APHY102 - Marieb - Chapter 19 - Blood Vessels

Terms Definitions
Blood is carried in a closed system of vessels that begins and ends at the _____.
What are the three types of blood vessels?
Arteries, Veins, Capillaries
What do arteries do?
Arteries carry blood away form the heart
What do veins do?
Veins carry blood toward the heart
What do capillaries do?
Capillaries contact tissue cells and directly serve cellular needs
Arteries and veins are composed of what three "tunics?"
1) Tunica interna
2) Tunica media
3) Tunica externa
What's the innermost layer of a vein or artery called?
Tunica interna
What's the outermost layer of a vein or artery called?
Tunica externa
What's the second deepest layer of a vein or artery called?
Tunica media (it's also the second most superficial. It lies in the middle)
What are capillaries composed of?
Endothelium with sparse basal lamina
What type of blood vessels are simply composed of endothelium with sparse basal lamina?
What's the lumen of a vein or artery?
The central blood-containing space.
What's the central blood-containing space of a vein or artery called?
What word describes the innermost layer of an organ, like the tunica interna?
What are the three layers of the tunica interna, from deepest (closest to lumen) to most superficial?
1) Endothelium
2) Subendothelial layer
3) Internal elastic lamina
What layer contains the external elastic lamina?
The tunica media
What are the elastic (conducting) arteries?
Thick-walled arteries near the heart; the aorta and its major branches
What arteries are described as "thick-walled arteries near the heart; the aorta and its major branches?"
The elastic, or conducting, arteries
What four characteristics make the elastic (conducting) arteries unique?
1) Large lumen allow low-resistance conduction of blood

2) All three tunics contain elastin

3) They can withstand and normalize large fluctuations in pressure

4) They allow blood to flow fairly continuously through the body
What's another word for elastic arteries?
Conducting arteries
What's another term for conducting arteries?
Elastic arteries
What's another term for muscular arteries?
Distributing arteries
What's another term for distributing arteries?
Muscular arteries
What do muscular (distributing) arteries do?
They deliver blood to body organs
What two physical properties make muscular (distributing) arteries unique?
1) Thick tunica media with more smooth muscle and less elastic tissue

2) Active in vasoconstriction
What are arterioles?
The smallest of arteries; arteries that lead to the capillary beds
What arteries are the smallest, and lead to capillary beds?
What important task are arterioles charged with?
Controlling flow of blood to the capillary beds by vasoconstriction and vasodilation
What are the smallest blood vessels?
What three physical properties make capillaries unique?
1) They only have one tunic -- the tunica interna

2) The tunica interna is only one cell thick

3) They allow RBC's to flow through the capillary wall, one at a time.
What are the three structural types of capillaries?
1) Continuous

2) Fenestrated (from the latin "fenestra," meaning "window")

3) sinusoidal (noun = sinusoids)
Where are continuous capillaries common?
skin and muscles
What are three physical properties that describe the continuous capillaries found in skin and muscles?
1) They have endothelial cells that provide an uninterrupted lining

2) Adjacent cells are held together with tight junctions

3) There are intercellular clefts of unjoined membranes that allow the passage of fluids
What type of capillary constitutes the blood-brain barrier?
Continuous capillaries
What special function do continuous capillaries in the brain serve?
They make up the blood-brain barrier
What physical property makes continuous capillaries in the brain unique?
The endothelia of these capillaries are completely joined by tight junctions (no clefts).
What's a pericyte?
It's a relatively undifferentiated cell that is part of the epithelial tissue of a blood cell. It can transform into many types of cells when needed. Important in angiogenesis. Also called ROUGET'S CELL
What do you call a type of relatively undifferentiated cell that helps make up the connective tissue around capillaries and other small blood vessels?
What's pinocytosis?
the uptake of fluid and dissolved substances by a cell by invagination and pinching off of the cell membrane
What three organs are most rife with fenestrated capillaries?
Kidneys, endocrine glands, small intestines
What are fenestrated capillaries particularly good at?
active absorption and filtrate formation
What physical properties are unique to fenestrated capillaries?
1) an endothelium riddled with pores, called fenestrations. Remember, fenestra is latin for "window."

2) Greater permeability to solutes and fluids than other capillaries
What's a quick description of a sinusoidal capillary (or a sinusoid blood vessel)?
A highly modified, leaky, fenestrated capillary with a large lumen
Where are sinusoidal capillaries found?
Bone marrow, liver, lymphoid tissue, some endocrine organs
What things make sinusoid blood vessels (sinusoidal capillaries) unique?
1) They allow large cells like proteins and RBCs to pass relatively freely.

2) Blood flows sluggishly within them, allowing for modification in various ways.

3) They have incomplete basement membranes and large intercellular clefts
What structure in the capillary bed connects the metarteriole directly to the postcapillary venule?
Thoroughfare channel
What structure separates true capillaries from the metarteriole at the capillary bed?
Precapillary sphincters
Describe a precapillary sphincter
It's a cuff of smooth muscle that surrounds each true capillary and regulates flow into the capillary
What structure regulates flow to true capillaries?
Precapillary sphincter
What two types of stimuli control blood flow at the capillary bed?
1) Vasomotor nerve impulses

2) Local chemical changes
What two types of vessels compose the capillary bed?
1) True capillaries (10 to 100 of them)

2) Thoroughfare channels (vascular shunts) -- allow capillary bed to be bypassed
What's a metarteriole?
Any of the tiny blood vessels that connect the smallest arterioles to the capillary bed. Also called "precapillary."
What type of blood vessel does a metarteriole branch off of?
Terminal arteriole
Terminal arterioles feed many tiny _____, blood vessels that connect to the capillary bed.
What's a venule?
Any of the minuscule veins that connect the capillary bed to larger systemic veins
What's unique about a venule?
A venule is extremely porous -- much like a capillary -- and allows WBCs and fluids to easily pass into body tissue from the bloodstream
Which venules are the smallest venules?
Postcapillary venules
Describe postcapillary venules
They're the smallest venules, composed of endothelium and a few pericytes. They are also very porous.
How many layers of smooth muscle do large venules have?
one or two (in the tunica media)
What are postcapillary venules composed of?
A single layer of epithelium around which a few pericytes congregate
What is formed when venules converge?
A vein
In a vein, what's thinner: the tunica media or the tunica externa?
The tunica media is thinner. The tunica externa is thick and contains collagen fibers and elastic networks.
What tunic of a vein contains collagen fibers and elastic networks?
The thick tunica externa
Blood veins are also referred to as ____ _____ since they hold 65% of the blood supply.
Capacitance vessels, blood reservoirs
Where will you find the blood pressure to be higher: in a vein, or in an artery?
Artery. Veins have MUCH lower blood pressure
Which has thinner walls -- veins or arteries?
Veins have thinner walls
Which has thicker walls -- veins or arteries?
Arteries have thicker walls
What special adaptations do veins demonstrate, assisting with blood flow back to the heart?
1) Large-diameter lumens
2) Valves (resembling semilunar heart valves) which prevent backflow
What's a venous sinus?
A venous sinus is a specialized, flattened vein with extremely thin walls (e.g., coronary sinus of the heart and dural sinuses of the brain).
The pumping action of the heart generates blood flow through the vessels along a ____ ____, always moving from ____- to _____-pressure areas
pressure gradient, higher, lower
What other statistic is "blood flow" equivalent to when you're considering the entire cardiovascular system?
Cardiac output (CO)
What differs blood flow from cardiac output?
Blood flow can be localized; i.e. specific organs can all have widely varying amounts of blood flow at any given time. Cardiac output is system-wide
What two factors result in blood pressure?
Blood flow and resistance. That's pressure for you.
Describe systemic pressure.
1) Highest in the aorta

2) Declines throughout length of pathway

3) It's 0 mm Hg in the right atrium
Where does the steepest change in blood pressure occur?
In arterioles, are changes in blood pressure exaggerated or de-emphasized?
Where is blood pressure more consistent: in arteries or in veins?
In veins
Arterial BP reflects what two factors of arteries close to the heart?
1) Elasticity

2) Amount of blood forced in
Blood pressure in elastic arteries near the heart is ____, meaning it rises and falls
Define systolic pressure
Amount of pressure exerted on arterial walls during ventricular contraction
Define diastolic pressure
The lowest level of arterial pressure during a ventricular cycle
What's a term that describes the lowest level of arterial pressure during a ventricular cycle?
Diastolic pressure
What term describes arterial blood pressure during ventricular contraction?
Sytolic pressure
How do you pronounce "systole?"
Sis - toe - lee
How do you pronounce "diastole?"
Die - ass - toe - lee
What's pulse pressure?
The difference between systolic and diastolic pressure.
What's a term defined as "the difference between systolic and diastolic pressure?"
Pulse pressure
What's MAP?
"Mean arterial pressure." This is the figure that REALLY matters when considering amount of blood flow to tissues.
What's an easy way to estimate MAP?
MAP = diastolic pressure + 1/3 pulse pressure
What range does capillary BP usually fall into?
20-40 mm Hg
What's desirable: low capillary BP or high capillary BP.

Low capillary BP -- high BP would rupture the tiny fragile walls.

Low BP is sufficient to force filtrate out into interstitial space and distribute nutrients, gases, and hormones between blood and tissues.
How much pressure is necessary to force filtrate out of capillaries into interstitial space, distribute nutrients, gases, and hormones between blood and tissues?
Not much. That's why capillary BP is low.
What's a decent estimate for the pressure gradient in the venous system?
20 mm Hg
How does a vein behave when cut?
It will spill blood with an even flow
How does an artery behave when cut?
It spurts out gobs of blood with the heartbeat
What two phenomena assist the venous system in returning blood to the heart, seeing as how venous BP is insufficient to do so?
1) Respiratory pump - local veins are squeezed during breathing, suck blood toward the heart

2) Muscular pump - contraction of skeletal muscles "milk" blood towards the heart
What prevents backflow during venous return?
valves, dummy.
What five factors influence blood pressure in general?
1) Heart rate
2) Blood volume
3) Cardiac output (CO)
4) Resistance
5) Viscosity
What branch of the autonomic nervous system increases activity in relation to the heart in order to stimulate increased heart rate?
What two factors are the most important factors in creating resistance in a blood vessel?
1) Size of vessel (smaller means more pressure)

2) Smoothness of vessel (rougher means more pressure)
What's a term for narrowing of blood vessels?
What kinds of drugs can cause vasoconstriction, thus increasing BP?
antihistamines, naphazoline nitrate, tetrahydrozoline hydrochloride
What's a common vasodilator that can decrease BP and help prevent heart attacks?
Does anemia increase or decrease blood pressure?
If it is anemia due to low RBC concentration, it will decrease blood pressure
What artery do we use to measure blood pressure? What artery is our "benchmark?"
brachial artery
BP in other blood vessels is ____ than arterial BP.
What's the average BP in a healthy adult?
120/80 mm Hg

(systolic comes first, diastolic comes last)
What two factors are the main causes of hypertension (high BP)?
1) Heart pumping with excessive force

2) Arterioles become narrower
What's hypotension?
Low blood pressure -- and it's usually a good sign. Unless, of course, it's chronic and due to malnutrition, addison's disease, or hypothyroidism.

Also, if it's acute, it's the clearest sign of circulatory shock
What's the vasomotor center?
The vasomotor center is a cluster of sympathetic neurons in the medulla that oversees changes in blood vessel diameter. Innervates SMOOTH MUSCLE, especially in arterioles
What's the cardiovascular center?
The vasomotor center plus the cardiac centers in the medulla that together regulate BP by altering CO and blood vessel diameter
What's a baroreceptor?
It's a receptor that can detect changes in blood pressure and communicate messages about these changes to the brain
What are the types of baroreceptors?
High pressure arterial baroreceptors and low pressure (cardiopulmonary) baroreceptor
What sort of receptor can sense changes in blood pressure and communicate messages about blood pressure to the brain?
Describe the chain of events that occurs when BP strays higher than nominal levels.
1) Baroreceptors detect the change, setting off the baroreceptor reflex

2) Cardioregulatory center increases parasympathetic stimulation of the heart while decreseaing sympathetic stimulation

3) Simultaneously with number 2, the vasomotor center decreases sympathetic stimulation of blood vessels

4) Stroke volume decreases, thus CO decreases. Vasodilation occurs, decreasing pressure. BP is reduced
Describe the chain of events that occurs when BP strays lower than nominal levels.
1) Change is detected by baroreceptors, setting of both the baroreceptor reflex AND the adrenal medullary mechanism

2) Due to baroreceptor reflex, parasympathetic stimulation of the heart is decreased, and sympathetic stimulation increased at the cardioregulatory center -- also, the vasomotor center increases sympathetic stimulation of blood vessels

3) At the same time, the adrenal medullary mechanism causes secretion of norepinephrine and and epinephrine from the adrenal medulla -- this is all due to increased sympathetic stimulation.

4) All the above measures cause vasoconstriction and increased HR, increasing BP
What prominent chemicals increase blood pressure?
1) Adrenal medulla hormones (epinephrine and norepinephrine)

2) Antidiuretic hormone (ADH) is a vasoconstrictor

3) Angiotensin II (released by kidney and is INTENSE as a vasoconstrictor)

4) Endothelium and prostoglandin-derived growth factor (PDGF) are vasoconstrictors
What chemicals decrease blood pressure?
1) Atrial natriuretic peptide (ANP)

2) Nitric oxide (NO) - brief but potent vasodilator

3) histamine, prostacyclin, kinins -- inflammatory chemicals in general

4) Alcohol, since it inhibits antidiuretic hormone (ADH)
What chain of events occurs when blood pH strays higher than nominal levels? (this is often caused by a decrease in blood CO2)
1) CHEMORECEPTOR REFLEX: chemoreceptors in the medulla oblongata detect the pH change

2) Vasomotor center decreases sympathetic stimulation of blood vessels and the cardioregulatory center increases parasympathetic activity while decreasing sympathetic stimulation of the heart.

3) Vasodilation occurs and CO decreases, because the body knows that low CO2 levels mean that too much blood is traveling to the lungs and thus decreases BP
What chains of events occur when blood pH strays lower than nominal levels? (often caused by an increase in CO2 or a large decrease in O2)
1) CHEMORECEPTOR REFLEX: Carotid and aortic bodies have chemoreceptors that detect the change. This reflex increases sympathetic stimulation of blood vessels and increased respiration rate (which in turns increases sympathetic stimulation of the heart and decreases parasympathetic stimulation of the heart). Vasoconstriction occurs and increases resistance while CO increases, increasing BP.

2) CHEMORECEPTOR REFLEX in the medulla oblongata -- cardioregulatory cetner increases CO by decreasing parasympathetic stimulation of the heart and increasing sympathetic stimulation

3) CNS - ISCHEMIC RESPONSE - chemoreceptors sense the pH change and the vasomotor increases sympathetic stimulation of blood vessels, constricting them and creating more resistance

FINALLY increased BP and CO cause more blood flow to lungs, fixing the problem, we hope.
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