BIOL 1911 Chapter Notes - Chapter 42.4: Red Blood Cell, Hemoglobin
29 Apr 2018
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42.4 – Blood components function in exchange,
transport, and defense
• fluid in a closed circulatory system can be much more specialized
Blood Composition and Function
• vertebrate blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma
• cellular elements (cells and cell fragments) occupy about 45% of the volume of blood; the remainder is plasma
Plasma
• dissolved in the plasma are ions and proteins that, together with the blood cells, function in osmotic regulation, transport
and defense
• inorganic salts in the form of dissolved ions are an essential component of the blood
o some buffer the blood
o other help maintaining osmotic balance
o concentration of ions in plasma directly affects the composition of the interstitial fluid where many of these
ions have a vital role in muscle and nerve activity
• because these salts have to fulfill all of these functions, they have to be kept within narrow concentrations ranges
• plasma proteins such as albumins also act as buffers against pH changes and help maintain the osmotic balance between
blood and interstitial fluid
o certain plasma proteins have additional functions
o immunoglobulins or antibodies combat viruses and other foreign agents that invade the body
o apolipoproteins escort lipids, which are insoluble in water and can travel in blood only when bound to proteins
o fibrinogens are clotting factors that help plug leaks when blood vessels are injured
• plasma also contains many other substances in transit including nutrients, metabolic wastes, respiratory gases and
hormones
• plasma has a much higher protein concentration than interstitial fluid although they are otherwise similar (b/c capillary
walls are not very permeable to proteins)
Cellular Elements
Erythrocytes
• red blood cells
• by far the most numerous blood cells
• main function is O2 transfer and their structure is closely related to this function
o small disks that are biconcave – thinner in center than at the edges
o shape increases surface area, enhancing the rate of diffusion of O2 across the plasma membrane
o mature mammalian erythrocytes lack nuclei – leaves more space in these tiny cells for hemoglobin, the iron-
containing protein that transports O2
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