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what are elastic (conducting) arteries?
Large, thick-walled arteries with elastin in all three tunics
Near the heart
Large lumen offers lows resistence
Act as presure reservoirs- expand and recoil as blood is ejected from the heart
What are Muscular (distributing) arteries?
Distal to elastic arteroes; deliver blood to body organs
Have thickest tunica media with more smooth ucsle
Active in vasoconstriction
What are arterioles?
lead to capillary beds
control flow into capillary beds via vasodialation and vasoconstriction
Where are capillaries found and what are their functions?
In all tissues excpet for cartilage, epithelia, cornea and lens of eye
functions: exchangr of gases, nutrients, wastes, hormones, etc.
Name the 3 structural types of capillaries
- 1. Continuous capullaries
- 2. Fenesrtated capillaries
- 3. Sinusoidal capillaries (sinusoids)
Describe continuous capillaries
abundant in the skin and muscles (most common)
- tight juntions connect cells
- intercellular clefts allow passage of fluids and small solutes
- found in the brain forming the brain blood barrier
Describe Fenestrated Capillaries
some contain pores (fenestrations)
more permeable than continuous capilarries
- functions in absorption of filtrate formation (such as in the SI, endocrine glands, and kidneys)
Describe Sinusoidal Capillaries
fewer tight junctions, larger clefts, larger lumens
allows large molecules and blood to pass between surrounding tissues
- found in liver, bone, spleen, adrenal medulla
describe the Capillary bed and its blood flow
- Consists of two type of vessels for microcirculation between arterioles and venules
- 1. vascular shunt (metarteriole-->thoroughfare channel)
- -directly connects the terminal arteriole and a postcapillary venule
- 2. true capillaries: exchange vessels
- blood flow:
- precapillary sphincters regulate bood flow into true capillaries
- regulated by local chemical conditions and vasomotor nerves
What is blood flow?
volume of blood flowing through a vessel, organ,or the entore circulation in a given period
measured in ml/min
Define blood pressure
force per unit area exerted on the wall of a blood vessel yb the blood
measured in mm Hg
- Opposition to flow
- measures the amount of friction blood encounters
- generally encountered in the peripheral systemic circulation
- Three important sources of Resistance
- 1. blood viscosity
- 2. total blood vessel length
- 3. blood vessel diameter
What is the relationship between blood flow, blood pressure, and resistance?
delta p= blood pressure gradiant
Resistance is the factor that changes most easily and often
What is systemic blood pressure?
the pumping action of the heart that generates blood flow
- -highest in the aorta
- -declines throughout the pathway
- -is 0 in the right atria
What are the 3 types of arterial pressure?
- Systolic pressure
- Diastolic pressure
Pulse pressure: difference between systolic and diastolic pressure
What is MAP?
Mean arterial pressure:
pressure that propels blood to the tissues
map= diastolic pressure + 1/3 pulse pressure
both MAP and PP decrease as you get farther from heart
What are the factors aiding in venous return to the heart?
1. respiratory "pump": pressure changes created during breathing move blood toward the heart by squeezing abdominal beins as thoracic beins expand
2. muscular "pump": contraction of skeletal muscles "milk" blood towards the heart and valves prevent backflow
3. Vasoconstriction of veins under sympathetic control
What are the main factors influencing BP?
- CO, Peripheral Resistance (PR) and blood volume
- (remember CO depends on SV)
Describe how the Baroceptors maintain homeostasis
- blood pressure rises-->baroceptors in carotid sinuses and aortic arch are stimulated-->these impulses stimulate the cardioihibitory system and inhibit vasomotor center -->sympathetic impulses to the heart cause lower HR, contractility, and CO2-->rate of vasomotor impulses allows vasodialation decreasing R-->lower CO2 and R return BP to normal range
- blood pressure drops-->baroceptors in carotid sinuses and aortic arch are inhibited-->impulses stimulate cardioaccelatory center and stimulate vasomotor center-->sympathetic impulses cause HR, contractility, and CO2 to rise-->vasomotor fibers stimulate vasoconstriction raising R-->higher CO2 and R return BP to homeostatic range
Describe how chemoceptor-initiated reflexes regulate BP
respond in rise to Co2, drop in pH or O2
increase blood pressure via the vasomotor center and cardioacceleratory center
What are the hormonal controls for BP?
Adrenal medulla hormones norepinephrin (NE) and epinephrine cause generalized vasocontriction and increase CO
Antiotensin II, generated by kdney release of renin causes vasocontriction
Antidiuretic hormone (ADH) causes intense vasoconstriction in cases of extremely low BP
Atrial Natriuretic Peptide (ANP) causes blood volume and BP to decline, causes generalized vasodialation
What is the Long term mechanism for BP regulation?
- -Baroceptors quickly adapt to chronic hight or low BP
- -Long term mechanisms alter blood volume instead
- -Kidneys act directly or indirectly to regulate arterial blood pressure
What is the direct renal mechanism?
Alters blood volume independelt yof hormones
- -increased BP or BV causes kidneys to eliminate more urine, thus reducing BP
- -decreased BP or BV causes the kidneys to conserve water, and BP rises
What is the indirect renal mechanism?
- The Renin-antiotensin mechanism
- -Arterial BP down leads to a release of Renin
- -Renin leads to production of angiotensin II (potent vasoconstrictor)
- -Angiotensin II leads to aldosterone secretion
- -Aldosterone secretion leads to renal reabsorption of NA+ and lower urin formation
- -Angiotensin II stimulates ADH release
How is blood pressure measured?
Pressure is increased in the cuff of a spygomomanometer until it exceeds the systolic pressure in the brachial artery
pressure is released slowly and examiner listens for first sign of brahical pulse in stethoscope called KOROTKOFF SOUNDS
This is the systolic pressure (normally 110-140 mm Hg)
These sounds disappear when the artery is no longer constricted and blood is flowing freely (diastolic pressure, normally 17-80 mmHg)
What is hypotension?
low blood pressure: systolic pressure below 100mm Hg
orthostatic hypotension: temporary low Bp and dizziness when suddely rising from a sitting or reclining position
chronic hypotension: hint of poor nutrition and warning sign for Addison's disease or hypothyroidism
acute hypotension: important sign of ciruclatory schock
What is hypertension?
high Bp: sustained leveles of 140/90 or higher
prolonged hypertension can cause heart failure, vascular disease, renal failure, and stroke
- Primary or essential hypertension: 90% of hypertensive conditions
- -due to several risk factors, but no definate cause
- Secondary Hypertension: less common
- treatment targets cause
What is autoregulation and what are the two types?
automatic adjudment of BF to each tissue in propoertion to its requirements at any given point in time
independent of MAP
- two types:
- 1. metabolic
- 2. myogenic
What are the metabolic controls of autoregulation?
- Vasodialation of arterioles and relaxation of precapillary schincters occur in response to:
- -declining tissue O2
- -substances from metabolically active tissues (H+. K+,adenosine, and prostaglandins) and inflammatory chemicals
- -relaxation of vascular smooth muscle
- -release of Nitric Oxide from vascular endothelial cells (major cause of vasodialation)
What are the myogenic controls of autoregulation?
**RESPONDS TO STRETCH**
myogenic responses of vascular smooth muscle keep tssue perfusion constant despite most fluctuations in systemic pressure
passive stretch promotes increased tone and vasoconstriction
reduced stretch promotes vasodialation and increases blood flow to the tissue
What is angiogenesis?
number of blood bessels to a region increases and existing vessels enlarge
common in heart when a coronary vessel is occluded or throughout the body in people in high-altitudes
What is hydrostatic pressure?
capillary hydrostatic pressure (HPc) (capillary blood pressure)
- tends to force fluids through walls (pushes)
- greater at the arterial end than the venule end of capillary
- Interstitual fluid hydrostatic pressure(HPif)
- -usually assumed to be 0
what is colloid osmotic pressure?
- capillary colloid osmotic pressure (OPc)
- about 26 mmHg
- Interstitual fluid osmotic pressure (OPif)
- -usually about 1 mm Hg due to low protein content
What is Net filtration Pressure?
comprises all the forces acting on a capillary bed
near the arterial end of the capillary bed, hydrostatic pressure wins and near the venous end osmotic forces dominate
excessive fluids are returned through lymphatic system