Skip to Main Content


The Composition of Blood


Blood circulates within the cardiovascular system to provide a vehicle for the distribution of respiratory gases, nutrients, water, electrolytes, hormones, antibodies, drugs, metabolic waste, and heat throughout the body. Most of the major negative feedback control systems of the body defend normal blood composition (e.g., blood glucose concentration, blood volume, and arterial O2 partial pressure). Blood is composed of cellular elements (i.e., red blood cells, white blood cells, and platelets), which are suspended in blood plasma. A person who weighs 70 kg has approximately 5 L of blood, of which about 2 L is occupied by the formed cellular elements and 3 L is plasma.


This chapter will discuss mainly the physiologic regulation of the red blood cell mass and the mechanisms that prevent bleeding.


Plasma Composition


Plasma is the part of the extracellular fluid that is contained within the cardiovascular system. It is a dilute solution, which by weight is approximately 92% water, 7% protein, and 1% small dissolved solutes (e.g., ions, urea, glucose, amino acids, and lipids). The normal plasma concentrations of selected ions and small molecules are almost the same as those in the interstitial fluid because of the free exchange of water and small solutes across most blood capillaries (Table 3-1). In contrast, most capillaries are impermeable to plasma proteins. The resulting difference in protein concentration between the plasma and the interstitial fluids creates a colloid osmotic (oncotic) pressure gradient that opposes the filtration of plasma out of the capillaries (Chapter 4). Albumin is the most abundant type of plasma protein and, therefore, is the greatest contributor to the plasma oncotic pressure. The major types of plasma protein and their functions are listed in Table 3-2.

Table Graphic Jump Location
Table 3-1Normal Plasma Composition
Table Graphic Jump Location
Table 3-2The Major Types of Plasma Proteins

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.


Create a Free MyAccess Profile

* Required Fields

Note: If you have registered for a MyAccess profile on any of the Access sites, you can use the same MyAccess login credentials across all sites.

Passwords must be between 6 and 40 characters long (no whitespace), cannot contain characters #, &, and must contain:
  • at least one lowercase letter
  • at least one uppercase letter
  • at least one digit

Benefits of a MyAccess Profile:

  • Remote access to the site off-campus on any device
  • Notification of new content via custom alerts
  • Bookmark your favorite content such as chapters, figures, tables, videos, cases and more
  • Save and download images to PowerPoint
  • Self-Assessment quizzes saved for quick review
  • Custom Curriculum access for both instructors and learners

Subscription Options

AccessPhysiotherapy Full Site: One-Year Subscription

Connect to the full suite of AccessPhysiotherapy content and resources including interactive NPTE review, more than 500 videos, Anatomy & Physiology Revealed, 20+ leading textbooks, and more.

$595 USD
Buy Now

Pay Per View: Timed Access to all of AccessPhysiotherapy

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.