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Shape of red blood cells

This photograph shows a few red blood cells.
Erythrocytes are biconcave discs with very shallow centers. This shape optimizes the ratio of surface area to volume, facilitating gas exchange. It also enables them to fold up as they move through narrow blood vessels.


Hemoglobin is a large molecule made up of proteins and iron. It consists of four folded chains of a protein called globin    , designated alpha 1 and 2, and beta 1 and 2 ( [link] a ). Each of these globin molecules is bound to a red pigment molecule called heme    , which contains an ion of iron (Fe 2+ ) ( [link] b ).


This figure shows the structure of hemoglobin. The left panel shows the protein structure and the right panel shows the chemical formula.
(a) A molecule of hemoglobin contains four globin proteins, each of which is bound to one molecule of the iron-containing pigment heme. (b) A single erythrocyte can contain 300 million hemoglobin molecules, and thus more than 1 billion oxygen molecules.

Each iron ion in the heme can bind to one oxygen molecule; therefore, each hemoglobin molecule can transport four oxygen molecules. An individual erythrocyte may contain about 300 million hemoglobin molecules, and therefore can bind to and transport up to 1.2 billion oxygen molecules (see [link] b ).

In the lungs, hemoglobin picks up oxygen, which binds to the iron ions, forming oxyhemoglobin    . The bright red, oxygenated hemoglobin travels to the body tissues, where it releases some of the oxygen molecules, becoming darker red deoxyhemoglobin    , sometimes referred to as reduced hemoglobin. Oxygen release depends on the need for oxygen in the surrounding tissues, so hemoglobin rarely if ever leaves all of its oxygen behind. In the capillaries, carbon dioxide enters the bloodstream. About 76 percent dissolves in the plasma, some of it remaining as dissolved CO 2 , and the remainder forming bicarbonate ion. About 23–24 percent of it binds to the amino acids in hemoglobin, forming a molecule known as carbaminohemoglobin    . From the capillaries, the hemoglobin carries carbon dioxide back to the lungs, where it releases it for exchange of oxygen.

Changes in the levels of RBCs can have significant effects on the body’s ability to effectively deliver oxygen to the tissues. Ineffective hematopoiesis results in insufficient numbers of RBCs and results in one of several forms of anemia. An overproduction of RBCs produces a condition called polycythemia. The primary drawback with polycythemia is not a failure to directly deliver enough oxygen to the tissues, but rather the increased viscosity of the blood, which makes it more difficult for the heart to circulate the blood.

In patients with insufficient hemoglobin, the tissues may not receive sufficient oxygen, resulting in another form of anemia. In determining oxygenation of tissues, the value of greatest interest in healthcare is the percent saturation; that is, the percentage of hemoglobin sites occupied by oxygen in a patient’s blood. Clinically this value is commonly referred to simply as “percent sat.”

Percent saturation is normally monitored using a device known as a pulse oximeter, which is applied to a thin part of the body, typically the tip of the patient’s finger. The device works by sending two different wavelengths of light (one red, the other infrared) through the finger and measuring the light with a photodetector as it exits. Hemoglobin absorbs light differentially depending upon its saturation with oxygen. The machine calibrates the amount of light received by the photodetector against the amount absorbed by the partially oxygenated hemoglobin and presents the data as percent saturation. Normal pulse oximeter readings range from 95–100 percent. Lower percentages reflect hypoxemia    , or low blood oxygen. The term hypoxia is more generic and simply refers to low oxygen levels. Oxygen levels are also directly monitored from free oxygen in the plasma typically following an arterial stick. When this method is applied, the amount of oxygen present is expressed in terms of partial pressure of oxygen or simply pO 2 and is typically recorded in units of millimeters of mercury, mm Hg.

Questions & Answers

describe the muscles found in the heart
Atotwe Reply
thank you very much
asalamu aleikum
what is a muscular system and details about it
Jackson Reply
what is the type of homones responseble for blenking of eyes
Moses Reply
what are the functions of cell?
Keyirangzile Reply
how does the femur act as a lever?
Mutoni Reply
what is stumac
Abdussalam Reply
What is phagocytosis
Mohamed Reply
Phagocytosis, process by which certain living cells called phagocyte
It is the process that is carried out by the immune system of the body, that certain specialized immune cells (macrophages, Nks, dendritic cells, etc) that engulf and neutralize the foreign substances that invades the body.
So that they can be predicate out of the body.
phagocytosis is the process by which living cell or yh plasma membrane engulf large molecules into it internal environment ... it also known as food feeding
all that you are say what does it mean?
simply is the way the immune system fights foreign bodies by engulfing them..
by the help of the immune cells...
what are the six types of connective tissues
Athieno Reply
loose and dense , cartilage and bone , blood and lymph
describe the structure of the liver
Atwebembeire Reply
what is specific name for spinal cord
Stanley Reply
what is the best description for skeletal muscular
what is the best description for skeletal muscular
costs of bones of skeleton, their joint s and voluntary
what are examples of long bones
example of long bones will be the femur tibia and humerus and even radius
so basically long bones are mostly in you hands and feets
skeletal muscular are voluntary and are attached to the bone by tendon which help maintain the posture and position of the body and it also protects internal organs in the abdominal region
The specific name for spinal cord is coccygeal segment
what are the hormones responseble for blenking of eyes.
Smallest unit of life
Kimberly Reply
The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Therefore, it is sometimes called the building block of life. Some organisms, such as bacteria or yeast, are unicellular—consisting only of a single cell—while others, for instance, mammalians, a
cells are the building blocks of life
Describe the complications of fracture
Zaifa Reply
functions of connective tissue
renah Reply
binding and structural support protection Insulation Transport of materials
what is a local potential
Nandi Reply
potential of neurons
response of neurons against sodium ion Chanel
The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside. At rest, there are relatively more sodium ions outside the neuron and more potassium ions inside that neuron.
what is tissues
Addai Reply
are groups of specialized cell that perform they same activity
a group of specialized cells of the same structure and function
a group of specialized cells that have the same structure and perform the same function
tissue is a group of specialised cells performing similar functions and are of the same embryonic origin
group of specialized cells that have similar structure and act together to perform a specific function
a group of specialised cell which has same function
a group of specialized cells that perform the same function.
group of one or more cell types that specialized to perform a particular function.

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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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