1. Capillaries Figure 15.25 Smallest blood vessels
Connect small arterioles and venules
Figure 15.25

2. Capillaries
Composed of endothelium, squamous epithelial cells
Slits in the walls affect permeability
Precapillary sphincters: smooth muscle that control blood flow to an area
Figure 15.28

3. Exchange Across Capillaries
Gases, nutrients, and metabolic byproducts move between blood stream and body cells
Diffusion:
lipid soluble substances and gases diffuse across the cell membrane
lipid-insoluble substances diffuse through pores
plasma proteins are too big to move through pores of slits
Osmosis: movement of water through pores

4. Exchange Across Capillaries
Filtration
hydrostatic pressure forces molecules through the membrane
colloid osmotic pressure is created by plasma proteins
These processes oppose each other
More fluid leaves capillaries than returns to it. Lymphatic vessels collect the excess fluid and return it to the venous circulation

5. Figure 15.30

6. Venules and Veins Venules continue from capillaries and join veins.
Veins have three layers but are thinner walled than arteries due to less developed tunica media.
Veins contain valves to help blood return to the heart.
Veins are the blood reservoir.

7. Figure 15.32

8. Blood Pressure Force of blood against the blood vessels
Arterial blood pressure corresponds to the cardiac cycle
Systolic pressure is achieved during ventricular systole
Diastolic pressure is achieved during ventricular diastole
The expansion and recoil of the vessels can be felt as the pulse

9. Figure 15.34

10. Heart Action
Heart action determines how much blood enters the arteries
Stroke volume: volume of blood discharged from the ventricle during each contraction
Cardiac Output: volume of blood discharged from the ventricle per minute
Blood pressure varies with cardiac output

11. Blood Volume and Resistance
Blood volume equals the formed elements and plasma volumes in the vasculature.
Blood pressure is directly proportional to the volume of blood within the cardiovascular system.
Figure 15.33

12. Blood Volume and Resistance
Peripheral resistance is friction between blood and blood vessel walls.
Peripheral resistance hinders blood flow and increases blood pressure.

13. Viscosity
Viscosity is the ease with which molecules flow past one another.
The greater the viscosity, the greater the resistance to flow.
Blood cells and plasma proteins increase blood viscosity.

14. Control of Blood Pressure
Blood pressure (BP) is determined by cardiac output (CO) and peripheral resistance (PR); BP = CO x PR
Starling’s Law of the Heart
The more blood returned to the heart, the greater the ventricular distension, the stronger the greater the stroke volume, the greater the cardiac output

15. Figure 15.37

16. Figure 15.38

17. Peripheral Resistance
Chemicals can affect smooth muscle
vasodilators
increased carbon dioxide and hydrogen
decreased oxygen
nitric oxide and bradykinin
vasoconstriction
angiotensin
endothelin

18. Venous Blood Flow Figure 15.40
Skeletal muscles contract and press on blood vessels and squeeze blood upward
Figure 15.40

19. Venous Blood Flow Valves prevent backflow of blood
Respiratory movements move blood back to the heart
during inspiration blood is squeezed out of the abdominal vessels into thoracic vessels

20. Paths of Circulation Figure 15.41 Pulmonary circuit Systemic circuit
vessels that carry blood from the heart to the lungs and back to the heart
Systemic circuit
carries blood from the heart to the body and back
arterial and venous systems
Coronary circuit
supplies the heart
Figure 15.41