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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

which nerve orginates from pons
Kripa Reply
trigeminal nerve
madhuri
demand and supply rules
jamac Reply
compative demand and supply
jamac
compare demand and supply
jamac
what are simple epithelial tissues
Ushie Reply
is a type of tissue which covers the external and internal part of the body
Fatou
more information would be better understanding.
Tasha
what is platelets
Lilian Reply
platelet is also known as thrombocyte.thrombo means clot.it is a formed element of blood formed from fragment of megakaryocyte surrounded by plasma membrane in the redbone marow
Adeyemo
what is diabetes insipidus
namrata Reply
it is an infection due to less or no secretion of ADH characterized by excretion of dilute urine
Meshack
Infection? I don't think any form of diabetes, whether it's mellitus or insipidus, is caused by an infection.
Matias
ya
Akanyijuka
it is the disorder of salt & water metabolism
Emma
diabetes inspidus is a condition were the liver can't produce insulin to convert the excess sugar to glycogen.
mangs
sorry that is for diabetes mellitus
mangs
what is septal cartilage
Arthur Reply
I don't understand please
Esther Reply
hey
Austine
good evening boss
Austine
Evening
Esther
good evening
Melissa
evening
Vitus
hi
Rodgers
good morning
Aurelia
hello
Helsa
you guys are from ?
Aurelia
Philippines
Helsa
im from india
Aurelia
Hello
Amos
why
Sami
wat
Rodgers
what's that
Gift
what's the medulla?
alhussiney Reply
The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum
Ludmila
define bone in simple terms
Mhoses Reply
bones are made up by collagen and calcium phosphate
Aurelia
yes
Confidence
Bones are the hard large calcareous connective tissue of which the adult skeleton of most vertebrates is chiefly composed
Olalekan
Bone is the substance that forms skeleton
Frances
good morning
Mrinal
Skelton muscles is any disorder of calcium
Mrinal
Bones protect the various organs of the body
Celina
Bone is a hard strong and durable type of connective tissue
Bkv
bone is a hard, calcareous connective tissue which gives structural support to the body and helpless in its locomotion!
Divya
It also is the main site for synthesis of the RBCs
Divya
thanks for your answers
Mhoses
A diagram of epithelial tissue
Emmanuel Reply
What does the urinary regulate blood pressure
Jennifer Reply
functions of melatonin
marion Reply
d. inversely proportional
John Reply
Airway resistance in the human lung is? a. Greatest in the generation of distal bronchioles in healthy people because these airways have the smallest radii b. Not increased during a forced expiration in a healthy subject c. Decreased when breathing through the mouth d. Inversely proportional
Maryam Reply
1. Chemical level 2. Cellular level 3.Tissue level 4. Organ level 5.Organ system level 5.Organismal level
Jamela Reply
d
HMD
High
HMD
hlw
Maryam
------is not a content of femoral canal? a. Fatty tissue b. Femoral nerve c. Lymph vessels d. Lymph node
Maryam
a
Alhassan

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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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