🎞️ Video

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https://www.youtube.com/watch?v=UIvU-OuZHww

📗 Lectura

<aside> 📚 **Bibliografía: "**Components of the blood" by OpenStax College, Biology (CC BY 4.0).

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Blood, by definition, is a fluid that moves through the vessels of a circulatory system. In humans, it includes plasma (the liquid portion), blood cells (which come in both red and white varieties), and cell fragments called platelets.

• Plasma is the main component of blood and consists mostly of water, with proteins, ions, nutrients, and wastes mixed in.
• Red blood cells are responsible for carrying oxygen and carbon dioxide.
• Platelets are responsible for blood clotting.
• White blood cells are part of the immune system and function in immune response.

Cells and platelets make up about 45% percent percent of human blood, while plasma makes up the other 55% percent percent. The diagram below shows red blood cells, white blood cells of different types (large, purple cells), and platelets.

Plasma

Plasma, the liquid component of blood, can be isolated by spinning a tube of whole blood at high speeds in a centrifuge. The denser cells and platelets move to the bottom of the tube, forming red and white layers, while the plasma remains at the top, forming a yellow layer.

The plasma is about 90% percent water, with the remaining 10% percent made up of ions, proteins, nutrients, wastes, and dissolved gases. The ions, proteins, and other molecules found in plasma are important for maintaining blood pH and osmotic balance, with albumin (the main protein in human plasma) playing a particularly important role.

Some of the molecules found in the plasma have more specialized functions. For example, hormones act as long-distance signals, antibodies recognize and neutralize pathogens, and clotting factors promote blood clot formation at the site of wounds. (Plasma that’s been stripped of its clotting factors is called serum.) Lipids, such as cholesterol, are also carried in plasma, but must travel with escort proteins because they don’t dissolve in water.

Red Blood Cells

Red blood cells, or erythrocytes, are specialized cells that circulate through the body and deliver oxygen to tissues. In humans, red blood cells are small and biconcave (thinnest in the center, just 7-8μm in size), and do not contain mitochondria or a nucleus when mature.

These characteristics allow red blood cells to effectively perform their task of oxygen transport. Small size and biconcave shape increase the surface area-to-volume ratio, improving gas exchange, while lack of a nucleus makes additional space for hemoglobin, a key protein used in oxygen transport. Lack of mitochondria keeps red blood cells from using any of the oxygen they’re carrying, maximizing the amount delivered to tissues of the body.