Goal of the Cardiovascular System: deliver blood to all parts of the body

• Does so by using different types of tubing, attached to a pulsatile pump

• Elastic arteries• Muscular arteries• Arterioles• Capillaries• Venuoles• Veins

• Distribution system broken up into areas called vascular beds

• Skin• Digestive (splanchnic)• Muscle

Structure of vasculature changes in response to different needs

Why does blood flow through this closed circuit?

• Blood flows down a pressure gradient

• The absolute value of the pressure is not important to flow, but the difference in pressure (DP or gradient) is important to determining flow.

What happens to pressure if we decrease the volume of a fluid filled compartment (i.e. ventricles during systole)?

P directly proportional to F

The resulting pressure is called the driving pressure in the vascular system

How does the flow differ in these two vessels?

Vascular system possesses different mechanisms for promoting continuous flow of blood to the capillaries:

Elastic recoil smooth m. regulation of diameter sphincters valves

Muscular arteries

Chemical Physiologic role Source Type

NE ( ) Baroreceptor reflex Sympathetic neurons Neural

Endothelin Paracrine Vascular endothelium Local

Serotonin Platelet aggregation, smooth muscle contraction

Neurons, digestive tract, platelets

Local, neural

Substance P Pain, increased capillary permeability

Neurons, digestive tract

Local, neural

Vasopressin Increase blood pressure during hemorrhage

Posterior pituitary Hormonal

Angiotensin II Increase blood pressure Plasma hormone Hormonal

Prostacyclin Minimize blood loss from damaged vessels before coagulation

endothelium local

Substances causing contraction in vascular smooth muscle

Chemical Physiologic role Source Type

Nitric oxide Paracrine mediator Endothelium Local

Atrial natriuretic peptide

Reduce blood pressure Atrial myocardium, brain

Hormonal

Vasoactive intestinal peptide

Digestive secretion, relax smooth muscle

Neurons Neural, hormonal

Histamine Increase blood flow Mast cells Local, systemic

Epinephrine (2) Enhance local blood flow to skeletal muscle, heart, liver

Adrenal medulla Hormonal

Acetylcholine (muscarinic)

Erection of clitoris, penis Parasympathetic neurons

neural

Bradykinin Increase blood flow via nitric oxide

Multiple tissues Local

Adenosine Enhance blood flow to match metabolism

Hypoxic cells local

Substances that mediate vascular smooth muscle relaxation

Even though there are many mechanisms for altering the radius of the vascular system, pressure still drops as blood moves further away from the heart. Why?

Resistance = tendency of the vascular system to oppose flow; Flow =

• Influenced by: length of the tube (L), radius of the tube (r), and viscosity of the blood ()

Poiseuille’s Law R = Lr4

• In a normal human, length of the system is fixed, so blood viscosity and radius of the blood vessels have the largest effects on resistance

1

R

All four tubes have the same driving pressure. Which tube has the greatest flow? The least flow? Why?

Even with a decrease in overall pressure, the pressure in the vessels is not constant. The pressure in the vessels mirrors the pressures generated in the heart – systolic and diastolic pressures. Systolic = ventricles contracting Diastolic = ventricles filling

Why does the diastolic pressure rise between the left ventricle and the arteries?

Normal blood pressure = 120/80

High blood pressure = 140/90

What could be happening to increase both the diastolic and systolic blood pressure?

Blood Pressure

• Reflects the driving pressures produced by the ventricles

• Because arterial pressure is pulsatile, a single value is used to represent the overall driving pressure. This is called the mean arterial pressure.

MAP = diastolic P + 1/3(systolic P-diastolic P)Why does diastolic pressure account for a greater proportion of the overall value?

SVR = systemic vascular resistance

CO = cardiac output

SV = stroke volume

MAP = Q x Rarterioles

Explain how these two equations are equivalent

What factors influence blood pressure?

• Blood volume

• Vascular resistance

• Autoregulation

• Autonomic influences

Regulation of Blood Pressure

• Main coordinating center is in the medulla oblongata of the brain; medullary cardiovascular control center

• Reflex control of blood pressure

•Baroreceptor reflex