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By the end of this section, you will be able to:
  • Describe the anatomy of erythrocytes
  • Discuss the various steps in the lifecycle of an erythrocyte
  • Explain the composition and function of hemoglobin

The erythrocyte    , commonly known as a red blood cell (or RBC), is by far the most common formed element: A single drop of blood contains millions of erythrocytes and just thousands of leukocytes. Specifically, males have about 5.4 million erythrocytes per microliter ( µ L) of blood, and females have approximately 4.8 million per µ L. In fact, erythrocytes are estimated to make up about 25 percent of the total cells in the body. As you can imagine, they are quite small cells, with a mean diameter of only about 7–8 micrometers ( µ m) ( [link] ). The primary functions of erythrocytes are to pick up inhaled oxygen from the lungs and transport it to the body’s tissues, and to pick up some (about 24 percent) carbon dioxide waste at the tissues and transport it to the lungs for exhalation. Erythrocytes remain within the vascular network. Although leukocytes typically leave the blood vessels to perform their defensive functions, movement of erythrocytes from the blood vessels is abnormal.

Summary of formed elements in blood

This table shows the different types of cells present in blood, the number of cells, their appearance, and a summary of their function.

Shape and structure of erythrocytes

As an erythrocyte matures in the red bone marrow, it extrudes its nucleus and most of its other organelles. During the first day or two that it is in the circulation, an immature erythrocyte, known as a reticulocyte    , will still typically contain remnants of organelles. Reticulocytes should comprise approximately 1–2 percent of the erythrocyte count and provide a rough estimate of the rate of RBC production, with abnormally low or high rates indicating deviations in the production of these cells. These remnants, primarily of networks (reticulum) of ribosomes, are quickly shed, however, and mature, circulating erythrocytes have few internal cellular structural components. Lacking mitochondria, for example, they rely on anaerobic respiration. This means that they do not utilize any of the oxygen they are transporting, so they can deliver it all to the tissues. They also lack endoplasmic reticula and do not synthesize proteins. Erythrocytes do, however, contain some structural proteins that help the blood cells maintain their unique structure and enable them to change their shape to squeeze through capillaries. This includes the protein spectrin, a cytoskeletal protein element.

Erythrocytes are biconcave disks; that is, they are plump at their periphery and very thin in the center ( [link] ). Since they lack most organelles, there is more interior space for the presence of the hemoglobin molecules that, as you will see shortly, transport gases. The biconcave shape also provides a greater surface area across which gas exchange can occur, relative to its volume; a sphere of a similar diameter would have a lower surface area-to-volume ratio. In the capillaries, the oxygen carried by the erythrocytes can diffuse into the plasma and then through the capillary walls to reach the cells, whereas some of the carbon dioxide produced by the cells as a waste product diffuses into the capillaries to be picked up by the erythrocytes. Capillary beds are extremely narrow, slowing the passage of the erythrocytes and providing an extended opportunity for gas exchange to occur. However, the space within capillaries can be so minute that, despite their own small size, erythrocytes may have to fold in on themselves if they are to make their way through. Fortunately, their structural proteins like spectrin are flexible, allowing them to bend over themselves to a surprising degree, then spring back again when they enter a wider vessel. In wider vessels, erythrocytes may stack up much like a roll of coins, forming a rouleaux, from the French word for “roll.”

Questions & Answers

why study anatomy?
esther Reply
to know the detailed functioning of the internay body organs
Jam
we study anatomy to know about the structure of the organs which in turn help to study physiology which is the knowledge related to function of the vital organ,and when we know the normal functionality we can understand the abnormalities in that organ,and the study of disease is called pathology
Lubabah
whats antonmy
Jaan Reply
the study of structure and function of internal body parts
Jam
is a branch of biology which describes the structures of the body and relationship from one part to another
esther
what is anatomy and physiology
mwitwa Reply
Anatomy is the study of structures of the body
Zunehri
Physiology the study functions of the body
Zunehri
anatomy is study of structure of body nd physiology is study of function of body.
PRIYANKA
anatomy is the study of internal body structures and physiology is the functioning of these structures in the body
Jam
what is lungs
Shipon Reply
it an organ found in our thoracic cavity
Richard
lungs are spongy organs where our respiration takesplace
Maryama
Lungs is a spongy organs located in the chest , is an a primary organs of respiration in human body and other Animals
Zunehri
lungs thorex me present hote hai ye organ hai and gas exchange (o2,co2 exchange)inka inka function hai.
PRIYANKA
lungs ka function hai
OM
pls am a student I don't know
Mavis
main function is respiration
faheem
respiration is the taking ing of oxygen by the body tissues and the removal of carbondioxide from the body tissues
Jam
what is heart beat,?
Naqeeb Reply
heart beat is the process briting
Mavis
what functions of heart
Muthu Reply
To circulate the blood
Arshad
it pump blood to the lungs
Laura
very twiest
Shipon
what should be the nature of cell
Kashish Reply
Cells die and reproduce
Nejat
knuckle of the middle finger
James Reply
because of the gases (nitrogen, oxygen)
Nejat
what is ketone bodies
Jaan
why the heart is protected with that sac
Joshua Reply
To prevent collision with the lungs, lubricates the heart, protects the heart from infection in the event a peripheral organ is effected, and stabilizes the heart within the mediastinum.
Jeremiah
This app should be updated too much as there is very little information for some topics.I hope you will consider my information....
aman Reply
adenohypophysis is made up of what type of cells and what is the name of those cells?
Mannu Reply
whatpassesthroughmaleovale
armstrong Reply
motor root of the trigeminal nerve
Vandana
what is the nervous system about
Joshua
what passes through foramen ovale?
Farah Reply
what are the organelles of a cell
Amina Reply
muscular system
Vandana
nucleus ribosome Golgi body call membrane cytoplasm
Sabina
these are the cellular components that functions to provide energy,remove waste and cell division
Waziri
Organelles of the cell are: Mitochondria,Ribosome,golgi apparatus, nucleus, secretory granules, nuclear e t c
Khadijah
what are local hormones
Richard
Local hormones are hormones that effect the cell that released them or cells near the releasing cell and they do not circulate within the blood stream.
Jeremiah
the trachea bifurcated into how many branches on the right lung
barbie
three lobes
Richard
Explain the normal flow of blood.
Shikha
how can we maintain the internal living things
Choolwe Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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