Transcript Cardiovascular System

Cardiovascular System
Blood Vessels and Hemodynamics
Dr. Michael P. Gillespie
Cardiovascular System
 Transports and delivers blood to the body to deliver oxygen,
nutrients, and hormones as well as carries away wastes.
 Blood vessels form a closed system of tubes, which carries
blood away from the heart, transports it to the tissues of the
body, and then returns it to the heart.
Hemodynamics
 Hemo – blood.
 Dynamics – power.
Main Types Of Blood Vessels
 Arteries – carry blood away from the heart.
 Arterioles – very small arteries.
 Capillaries – tiny vessels which allow exchange of substances
between the blood and body tissues.
 Venules – very small veins.
 Veins – carry blood back to the heart.
Vaso Vasorum
 Larger blood vessels require oxygen and nutrients just like
other tissues of the body.
 Vaso vasorum (vasculature of the vessels) are located within
the walls of larger vessels and supply them.
Tunics (Coats) Of Arteries
 Tunica interna (intima) – contains a lining of endothelium
which makes contact with the lumen and blood.
 Tunica media – thickest layer and has high compliance
(stretches).
 Tunica externa – outer coat, elastic and collagen fibers.
Changes In Vascular Diameter
 Vasoconstriction – a decrease in the diameter of the lumen of
a blood vessel.
 Sympathetic stimulation causes the smooth vessels of the vessels
to contract, squeezing the vessel wall and narrowing the lumen.
 Occurs when an artery or an arteriole is damaged, producing
vascular spasm and limiting the blood flow to reduce blood loss.
Changes In Vascular Diameter
 Vasodilation – an increase in the diameter of the lumen of a
blood vessel.
 Occurs when sympathetic stimulation decreases or when nitric
oxide, K+, H+, and lactic acid are present.
Elastic Arteries
 Elastic arteries propel blood forward while the ventricles
are relaxing.
 Blood is ejected from the heart and stretches the walls of
the elastic arteries.
 The stretch of the arteries stores mechanical energy and
act as a pressure reservoir.
 The vessels recoil and convert stored (potential) energy
in the vessel into kinetic energy of the blood.
Muscular Arteries
 Medium sized arteries are muscular arteries.
 They contain more smooth muscle and fewer elastic
fibers than elastic arteries.
 They are capable of greater vasoconstriction and
vasodilation.
 They are called distributing arteries because they
distribute blood to various parts of the body.
Arterioles
 A very small (almost microscopic) artery that delivers
blood to capillaries.
 Arterioles regulate resistance.
 Vasoconstriction of arteriole walls increases resistance to
capillaries and vasodilation of arteriole walls decreases
resistance.
 Resistance regulates blood flow to the capillaries.
Capillaries
 Microscopic vessels that connect arterioles to venules.
 The flow of blood from arterioles to venules is
microcirculation.
 Tissues with high metabolic requirements, such as
muscles, liver, kidneys, and nervous system, have more
capillaries.
 Tissues with lower metabolic requirements, such as
tendons and ligaments, contain fewer capillaries.
Capillaries
 Capillaries are absent in a few tissues, such as covering and
lining epithelia, the cornea of the lens of the eyes, and
cartilage.
 Exchange vessels – exchange nutrients between blood and
tissue cells through the interstitial fluid.
Capillaries
 Single layer of endothelial cells.
 Branch extensively to increase surface area for exchange.
 Usually only a small part of the capillary network is active;
However, when a tissue is active (i.e. Contracting muscle) the
entire network fills with blood.
Metarteriole
 A metarteriole (met = beyond) – is a vessel that
emerges from an arteriole and supplies a group of 10 –
100 capillaries (capillary bed).
 The proximal end of the metarteriole is surrounded by
smooth muscle fibers, which regulate blood flow
through the capillary bed.
 The distal end of the metarteriole has a thoroughfare
channel, which bypasses the capillary bed.
True Capillaries
 True capillaries emerge from arterioles or metarterioles.
 Precapillary sphincter – ring of smooth muscle that
controls blood flow into a true capillary.
 Vasomotion – intermittent contraction and relaxation
of precapillary sphincters and metarteriole smooth
muscle (5-10 times per minute).
Types Of Capillaries
 Continuous capillaries  Continuous tube interrupted only by intercellular clefts.
 Found in smooth muscle, connective tissue, and lungs.
Types Of Capillaries
 Fenestrated capillaries (fenestr = window)  The plasma membranes have fenestrations (small pores).
 Located in the kidneys, villi of the SI, choroid plexus of the
ventricles of the brain, cilary processes of the eyes, and
endocrine glands.
Types Of Capillaries
 Sinusioids –
 Wider and more winding than other capillaries.
 Unusually large fenestrations which allow protein and blood to
pass from the tissues into the bloodstream.
 Found in the liver, spleen, anterior pituitary, and parathyroid
glands.
Venules
 Small veins formed when several capillaries unite.
 The walls of the smallest venules (closest to the capillaries)
are very porous and serve as a site of emigration for white
blood cells.
Veins
 Veins contain the same three coats as arteries.
 The lumen of a vein is larger than that of a comparable
artery.
Veins
 Many veins also contain valves (especially in the lower limbs).
 The valves are thin folds of the tunica interna. The cusps
point toward the heart.
 The valves prevent backflow of returning blood in the lower
pressure venous system.
Vascular (Venous) Sinus
 A vascular (venous) sinus is a vein with a thin endothelial wall
that has no smooth muscle to alter its diameter.
 Examples:
 Dural venous sinuses (supported by dura mater).
 Coronary sinus of the heart.
Varicose Veins
 Leaky valves can cause veins to become dilated and
twisted in appearance.
 This is most common in the esophagus and veins of the
lower limb, although it can occur in any veins.
 Hemorrhoids are varicose veins in the anal canal.
 Deeper veins are not as susceptible because surrounding
skeletal muscles prevent their walls from stretching.
Anastomoses
 The union of the branches of two or more arteries
supplying the same body region is called an
anastomosis.
 Anastomoses between arteries provide alternate routes
for blood to reach a tissue or an organ.
 The alternate route of blood flow is known as
collateral circulation.
 Arteries that do not anastomose are known as end
arteries.
Blood Distribution
 The largest portion of your blood volume at rest is in the
veins (60%).
 Systemic capillaries hold about 5%.
 The veins and venules function as a blood reservoir.
 Blood can be diverted quickly if the need arises through
venoconstriction.
 The veins of the abdominal organs and skin serve as
principal blood reservoirs.
Capillary Exchange
 The mission of the cardiovascular system is to keep blood
flowing through the capillaries to allow for exchange of
nutrients and waste products with the interstitial fluid.
 Substances enter and leaved the capillaries through three
basic mechanisms:
 Diffusion.
 Transcytosis.
 Bulk flow.
Diffusion
 Substances diffuse down their concentration gradients (from
areas of high concentration to low).
 All plasma solutes except proteins pass easily across most
capillary walls.
 Water soluble substances such as glucose and amino acids
pass easily through either fenestrations or intercellular clefts.
Diffusion
 Lipid-soluble materials (O2, CO2, & steroid hormones)
pass through the lipid bilayer.
 Liver capillaries have large gaps which do allow proteins
to pass through. Hepatocytes synthesize proteins such as
fibrinogen (clotting) and albumin (osmotic pressure),
which diffuse into the blood.
 Brain capillaries have tight junctions, which allow only a
few substances to enter and leave. This forms the bloodbrain barrier.
Transcytosis
 Substances within the blood plasma are enclosed in tiny
pinocytic vesicles that enter endothelial cells by endocytosis.
 They move across the membrane and exit the other side by
exocytosis.
Transcytosis
 This method of transport is utilized for large, lipid-insoluble
molecules that cannot cross the capillary walls in any other
way.
 Insulin enters the blood this way and some maternal
antibodies enter the fetal circulation this way.
Bulk Flow: Filtration &
Reabsorption
 Bulk flow is a process by which large numbers of ions,
molecules, or particles in a fluid move together in the same
direction.
 It occurs from an area of high pressure to an area of low
pressure at a rate faster than diffusion would produce alone.
 Regulates relative volumes of fluids rather than
concentrations of solutes.
Bulk Flow: Filtration &
Reabsorption
 Continues as long as pressure variances exist.
 Pressure driven movement of fluid and solutes from blood
capillaries to interstitial fluid is termed filtration.
 Pressure driven movement of fluid and solutes from
interstitial fluid into blood capillaries is called reabsorption.
Pressures Involved In Filtration And
Absorption
 Blood hydrostatic pressure (BHP) – pressure from the
pumping action of the heart promotes filtration.
 Interstitial fluid osmotic pressure filters blood promotes
filtration.
Pressures Involved In Filtration And
Absorption
 Blood colloid osmotic pressure (BCOP) promotes
reabsorption.
 Interstitial fluid hydrostatic pressure promotes reabsorption.
 Net filtration pressure is the balance of these pressures
(NFP).
Starling’s Law Of The Capillaries
 The volume of fluid and solutes reabsorbed normally is
almost as large as the volume filtered.
Edema
 If filtration greatly exceeds reabsorption, the result is edema
(swelling), an abnormal increase in interstitial fluid volume.
Excess Filtration
 Increased capillary blood pressure.
 Increased permeability of capillaries which allows plasma
proteins to escape. Chemical, bacterial, thermal, or
mechanical agents can damage capillary walls.
Inadequate Reabsorption
 Decreased concentration of plasma proteins associated with
liver disease, burns, malnutrition, and kidney disease.
Hemodynamics
 Hemodynamics refer to the factors that affect blood flow.
 Blood flow is the volume of blood that flows through any
tissue in a given period of time.
 Cardiac output (CO) is the total blood flow.
 Cardiac output (CO) – heart rate (HR) * stroke volume
(SV).
Factors That Determine Distribution Of
Cardiac Output
 Pressure difference drives blood flow through a tissue.
 Blood flows from regions of higher to lower pressure.
 Resistance to blood flow in specific blood vessels.
 The higher the resistance, the smaller the blood flow.
Blood Pressure
 Contraction of the ventricles generates blood pressure (BP).
 Systolic blood pressure is the highest pressure attained in the
arteries during systole.
Blood Pressure
 Diastolic blood pressure is the lowest arterial pressure
during diastole.
 Mean arterial blood pressure (MABP) is the average
pressure in the arteries.
 MABP = diastolic BP + 1/3 (systolic BP – diastolic BP).
 Blood pressure also depends on the total volume of
blood in the cardiovascular system.
Resistance
 Vascular resistance is the opposition to blood flow due to
friction between blood and the walls of blood vessels.
 Vascular resistance depends upon:
 The size of the blood vessel lumen.
 Blood viscosity.
 Total blood vessel length.
 Systemic vascular resistance (SVR) is the total peripheral
resistance from all factors combined.
Venous Return
 Venous return to the heart is caused by the following:
 Pressure generated from contractions of the heart’s left
ventricle.
 Skeletal muscle pump.
 Respiratory pump.
Velocity Of Blood Flow
 The speed or velocity of blood flow is inversely related to the
cross-sectional area.
 Each time an artery branches, the cross sectional area
increased and the velocity decreases.
 Each time a venule merges to form a vein, the cross sectional
area decreases and the velocity increases.
Syncope
 Syncope, or fainting, is a sudden, temporary loss of
consciousness that is not due to head trauma.
Syncope
 It is commonly due to cerebral ischemia.
 Causes:
 Vasodepressor syncope – sudden emotional stress.
 Situational syncope – pressure stress associated with urination,
defecation, or severe coughing.
 Drug-induced syncope – antihypertensives, diuretics,
vasodilators, & tranquilizers.
 Orthostatic hypotension – an excessive decrease in blood
pressure that occurs upon standing up.
Control Of Blood Pressure & Blood
Flow
 Negative feedback systems control blood pressure by
adjusting the following factors:
 Heart rate.
 Stroke volume.
 Systemic vascular resistance.
 Blood volume.
Cardiovascular Center
 The cardiovascular (CV) center of the medulla oblongata
regulates heart rate and stroke volume.
 Sympathetic nerves reach the heart via the cardiac
accelerator nerves. Sympathetic stimulation increases the
heart rate and contractility.
Cardiovascular Center
 Parasympathetic stimulation decreases the heart rate and is
conveyed by the vagus nerves (cranial nerve X).
 The CV center sends impulses to smooth muscle in blood
vessel walls via vasomotor nerves. They moderate the rate
of vasoconstriction (vasomotor tone).
Neural Regulation Of Blood
Pressure
 Baroreceptor Reflexes – baroreceptors are pressure-
sensitive receptors located in the aorta, internal carotid
arteries, and other large arteries of the neck and chest.
 Carotid sinus reflex – carotid sinuses are small widenings of the
right and left internal carotid arteries. Pressure stretches the
wall of the carotid sinus. Signals are sent to the CV center via
the glossopharyngeal nerves (CN IX).
 Aortic reflex – signals are sent to the CV center via the vagus
nerves (CN X).
Carotid Sinus Massage & Carotid Sinus
Syncope
 Carotid sinus massage involves massaging the neck over the
carotid sinus, to slow the heart rate in a person who has
paroxysmal superventricular tachycardia (originates in the
atria).
 Carotid sinus syncope – fainting due to excessive pressure on
the carotid sinus from hyperextension of the head or tight
collars.
Chemoreceptor Reflexes
 Chemoreceptors monitor the chemical composition of the
blood.
 They are located close to the baroreceptors in carotid bodies
and aortic bodies.
Chemoreceptor Reflexes
 They detect changes in blood level of O2, CO2, and H+.
 Hypoxia, acidosis, or hypercapnia stimulates the
chemoreceptors to send impulses to the cv center producing
sympathetic stimulation and vasoconstriction.
Hormonal Regulation Of Blood
Pressure
 Renin-angiotensin-aldosterone (RAA) system raises
blood pressure.
 Angiotensin II is a vasoconstrictor and stimulates aldosterone
which increases absorption of Na+ ions by the kidneys.
 Epinephrine and norepinephrine raise blood pressure.
 Increase cardiac output by increasing heart rate.
 Cause vasoconstriction of arterioles in the skin and abdomen
and vasodilatation of arterioles in cardiac and skeletal muscles.
Hormonal Regulation Of Blood
Pressure
 Antidiuretic hormone (ADH) raises blood pressure.
 Causes vasoconstriction.
 Atrial natriuretic peptide (ANP) lowers blood pressure.
 Causes vasodilatation and promotes loss of salt and water in the
urine.
Autoregulation Of Blood Pressure
 Physical changes.
 Warming promotes vasodilation and cooling causes
vasoconstriction.
 Myogenic response – smooth muscle contracts more forcefully
when it is stretched and relaxes when stretching lessens.
Autoregulation Of Blood Pressure
 Vasodilating and vasoconstricting chemicals.
 Vasodilating chemicals include K+, H+, lactic acid, ATP, and
nitric oxide (NO). Kinins and histamine are released from
tissue trauma and cause vasodilation.
 Vasoconstricting chemicals include thromboxane A2,
superoxide radicals, serotonin (from platelets), and endothelins.
Checking Circulation