Transport In Mammals - Session 3

Our blood consists of different types of cells. Red blood cells are specialized cells that undertake a crucial role in the circulatory system. Their primary function is to transport oxygen from the lungs to the body's tissues and organs. They also carry carbon dioxide from the tissues again to the lungs for exhalation.

Red blood cells are also called erythrocytes. Red blood cells are disc-shaped, biconcave structures without a nucleus. This shape increases the surface area of the cell, facilitating the exchange of gases. Do you know how the red blood cells transport oxygen and carbon dioxide?.

Red blood cells are composed mainly of hemoglobin. Hemoglobin is a protein that binds with oxygen and carbon dioxide. Hemoglobin is responsible for the transport of oxygen and carbon dioxide. Red blood cells also contain few organelles, such as mitochondria. This is because their primary function is oxygen transport, and they do not undergo cell division.

Let us understand how hemoglobin transports oxygen and carbon dioxide. Hemoglobin is a complex protein made up of four subunits. There are two alpha globin units and two beta globin units.Each subunit contains an iron atom. An Iron atom can bind with one molecule of oxygen.

Hemoglobin has a high affinity for oxygen, especially when oxygen levels are high. We know that oxygen levels are high in lungs. Initially, oxygen binds to one subunit. This induces a conformational change that makes it easier for the other subunits to bind with oxygen. The hemoglobin attached with oxygen is called oxyhemoglobin.

The resulting oxyhemoglobin is transported through arteries to various tissues. We know that tissues have lower level of oxygen. Oxyhemoglobin releases oxygen in tissues that have lower oxygen level. How does hemoglobin transport carbon dioxide from tissues to the lungs?

There are amino groups in hemoglobin. Carbon dioxide can bind to amino groups of hemoglobin. This results in the formation of carbaminohemoglobin. Carbaminohemoglobin is transported again to the lungs. Carbaminohemoglobin releases carbon dioxide in the lungs.

Red blood cells contribute to maintaining the pH of the blood by acting as buffers. They can take up or release hydrogen ions to help regulate the blood's acidity. Red blood cells have a lifespan of about 120 days. Old or damaged red blood cells are removed from circulation by the spleen and liver. New red blood cells are produced in the bone marrow.

Blood is also composed of white blood cells. White blood cells are also known as leukocytes. White blood cells typically have a nucleus that distinguishes them from red blood cells. White blood cells undertake a central role in defending the body against infections, pathogens, and foreign substances. Most white blood cells can move and change shape. This allows them to migrate to sites of infection or inflammation.

There are different types of white blood cells, each with specific functions and characteristics. Neutrophils are most abundant white blood cells. Neutrophils engulf and digest bacteria through phagocytosis. Neutrophils are quick responders to infections.

Lymphocytes are a type of white blood cells that have a central role in the immune system. Lymphocytes are characterized by their circular or slightly indented nucleus.They can be broadly categorized into two main types. These are B lymphocytes and T lymphocytes.

B Lymphocytes are primarily responsible for the production of antibodies, also known as immunoglobulins. Antibodies are proteins that recognize and bind to specific antigens. Antigens can be components of pathogens like bacteria or viruses. This binding marks the pathogens for destruction by other immune cells.

T lymphocytes have a crucial role in cell-mediated immunity. Unlike B lymphocytes, T lymphocytes do not produce antibodies directly. Instead, they recognize infected or abnormal cells. They directly destroy them or regulate immune responses.

Monocytes are a type of white blood cell. Monocytes are characterized by their large size and kidney shaped nucleus. Monocytes are professional phagocytes. They are adept at engulfing and digesting foreign particles, such as bacteria, dead cells, and other debris.

Monocytes are produced in the bone marrow and released into the bloodstream. They circulate in the blood for a relatively short period, typically a few days to a few weeks. Upon encountering signals of infection or inflammation, monocytes migrate out of the bloodstream into tissues. Upon reaching tissues, they can mature into macrophages. Macrophages are versatile immune cells with enhanced phagocytic abilities. They are essential for maintaining tissue homeostasis and responding to infections.