1. Human Anatomy and Physiology II
BLOOD VESSELS
Chapter 19
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2. Overview of Blood Vessels
Arteries
Carry blood away from the heart
Oxygenated except for pulmonary circulation and umbilical vessels of a fetus
Capillaries
Contact tissue cells and directly serve cellular needs
Veins
Carry blood toward the heart

3. Elastic arteries Muscular arteries Arterioles Capillaries
Venous system
Arterial system
Large veins
(capacitance
vessels)
Heart
Elastic arteries
(conducting
vessels)
Large
lymphatic
vessels
Lymph
node
Muscular arteries
(distributing
vessels)
Lymphatic
system
Small veins
(capacitance
vessels)
Arteriovenous
anastomosis
Lymphatic
capillary
Sinusoid
Arterioles
(resistance vessels)
Postcapillary
venule
Terminal arteriole
Metarteriole
Thoroughfare
channel
Capillaries
(exchange vessels)
Precapillary sphincter

4. Vein Artery Capillary Tunica intima • Endothelium Valve
• Subendothelial layer
Internal elastic lamina
Tunica media
(smooth muscle and
elastic fibers)
External elastic lamina
Tunica externa
(collagen fibers)
Lumen
Vein
Lumen
Artery
Capillary
network
Basement membrane
Endothelial cells
Capillary

5. Arterial System Vary by size and function Three types Elastic arteries
Muscular arteries
Arterioles

6. Elastic (Conducting) Arteries
Large thick-walled arteries with elastin in all three tunics
Aorta and its major branches
Large lumen offers low-resistance
Act as pressure reservoirs
—expand and recoil as blood is ejected from the heart

7. Muscular (Distributing) Arteries
Distal to elastic arteries
Deliver blood to body organs
Have thick tunica media with more smooth muscle
Active in vasoconstriction

8. Arterioles Smallest arteries Lead to capillary beds
Control flow into capillary beds via vasodilation and vasoconstriction

9. Capillaries Smallest of all blood vessels
Size allows only a single RBC to pass at a time
In all tissues except for cartilage, epithelia, cornea and lens of eye
Functions
exchange of gases, nutrients, wastes, hormones, etc.

10. What vessels carry blood away from the heart?
Capillaries
Veins
Arteries

11. (a) Sphincters open—blood flows through true capillaries.
Precapillary
sphincters
Metarteriole
Vascular shunt
Terminal arteriole
Postcapillary venule
Thoroughfare channel
True capillaries
(b) Sphincters closed—blood flows through metarteriole
thoroughfare channel and bypasses true capillaries.
Terminal arteriole
Postcapillary venule

12. Venous System Carry blood from capillaries to heart
Blood pressure is lower than in arteries
Two types
1. Venules
2. Veins

13. Venules Formed when capillary beds unite
Very porous; allow fluids and WBCs into tissues
Postcapillary venules consist of endothelium and a few pericytes
Larger venules have one or two layers of smooth muscle cells

14. Veins Formed when venules converge
Called capacitance vessels (blood reservoirs);
Adaptations
1. Larger lumens
2. Valves prevent backflow of blood
Heart 8%
Capillaries 5%
Systemic arteries
and arterioles 15%
Pulmonary blood
vessels 12%
Systemic veins
and venules 60%

15. Did You Know? Did you know that if you took the blood
vessels out of a child and laid them out in
a straight line it would be over 60,000 miles
long!

16. Systemic Blood Pressure
The pumping action of the heart generates blood flow
Pressure results when flow is opposed by resistance (friction)
Systemic pressure
Is highest in the aorta
Declines throughout the pathway

17. Systolic pressure
Mean pressure
Diastolic
pressure

18. Arterial Blood Pressure
Systolic pressure
pressure exerted during ventricular contraction
Diastolic pressure
lowest level of arterial pressure
Pulse pressure
difference between systolic and diastolic pressure

19. Maintaining Blood Pressure
The main factors influencing blood pressure
Cardiac output (CO)
Peripheral resistance (PR)
Blood volume

20. Maintaining Blood Pressure
Neural Controls
Baroreceptors
sense pressure changes
Chemoreceptors
sense changes in CO2 or blood pH

21. Maintaining Blood Pressure
Hormonal Controls
Norepinephrine and Epinephrine
enhance fight or flight response
vasoconstriction
Angiotensin II
Atrial Natiuretic Peptide
vasodilation
Antidiuretic Hormone

22. Homeostatic Imbalances
Alterations in Blood Pressure
Hypotension
Low blood pressure
Systolic pressure below 100 mm Hg
Often associated with long life and lack of cardiovascular illness

23. Homeostatic Imbalances
Alterations in blood pressure
Hypertension
High blood pressure
Sustained elevated arterial pressure of 140/90 or higher
May be transient adaptations during fever, physical exertion, and emotional upset
Often persistent in obese people

24. Homeostatic Imbalances
Atheroschlerosis