Lectures 1-3

Arterial blood pressure

Force exerted by blood on arterial walls determined by cardiac output and systemic vascular resistance

Pulse pressure

Difference between systolic and diastolic pressure

Mean arterial pressure (MAP)

Diastolic plus one third pulse pressure

Neural regulation of BP

Fast, short-term control via autonomic nervous system and cardiovascular center in medulla

Norepi channels/effects in heart

Sympathetic, Beta 1 (most), Beta 2 and Alpha 1 → + inotropy/contraction, + chronotropy/heart rate, + dromotropy/conduction velocity AV node, exercise= cardiac sympathetic fibers release (not adrenal medulla)

ACh channels/effects in heart

Parasympathetic, M2 → - inotropy/contraction, -chronotropy/heart rate, - dromotropy/conduction velocity AV node

Norepi channels/effects in blood vessels

Sympathetic, Alpha 1 (most), alpha 2 and beta 2 → increased vascular tone

ACh channels/effects on blood vessels

Parasympathetic, M3 → decreased vascular tone

Renal regulation of BP

Long-term control via regulation of extracellular fluid volume and RAAS

Hormonal regulation of BP

Uses circulating hormones to cause vasoconstriction or vasodilation

Local regulation of BP

Uses local vasoactive substances to adjust vessel diameter

Cardiovascular center

Located in medulla integrates input to regulate heart and vessels

Baroreceptor reflex

Primary short-term mechanism responding to stretch in carotid sinus and aortic arch (increased BP= increased firing, decreases sympathetic and increases parasymp to lower BP)

Baroreceptors locations

Aortic arch → vagus nerve, carotid body → glossopharyngeal nerve

Chemoreceptors

Respond to low oxygen, high carbon dioxide, and low pH to increase sympathetic activity, peripheral (near carotid/aorta) and central (medulla)

Ischemic brain reflex

Severe hypotension causes insufficient blood flow to brain + intense sympathetic response/systemic constriction to raise BP (increased MAP)

Cushing reflex

Increased intracranial pressure leads to ischemia to brainstem → strong sympathetic reaction leadding to increased BP/MAP and reflex bradycardia

Pain reflex

Pain from myocardial ischemia/infarction → increases sympathetic activity raising BP and heart rate, sweating

Vasovagal reflex/Syncope

Increased vagal tone → sympathetic withdrawal of vascular tone, decreases heart rate and BP/MAP causing fainting (blood flow to brain decreases)

Long-term BP regulation

Primarily controlled by kidneys, hormones and local vascular mechanisms

Effective circulating volume

Volume of blood effectively perfusing tissues regulated by renal and hormonal systems

Renin-angiotensin-aldosterone system (RAAS)

Hormonal system increasing BP via vasoconstriction and fluid retention

Angiotensin II

Potent vasoconstrictor increasing calcium and vascular tone

Atrial natriuretic peptide (ANP)

Decreases BP by promoting sodium and water excretion and vasodilation

Vasopressin (ADH)

Increases water reabsorption and causes vasoconstriction increasing BP

Local autoregulation

Ability of tissues to maintain constant blood flow despite pressure changes

Active hyperemia

Increased blood flow in response to increased metabolic activity

Reactive hyperemia

Increased blood flow following temporary occlusion

Myogenic response

Vascular smooth muscle contracts when stretched and relaxes when pressure decreases

Metabolic vasodilation

Hypoxia and metabolites cause vasodilation to increase blood flow

Endothelial function

Maintains balance between vasodilation and vasoconstriction via released factors

Nitric oxide (NO)

Key vasodilator that also has anti-inflammatory and anti-thrombotic effects

Prostaglandin I2 (PGI2)

Endothelial vasodilator derived from arachidonic acid

Endothelin

Potent vasoconstrictor produced by endothelium

Histamine

Vasodilator released during inflammation increasing capillary permeability

Control of arterioles

Basal tone local metabolites and sympathetic vasoconstriction regulate diameter

Control of veins

Sympathetic tone and pressure regulate venous capacitance and blood distribution

Microcirculation

Includes arterioles capillaries and venules responsible for exchange and resistance

Role of arterioles

Primary resistance vessels controlling blood flow and pressure

Role of capillaries

Site of exchange of gases nutrients and waste

Role of venules

Capacitance vessels determining blood volume distribution

Precapillary sphincters

Regulate entry of blood into capillaries

Vasomotion

Intermittent contraction of sphincters controlling capillary perfusion

Capillary types

Continuous fenestrated and sinusoidal differing in permeability

Bulk flow

Movement of fluid driven by pressure gradients across capillaries

Diffusion in capillaries

Movement of solutes down concentration gradients following Fick’s law

Starling forces

Hydrostatic and oncotic pressures determining fluid movement across capillaries

Net filtration pressure (NFP)

Net force driving fluid out of or into capillaries

Filtration vs reabsorption

Filtration dominates at arterial end and reabsorption at venous end

Lymphatic system

Returns excess interstitial fluid to circulation and maintains fluid balance

Lymphatic pump

Uses vessel contraction skeletal muscle and valves to move lymph

Edema

Excess accumulation of fluid in tissues due to imbalance of filtration and removal

Causes of edema

Increased hydrostatic pressure decreased oncotic pressure increased permeability or impaired lymph drainage

Special circulations

Organ-specific blood flow regulation based on metabolic and functional needs

Coronary circulation

Primarily regulated by local metabolites to match oxygen supply to demand

Coronary blood flow timing

Greatest during diastole due to vessel compression in systole

Cerebral circulation

Highly regulated to maintain constant flow and prevent pressure changes

Cerebral blood flow control

Driven by CO2 pH metabolic activity and autoregulation

Functional hyperemia in brain

Increased blood flow to active brain regions

Skeletal muscle circulation

Regulated by metabolites during exercise overriding sympathetic tone

Skeletal muscle blood flow changes

Increases dramatically during exercise to meet oxygen demand

Cutaneous circulation

Regulates heat loss via changes in blood flow to skin

Thermoregulation in skin

Sympathetic control adjusts vasoconstriction or vasodilation based on temperature