1. Blood Vessels & Blood Pressure
Keri Muma
Bio 6

2. Types of Blood Vessels Heart Veins Arteries Arterioles Venules
Capillary Beds

3. Types of Blood Vessels

4. Blood Flow Flow rate – volume of blood per unit time Depends on:
Pressure gradient
Flow rate – volume of blood per unit time
Depends on:
Pressure gradient – difference in pressure between the beginning and ending of a vessel
Vascular resistance – hindrance or opposition to blood flow through a vessel
F = ∆P/R

5. Blood Flow Resistance As resistance increases flow rate decreases
Factors affecting resistance
Viscosity – friction between molecules increases resistance (# of circulating RBC)
Length – increased surface area increases resistance (remains constant in body)
Elasticity
Peripheral resistance

6. Resistance
Peripheral resistance – friction between the blood and the vessel wall
Radius the main determinant of resistance
Increased surface area exposed to blood increases resistance
Flow is faster in larger vessels than smaller

7. Arteries
Elastic arteries – offer little resistance due to their large diameter and elastic properties
Function – maintain constant flow of blood through capillaries despite ventricular systole and diastole
Arteries distend during systole
Recoils pushing blood forward during diastole

8. Blood Pressure Force exerted by the blood on the vessel wall
Systolic pressure – maximum pressure during ventricular systole
Diastolic pressure – minimum pressure following ventricular diastole and blood moving forward into arterioles
Pulse pressure – difference between the two

9. Blood Pressure
Mean arterial pressure – average pressure in the vessel throughout the cardiac cycle
MAP = DP + 1/3 (pulse pressure)
MAP = cardiac output x total peripheral resistance
CO = stroke volume x HR
TPR = radius and viscosity

10. Arterioles Arterioles – small radii, have more resistance
Can adjust diameter to:
Vary distribution of blood to organs
Regulate arteriole pressure
Vasoconstriction
(increased contraction of circular smooth
muscle in the arteriolar wall, leads to increased resistance and decreased
flow through the vessel)
Vasodilation
(decreased contraction of circular smooth
muscle in the arteriolar wall, leads to decreased resistance and increased flow
through the vessel)

11. Arterioles
Arteriole smooth muscle always displays a state of vascular tone (partial constriction)
Maintained by:
Myogenic activity of smooth muscle cells
Sympathetic fibers
Factors influencing the level of smooth muscle contraction:
Intrinsic (local) controls – determines distribution of cardiac output
Extrinsic controls – regulates systemic blood pressure

12. Intrinsic Controls Chemical
Increased metabolic activity triggers vasodilation
Decreased O2
Increased CO2
Increased adenosine
Increased NO
Histamine and prostaglandins - vasodilation

13. Intrinsic Controls Physical influences Temperature
Heat – vasodilation
Cold - vasoconstriction
Myogenic response to stretch
Increased perfusion – increases stretch triggers vasoconstriction
Decreased perfusion – decreased stretch triggers vasodilation

14. Extrinsic Controls Sympathetic Nervous System Hormones
Maintains overall MAP for the system but local regulation can over ride it for tissues that need increased blood flow
Hormones
ADH - constriction
Angiotensin II - constriction
NE / Epinephrine
α receptors – constriction
Β receptors – dilation (skeletal and cardiac)
Atrial Natriuretic Peptide - dilation

16. Blood pressure
Short term regulation – adjustments occur within seconds
Baroreceptors monitor MAP and initiate reflex responses to maintain BP homeostasis
Receptors - found in the carotid sinus and aortic arch
Cardiovascular control center in the medulla
Response – adjusts parasympathetic / sympathetic activity

17. Baroreceptor Reflex

18. Blood Pressure Long term regulation – minutes to days
Involves adjusting blood volume
Hormones
Renin – angiotensin II – aldosterone pathway
ADH

19. Capillaries
Site for exchange of materials between the blood and the tissues
Precapillary sphincters control the flow of blood through the capillary beds
Smooth muscle that respond to local controls

20. Relationship between plasma and interstitial fluid

21. Capillaries Factors that influence diffusion
Minimal diffusion distance
Maximized surface area for exchange (600m2)
Maximized time for exchange (slow velocity of flow)

22. Capillaries Exchange of solutes across capillary wall
Fat soluble solutes pass through endothelial cells
Small water soluble solutes pass through pores
Plasma proteins are too large to pass
Protein hormones cross by vesicular transport

23. Capillaries
Movement of fluid across the capillary wall occurs because of differences in hydrostatic and osmotic pressures
Plasma hydrostatic pressure – exerted on the vessel wall due to pushing of blood
Plasma osmotic pressure – created by movement of water as it is pulled down its concentration gradient

24. Net Filtration Pressure
Takes into account all hydrostatic and osmotic forces on the capillary
Determines if there is a net gain or net loss of fluid from the blood

25. Capillaries Involves:
Bulk flow – movement of fluid across the capillary walls
Involves:
Ultrafiltration – movement out of the capillary into the interstitial fluid, occurs at the arteriole end
Reabsorption – movement into the capillary from the interstitial fluid, occurs at the venule end

26. Lymphatic Vessels More fluid is filtered into the ECF that reabsorbed
This extra fluid is picked up by lymph capillaries
Fluid leaks into lymph capillaries when interstitial pressure is high and one-way flap-like valves prevent lymph from leaking back out

27. Lymphatic Vessels
Fluid is returned back to the blood by the lymph system
Pump-less one way system
Lymph moves towards the heart
Flow is accomplished by:
Valves
Milking action of skeletal muscle
Contraction of smooth muscle in vessel walls
Pressure changes in the thorax

28. Veins Carry blood back to heart
Large diameter, little resistance, low pressure
At rest contains more than 60% of the total blood volume

29. Veins Factors affecting venous return: Pressure gradient
One-way valves
Skeletal muscle contraction
Respiratory pump
Cardiac suction
Sympathetic activity

30. Venous Return

31. Summary:

32. Cardiovascular Disease
Cardiovascular disease accounts for over half of all deaths in the United States
Myocardial infarction - heart attack
Aorta
When heart muscle does not receive blood, cells will quickly die
Cause by blockage of coronary arteries
Coronary artery
Blockage
Dead muscle tissue
Figure 23.14

33. Cardiovascular Disease
Atherosclerosis
Narrowing of the arteries by plaques of cholesterol and other substances that form in the inner walls of arteries
Figure 23.15

34. Atherosclerosis

35. Treatments for Cardiovascular Disease
Life style changes and drugs
Angioplasty – use balloon or laser to remove the blockage from the artery
Or insert a stent to keep artery open
Coronary bypass surgery – use another blood vessel from another part of the body as a bridge to get around the blockage