Blood Functionally Connects
the Body Organ Systems
LEARNING OBJECTIVES
1.
Describe
the functions of blood.
3.
identify
the blood cells that make up formed
2.
Outline
the components of plasma.
elements.
W
hile blood looks like a
homogeneous
liquid, it
is actually a liquid connective tissue that con-
sists of cells surrounded by a liquid extracel-
lular matrix. Blood is thicker than water and
has a temperature of about 37°C
and a pH of 7.35 to 7.45. An aver-
age adult male has about 5 to 6 L
(1.5 gal) of circulating blood vol-
ume, while a female has about 4 to
5 L (1.2 gal); the difference in blood volume is mainly due to
differences in average body size. Blood makes up 8% of your
body weight, while other fluids and tissues make up 92%.
Blood has three major functions:
T ran sportation
—Blood delivers oxygen from the lungs
to the cells of the body, moves carbon dioxide from
the cells to the lungs, and carries nutrients, waste
products, and hormones to various destinations.
R e g u la tio n
—Blood helps to maintain a steady pH of
body fluids. It also distributes heat, thereby adjusting
body temperature. Blood’s osmotic pressure influences
the water content of cells and tissues.
P rotection
—Blood forms seals or clots in response to
injury, thereby preventing blood loss and maintaining
cardiovascular
function.
White
blood
cells
protect
against disease by ingesting invading bacteria and
producing antibodies. Blood also contains proteins that
protect against disease.
Blood has two components: a liq-
uid
component
called
plasma
and
cellular
components
called
formed
elements
.
These
two
components can be separated by
placing a container of whole blood
into a centrifuge, which spins the
blood at high speed. The formed
elements sink to the bottom because they are denser than
the plasma. Let’s first take a look at plasma.
plasma is the liquid portion of Blood
When you separate whole blood into its components
(Figure 10.1), you find that over half of it is plasma.
Most of plasma is water, with some proteins and oth-
er solutes mixed in. The proteins, including albumins,
globulins, and fibrinogen, are made mainly in the liver.
These proteins help maintain osmotic pressure (albu-
mins), defend against foreign substances (globulins),
and help form blood clots (fibrinogen). Other solutes
include various salts or electrolytes, nutrients, wastes,
hormones, and gases.
Formed elements Consist
of the Many types of Blood Cells
The remaining 45% of blood by weight consists of cells
that are collectively called formed elements. The formed
elements consist primarily of red blood cells and, to a
much smaller extent, platelets and white blood cells. The
different types of cells have different functions. Let’s look
at each one.
Red blood cells (RBCs)
, or
erythrocytes
(e-RITH-
ro-sits), are about 7-8 p,m in diameter and have a unique
biconcave
,
disc-like
shape
(see
Figure
10.1).
This
shape
pro-
vides a large surface area for the
exchange
of
gases,
specifically
oxygen and carbon dioxide. Red
blood cells have no nucleus and few organelles. Their flex-
ible plasma membrane allows them to easily maneuver
through the various vessels of the circulation. The per-
centage of total blood volume occupied by red blood cells
is termed the
hematocrit
(he-MAT-o-krit).
W
homogeneous
(ho-
mo-JE-ne-us) Uniform
in structure or compo-
sition throughout.
plasma
A liquid
extracellular matrix in
blood that contains
dissolved substances.
formed elements
Cells and cell frag-
ments in blood.
biconcave
(bT-KON-
kav) Inwardly curved
on both sides or
surfaces.
288 CHAPTER 10
The Cardiovascular System: Blood
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