birds.

They have two air sacs, one posterior and one anterior. They have lungs in between these two groups of air sacs. Air flows in one direction over the lung epithelium, instead of two directions in mammals. They have two stages of breathing.

1. They inhale. The posterior air sac pulls in air from outside, and the anterior air sac pulls in air from lungs. Pressure decreases due to air sac expansion.

2. They exhale. The posterior air sac pushes air into lungs, and the anterior air sacs push air back into environment. Pressure increases due to air sac contraction.

What’s a possible reason why breathing in birds is more efficient than in humans?

Gravity pulls oxygen down to Earth. Even if percentage of oxygen is 21% in air still, there is less PO₂ in the atmosphere. Birds have their special own of ventilation to get fresh, oxygen-rich air and never keep oxygen-poor air.

Insects have a different way of breathing too! Explain their breathing.

They have a tracheal system, wherein: There is an external opening called a spiracle, directly connected to a trachea. The trachea that branches off into tracheoles, which deliver air directly to cells throughout the body. They do not only have one trachea, they have multiple—tracheae. Breathing occurs through muscular expansion and relaxation of abdomen.

What’s a possible reason why breathing in insects is more efficient than in humans?

Insects deliver oxygen from respiratory surface to tissue without the hassle of respiratory surface to capillary to tissue.

Lymph

The fluid surrounding and bathing cells in tissues.

Blood

The fluid circulating in circulatory system, transporting oxygen, nutrients, and waste products.

Transport mechanism

Pathway of connecting collection sites to removal or usage sites.

What’s the transport mechanism for nutrients?

1. Nutrients are collected at the gut.

2. Nutrients are used by body tissues.

3. Body tissues produce used-up nutrients as n-waste.

4. Renal organs remove n-waste.

What’s the transport mechanism for water?

1. Water is collected by the gut and respiratory surfaces.

2. Water is removed by respiratory surfaces and renal organs.

What’s the transport mechanism for oxygen?

1. Oxygen is collected by respiratory surfaces.

2. Body tissues “exchange” oxygen with the production of carbon dioxide.

3. Respiratory surfaces remove carbon dioxide.

What are the three types of animals with different instruments for transport mechanisms, and how do they work?

• Animals that have no instrument for transport mech at all, and rely on diffusion and distance of cells to nutrients. E.g. Nematoda and Porifera.

• Animals that have gastrovascular cavities as their instrument of transport mechanism. E.g. Cnidarians and Platyhelminthes..

• Animals that have a circulatory system as their instrument of transport mech consisting of a pump and pipes, i.e. blood vessels.

What are the two types of circulatory systems?

Open and closed.

What’s a closed circulatory system?

Circulatory system wherein one fluid, blood, is completely contained within vessels, and a second body fluid, lymph, bathes the tissues.

How does a closed circulatory system help the transport mechanism of requirements to live?

1. A heart pumps blood through the arteries to tissues.

2. Capillaries at tissues are exchange sites.

3. Veins carry blood back to the heart.

What’s an open circulatory system?

Circulatory system wherein the same body fluid that bathes the tissues, i.e. hemolymph, is pumped by the heart.

How does a open circulatory system help the transport mechanism of requirements to live? Which animals have this?

1. Heart pumps hemolymph into open-ended arteries, spilling into spaces, i.e. sinuses, surrounding tissues.

2. Openings in the heart, i.e. ostia, allow hemolymph to enter to be pumped again.

Common in arthropods and most molluscs.

Advantages of closed system over open system?

Create more pressure, more flow, greater nutrient delivery.

Advantages of open system over gastrovascular cavity?

Heart still beats, creating pressure to deliver hemolymph.

Even if not as efficient as CCS, it is more efficient than GVC.

O₂ has low solubility in water and blood. What makes the transport mechanism of this requirement to be more efficient and possible?

Proteins called respiratory pigments circulate with the blood or hemolymph and increase O₂ amount carried in the circulatory fluid.

There are two respiratory pigments that you should know about, what are they?

Hemocyanin and hemoglobin.

Hemocyanin

Made of one protein subunit, uses two Cu atoms binding to O₂. Its colour is gray-blue when O₂ is bound, and colourless when not.

Hemoglobin

Made of four protein subunits, with each containing a Fe atom. Its colour is bright red when O₂ is bound, and darker red when not.

Where is CO₂ concentration the highest? How about lowest?

Highest at where it is produced, i.e. in tissues. Lowest at where it is removed, i.e. respiratory surface.

CO₂ is highly soluble in water and thus in blood. It doesn’t need a carrier. However, what is its transport mechanism?

At the tissue.

1. Diffuses from tissue, through the capillary, and into red blood cells.

2. Carbonic anhydrase catalyzes the reaction to turn CO₂ to H₂CO₃, with some hemoglobin picking up a bit of CO₂ and protons.

3. H₂CO₃ dissociates into HCO₃^- and H⁺.

Move to respiratory surface.

1. Carbonic anhydrase catalyzes the reverse reaction of turning H₂CO₃ back into CO₂.

2. CO₂ diffuses from red blood cells to alveolar airspace.