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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

what is amenorrhoea
Adamu Reply
either due to gestational phase or lactational phase amenorrhoea is divided into two namely primary and secondary amenorrhoea ..the gestational phase and lactational phase marks a temporary cease in menstrual flow which is termed secondary amenorrhoea...
Fatukasi
amenorrhoea is simply a stop or cease in menstrual flow..primary amenorrhoea marks menopause
Fatukasi
try again
Mohd
what are data colletion method in community diagnodis
loice Reply
50 prefix and surfix
Martha Reply
why arteries deeper than veins?!
Cismaan Reply
arteries colour of blood is deeper than that of vein because its blood contains oxygen which is adhered to haemoglobin(a protein which gives the blood its red color) , while vein contains deoxygenated blood(blood without oxygen)
olusoga
As we know, vein carries used blood to the heart. when we say used blood, we mean to say, blood that its content(oxygen and other nutrients) has been used up.
olusoga
Arteries are deeper b'cuz they need to be protected.......If they are ruptured they cannot form clot and repair themselves.... Moreover, the pressure of blood is too high for the artery to form the clot and repair itself....... Hence, Arteries are deeper than veins........
AMEL
Than u all. Special thanks too AMEL JEELANI.
Cismaan
You're welcome......
AMEL
Thanks all
describe the location of the macula densa and explain its role in the regulation of renin secretion and in tubuglomerular feedback
mwamba Reply
its located near the vascular pole of the glomurelus also regulate blood pressure and the filtration rate of glomurelus
adam
what are the three methods of data collection used during a community diagnosis
loice
Interviews. Questionnaires and Surveys. Observations.
edna
Describe two early induced responses and what pathogens they affect
olivia Reply
what are pathogens
Priscilla
pathogens are disease-causing agents/organisms
olusoga
pathogen are the causative of disease
Marco
thank you sister
Priscilla
mmmmm
Asad
kkkjjjjjjjhgghkkgkgkkjkjkjgjkhjigjkh
Asad
What are organelles
RAPHERA Reply
The are little organs found in cells of living things... Eg gogi apparatus
Lombe
what is anatomy
Linda Reply
is the study of the structures of the body and how they relates to each other
Agyemang
Anatomy is the study of the structures of body parts and how they relates to each other
Agyemang
is the study of the structure of the body and how they relates to each other
NAOMI
what are the difference between Pacinian corpuscle and cutaneous vascular plexus?
thivya Reply
what are membranous epithelial tissues
Naa Reply
they are the lining and covering epithelial tissues which cover body surfaces and line cavities... they're grouped into simple and stratified according to the number of layers and squamous, cuboidal and columnar according to their shape
Ophelia
what is an acina
Nuella
acina is known to be the basic functional unit of the lungs .(singular:- acinus) this is where the alveoli(the gaseous exchange site) is found...
Fatukasi
what happens to the unfertilized egg
Wuraola
the study of tissues is called
Scandy Reply
histology
Sirius
microscopic or histology anatomy
Shan
What specific types of biological macromolecules do living things require and why?
Marieland Reply
what is partial pressure?
Tariq Reply
it is the pressure exerted by mixture of gases...
Fatukasi
What is the Important of studying anatomy and philosophy
Michael Reply
because to know the mechanisms of our body
Tariq
to discover the regional structural of human body based on physically and also biochemically.
thivya
how many region do we have in human body
nsofor Reply
head thorax abdomen and many kind of...
Shan
what is principal ponatine nucleas
Tariq
Human body can be divided into different regions on the basis of: 1. Systems: e.g. digestive system, respiratory system, excretory system etc.. 2. Parts: e.g. head, thorax, neck, upper limbs, lower limbs etc..
AMEL
we have 9 region in d human body
ZAINAB

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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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