Blood Vessels and Circulation Review

These flashcards cover the histology, classification, and physiology of blood vessels as well as mechanisms of blood pressure regulation and capillary dynamics based on the lecture transcript.

Arteries

Blood vessels that carry blood away from the heart, often described by the terms “branch” and “supply”.

Veins

Blood vessels that carry blood toward the heart, often described by the terms “merge” and “drain”.

Lumen

The hollow space within a blood vessel that carries the blood.

Tunica Intima

The innermost layer of a vessel wall, consisting of simple squamous endothelium and its underlying connective tissue.

Tunica Media

The middle layer of a vessel wall composed of smooth muscle; it is the thickest layer in arteries.

Vasoconstriction

The narrowing of the lumen caused by the contraction of smooth muscle in the tunica media.

Vasodilation

The enlargement of the lumen caused by the relaxation of smooth muscle in the tunica media.

Tunica Externa

The outer layer of connective tissue providing support to vessels, containing nerve fibers and small vessels; it is the thickest layer in veins.

Vasa vasorum

A series of small vessels that bring blood to the walls of large vessels.

Elastic arteries

Highly elastic vessels such as the aorta and its branches, with a diameter of $1.0 - 2.5 \text{cm}$, which act as pressure reservoirs.

Muscular arteries

Vessels supplying muscles and organs, with a diameter of $0.3 \text{mm} - 1.0 \text{cm}$, featuring a thick tunica media to regulate blood flow.

Arterioles

The smallest arteries, with a diameter of $10 \mu\text{m} - 0.3 \text{mm}$, that regulate blood supply to capillary beds.

Venules

The smallest of the veins, with a diameter of $8 - 100 \mu\text{m}$, that drain blood from capillary beds.

Venous Sinuses

Large flat veins that are not true vessels, supported by surrounding tissues rather than tunics.

Capillaries

The smallest vessels ($D = 8 - 10 \mu\text{m}$, Length = $1 \text{mm}$) that allow for the exchange of solutes with tissues and consist of only the tunica intima.

Pericytes

Muscle-like cells that provide support for capillaries.

Continuous Capillaries

The most common type of capillary, found in muscle and skin, characterized by a continuous sheet of endothelial cells.

Intercellular clefts

Small gaps between endothelial cells that allow for the movement of some fluid and solutes.

Fenestrated Capillaries

Highly permeable capillaries found in the kidneys, small intestine, and endocrine glands that contain small holes called fenestrations for filtration and absorption.

Sinusoid Capillaries

Highly permeable capillaries found in the liver, bone marrow, and lymph tissues with large lumens, large fenestrations, and large intercellular clefts.

Capillary bed

An interweaving network of $10 - 100$ capillaries located between an arteriole and a venule performing microcirculation.

Vascular shunt

A vessel that allows blood to bypass a capillary bed.

Precapillary sphincters

Muscle rings that regulate blood flow into the true capillaries based on local tissue needs.

Anastomoses

Additional vessels that create alternate pathways into, out of, or around capillary beds.

Portal Systems

Circulatory pathways that contain two capillary beds separated by a portal vein.

Blood Flow

The volume of blood passing through a vessel in a given amount of time, expressed as $\text{mL/min}$, calculated by the formula $\text{Flow} = \Delta P/R$.

Peripheral Resistance

The friction encountered by blood reducing flow, determined by blood viscosity, total vessel length, and vessel diameter.

Systolic pressure

The peak arterial pressure caused by heart contractions, averaging $120 \text{mmHg}$.

Diastolic pressure

The low arterial pressure resulting from heart relaxation, averaging $80 \text{mmHg}$.

Pulse pressure

The difference between systolic and diastolic pressures, which creates a palpable pulse in an artery.

Mean Arterial Pressure (MAP)

The average pressure in a vessel driving blood movement, calculated as $\text{MAP} = \text{diastolic P} + (\text{pulse P}/3)$.

Baroreceptors

Stretch receptors in large arteries that measure pressure and send impulses to the medulla to regulate heart rate and vessel diameter.

Atrial Natriuretic Peptide (ANP)

A hormone from the heart's atria that decreases blood pressure by causing vasodilation and increasing urine output to decrease blood volume.

Antidiuretic Hormone (ADH)

A hormone from the hypothalamus that increases blood pressure by decreasing urine output to increase blood volume.

Angiotensin II

A kidney hormone that increases blood pressure by causing vasoconstriction and stimulating aldosterone release.

Renin

An enzyme released by the kidneys in response to low pressure that converts Angiotensinogen into Angiotensin I.

Auscultatory method

A method of measuring blood pressure by listening for Korotkoff sounds using a cuff, pressure gauge, and stethoscope.

Hypertension

High blood pressure defined as a reading of $140/90 \text{mmHg}$ or above.

Hypotension

Low blood pressure, typically characterized by a systolic pressure below $100 \text{mmHg}$.

Angiogenesis

The growth of new blood vessels into a tissue to meet a new metabolic need or growth.

Tissue perfusion

The flow of blood through tissues for delivery of nutrients, gas exchange, absorption, or filtration.

Exercise hyperemia

A major increase in blood flow to skeletal muscle during activity, triggered by low $O_2$ and high waste levels.

Bulk flow

The movement of plasma out of and then back into a capillary based on the balance of hydrostatic and colloid osmotic pressures.

Hydrostatic pressure

The pressure exerted by a fluid against a vessel wall, which is equivalent to blood pressure ($HP_b$).

Colloid osmotic pressure

The pressure generated by nondiffusable solutes, such as proteins, that draws water towards themselves.

Net Filtration Pressure (NFP)

The pressure generated by the balance between hydrostatic and colloid osmotic pressure; calculated as $\text{NFP} = \text{Net HP} - \text{Net COP}$.

Arteriosclerosis

The thickening and stiffening of arteries caused by fatty plaque deposits, which increases peripheral resistance and blood pressure.

Circulatory shock

A condition where blood vessels are inadequately filled with blood, preventing normal circulation.

Hypovolemic shock

A type of circulatory shock resulting from excessive blood loss.

Vascular shock

A type of circulatory shock caused by extreme vasodilation, often due to a systemic allergic reaction (anaphylaxis).