What Are the Main Types and Effects of Hypoxia in Biology?
What is Hypoxia?
Hypoxia is a medical condition in which a region in the body is deprived of sufficient oxygen supply at the tissue level. It is a condition characterized by the absence of sufficient oxygen levels in the tissue affecting normal bodily functions. Hypoxia can be generalized in which the whole body is affected or local in which a region or a part of the body is affected. It is different from hypoxemia, a condition characterized by the blood which is deprived of oxygen. Hypoxia indicates tissues deprived of sufficient oxygen supply. Hypoxia may prove to be fatal if it turns into Anoxia, which is extreme hypoxia, which indicates a complete absence of oxygen in the tissues.
Hypoxia can be fatal and affect vital organs like the brain, heart, etc. Generally, its symptoms occur a few minutes after the deficiency in oxygen supply and the effects may be irreversible. Hypoxia may affect healthy individuals under certain circumstances. Different types of physical conditions give rise to different types of Hypoxia, which we will now study in detail.
Types of Hypoxia
Hypoxic Hypoxia
Hypoxic Hypoxia occurs when the atmospheric oxygen decreases. In high altitude, during drowning, or under certain conditions, when airways get choked and deprived of oxygen, and there’s an inadequate supply of oxygen to the lungs it results in this condition.
Anemic Hypoxia
This condition indicates blood's decreased ability to carry oxygen. It also implies a lesser number of hemoglobin molecules available for the binding of oxygen. Anemic Hypoxia can be a result of hemoglobin disorders like sickle cell anemia.
Stagnant Hypoxia
Blood contains hemoglobin which is an oxygen-binding molecule. Less blood supply naturally suggests less hemoglobin and less binding sites for oxygen. Thus, stagnant hypoxia is a condition in which blood flow becomes abnormally low in a state of shock or syncope or other states. Abnormally less flow of blood leads to oxygen starvation and stagnant hypoxia.
Histotoxic Hypoxia
In this case, cells or tissue in the body become inefficient to use up the oxygen carried by the bloodstream, despite normal oxygen supply and delivery of oxygen to such cells and tissues. It majorly occurs under the circumstances of poisoning.
Metabolic Hypoxia
Under conditions of stress or high metabolic activity, cells and tissues require more oxygen. Although this demand is fulfilled by the body in most cases, when the oxygen demand exceeds the oxygen supply, it results in metabolic hypoxia.
Causes of Hypoxia
Hypoxia is a condition that may occur due to various causes. Some of the common causes of hypoxia are listed below-
Asthma attacks leading to narrowing of the airways.
Collapsed lungs, fluid in the lungs, blood clot in an artery in the lungs, or scarred and damaged lungs.
Extremely distressing situations leading to a heart attack or lung damage causing hypoxia.
Lung related disorders like bronchitis, pulmonary edema leading to Hypoxia.
Heart ailments.
Conditions like anemia, sickle cell anemia, etc.
Environmental factors like low oxygen levels in high altitudes.
Accidents leading to brain injury and brain hemorrhage.
The inability of the tissues to absorb the oxygen supplied.
Carbon dioxide build-up due to being enclosed in closed spaces.
Inhalation of inert gases that lead to the sudden and severe onset of hypoxia.
Insufficient supply of oxygen-rich blood to the brain that impairs mental acuity, and results in brain damage and disorders.
Genetic disorders.
Congenital heart diseases.
Signs of Hypoxia
Common symptoms of hypoxia are as follows-
Headache
Shortening of breath called dyspnea
Syncope
Sluggishness
Ambivalence in decision making
Increased heart rate or breathing rate or both
Anxiety
Impaired motor coordination
Cyanosis
Impaired vision
How to Treat Hypoxia
Though the medical treatment of hypoxia involves the cause, type, and severity of hypoxia, the goal is to increase the oxygen supply. When common symptoms of hypoxia occur, which includes shortness of breath, oxygen therapy is provided to the patient. The patient is also given a mechanical ventilator under severe conditions. An increased supply of oxygen is provided to the body tissue by keeping the pressure in check. This greatly improves the condition of the patient who has suffered or is suffering from hypoxia. A few cases also involve supplying liquid oxygen to the body of the patient. Medications are also prescribed by doctors to treat some conditions of hypoxia.
Some of the passive measures include avoiding environmental or physical factors that trigger hypoxia. This means avoiding smoking, adopting a healthy diet, exercising regularly, performing yoga and breathing exercises, etc.
FAQs on Hypoxia: Meaning, Types, Causes & Symptoms
1. What is hypoxia, and how is it different from hypoxemia?
Hypoxia is a medical condition where the body's tissues are deprived of an adequate oxygen supply to perform their normal functions. It can affect the entire body (generalised hypoxia) or a specific region (local hypoxia). In contrast, hypoxemia refers specifically to low levels of oxygen in the arterial blood. While severe hypoxemia is a common cause of hypoxia, they are not the same; it's possible to have hypoxia even with normal blood oxygen levels if the cells cannot use the oxygen effectively (as in histotoxic hypoxia).
2. What are the four main types of hypoxia, as per the NCERT syllabus?
The four primary types of hypoxia relevant to the Class 11 and 12 Biology syllabus are:
- Hypoxic Hypoxia: Occurs when there is insufficient oxygen in the air being breathed, leading to low oxygen levels in the blood. A classic example is the effect of high altitude.
- Anemic Hypoxia: Results from a decreased oxygen-carrying capacity of the blood. This can be due to a low red blood cell count (anemia) or the presence of dysfunctional hemoglobin, such as in carbon monoxide poisoning.
- Stagnant (or Ischemic) Hypoxia: Happens when blood flow to the tissues is too slow to deliver adequate oxygen, even if the blood itself is well-oxygenated. This is seen in conditions like heart failure or shock.
- Histotoxic Hypoxia: Occurs when the body's cells are unable to utilize the oxygen delivered to them. This is typically caused by a toxin, such as cyanide, which interferes with cellular respiration.
3. What are the common physiological causes of hypoxia?
Hypoxia can be triggered by a variety of physiological factors, often related to the respiratory and circulatory systems. Common causes include:
- Respiratory Disorders: Conditions like severe asthma, pneumonia, or Chronic Obstructive Pulmonary Disease (COPD) can impair gas exchange in the lungs.
- Cardiovascular Issues: Heart failure or a heart attack can lead to stagnant hypoxia by reducing blood circulation.
- Anemia: A significant decrease in hemoglobin or red blood cells reduces the blood's ability to transport oxygen.
- Environmental Factors: Ascending to high altitudes where the partial pressure of oxygen is low is a primary cause of hypoxic hypoxia.
- Poisons or Toxins: Substances like carbon monoxide and cyanide can interfere with oxygen transport or cellular use, respectively.
4. What are the key physiological symptoms of developing hypoxia?
The body shows several signs as it becomes deprived of oxygen. Early symptoms often involve the nervous system and include confusion, restlessness, headache, and shortness of breath (dyspnea). As the condition worsens, more severe symptoms appear, such as:
- Tachycardia: An abnormally fast heart rate as the body tries to compensate by pumping blood faster.
- Cyanosis: A bluish discolouration of the skin, lips, and nail beds due to high levels of deoxygenated hemoglobin.
- Impaired Judgement: Difficulty with coordination and decision-making.
- Loss of Consciousness: In severe cases, the brain cannot function, leading to fainting or coma.
5. Why are the brain and heart the organs most vulnerable to the effects of hypoxia?
The brain and heart are the most susceptible to oxygen deprivation due to their extremely high metabolic rates and constant energy demands. Both organs rely almost exclusively on aerobic respiration to generate the vast amounts of ATP needed for their functions (like nerve impulse transmission and muscle contraction). They have very limited oxygen or glucose reserves and cannot sustain function through anaerobic metabolism for long. Therefore, any significant drop in oxygen supply can lead to irreversible cell damage and functional failure within minutes.
6. How exactly does high altitude cause hypoxic hypoxia?
At high altitudes, the percentage of oxygen in the air (about 21%) remains the same, but the total atmospheric pressure is lower. This results in a lower partial pressure of oxygen (pO2) in the inspired air. According to the principles of gas exchange, the diffusion of oxygen from the alveoli in the lungs into the blood is driven by this pressure gradient. A lower atmospheric pO2 reduces this gradient, making it harder for oxygen to bind to hemoglobin. This leads to decreased oxygen saturation of the blood (hypoxemia), causing hypoxic hypoxia throughout the body's tissues.
7. How does the body's long-term acclimatisation to hypoxia work?
When a person remains at high altitude for an extended period, the body undergoes physiological acclimatisation to cope with chronic hypoxia. Key long-term responses include:
- Increased Erythropoiesis: The kidneys detect low oxygen levels and release the hormone erythropoietin (EPO), which stimulates the bone marrow to produce more red blood cells. This increases the total oxygen-carrying capacity of the blood.
- Increased Myoglobin: The concentration of myoglobin, an oxygen-binding protein in muscles, increases to facilitate oxygen storage and delivery within muscle tissue.
- Increased Capillary Density: The body grows more capillaries in tissues, reducing the diffusion distance for oxygen from blood to cells.
- Increased 2,3-DPG: Red blood cells increase their concentration of 2,3-diphosphoglycerate, which helps unload oxygen more readily from hemoglobin to the tissues.
