1. The Cardiovascular System: Blood Vessels and Circulation
Chapter 16

2. 5 Types of Vessels Arteries Arterioles Capillaries Venules Veins
Carry blood away from the heart to body tissues
Aorta and pulmonary trunk
Arterioles
Within a tissue or organ branch into numerous microscopic vessels called capillaries
Capillaries
Groups of capillaries reunite to form small veins:
Venules
Merge to form larger vessels:
Veins
Blood vessels that carry blood from the tissues back to the heart
Blood reservoirs
Certain veins function as reservoirs b/c contain so much of blood

3. Arteries and Arterioles
Arteries have 3 tissue layers surrounding lumen (hollow space)
Endothelium
Inner layer composed of simple squamous epithelium, a basement membrane, and elastic tissue (internal elastic lamina)
Middle layer: smooth muscle and elastic tissue
Outer layer: mainly of elastic and collagen fibers
Vasoconstriction
Decrease in diameter of the lumen of a blood vessel
Increase in sympathetic stimulation

4. Arteries and Arterioles
Vasodilation
Decrease in sympathetic stimulation
Increase in lumen diameter
Elastic arteries
High proportion of elastic fibers
Help propel blood while ventricles are relaxing b/c relax
Stretch when blood ejected from heart
Ex. Aorta and braciocephaliic, common carotid, subclavian, vertebral, pulmonary, and common iliac arteries
Muscular arteries
Great vasoconstriction and vasodilation
Ex. Brachial artery (arm) and radial artery (forearm)

5. Arteries and Arterioles
A very small, microscopic artery that delivers blood to capillaries
Big role in blood flow from arteries  capillaries

6. Capillaries Are microscopic vessels that connect arterioles to venules
Exchange vessels b/c exchange of nutrients and wastes b/w the body’s cells and blood
Body tissues w/high metabolic requirements (muscles, liver, kidneys, NS) have many capillary networks

7. Capillaries Very thin walls, allows many substances to pass through
Precapillary sphincters: rings of smooth muscle at the point where capillaries branch from arterioles
Numerous, so blood flows slowly through them
Capillary exchange: the movm’t of substances into/out of capillaries

8. Capillary Exchange 1. Diffusion
O2, CO2, glucose, amino acids, and hormones by simple diffusion
Plasma solutes
Sinusoids: gaps b/w endothelial cells in smallest blood vessels in the liver
But too large to allow proteins like fibrinogen and albumin to enter bloodstream

9. Capillary Exchange 2. Bulk flow: filtration and reabsorption
Bulk flow: is a passive process by which large numbers of ions, molecules, or particles move together in same direction
From area of high pressure  low pressure
Continues if pressure difference exists
Two opposing pressure drive bulk flow:
1. capillary blood pressure
2. colloid osmotic pressure

10. Capillary Exchange: Bulk Flow
1. Capillary blood pressure
Pressure of blood against the walls of capillaries pushes fluid out of capillaries into interstitial fluid
2. Colloid osmotic pressure
Opposing pressure
Pulls fluid into capillaries
Presence of proteins in plasma and their virtual absence in interstitial fluid gives blood the higher osmotic pressure

11. Capillaries: Bulk Flow
Filtration: water and solute flow out of the blood capillary into the surrounding interstitial fluid via bulk flo
Capillary blood pressure higher than blood osmotic pressure for first half of capillary
Midway through capillary, pressure drops  reabsorption
Reabsorption
Water and solutes move via bulk flow from interestitial fluid into the blood capillary

12. Capillaries: Bulk Flow
Autoregulation: the ability of a tissue to automatically adjust its blood flow to match its metabolic demands
Regulation of vasodilation and vasoconstriction

13. Venules and Veins When several capillaries unite  venules
Venules: receive blood from capillaries and empty blood into veins return blood to heart

14. Venules and Veins: Structure
Venules = little veins
Similar to arterioles
Walls thinner near capillary end and thicker towars the heart
Veins
Structure similar to arteries
Outer layer is thickets, and lumen wider than artery
In some veins, inner layer folds in = valves (prevent backflow of blood)
Varicose veins: due to weak venous valves
Blood backflows, causing increase in blood pressure, pushes vein wall outwards
Loss of elasticity and stretch

15. Venous Return
The volume of blood flowing back to the heart through systemic veins
1. Contractions of the heart
2. the skeletal muscle pump: (p.395 in leg)
1. while standing, venous valves closer and farther from heart closed, blood flow to heart
2. contraction of leg muscles, compress veins
Pushes blood through valve closer to heart  milking
At same time, valve farther from heart is uncompressed and closes as blood pushed against it
3. muscle relaxation: pressure falls in compressed section of veins, causes valve closer to heart to close
Valve farther from heart opens b/c blood pressure of foot is higher than in leg

16. Venous Return
3. Respiratory Pump: based on alternating compression an decompression of veins
During inhalation the diaphragm moves downward  decrease pressure in thoracic cavity and increase pressure in abdominal cavity abdominal veins compressed greater volume of blood moves from compressed abdominal veins to decompressed thoracic veins and then into right atrium
Exhalation: valves in veins prevent backflow of blood from thoracic veins to abdominal veins

17. Cardiovascular System
Circulatory I

18. Blood Pressure Blood flows from high pressure  low pressure
Blood pressure (BP): the pressure exerted by blood on the walls of a blood vessel
Highest in aorta and large systemic arteries
Falls as distance from left ventricle increases

19. Resistance
Vascular Resistance: opposition to blood flow due to friction b/w blood and the walls of blood vessels
Depends on:
1. size of lumen
2. Blood viscosity
3. Total blood vessel length

20. Vascular Resistance 1. Size of lumen
Smaller the lumen, greater is resistance to blood flow
Increase in BP

21. Vascular Resistance 2. Blood viscosity Viscosity (thickness)
Higher blood viscosity, higher resistance
Increases if
dehydration or
polycythemia (high number of red blood cells)
Decreases if
depletion of plasma proteins or RBCs b/c of anemia or hemorrhage decrease BP

22. Vascular Resistance 3. Total blood vessel length
Resistance increases when total length of all blood vessels increases
Longer the length  greater contact of blood and vessel wall  causes friction
higher BP

23. Measurement of Blood Pressure:
Brachial artery in left arm
Device: sphygmomanometer
Pressure cuff inflated, artery compressed and blood flow stops
Stethoscope below cuff, then cuff deflated

24. Blood Pressure Systolic Blood Pressure (SBP)
First sound as cuff is deflated as artery is opening
Force with which blood is pushing against arterial walls during ventricular contraction
Diastolic Blood Pressure (DBP)
Sounds become faint
Represents force exerted by blood remaining in arteries during ventricular relaxation