Cardiovascular System: Hemodynamics and Regulation

Heart and Cardiovascular System

Transports material via the blood (gases, nutrients, wastes). It facilitates communication between organ systems, organs, and cells. Supports defense against pathogens. Immune system and setting whole0body metabolism.

Systemic Circulation

Left side with systemic arteries, capillaries, and veins (pumped from eft side and returned to right atrium de-O2)

Pulmonary Circulation

Right side with pulmonary arteries, capillaries, and veins (pumped from right side to left atrium with O2 blood)

Structure of CV

Vascular beds are arranged in parallel and blood volume is 5 L (across circulation and within tissues)

Heart

Pump (R and L), with each side having a atria (primer pump) and ventricle (major pump)

Atria

Receives blood and hyper-fill ventricles

Ventricles

The right ventricle pump blood out, right ventricle pumps to the lungs and left ventricle pumps to the body.

Septum

Divides L and R of heart

R Atria

Receives blood from body

L Atria

Receives blood from lungs

R Ventricle

Pumps blood to lungs for gas exchange

L Ventricle

Pumps blood to the body

Atrioventricular Valves (AV)

Separate atria from ventricle, opening during relaxation (atrial pressure > ventricular pressure), and closed during contraction (atrial pressure < ventricular pressure)

Tricuspid Valve

Right side valve

Mitral of Bicuspid

Left side valve

Valve Motion

Driven passively by pressure gradients

Semilunar Valves

Separate great arteries from the ventricles (atrial pressure > ventricular pressure), and closed during contraction (atrial pressure < ventricular pressure)

Pulmonary Valve

R ventricle and pulmonary artery

Aortic Valve

L ventircle and aorta

Vasculature

Passive conduits, delivering blood to and from tissues where nutrients and waste are exchanged 

Hemodynamics

Principles that govern blood flow in CV system

Endothelial Cells

Single layer that lines all blood vessels

Elastic Fibers

Convey elastic properties to certain types of vessels

Collagen Fibers

Stiffer than elastic, and when combined contributes to passive stiffness of vessels

Vascular Smooth Muscle Cells

Active contraction is responsible for active tension in blood vessels.

Capillaries

Permit diffusion between blood and tissue (only one), with very high SA, and simple squamous epithelium (small diffusion distance)

Diffusion

Solutes move along their concentration gradient

Bulk Flow

Water and solutes flow together through pores; proteins stay inside

Lymphatic Vessels

Pick up excess fluid from capillary beds and return it to the venous system. Fluid cleaned, filtered, and immune system checked. Low-pressure one-way valves formed by overlapping epithelia and are permeable to large proteins and particles. Fluid cleaned, filtered, immune system checked.

Venous Return

Return blood to the heart with low pressure. Depends on HR, SNS, skeletal muscles, and respiratory P, venous valves, cardiac suction, blood volume.

Flow of Vasculature

Depends on vessel types as they have different diameters, area, and cell composition

Velocity of Blood Flow

Rate of displacement of blood per unit of time

Velocity (V)

Flow (Q) / Cross-sectional area (A)

Cardiac Output

Rate at which blood is pumped from either ventricle

Laminar Flow

Velocity of flow in the center of the vessel greater than outer edges. 

Turbulent Flow

Blood flows in all directions in the vessel and is continually mixing within the vessel. Common at vascular bifurcations and branches and atheromas.

Sheer Stress

Blood travels at different velocities within a vessel causing blood to go in different directions.

Reynolds Number

Predicts type of flow (laminar or turbulent)

Type of Flow

Dependent on diameter, velocity, and viscosity

Arterioles 

High resistance is a major determinant of flow rate in the body. Do not expand or recoil like arteries; flow rate is determined by resistance. 

Flow Rate Resistance

Small radius vessels have high resistance, meaning they have less flow rate.

Different Types of Vessles

Different internal dimensions and therefore different resistance

Resistance

Inversely proportional to the radius of a vessel to the 4th

Directly proportional to the length and viscosity of blood

Blood Pressure

Systolic over Diastolic Pressure. Differs at different vessels.

Regulation of Blood Pressure

BP not equal throughout CV to create driving force for blood flow 

Pressure

Force per unit area

Driving Pressure

Created by ventricles (systolic P)

Diastolic Pressure

Created by contraction of SM lining the arteries

SM Relaxtion

Blood vessels dilate and BP decreaes

SM Contraction

Blood vessels constrict and BP increases

Larger Vessels

Have SM cells and elastic fibers, which is dependent on calcium signaling, decreasing with aging and disease

Vessel Compliance

Volume of blood the vessel can hold at a given pressure (Volume/Pressure). The more volume it can hold at a given pressure

Arterial Pressure

Controlled by local blood flow or cardiac output (MAP = CO x R)

Cardiac Output

HR and ventricular volumes at systole and diastole 

CO

HR x SV

SV

EDV - ESV

End Systolic Volume (ESV)

Volume of blood in the ventricle after contraction

End Diastolic Volume (EDV)

Volume of blood in the ventricle before contraction

Stroke Volume (SV)

Volume of blood the heart's left ventricle ejects during each single contraction

Fick Principle

Uptake and release of O2 is a product of the difference in the arterial and venous flow of the substance times the blood flow of the organ.

Blood Flow to Organ

1. Amount of O2 taken up by organ (VO2)

2. Concentration of O2 entering organ (arterial blood)

3. Concentration of oxygen leaving the organ (venous blood)

CO in Ficks Principle

VO2 / (arterial [O2] - venous [O2])

Blood Flow Driver

Difference in pressure between arterial and venous sides of circulation (venous has less pressure, therefore P moves towards gradient)

Mean Arterial Pressure

Driving force for blood flow, maintained at high constant level (100 mm Hg). Arteries are elastic, allowing them to transfer pressure from heart to circulation.

Elastic Properties of Large Arteries

Stretch to receive blood from the ventricles, and then recoil to push blood out of circulation.

Pressure Reservoirs

Arteries stretch and expand when heart contracts and then recoil when relaxed.

Vasodilation

Increase blood flow to the tissues will be triggered when tissues are more metabolically active (decreased O2, increased CO2, increased acid)

Vasoconstriction

Decrease blood flow to less active tissues

Nitric Oxide

Causes vasodilation by relaxation of SM via G protein-coupled receptor mechanism and phosphorylation of myosin.

Paracrine Signals

Endothelial cells in all blood vessels release this in response to metabolic changes.

Endothelin (EDN)

Causes vasoconstriction (pulmonary hypertension)

Vascular Endothelial Growth Factor (VEGF)

Causes new vessel growth

Histamine

Local chemical mediator released by inflamed or damaged tissue, causing vasodilation to increase blood flow to damaged areas (more WBC)

Stretch Response

Causes vasoconstriction of the arteriole to compensate, an auto-regulated myogenic response. Occurring when pressure changes are higher than normal, normalizes flow to tissues even with increased pressure.

Internal Stress

By high BP cause the release of nitric oxide and then causing vasodilation.

Heat

Causes vasodilation promoting increased blood flow to tissue

Cold

Causes vasoconstriction, counteracting inflammation and histamine release

Sympathetic Nervous System (SNS)

Extensively innervates arteriole SM, causing vasoconstriction (NE release adrenergic receptors)

Hormones

Released from adrenal medulla, E, NE, reinforce SNS activity and cause vasoconstriction

Vasopressin (ADH)

Vasoconstriction, retains water and increases blood volume

Angiotensin II

Vasoconstriction, retains Na+ and H2O, increases blood volume.

Blood Pressure Control

Drop in BP triggers kidney release of renin, which releases angiotensin II, triggering vasoconstriction, causing increased BP

Baroreceptor Reflex

Artery walls stretch and relax to maintain BP. Sudden changes in BP lead to rapid changes in walls, sensed by baroreceptors. This transmits regulatory info to CV control regions of brainstem (increase HR)

Heart Failure

Weakened heart muscle cannot pump enough blood

CO

VO2 / (Arterial [O2] - Venous [O2]

Blood Flow Determined By

Pressure difference and resistance of blood flow

Poiseuille Equation

Measure of resistance

Factors Determining Resistance

R is inversely proportional to the radius of the vessel (to the 4th). R is directly proportional to the length of the vessel and the viscosity of the blood.