Ventilation

Question 1

What are the four components of respiration?

Answer 1

1. Bulk transport
2. Exchange of gases between respiratory medium and circulatory fluid
3. Transport in body fluid
4. Exchange of gases between circulatory fluid and tissues

Question 2

What is the difference between external and internal respiration?

Answer 2

External respiration involves getting the respiratory medium into the body to exchange sites while internal respiration involves the exchange of gases and transport inside of the body.

Question 3

Keeping Fick’s Law in mind, how could you hypothetically increase the rate of diffusion?

Answer 3

Rate = K x A x G/D
So: to increase diffusion you could increase the surface area, decrease the distance traveled, or increase the gradient (partial pressure for gases).

Question 4

What is the relative percentage of oxygen in dry air?

Answer 4

21%

Question 5

What is the relative percentage of carbon dioxide in dry air?

Answer 5

less than 1%, there’s very little.

Question 6

What is the pressure at sea level?

Answer 6

760 mmHg

Question 7

Which has less oxygen, dry air or humid air?

Answer 7

Humid air. The presence of humidity in the air means the total percentage occupied by other gases will decrease, and thus their partial pressures will also decrease.

Question 8

What factors affect partial pressure?

Answer 8

Altitude: Higher altitudes have lower total pressures and thus they must have lower partial pressures (relative to sea level)
Humidity: More humid areas will have lower partial pressures compared to low humidity areas at the same altitude.

Question 9

What factors affect solubility of gases in water?

Answer 9

Temperature: Colder fluids hold more gases
Salinity: If there is lots of stuff dissolved, more stuff doesn’t want to dissolve
Partial pressure of surroundings: If the air’s partial gas pressure is higher than the water’s, gases will dissolve until they reach partial pressure equilibrium.

Question 10

What are some factors that influenced the evolution of respiratory systems?

Answer 10

The size of an organism: Diffusion only works over very short distances. Larger organisms needed something new.
Metabolic rates: Higher metabolism means higher oxygen demand
Habitat: terrestrial, aquatic, humid, altitude, temperature. Lot of variety.

Question 11

Describe the differences between tidal and unidirectional ventilation.

Answer 11

In tidal ventilation, respiratory medium enters and exits by the same pathway. In unidirectional ventilation, it’s a one-way path.

Question 12

What portions of the mammalian respiratory system constitute the upper airways? What is the function of the upper airways?

Answer 12

The mouth, nose, pharynx, and larynx. The main role is to condition the air to enter the body with the mouth, nose, and pharynx filtering and humidifying the air and the larynx allowing us to make sound.

Question 13

What are the divisions of the lower airways? How do they differ?

Answer 13

The lower airways consist of the trachea, bronchi, conducting and respiratory bronchioles and alveoli. The former three are part of the conducting zone, the latter two are the respiratory zone. The conducting zone transports the respiratory medium to the respiratory zone, where gas exchange occurs.

Question 14

What is the functional unit of respiration?

Answer 14

The alveolus/alveoli.

Question 15

Describe the mucus escalator process and its function.

Answer 15

In the conducting zone, goblet cells secrete mucus to capture more particles and cilia beat upwards to move this mucus to the pharynx, where we swallow it.

Question 16

How does cystic fibrosis affect respiration?

Answer 16

It impacts the secretions of goblet cells and creates thickened mucus, making it much harder to breathe.

Question 17

What are some key features of the respiratory zone?

Answer 17

Large surface area for gas diffusion, moist for gases to dissolve, and macrophages to get rid of any additional particles and bacteria.

Question 18

Why do alveoli tend to collapse? What prevents this from happening?

Answer 18

Alveoli are wrapped in fibers called elastins which act like rubber bands. Alveoli are also covered in a moist inner layer and surface tension pulls this liquid together to attempt to make a droplet.
A surfactant opposes the surface tension and the pleural sac opposes the elastin by holding the lungs open with pleural pressure. The visceral pleura is attached to the alveoli and these lung collapsing forces pull the pleura inwards, but the parietal pleura attached to the ribs and chest wall pull the pleural sac outwards. This thus generates a negative pressure space within the pleural fluid that holds open the lung.

Question 19

What are the functions of the pleural sac?

Answer 19

To make smooth, free movement and to hold the lungs open.

Question 20

What are the steps of inhalation?

Answer 20

1. External intercostals contract, this squeezes the ribs together and lifts the ribcage upwards.
2. The diaphragm contracts and expands the chest cavity downwards
3. The parietal pleura is pulled outwards
4. The visceral pleura is dragged down with everything else
5. The lung expands and negative pressure sucks in air.

Question 21

What are the steps of passive exhalation? Of active exhalation?

Answer 21

At rest it’s passive.
1. Relax external and internal intercostals and diaphragm
2. Elastic recoil of the chest cavity (collapsing forces of elastins and surface tension) which increases the lung air pressure
3. Air is pushed out

During exercise it’s active.
1. Contract internal intercostals to compress everything
2. The abdominal muscles contract to squeeze everything and push the diaphragm back up
3. This results in an increase in lung air pressure, air is pushed out.

Question 22

Define lung compliance.

Answer 22

Lung compliance is how easy or hard it is to expand the lung. A very compliant lung increases volume easily, a very stiff lung does not.

Question 23

What are some diseases that affect compliance?

Answer 23

Emphysema: the alveoli fuse and reduce the surface area of the lung. Increased compliance, harder to exhale.
Pulmonary Fibrosis: Scar tissue builds up and reduces surface area for gas exchange, this decreases compliance and makes it harder to inhale.
Particulates can damage the lung and cause these diseases. They can both occur at once making hard inhales and exhales.

Question 24

What is pleurisy?

Answer 24

An inflammation of the pleura, it causes painful breathing due to friction of the lungs.

Question 25

What is dead space? What are the types of dead space?

Answer 25

Dead space is area in the lung that doesn’t contribute to gas exchange. It’s full of stale air.
There are three types.
Anatomical dead space: this is the volume of the conducting zone. When we exhale we don’t remove all the air from our lungs, and as there are no alveoli in the conducting zone no gas exchange occurs.
Alveolar dead space: a reduction in the size or number of alveoli being used due to disease or natural causes (pulmonary fibrosis or just sitting down)
Physiological deadspace: The total sum of alveolar and anatomical dead space.

Question 26

What are the two main reasons the lung has lower partial pressure of oxygen compared to the atmospheric air?

Answer 26

Humidity and dead space.

Question 27

Define these spirogram terms: total capacity, tidal volume, functional residual capacity, expiratory reserve volume, inspiratory reserve volume, residual volume, inspiratory capacity, vital capacity.

Answer 27

Total capacity: the entire spirogram
Tidal volume: the span of normal breathing (inhale + exhale)
Functional residual capacity: expiratory reserve volume + residual volume
Expiratory reserve volume: the maximum volume of an exhale above a normal exhale
Inspiratory reserve volume: the maximum volume of an inhale above a normal inhale
Residual volume: dead space
Inspiratory capacity: the maximum amount of air you can inhale (tidal volume + inspiratory reserve volume)
Vital capacity: the maximum you can inhale to the maximum you can exhale.

Question 28

What are the basic types of ventilatory structures?

Answer 28

The lung, the external gill, and the internal gill. The lung is respiratory tissue projected into the body, the external gill is fully external and the internal gill is external to the viscera but covered by a protective layer.

Question 29

Describe the flow of air through a bird’s lung. What differences does it have to a mammalian tidal lung?

Answer 29

On the first inhale air moves to the posterior air sac. On the first exhale the air moves to the parabronchi. On the second inhale the air moves to the anterior air sac. On the second exhale the air exits the trachea.
There is less dead space due to unidirectional flow and bird lungs are rigid due to the parabronchi. This supports flight due to the maintenance of a higher partial pressure gradient.

Question 30

Describe the flow of air through an insect. What differences does this have to mammalian tidal lungs?

Answer 30

Insects have a network of gas filled tubes called a tracheal system. They ventilate by pumping these tubes.
It differs from mammals because it isn’t a lung but it is still tidal.

Question 31

What are some examples of invertebrate ventilation?

Answer 31

Insect tracheal systems, spider and scorpion tidal book lungs, squid unidirectional mantle -> siphon flow, diffusion across skin.

Question 32

How does size affect gas exchange surface area? How do exotherms and endotherms compare in gas exchange surface area at the same size?

Answer 32

Increased size = increased gas exchange surface area. Exotherms have lower metabolic rates and thus lower oxygen demand and have lower gas exchange surface areas. On the slide tuna is an exception because it has partial heterothermy to support fast swimming.

Question 33

Define countercurrent, concurrent, and crosscurrent gas exchange. Where can they be found? Which is most efficient?

Answer 33

Countercurrent: Respiratory medium and blood are flowing in opposite directions. Most efficient, allows most oxygen intake. Fish gills.
Concurrent: Respiratory medium and blood are flowing in the same direction. Least efficient. Mammal lungs.
Crosscurrent: Blood flows perpendicular to respiratory medium. Better than concurrent, worse than countercurrent. Bird lungs.
Invertebrates don’t usually have tightly organized flow.

Question 34

Is dissolved oxygen enough to supply our respiratory demands? If not, how do we accommodate for this deficit?

Answer 34

It is not, we accommodate this through respiratory pigments in the circulatory medium (hemoglobin and myoglobin in blood for vertebrates) that bind oxygen.

Question 35

What are the three main respiratory pigments and what are their characteristics?

Answer 35

Hemoglobin: 4 heme and 4 globin. Bright red when saturated with oxygen, dark red when not. In vertebrates.
Myoglobin: 1 heme 1 globin in vertebrates (muscles specifically)
Hemocyanin: in molluscs and arthropods, copper-based

Question 36

Why does the presence of a respiratory pigment allow for greater oxygen transport?

Answer 36

When hemoglobin (for example) binds to oxygen, it removes this oxygen from the blood and decreases the partial pressure of oxygen in the blood. Thus, due to pressure gradients, more oxygen will be pushed to dissolve into the blood, allowing for more transport.

Question 37

What is cooperativity?

Answer 37

Cooperativity in respiration involves the binding of an oxygen to one heme site on a hemoglobin increasing the affinity of the other heme sites for oxygen. It does not affect myoglobin because it has only one heme and if it affects hemocyanin we did not discuss it.

Question 38

How are the oxygen dissociation curves for myoglobin and hemoglobin shaped? Why do they differ?

Answer 38

Myoglobin has a sharp incline and a plateau. Hemoglobin is s-shaped. This is due to cooperativity. Notably: myoglobin at low partial oxygen pressures is better at becoming saturated than hemoglobin and myoglobin’s plateau is lower than hemoglobin’s.

Question 39

What is a P50?

Answer 39

The partial pressure required to saturate a pigment to 50%. It’s a measure of affinity. A higher P50 means a lower affinity and vice versa. Ex: because of their shapes on the oxygen dissociation curve, myoglobin has a higher affinity for oxygen than hemoglobin because it has a lower P50.

Question 40

What factors reduce hemoglobin’s oxygen affinity?

Answer 40

Heat, organic phosphates, low pH, and increased CO2. We see these conditions during exercise, it’s why hemoglobin releases oxygen in working tissues.

Question 41

What is a Bohr shift? A Reverse Bohr shift? A Root shift? What’s a key difference to keep in mind to identify them?

Answer 41

A Bohr shift is a shift to the right of an oxygen dissociation curve based on a lower pH. This means a lower oxygen affinity. This is relevant during exercise (lactic acid).
A reverse Bohr shift is a shift to the left of an oxygen dissociation curve based on a higher pH. This means a higher oxygen affinity. This can be seen in the lung.
A Root shift is a shift down in the maximum saturation of an oxygen dissociation curve due to a lower pH.

The Bohr shifts move to the left (reverse) or right (normal) and the maximum saturation remains the same. A Root shift is not found in mammals and the maximum saturation is decreased.

Question 42

What are some key relationships in the carbonic acid reaction to understand?

Answer 42

An increase in dissolved CO2 will push the reaction right and create more bicarbonate and dissolved hydrogen ions (and carbonate). An increase in bicarbonate will push the reaction left and increase the amount of dissolved carbon dioxide and water (and carbonic acid) and decrease the amount of dissolved hydrogen ions (and carbonate)

Question 43

What three ways is CO2 present in the blood?

Answer 43

Pure dissolved CO2: 10%. Only part that counts to PCO2
Bicarbonate: 80% most important
Bound to Hb: the rest. Related to the Haldane effect (Hb with less O2 has higher affinity for CO2, vice versa)

Question 44

How does CO2 loading occur in the blood? How does CO2 unloading occur at the lungs?

Answer 44

Working tissues have an increased PCO2. This pushes CO2 into the blood. Some of it dissolves, some of it pushes the carbonic acid reaction to make bicarbonate via carbonic anhydrase and protons (which associate with proteins), and some of it enters red blood cells. In these red blood cells some carbonic anhydrase is present, creating bicarbonate and protons again (which associate with proteins OR hemoglobin, causing dissociation of oxygen) and some of the carbon dioxide directly associates with hemoglobin causing the dissociation of oxygen. In the red blood cell there is also a rapid anion exchange protein in the cell wall which through a chloride shift exchanges a chloride into the cell for a bicarbonate out of the cell, thus pushing the carbonic acid reaction to the right inside the blood cell
.

At the lungs, the rapid anion exchange protein stops. This drives the carbonic acid reaction to the left because of a build up of bicarbonate. This increases the partial pressure of CO2 in the plasma which diffuses out of the blood and into the alveoli.

Question 45

What are some ways organisms raise blood pH?

Answer 45

1. Rid excess CO2 by breathing quickly (respiratory alkalosis), causing the carbonic acid reaction to shift to the left (removing protons and bicarb)
2. Rid excess protons: proteins soak up them, kidneys remove them, and bicarbonate can buffer them when the protons are from PROCESSES OTHER THAN BREATHING.
   AQUATIC ONLY: Ion exchange sites on the skin and gills, proton pumps remove protons (V-type ATPase in apical membrane of MRCs)

Question 46

What are some ways organisms lower blood pH?

Answer 46

1. Hold onto more CO2 by breathing slowly (respiratory acidosis), driving the carbonic acid reaction to the right (more protons and bicarb)
2. Kidney removes bicarbonate from the blood, driving the carbonic acid reaction to the right (more proteins and bicarb)
   AQUATIC ONLY: Ion exchange sites on the skin and gills, chloride shift moves the bicarbonate out of the body (in exchange for chloride. Electroneutral anion exchanger in apical membrane of MRCs and pavement cells)

Question 47

What is the oxygen cascade?

Answer 47

A sequential decrease in oxygen partial pressures at each respiratory stage to make sure oxygen is able to be offloaded to each place it is required.

Question 48

What is V/Q matching? How does it work as a form of control?

Answer 48

V/Q matching is ventilation/perfusion. It refers to matching the flow of the respiratory medium to the flow of blood in the lungs.

Question 49

What are some ways mammals handle a V/Q ratio that is too low or too high with local control?

Answer 49

Too much CO2: increase ventilation by relaxing the alveolar duct muscle
Too little O2: decrease perfusion by contracting capillary muscles.
THESE ARE NOT MUTUALLY EXCLUSIVE.

Question 50

What is high altitude pulmonary edema?

Answer 50

A condition where at high altitudes, the partial oxygen pressure is so low that the oxygen cascade breaks, causing so much constriction of the capillaries surrounding the alveoli that fluid gets squeezed out of the capillaries into the alveoli. Treatment involves getting to a lower altitude and breathing pure oxygen.

Question 51

Systemic control differs from local control in that it responds to changes in pH or the partial pressure of oxygen. Why are these the factors that it monitors and how does this differ in aquatic and terrestrial organisms?

Answer 51

In terrestrial organisms, it primarily responds to pH because we have a fair amount of oxygen available. This is because the pH of the blood is directly tied to the carbonic acid reaction which is tied to the amount of carbon dioxide in the blood. Carbon dioxide and oxygen diffuse at similar rates, so monitoring one tends to make the other correct.
In aquatic organisms, it primarily responds to the partial pressure of oxygen because there isn’t a lot of oxygen available.

Question 52

In mammals, what are our pH and PO2 sensors?

Answer 52

For PO2 we rely on peripheral sensors called our carotid and aortic bodies associated with the carotid and aorta.
For pH we rely on our central sensor in our medulla which detects changes to our cerebrospinal fluid’s pH and is our primary sensor. We additionally also rely on carotid and aortic bodies.

Question 53

How do peripheral sensors act as controls during exercise? When vomiting?

Answer 53

1. An increase in lactic acid lowers the blood pH, this is detected and responded to by an increase in breathing rate.
2. Vomiting removes acids and increases our blood pH as a consequence, this is responded to by a decrease in breathing rate.

These push the carbonic acid reaction to the left and right respectively.