o   Aortic mean arterial pressure = 90 mm Hg

o   Central venous pressure in large returning veins = 2-8 mm Hg

o   Pulmonary artery pressure = 15 mm Hg

o   Pulmonary venous pressure = 0

o  ΔP of pulmonary circuits is much lower than systemic circuit

o   Flow in both circuits is same ~ 5 L/min

o   How? Resistance has to be higher or lower to = 5

    How is the flow rate equal in both the pulmonary and systemic circuits?

 Resistance has to be higher or lower to = 5

Where is pressure drop the greatest as blood travels through the various types of vessels in the systemic and pulmonary circuits?

 Pressure drops as blood travels through circuits – 14.3

                               i.   Systemic circuit – starts at 90, ends at 0

                              ii.   Pulmonary circuit – starts at 30, ends at 0

                             iii.   Greatest pressure drop at arterioles

 Resistance impedes blood flow

                               i.   Increased radius, decreased resistance

                              ii.   Increased length, increased resistance

                             iii.   Blood viscosity – increased concentration of cells/proteins, increased resistance

What is total peripheral resistance?

  Total peripheral resistance (TPR)

                               i.   Combined resistance of all vessels in the systemic network

                              ii.   Vasoconstriction – increased TPR

                             iii.   Vasodilation – decreased TPR

relationship between cardiac output, mean arterial pressure and total peripheral resistance.

a.   Pressure gradients and resistance

                               i.   Fact: flow = ΔP/R

                              ii.   Flow is cardiac output (CO)

                             iii.   ΔP=MAP

                             iv.   Resistance = TPR

                              v.   Therefore, CO=MAP/TPR

 What are common characteristics of all blood vessels?  How does lumen size and thickness of smooth muscle vary between the different types of vessels?  What is the order of vessels through which blood moves to and from the heart?

1.  Lumen-hollow interior

2.  Endothelium-lining, release and respond to chemical messengers

3.  Smooth muscle-regulate vessel diameter

4.  CT-vessel strength and elasticity

                                 Brachial artery, close to and same height as heart

                               i.   Systolic-highest pressure, ventricular contraction

                              ii.   Diastolic-minimum pressure, ventricular relaxation

                               i.   Laminar flow-free flow of blood through an artery

                              ii.   Turbulent flow – blood cells hit side of wall, but can slowly flow through artery

                                 Pulse pressure, PP=SP-DP

                               Mean arterial pressure (MAP) is weighted mean, average pressure in arteries during one cardiac cycle: 

MAP=[SP+(2 x DP)]/3

a.   Arterioles-major regulators of BP and direct blood flow

                               i.   60% of TPR attributable to arterioles

                              ii.   Largest pressure drop

                             iii.   Little elastic material, lots of SM

                               i.   Intrinsic mechanisms-local metabolites that regulated blood flow to match local needs

a.   Intrinsic control

                               i.   Extrinsic-autonomic nervous system and hormones regulate MAP

a.   extrinsic control by sympathetic innervations

                               i.   Epinephrine-binding to B2 receptors à vasodilation…………………binding to alpha1 receptors àvasoconstriction

                              ii.   Arteriolar SM of skeletal and cardiac has lots of B2

                             iii.   Arteriolar SM of most other tissues (especially guts) has mostly alpha1

It acts on the kidneys

                               i.   Antidiuretic hormone (ADH) – posterior pituitary limits urine output, increases blood volume

1.  AKA vasopressinàvasoconstriction in most tissues (at very high doses)

                               i.   Other plasma precursors converted to angiotensin II which promotes vasoconstriction Ang I à Ang II à increased BP

1.  Increased ACE ang converting enzyme

2.  ACE inhibitors-lower BP

                               i.   Walls are one cell thick

                              ii.   O2, CO2, monosaccharides, amino acids, H20, need to cross only a short distance

                             iii.   Body capillary surface area >600m²

                             iv.   Easy access for all cells

                              v.   Exists in networks (beds)

a.   Most capillaries are continuous

                               i.   14.17

                              ii.   Continuous- relatively tight, proteins cannot leave lumen

                             iii.   Fenestrated- porous, proteins and large species can leave lumen (kidneys and intestines)

                               i.   ΔP causes flow

                              ii.   ΔP varies along length of capillary

                             iii.   Fluid exchange between capillary and surrounding tissue

                               i.   Hydrostatic pressure (P)-fluid pressure

                              ii.   Oncotic pressure (π) – osmotic pressure exerted by non-permeable proteins

                               i.   Capillary hydrostatic pressure P_CAP

                              ii.   Capillary oncotic pressure π_CAP

                             iii.   Interstitual hydrostatic P_IF

                             iv.   Interstitual oncotic π_IF

                                Wet filtration pressure (NFP)=(P_CAP+ π_CAP)

                               i.   Hydrostatic pressure is only thing that changes significance!

                              ii.   Filtration occurs at arteriolar end, absorption at venule (14.20)

Why is all filtered fluid not absorbed?  Where does the remainder go to?  What happens if the fluid is not returned back to the cardiovascular system?

a.   Loss of fluid from CAP into IF is retrieved by lymphatic system

                               i.   3 L/day enters lymphatics, eventually returns to blood

                              ii.   Lymph is clear with yellow tinge

                             iii.   Failure of lymph-net accumulation of IF

a.   Large veins are large diameter, thin walled

                               i.   Highly compliant volume reservoir

                               i.   Central veins-in thoracic cavity

                              ii.   Peripheral veins-outside thoracic cavity-equipped with one-way valves

                                  Veins contain highest proportion of blood volume at rest

1. Skeletal muscle pump
2. respiratory pump
3. blood volume
4. venomotor tone

a.   . Venous return is aided by respiratory pump

                               i.   Inhalation expands rib cage, pulls diaphragm down

                              ii.   Increases abdominal pressure, decreases thoracic pressure

                             iii.   ΔP favors venous return

                             iv.   Exhalation reverses ΔP, but valves in abdominal veins prevent backflow

a.   Blood volume influences venous return

                               i.   Increased blood volume=increased venous pressure and increased venous return

                              ii.   Bleeding or dehydration=decreased venous return

                             iii.   Failure to excrete H2O and salts leads to fluid accumulation, hypertension (high MAP)

                               i.   Alpha receptors in SM of veins

                              ii.   Contract in response to increased sympathetic output

                             iii.   Increased venous pressure, increased venous return to heart

1.     How do baroreceptors regulate pressure via negative feedback mechanisms?

a.   Baroreceptors are pressure sensors

                               i.   Relay to control center in brainstem

                              ii.   Increase stretch of vessel causes increased parasympathetic output to SA node, decreased sympathetic

                             iii.   Decreased HR & SV àdecreased MAP

                             iv.   Orthostatic hypotension

What different dysfunctions lead to heart failure?

a.   Heart failure is inability to maintain adequate CO

                               i.   Weak myocardium (ie myocardial infarction)

                              ii.   Reduced HR through conduction block

                             iii.   Valve obstruction

                             iv.   May affect 1 or both sides

a.   Inadequate left ventricle activity leads to congestive heart failure

                               i.   Failure to contract increases left atrial pressure

                              ii.   Decrease in venous return from pulmonary circuit

Pulmonary congestion and edema- shortness of breath, fatigue, death

a.   Congestive heart failure treated with digitalis

                               i.   Digitalis inhibits Na+/K+ ATPase

                              ii.   Leads to accumulation of intracellular [Na+]i

                             iii.   Increased [Na+]i leads to increased [Ca2+]i

                             iv.   Increased [Ca2+]i gives stronger myocardium contraction