Overview of Circulation & Vascular Distensibility and Functions - - PowerPoint PPT Presentation

Overview of Circulation & Vascular Distensibility and Functions

Chad Smurthwaite & Alex Goncharov

Chapter 14 - Overview of the Circulation; Biophysics of Pressure, Flow and Resistance

Blood Distribution

aorta arteries arterioles vena cava veins venules capillaries Heart

Blood Distribution Continued

Pulmonary - 9% Heart - 7% Arterial System Arteries - 13% Arterioles and Capillaries - 7% Venous System Veins, Venules, and Venous Sinuses - 64%

Arterial System

Made of two types of vessels

Conductance Vessels: Largest arteries with the thickest lumen near the heart. They contain much more elastin that allows them to expand and recoil as the heart ejects blood allowing a constant flow of blood. Resistance Vessels - Smaller arteries that contain more smooth muscle that constrict and relax to allow vasoconstriction and vasodilation

Venous System

Capacitance Vessels: Veins with large lumens and thin walls that allow expansion for storage of blood.

Capillaries

Capillary Beds: Smallest blood vessels that allow for exchange of gases, hormones and nutrients for most tissues in the body.

Blood Pressure Throughout the Circulatory System

Pressure ranges between 120 and 80 mmHg in large arteries. Pressure then falls

• ff.

Venous system very low pressure system.

Blood Flow

Rate of flow: Ohm’s law

Proportional to the pressure difference Inversely Proportional to the resistance

Flow = ΔPressure/ Resistance

Conductance and Poiseuille’s Law

Conductance: A measure of the blood flow through a vessel for a given pressure difference. Conductance = 1/resistance Conductance ∝ Diameter4 Poiseuille’s Law

Types of Flow

Laminar Flow: When blood flows in streamlines, with each layer remaining the same distance from the lumen. Turbulent Flow: Blood is flowing in all directions in the vessel and continually mixing within the vessel.

Series vs. Parallel Circuits Series Circuits: When blood vessels are arranged in series

Parallel Circuits: When blood vessels branch and converge Rtotal = R1 + R2 + R3 + R4 …..

Autoregulation of Tissue Blood Flow (Perfusion)

Autoregulation: The automatic adjustment of blood flow to each tissue in proportion to the tissue’s requirements at any moment.

Metabolic Theory: When blood flow is too low to meet metabolic needs, oxygen levels decline and metabolic products accumulate. Metabolic factors- low oxygen, increases in hydrogen ions, potassium, adenosine, and prostaglandins. Myogenic Theory: When vascular smooth muscle responds directly to a passive stretch by increased tone, which increases blood flow. Both work together to determine the final autoregulatory response for a given tissue

Chapter 15 - Vascular Distensibility and Functions

• f the Arterial and Venous Systems

Vascular Distensibility and Compliance

Vascular Distensibility: The ability of a blood vessel wall to expand and contract passively with changes in pressure. All blood vessels are distensible Allows for non pulsatile flow at the capillaries Reservoir function of Veins: can expand to store 0.5 to 1.0 L of extra blood

Distensibility

Veins are 8x more distensible than arteries Pulmonary arteries are 6x more distensible than systemic arteries.

Compliance (Capacitance)

Total quantity of blood that can be stored in a given portion of the circulation

Volume-Pressure Curves

Arterial vs. venous distensibility Sympathetic stimulation/inhibition

Delayed Compliance - stress relaxation

Works when blood volume is added or lost

Functions of Arterial vs. Venous Systems

Arterial Pressure Pulsations The difference between systolic and diastolic is pulse pressure Affects Pulse Pressure:

• 1. stroke volume output of the heart
• 2. compliance of arterial tree

Abnormal pressure pulse contours

Pulse Pressure Transmission

Venous Pressure - Central Venous Pressure vs Peripheral Venous Pressure

• 1. Right Atrial Pressure (Central Venous Pressure)

Pressure taken in vena cava -- right before right atrial pressure Values: Normal = 0.0 mm Hg Can increase to 20-30 mmHg in heart failure Lower limit -3 to -5 mm Hg

Venous Resistance

low resistance - compressions can lead to collapses

Peripheral Venous Pressure

Pressure driving blood back to heart is about 7 mm Hg. If there is pressure gradient from veins to the heart, blood will flow back to the heart. Valves/Muscles Pumps