CIRCULATORY PHYSIOLOGY {ST1}

CIRCULATORY PHYSIOLOGY {ST1} BY RANJEET RAMAN

I.Factors Involved in Blood Circulation • A.Blood Flow - the actual VOLUME of blood moving through a particular site (vessel or organ) over a certain TIME period (liter/hour, ml/min)

B.Blood Pressure - the FORCE exerted on the wall of a blood vessel by the blood contained within (millimeters of Mercury; mm Hg) • blood pressure = the systemic arterial pressure of large vessels of the body (mm Hg)

C.Resistance to Flow (Peripheral Resistance) - the FORCE resisting the flow of blood through a vessel (usually from friction) • 1.viscosity - a measure of the "thickness" or "stickiness" of a fluid flowing through a pipe • a.V water < V blood < V toothpaste • b.water flows easier than blood

2.tube length - the longer the vessel, the greater the drop in pressure due to friction • 3.tube diameter - smaller diameter = greater friction • Relation Between Blood Flow, Pressure, Resistance • difference in blood pressure ( P)

Blood Flow (F) =peripheral resistance (R) • a.increased P -> increased flow • b.decreased P -> decreased flow • c.increased R (vasoconstriction) -> DECREASED flow d.decreased R (vasodilation) -> INCREASED flow

II.Systemic Blood Pressure • A.Blood Pressure Near the Heart • 1.HEART produces blood pressure by pumping the blood 2.Blood pressure decreases with distance from Heart • 3.systolic arterial blood pressure - pressure in aorta (& major arteries) in middle of ventricular contraction (120 mm Hg in healthy adult)

4.diastolic arterial blood pressure - pressure in aorta (& major arteries) during ventricular diastole, when semilunar valves are closed (80 mm Hg in healthy adult) • 5.mean arterial pressure (MAP) - the "average" blood pressure produced by the heart (93 mm Hg in healthy adult

mean arterial pressure = diastolic pressure + 1/3 pulse pressure • **pulse pressure = systolic pressure - diastolic pressure • 6.blood pressure decreases throughout system • L ventricle -->120 mm Hg • arteries-->120 - 60 mm Hg • arterioles-->60 - 40 mm Hg • capillaries-->40 - 20 mm Hg • venous-->20 - 10 mm Hg • R atrium-->10 -0 mm Hg

7.venous return - venous blood pressure is so low, other factors contribute to venous blood flow • a. respiratory pump - breathing action of thorax "squeezes" blood back toward the heart b. muscular pump - contraction/relaxation of skeletal muscles "milk" blood up veins to heart

III.Factors Affecting Blood Pressure • . Cardiac Output ( = stroke volume X heart rate) • CO = SV (ml/beat) x HR (beats/min) • =70 ml/beat x 60 beats/min = 4200 ml/min • 1.increased cardiac output -> increased blood pressure 2.increased stroke volume -> increased blood pressure 3.increased heart rate-> increased blood pressure

B.Peripheral Resistance • 1.arteriole constriction ---> increased blood pressure 2.resistance inversely proportional to the "fourth power" of the radius change

C.Blood Volume • 1.hemorrhage - decrease in blood pressure 2.salt/fluid - increase in blood pressure 3.polycythemia - increase in blood viscosity 4.RBC anemia - decrease in blood viscosity • IV.Regulation of Blood Pressure

A.Nervous System Control • 1.control of arteriole diameter • 2.directs blood flow to proper organs and tissues that need it 3.REFLEX PATHWAY: • baroreceptors/chemoreceptors/brain --> • afferent nerve fibers-->medulla (vasomotor center) --> • vasomotor (efferent) nerve fibers -->smooth muscle of arterioles

B.Vasomotor Fibers to Smooth Muscle of Arterioles • 1. sympathetic fibers that release norepinephrine (NE); cause vasoconstriction of arterioles • C. Vasomotor Center of the Medulla

1.Sympathetic neuron cell bodies in the medulla 2.receive input from baroreceptors, chemoreceptors, and brain 3.vasomotor tone - general constricted state of arterioles set by vasomotor center

D.Baroreceptors • 1.blood pressure receptors large arteries (carotid sinuses, aortic arch, neck/thorax arteries) 2.send blood pressure information to vasomotor center of medulla • increased pressure --> decreased pressure --> inhibits vasomotor center --> stimulates vasomotor center -> vasodilation vasoconstriction

E. Chemoreceptors • 1.located in aortic arch and carotid arteries a.carotid and aortic bodies • 2.monitor OXYGEN and pH levels of the blood • low OXYGEN or low pH -------> increase blood pressure, return blood to lungs quickly • F.Higher Brain Centers Control on BP

1.hypothalamus & cortex also effect vasomotor area • G.Chemical Controls of Blood Pressure • 1.hormones of adrenal medulla - "fight-or-flight" response to fear; release of norepinephrine and epinephrine from adrenal medulla; causes vasoconstriction and increased BP

2.atrial natriuretic factor (ANF) - secreted by the atria of the heart, promotes general decline in blood pressure kidney releasing more Na+ and water, reducing fluid volume • 3.antidiuretic hormone (ADH) - released by the hypothalamus, causes increase in blood pressure by getting the kidneys to conserve water in the body; e.g. during hypotensive situations

4.endothelium derived factors • a.endothelin - strong vasoconstrictor • b.endothelium derived relaxing factor - vasodilation • 5.alcohol - causes vasodilation • H. Renal (Kidney) Regulation

1.direct regulation - fluid loss through urine • a. low pressure/volume --> conserve water b. high pressure/volume --> release more water • 2.renin-angiotensin mechanism • low blood pressure -->release of renin -->formation of angiotensin II--> vasoconstriction release of aldosterone --> Na+/water reabsorption (by kidney) V.Variations in Blood Pressure

A.Measuring Blood Pressure • 1.vital signs - blood pressure, pulse, respiratory rate, and body temperature • 2.auscultory method of blood pressure measurement

a.“sphygmomanometer” wrapped around upper arm b.inflate above systolic pressure of brachial a. • c.pressure released, first sounds - systolic pr. • d.disappearance of sounds - diastolic pr. • B.Hypotension (below normal blood pressure, < 100/60)

1.factors - age, physical conditioning, illness • 2.orthostatic hypotension - generally in elderly, drop in blood pressure during postural changes • 3.chronic hypotension - ongoing low blood pressure

a.low blood protein levels (nutrition) • b.Addison’s disease (adrenal cortex malfunction) c.hypothyroidism d.also sign of various types of cancer • C.Hypertension (above normal blood pressure at rest, > 140/90)

1.factors - weight, exercise, emotions, stress 2.chronic hypertension - ongoing high blood pressure • a.prevalent in obese and elderly • b.leads to heart disease, renal failure, stroke c.also leads to more arteriosclerosis d.primary hypertension - unidentified source

i.high Na+, cholesterol, fat levels • ii.clear genetic component (in families) iii.diuretics - promote water removal iv.NE blockers - slow vasoconstriction • e.secondary hypertension - identifiable disorder • i.kidney disorders • ii.endocrine (hormone) disorders • iii.arteriosclerosis

VI.Blood Flow in the Body • A.General Features • 1.delivery of oxygen and removal of carbon dioxide 2.gas exchange in the lungs 3.absorption and delivery of nutrients from GI tract 4.processing/waste removal in the kidneys 5.normal blood flow at rest abdominal organs24% skeletal muscle20% kidneys20% brain13% heart4% other15%

B.Velocity of Blood Flow • 1.velocity directly related to the TOTAL cross-sectional area of the vessel(s) • FASTESTaorta40-50 cm/s • arteries20-40 cm/s • arterioles1-20 cm/s • SLOWESTcapillaries0.1-1 cm/s

C.Local Regulation of Blood Flow • 1.autoregulation - regulation of blood flow by altering arteriole diameter • a.oxygen and carbon dioxide levels • b.prostaglandins, histamines, kinins • c.needy areas --> more blood flow. • 2.myogenic response - change in flow through arteriole in response to stretch of smooth muscle

3.reactive hyperemia - increase in blood flow to area where an occlusion has occurred • 4.increased vasculature - results from prolonged lack of oxygen/nutrients to an area (eg. heart)

D.Blood Flow to Skeletal Muscles • 1.active (exercise) hyperemia - increased blood flow to muscles during heavy activity • a. decreased oxygen and increased lactic acid b. visceral organ blood flow is decreased • E.Blood Flow to The Brain • 1. MUST maintain constant blood flow (750 ml/min) 2. sensitive to low pH and high carbon dioxide 3.blood pressure tightly regulated in the brain a.fainting -> below 60 mm Hg b.edema (brain swelling) -> above 180 mm Hg

F.Blood Flow to The Skin • 1.intimately involved in temperature regulation • increased body temperature -> • hypothalamic inhibition of vasomotor area -> vasodilation of vessels in skin -> increased blood flow -> sweating -> (bradykinin -> more vasodilation)

G.Blood Flow to the Lungs • 1.short pathway from heart, less pressure required 2.low oxygen level --> vasoconstriction • H.Blood Flow to the Heart • 1.blood to coronary arteries during diastole 2.vasodilation from ADP and carbon dioxide • VII.Blood Flow in the Capillaries

A.Exchange of Gases and Nutrients • 1.diffusion - all molecules move DOWN the concentration gradient (from HIGH to LOW) into or out of the blood • 2. oxygen/nutrients(blood------> body cells) carbon dioxide/ wastes(body cells------> blood)

B.Fluid Movements • 1.hydrostatic pressure - force from the capillary wall on the blood itself a.filtration pressure - the pressure forcing fluid and solutes through capillary clefts

2.osmotic pressure - force driving fluid in the direction of HIGHER solute concentration 3.movement out:Hydrostatic pressure > Osmotic difference movement in :Hydrostatic pressure < Osmotic difference • 4.normal fluid movement 1.5 ml/min in the entire body

C.Circulatory Shock • 1.circulatory shock - blood pressure gets so low that blood will not flow adequately • 2.hypovolemic shock - circulatory shock resulting from loss of fluid (bleeding, diarrhea, burn) a.heart rate increases rapidly b.general vasoconstriction of vessels

3. vascular shock - extreme vasodilation causes sudden drop in blood pressure a. snake and spider bites with NE blockers b.septicemia bacterial infection • 4.cardiogenic shock - heart is unable to provide sufficient blood pressure

CIRCULATORY PHYSIOLOGY {ST1}