Blood vessels

5 Functions of Blood Vessels

Transport blood, distribute blood, exchange substances, regulate blood pressure, and regulate body temperature.

Capillary Beds

Networks of capillaries where gases, nutrients, and wastes are exchanged.

Precapillary Sphincters

Smooth muscle rings that control blood flow into capillary beds.

Resistance

Opposition to blood flow caused by friction.

Blood Pressure

Force exerted by blood against vessel walls.

Blood Flow

Movement of blood through blood vessels.

Variables That Influence Resistance

Vessel diameter, blood viscosity, and vessel length.

Short-Term BP Control

Rapid nervous system regulation through the autonomic nervous system and baroreceptor reflex.

Long-Term BP Control

Kidney regulation of blood volume through sodium and water balance.

Pulse Pressure

Difference between systolic and diastolic blood pressure.

Factors That Increase MAP

Increased cardiac output or peripheral resistance.

Greatest Drop in Blood Pressure

Across the arterioles because they create the greatest resistance.

Interstitial Fluid

Fluid surrounding tissue cells that allows substances to move between blood and cells.

Four Methods of Gas and Nutrient Exchange

Diffusion, transcytosis, filtration, and reabsorption.

Hydrostatic Pressure

Fluid pressure that pushes water out of capillaries.

Colloid Osmotic Pressure

Pull created by plasma proteins that draws water into capillaries.

Filtration Pressure

Net pressure that determines whether fluid moves out of or into capillaries.

Lymphatic Vessels

Vessels that return excess tissue fluid to the bloodstream.

Edema

Excess fluid buildup in body tissues.

Venous Return

Movement of blood back to the heart.

Skeletal Muscle Pump

Muscle contractions squeeze veins, pushing blood toward the heart.

Respiratory Pump

Pressure changes during breathing help move blood toward the heart.

Venous Valves

Prevent blood from flowing backward in veins.

Venoconstriction

Narrowing of veins that increases venous return.

Blood Volume

Total amount of blood circulating in the body.

Short-Term BP Control

Rapid regulation of blood pressure by the nervous system.

Long-Term BP Control

Regulation of blood pressure by the kidneys through control of blood volume.

Baroreceptors

Stretch receptors in the carotid sinus and aortic arch that detect blood pressure changes.

Chemoreceptors

Receptors that detect changes in oxygen, carbon dioxide, and blood pH.

Cardioacceleratory Center

Medullary center that increases sympathetic stimulation, raising heart rate and contractility.

Cardioinhibitory Center

Medullary center that increases parasympathetic stimulation, lowering heart rate.

Vasomotor Center

Medullary center that controls sympathetic regulation of blood vessel diameter.

Vasomotor Tone

Continuous sympathetic stimulation that keeps blood vessels partially constricted.

Epinephrine

Hormone from the adrenal medulla that increases cardiac activity and affects blood vessel diameter.

Norepinephrine

Hormone from the adrenal medulla that mainly causes vasoconstriction.

Angiotensin II

Powerful vasoconstrictor that increases blood pressure and stimulates aldosterone, ADH, and thirst.

ANP

Hormone released by stretched atria that increases sodium and water excretion, lowering blood pressure.

ADH

Hormone released by the posterior pituitary that increases kidney water reabsorption and can cause vasoconstriction.

Long-Term Control of BP

Primarily maintained by the kidneys regulating sodium and water balance.

Blood Volume and Blood Pressure

Increased blood volume generally increases blood pressure; decreased blood volume lowers it.

Direct Kidney Control of BP

Kidneys adjust blood pressure by changing sodium and water excretion.

Indirect Kidney Control of BP

Kidneys regulate blood pressure through renin release and the RAAS pathway.

Renin Release

Stimulated by decreased kidney blood pressure, decreased NaCl delivery, or increased sympathetic stimulation.

Renin

Enzyme released by the kidneys that converts angiotensinogen into angiotensin I.

ACE

Enzyme that converts angiotensin I into angiotensin II.

ACE Inhibitors

Medications that block ACE, lowering angiotensin II and treating hypertension.

RAAS Cascade

Decreased BP → renin → angiotensin I → ACE → angiotensin II → vasoconstriction, aldosterone and ADH release → increased blood volume and BP.

Angiotensin II Effects

Vasoconstriction, increased aldosterone, increased ADH, increased thirst, and increased blood pressure.

Other Methods of BP Control

Baroreceptor reflexes, chemoreceptors, hormones, autoregulation, and kidney regulation.

Metabolic Autoregulation

Local regulation of blood flow based on tissue metabolism; increased metabolism causes vasodilation.