VESS-HELL

Arteries vs veins (anatomy difference)

Arteries have thicker muscular walls, smaller lumens, and higher pressure; veins have thinner walls, larger lumens, and valves to prevent backflow

Elastic arteries

Large arteries near the heart that stretch and recoil to smooth out pressure surges

Muscular arteries

Medium arteries that distribute blood and regulate flow to organs

Arterioles

Small arteries that control resistance and major changes in blood pressure

Capillaries

Microscopic exchange vessels for gases, nutrients, and wastes

Why elastic arteries are near heart

They must withstand and smooth out high-pressure blood leaving the heart

Muscular artery function

Direct blood to specific organs by vasoconstriction and vasodilation

Arteriole function in BP control

Primary site of resistance control and blood pressure regulation

Why pressure is high in aorta and major arteries

Close to heart pumping force creates strong pressure pulses

Why pressure becomes continuous in arterioles/capillaries

Resistance and branching dampen pulsatile flow into steady flow

Why blood pressure decreases away from heart

Energy is lost to resistance and vessel branching

Tissues without capillaries

Cartilage, epidermis of skin, cornea, and lens (avascular tissues)

Continuous capillaries

Most common capillaries with tight junctions allowing selective permeability

Fenestrated capillaries

Capillaries with pores allowing faster exchange (kidneys, intestines, endocrine glands)

Sinusoidal capillaries

Large, leaky capillaries allowing cells and proteins to pass (liver, spleen, bone marrow)

Vascular shunt purpose

Bypasses true capillary bed to regulate blood flow based on tissue needs

Precapillary sphincters

Rings of smooth muscle that open/close entry into capillary beds

Location of precapillary sphincters

At the arterial side of capillary beds

Blood vessel flow order

Arteries → arterioles → capillaries → venules → veins

Which holds more blood

Veins hold more blood because they are high-capacitance, low-pressure reservoirs

Why veins hold more blood

Thin walls and large lumens allow them to expand and store large volumes

How blood returns through veins (3 mechanisms)

Skeletal muscle pump, respiratory pump, and venous valves

Skeletal muscle pump

Muscle contraction squeezes veins and pushes blood toward the heart

Why squeezing a vein moves blood forward

Valves prevent backflow so pressure forces blood one direction

Respiratory pump function

Pressure changes during breathing draw blood toward the heart

Why breathing increases venous return

Inhalation lowers thoracic pressure and raises abdominal pressure, pulling blood upward

Varicose veins cause

Damaged or weakened venous valves cause blood pooling and vein enlargement

What varicose veins are

Enlarged, twisted superficial veins due to valve failure

Anastomoses definition

Connections between blood vessels that create alternate pathways for blood flow

Why anastomoses are important

Provide collateral circulation if one pathway is blocked, especially around joints

Blood pressure equation

Blood pressure = cardiac output × total peripheral resistance

Cardiac output factors

Heart rate and stroke volume determine cardiac output

How heart rate affects cardiac output

Increased heart rate increases cardiac output (to a limit)

How stroke volume affects cardiac output

Increased stroke volume increases cardiac output

Contractility effect on cardiac output

Increased contractility increases stroke volume and cardiac output

Preload effect on cardiac output

Increased preload increases stroke volume via greater stretch

Afterload effect on cardiac output

Increased afterload decreases stroke volume by increasing resistance

Resistance factors

Vessel diameter, viscosity, vessel length, and turbulence

How vessel diameter affects resistance

Smaller diameter greatly increases resistance

How blood viscosity affects resistance

Thicker blood increases resistance and raises blood pressure

How vessel length affects resistance

Longer vessels increase resistance due to more friction

How turbulence affects resistance

Irregular flow increases resistance and energy loss

Brain region controlling BP

Medulla oblongata

Baroreceptors location

Carotid sinuses and aortic arch

What baroreceptors do

Detect blood pressure changes and send signals to brain

Sympathetic effect on heart

Increases heart rate and contractility

Sympathetic effect on blood vessels

Vasoconstriction increases resistance and blood pressure

Parasympathetic effect on heart

Decreases heart rate

Parasympathetic effect on blood vessels

Minimal direct effect on most vessels

Overall sympathetic effect on blood pressure

Increases blood pressure by raising CO and resistance

Adrenal gland hormone controlling BP

Epinephrine (and norepinephrine)

Epinephrine effect on BP

Increases heart rate, contractility, and vasoconstriction/vasodilation depending on receptors

Heart hormone controlling BP

Atrial natriuretic peptide (ANP)

ANP function

Lowers blood pressure by promoting sodium and water loss and vasodilation

Hypertension definition

Systolic ≥ 130 mmHg or diastolic ≥ 80 mmHg (commonly used clinical cutoff)

Hypertension risk factors

Obesity, high salt diet, stress, smoking, inactivity, genetics

Hypertension complications

Heart failure, stroke, kidney damage, vascular damage

Hypotension definition

Systolic < 90 mmHg or diastolic < 60 mmHg

Hypotension effects

Dizziness, fainting, poor organ perfusion