CH47: Gas Exchange

What are the two primary respiratory gases that animals must exchange with the environment?

Oxygen O2 and carbon dioxide CO2

What are the three main components of a gas exchange system in animals?

Specialized body surfaces, ventilation mechanisms, and perfusion mechanisms.

What physical process is the only means of gas exchange between an animal's internal body fluids and the external medium?

Diffusion.

According to the principles of diffusion, molecules exhibit net movement from an area of _____ concentration to an area of _____ concentration.

higher; lower

How is the concentration of a gas in a mixture of gases typically expressed?

As its partial pressure.

A gas will diffuse from a mixture where its partial pressure is _____ to a mixture where its partial pressure is _____.

higher; lower

What two factors determine the amount of a gas that can be held in a liquid?

The partial pressure of the gas phase and the solubility of the gas in the liquid.

How does temperature affect the solubility of a gas in a liquid?

Solubility is higher at lower temperatures.

What is the name of the law that describes the rate of diffusion?

Fick's law of diffusion.

What is the formula for Fick's law of diffusion?

Q = DA x ((p1-p2)/L)

How do aquatic invertebrates with no internal gas exchange systems, like flatworms, maximize surface area?

They are typically very small or have flat bodies.

What do larger aquatic animals have?

specialized gas exchange surfaces, such as gills

What adoptions do air breathing Animals have to minimize path length for diffusion of gases in aqueous media?

mitochondria are in the aqueous cytosol, cells are bathed in extracellular fluid, respiratory surfaces are covered in a thin film of fluid

Why is it easier for terrestrial animals to obtain oxygen from air than for aquatic animals to obtain it from water?

The oxygen content of air is much higher, and oxygen diffuses much faster through air.

What challenge do ectothermic, water-breathing animals face as water temperature increases?

Their metabolic rate and need for oxygen increase, while the oxygen concentration in the warmer water decreases.

What happens to the partial pressure of oxygen Po2 as altitude increases?

The partial pressure of oxygen decreases.

Why is the removal of carbon dioxide CO2 from the body generally easier than the uptake of oxygen?

Atmospheric CO2 is very low, creating a large pressure gradient for its exit from the body.

List four adaptations animals have evolved to maximize respiratory gas exchange.

Increased surface area, maximized partial pressure gradients, minimized diffusion path length, and minimized diffusion in aqueous medium.

Salamanders use _____, which are highly branched and folded extensions of the body surface, for gas exchange.

external gills

What is a primary advantage of internal gills, as seen in crayfish, over external gills?

They are protected from predators and physical damage.

What are lungs?

Internal cavities used for respiratory gas exchange with air in terrestrial vertebrates.

What is the tracheal system found in insects?

A system of air-filled tubes that branch throughout the body for gas exchange.

The active movement of air or water over gas exchange surfaces is called _____.

ventilation

The circulation of blood over the internal side of gas exchange surfaces is called _____.

perfusion

In insects, what are the external openings of the tracheal system that can be closed to limit water loss?

Spiracles.

In the insect respiratory system, tracheae branch into smaller tubes called _____.

tracheoles

The actual sites of gas exchange in the insect tracheal system are the tiny, fluid-filled endings called _____.

air capillaries

What mechanism do fish use to maximize gas exchange efficiency in their gills?

Countercurrent flow.

In fish gills, what are the thin, folded structures on the gill filaments that serve as the primary site of gas exchange?

Lamellae.

In countercurrent exchange in fish gills, blood flows in the _____ direction to the flow of water over the lamellae.

opposite

Why is countercurrent flow more efficient for gas exchange than concurrent flow?

It maintains a partial pressure gradient for oxygen diffusion across the entire length of the exchange surface.

In the diagram of concurrent flow, what is the maximum oxygen saturation the blood can reach?

50%, the point of equilibrium with the water.

Blood vessels that bring deoxygenated blood to the gills are called _____ vessels.

afferent

Blood vessels that carry oxygenated blood away from the gills are called _____ vessels.

efferent

How does the air flow in bird lungs differ from that in mammal lungs?

Bird lungs have unidirectional air flow, whereas mammal lungs have bidirectional (tidal) flow.

What is 'dead space' in the context of mammalian lungs?

The volume of air that remains in the lungs after exhalation and mixes with fresh inhaled air.

Why is the unidirectional flow in bird lungs so efficient?

It minimizes dead space, so fresh incoming air doesn't mix with stale air, maintaining a high Po2 gradient.

In the avian respiratory system, what are the fine, gas-exchanging tubes that run parallel to one another through the lungs?

Parabronchi.

What is the role of air sacs in the avian respiratory system?

They act as reservoirs, receiving and holding air, but are not sites of gas exchange.

The actual sites of gas exchange in bird lungs are the tiny _____ that branch off the parabronchi.

air capillaries

Trace the unidirectional path of a single breath of air through the avian respiratory system.

Trachea -> posterior air sacs -> parabronchi (lungs) -> anterior air sacs -> trachea.

How many full cycles of inhalation and exhalation does a single breath of air remain in a bird's respiratory system?

Two cycles.

What is tidal ventilation?

A type of breathing where air flows in and out of the lungs by the same path.

What is the term for the amount of air that moves in and out of the lungs per breath when at rest?

Tidal volume (TV).

The additional amount of air that can be forcefully inhaled after a normal inhalation is called the _____.

inspiratory reserve volume (IRV)

The additional amount of air that can be forcefully exhaled after a normal exhalation is called the _____.

expiratory reserve volume (ERV)

What is vital capacity (VC), and how is it calculated?

The maximum amount of air that can be moved in and out of the lungs; calculated as TV + IRV + ERV.

What is residual volume (RV)?

The amount of air that cannot be expelled from the lungs, even with forceful exhalation.

Why is the partial pressure of oxygen Po2 in the alveoli always lower than in the atmosphere?

Fresh inhaled air is diluted by the residual volume (RV) of air remaining in the lungs.

Trace the path of air into the human lungs, starting from the mouth/nasal passage.

Mouth/nasal passage -> pharynx -> trachea -> bronchi -> bronchioles -> alveoli.

What are the tiny, thin-walled air sacs in the human lungs that are the primary sites of gas exchange?

Alveoli.

What is the approximate combined surface area of the alveoli in human lungs?

About 70 square meters.

The mechanism by which cilia continuously sweep mucus and trapped particles out of the airways is known as the _____.

mucus escalator

What is the function of lung surfactant?

It reduces the surface tension of the fluid lining the alveoli, making it easier to inflate the lungs.

What is respiratory distress syndrome (RDS) in premature babies caused by?

An inability to produce sufficient lung surfactant, making breathing extremely difficult.

What is the name of the sheet of muscle at the bottom of the thoracic cavity that is crucial for breathing?

The diaphragm.

What is the function of the fluid within the pleural space between the lungs and the thoracic cavity wall?

It helps the pleural membranes slide past each other during breathing and creates surface tension that holds them together.

What happens to a lung if the thoracic cavity is punctured, allowing air to enter the pleural space?

The lung collapses (deflates).

What is the primary action that causes inhalation in humans?

The diaphragm contracts and pulls downward, expanding the thoracic cavity.

During quiet breathing, what causes exhalation?

The diaphragm relaxes, and the elastic recoil of the lung tissues pushes air out.

Which set of intercostal muscles contracts to lift the ribs up and outward, expanding the thoracic cavity during forceful inhalation?

The external intercostal muscles.

Which set of intercostal muscles contracts to pull the ribs down and inward, decreasing the thoracic cavity volume during forceful exhalation?

The internal intercostal muscles.

What is the primary protein in vertebrate red blood cells that transports oxygen?

Hemoglobin.

Where in the body are red blood cells (RBCs) produced?

In the bone marrow.

Describe the basic structure of a hemoglobin molecule.

It is a protein with four polypeptide subunits, each surrounding an iron-containing heme group.

How many molecules of oxygen O2 can one molecule of hemoglobin carry when fully saturated?

Four molecules.

What is positive cooperativity in the context of hemoglobin?

When one oxygen molecule binds to a hemoglobin subunit, it changes the protein's shape, increasing the affinity of the other subunits for oxygen.

The sigmoidal (S-shape) of the oxygen-hemoglobin dissociation curve is a result of what property?

Positive cooperativity.

In a healthy person at rest, what is the approximate oxygen saturation of hemoglobin in blood leaving the lungs?

100% (or very close to it).

In a healthy person at rest, what is the approximate oxygen saturation of hemoglobin in deoxygenated blood returning to the heart?

About 75%.

What does the 75% oxygen saturation in returning venous blood represent?

An oxygen reserve that can be released to tissues during high metabolic demand.

How does carbon monoxide (CO) cause poisoning?

It binds to hemoglobin with an affinity about 240 times higher than oxygen, preventing oxygen transport.

What is myoglobin, and where is it found?

An oxygen-binding protein, consisting of a single polypeptide, found in muscle cells.

How does myoglobin's affinity for oxygen compare to that of hemoglobin?

Myoglobin has a much higher affinity for oxygen, binding it even at low partial pressures.

Why do diving mammals have high concentrations of myoglobin in their muscles?

It serves as an oxygen reserve for their muscles during long periods underwater.

How does fetal hemoglobin differ structurally from adult hemoglobin?

Fetal hemoglobin contains two γ-globin chains instead of the two β-globin chains found in adult hemoglobin.

Why is it advantageous for fetal hemoglobin to have a higher affinity for oxygen than maternal adult hemoglobin?

It allows for the efficient transfer of oxygen from the mother's blood to the fetus's blood across the placenta.

What is the Bohr effect?

The phenomenon where a decrease in blood pH (increase in acidity) causes hemoglobin to decrease its affinity for oxygen and release it more readily.

A decrease in blood pH causes the oxygen-hemoglobin dissociation curve to shift in which direction?

To the right.

What substance, produced in red blood cells under low-oxygen conditions, lowers hemoglobin's affinity for oxygen?

2,3-bisphosphoglyceric acid (2,3-BPG).

Under what conditions do 2,3-BPG levels in red blood cells increase?

During adaptation to high altitudes, during strenuous exercise, and during pregnancy.

An increase in 2,3-BPG shifts the oxygen-hemoglobin dissociation curve to the _____, promoting oxygen _____ to tissues.

right; release

What are the three main ways carbon dioxide CO2 is transported in the blood?

Dissolved in plasma (about 5%), bound to hemoglobin (about 20%), and as bicarbonate ions HCO3- (about 70%).

What enzyme, found in red blood cells and endothelial cells, catalyzes the rapid conversion of CO2and water to carbonic acid?

Carbonic anhydrase.

The conversion of CO2 to bicarbonate ions HCO3- keeps the partial pressure of CO2 low in the blood, facilitating its diffusion _____ the tissues.

away from

In the lungs, the reaction catalyzed by carbonic anhydrase is reversed. What does bicarbonate reform into?

Carbon dioxide CO2 and water H2O, allowing the CO2 to be exhaled.

What part of the brainstem contains the primary rhythm-generating neural circuit for breathing?

The medulla.

The _____ nerve, formed by axons from the medulla, innervates the diaphragm to initiate inhalation.

phrenic

What is the role of the pons in the regulation of breathing?

It helps to regularize and smooth out the basic respiratory rhythm generated by the medulla.

What happens to breathing if the brainstem is cut below the pons but above the medulla?

Breathing continues, but it becomes irregular.

What happens to breathing if the spinal cord is severed in the neck, below the medulla?

Breathing ceases completely.

In mammals, what is the primary metabolic feedback stimulus for regulating the rate of breathing?

The partial pressure of carbon dioxide Pco2 in the blood.

How does the primary feedback for breathing in water-breathing animals differ from that in mammals?

In water-breathers, oxygen O2 level is the primary feedback stimulus for gill ventilation.

Where is the major site of sensitivity to blood Pco2 located?

On the ventral surface of the medulla.

Chemosensors in the medulla are directly stimulated by the concentration of what ion in the cerebrospinal fluid?

Hydrogen ions H+, which form when CO2 reacts with water.

What are the names of the neural tissue nodes in the large blood vessels that monitor blood oxygen levels?

The carotid bodies and aortic bodies.

What condition do the carotid and aortic bodies primarily respond to?

A significant fall in the partial pressure of oxygen Po2 in the blood.

What is perfusion?

The mechanism that circulates extracellular fluids (like blood) on the internal side of a gas exchange surface.

What property of gases means their molecular concentration increases as pressure increases?

They are compressible.

Why must respiratory surfaces for air-breathing animals remain moist with a thin film of fluid?

Oxygen and carbon dioxide must dissolve in this fluid before they can diffuse across the cell membranes.