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Histology Spotlight - Blood

Welcome to the wonderful world of histology. Histology is how we study the human body on the cellular level. This week we are going to take a look at blood histology.

Blood vessels are composed of three layers, going from inner to outer we have the tunica intima, tunica media, and tunica adventitia. The innermost layer, the tunica intima, has endothelial cells and the basal lamina. The tunica media is made up of smooth muscle and the tunica adventitia is made up of connective tissue.

These layers are seen in both veins and arteries, however, the tunica media is a lot thicker in arteries.

The average human has 5 litres of blood in their body. Blood itself is made up of red blood cells, white blood cells, platelets, and plasma. Plasma contains water, proteins, and nutrients. Most of the blood's protein is produced in the liver. This includes serum albumin which helps the blood to clot.

Red blood cells are biconcave discs that are only 7µm in diameter. They have no nucleus. They contain haemoglobin, a protein responsible for transporting oxygen in the body. Red blood cells last for an average of 120 days. Aged and deformed cells are removed by the spleen.

White blood cells are part of the immune system and help in defending the body. There are many specialised white blood cells, including neutrophils, eosinophils, basophils, lymphocytes, and monocytes.

Neutrophils are granulocytes and are the most common type of leukocyte. They get their name for being neutral - they stain poorly with both basic and acidic dyes. They ingest bacteria or damaged cells and are produced in the bone marrow.

Eosinophils get their name from staining well with the dye eosin, commonly used in the histology lab. They help with inducing and maintaining inflammation as seen in an allergic reaction.

Basophils are rare granulocytes that work in allergic reactions. They contain granules such as histamine.

Monocytes are found in the blood and bone marrow and act as precursors of tissue macrophages.

Lymphocytes can be classed as B cells and T cells. They participate in the specific immune response.

Platelets are small cell fragments found in the blood and they play a role in clotting.

Blood is a lot more detailed than you may think!

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