Physiology of Respiratory Control and Hemoglobin

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Questions and Answers

What response occurs in the respiratory system when tidal volume is limited?

Increased respiratory rate (correct)

Decreased respiratory rate

Decreased minute ventilation

Increased tidal volume

Which type of hemoglobin is primarily composed of two α and two β chains?

HbS

HbA (correct)

HbA2

HbF

What is a physiological response to exercise regarding O2 consumption?

Increased O2 consumption (correct)

Fluctuating O2 consumption

No change in O2 consumption

Decrease in O2 consumption

What is associated with carbon monoxide poisoning in terms of cardiac pathology?

Myocarditis Signup and view all the answers

What effect does living at high altitude have on erythropoietin synthesis?

Increases erythropoietin synthesis Signup and view all the answers

What effect does an increase in temperature have on the O2-hemoglobin dissociation curve?

Causes it to shift to the right Signup and view all the answers

How does 2,3-BPG affect the affinity of hemoglobin for O2?

Decreases the affinity Signup and view all the answers

What role does erythropoietin (EPO) play in response to hypoxia?

It promotes the synthesis of red blood cells Signup and view all the answers

What happens to the O2-hemoglobin dissociation curve during high altitudes?

It shifts to the right Signup and view all the answers

In which zone of the lung is blood flow (Q) the highest?

Zone 3 Signup and view all the answers

Which statement describes the effect of decreased pH on the O2-hemoglobin dissociation curve?

It shifts to the right Signup and view all the answers

How does carboxyhemoglobin affect the loading and unloading of O2?

It decreases O2 unloading Signup and view all the answers

What mechanism primarily shifts the O2-hemoglobin dissociation curve to the left?

Increased pH Signup and view all the answers

During the buffering process in red blood cells, what happens to H+ ions generated from H2CO3?

They are buffered by deoxyhemoglobin Signup and view all the answers

What is the potential number of O2 molecules that a myoglobin molecule can bind?

1 Signup and view all the answers

What is the most common cause of cyanide poisoning?

Smoke inhalation Signup and view all the answers

Which treatment helps to convert cyanide to thiocyanate?

Sodium thiosulfate Signup and view all the answers

What characterizes the skin appearance of a patient with cyanide poisoning?

Cherry-red skin discoloration Signup and view all the answers

How does cyanide affect aerobic metabolism?

It inhibits aerobic metabolism, leading to hypoxia Signup and view all the answers

What causes the increased O2 binding affinity of fetal hemoglobin?

Decreased levels of 2,3-BPG Signup and view all the answers

What is the effect of a puncture in the intrapleural space?

Development of a pneumothorax Signup and view all the answers

What is the primary determinant of arterial and alveolar Pco2 when CO2 production is constant?

Alveolar ventilation Signup and view all the answers

Which of the following describes methemoglobin?

It is iron in the ferric (Fe3+) state Signup and view all the answers

Induced-methemoglobinemia can be used to treat cyanide poisoning by what mechanism?

Binding cyanide with methemoglobin Signup and view all the answers

What is the physiologic dead space composed of?

Anatomic dead space plus alveolar dead space Signup and view all the answers

Study Notes

Respiratory Control

When tidal volume is limited, the respiratory control centers increase the respiratory rate to restore minute ventilation

Exercise Response

Exercise decreases venous O2 content
Exercise increases ventilation rate to meet O2 demand
Exercise increases O2 consumption
Exercise increases pulmonary blood flow, due to increased cardiac output
Exercise increases venous CO2 content

Hemoglobin

Most adult hemoglobin is composed of 2 α and 2 β subunits; known as HbA
One normal type of hemoglobin is HbA2 which is composed of two α and two δ chains
One normal type of hemoglobin is HbF which is composed of two α and two γ chains

Erythropoietin

Synthetic erythropoietin (e.g., epoetin) is often supplemented in chronic kidney disease
Living at high altitude chronically causes hypoxia which increases the synthesis of erythropoietin, causing polycythemia

Poisoning

Many patients with inhalation injury present secondary to burns, CO inhalation, cyanide or arsenic poisoning

Carbon Monoxide Poisoning

Carbon monoxide poisoning is associated with myocarditis
Hypoxia may be caused by carbon monoxide poisoning, which decreases the O2 content of blood
Carbon monoxide poisoning presents with a cherry-red skin appearance
The most common cause of cyanide poisoning is smoke inhalation

Cyanide Poisoning

Carbon monoxide, cyanide, and sodium azide are inhibitors of complex IV of the ETC
Patients with cyanide poisoning have a narrowing of the venous-arterial PO2 gradient
Patients with cyanide poisoning present with an "almond" breath odor and cherry-red skin discoloration
One treatment for cyanide poisoning is sodium thiosulfate, which helps restore rhodanese-mediated metabolism of cyanide to thiocyanate
One treatment for cyanide poisoning is sodium nitrite, which induces methemoglobinemia
Cyanide may inhibit the ETC by binding Fe3+, preventing transfer of electrons to O2 in complex IV
The increased O2 binding affinity of fetal hemoglobin results from decreased affinity of HbF for 2,3-BPG
Cyanide inhibits aerobic metabolism, resulting in hypoxia unresponsive to supplemental O2

Lung Volumes & Capacities

Functional residual capacity (FRC) may be measured using helium dilution or body plethysmography
The volume of the anatomic dead space plus the alveolar dead space comprises the "physiologic dead space"

Gas Exchange & Ventilation

If CO2 production is constant, then the arterial and alveolar Pco2 is determined by alveolar ventilation
The difference between PAO2 − PaO2 is known as the alveolar-arterial (A-a) gradient and is normally 5 - 10 mmHg in a non-smoking young adult

Lung Mechanics

The slope of a respiratory system pressure-volume curve represents lung compliance
Hysteresis occurs due to the need to overcome surface tension forces during lung inflation (inspiration)
At functional residual capacity, the inward pull of the lung is balanced by the outward pull of the chest
If a sharp object punctures the intrapleural space, the intrapleural pressure becomes equal to atmospheric pressure, causing a pneumothorax
When lung volume is less than FRC, there is a net expanding force on the lung-chest wall system
When lung volume is greater than FRC, there is a net collapsing force on the lung-chest wall system
Alveoli have increased tendency to collapse on expiration

Airway Resistance

Airway resistance is inversely proportional to the fourth power of the radius of the airway
The transpulmonary pressure across the lungs is calculated as alveolar pressure minus intrapleural pressure

Lung Diffusing Capacity (DL)

The lung diffusing capacity (DL) decreases in emphysema due to decreased surface area (A)
The lung diffusing capacity (DL) decreases in pulmonary fibrosis due to increased wall thickness (Δx)
The lung diffusing capacity (DL) increases during exercise due to increased surface area (A)

Physiologic Shunt

The partial pressure of O2 in arteriolar blood is slightly lower than alveolar air due to the "physiologic shunt"
The two sources of the physiologic shunt are bronchial blood flow and a small portion of coronary venous blood

Gas Transport

The total gas concentration in solution is equal to the dissolved gas + bound gas + chemically modified gas
In perfusion-limited gas exchange, diffusion can be increased only if blood flow increases
At high altitude the partial pressure gradient of O2 is lower and thus equilibration takes longer
O2 is carried in blood in two forms: dissolved (2%) or bound to hemoglobin (98%)
Each subunit of hemoglobin contains a heme moiety, which is an iron-binding porphyrin and a polypeptide chain

Methemoglobin

If hemoglobin contains iron in the ferric (Fe3+) state, it is called methemoglobin
Methemoglobin has an increased affinity for cyanide relative to hemoglobin
Methemoglobinemia may present with cyanosis and chocolate-colored blood
Induced-methemoglobinemia (i.e.nitrites followed by thiosulfate) may be used to treat cyanide poisoning
Methemoglobinemia can be treated with methylene blue or vitamin C (ascorbic acid)

Hemoglobin Oxygen Affinity

The taut form of hemoglobin has a low affinity for O2
The relaxed form of hemoglobin has a high affinity for O2
The sigmoidal shape of the oxygen-hemoglobin dissociation curve is due to positive cooperativity (increased affinity for each successive O2 bound)
A myoglobin molecule has the potential to bind 1 O2 molecule(s)

Shifts in the O2-Hb Dissociation Curve

Shifts of the O2-Hb dissociation curve to the right occur when there is decreased affinity of hemoglobin for O2
Shifts of the O2-Hb dissociation curve to the right cause increased unloading of O2 at tissues
An increase in temperature causes the O2-hemoglobin dissociation curve to shift to the right
An increase in 2,3-BPG causes the O2-hemoglobin dissociation curve to shift to the right
2,3-BPG decreases the affinity of hemoglobin for O2 by binding to hemoglobin β chains
High altitudes indirectly cause the O2-hemoglobin dissociation curve to shift to the right
An increase in pH causes the O2-hemoglobin dissociation curve to shift to the left
A decrease in temperature causes the O2-hemoglobin dissociation curve to shift to the left
An increase in hemoglobin F causes the O2-hemoglobin dissociation curve to shift to the left

Carbon Monoxide (CO) Binding

Carboxyhemoglobin is a form of hemoglobin bound to CO in place of O2
Carboxyhemoglobin causes the O2-hemoglobin dissociation curve to shift to the left
Carboxyhemoglobin causes decreased unloading of O2 at tissues

Erythropoiesis

Erythropoietin (EPO) is a hormone synthesized in the kidneys in response to hypoxia
Hypoxia-inducible factor 1α acts in renal fibroblasts to cause synthesis of the mRNA for erythropoietin

CO2 Transport

Deoxygenated hemoglobin may act as a buffer for H+ ions
Decreased O2 binding to hemoglobin causes increased affinity for CO2 and H+ (Haldane effect)
Increased O2 binding to hemoglobin causes decreased affinity for CO2 (Haldane effect)
In red blood cells (in plasma), CO2 is combined with H2O via the enzyme carbonic anhydrase, forming H2CO3
The H+ in red blood cells (from H2CO3) is buffered by deoxyhemoglobin
The HCO3- in red blood cells (from H2CO3) is transported into the plasma in exchange for Cl-
In the lungs, oxygenation of hemoglobin promotes H+ release from its buffering sites
In the lungs, HCO3- enters the red blood cells in exchange for Cl-

Pulmonary Vascular Resistance

Fetal pulmonary vascular resistance is very high because of generalized hypoxic vasoconstriction
Decreased Po2 (hypoxia) causes vasoconstriction in the pulmonary circulation
Increased Pco2 (hypercapnia) causes vasoconstriction in the pulmonary circulation
Decreased Po2 (hypoxia) causes vasodilation in the systemic circulation
Increased Pco2 (hypercapnia) causes vasodilation in the systemic circulation

Pulmonary Blood Flow Zones

In zone 1 (apex) of the lung, blood flow (Q) is lowest
In zone 3 (base) of the lung, blood flow (Q) is highest
Rank the following variables for zone 1 of the lung: PA, Pa, and Pv PA ≥ Pa > Pv
Rank the following variables for zone 2 of the lung: PA, Pa, and Pv Pa > PA > Pv

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Description

This quiz covers crucial concepts related to respiratory control, the effects of exercise on ventilation and blood flow, hemoglobin structure, and the role of erythropoietin in oxygen transport. Explore how these physiological factors interact during various conditions, including exercise and hypoxia.