Blood Vessels LECTURE A&P II Exam 1

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

Distal to elastic arteroes; deliver blood to body organs

Have thickest tunica media with more smooth ucsle

Active in vasoconstriction

smallest arteries

lead to capillary beds

control flow into capillary beds via vasodialation and vasoconstriction

In all tissues excpet for cartilage, epithelia, cornea and lens of eye

functions: exchangr of gases, nutrients, wastes, hormones, etc.

• 1. Continuous capullaries
• 2. Fenesrtated capillaries
• 3. Sinusoidal capillaries (sinusoids)

abundant in the skin and muscles (most common)

Least permeable

• tight juntions connect cells
• intercellular clefts allow passage of fluids and small solutes

• found in the brain forming the brain blood barrier
• 

some contain pores (fenestrations)

more permeable than continuous capilarries

• functions in absorption of filtrate formation (such as in the SI, endocrine glands, and kidneys)
• 

leaky capillaries

fewer tight junctions, larger clefts, larger lumens

usually fenestrated

allows large molecules and blood to pass between surrounding tissues

• found in liver, bone, spleen, adrenal medulla
• 

• 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
• 

volume of blood flowing through a vessel, organ,or the entore circulation in a given period

measured in ml/min

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

delta p= blood pressure gradiant

Resistance is the factor that changes most easily and often

the pumping action of the heart that generates blood flow

• -highest in the aorta
• -declines throughout the pathway
• -is 0 in the right atria

• Systolic pressure
• Diastolic pressure

Pulse pressure: difference between systolic and diastolic pressure

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

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

• CO, Peripheral Resistance (PR) and blood volume
• (remember CO depends on SV)

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• 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

respond in rise to Co2, drop in pH or O2

increase blood pressure via the vasomotor center and cardioacceleratory center

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

Renal 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

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

• 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
• 

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)

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

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

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

• 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

• Effects:
• -relaxation of vascular smooth muscle
• -release of Nitric Oxide from vascular endothelial cells (major cause of vasodialation)

**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

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

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

• capillary colloid osmotic pressure (OPc)
• about 26 mmHg
• *sucks*

• Interstitual fluid osmotic pressure (OPif)
• -usually about 1 mm Hg due to low protein content

OPc-OPif=25mm Hg

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