Chapter 21: The Cardiovascular System: Blood Vessels and Hemodynamics Flashcards
contrast the structure and function of arteries, arterioles, capillaries, venules, and veins.
Hemodynamics – the forces involved in circulating blood throughout the body
Contribution of CVS to other systesms:
a) Blood delivers clotting factors and WBCs that aid in hemostasis when skin is damaged.
b) Blood delivers calcium and phosphate ions that are needed for building bone extracellular matrix.
d) Blood carries newly absorbed nutrients and water to the liver.
e) Blood circulates cells and chemicals that carry out immune functions.
(NOT c) Blood carries carbon dioxide to body tissues and removes oxygen for use by other organs.)
structure and function of blood vessels
(Deep to Superficial) Tunica interna -> Tunica Media -> Tunica Externa
ARTERIES
1 tunica interna (intima) – the deepest layer of an artery or vein
- consists of a lining of endothelium, basement membrane, and internal elastic lamina (not in all vessels)
- is in direct contact with blood within the lumen
II. lumen – the space within an artery, vein or other tubular structure (intestine,
renal tubule, etc)
III. endothelium – innermost layer of the tunica interna. Epithelial.
- continuous with the endocardial lining of the heart
- thin layer of squamous cells that line the entire cardiovascular system
- actions: influence blood flow, secrete local chemical mediators that influence contractile state of vessel’s overlying smooth muscle, assist with capillary permeability, reduce surface friction within lumen.
IV. basement membrane – second layer, deep to endothelium
- provides a physical support base for the epithelial layer
- framework of collagen fibers: provides significant tensile strength and resilience for stretching and recoil.
- Anchors the endothelium to the underlying connective tissue and regulates molecular movement.
- Important role in guiding cell movements during tissue repair of blood vessel walls
V. internal elastic lamina – outermost part of tunica interna
- forms boundary between tunica interna and tunica media
- thin sheet of elastic fibers with variable number of window-like openings (like Swiss cheese) i. the openings facilitate diffusion of materials through the tunica interna to thicker tunica media.
2. tunica media – intermediate coat of an artery or vein responsible for vasononstriction
- Composed of smooth muscle and elastic fibers
- Greatest variation among different vessel types i. In most vessels it is a relatively thick layer comprising mainly smooth muscle cells and substantial amounts of elastic fibers
- Smooth muscle cells: Primary role = regulate the diameter of lumen. i. Increased sympathetic stimulation typically stimulates smooth muscle to contract, squeezing the vessel and narrowing the lumen
VII. Vasoconstriction – decrease in lumen size of a blood vessel caused by contraction of the smooth muscle in the vessel wall a. Remember: Vascular spasm = smooth muscle contracting due to damage to a small artery or arteriole
VIII. Vasodilation – an increase in the lumen size of a blood vessel caused by relaxation of smooth muscle in the vessel wall.
IX. external elastic lamina – part of the tunica media a. Separates the tunica media from the tunica externa
3. tunica externa – superficial coat of an artery or vein
- Composed of elastic and collagen fibers
- Helps anchor the vessels to the surrounding tissues
- Contains numerous nerves and in large blood vessels, tiny blood vessels that supply the tissue of the vessel wall.
XI. vasa vasorum – small vessels that supply nutrients to the larger arteries and veins a. Vessels to the vessels
Arteries
Compliance – vessel walls stretch easily or expand without tearing in response to a small increase in pressure a. Arteries exhibit high compliance.
Elastic arteries – largest arteries in the body
- Largest artery diameter but vessel walls are relatively thin (1/10th total diameter)
- Include the aorta and pulmonary trunk and the aorta’s major initial branches: brachiocephalic, subclavian, common carotid, common iliac arteries.
- Important function: help propel blood onward while the ventricles are relaxing.
- Characterized by well defined internal and external elastic laminae and a thick tunica media dominated by elastic fibers
elastic lamellae – elastic fibers in the thick tunica media of the elastic arteries
pressure reservoir – the elastic arteries receive blood from ventricles, expand, and momentarily store mechanical energy. Then the elastic fibers recoil and convert the stored energy into kinetic energy of the blood.
- Because they conduct blood from the heart to medium sized more muscular arteries, elastic arteries AKA conducting arteries
muscular arteries – medium sized arteries
- Nica media contains more smooth muscle and fewer elastic fibers than elastic arteries
- Smooth muscle makes up approx 75% of the total mass of the artery walls
- Walls are relatively thick, 25% total diameter
- Capable of greater vasoconstriction and vasodilation to adjust rate of blood flow
- Well defined internal elastic lamina but thin external elastic lamina
- Tunica media varies from 3-40 layers of circumferentially arranged smooth muscle cells
- Less elastic tissue so unable to recoil and propel blood like the elastic arteries
- The thick muscular tunica media contracts and maintains a state of partial contraction
- Vascular tone – state of partial contraction of blood vessels that stiffens the vessel wall and is important in maintaining vessel pressure and efficient blood flow.
- g. Tunica externa is often thicker than the tunica media in muscular arteries i. Contains fibroblasts, collagen fibers, and elastic fibers all oriented longitudinally. 1. Structure permits vessel diameter to change but prevents shortening or retraction of the vessel when cut.
- h. Vary in size from 0.5mm entering organs to pencil-sized femoral and axillary arteries
distributing arteries – muscular arteries are AKA distributing arteries because they branch and ultimately deliver blood to each of the various organs
Anastomoses – union of the branches of two or more arteries supplying the same body region a. Provide alternate routes for blood to reach a tissue or organ
collateral circulation – the alternate route taken by blood through an anastomosis
end arteries – arteries that do not anastomose
- Obstruction of an end artery interrupts blood flow to a whole segment of an organ, producing necrosis of that segment
- However, blood routes may also be provided by nonanastomosing vessels that supply the same region
ARTERIOLES – small arteries key in regulating blood flow into capillaries
have high pulsing blood pressure
- Abundant microscopic vessels that regulate flow of blood into the capillaries
- Approx 400 million arterioles
- Range from 15 to 300 micrometers in diameter
- Vessel wall is ½ total vessel diameter
- Arterioles have a thin tunica interna with a thin, fenestrated internal elastic lamina that disappears at the terminal end.
- Tunica media consists of 1-2 layers of smooth muscle with circular orientation in the vessel wall.
Metarteriole – terminal end of the arteriole
- This region tapers towards the capillary junction.
- Forms a bypass route for blood to skip the capillary network when the precapillary sphincters contract
precapillary sphincters – a ring of smooth muscle at the metarteriole-capillary junction that monitors and regulates blood flow into capillaries
Resistance – the opposition to blood flow due to friction between blood and the walls of blood vessels
- Arterioles play a key role in regulating blood flow from arteries into capillaries by regulating resistance and AKA resistance vessels
- Arterioles contract and relax to increase/decrease vessel diameter which in turn increases/decreases friction of blood against vessel walls affecting resistance.
CAPILLARIES – microscopic blood vessel between an arteriole and a venule. AKA exchange vessels.
- Materials are exchanged between blood and interstitial fluid within capillaries.
- Diameters of 5-10 micrometers
- Approx 20 billion short, branched interconnecting vessels among individual cells of the body. Large surface area
- Number of capillaries in body part varies based on metabolic activity.
- High in muscles, brain, liver, kidneys, and nervous system
- Lower in tendons and ligaments
- Absent in all covering and lining epithelium, cornea and lens of the eye, and cartilage.
- e. Blood flow through most tissues varies based on metabolic needs i. Only a small amount of the capillary network is used when needs low, but when active, the entire network fills
- f. Capillaries lack tunica media and a tunica externa
- g. Composed of a single layer of endothelial cells and a basement membrane.
Microcirculation – the flow of blood from a metarteriole through capillaries and into a postcapillary venule
capillary bed – a network of 10-100 capillaries that arises from a single metarteriole.
Vasomotion – intermittent contraction and relaxation of precapillary sphincters causing intermittent blood flow through capillaries
- May occur 5-10x per minute
- Partly due to chemicals released by the endothelial cells Ex. Nitric oxide
thoroughfare channel – a distal end of a metarteriole with no smooth muscle that resembles a capillary and provides a direct route from blood from the arteriole to a venule, bypassing capillaries
continuous capillary – plasma membrane of endothelial cells forms a continuous tube that is interrupted only by intercellular clefts
- Intercellular clefts – between neighboring endothelial cells
- Continuous capillaries found in CNS, lungs, muscle tissue, and skin
fenestrated capillary – capillaries with small pores ranging from 70-100 nanometers in diameter in the plasma membranes of endothelial cells.
- Found in the kidneys, villi of small intestine, choroid plexuses of the ventricles of the brain, ciliary processes of the eyes, and most endocrine glands.
Sinusoid – thin walled leaky type of capillary
- Endothelial cells have many unusually large fenestrations
- Incomplete or absent basement membrane
- Very large intercellular clefts that allow proteins and in some cases blood cells to pass from a tissue into the bloodstream. i. Ex. New blood cells enter the blood stream through the sinusoids of red bone marrow
- Sinusoids also contain specialized lining cells adapted to the function of the tissue
- Ex. In the liver, sinusoids contain phagocytic cells that remove bacteria and debris from the blood.
- Found in the liver, spleen, anterior pituitary, parathyroid, and adrenal glands.
- The name of the portal system gives the location of the second capillary network i. Ex. Liver (hepatic portal circulation) and pituitary gland (hypophyseal portal system)
portal system – when blood passes from one capillary network into a portal vein and into a second capillary network
Venules – small veins
- Thin walls, do not readily maintain their shape
- Drain the capillary blood and being the return of blood back toward the heart
postcapillary venules – the smallest venules
- 10-50 micrometers in diameter
- Have loosely organized intercellular junctions (the weakest endothelial contacts in entire vascular tree)
- Very porous
- Serve as sites of exchange of materials and WBC emigration and therefore form part of microcirculatory exchange unit along with capillaries
muscular venules – postcapillary venules upstream from the capillaries that have acquired 1-2 layers of circularly arranged smooth muscle cells
- Thicker walls and material exchange can no longer occur
- 50-200 micrometer diameter
- The thin walls of both the postcapillary and muscular venules are the most distensible elements of the vascular system i. Allows them to expand and serve as reservoirs for accumulating large volumes of blood.
Veins – larger vessels that return blood to the heart
- Less distinct structural changes than arteries as they increase in size
- Very thin walls relative to total diameter (less than 10% vessel diameter)
- Range from 0.5mm to 3cm
- Same 3 layers as arteries, but relative thickness is different
- Tunica interna is thinner than arteries
- Tunica media is much thinner than in arteries with relatively little smooth muscle and elastic fibers
- Tunica externa of veins is the thickest layer and consists of collagen and elastic fibers
- Veins lack internal or externa elastic laminae
- Distensible enough to adapt to variations in the volume and pressure of blood passing through them but not designed to withstand high pressure
- Lumen of a vein is larger than a comparable sized artery, often appears collapsed when sectioned.
Valves – thin folds of tunica interna that form flaplike cusps projecting into the lumen, pointing toward the heart.
- Prevent back flow of blood
vascular sinus or venous sinus – a vein with a thin endothelial wall that lacks a tunica media and tunica externa and is supported by surrounding tissue.
- Has no smooth muscle to alter its diameter.
- The surrounding dense connective tissue replaces the tunica media and externa in providing support
- Ex. Dural venous sinuses – supported by the dura mater, convey deoxygenated blood from brain to the heart
- Ex. 2 Coronary sinus of the heart
anastomotic veins – channels that cross the artery accompanying paired veins connecting in ladder like rungs
superficial veins – veins located in the subcutaneous layer deep to the skin
- Course through the subcutaneous layer unaccompanied by parallel arteries
- Amount of blood flow in superficial veins varies from location to location within the body.
- Connected to the superficial veins by anastomoses.
deep veins – veins that travel between the skeletal muscles.
- One way valves allow blood to pass from superficial to deep veins i. Malfunction of these valves develops varicose veins.
blood reservoirs – systemic veins and venules that contain large amounts of blood that can be moved quickly to parts of the body requiring the blood.
- 64% of blood is in the system veins and venules at any given time
- Principle blood reservoirs are veins of the abdominal organs (esp. Liver and spleen) and the veins of the skin.
outline the vessels through which the blood moves in its passage from the heart to the capillaries and back.
Venoconstriction – constriction of veins which reduces the volume of blood in reservoirs and allows a greater blood volume to flow to skeletal muscles
Identify, in order, the vessels through which the blood moves in its passage from the heart to the
capillaries and back.
A. arteries
B. arterioles
C. capillaries
D. venules
E. Veins
discuss the pressures that cause movement of fluids between capillaries and interstitial spaces.
capillary exchange - the movement of substances between blood and interstitial fluid
Diffusion – most important method of capillary exchange
- Substances that enter and leave capillaries by simple diffusion: O2, CO2, glucose, amino acids, hormones
- O2 and nutrients are normally present in higher concentration in the blood, diffuse down concentration gradient into interstitial fluid and then body cells
- CO2 and other wastes diffuse from cells to interstitial fluid and into blood
- Substances can cross the walls of a capillary by diffusing through the intercellular clefts or fenestrations or by diffusing through the endothelial cells.
- Intercellular clefts or fenestrations: water soluble substances such as glucose and amino acids
- Directly through lipid-bilayer of endothelial cell plasma membranes: lipid soluble materials such as O2, CO2, steroid hormones
- Sinusoids allow proteins and blood cells to pass through their walls
- Brain capillaries contain tight junctions; only select materials pass through = BBB 1. Areas in the brain that lack the BBB undergo capillary exchange more freely (Hypothalamus, pineal gland, pituitary gland)
Transcytosis – substances that cross cells by endocytosis within pinocytic vesicles, move across the cell, and exit on the other side by exocytosis.
- Important for large lipid insoluble molecules that cannot cross capillary walls in any other way. i. Ex. Hormone insulin, certain antibodies (also proteins) pass from maternal circulation into fetal circulation by transcytosis
bulk flow – passive process by which large numbers of ions, molecules, or particles in a fluid move together in the same direction
- The substances move at rates far greater than can be accounted by diffusion alone
- Occurs from an area of higher pressure to lower pressure, continues as long as a pressure difference exists.
- Important for the regulation of relative volumes of blood and interstitial fluid
- The flow of a liquid through a filter (or membrane that acts like a filter) due to a hydrostatic pressure; occurs in capillaries due to blood pressure
Filtration – pressure driven movement of fluid and solutes from blood capillaries into interstitial fluid
Reabsorption – pressure driven movement from interstitial fluid into blood capillaries
net filtration pressure (NFP) - the balance of 3 pressures that promote filtration and reabsorption
- The balance of these 3 pressures determines whether the volumes of blood and interstitial fluid remain steady or change
Starling law of the capillaries – near equilibrium where the volume of fluid and solutes reabsorbed is normally almost as large as the volume filtered.
blood hydrostatic pressure (BHP) - the pressure generated by the pumping action of the heart
- Within vessels, the hydrostatic pressure is due to the pressure that water in blood plasma exerts against blood vessel walls
- About 35mmHg at the arterial end of a capillary, about 16mmHg at the capillary’s venous end.
- BHP “pushes” fluid out of capillaries into interstitial fluid
interstitial fluid hydrostatic pressure (IFHP) - the opposing pressure of the interstitial fluid
- IFHP “pushes” fluid from interstitial spaces back into capillaries
- Close to zero but difficult to measure, varies from very small positive to very small negative values
- Assume IFHP = 0mmHg all along the capillaries.
Edema – an abnormal accumulation of interstitial fluid
a. When filtration greatly exceeds reabsorption
b. Not usually detectable in tissues until interstitial fluid volume is 30% above normal
c. Excess filtration or inadequate reabsorption
1. Excess filtration
- Increased capillary blood pressure causes more fluid to be filtered from capillaries
- Increased permeability of capillaries raises interstitial osmotic pressure by allowing some plasma proteins to escape. Such leakiness may be caused by chemical, bacterial, thermal, or mechanical agents on capillary walls
-
Inadequate reabsorption 1. Decreased concentration of plasma proteins that lowers the blood colloid osmotic pressure. Inadequate synthesis or dietary intake or loss of plasma proteins is associated with liver disease, burns, malnutrition, and kidney disease.
- Averages 26 mmHg in most capillaries
blood colloid osmotic pressure (BCOP) - a force caused by the colloidal suspension of large proteins in plasma
- Effect is to “pull” fluid from interstitial spaces into capillaries
- The largest driving force for pulling fluid from the interstitial spaces back into the capillaries
interstitial fluid osmotic pressure (IFOP) - opposes BCOP
- “pulls” fluid out of capillaries into interstitial fluid
- Normally very small, 0.1-5mmHg because only tiny amounts of protein are present in interstitial fluid.
- The small amount of protein that leaks from blood plasma into interstitial fluid does not accumulate there because it passes into lymph in lymphatic capillaries and is eventually returned to the blood.
XIII. NFP = (BHP + IFOP) - (BCOP + IFHP)
- = pressures that promote filtration – pressures that promote reabsorption
- The balance of pressures determines whether fluid leaves or enters capillaries
- At the arterial end of a capillary, NFP is about 10mmHg, at the venous end it is about –9mmHg so fluid is filtered at the arterial end and reabsorbed at the venous end. a. About 85% of the fluid filtered out is reabsorbed, the remainder and the few plasma proteins that escape into interstitial fluid enter lymphatic capillaries.
explain the factors that regulate the volume of blood flow.
hemodynamics: factors affecting blood flow
blood flow – the volume of blood that flows through any tissue in a given time (in mL/min)
blood pressure – the force exerted by blood against the walls of blood vessels due to contraction of the heart. Influenced by the elasticity of the vessel walls.
- Clinically, a measure of the pressure in arteries during ventricular systole and diastole.
systolic blood pressure – force exerted by blood on arterial walls during ventricular contraction TOP
diastolic blood pressure – force exerted by blood on arterial walls during ventricular relaxation BOTTOM
mean arterial blood pressure (MAP) - average blood pressure in arteries, roughly 1/3 between diastolic and systolic. MAP = 1/3(SBP) + 2/3(DBP)
Pulse pressure SBP - DBP
vascular resistance – the opposition to blood flow due to friction between blood and the walls of blood vessels. a. 3 factors: size of lumen, blood viscosity, total blood vessel length.
size of lumen – the smaller the lumen, the greater the resistance. Vasoconstriction narrows the lumen, BP rises, vasodilation widens it, BP drops.
blood viscosity – depends mostly on the ratio of RBCs to plasma volume and a small bit on concentration of proteins in plasma.
- Higher viscosity = high resistance.
- Any condition that increases viscosity: dehydration, polycythemia (high RBC #), etc increases BP
- Loss of plasma proteins or RBCs (ex. Anemia or hemorrhage) decreases viscosity and BP.
total blood vessel length – resistance to blood flow through a vessel is directly proportional to the length of the blood vessel.
- Longer vessel = more resistance
- Obesity = more blood vessels = greater total length = hypertension
systemic vascular resistance (SVR) or total peripheral resistance (TPR) - refers to all of the vascular resistances offered by systemic blood vessels
- Vein and artery diameter is large, offer little resistance.
- Most resistance comes from arterioles, capillaries, and venules
- Arterioles control SVR and therefore BP and blood flow to tissues, by changing their diameter. i. Only a slight change in diameter = large effect on SVR.
- Main center for regulation of SVR is in the vasomotor center in the brain stem.
Increases:
a) Decreased diameter of systemic arterioles
b) Increased blood viscosity
d) Increased vasoconstriction of systemic arterioles
e) Increased red blood cell count
(NOT c) Decreased length of the systemic circulatory route)
venous return – the volume of blood flowing back to the heart through systemic veins
- Occurs due to the pressure generated by contractions of the heart’s left ventricle.
- Pressure difference from venules (average 16mmHg) to the right ventricle (0mmHg) is usually sufficient to cause venous return to the heart.
- Pressure increase in the right atrium or ventricle will cause decreased venous return
- Two mechanisms help pump blood from lower body back to the heart: skeletal muscle pump, respiratory pump
All aid in venous return:
a) the skeletal muscle pump.
b) the respiratory pump.
d) venoconstriction
e) venous valves.
(NOT c) blood viscosity.)
explain how blood pressure changes throughout the cardiovascular system.
control of blood pressure and blood flow - several negative feedback systems control BP by adjusting heart rate, stroke volume, SVR, and blood volume.
Increseas arterial blood pressure:
a) Increased blood volume
b) Increased sympathetic stimulation
c) Increased heart rate
d) Increased stroke volume
(NOT INCREASED ARTERIOLAR VASODILATION)
cardiovascular (CV) center - in the medulla oblongata
- Helps regulate heart rate, stroke volume, force of contraction, and blood vessel diameter
- Some neurons stimulate the heart (cardiostimulatory center), others inhibit the heart (cardioinhibitory center), others control blood vessel diameter (vasoconstrictor center or vasodilator center)
- CV center receives input from both higher brain regions and sensory receptors
- Cerebral cortex, limbic system (ex. anticipatory response prior to running a race), and hypothalamus (ex. Temp change stimulates CV center to dilate vessels, increases heat loss) send nerve impulses that affect the CV center
- 3 main sensory receptor types that provide input to the CV center: proprioceptors, baroreceptors, chemoreceptors
Proprioceptors – monitor movements of joints and muscles and provide input to the CV center during physical activity i. Their activity accounts for the rapid increase in heart rate at the beginning of exercise
Baroreceptors - monitor changes in pressure and stretch in the walls of blood vessels (Increased systemic vascular resistance)
Chemoreceptors – monitor the concentration of various chemicals in the blood.
cardiac accelerator nerves – pathway for sympathetic impulses to reach the heart from the CV center i. Increase in sympathetic stimulation increases heart rate and contractility. Decrease = opposite
vagus (X) nerves – pathway for parasympathetic stimulation to reach the heart from the CV center
- Parasympathetic stimulation decreases heart rate
- The opposing sympathetic and parasympathetic influences control the heart.
vasomotor nerves – pathway for CV center to send impulses to smooth muscle in blood vessel walls.
- Sympathetic neurons that exit the spinal cord through all thoracic and first one or two lumbar spinal nerves and then pass into the sympathetic trunk ganglia.
- From there, impulses propagate along sympathetic neurons that innervate blood vessels in viscera and peripheral areas.
- Vasomotor region of CV continually sends impulses over these routes to arterioles throughout body, especially in skin and abdominal viscera.
vasomotor tone – moderate state of tonic contraction or vasoconstriction that results from the continual impulses from CV center to smooth muscle in arterioles throughout the body. i. Sets the resting level of systemic vascular resistance.
neural regulation of blood pressure – nervous system regulates BP via negative feedback loops that occur as two types of reflexes: baroreceptor and chemoreceptor reflexes.
- baroreceptor reflexes - two most important are carotid sinus reflex and the aortic reflex. Baroreceptors are pressure sensitive sensory receptors. Located in aorta, internal carotid arteries, and other large arteries in the neck and chest. Send impulses to the CV center to help regulate BP.
- carotid sinus reflex – reflex that helps regulate BP in the brain.
- Carotid sinus – small widenings of the R and L internal carotid arteries just superior to where they branch from the common carotid arteries.
- BP stretches the wall of the carotid sinus which stimulates the baroreceptors.
- Nerve impulses propagate from carotid sinus baroreceptors over sensory axons in the glossopharyngeal (IX) nerves to the CV center in the medulla oblongata.
- aortic reflex – a reflex that helps maintain normal systemic BP
- Baroreceptors in the wall of the ascending aorta and arch of the aorta initiate the aortic reflex
- Nerve impulses from aortic baroreceptors reach the CV center via sensory axons of the vagus (X) nerves.
Mechanism of reflex:
- BP falls – baroreceptors stretched less
- Nerve impulses sent more slowly to CV center
- CV center decreases parasympathetic stimulation of the heart via motor axons of the vagus nerves and increases sympathetic stimulation of the heart via cardiac accelerator nerves
- Increase sympathetic activity also increases epinephrine and norepinephrine, causing the heart to beat faster and more forcefully
- Increase in BP makes baroreceptors send impulses faster, CV center increases parasympathetic stimulations and decreases sympathetic.
- Result is decreased heart rate and force of contraction. Vasodilation lowers systemic vascular resistance. BP is lowered.
chemoreceptor reflexes - detect presence of certain chemicals.
- carotid bodies – cluster of chemoreceptors on or near the carotid sinus that respond to changes in blood levels of O2, CO2, and H+ ions
- aortic bodies – cluster of chemoreceptors on or near the arch of the aorta that respond to changes in blood levels of O2, CO2, and H+ ions.
- Respond to hypoxia (low O2 availability), acidosis (increase H+ concentration) or hypercapnia (CO2 excess)
- Also provide input to the respiratory center in the brain stem to adjust breathing rate.
hormonal regulation of blood pressure - several hormones help regulate BP and blood flow by altering cardiac output, changing SVR, or adjusting the total blood volume.
renin angiotensin aldosterone (RAA) system
- Renin – secreted into bloodstream by juxtaglomerular cells in kidneys. 1. Renin and angiotensin-converting enzyme (ACE) act on their substrates to produce the active hormone angiotensin II
- angiotensin II - raises BP in two ways
- Angiotensin II is a potent vasoconstrictor, raising BP by increasing systemic vascular resistance
- Stimulates secretion of aldosterone
- Aldosterone - increases reabsorption of Na+ ions and water by the kidneys. 1. Water reabsorption increases total blood volume, increasing BP
epinephrine and norepinephrine - released by the adrenal medulla in response to sympathetic stimulation
- Increase cardiac output by increasing rate and force of heart contractions
- Also cause vasoconstriction of arterioles and veins in skin and abdominal organs and vasodilation of arterioles in cardiac and skeletal muscles, helping increase blood flow to muscle during exercise
antidiuretic hormone (ADH) or vasopressin - produced by the hypothalamus, released from posterior pituitary in response to dehydration or decreased blood volume
- Causes vasoconstriction, increasing BP
- Also promotes water retention from lumen of kidney tubules back into blood stream, increasing blood volume and decreasing urine output
- Lowers BP by causing vasodilation and promoting loss of salt and water in the urine, reducing blood volume.
atrial natriuretic peptide (ANP) - released by cells in atria of the heart.
autoregulation of blood flow
Autoregulation - the ability of a tissue to automatically adjust its blood flow to match its metabolic demands.
- Important in cardiac and skeletal muscle where demand for O2 and nutrient/waste removal can increase 10-fold during physical activity. 1. By contributing to increased blood flow through the tissue
- Also controls regional blood flow in the brain 1. Blood distribution to various parts changes for different mental and physical activities 1. Ex. While talking, high blood flow to motor speech area, while listening, high blood flow to auditory areas.
myogenic response - by smooth muscle in arteriole walls
i. Contracts more forcefully when stretched, relaxes when stretching lessens 1. Ex if blood flow through an arteriole decreases, stretching of the arteriole walls decreases, which results in smooth muscle relaxing and producing vasodilation which increases blood flow.
vasodilating and vasoconstricting chemicals - several types of cells: WBC, platelets, smooth muscle fibers, macrophages, and endothelial cells, release a variety of chemicals that alter blood-vessel diameter.
- Vasodilating chemicals – From metabolically active cells: K+, H+ lactic acid (lactate), adenosine (from ATP), from endothelial cells: nitric oxide (NO), from tissue trauma or inflammation: kinins and histamine
- Vasoconstrictors – thromboxane A2, superoxide radicals, serotonin (from platelets), and endothelins (from endothelial cells)
Important to note – difference between pulmonary and systemic circulation responses to low O2 levels
- Systemic circulation dilates in response to low O2, increasing blood flow and delivery of O2
- Pulmonary circulation constricts in response to low O2, decreasing blood flow through oxygen-poor alveoli and sending blood to better-ventilated areas of the lungs.XII. skeletal muscle pump – blood vessels contained within leg muscles are compressed and relax alternately. This causes valves to open and close leading blood upward toward the heart.
respiratory pump – also based on alternating compression and decompression of veins. During inhalation, diaphragm moves downward, causes decrease in thoracic cavity pressure and increase in abdominal cavity pressure. Therefore abdominal veins are compressed, blood moves from compressed abdominal veins into the decompressed thoracic veins and then to right atrium. During exhalation, valves in veins prevent backflow from thoracic to abdominal veins
velocity of blood flow – speed of blood flow in cm/sec.
- Inversely related to the cross-sectional area.
- Velocity is the slowest where the total cross sectional area is the greatest – Ex. Capillaries have huge cross-sectional area and blood flows very slowly (0.1cm/sec) while aorta is much smaller cross sectional area and flows 40cm/sec.
- Each branch in an artery increases cross sectional area.
- Each site of two veins joining decreases cross sectional area
circulation time – time required for a blood cell to pass from right atrium, through pulmonary circulation, to left atrium, through systemic circulation down to the foot, and back to the right atrium
- In a resting person, normally about 1 minute.
describe the factors that determine mean arterial pressure and systemic vascular resistance.
describe the relationship between cross-sectional area and velocity of blood flow.
describe how blood pressure is regulated.
define pulse and systolic, diastolic, and pulse pressures.
checking circulation
- Pulse – the rhythmic expansion and elastic recoil of a systemic artery after each contraction of the left ventricle.
- Tachycardia – resting heart rate over 100 bpm
- Bradycardia – resting heart rate below 50 bpm measuring blood pressure
- blood pressure – refers to the pressure in arteries generated by the left ventricle during systole and the pressure remaining in the arteries when the ventricle is in diastole. a. Usually measured in the brachial artery in left arm
- Sphygmomanometer – blood pressure measuring device
- systolic blood pressure (SBP) - first sound heard upon releasing air from the BP cuff
- diastolic blood pressure (DBP) - the force exerted by the blood remaining in arteries during ventricular relaxation. Measured by when the pulse sounds disappear while measuring BP
- Korotkoff sounds – the sounds heart while taking BP.
- pulse pressure – the difference between systolic and diastolic pressure
- Normally about 40mmHg
- Provides info about the condition of the cardiovascular system i. Ex. Conditions such as atherosclerosis and patent ductus arteriosus increase pulse pressure greatly
- The normal ratio of systolic to diastolic to pulse pressures is 3:2:1
Common pulse points: : superficial temporal artery, brachial artery and common carotid artery
Wrist pulse point: radial artery
define shock.
Shock – failure of the cardiovascular system to deliver enough oxygen and nutrients to meet cellular metabolic needs.
- Varied causes of shock but all are characterized by inadequate blood flow to body tissues
- Cells switch from aerobic to anaerobic production of ATP, lactic acid accumulates in body fluids
- If shock persists, cells and organs become damaged, and cells may die unless proper treatment begins quickly
- Homeostatic mechanisms can compensate for up to 10% blood volume drop.
- At more than 10-20% blood volume loss or if the heart cannot bring BP up sufficiently, compensatory mechanisms may fail to maintain adequate blood flow to tissues. Shock becomes lifethreatening, damaged cells start to die.
describe the four types of shock.
4 types of shock: hypovolemic shock, cardiogenic shock, vascular shock, and obstructive shock
- hypovolemic shock – decreased blood volume
- Common cause: acute hemorrhage from internal or external bleeding
- Also caused by loss of body fluids through excessive sweating, diarrhea, or vomiting
- DM can cause excessive loss of fluid in the urine
- Finally, may be caused by inadequate intake of fluid
- Volume of body fluid falls, venous return to heart declines, filling of heart lessens, stroke volume decreases, cardiac output decreases
a) Adrenal cortex releases aldosterone.
b) Kidneys conserve salt and water.
c) Heart rate increases.
e) Heart contractility increases.
(NOT d) Systemic arterioles vasodilate.)
- a) Activation of the renin-angiotensin-aldosterone (RAA) system.
b) Secretion of antidiuretic hormone (ADH)
c) Activation of the sympathetic division of the ANS.
e) Release of local vasodilators. - (NOT d) Release of atrial natriuretic peptide (ANP).)
- Treatment – replacing fluid volume ASAP
2. cardiogenic shock – poor heart function
- Heart fails to pump adequately, most often due to an MI
- Other causes include poor perfusion of the heart (ischemia), heart valve problems, excessive preload or afterload, impaired contractility of heart muscle fibers, and arrhythmias
3.vascular shock – inappropriate vasodilation
- Ex. Anaphylactic shock – releases histamine and other mediators that cause vasodilation
- Ex. Neurogenic shock – vasodilation may occur following trauma to the head that causes malfunction of the cardiovascular center in the medulla.
- Ex. Septic shock – stemming from certain bacterial toxins that produce vasodilation.
4. obstructive shock – obstruction of blood flow
- Occurs when blood flow through a portion of the circulation is blocked
- Ex. Pulmonary embolism – a blood clot lodged in a blood vessel of the lungs.
explain how the body’s response to shock is regulated by negative feedback.
homeostatic responses to shock with the feedback systems – negative feedback systems that work to return cardiac output and arterial blood pressure to normal
Cardiac output dependent on heart rate and stroke volume.
Activation of the renin-angiotensin-aldosterone system
- Decreased blood flow to the kidneys causes the kidneys to secrete renin and initiates the renin-angiotensin-aldosterone system. 1. Angiotensin II causes vasoconstriction and stimulates the adrenal cortex to secrete aldosterone which increases reabsorption of Na+ and water by the kidneys. The increases in systemic vascular resistance and blood volume help raise blood pressure
Secretion of antidiuretic hormone
- In response to decrease BP, the posterior pituitary releases more ADH.
- ADH enhances water reabsorption by the kidneys, which conserves remaining blood volume
- It also causes vasoconstriction which increases systemic vascular resistance.
Activation of the sympathetic division of the ANS
- As BP decreases, aortic and carotid baroreceptors initiate powerful sympathetic responses throughout the body.
- Vasoconstriction of arterioles and veins of the skin, kidneys, and other abdominal viscera (vasoconstriction does not occur in the brain or heart)
- Constriction of arterioles increases systemic vascular resistance, and constriction of veins increases venous return. 1. Both effects help maintain an adequate BP.
Sympathetic stimulation also increases heart rate and contractility and increases secretion of epinephrine and norepinephrine by the adrenal medulla.
- These hormones intensify vasoconstriction and increase heart rate and contractility, all of which Release of local vasodilators
- In response to hypoxia, cells liberate vasodilators, including K+, H+, lactic acid, adenosine, and nitric oxide, that dilate arterioles and relax precapillary sphincters.
- Such vasodilation increases local blood flow and may restore )2 level to normal in part of the body.
- However, vasodilation also has the potentially harmful effect of decreasing systemic vascular resistance and thus lowering BP.
signs and symptoms of shock
- Systolic BP is less than 90mmHg
- Resting heart rate is rapid due to sympathetic stimulation and increased blood levels of epinephrine and norepinephrine
- Pulse is weak and rapid due to reduced cardiac output and fast heart rate
- Skin is cool, pale, clammy due to sympathetic constriction of skin blood vessels and sympathetic stimulation of sweating
- Mental state is altered due to reduced O2 to the brain
- Urine formation is reduced due to increased levels of aldosterone and ADH
- Person is thirsty due to loss of extracellular fluid
- PH of blood is low (acidosis) due to buildup of lactic acid
- Person may have nausea because of impaired blood flow to the digestive organs from sympathetic vasoconstriction
define systemic circulation and explain its importance.
circulatory routes
systemic circulation - includes all routes that oxygenated blood flows through from left ventricle through the aorta to all organs of the body and deoxygenated blood returns to the right atrium.
- coronary circulation - subdivision of systemic circulation that supplies the myocardium of the heart
- cerebral circulation - subdivision of systemic circulation that supplies the brain
- All systemic arteries branch from the aorta
- Nutrient arteries supplying the lungs are part of systemic circulation
- All veins of the systemic circulation drain into the superior vena cava, inferior vena cava, or coronary sinus which all in turn empty into the right atrium
hepatic portal circulation - blood flow from the GI organs to the liver before returning to the heart
- Carries venous blood from GI organs and spleen to the liver
- Hepatic portal vein receives blood from capillaries of GI organs and spleen and delivers it to the sinusoids of the liver.
- Superior mesenteric and splenic veins unite to form the hepatic portal vein.
- After a meal, hepatic portal blood is rich in nutrients from GI tract, the liver stores some and modifies some before they pass into generalcirculation i. Liver converts glucose to glycogen for storing, detoxifies harmful substances such as alcohol, and destroys bacteria by phagocytosis
- Superior mesenteric vein – drains blood from small intestine, portions of large intestine, stomach, and pancreas
- Splenic vein – drains blood from stomach, pancreas, and portions of large intestine
- Inferior mesenteric veins drain portions of the large intestine and drain into the splenic vein
- Right and left gastric veins drain the stomach and open directly into the hepatic portal vein i. Cystic vein drains the gall bladder directly into the hepatic portal vein
- Hepatic veins – blood leaves sinusoids of liver through the hepatic veins which drain into the inferior vena cava.
pulmonary circulation - the flow of deoxygenated blood from right ventricle to the lungs and return of oxygenated blood from lungs to left atrium.
a. Pulmonary trunk – emerges from right ventricle, passes superiorly, posteriorly, and to the left. Then divides into two branches:
- Right pulmonary artery
- Left pulmonary artery
- On entering lungs, the arteries subdivide to form capillaries around the alveoli within the lungs.
b. Pulmonary veins – exit the lungs carrying oxygenated blood to the left atrium. \i. Two left and two right pulmonary veins enter the left atrium.
fetal circulation - exists only in the fetus, contains special structures that allow the developing fetus to exchange materials with mother.
- Differs from postnatal circulation because the lungs, kidneys, and GI organs do not function until after birth.
- Fetus obtains nutrients from maternal blood and eliminates wastes into it through the placenta by way of umbilical cord
- Placenta and mother’s CV system interact through many small blood
- Foramen ovale opeining b/w right and left atria
- When umbilical cord tied - arteries close by filling with connective tissue
identify the four principal divisions of the aorta.
locate the major arterial branches arising from each division.
