The Cardiovascular System
Chapters 19, 20, 21
The Closed Circulatory System
• Blood is confined to vessels
• Heart pumps blood into large vessels
that branch into smaller ones leading
into the cells
• Nutrients & wastes are exchanged by
diffusion
Three Major Elements:
Blood Vessels, Blood, Heart
I. Blood Vessels
3 layers:
1. Endothelim - epithelial inner lining (tunica
intima)
2. smooth muscle & elastic connective tissue
(tunica media)
3. connective tissue covering (tunica externa)
Types of blood vessels:
Arteries → Arterioles → Capillaries → Venules
Arteries:
• Carry oxygenated blood away from the heart
• Thicker & more elastic walls than veins
• Arteries are thicker and more elastic because they
are closer to the pumping action of the hear
Veins:
• Carry deoxygenated blood
towards the heart
• Less elastic and thinner walls
than arteries
• Valves prevent backflow of
blood
• When valves don’t close
properly = varicose veins
When you walk and your leg muscles squeeze, the venous pump works well.
But when you sit or stand, especially for a long time, the blood in your leg
veins can pool and the pressure in your veins can increase. If you are a
susceptible individual, your veins can stretch if you repeatedly sit or stand for a
long time. This stretching can sometimes weaken the walls of your veins and
damage your vein valves. Varicose veins may result. Spider veins are mild
varicose veins.
Capillaries:
• Smallest blood vessels found almost near all body
cells
• Exchange of nutrients, gases & metabolic wastes
(through diffusion)
• Only one cell thick – contain only tunic intima
• Link arteries & veins
II. Blood
A. Plasma
•
•
•
•
55% of blood
Liquid portion of the
blood
91.5% of plasma = water
Also contains dissolved
hormones, antibodies,
nutrients, wastes, gases
Blood Cont.
B. Erythrocytes - Red Blood
Cells (RBCs)
• Formed in the bone marrow
• Hemoglobin carries oxygen
• Do not have a nucleus and
live only about 120 days
Blood Cont.
C. Leukocytes – White
Blood cells (WBCs)
• Fight infection and are
formed in the bone
marrow
• Many types
Blood Cont.
D. Thrombocytes
– Platelets
• Clot blood by
sticking
together via
protein fibrin