Question

A large proportion of oxygen is left unused in the human blood even after uptake by the body tissue. This oxygen (a) Is enough to keep oxyhaemoglobin saturation at \(96 \%\) (b) Helps in releasing more oxygen to epithelial tissues. (c) Acts as reserve during muscular exercise. (d) Raise \(\mathrm{pCO}_{2}\) of blood to \(75 \mathrm{~mm} \mathrm{Hg}\).

Short answer

The statements (a) and (c) are correct. The remaining oxygen in the blood maintains the saturation of oxyhaemoglobin and serves as a reserve during times of oxygen demand, such as during physical exercise. The statements (b) and (d) are incorrect, as the remaining oxygen does not directly contribute to releasing more oxygen to the tissues and does not impact \(pCO_{2}\) in the blood.

Step-by-step solution

Review Statement 1

(a) Is enough to keep oxyhaemoglobin saturation at \(96 \%\). \nThis statement is plausible as oxyhaemoglobin saturation levels are usually around \(95\% - 98 \% \) in a healthy individual. The remaining oxygen in the blood does contribute to keeping these levels high.

Review Statement 2

(b) Helps in releasing more oxygen to epithelial tissues. \nThe extra oxygen in the blood doesn't directly help releasing more oxygen to epithelial tissues. Oxygen release depends on the requirement of the individual cells and the gradient between blood oxygen level and tissue oxygen level.

Review Statement 3

(c) Acts as reserve during muscular exercise. \nUpon exertion, such as during an exercise, the need for oxygen in muscle tissues increases. The remaining oxygen in the blood stream does act as a reserve during such times.

Review Statement 4

(d) Raise \(pCO_{2}\) of blood to \(75 \mathrm{~mm}~Hg. \nThe statement is not correct as remaining oxygen in the blood does not contribute to carbon dioxide pressure. It is rather the metabolic activity that could increase \(pCO_{2}\) in the blood. A \(pCO_{2}\) of \(75 \mathrm{~mm} \mathrm{Hg} \) would be significantly higher than in a healthy individual and would be indicative of a pathological state, likely related to the inability to adequately eliminate carbon dioxide.

Key concepts

Oxyhaemoglobin Saturation

In our bloodstream, oxygen binds to a protein called hemoglobin, creating a complex known as oxyhaemoglobin. This binding is crucial as it allows oxygen to be transported efficiently throughout our body. Oxyhaemoglobin saturation refers to the percentage of hemoglobin molecules that are bound with oxygen. In a healthy person, this saturation usually stands between 95% to 98%. However, even after our tissues use up oxygen, a large proportion remains in the blood. This ensures that our oxyhaemoglobin saturation levels remain high, generally around 96%. This constant level is essential because:

• It provides a buffer or reserve of oxygen that can be quickly utilized.
• It ensures efficient transport of oxygen to all body tissues.
• It supports cellular metabolism since oxygen is a key player in energy production.

Understanding this process is pivotal for grasping how our body maintains oxygen homeostasis. It's not just the availability of oxygen, but how efficiently it is transported and delivered that matters.

Metabolic Activity

The metabolic activity of our body refers to the chemical processes that occur within cells to sustain life. Oxygen is vital for metabolism because it allows cells to convert nutrients into energy. During these metabolic processes, various by-products are produced, including carbon dioxide (CO₂). Here’s why oxygen and metabolism are closely linked:

• Oxygen acts as a final electron acceptor in cellular respiration, which is crucial for energy production.
• Increased metabolic activity, such as during exercise, leads to higher demand for oxygen.
• Carbon dioxide levels increase as a by-product of metabolism, requiring efficient removal from the body.

It’s essential to understand that the remaining oxygen in the blood, following tissue uptake, does not directly increase CO₂ levels. Instead, it's the activity of metabolism itself that affects the rise of CO₂. Typically, a high blood level of CO₂, such as 75 mm Hg, indicates a state of imbalance or pathology, as the body struggles to expel CO₂ efficiently.

Muscular Exercise Reserve

Engaging in muscular exercise significantly increases the demand for oxygen within muscle tissues to support the heightened metabolic activity. Muscles require this oxygen to continue producing the energy needed for prolonged activity. The body cleverly manages this demand by tapping into its reserve of oxygen in the blood:

• During exercise, this reserve becomes critical in maintaining energy production.
• The oxygen reserve ensures muscles can function efficiently and sustain exertion.
• This is why regular exercise increases the body's capacity to utilize stored oxygen effectively.

Without this reserve, muscles would fatigue much faster, leading to decreased performance and quicker exhaustion. Thus, understanding how oxygen reserves are used during exercise helps us appreciate the body's remarkable ability to adapt to physical stress.