14-2 Blood and Blood Vessels
BLOOD VESSELS

Blood circulates through the body
through a series of vessels
1. Arteries: blood vessels that carry
blood away from the heart
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Except for the pulmonary arteries, all arteries carry
oxygenated blood
With each contraction the heart forcefully ejects
blood into arteries
The artery’s wall expands and then returns to its
original size
Blood passes from the arteries into a network of
smaller arteries called arterioles
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2. Capillaries
blood vessels in which gases, nutrients,
hormones and other molecules are transferred
from the blood to the body’s cells
 No cell in your body is more than a few cell
diameters away from a capillary
 Capillary walls are only one cell thick—gas and
nutrient molecules easily pass through their thin
walls
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**INTERESTING FACT: If all the capillaries of
your body were laid end to end, they would
extend all the way across the US!!!!
3. Veins

blood vessels that return the blood to the
heart
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The walls of veins consists of a much thinner
layer of smooth muscle than the walls of the
arteries
They are farther away from the heart pump so
therefore are exposed to less pressure
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The flow of blood in veins is helps by
contractions of skeletal muscles

when muscles contract they squeeze
against veins and help force blood
toward the heart
B) BLOOD PRESSURE
Blood moves through our system
because it is under pressure
 This pressure is caused by the
contraction of the heart and by muscles
that surround blood vessels
 Blood pressure: a measure of force that
blood exerts against the walls of a blood
vessel
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Blood pressure is always highest in the
two main arteries that leave the heart
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Both high and low blood pressure can
cause problems to our health

High blood pressure is very common in
Americans—hypertension

Blood pressure is measured with two
numbers
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1—systolic: the pressure of the blood when the heart
contracts
2—diastolic: the pressure of the blood when the heart
relaxes
blood pressure is given as the systolic
number over the diastolic number
C) BLOOD
“River of Life”
 blood: type of connective tissue containing
various substances and cells

Blood serves many functions:
collects oxygen from the lungs
 collects nutrients from the digestive tract
 collects waste products from tissues
 helps to regulate body temperature
 helps fight infections
 helps repair damaged blood vessels

Blood is made up of various
components:
1. Blood Plasma
 Accounts for 60% of
the blood
 Liquid portion of the
blood—90% water and
10% solutes
 The other solutes
include nutrients,
gases, enzymes,
hormones and waste
products
2. Red Blood Cells

Cells that carry oxygen

Each mL of blood
contains 5 million RBCs

RBCs have a biconcave
shape—this means that
they are narrower in the
center than along the
edges
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Also known as
ERYTHROCYTES
Carry hemoglobin—ironcontaining protein that
enables RBCs to carry
oxygen—it also gives
RBCs their color
Since mature RBCs
carry so much
hemoglobin, they do not
have nuclei or
organelles
3) White Blood Cells
“army” of the body
 Also known as
LEUKOCYTES
 The main function of
the WBCs is to
protect the body
against invasion by
foreign cells or
substances
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Outnumbered by
RBCs almost 500 to
1
 larger than RBCs—
do contain nuclei—
almost colorless
 there are different
types of WBCs with
different functions
4) Platelets

Platelets are not cells—they are tiny
fragments of cells

Play an important role in blood clotting—
they clump together and form a plug at
the site of the wound
D) BLOOD TYPES

Blood type is determined by the type of
antigen present on the surface of RBCs

Antigen: a protein or carbohydrate that acts
as a signal which cause antibodies to be
made

If a person has A antigens—they are type A

if a person has B antigens—they are type B
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if a person has both antigens—they are AB

if a person has neither A nor B—they are
type O
 Type
AB is known as the universal
receiver—they can receive any type of
blood
 Type
O is known as the universal
Donor, meaning they can donate blood
to anyone