Cardiovascular System: Blood Vessels Flashcards
Blood vessels
- delivery system of dynamic structures that begins and ends at the heart
- arteries: carry blood away from the heart; oxygenated EXCEPT for pulmonary circulation and umbilical vessels of a fetus (branch)
- Capillaries: contact tissue cells and directly serve cellular needs
- veins: carry blood toward the heart (converge)
structure of blood vessel walls
arteries and veins:
- tunica intima (inner coat)
- tunica media (middle coat)
- tunica externa (outer coat)
Lumen:
*central blood-containing space
Capillaries:
*endothelium with sparse basal lamina
arterial system
3 groups of arteries:
-> Elastic arteries- near heart (stretch). able to withstand high pressure (aorta)
- > muscular arteries- distributes to organs, thick tunica media
- > arterioles- smallest of arteries
capillaries
- Microscopic blood vessels
- Walls of thin tunica intima, one cell thick
- Size allows only a single RBC to pass at a time
- Most tissues are rich in capillaries except tendons & ligaments and absent for cartilage
- Consist of two types of vessels:
1. Vascular shunt (metarteriole—thoroughfare channel):
- True capillaries –
Branch off the metarteriole or terminal arteriole
blood flow through capillary beds
- Precapillary sphincters regulate blood flow into true capillaries
- Regulated by local chemical conditions and vasomotor nerves
sphincters open- blood flows thru true capillaries
true
sphincters closed- blood flows thru metarteriole thoroughfare channel and bypass true capillaries
true
veins
- have thinner walls, larger lumens than arteries
- lower BP than arteries
- called capacitance vessels (blood reservoirs); contain up to 65% of the blood supply
- adaptations that ensure return of blood to the heart:
1. large-diameter lumens offer little resistance
2. valves prevent backflow of blood
-venous sinuses: flattened veins with extremely thin walls (e.g., coronary sinus of heart, dural sinus of brain)
varicose veins
- looks clumpy thru skin
- distorted shape
vascular anastomoses
- interconnections of blood vessels
- arterial anastomoses provide alternate pathways (collateral channels) to a given body region… common at joints in abdominal organs, brain, heart
- vascular shunts of capillaries are examples of arteriovenous anastomoses
- venous anastomoses are common (saphenous vein in CABG)
Bloofd flow
- Volume of blood flowing through a vessel, an organ, or the entire circulation in a given period, based on needs
- Measured as ml/min
- Equivalent to cardiac output (CO) for entire vascular system
blood pressure (BP)
- Force per unit area exerted on the wall of a blood vessel by the blood
- Expressed in mm Hg
- The pressure gradient provides the driving force that keeps blood moving from higher to lower pressure areas
Resistance
opposition to flow
-measure of the amount of friction blood encounters
3 important sources of resistance:
- blood viscosity
- total blood vessel length
- blood vessel diameter
Resistance: blood viscosity
The “stickiness” of the blood due to formed elements and plasma proteins
resistance: total blood vessel length
the longer the vessel, the greater the resistance
resistance: blood vessel diamter
arterioles are the major determinants of peripheral resistance
-abrupt changes in diameter or fatty plaques from atherosclerosis dramatically increase resistance
Relationship Between Blood Flow, Blood Pressure, and Resistance (F= ΔP/R)
- Blood flow (F) is directly proportional to the blood pressure gradient (ΔP)
- If increase in BP, blood flow speeds up
- Blood flow is inversely proportional to peripheral resistance (R)
- If R increases, blood flow decreases
- R is more important in influencing local blood flow because it is easily changed by altering blood vessel diameter
systemic blood pressure
-pressure results when flow is opposed by resistance
systemic pressure:
- highest in the aorta
- declines throughout the pathway
- is 0 mm Hg in the right atrium
-steepest drop occurs in arterioles
systolic pressure (arterial blood pressure)
pressure exerted during ventricular contraction (120)
diastolic pressure (arterial blood pressure)
lowest level of arterial pressure (70-80), indicates peripheral resistance
pulse pressure (arterial blood pressure)
difference between systolic and diastolic pressure
Mean arterial pressure (MAP)
pressure that propels the blood to the tissues
-MAP= slightly less than the average btwn systolic and diastolic pressure
bc diastole is longer than systole… if BP=120/80 then MAP= 96
pulse pressure and MAP both decline with increasing distance from the heart
capillary: blood pressure
- Ranges from 15 to 35 mm Hg
- Low capillary pressure is desirable
High BP would rupture fragile, thin-walled capillaries
veins: BP
- changes little during cardiac cycle
- small pressure gradient, about 15 mm Hg
factors aiding venous return
- Respiratory “pump”: pressure changes created during breathing
- Muscular “pump”: contraction of skeletal muscles “milk” blood toward the heart and valves prevent backflow
- Vasoconstriction of veins under sympathetic control
Maintaining BP
The main factors influencing blood pressure:
- Cardiac output (CO)
- Peripheral resistance (PR)
- Blood volume
Important and vital to bring blood to organs
Cardiac Output (CO) (what determines CO?)
- determined by venous return and neural and hormonal controls
- Resting heart rate is maintained by the PNS
- stroke volume is controlled by venous return (EDV)
- during stress, the cardioacceleratory center increases heart rate and stroke volume via sympathetic stimulation
- ESV decreases and MAP increases
Of the following cardiovascular components, which contains the majority of the body’s blood volume at any one time?
systemic veins and venules
Of the following blood vessel components, which is the most critical in regulating systemic blood pressure?
tunica media
What is the major factor controlling stroke volume during resting periods?
venous return to the heart
control of blood pressure
-> F= change Pressure/ Resistance
- > short-term neural and hormonal controls
- counteract fluctuations in BP by altering peripheral resistance
- > long-term renal regulation (kidneys)
- counteract fluctuations in BP by altering blood volume
short term mechanisms: neural controls
-neural controls operate via reflex arcs that involve:
*Baroreceptors- mechanoreceptors (stretch) and chemoreceptors (chemicals)
*located in carotid sinuses
and aortic arch
- vasomotor centers- located in medulla
* maintains vasomotor tone (moderate constriction of arterioles)
*vascular smooth muscle
short term mechanisms: baroreceptor-initiated reflexes
increased BP stimulates baroreceptors to increase input to the vasomotor center
- inhibits the vasomotor center, causing arteriole dilation and venodilation
- stimulates the cardioinhibitory center
- used as an emergency brake to avoid abnormally high BP
**Baroreceptors in carotid sinus protect blood supply to brain
Elderly often have blunted baroreceptors – can cause lightheadedness on sit to stand
short term mechanisms: chemoreceptor-initiated reflexes
- chemoreceptors respond to rise in CO2, drop in pH or O2
- increase blood pressure via the vasomotor center and the cardioacceleratory center
- are more important in the regulation of respiratory rate
- located in carotid sinus and aortic arch
influence of higher brain centers
-Impulses from cerebrum pass thru CV centers in medulla
- Variations in emotional state may affect CV responses (fight/flight)
- Anticipatory HR
- White coat phenomena
Voluntary control over HR/BP thru biofeedback/meditation
hormonal controls
- > short term regulation thru changes in peripheral resistance
- > long term regulation thru changes in blood volume
short term mechanisms: hormonal control
- adrenal medulla hormones: NE and E
- angiotensin II, generated by kidney release of renin, causes vasoconstriction
- atrial natriuretic peptide (ANP) from atria in heart, causes vasodilation
- ADH (hypothalmus)- intense vasoconstriction when BP falls dangerously low
Long term mechanisms: renal regulation
kidneys act directly and indirectly to regulate arterial BP by altering blood volume
- direct renal mechanism (at kidney)
- indirect renal (renin-angiotensin) mechanism
direct renal mechanism (kidney)
- alters blood volume independently of hormones
- increased BP or blood volume causes the kidneys to eliminate more urine, thus reducing BP (rate of which blood filters thru kidney tubules speeds up, faster filtrate flow and kidneys cannot reabsorb fast enough)
*decreased BP or blood volume causes the kidneys to conserve water, and BP rises
indirect mechanism
the renin angiotensin mechanism:
- decreased arterial blood pressure-> release of renin
- renin-> production of angiotensin II
angiotensin II:
- adrenals secrete aldosterone which enhances renal reabsorption of Na
- causes posterior pituitary to release ADH
- triggers sensation of thirst
- causes vasoconstriction which increases BP by increasing resistance
- adrenals secrete aldosterone which enhances renal reabsorption of Na
-kidneys release renin
alterations in BP
- Hypotension: low BP
- systolic pressure below 100 mm Hg
- often associated with long life and lack of cardiovascular illness
- hypertension: high BP
- sustained elevated arterial pressure of 140/90 or higher
- may be transient adaptations during fever, physical exertion, and emotional upset
- often persistent in obese ppl
circulatory shock
inadequate blood flow to meet tissue needs
hypovolemic shock
results from large scale blood loss
vascular shock
results from extreme vasodilation and decreased peripheral resistance, i.e anaphylaxis (allergic response)
cardiogenic shock
results when an inefficient heart cannot sustain adequate circulation (pump failure)
transient vascular shock
prolonged exposure to heat, sun stroke
velocity of blood flow
- changes as it travels thru the systemic circulation
- is fastest in the aorta, slowest in the capillaries, increases again in veins
- slow capillary flow allows enough time for exchange btwn blood and tissues
autoregulation of blood flow
- local regulation of blood flow, controlled intrinsically by changing diameter
1. metabolic: stimulated by shortage of O2 or inflammatory chemicals
- myogenic: involves the local response of smooth muscle to passive stretch
* passive stretch involves vasoconstriction
* reduced stretch promotes vasodilation
intrinsic mechanisms (autoregulation)
distribute blood flow to individual organs and tissues as needed
extrinsic mechanisms
maintain mean arterial pressure (MAP)
-redistribute blood during exercise and thermoregulation
long term autoregulation
angiogenesis:
-occurs when short term autoregulation cannot meet tissue nutrient requirements
- the # of vessels to a region increases and existing vessels enlarge
- common in the heart when a coronary vessel is occluded, or throughout the body in people in high altitude areas
blood flow: skeletal muscles
during muscle activity:
- blood flow increases in direct proportion to the metabolic activity
- local controls override sympathetic vasoconstriction
-muscle blood flow can increase 10x or more during physical activity
blood flow and exercise
-major portion to working muscles
-shunting of blood:
kidneys practically shut down
-blood flow is not disturbed:
brain and heart
blood flow: brain
-Blood flow to the brain is constant, as neurons are intolerant of ischemia
- Metabolic controls
- Declines in pH, and increased carbon dioxide cause marked vasodilation
- Myogenic controls
- Decreases in MAP cause cerebral vessels to dilate
*Increases in MAP cause cerebral vessels to constrict (protects)
blood flow: brain
- The brain is vulnerable under extreme systemic pressure changes
- MAP below 60mm Hg can cause syncope (fainting)
- MAP above 160 can result in cerebral edema
- Increases capillary permeability
blood flow: lungs
- autoregulatory mechanism is opposite of that in most tissues:
- low O2 levels cause vasoconstriction; high levels promote vasodilation
*allows for proper O2 loading in the lungs
blood flow: heart
during ventricular systole
- coronary vessels are compressed
- myocardial blood flow ceases
- stored myoglobin supplies sufficient O2
blood flow: heart
during strenuous exercise:
*coronary vessels dilate in response to local accumulation of vasodilators
*blood flow many increase 3-4x
circulatory pathways
Two main circulations:
-> Pulmonary circulation:
short loop that runs from the heart to the lungs and back to the heart
-> Systemic circulation:
long loop to all parts of the body and back to the heart
