ANATOMY EXAM #3 - Blood Vessels

Lumen

The inside of blood vessels, where blood is contained

How many layers do most blood vessels have?

3

What does the innermost layer have and how does it allow for smooth blood flow?

Tunica intima

• Single layer of squamous epithelial cells (endothelium) and thin subendothelial layer

• Reduces friction, releases lubricating substances, maintaining a non-stick surface

What does the middle layer contain and how does it allow for vasoconstriction and vasodilation?

Tunica media

• Smooth muscle cells and elastic fibers (elastin)

• Thickest

• Responsible for constriction and relaxation

How many layers do capillaries have?

1

Vasodilation

Relaxation, increase in lumen diameter

Vasoconstriction

Contraction, decrease in lumen diameter

What are 3 types of arteries?

• Elastic

• Muscular

• Arterioles

Function of Elastic Arteries

• “Pressure reservoirs”

• Close to heart, ex. Aorta

• Big diameter → large lumen → allows for continuous blood flow downstream

• Elastin -? maintain pressure gradient

• Feed into muscular arteries

Function of Muscular Arteries

• “Distributing arteries”

• Deliver blood to body organs

• Ex. femoral artery

• Feed into arterioles

Function of Arterioles

• “Resistance vessels”

• Control flow of blood to capillaries

• Feed into capillaries

What is the function of capillaries?

• Exchange of gasses, nutrients, wastes hormones between blood and interstitial fluid

• Supply almost every cell

What are 3 types of capillaries?

• Continuous

• Fenestrated

• Sinusoidal

  • Ranked least to most permeable

Function of Continuous Capillaries

• Endothelial layer

• Most common

• Least permeable, layer with pores

Where are sinusoidal cpillaries located?

In limited locations, such as liver, spleen, red bone marrow

What are capillary beds?

• Network of capillaries between arterioles and venules

• Microcirculation: Flow of blood from arteriole to a venule through a capillary bed

• Blood flow into capillary bed is controlled by the diameter of arterioles

Venules

Where capillary beds unite

Veins

• Where venules converge (capacitance vessels)

• Have enlarged lumen so more space for blood, act as blood reservoir

What is blood flow?

• Volume of blood flowing through a vessel, organ, or entire circulation in a given period

• mL/min

• Relatively constant, varies at individual organ level based on needs

• Equivalent to CO for entire vascular system

What is blood pressure?

Force per unit area exerted on the wall of blood vessel by blood

• mm/Hg

• Often referring to systematic arterial pressure

Is blood flow constant?

No, it is pulsatile in arteries and continuous in veins. It is dynamic, or responding to body’s metabolic needs.

What is resistance?

Opposition to flow, “Total peripheral resistance” (TPR)

What are three factors that influence resistance?

• Blood Vessel Radius (STRONGEST FACTOR)

  • The more contracted, the more resistance

• Blood Viscosity: Thickness of blood due to formed elements and plasma proteins

  • Increased viscosity equals increased resistance

• Blood Vessel Length:

  • The longer the vessel, the greater the resistance encountered

What is the relationship between blood flow, pressure and resistance?

F= Change in P/R

R x F = Change in P

R = Change in P/F

Which of pressure and resistance influence blood flow the most locally?

Resistance

Which of pressure and resistance influence blood flow the most globally?

Pressure/Cardiac Output

What are three types of blood pressure?

• Systolic

• Diastolic

• Pulse

Systolic Pressure

• Pressure exerted in aorta during ventricular contraction

• Averages 120 mm Hg in normal adult

Diastolic Pressure

• Lowest level of aortic pressure when heart is at rest

• Averages 80 mm Hg in normal adult

Pulse pressure

Difference between systolic and diastolic pressure

Pulse

Throbbing of arteries due to difference in pulse pressures, which can be felt under skin

When is systemic blood pressure the highest?

In the aorta

When is the steepest drop in systemic blood pressure?

In the arterioles

What two factors determine arterial blood pressure?

• Elasticity of arteries close to heart

• Volume of blood forced into them at any time

Is arterial blood pressure constant?

No, blood pressure near heart is pulsatile. It rises and falls with each heartbeat.

What is mean arterial pressure?

Average arterial pressure

Why is MAP not simply an average of diastolic and systolic pressure?

• Heart spends more time in diastole, so not just a simple average of diastole and systole

• MAP = diastolic + 1/3 pulse pressure

Why does capillary blood pressure have to be low?

• Made of thin, single-layered vessels

• Allows sufficient time for slow exchange of nutrients, oxygen and waste

What helps maintain venous blood pressure?

Regular exercise, muscle movement, and hydration

• Needed for efficient venous return to the heart

What factors aid in venous blood pressure?

• Skeletal pump

• Respiratory pump

• One-way venous valves

• Sympathetic vasoconstriction

• Cardiac suction

What factors regulate blood pressure?

• Neutral controls

• Baroreceptors

• Chemoreceptors

• Cardiovascular center of medulla

• Vasomotor center in brain

• Higher brain centers

What is the equation for the change in pressure of MAP?

MAP = diastolic - 1/3 systolic

STUDY THE LARGE MAP OF INFLUENCES

STUDY THIS HARD PLS

What are two short term mechanisms for regulating blood pressure?

• Baroreceptor reflex

• Chemoreceptor reflex

What are long-term mechanisms for regulating blood pressure?

Hormonal Controls, Renal Regulation

How do neural controls operate?

• Body senses changes in blood pressure, blood pH, etc.

• Causes a change in blood pressure and heart rate as a response through centers in the brain

What brain centers are involved in regulating blood pressure?

• Cardiovascular center of medulla

• Vasomotor center in brain

• Higher brain centers

Cardiovascular Center

• Part of the medulla oblongata leads to changes in HR

• Responds to:

  • Changes in BP in Blood volume (detected by baroreceptors)

  • Changes in blood pH, CO2 and O2 levels (detected by chemoreceptors)

• Changes heart rate by sending nerve impulses via:

  • Sympathetic fibers

  • Parasympathetic fibers

Vasomotor Center

• Part of the medulla oblongata -> changes BP

• Works with the cardiovascular center

• Responds to:

  • Changes in BP in Blood volume (detected by baroreceptors)

  • Changes in blood pH, CO2 and O2 levels (detected by chemoreceptors)

• Changes blood pressure by:

  • When stimulated -> increased sympathetic drive -> vasoconstriction -> increased BP

  • When inhibited -> decreased sympathetic drive -> vasodilation -> decreased BP

Where are baroreceptors located?

Carotid sinuses, aortic arch, and walls of large arteries of neck and thorax

What do baroreceptors respond to?

• Baroreceptors respond to changes in MAP

• If MAP is high -> baroreceptors are activated -> decreases HR and decreases BP

• Dizzy when you stand up, baroreceptors help with this

How do baroreceptors alter cardiac output?

• Vasodilation/constriction

• Alteration in CO by changing heart rate and contractility

Baroreceptor response to Low MAP

• Decreased MAP

• Baroreceptors are inhibited

• Cardiovascular center

  • Increased sympathetic stimulation

  • Decreased parasympathetic stimulation

  • Increased HR, increased contractility, increased CO

• Results in increased BP

Baroreceptor response to High MAP

• Increased MAP

• Baroreceptors are stimulated

• Cardiovascular center

  • Decrease sympathetic stimulation

  • Increase parasympathetic

  • Decreased HR, decreased contractility, increased CO

• Inhibition of vasomotor center

  • Vasodilation -> decreased resistance

• Results in decreased BP

• High BP stimulates, Low BP inhibits

Where are chemoreceptors located?

Aortic arch and large arteries of neck

What do chemoreceptors detect?

Detect an increase in CO2, or drop in pH or O2 (indicate decreased breathing, need to pump more blood to tissues)

How do chemoreceptors cause increased BP?

• Works via cardiovascular and vasomotor centers

• Increasing CO via increased sympathetic activity

• Vasoconstriction via increased sympathetic activity

What hormones regulate blood pressure?

• Adrenal medulla hormones

• Angiotensin II

• Aldosterone

• Atrial Natriuretic Peptide

How do adrenal medulla hormones regulate blood pressure?

Epinephrine and norepinephrine increase CO and vasoconstriction → increases MAP

How does angiotensin II regulate blood pressure?

• Stimulates vasoconstriction → increase MAP

• Essential to life

How does aldosterone regulate blood pressure?

• Increases BP by increasing blood volume → MAP

• Triggered by angiotensin II

How does atrial natriuretic peptide regulate blood pressure?

• Decreases BP by antagonizing aldosterone

• Causing decreased blood volume → decreased MAP

How does atrial natriuretic peptide decrease blood volume?

Promotes renal excretion of sodium and water

How does aldosterone alter blood pressure?

Signals kidneys to retain sodium and water while excreting potassium, which increases blood volume

What two mechanisms by which renal regulation alters blood pressure?

• Direct renal mechanism

• Indirect renal mechanism

Direct renal mechanism

• If there is increased BP or blood volume

  • Elimination of more urine -> decreased blood volume -> decreased BP

• If there is decreased BP or blood volume

  • Kidneys conserve water -> increased volume -> increased BP

Indirect renal mechanism

• Decreased BP

• Release of renin by kidneys

• Renin enters blood

  • Don't need to know

  • Don't need to know

• Angiotensin does something with blood, check slides