1. Entry slip: What is the function of leukocytes?
Lesson 4.4- Compare the structure and function of
blood vessels.
(pp306-307) of Biology-McGraw-Hill Ryerson)
I. Terms:
a.Arteries: blood vessels that carry blood
away from the heart
i. Arterioles are smaller arteries (like
bronchioles are smaller bronchii)
b.Veins: blood vessels that carry blood back
towards the heart
i. Venules are smaller veins
c. Smooth muscle: muscle in your body that
is involuntarily controlled (you have no
control over it) such as the muscle in your
intestines that helps push food along
II. Arteries (3 layers):
a. Outter layer(structure): connective tissue
and some elastic fibres

2. i. Function(f): holds the artery’s shape
(like pleura in lungs)
b. Middle layer(s): thick layer of elastic fibres
combined with smooth muscle
i. ***Elastic fibres (f): allows the
arteries to expand a little as a wave of
blood rushes by (this expansion is
what we feel as a “pulse”)
A. Palpate pulses: radial, brachial,
temporal, doraslis pedus, femoral
ii. ***Smooth muscle (f): constricts to
control blood pressure (the more
they constrict the greater the blood
pressure)
c. Inner layer(s): endothelial cells: special
cells that are very slippery
i. (f): reduces friction to allow blood to
flow by easily
d. Notes on arteries: arteries have a smaller
inner space than veins to increase blood
pressure

3. III.Veins (3 layers and valve):
a. Outter layer(s): connective tissue and
some elastic fibres
i. (f): holds the vein’s shape
b. Middle layer(s): very thin layer of elastic
fibres and smooth muscle
i. (f) does very poor job of expanding or
constricting
c. Inner layer(s): endothelial cells: special
cells that are very slippery
i. (f): reduces friction to allow blood to
flow by easily
d.Valves: special structures along veins that
prevent blood from flowing backwards
i. (f): keeps blood flowing in the right
direction towards the heart
A. Once blood has reached the
capillaries and has to return to
the heart, it is moving very
slowly. The heart cannot “pump”

4. blood in the veins at all at this
point. Blood higher than your
heart (in your head, neck and
shoulders) easily flows down to
the heart. Blood lower than your
heart however needs something
to prevent gravity from pulling it
down. When the big muscles in
your legs contract because you
are moving them, blood in the
veins is squeezed up, and once it
passes by a valve, it cannot flow
back. This continues until the
blood has reached your heart.
B. Valves that do not work properly
anymore become “varicose”
IV.Capillaries (One layer- only one cell thick)
a.Single layer of endothelial cells-
i. (f): allows blood to flow by easily
ii. (f): capillary walls are extremely thin
(one cell thick) to allow the diffusion
of nutrients and wastes across the

5. capillary wall to and from all of the
body’s cells
b. Notes on capillaries: capillaries are
microscopic: you cannot see them. They
are only as wide as a white blood cell (the
largest particle size of all blood
components) so as to just allow them by.
V. Youtube search:
a. “Mechanism of Vein” -
kosasihiskandarsjah
b.“Varicose Vein 1”
I. Homework Assignment:
a.Based on information about the valves in
veins, describe why human tend to sleep
lying down. As well, describe one time that
you were forced to sleep in a sitting
position (like on an airplane, bus or on a
long car ride) and how enjoyable this sleep
was. Go into detail. 100 words minimum.
b. Due next class.