Problem 165 - Objective Biology for NEET

Question

Assertion: WBCs accumulate at the site of wounds by diapedesis. Reason: It is the squeezing of leucocytes from the endothelium.

Step-by-Step Solution

Answer

Yes, the assertion and reason are correct. White blood cells (WBCs) accumulate at the site of wounds through diapedesis, which is indeed the process of leucocytes squeezing out from the endothelium to reach an injury site.

Step 1: Explanation of Diapedesis

Diapedesis is the process where white blood cells (leucocytes) move out of the circulatory system and towards the site of tissue damage or infection. It involves the cells changing shape to squeeze between the cells of the blood vessels (endothelium).

Step 2: Relation of Diapedesis to WBCs

White blood cells are a key part of the body's immune system and play a critical role in defending the body against infectious diseases and foreign substances. When an infection or injury occurs, causing tissue damage, the WBCs undergo diapedesis to accumulate at the injury site and contribute to the healing process.

Step 3: Verification of Assertion-Reason Pair

As both the assertion and reason correctly describe the phenomenon of diapedesis and establish its role in WBCs' movement towards wound sites, the assertion-reason pair is correct.

Key Concepts

White Blood Cells

White blood cells (WBCs), also known as leukocytes, are crucial components of your immune system. Their main role is to protect your body against infections and foreign invaders. There are several types of WBCs, including neutrophils, lymphocytes, monocytes, eosinophils, and basophils, each with a unique function in the bodys defense mechanism.

Neutrophils, for example, are the first responders to infection sites, where they engulf and destroy pathogens through a process called phagocytosis. Lymphocytes come in two main types: B cells, which are responsible for antibody production, and T cells, which either help other immune cells or kill infected cells and cancer cells directly. The variation in WBC types ensures a comprehensive defense system capable of tackling different threats to our health.

Immune System

The immune system is an intricate network of cells, tissues, and organs that work in harmony to defend the body against disease-causing microorganisms such as bacteria, viruses, fungi, and parasites. It can be categorized into two main components: the innate immune system, which provides immediate defense, and the adaptive immune system, which develops a targeted response based on recognition of specific pathogens.

The innate system encompasses barriers like the skin, and cellular defenses including natural killer cells and macrophages. The adaptive system involves the production of antibodies by B cells and the action of T cells, allowing for a more powerful and long-lasting immunity. Together, these systems deploy a range of defensive tactics, from simply barring entry to pathogens to remembering and quickly responding to past infections.

Leukocyte Migration

Leukocyte migration, or leukocyte trafficking, refers to the movements of white blood cells throughout the body and to sites of injury or infection. This highly coordinated process is crucial for maintaining tissue health and for the immune response to challenges. One key aspect of this migration is diapedesis, where leukocytes exit the bloodstream and move towards the tissues where they're needed.

During an inflammatory response, signaling molecules called chemokines guide leukocytes to the site of damage. They bind to the endothelium of blood vessels and then squeeze through the vessel walls, a process facilitated by their flexible shape. This ability to relocate so precisely is vital, as it allows WBCs to directly encounter and combat pathogens or to help with tissue repair, minimizing damage and promoting recovery.