Page 124 - 84 human physiolofy part-1

Chapter 7

Red Blood Cells

Overview

Red blood cell (erythrocyte) also known as "RBC's". RBC’s are formed
in the myeloid tissue or most commonly known as red bone marrow, although
when the body is under severe conditions the yellow bone marrow, which is
also in the fatty places of the marrow in the body will also make RBC’s. The
formation of RBC’s is called erythropoiesis ( erythro / red; poiesis /
formation). Red blood cells lose nuclei upon maturation, and take on a biconcave, dimpled, shape.
They are about 7-8 micrometers in diameter. There are about 1000x more red blood cells than white
blood cells. RBC's live about 120 days and do not self repair. RBC's contain hemoglobin which
transports oxygen from the lungs to the rest of the body, such as to the muscles, where it releases the
oxygen load.The hemoglobin gets it's red color from their respiratory pigments.

Shape

RBC'S have a shape of a disk that appears to be “caved in” or almost flattened in the middle; this is
called bi-concave. This bi-concave shape allows the RBC to carry oxygen and pass through even the
smallest capillaries in the lungs. This shape also allows RBCs to stack like dinner plates and bend as
they flow smoothly through the narrow blood vessels in the body. RBC's lack a nucleus (no DNA) and
no organelles, meaning that these cells cannot divide or replicate themselves like the cells in our skin
and muscles. RBC’s have a short life span of about 120 days, however, as long as our myeloid tissue is
working correctly, we will produce about 2-3 million RBC's per second. That is about 200 billion a
day! This allows us to have more to replace the ones we lose.

Main Component

The main component of the RBC is hemoglobin protein which is about 25 million per cell. The
word hemoglobin comes from hemo meaning blood and globin meaning protein. This is the protein
substance of four different proteins: polypeptide globin chains that contain anywhere from 141 to 146
amino acids. Hemoglobin also is responsible for the cell’s ability to transport oxygen and carbon
dioxide. This hemoglobin + iron + oxygen interact with each other forming the RBC's bright red color.
You can call this interaction by product oxyhemoglobin. Carbon Monoxide forms with hemoglobin
faster that oxygen, and stays formed for several hours making hemoglobin unavailable for oxygen
transport right away. Also a red blood cell contains about 200 million hemoglobin molecules. If all this
hemoglobin was in the plasma rather than inside the cells, your blood would be so "thick" that the heart
would have a difficult time pumping it through. The thickness of blood is called viscosity. The greater
the viscosity of blood, the more friction there is and more pressure is needed to force blood through.

Functions

The main function is the transportation of oxygen throughout the body and the ability of the blood
to carry out carbon dioxide which is called carbamino – hemoglobin. Maintaining the balance of
blood is important. The balance can be measured by the acid and base levels in the blood. This is called
pH. Normal pH of blood ranges between 7.35-7.45; this normal blood is called Alkaline (less acidic

124 | Human Physiology