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January 10,

2016

BLOOD

1.

Composition

AND FUNCTIONS OF BLOOD

Blood is the

only fluid tissue in the body

Although

blood appears to be a thick homogeneous liquid, the microscope reveals that it

has both solid and liquid components.

A.

Components

i.

Blood

is a complex connective tissue in which living blood cells, the formed

elements, are suspended in a nonliving fluid matrix called plasma.

ii.

The

collagen and elastin fibers typical of other connective tissues are absent from

blood, but dissolved proteins become visible as fibrin strands during blood

clotting.

iii.

If

a sample of blood is spin in a centrifuge, the formed elements, being heavier,

are packed down by centrifugal force and the plasma rises to the top.

iv.

Most

of the reddish mass at the the bottom of the tube is erythrocytes, the formed elements that function in oxygen

transport.

1.

Red

blood cells

v.

Although

it is barely visible there is a thin, whitish layer called the buffy coat

at the junction between the erythrocytes and the plasma.

1.

This

layer contains the remaining formed elements:

a.

Leukocytes

i.

White

blood cells that act in various ways to protect the body

b.

Platelets

i.

Cell

fragments that help stop bleeding.

vi.

Erythrocytes

normally account for about 45% of the total volume of a blood sample.

1.

A

percentage known as the hematocrit

vii.

White

blood cells and platelets contribute less than 1% and plasma makes up most of

the remaining 55% of whole blood.

B.

Physical Characteristics and Volume

i.

Blood is a sticky, opaque, fluid with a characteristic

metallic taste.

ii.

Depending on the amount of oxygen it is

carrying, the color of blood varies from scarlet (oxygen-rich) to a dull red

(oxygen-poor).

iii.

Blood is heavier than water and about five times

thicker (more viscous) largely because of its formed elements.

iv.

Blood is slightly alkaline with a pH between

7.35 and 7.45.

v.

Its temperature is always slightly higher than

body temperature (~38˚C, or 100.4˚F)

vi.

Blood accounts for approximately 8% of body

weight, and its volume in healthy men is 5 to 6 liters, or about 6 quarts.

C.

Plasma

i.

D.

Formed Elements

i.

Erythrocytes

ii.

Leukocytes