Chapter 18: Cardiovascular System II: The Blood Vessels
Vasa Vasora
" vessels to the vessels" they supply outermost blood vessels with oxygen and nutrients because they are too far way from the lumen.
Autoregulation
"self-regulation" ensures that correct amount of blood is delivered to match a tissue's level of activity.
Viscosity
"thickness" of a liquid. It's inherent resistance that all liquids have to flow. The more viscous a liquid is, the more its molecules resist being put into motion and staying in motion.
What effect does the sympathetic nervous system have on blood pressure?
Blood pressure rises when the sympathetic nervous system kicks in.
What determine peripheral resistance?
Blood vessel length, blood vessel diameter, blood viscosity and obstructions in vessels.
The magnitude of this gradient is one factor that determines
blood flow, which is the amount of blood that flows per minute. In general, this value matches the cardiac output of about 5-6 liters/min.
Resistance is mainly determined by 3 variables :
blood vessel radius, blood viscosity and blood vessel length
Resistance is mainly determined by 3 things:
blood vessel radius, blood viscosity, and blood vessel length. Of these variables, vessel radius is the quickest to change, whereas vessel length is, of course, the slowest.
Blood pressure is the outward force the blood exerts on the wall of the
blood vessels
If BP goes up so does
blood volume. Think about blowing up a balloon.
Pericytes
cells found "around" some capillaries. They have contractile filaments and appear to control blood flow through capillary.
Endothelial cells joined by many tight junctions
continuous capillary
Least leaky, allow a narrow range of substances to cross the capillary wall
continuous capillary
located in the skin, muscle tissue, and most nervous and connective tissue
continuous capillary
Systolic Pressure
contraction phase - average 120 mm Hg
What does myogenic mechanism do?
counters a change in blood flow by altering arteriolar resistance. Blood flow is related inversely to resistance. If resistance increases, velocity decreases.
The velocity with which blood flows is largely determined by the
cross sectional area of the blood vessel
Perfusion to the tissues of the heart ______ during systole and _____ during diastole.
decrease increase
As resistance increases, blood flow
decreases
As the cross sectional area increases, the velocity of blood flow
decreases
blood vessel radius - as a radius increases (dilates) resistance to blood flow
decreases (vice versa)
If a patient has high BP what can we give them to get rid of the water?
diaretics
Which 2 hormones cause vasoconstriction and where is it released from?
epinephrine and norepinephrine released from adrenal medulla. Increase peripheral resistance elevates BP
Edema
excessive amount of water in the interstitial fluid
Contain fenestrations in their endothelial cells
fenestrated capillaries
Some capillaries have small pores within their endothelial cells, called
fenestrations "window" Water is able to move freely through these pores when a gradient exists, as well as small substances such as monosaccharides and amino acids that are dissolved in the water.
Hydrostatic pressure
force that a fluid exerts on wall of its container. blood pressure is equal to hydrostatic pressure. HP pushes water out of the capillary. If HP is higher than OP, water leaves the capillary by filtration.
Elastic Arteries
Largest diameter arteries. They are known as the conducting arteries. They conduct blood under high pressure to organs. They include the aorta and immediate branches near the heart. they stretch with each ventricular systole.
Sinusoidal capillary
Leakiest capillary with large pores and irregular shape because their boundaries are determined by organ in which they reside.
Hemodynamics
hemo = blood dynamic = movement ciruclation blood flow in cardiovascular system
When CO increases, blood pressure will
increase (vice versa)
Blood flow increases when the pressure gradient
increases ( and vice versa)
Tunica Intima
inter attached to blood. composed of endothelium.
Capillary
is the exchange system. They are in between - single cell wall with the smallest diameter in vessels.
Blood pressure
is the outward force that the blood exerts on the walls of the blood vessels.
Does the myogenic mechanism slow down or speed up blood flow when arteriolar pressure rises?
it slows down blood flow by increasing resistance when arteriolar pressure rises.
Muscular Artery
known as the distributing arteries. Thick walled arteries and contain a well-developed tunica media. control blood flow to organs. Regulates BP. Due to the predominance of smooth muscle cells, the diameter of muscular arteries does change significantly with vasoconstriction and vasodilation. This allows the nervous and endocrine systems to adjust local blood flow to different organs by changing the vessel diameter.
Vascular anastomoses
locations where vessels connect via pathways called collateral vessels
The flow of blood that takes place within the body's capillary beds is collectively called the ? and involves 2 types of vessels called ?
microcirculation 2 vessels: true capillaries (where materials are exchanged) and a small, central vessel
Tunica Media
middle layer. this layer has 2 components: smooth muscle - control the diameter of the blood vessel and so the amount of blood that flows to organs AND elastic fibers called the external elastic lamina.
Venous anastomosis
most common type. neighboring veins are connected by small collaterals; smaller veins are often so interconnected they form complex, weblike patterns. "spider veins"
Filtration
movement of water across a capillary which is a movement of a fluid by a force such as pressure or gravity.
What are the two types of auto regulatory controls?
myogenic mechanism and metabolic controls
Osmotic pressure is determined almost exclusively by
number of particles, not their size.
Osmotic Pressure
osmosis involves movement of water from a solution with a lower solute concentration to one with a higher solute concentration; # of solute particles in a solution determines its osmolarity. OP draws water in capillary. If OP is higher than HP, water enters the capillary by osmosis.
Tunica Externa
outermost layer. Is composed of dense irregular collagenous connective tissue that supports the blood vessel and prevents it from over stretching.
Perfusion to the heart increases dramatically during strenuous activity due to a low level of _______ in the interstitial fluid, which triggers ________.
oxygen vasodilators; directly dilate the arterioles serving the myocardium and so greatly increase increase perfusion.
There is little resistance but the further away the more
peripheral resistance increases, blood pressure also increases.
Peripheral chemoreceptor
play role in regulation of breathing, but also affect BP chemo = detect chemical reflex Feed back to the meduall to lower or higher O2.
Capillary exchange
primary function is nutrients, gases, ions, and wastes must be able to cross the wall and travel between the blood in the capillary and tissue cells.
What is the overall purpose of the baroreceptor reflex ?
protect the body from sudden increases or decreases in blood pressure from moment to moment. It adjusts blood pressure with changes in position Example: when you get up from bed in the morning
These pressure changes the arteries to expand and recoil with each heartbeat known as a
pulse
The pulse can be felt, or palpated, through the skin in superficial arteries known as
pulse points
What do blood vessels do?
regulate blood flow to tissues, control blood pressure, and secrete a variety of chemicals.
What is the second factor that determines blood flow?
resistance which is any impedance to blood flow.
Three main factors that influence blood pressure are
resistance, cardiac output and blood volume
Central chemoreceptors
respond to decrease in pH, triggers another feedback loop that *indirectly* increases activity of sympathetic neurons which results in vasoconstriction and rise in blood pressure.
Diastolic Pressure
rest phase - 80 mm Hg
Renin
secretion from kidneys, triggered when bp drops, begins process that activates angiotensin-II; induces thirst, causes sodium ion retention and as a result increases blood volume.
Extremely leaky, allow large substances to cross the capillary walls
sinusoidal capillary
Arterial anastomoses
supply nutrients and supply oxygen for the heart and brain.
Perfusion to the skin is regulated by the _____ ______ ____ as part of the body's _____ ______ physiology.
sympathetic nervous system temperature regulation physiology
What are systole and diastole?
systole = contraction diastole = relaxation
Why do arteries pulsate?
the BP in systemic arteries is pulsatile - increases during ventricular systole and decreases during ventricular diastole. These pressure changes causes the arteries to expand and recoil with each heart beat, known as the pulse.
Mean Arterial Pressure
the average pressure in the systemic arteries during an entire cardiac cycle.
How does the heart drive blood through the blood vessels?
the left ventricle pushes the blood through the vessels
What does the myogenic mechanism do when arteriolar pressure lowers?
the mechanism speeds up blood flow by decreasing resistance.
Vascular Anastomosis
the neighboring veins are connected by collaterals.
Celiac Trunk
the short "abdominal cavity" splits immediately into 3 separate arteries. Common hepatic arteryL right side to liver Gastroduodenal artery: stomach, pancreas, and duodenum Hepatic artery proper: liver and gallbladder
Arteriole
the smallest arteries. Thin walls with all 3 tunics. smaller than a human hair. They control blood flow to tissues and feed capillary beds.
Which system has longer blood vessel lengths?
the systemic circuit. the longer the blood vessel the greater the resistance, more pressure is needed to propel blood through a long vessel than a short one.
What prevents a blood vessel from over stretching ?
the tunica externa - it supports the blood vessel and prevents over stretching.
Blood Flow
the volume of blood that flows per minute. Blood flow matches cardiac output and if pressure gradient increases blood flow will increase.
Resistance
this also determines blood flow. if resistance increases, blood flow decreases.
Pulse Pressure
this is the difference between the systolic and diastolic pressure.
Why is tissue perfusion tightly regulated?
to ensure that the metabolic needs of all tissues are met at all times.
All blood vessels are tubular organs that contain a central space called _______ ? and surrounded by several tissue layers, and tuns. The three tunics of the blood vessel wall are the ?
tunica intima, tunica media, and tunica externa
What is a powerful vasoconstrictor ?
Angiotensin - II
What else is triggered to increase sodium and water from kidneys to increase blood volume?
Angiotensin - II also triggers secretion of aldosterone from adrenal gland.
Subclavian Artery
Arterial supply of upper limb is derived entirely from subclavian artery, which changes it name to axillary artery.
Are veins or arteries under more pressure?
Arteries
True or False: The longer the blood vessel the greater the resistance
True
If HR is too fast why will SV go down?
because it will not have enough time to refill.
What is the advantage of the slow capillaries?
02 and nutrients more time to exchange the stuff
What are the 2 steps of Short-term mechanisms by which the parasympathetic nervous system decreases blood pressure ? And what hormone is released?
1. Parasympathetic neurons, via the vagus nerve, decrease heart rate, which decreases cardiac output. 2. Sympathetic neurons in the medulla of the brainstem are inhibited by parasympathetic neurons. A decrease in sympathetic stimulation causes vasodilation and lower peripheral resistance. The axons of the parasympathetic system, via the vagus nerve, release acetylcholine primarily onto certain cardiac pacemaker cells (particularly the sinoatrial [SA] and atrioven- tricular [AV] nodes) and atrial cardiac muscle cells.
What are the 2 steps of Short-term mechanisms by which the sympathetic nervous system increases blood pressure ? And what 2 hormones are released ?
1. Sympathetic neurons increase heart rate and contractility, which increases cardiac output 2. Sympathetic neurons cause vasoconstriction of arterioles, which increases peripheral resistance. norepinephrine and epinephrine
What is the purpose of the cerebral arterial circle "circle of willis"
1. helps to equalize pressure in the arteries of the brain and minimize changes in systemic arterial pressure 2. provides collateral circulation that allows blood to continue flowing to the brain even if blood flow through one of the brain's major arteries is disrupted.
At rest only what percent of capillary beds are fully open?
25 percent
Why is a greater percentage of blood found in veins? Why is this important?
70 % of total blood in body is located in the veins. Veins act as blood reservoirs. Veins have larger lumen and can carry more blood.
Blood flow to the brain is maintained nearly constantly at ______ ; however perfusion to areas of the brain varies with ____ ______.
750 ml/min neuronal activity
When BP decreases, what is triggered?
ADH to trigger thirst and increase amount of water retained by kidneys; raise blood volume & raise bp
Endocrine System regulates blood volume through release of (4 things)
ANP, angiotensin - II , antidiuretic hormone (ADH) and aldosterone.
Peripheral Resistance
As peripheral resistance increases, blood pressure increases.
What rate does venous blood must be returned back to heart?
At the same rate that it is pumped into arteries.
What causes a mild decrease in peripheral resistance and where is it secreted from?
Atrial natriuretic peptide (ANP) - bc it is an anti aldosterone, so it gets rid of NA and H20
When BP increases, atrial cells secrete
Atrial natriuretic peptide, which cause kidneys to excrete more water and sodium ions to decrease blood volume, therefore lower BP
Negative Feedback Loop for baroreceptor reflex
BP above normal range - Baroreceptors in the carotid sinus detect the increased pressure and fire action potentials at a faster rate. The medulla oblongata is notified. Parasympathetic neurons in the medulla oblongata inhibit sympathetic activity, inducing vasodilation and decreased heart rate, lowering cardiac output. Blood pressure decreases, and feedback decreases response from the medulla.
What is the majority of capillary? Located in muscles, skin, and most nervous and connective tissue?
Continuous least "leaky" because their endothelial cells are joined together by tight junctions.
What are the 3 types of capillaries? Capillaries in different parts of body have slightly different functions and structes.
Continuous Fenestrated Sinusoidal
How does the last division of the aorta end, and what structures do these vessels supply?
Descending abdominal aorta pierces the diaphragm and enters the abdominopelvic cavity. at the 4th lumbar vertebra it splits into its terminal branches: the right and left common iliac arteries - then these arteries split into the internal iliac arteries which supply the pelvic structure and the external iliac arteries which supply the lower limbs.
Arteries are classified in 3 classes by function and structure. What are the 3 classes ?
Elastic Artery Muscular Artery Arteriole
What are the hormones that control cardiac output?
Epinephrine, Norepinephrine and Thyroid Hormone
How are capillaries structured?
Extremely thin vessels. Each vessel consists only of an endothelium rolled into a tube and small amount of basal lamina secreted by endothelial cells.
Located in kidneys, endocrine glands and small intestine
Fenestrated capillary
Net Filtration Pressure
Hydrostatic pressure (pushing water out) MINUS colloid pressure (pulling water in) = NFP (overall force)
The increase in blood flow to skeletal muscle during exercise is called ____. When exercise begins the _____ arterioles dilates, which triggers the ____ to dilate, which finally triggers the ____ ____ to dilate.
Hyperemia Terminal arterioles >> arterioles >> feed artery
Aorta
Largest artery in body. it begins at the left ventricle and has 4 divisions.
Mean Arterial Pressure formula (MAP)
Map = Diastolic Pressure + 1/3 (systolic pressure - diastolic pressure)
A cell is actively metabolizing glucose and producing carbon dioxide and consuming oxygen at a high rate. What effect will this have on local arterioles?
Metabolic control - will call the arterioles to dilate / relax.
Why is it important that a vessel be able to stretch ?
Needs to be able to stretch for mechanical reasons so we can move body parts and blood flowing mechanism.
What 3 things determine blood pressure?
Peripheral resistance, Cardiac Output and Blood Volume
Baroreceptor Relfex
Rapid Automatic Predictable Stereotype to a response Baro means pressure
Which capillary is located in the liver, spleen, lymphoid organ and bone marrow to transfer large substances such as blood cells and large proteins between interstitial fluid and blood?
Sinusoidal capillary
Vessel Compliance
Small increases in blood volume are offset by the ability of the vessels to stretch. Veins are the most compliant vessels, and they stretch to accommodate the added fluid when blood volume increases, with only a small rise in pressure.
How is a vessel formed?
Small veins merge with other veins to become vessels.
What mechanisms are in place to assist in venous return?
Smooth muscle in vein walls can contract under sympathetic nervous system. Stimulation to increase rate of venous return.
What determine Cardiac Output?
Stroke Volume and Heart Rate
True or False: The total volume of blood is directly linked to the amount of water in the blood— when the blood contains more water, blood volume increases, and vice versa. As blood volume increases, blood pressure increases. T
True
What happens when veins can no longer stretch to hold the blood volume?
The blood volume moves to the arteries and since they are way less compliant the blood pressure will increase too.
Which structures allow a vessel to stretch?
The elastic fibers give the vessel the properties of distensibility ( stretch when pressure is UP ) and elasticity to recoil back to original size when the stretching force is removed.
What do elastic fibers do ?
The elastic fibers give the vessel the properties of distensibility, ability to stretch when subjected to increased pressure, and elasticity, or the ability to recoil back to the original size when the stretching force is removed.
Carotid and aortic sinuses
These receptors depolarize and fire rapid action potentials in response to pressure exerted on the arterial wall; this triggers the baroreceptor reflex.
Veins
Thin walled vessels with large lumens; little smooth muscle and valves. This returns blood to the heart.
Venule
Thin walls, little smooth muscle. If they are small they only have a tunica intima, but larger ones have all 3 tunics. They drain capillary beds.
Fenestrated capillary
This capillary is much leakier because their endothelial cells contain fenestrations (pores) Pores allow diffusion to take place much more quickly than it does in continuous capillaries. They are located in places that require substances to rapidly enter or exit blood.
Peripheral resistance is increased by conditions that increase blood viscosity and is decreased by conditions that decrease blood viscosity. What is an example?
This makes sense logically—the flow in a pipe filled with maple syrup (higher viscosity) is going to be much slower than the flow in one of the same diameter filled with water (lower viscosity).
How does the myogenic mechanism regulate local tissue perfusion?
This mechanism counters a change in blood flow by altering arteriolar resistance. If resistance goes up, velocity goes down. Example: It speeds up blood flow by decreasing resistance when arteriolar pressure lowers.
Larger molecules must cross the endothelial cells by
Transcytosis. Molecules are taken into cell by endocytosis and then are moved out other side of cell by exocytosis.
Which system controls long term maintenance of blood pressure?
Urinary system Bp (Up) NA H20 (down) Bp (down) Na H20 (up) amount of body water lost as urine affects blood volume
Why does venous blood need assistance returning to the heart?
Venous circuit is under such low pressure that there isn't much of a driving force to propel venous blood back to heart.
Tissue Perfusion
blood flow to a tissue through a capillary bed. It is tightly regulated to ensure that metabolic needs of all tissues are met at all times.
What determine blood volume ?
Water loss and water gain
Does blood have a high viscosity?
Yes, blood has a high viscosity due to the # of proteins and cells it contains.
Cerebral Arterial Circle "circle of Willis" is composed of
anterior and posterior communicaitong arteries anterior and posterior cerebral arteries the internal carotid artery
Capillary beds
are capillaries found in clusters. They wind their way between cells of most tissues in body.
Venous Valve
are extensions of the tunica intima that overlap and prevent blood from flowing backward in the venous circuit.
Veins
are the collection system. They drain blood from capillary beds and return to heart. They follow the opposite pattern of arteries.
Arteries
are the distribution system of vasculature. As they travel away from heart they branch into vessels of progressively smaller diameter that supply most tissues in body with blood.
Arteriovenous anastomosis
artery empties directly into a vein without passing through a capillary bed. Detour - because the capillary has some issues and the vein still gets original stuff from artery.
What are the 4 divisions of the aorta?
ascending aorta aortic arch descending thoracic aorta descending abdominal aorta
