1. Anatomy and Physiology
Martini’s Visual
Anatomy and Physiology
First Edition
Martini w Ober
Chapter 18 The Heart and Cardiovascular Function
Lecture 4
105 min, 37 slides

2. Lecture Overview Arteries and arterioles
Capillaries and capillary exchange
Veins and venules
Blood pressure and its regulation

3. Overview of Blood Vessels
arteries
carry blood away from ventricles of heart
arterioles
receive blood from arteries
carry blood to capillaries
capillaries
sites of exchange of substances between blood and body cells
venules
receive blood from capillaries
veins
carry blood toward atria of heart
Know the function of each of these types of vessels

4. Overview of Blood Vessels
Note the absence of smooth muscle in capillaries
We have about 60,000 miles of blood vessels in our bodies!
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

5. Overview of Blood Vessels
Note the absence of smooth muscle in capillaries
We have about 60,000 miles of blood vessels in our bodies!
Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

6. Arteries and Arterioles
Inner layer – tunica intima (interna) Middle layer – tunica media Outer layer – tunica externa (adventitia)
Artery
thick strong wall
endothelial lining
middle layer of smooth muscle and elastic tissue
outer layer of connective tissue
carries blood under relatively high pressure
Arterioles
thinner wall than artery
endothelial lining
smooth muscle tissue
small amount of connective tissue
control blood flow into capillary beds

7. Comparison of Walls of Arteries and Veins
Smooth muscle of the tunica media in both arteries and veins is innervated by the sympathetic nervous system.
Figure from: Hole’s Human A&P, 12th edition, 2010

8. Arteriole smallest arterioles only have a few smooth muscle fibers
can vasoconstrict (decrease diameter) or vasodilate (increase diameter)
Figure from: Hole’s Human A&P, 12th edition, 2010
Most important in controlling blood flow to capillary beds
Arterioles are specialized for controlling blood flow

9. Metarterioles Each metarteriole supplies about 10-100 capillary beds
Figure from: Hole’s Human A&P, 12th edition, 2010
Each metarteriole supplies about capillary beds
Metarterioles form arteriovenous shunts that can bypass capillary beds

10. Capillaries smallest diameter blood vessels (fit 1 RBC at a time)
extensions of inner lining of arterioles
walls consist of endothelium and basement membrane only – NO smooth muscle
semipermeable (plasma fluid can escape, but not proteins)
Figure from: Hole’s Human A&P, 12th edition, 2010
3 types:
- continuous (muscle)
- fenestrated (endocrine glands, kidney, small intestine)
- sinusoids (liver, spleen, bone marrow)

11. Capillary Network
Blood can follow different pathways through metabolically active/inactive tissues
Figures from: Hole’s Human A&P, 12th edition, 2010

12. Differences in Blood Flow: At Rest/Exercise
Figures from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

13. Regulation of Capillary Blood Flow
Figure from: Hole’s Human A&P, 12th edition, 2010
Precapillary sphincters
may close a capillary
respond to needs of the cells
low oxygen and nutrients cause sphincter to relax

14. Exchange in the Capillaries
major mechanism involved in exchange of solutes is diffusion
substances move in and out along the length of the capillaries according to their respective concentration gradients
Fluid movement in systemic capillaries is determined by two major factors
1. hydrostatic pressure; varies along portions of capillary
2. osmotic pressure; remains about the same along the length of the capillary
Excess tissue fluid is drained via lymphatics
Figure from: Hole’s Human A&P, 12th edition, 2010

15. Forces Acting Across Capillary Walls
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
What occurrences would increase the net amount of fluid leaving the capillaries?
What would decrease the net amount of fluid leaving the capillaries?

16. Venules and Veins Venule thinner wall than arteriole; larger lumen
less smooth muscle and elastic tissue than arteriole
Vein
thinner wall than artery; larger lumen
three layers to wall but middle layer is poorly developed
some have flaplike valves
carries blood under relatively low pressure
serves as blood reservoir
are able to constrict (sympathetic innervation)

17. Venous Valves
Figure from: Hole’s Human A&P, 12th edition, 2010
Valves aid one-way blood flow since pressure is low in veins
If the walls of veins near valves become weakened, valves may fail, blood will pool, vessels will become distended, e.g., varicose veins

18. Blood Volumes in Vessels
Figure from: Hole’s Human A&P, 12th edition, 2010
Important for control of blood pressure
At any one time, most of the body’s blood is in the venous system; thus they are a major factor influencing venous return to the heart.

19. Venous Blood Flow not just a direct result of heart action
depends on skeletal muscle contraction (skeletal muscle pump)
depends on breathing (respiratory pump)
depends on venoconstriction
Figure from: Hole’s Human A&P, 12th edition, 2010

20. Some Blood Flow Preliminaries
Blood flow is the volume of blood that flows through any tissue in a given amount of time
Total blood flow = CO (ml/min)
Two important factors influence how the CO gets distributed to the body
Pressure that drives the blood through a tissue
Resistance to blood flow (OPPOSES FLOW)
Blood Flow (CO)  Pressure / Resistance
Perfusion is the Flow per volume/mass of tissue.

21. Vascular Resistance
The resistance to blood flow (vascular resistance) is dependent upon several factors
Size of the lumen of the blood vessel (R 1/r4)
Smaller lumen = more resistance to flow
Larger lumen = less resistance to flow
**Main physiological control of resistance and flow
Blood viscosity (thickness) which is determined by the ratio of RBCs to plasma
Increased viscosity = more resistance to flow
Total blood vessel length (Let’s gain a few pounds; 200 MILES / pound of adipose!)
Longer total blood vessel length = more resistance to flow
Turbulence (increased turbulence = more resistance)
Recall: Blood Flow (CO)  Pressure / Resistance

22. Arterial Blood Pressure
Blood Pressure – force the blood exerts against the inner walls of the blood vessels
Arterial Blood Pressure
rises when ventricles contract
falls when ventricles relax
systolic pressure – maximum pressure
diastolic pressure – minimum pressure
Pulse pressure – difference between systolic and diastolic pressures (systolic : diastolic : pulse pressure ~ 3:2:1)
- Pulse pressures usually rise with age because of an increase in blood vessel resistance (arteriosclerosis)
Recall: Blood Flow (CO)  Pressure / Resistance
Pulse pressure is an indication of the stress exerted on the small arteries by the pressure surges generated by the heart. (Alternate expansion and contraction of small (muscular, but not extensively elastic) arteries puts stress on the vessel walls. This is alleviated by the expansion and contraction of the ELASTIC arteries, that are built to take higher pressures.)
In capillaries and veins, blood flows pretty much at a constant speed rather than being pulsatile.

23. Mean Arterial Pressure
Mean Arterial Pressure (MAP) – Average effective pressure driving blood flow through the systemic organs
MAP = CO x Total Peripheral Resistance (TPR)
**Thus ALL changes in MAP result from changes in either cardiac output or peripheral resistance
If CO increases, MAP ? If TPR decreases, MAP ?
If TPR decreases, what must be done to keep MAP the same?
If blood volume decreases, what must be done to keep MAP the same?
MAP can be estimated by the equation:
diastolic bp + (pulse pressure / 3) (Roughly 1/3 of the way between systolic and diastolic pressures)

24. Pulse
A ‘pulse’ is a rhythmic pressure wave accompanying each heartbeat.
Figure from: Hole’s Human A&P, 12th edition, 2010
The alternate expanding and recoiling of the arterial wall that can be felt (palpated) easily at certain locations on the body

25. Factors That Influence Arterial Blood Pressure
BP (MAP) = Cardiac output x Peripheral Resistance
Figure from: Hole’s Human A&P, 12th edition, 2010 CO
Know this!
TPR
Decrease in the above factors has the opposite effect, i.e., blood pressure decreases

26. Central Venous Pressure
Central Venous Pressure = pressure in the vena cava near the right atrium (~ 2-4 mm Hg)
determines the filling pressure of the right ventricle
determines the EDV of the right ventricle which
**determines ventricular stroke volume (Frank-Starling)
affects pressure within the peripheral veins
weakly beating heart causes an increase in central venous pressure (backup of blood)
increase in central venous pressure causes blood to back up into peripheral veins

27. Regulation of Blood Flow/Pressure
Blood flow/pressure can be affected by
1) Autoregulation
Local factors within tissue capillary beds
Cause localized reaction
2) Neural mechanisms
Responses to changes in arterial pressure or blood gas levels (baroreceptors or chemoreceptors)
Cause more widespread changes
VERY rapid
3) Endocrine mechanisms (will be covered with endocrine/urinary systems)
Enhance short-term adjustments
Direct long-term changes
Work mainly through changes in blood volume

28. Autoregulation of Blood Flow/Pressure
Local changes in response to metabolic needs of tissues
Occurs at the level of the precapillary sphincters; not dependent on neural or hormonal mechanisms
Changes in local blood flow may, or may not, necessitate activation of neural and/or hormonal mechanisms

29. Autoregulation of Blood Flow/Pressure
Local vasodilators increase blood flow
Decreased O2 (except pulmonary circulation) or increased CO2
Increase in lactic acid production
Release of nitric oxide (NO)
Increased K+ or H+
Mediators of inflammation (histamine, NO)
Elevated local temperature
Local vasoconstrictors decrease blood flow
Prostaglandins, thromboxanes (released by activated platelets and WBCs)
Endothelins released by damaged endothelial cells

30. Neural Control of Blood Pressure
Controlling cardiac output and peripheral resistance regulates blood pressure
Know this!
Figure from: Hole’s Human A&P, 12th edition, 2010

31. Neural Control of Blood Pressure
If blood pressure rises, baroreceptors initiate the cardioinhibitory reflex, which lowers the blood pressure
Know this!
Figure from: Hole’s Human A&P, 12th edition, 2010

32. Neural Control of Blood Pressure
Dilating arterioles helps regulate (lower) blood pressure
Know this!
Figure from: Hole’s Human A&P, 12th edition, 2010

33. Hormonal Control of Blood Pressure
Changes blood pressure by changing the volume of the blood
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

34. Hormonal Control of Blood Pressure
Changes blood pressure by changing the volume of the blood
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

35. Factors Affecting Blood Pressure (MAP)
1/radius4; Vessel length; Viscosity; Turbulence
MAP (BP)
TPR
ANS Parasympathetic Sympathetic HR
Contractility CO
= HR x SV
ESV
Afterload SV
= EDV - ESV
EDV
CVP
Figure adapted from: Aaronson & Ward, The Cardiovascular System at a Glance, Blackwell Publishing, 2007
MAP – Mean Arterial Pressure = Average effective pressure driving blood flow through the systemic organs
**The MAP is dependent upon CO and TPR, i.e., MAP = CO x TPR
TPR – Total Peripheral Resistance; depends upon *blood vessel radius, vessel length, blood viscosity, and turbulence

36. Factors Affecting Blood Pressure (MAP)
Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001
Three major factors influence SV: preload, afterload, and contractility (inotropy).
Preload correlates to the degree of stretch of the cardiac muscle fibers before contraction. The resting length of cardiac muscle is shorter than optimal (unlike skeletal muscle where the resting length is optimal). The stretch of cardiac muscle during ventricular filling places the cardiac muscle sarcomeres at a more optimal length. Therefore, and increased rate of venous return (like a slow heart rate that allows more filling time, or exercise that increases the rate of venous blood flow back to heart), or an increased amount of venous return will cause an increased SV and, thus, and increased CO.
Contractility is an increased force of contraction independent of muscle stretch and EDV. Direct result of greater Ca influx into the cytoplasm from the extracellular fluid which is a result of sympathetic stimulation. Other factors include glucagon, thyroid hormone, epinephrine, and digitalis. These are positive inotropic agents. Factors that decrease contractility (negative inotropic agents) include acidosis, hyperkalemia, and Ca channel blockers.
Afterload is the pressure that the ventricles have to overcome in order to eject blood (back pressure on semilunar valves due to presence of blood in vessels; about 80 mm Hg in systemic circuit, 8 mm Hg in pulmonary circuit). Hypertension had a great effect on increasing afterload and consequently reducing SV (increasing ESV) and CO.
MAP = X TPR
1 / radius4
Vessel length
Viscosity
Turbulence

37. Review
The blood vessels form a closed circuit for distribution of the blood from the heart to the tissues and back again.
The vessels of the CVS include
Arteries - carry blood away from ventricles of heart; this walled; elastic
Arterioles - receive blood from arteries/carry blood to capillaries; major flow regulators
Capillaries - sites of exchange of substances between blood and body cells
Venules - receive blood from capillaries
Veins - carry blood toward atria of heart

38. Review Capillary-tissue exchange is dependent upon Blood pressure
Diffusion (Exchange of solutes)
Osmosis (colloid osmotic pressure)
Filtration
Vesicular transport
Blood pressure
Is the force exerted on vessel walls by the blood
Is usually measured as arterial blood pressure
Systolic – maximum pressure during ventricular systole
Diastolic – minimum pressure during ventricular diastole
Pulse pressure = systolic – diastolic
Mean arterial pressure = CO X TPR
Exchange of fluid

39. Review Factors influencing blood pressure
Cardiac output (CO)
Blood volume
Blood viscosity
Peripheral resistance (PR)
Cardiovascular system function can be regulated by
Tissue autoregulation
Neural mechanisms
Endocrine mechanisms

40. Review
Veins are a large reservoir of blood and exert a large effect upon blood pressure
Venous blood flow depends upon
Skeletal muscle contraction
Breathing movement
Vasoconstriction of veins (venoconstriction)
Central venous pressure is the pressure near the right atrium
If CVP increases, blood may back up
Increased CVP can lead to edema