APK2105C Chapter 14: Blood Vessels, Blood Flow, and Blood Pressure

Flashcards covering the physical laws of blood flow, vessel anatomy, blood pressure calculation and measurement, and the intrinsic and extrinsic mechanisms of cardiovascular regulation.

Cardiac Output (CO)

The amount of blood flowing out of the heart per minute, calculated by the formula $CO = HR \times SV$.

Bulk Flow

The movement of a medium (air, liquid, gas) driven by a pressure gradient ($\Delta P$) where the direction is always down the gradient.

Systemic Pressure Gradient

The driving force for systemic blood flow, calculated as $\Delta P = MAP - CVP$.

Central Venous Pressure (CVP)

The pressure in the vena cava, which is typically noted as $0\,mm\,Hg$.

Poiseuille’s Law

An equation describing the resistance ($R$) encountered by a fluid flowing through a tube: $R = \frac{8L\eta}{\pi r^4}$.

Vessel Radius

The physical dimension that most significantly impacts resistance; if this is decreased by $1/2$, resistance increases $16$-fold.

Total Peripheral Resistance (TPR)

The combined resistance of all the vessels in the systemic network.

Mean Arterial Pressure (MAP)

The average pressure in the aorta during a cardiac cycle, calculated as $MAP = \frac{SBP + DBP + DBP}{3}$.

Compliance

The ease with which a vessel expands, defined as the change in volume per unit change in distending pressure: $Compliance = \frac{\Delta V}{\Delta DP}$.

Pressure Reservoir

A characteristic of arteries due to their abundant collagen and elastic fibers, which provide stiffness and flexibility with low compliance.

Arterioles

Vessels that provide the greatest amount of resistance to blood flow, accounting for more than $60\%$ of Total Peripheral Resistance (TPR).

Korotkoff sounds

Audible vibrations caused by turbulent flow in a compressed artery during blood pressure measurement when cuff pressure is between systolic and diastolic levels.

Active Hyperemia

An intrinsic control mechanism where increased metabolic activity leads to decreased oxygen and increased carbon dioxide, promoting vasodilation and increased blood flow.

Reactive Hyperemia

A type of intrinsic regulation where blood flow increases in response to a previous reduction in flow.

Myogenic Response

An intrinsic mechanism where increased perfusion pressure stretches arteriolar smooth muscle, causing constriction and increased resistance to maintain constant flow.

Nitric Oxide

A chemical messenger produced by endothelial cells that leads to vasodilation; it was formerly known as Endothelium-Derived Relaxing Factor (EDRF).

$\alpha$ Receptors

Adrenergic receptors present in all vascular smooth muscle that cause vasoconstriction when activated by norepinephrine released from sympathetic neurons.

$\beta_2$ Receptors

Adrenergic receptors present in the smooth muscle of liver, coronary, and skeletal muscle arterioles that cause vasodilation when bound by epinephrine.

Vasopressin (ADH)

A hormone released from the neurohypophysis that causes vasoconstriction and acts as an anti-diuretic by increasing water reabsorption in the kidneys.

Angiotensin II

A plasma protein that acts as a potent vasoconstrictor and stimulates the secretion of aldosterone and ADH.

Volume Reservoir

A characteristic of veins due to their high compliance, allowing them to hold approximately $60\%$ of systemic blood volume at rest.

Skeletal Muscle Pump

An extrinsic factor where the contraction of skeletal muscles compresses veins to drive blood toward the right atrium.

Respiratory Pump

A mechanism where inhalation increases abdominal pressure and decreases thoracic pressure, creating a gradient that drives blood from the abdomen to the thorax.

Venomotor Tone

The degree of tension in venous walls; sympathetic activation of $\alpha$ receptors causes venoconstriction, increasing venous pressure and return.

Arterial Baroreceptors

High-pressure sensors located in the carotid sinus and aortic arch that monitor blood pressure by changing the frequency of action potentials conducted to the CNS.

Baroreceptor Reflex

A neural pathway that regulates MAP by adjusting parasympathetic and sympathetic activity to the SA node, ventricles, and vessels in response to pressure changes.

Low Pressure Baroreceptors

Also known as volume receptors, these are located in the walls of the large veins and the right atrium.