Lecture 4: Blood Vessels & Hemodynamics Flashcards
what is hemodynamics
study of flow together with the differnet forces that regulate blood flow int he body
what is the capillary blood flow in healthy conditions
-equals cardiac output
-determined by pressure (P) and resistance (R)
what is pressure (P)
the force generated by the heart to overcome resistance
pressure gradient (^P)
difference in pressure from one end of a vessel to the other
what is vascular resistance (R)
opposition to blood flow due to friction between blood and the walls of blood vessels
what does higher resistance (R) mean
it shows smaller blood flow
what does resistance (R) depend on
-Lumen size (vessels diameter): inverse relationship; has the greatest influence
-Blood Viscosity: direct proportional relationship
-Total blood vessels length: direct proportional relationship
what is velocity
the rate of change of the object’s position with respect to a frame of reference and time
describe the velocity of blood flow
-blood flow is the volume of blood that moves througha tissue in a given period
velocity of blood flow between aorta and capillaries
fastest aorta, slowest in capillaries, then increases again in veins
what is speed in velocity of blood flow related to
speed is inversely related to total cross-sectional area
why is blood flow the slowest in the capillaries
-capillaries have the largest area so the slowest flow
-slow capillary flow allows aadewuate time for exchange between blood and tissues
what is tissue perfusion
the flow of blood through body tissues
what is tissue perfusion involved in
- delivery of O2 and nutrients to, and removal of wastes from tissue cells
- gas exchange (lungs)
- absorption of nutrients (digestive tract)
- urine formation (kidneys)
-rate of flow is right amount to provide proper function to that tissue of organ
how is blood flow controlled
rate of flow is controlled by intrinsic and extrinsic factors
what are intrinsic controls of blood flow
-control is entirely from within the tissue or organ
-uses paracrines or or properties of muscle tissue
-also known as autoregulation or local control
what are extrinsic controls on blood flow
-control is from outside of the tissue or organ
-uses nerves or hormones
what are examples of when both intrinsic and extrinsic control mechanisms occur
-stroke volume in the heart
-arteriolar diameter
-glomerular filtration in kidneys
blood flow to the skeletal muscles at rest vs. during exercise
-at rest: they receive ~20% of total body
-during exercise: >70% of blood
what are some intrsinsic controls for blood flow to skeletal muscles during exercise
skeletal muscle arterioles dilate, increasing blood flow to muscle
what are some extrinsic controls for blood flow to skeletal muscles during exercise
decrease blood flow to organs such as kidneys and digestive organs
what is autoregulation
local (intrinsic) conditions that regulate blood flow to that area
what two types of intrinsic machanisms determine final autoregulatory response
-metabolic controls
-myogenic controls
what is active hyperemia
- intial stimulus: exercising skeletal muscle
- physiological response: lower O2, higher CO2 and H+ and other metabolic factors in extracellular fluid -> vasodilation of arterioles (overrides extrinsic sympathetic input)
- result: higher muscle blood flow (active hyperemia)
what is taken during vital signs (V/S)
pluse (HR), BP, respiratory (breathing) rate, and body temp
what is a pulse
-pressure wave due to alternating expansion and recoil of elastic arteries
-after systole of left ventricle
-strongest in aorta; weaker in arterioles and disappears in capillaries
-pulse rate is same as normal heart rate
taking a pulse
-radial pulse (taken at wrist): most routinely used, but there are other clinically important pulse points
-pressure points: areas where arteries are close to body surface, can be compressed to stop blood flow in event of hemorrhaging
what are some common pulse points and where to find them
-superficial temporal artery: found medial to ear
-facial artery: found on mandible (lower jawbone) on line with corners of mouth
-common carotid artery: lateral to larynx (voice box)
-brachial artery: found medial side of biceps brachii muscle
what is the relationship between blood flow and pressure
blood flow (F) is directly proportional to blood pressure gradient (^P)
-if ^P increases, blood flow speeds up
what is the relationship between blood flow and resistance
blood flow (F) is inversely proportional to peripheral resistance (R)
-if R increases, blood flow decreases, so F= ^P/R
where is systemic BP highest
it’s highest in aorta and declines throughout pathway
-ssteepest drop occurs in arterioles
what are the two factors that determine to arterial BP
- Elasticity (compliance or distensibility) of arteries close to heart
- volume of blood: forced into them at any time
BP near heart is what?
it is pulsatile: rises and falls with each heartbeat
what is systolic pressure
-pressure exerted in aorta during ventricular contraction
-left ventricle pumps blood into aorta-> stretches aorta
-averages ~120 mm Hg in normal adult
what is diastolic pressure
lowest level of aortic pressure when heart is at rest; ~80 mm Hg
what is pulse pressure
difference between systolic and diastolic pressure
what is mean arterial pressure (MAP)
-average pressure during one cardiac cycle
-pressure that propels blood tiissues
-pulse pressure phases out near end of arterial tree
-both pulse pressure nad MAP decline with increasing distance from heart
how do you calculate MAP
diastolic pressure + 1/3 pulse pressure
how do you measure blood pressure
systemic arterial BP is measured indirectly bu ausculatory methods usinf a sphygmomanometer
steps in taking BP
- wrap cuff around arm superior to elbow
- increase pressure in cuff until it exceeds systolic pressure in brachial artery
- pressure is released slowly, and examiner listens for sounds of Korotkoff with a stethescope
SBP and DBP when taking BP
systolic pressure: pressure when sounds first occur as blood starts to spurt through artery
diastolic pressure: pressure when sounds disappear because artery is no longer constricted; blood is flowing freely
what is venous BP
-changes little during cardiac cycle
-small pressure gradient, only ~15 mmHg
-if vein is cut, low pressure of venous system causes blood to flow out smoothly
-if artery cut, blood spurts out because pressure is higher
-low pressure is due to cumulative effects of peripheral resistance
-low pressure of venous side requies adaptations to helo with venous return
what is venous return
volume of blood flowing back to the heart through the systemic veins, occurs due to the pressure generated by contractions of the left ventricle
what are the three factors aiding venous return and explain them
- muscular pump: contraction of skeletal muscles “milks” blood back toward heart; valves prevent backflow
- respiratory pump: pressure changes during breathing move blood toward heart by squeezing abdonimal veins as thoracic veins expand
- sympathetic venoconstriction: under sympathetic control, smooth muscles constrict, pushing blood back toward hearrt
whaat different body systems maintain BP
it requires cooperation of heart, blood vessels, and kidneys which are all supervised by the brain
what three main factors regulate blood pressure
- cardiac output (CO)
- peripheral resistance (PR)
- blood volume
recall slide 19
recall slide 19
recall slide 19
recall slide 19
factors that increase MAP (review slide 20)
^ SV & ^ HR = ^ CO= ^MAP
lower diameter of blood vessels, ^blood viscosity, ^blood vessel length=^ total peripheral resistance= ^MAP
direct renal mechanism for control of BP
indirect renal machanism (renin-angiotensin-aldosterone) for control of BP
effects of some selected hormones on BP
effects of some selected hormones on BP
what are homeostatic imbalances in BP
-transient elevations in BP occur during changes in poster, physical exertion, emotional upset, fever
-age, sex, weight, mood, and posture may also cause BP to vary
what is hypertension
-sustained elevated arterial pressure of 140/90 mmHg or higher
-prolonged hypertension is major cause of heart failure, vascular disease, renal failure, and stroke
what is prehypertension
-values elevated but not yet in hypertension range
-may be trnasient adaptations during fever, physical exertion, and emotional uspset
-often persistent in obese people
what is primary hypertension
-90% of hypertensive conditions
-no underlying cause identified
-risk factos: heredity, diet, obesity, age, diabetes mellitus, stress, and smoking
-no cure but can be controlled by: restrict salt/ fat/ cholesterol intake, increase exercise, lose weight, stop smoking, antihypertensive drugs
what is secondary hypertension
-less common
-due to identifiable disorders: obstructed renal arteries, kidney diease, and endocrine disorders such a hyperthyroidism and Cushing’s syndrome
-treatment: focuses on correcting underlying cause
what is hypotension
-low BP <90/60
-usually not a concern unless it causes inadequate blood flow to tissues
-often asssociated with long life; and lack of cardiovascular illness
what is orthostatic hypotension
temporarylow BP and dizziness when suddenly rising from sitting or reclining position
what is chronic hypotension
suggests poor nutrition and warning signs for Addison’s disease or hypothyroidism
what is acute hypotension
important sign of circulatory shock
what is circulatory shock
condition where blood vessels inadequately fill and cannot circulate blood normally-> inadequate CO: inadequate blood flow cannot meet tissue needs (lack of O2 delivery)
what is hypovolemic shock
large-scale blood loss due to trauma, vessel rupture
what is vascular shock
extreme vasodilation and decreased PR: anaphylactic shock, neurogenic shock, spetic shock
what is cardiogenic shock
an inefficient heart cannot sustain adequate circulation: ischemia, valve defects, impaired CCS
what is obstructive shock
blockade of blood circulation: pulmonary embolism
what are homeostatic responses to shock
-negative feedback mechanisms work to return CO to normal
-activation of renin-angiotensin-aldosterine system
-secretion of antidiuretic hormone
-activation of the sympathetic division of the ANS
-release of local vasodilators
