Question

Partial pressure (in \(\mathrm{mmHg}\) ) of \(\mathrm{CO}_{2}\) in atmospheric air, alveoli, deoxygenated blood, oxygenated blood and tissues are (a) \(159,104,40,95,40\) (b) \(104,40,40,95,159\) (c) \(0.3,40,45,40,45\) (d) \(159,104,45,95,40\)

Short answer

Option (c) is the correct answer.

Step-by-step solution

Understand the concept of Partial Pressure

Partial pressure is the pressure that would be exerted by one of the gases in a mixture if it occupied the same volume on its own. It plays a vital role in respiration as the difference in partial pressure from a high pressure area to a low pressure area drives the oxygen and \(\mathrm{CO}_{2}\) exchange.

Analyze given options

The value of \(\mathrm{CO}_{2}\) partial pressure are given for atmospheric air, alveoli, deoxygenated blood, oxygenated blood and tissues for each option, in that order.

Select the right option

Option (c) is correct. The partial pressure of \(\mathrm{CO}_{2}\) in atmospheric air is low, approximately \(0.3 \mathrm{mmHg}\). In alveoli, it increases to \(40 \mathrm{mmHg}\), indicating \(\mathrm{CO}_{2}\) being released into the alveoli to be exhaled. Deoxygenated blood carries more \(\mathrm{CO}_{2}\) resulting in higher partial pressure (\(45 \mathrm{mmHg}\)). The \(\mathrm{CO}_{2}\) gets diffused in the lungs and the oxygenated blood carries less \(\mathrm{CO}_{2}\) leading to lower partial pressure (\(40 \mathrm{mmHg}\)). The tissues, with metabolism occurring actively producing \(\mathrm{CO}_{2}\), again have higher partial pressure of \(\mathrm{CO}_{2}\) (\(45 \mathrm{mmHg}\)).

Key concepts

Respiratory Physiology

Respiratory physiology involves understanding how gases like oxygen and carbon dioxide move in and out of the body. It focuses on the mechanisms by which breathing is controlled and how gas exchange occurs. This process ensures that oxygen enters the bloodstream while carbon dioxide is removed. The key components include the lungs, airways, and respiratory muscles.
The pressure differences between gases inside and outside the body drive this gas transfer. More specifically, when you inhale, the diaphragm contracts, creating a negative pressure inside the lungs, which draws atmospheric air in. Exhalation is usually passive, as muscles relax and air is pushed out due to natural elastic recoil of the lungs.
Understanding respiratory physiology helps in identifying various disorders and in designing medical interventions targeting the respiratory system.

Gas Exchange

Gas exchange is the process by which oxygen is absorbed into the bloodstream and carbon dioxide is released from it. This essential exchange occurs in the lungs' small air sacs called alveoli, which are surrounded by capillaries.
Gas exchange relies heavily on the concept of partial pressure. Each gas in a mixture of gases exerts its own pressure, called partial pressure, proportionate to its concentration. This partial pressure gradient is crucial for gas exchange.

• Oxygen in the alveoli has a higher partial pressure than in the deoxygenated blood.
• Carbon dioxide in the deoxygenated blood has a higher partial pressure than in the alveoli.

Thus, gases move from areas of higher partial pressure to lower partial pressure, enabling necessary atmospheric gases to support life.

Carbon Dioxide Transport

Transport of carbon dioxide (CO₂) in the blood occurs primarily in three forms. Understanding these forms is key for comprehending how CO₂ levels are regulated and maintained in the body.

• Dissolved CO₂: Roughly 7% of CO₂ is dissolved directly in the plasma.
• Carbaminohemoglobin: About 23% bonds with hemoglobin in red blood cells.
• Bicarbonate ions: The remaining 70% is transported as bicarbonate ions. CO₂ reacts with water to form carbonic acid, which dissociates to bicarbonate and hydrogen ions.

Partial pressure of CO₂ is essential for this transport, as changes in partial pressures drive the conversion between these different forms. Efficient conversion and transport mechanisms help maintain the acid-base balance of the blood.

Alveolar Gas Exchange

Alveolar gas exchange is the intricate process taking place in the lungs where gases are swapped between the alveoli and blood. This exchange ensures the removal of carbon dioxide from the blood and the uptake of oxygen to be circulated throughout the body.
During this process:

• Oxygen diffuses from the alveoli into the blood because the partial pressure of oxygen is higher in the alveoli than in the capillary blood.
• Carbon dioxide diffuses from the blood into the alveoli since its partial pressure is higher in deoxygenated blood.

Efficient alveolar gas exchange is crucial for maintaining overall respiratory health and enables the body to function optimally. Issues in gas exchange can lead to respiratory disorders, emphasizing the importance of understanding its mechanics.