Red Blood Cell Structure and Function | Anatomy and Physiology

Red Blood Cells

Red blood cells, or erythrocytes, are the most common type of blood cell. According to the video, they are also the most common cell type in the body, with roughly 20–30 trillion in an adult. They develop from reticulocytes.

Shape and flexibility

Red blood cells have a biconcave shape, curving inward on both sides. This shape helps them pass through narrow capillaries and gives them a high surface-area-to-volume ratio, allowing oxygen and carbon dioxide to move in and out more readily.

Proteins such as spectrin help their membranes flex, enabling the cells to squeeze through tight spaces.

Missing structures

Mature red blood cells lack a nucleus and DNA, endoplasmic reticulum, and mitochondria. This leaves more room for gas transport and means they do not use the oxygen they carry to make ATP.

Gas Transport

Oxygen

Hemoglobin consists of four globin proteins—two alpha and two beta—each associated with an iron-containing heme group. Each heme group can bind one oxygen molecule, so a hemoglobin molecule can carry up to four.

The video estimates that each red blood cell contains about 300 million hemoglobin molecules, giving it a capacity of about 1.2 billion oxygen molecules. In the lungs, hemoglobin binds oxygen to form oxyhemoglobin, which is bright red. In tissues, hemoglobin’s affinity for oxygen decreases, allowing it to release oxygen where it is needed.

Carbon dioxide

Carbon dioxide travels in the blood by three routes:

• About 7% is dissolved in the blood.
• About 70% is converted into bicarbonate by the enzyme carbonic anhydrase.
• About 23% binds to hemoglobin, forming carbaminohemoglobin.

Blood carries carbon dioxide back to the lungs, where it is released and exhaled.

Speakers and Sources

• Speaker: One unnamed narrator/presenter.
• Source: Interactive Biology.
• The narrator refers to a previous video about red blood cell development and another about oxygen release and the Bohr effect. These videos are mentioned but are not featured in the subtitles.

The video ends by previewing a follow-up on disorders of erythrocytes.