The circulatory system transports blood, nutrients, oxygen, hormones, and other materials throughout the body. It consists of the cardiovascular system, which circulates blood, and the lymphatic system, which circulates lymph. Blood is pumped from the heart through arteries and returns to the heart through veins. The lymphatic system returns filtered blood plasma from tissues as lymph. Hemodynamics refers to the study of blood flow and circulation. Key factors that influence blood flow include blood pressure, vessel diameter, blood viscosity, and respiration.

1. HEMODYNAMICS
The circulatory system is an organ system that permits blood and lymph circulation to transport nutrients (such as amino acids
and electrolytes), oxygen, carbon dioxide, hormones, blood cells, etc. to and from cells in the body to nourish it and help to fight diseases,
stabilize body temperature and pH, and to maintain homeostasis.
This system is often seen as strictly as a blood distribution network, but some consider the circulatory system to be composed collectively
the cardiovascular system, which distributes blood, and the lymphatic system, which circulates lymph.[1]
Blood is a fluid consisting
of plasma, red blood cells, white blood cells, and platelets that is circulated by the heart through the vertebratevascular system, carrying oxygen
and nutrients to and waste materials away from all body tissues. Lymph is essentially recycled excess blood plasma after it has been filtered from
the interstitial fluid (between cells) and returned to the lymphatic system. The cardiovascular (from Latin words meaning 'heart'-'vessel') system
comprises the blood, heart, and blood vessels.[2]
The lymph, lymph nodes, and lymph vessels form the lymphatic system, which returns filtered
blood plasma from the interstitial fluid (between cells) as lymph.
While humans, as well as other vertebrates, have a closed cardiovascular system (meaning that the blood never leaves the network
of arteries, veins and capillaries), some invertebrate groups have an open cardiovascular system. The lymphatic system, on the
other hand, is an open system providing an accessory route for excess interstitial fluid to get returned to the blood.[3]
. The
essential components of the human cardiovascular system are the heart, blood, andblood vessels.
[4]
It includes: the pulmonary
circulation, a "loop" through the lungs where blood is oxygenated; and the systemic circulation, a "loop" through the rest of the
body to provide oxygenated blood. An average adult contains five to six quarts (roughly 4.7 to 5.7 liters) of blood, accounting for
approximately 7% of their total body weight.
[5]
Blood consists of plasma, red blood cells, white blood cells, and platelets. Also,
the digestive system works with the circulatory system to provide the nutrients the system needs to kelosed
cardiovascular system[edit]
The cardiovascular systems of humans are closed, meaning that the blood never leaves the network of blood vessels. In contrast, oxygen and
nutrients diffuse across the blood vessel layers and enters interstitial fluid, which carries oxygen and nutrients to the target cells, and carbon
dioxide and wastes in the opposite direction. The other component of the circulatory system, the lymphatic system, is not closed.

2. Heart[edit]
Main article: Human heart
The heart pumps oxygenated blood to the body and deoxygenated blood to the lungs. In the human heart there is one atrium and one ventricle for
each circulation, and with both a systemic and a pulmonary circulation there are four chambers in total: left atrium, left ventricle, right
atrium and right ventricle. The right atrium is the upper chamber of the right side of the heart. The blood that is returned to the right atrium is
deoxygenated (poor in oxygen) and passed into the right ventricle to be pumped through the pulmonary artery to the lungs for re-oxygenation and
removal of carbon dioxide. The left atrium receives newly oxygenated blood from the lungs as well as the pulmonary vein which is passed into the
strong left ventricle to be pumped through the aorta to the different organs of the body.
ep the heartpumping.[
Coronary circulation[edit]
Main article: Coronary circulation
Coronary circulatory system provides a blood supply to the myocardium (the heart muscle). It arises from the aorta by two coronary arteries, the
left and the right, and after nourishing the myocardium blood returns through the coronary veins into the coronary sinus and from this one into the
right atrium. Back flow of blood through its opening during atrial systole is prevented by the Thebesian valve. The smallest cardiac veins drain
directly into the heart chambers.[6]
e pulmonary circulatory system is the portion of the cardiovascular system in which oxygen-depleted blood is pumped away from the heart, via
the pulmonary artery, to the lungs and returned, oxygenated, to the heart via the pulmonary vein.
Oxygen deprived blood from the superior and inferior vena cava, enters the right atrium of the heart and flows through the tricuspid valve(right
atrioventricular valve) into the right ventricle, from which it is then pumped through the pulmonary semilunar valve into the pulmonary artery to the
lungs. Gas exchange occurs in the lungs, whereby CO2 is released from the blood, and oxygen is absorbed. The pulmonary vein returns the now
oxygen-rich blood to the left atrium
ystemic circulation[edit]
Main article: Systemic circulation
Systemic circulation is the circulation of the blood to all parts of the body except the lungs. Systemic circulation is the portion of the cardiovascular
system which transports oxygenated blood away from the heart through the aorta from the left ventricle where the blood has been previously

3. deposited from pulmonary circulation, to the rest of the body, and returns oxygen-depleted blood back to the heart. Systemic circulation is,
distance-wise, much longer than pulmonary circulation, transporting blood to every part of the body.[6]
Hemodynamics, meaning literally "blood movement" is the study of blood flow or the circulation.
All animal cells require oxygen (O2) for the conversion of carbohydrates, fats and proteins into carbon dioxide (CO2), water and
energy in a process known as aerobic respiration. The circulatory system functions to transport the blood, to deliver O2, nutrients and
chemicals to the cells of the body to ensure their health and proper function, and to remove the cellular waste products.
The circulatory system is a connected series of tubes, which includes the heart, the arteries, the microcirculation, and the veins.
The heart is the driver of the circulatory system generating cardiac output by rhythmically contracting and relaxing. This creates
changes in regional pressures, and, combined with a complex valvular system in the heart and the veins, ensures that the blood moves
around the circulatory system in one direction. The “beating” of the heart generates pulsatile blood flow which is conducted into the
arteries, across the micro-circulation and eventually, back via the venous system to the heart. The aorta, the main artery, leaves the left
heart and proceeds to divide into smaller and smaller arteries until they become arterioles, and eventually capillaries, where oxygen
transfer occurs. The capillaries connect to venules, into which the deoxygenated blood passes from the cells back into the blood, and
the blood then travels back through the network of veins to the right heart. The micro-circulation (the arterioles, capillaries, and
venules) constitutes most of the area of the vascular system and is the site of the transfer of O2, glucose, and enzyme substrates into the
cells. The venous system returns the de-oxygenated blood to the right heart where it is pumped into the lungs to become oxygenated
and CO2 and other gaseous wastes exchanged and expelled during breathing. Blood then returns to the left side of the heart where it
begins the process again. Clearly the heart, vessels and lungs are all actively involved in maintaining healthy cells and organs, and all
influence hemodynamics.

4. The factors influencing hemodynamics are complex and extensive but include CO2, circulating fluid volume, respiration, vascular
diameter and resistance, and blood viscosity. Each of these may in turn be influenced by physiological factors, such as diet, exercise,
disease, drugs or alcohol, obesity and excess weight.
Our understanding of hemodynamics depends on measuring the blood flow at different points in the circulation. A basic approach to
understanding hemodynamics is by “feeling the pulse”. This gives simple information regarding the strength of the circulation via
the systolic stroke and the heart rate, both important components of the circulation which may be altered in disease.
Coronary circulation
It is the circulation of blood in the blood vessels of the heart muscle (the myocardium). The vessels that deliver oxygen-rich blood to
the myocardium are known as coronary arteries. The vessels that remove the deoxygenated blood from the heart muscle are known as
coronary veins.
The coronary arteries that run on the surface of the heart are called epicardial coronary arteries. These arteries, when healthy, are
capable of autoregulation to maintain coronary blood flow at levels appropriate to the needs of the heart muscle. These relatively
narrow vessels are commonly affected by atherosclerosis and can become blocked, causing angina or a heart attack. The coronary
arteries that run deep within the myocardium are referred to as subendocardial.
The coronary arteries are classified as "end circulation", since they represent the only source of blood supply to the myocardium: there
is very little redundant blood supply, which is why blockage of these vessels can be so critical.
Both of these arteries originate from the left side of the heart at the beginning (root) of the aorta, immediately above the aortic valve.
The left coronary artery originates from the left aortic sinus, while the right coronary artery originates from the right aortic sinus.

5. Variations
Four percent of people have a third, the posterior coronary artery. In rare cases, a person will have one coronary artery that runs
around the root of the aorta. Occasionally, a coronary artery will exist as a double structure (i.e. there are two arteries, parallel to each
other, where ordinarily there would be one).
Coronary artery dominance
The artery that supplies the posterior descending artery (PDA)[1]
posterior interventricular artery) determines the coronary dominance.
[2]
 If the posterior descending artery (PDA) (a.k.a. posterior interventricular artery) is supplied by the right coronary
artery (RCA), then the coronary circulation can be classified as "right-dominant".
 If the posterior descending artery (PDA) is supplied by the circumflex artery (CX), a branch of the left artery, then the
coronary circulation can be classified as "left-dominant".
 If the posterior descending artery (PDA) is supplied by both the right coronary artery (RCA) and the circumflex artery, then
the coronary circulation can be classified as "co-dominant".
Approximately 70% of the general population are right-dominant, 20% are co-dominant, and 10% are left-dominant.[2]
A precise
anatomic definition of dominance would be the artery which gives off supply to the AV node i.e. the AV nodal artery. Most of the
times this is the right coronary artery.

6. Blood supply of the papillary muscles
The papillary muscles attach the mitral valve (the valve between the left atrium and the left ventricle) and the tricuspid valve (the
valve between the right atrium and the right ventricle) to the wall of the heart. If the papillary muscles are not functioning properly,
the mitral valve may leak during contraction of the left ventricle. This causes some of the blood to travel "in reverse", from the left
ventricle to the left atrium, instead of forward to the aorta and the rest of the body. This leaking of blood to the left atrium is known
as mitral regurgitation. Similarly, the leaking of blood from the right ventricle through the tricuspid valve and into the right atrium can
also occur, and this is described as tricuspid insufficiency or tricuspid regurgitation.
The anterolateral papillary muscle more frequently receives two blood supplies: left anterior descending (LAD) artery and the left
circumflex artery (LCX). It is therefore more frequently resistant to coronary ischemia (insufficiency of oxygen-rich blood). On the
other hand, the posteromedial papillary muscle is usually supplied only by the PDA. This makes the posteromedial papillary muscle
significantly more susceptible to ischemia. The clinical significance of this is that a myocardial infarction involving the PDA is more
likely to cause mitral regurgitation.
Coronary flow
During contraction of the ventricular myocardium (systole), the subendocardial coronary vessels (the vessels that enter the
myocardium) are compressed due to the high intraventricular pressures. However, the epicardial coronary vessels (the vessels that run
along the outer surface of the heart) remain patent. Because of this, blood flow in the subendocardium stops. As a result most
myocardial perfusion occurs during heart relaxation (diastole) when the subendocardial coronary vessels are patent and under low
pressure. This contributes to the filling difficulties of the coronary arteries. Compression remains the same. Failure of oxygen delivery
caused by a decrease in blood flow in front of increased oxygen demand of the heart results in tissue ischemia, a condition of oxygen

7. debt. Brief ischemia is associated with intense chest pain, known as angina. Severe ischemia can cause the heart muscle to die from
hypoxia, such as during a myocardial infarction. Chronic moderate ischemia causes contraction of the heart to weaken, known as
myocardial hibernation.
In addition to metabolism, the coronary circulation possesses unique pharmacologic characteristics. Prominent among these is its
reactivity to adrenergic stimulation. The majority of vasculature in the body constricts to norepinephrine, a sympathetic
neurotransmitter the body uses to increase blood pressure. In the coronary circulation, norepinephrine elicits vasodilation, due to the
predominance of beta-adrenergic receptors in the coronary circulation. Agonists of alpha-receptors, such as phenylephrine, elicit very
little constriction in the coronary circulation.
Skeletal muscle circulation
The skeletal muscle pump, which is triggered by the contraction of your muscles, helps to push blood traveling through the veins back
to the heart. Since blood pressure in the veins is lower than arteries and veins are generally traveling against gravity, the skeletal
muscle pump is crucial in circulation.
Arterial blood pumping
Between muscle contractions, intramuscular pressure transiently returns to a level below the venous blood pressure and blood from the
capillary system refills the veins until the next contraction. It is postulated that this change in pressure may be great enough to actually
create a vacuum that draws blood from the arterial side to the venous side. It is hypothesized that this vacuum during rhythmic
contraction actually increases blood flow through the muscle and may be responsible for a portion of the increase in muscle blood

8. flow immediately at the onset of activity. While this explanation is attractive because it would explain the readily observable tight
coupling between muscle contraction and a rapid increase in muscle blood flow, recent evidence has emerged that cast doubts on this
theory. Experiments have shown that a strong muscle contraction can occur without a corresponding increase in skeletal muscle blood
flow. Given the proposed manner of action of the muscle pump to increase arterial blood flow, it would seem impossible for a muscle
contraction and skeletal muscle hyperemia to be uncoupled.
Activation of skeletal muscle fibers by somatic nerves results in vasodilation and functional hyperemia. Sympathetic nerve activity is
integral to vasoconstriction and the maintenance of arterial blood pressure. Thus the interaction between somatic and sympathetic
neuro effector pathways underlies blood flow control to skeletal muscle during exercise. Muscle blood flow increases in proportion to
the intensity of activity despite concomitant increases in sympathetic neural discharge to the active muscles, indicating a reduced
responsiveness to sympathetic activation. However, increased sympathetic nerve activity can restrict blood flow to active muscles to
maintain arterial blood pressure.
SPLEEN AND SPLEENIC CIRCULATION
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells (also referred to as
erythrocytes) and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood
cells and holds a reserve of blood in case of hemorrhagic shock while also recycling iron. As a part of themononuclear phagocyte
system, it metabolizes hemoglobin removed from senescent erythrocytes. The globin portion of hemoglobin is degraded to its
constitutive amino acids, and the heme portion is metabolized to bilirubin, which is subsequently shuttled to the liver for removal. It
synthesizes antibodies in its white pulp and removes antibody-coated bacteria along with antibody-coated blood cells by way of blood

9. and lymph node circulation. The spleen is brownish. Recently, it has been found to contain in its reserve half of the body's
monocytes within the red pulp. These monocytes, upon moving to injured tissue (such as the heart), turn into dendritic cells and
macrophages while promoting tissue healing. It is one of the centers of activity of the reticuloendothelial system and can be
considered analogous to a large lymph node, as its absence leads to a predisposition toward certain infections
Flow of blood through the spleenic artery and arterioles to either the capillaries, e. g. white pulp, or the highly permeable sinuses of
the red pulp.
 Splenic venous blood drains into the portal vein and passes through the liver before re-entering the general circulation
 Splenic venous blood drains into the portal vein and passes through the liver before re-entering the general circulation
 Closed circulation through the spleen, blood empties from the vessels of the white pulp into sheathed capillaries of the red pulp
and then directly into the sinuses.
 Open circulation, blood empties from the sheathed capillaries into the splenic cords and then enters the sinuses through slits in
the wall.
FETAL CIRCULATION
The circulatory system of a human fetus works differently from that of born humans, mainly because the lungs are not in use: the fetus
obtains oxygen and nutrients from the woman through the placenta and the umbilical cord.
Blood from the placenta is carried to the fetus by the umbilical vein. About half of this enters the fetal ductus venosus and is carried to
the inferior vena cava, while the other half enters the liver proper from the inferior border of the liver. The branch of the umbilical

10. vein that supplies the right lobe of the liver first joins with the portal vein. The blood then moves to the right atrium of the heart. In the
fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows from the right into the left
atrium, thus bypassing pulmonary circulation. The majority of blood flow is into the left ventricle from where it is pumped through
the aorta into the body. Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-
enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the woman's circulation.
How does the mother supply oxygen and nutrients to the fetus?
The maternal blood supplies the fetus with oxygen and nutrients (water, glucose, amino acids, vitamins, and inorganic salts) and
carries away its wastes. The mother does this all throughout the fetal stage of development. Oxygen, nutrients and waste products
diffuse back and forth between the maternal and fetal blood through the placental membrane. The umbilical blood vessels carry these
substances to and from the fetal body.
Fetal hemoglobin exists in higher percentages in the fetal circulation. Fetal hemoglobin differs chemically from adult hemoglobin. It
possesses greater affinity for oxygen and can carry twenty to thirty percent more oxygen at a particular oxygen partial pressure.
Fetal circulation relies on the difference between fetal and maternal hemoglobin. The difference allows a diffusion of oxygen from
the mother's circulatory system to the fetus. The placenta acts as the respiratory center for the fetus. It also filters for plasma nutrients
and wastes. The uterine arteries carry oxygenated blood to the placenta and permeate the sponge-like material there. Oxygen then
diffuses from the placenta to the chorionic villus and then to the umbilical vein.

11. What is the mechanism of fetal circulation?
In fetal circulation, the placenta, through the umbilical vein, carries blood to the fetus. The umbilical vein delivers half of this blood
volume to the fetal ductus venosus. The ductus venosus carries the blood into the inferior vena cava. The umbilical vein delivers the
other half of the blood volume to the liver through the inferior border of the liver in the right lobe by joining with the portal vein.
From the liver, the blood then moves to the right atrium of the heart.
The foramen ovale exists in the fetus. This is an opening between the right and left atrium. Most of the blood flows through this
foramen directly into the left atrium from the right atrium; thus, bypassing pulmonary circulation. From here, the blood flows into the
left ventricle. The left ventricle pumps blood through the aorta into the body. Some of the blood moves from the aorta through the
internal iliac arteries to the umbilical arteries, and re-enters the placenta.
Another mechanism different in fetal circulation is that some of the blood enters the right ventricle. The right ventricle pumps the
blood into the pulmonary artery. The fetus does not use its lungs yet for respiration. Amniotic fluid suspends the fetus and, through
the ductus arteriosus, the pulmonary artery and the aorta are connected. This connection directs most of the fetal blood away from the
lungs.
Fetal circulation changes at birth. When the fetus becomes an infant, the infant breathes for the first time and the foramen ovale and
ductus arteriosus close. The blood no longer bypasses the pulmonary circulation; thus, the neonate’s blood becomes oxygenated in the
newly-operational lungs.

12. The flow of blood from the right ventricle through the pulmonary artery to the lungs, where carbon dioxide is exchanged for oxygen,
and back through the pulmonary vein to the left atrium
PULMONARY CIRCULATION
Some of the blood from the right atrium does not enter the left atrium, but enters the right ventricle and is pumped into the pulmonary
artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which
directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended
in amniotic fluid).
• Fetaus
• Foramen ovale
• Ductus arteriosus
• Extra hepatic fetal portion of left fetal umbilical vein
• Intrahepatic portion of left fetal umbilical vein
• Proximal portion of fetal left and right umbilical arteris
• Distal portion of fetal left and right umbilical arteris
•
• Adult
• Foramen ovalis
• Ligamentum arteriosum

13. • Ligamentum teres hepatis
• Ligamentum venosum
• Umbilical branches of linternal iliac arteries
• Medical umbilical ligaments
MICROCIRCULATION
The microcirculation is a term used to describe the small vessels in the vasculature which are embedded within organs and are
responsible for the distribution of blood within tissues; as opposed to larger vessels in the macrocirculation which transport blood to
and from the organs. The vessels on the arterial side of the microcirculation are called the arterioles, which are well innervated, are
surrounded by smooth muscle cells, and are 10-100 µm in diameter. Arterioles carry the blood to the capillaries, which are not
innervated, have no smooth muscle, and are about 5-8 µm in diameter. Blood flows out of the capillaries into the venules, which have
little smooth muscle and are 10-200 µm. The blood flows from venules into the veins. In addition to these blood vessels, the
microcirculation also includes lymphatic capillaries and collecting ducts. The main functions of the microcirculation include the
regulation of 1. blood flow and tissue perfusion 2. blood pressure, 3. tissue fluid (swelling or edema), 4. delivery of oxygen and other
nutrients and removal of CO2 and other metabolic waste products, and 5. body temperature. The microcirculation also has an
important role in inflammation.
Most vessels of the microcirculation are lined by flattened cells, the endothelium and many are surrounded by contractile cells
the smooth muscle or pericytes. The endothelium provides a smooth surface for the flow of blood and regulates the movement of

14. water and dissolved materials in the plasma between the blood and the tissues. The endothelium also produce molecules that
discourage the blood from clotting unless there is a leak. The smooth muscle cells can contract and decrease the size of the arterioles
and thereby regulate blood flow and blood pressure.
BLOOD PRESSURE
Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital
signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation.
During each heartbeat, BP varies between a maximum (systolic) and a minimum (diastolic) pressure. The mean BP, due to pumping
by the heart and resistance to flow in blood vessels, decreases as the circulating blood moves away from the heart through arteries.
Blood pressure drops most rapidly along the small arteries and arterioles, and continues to decrease as the blood moves through
the capillaries and back to the heart through veins. Gravity, valves in veins, and pumping from contraction of skeletal muscles are
some other influences on BP at various places in the body.
The measurement blood pressure without further specification usually refers to the systemic arterial pressure measured at a
person's upper arm. It is measured on the inside of an elbow at the brachial artery, which is the upper arm's major blood vessel that
carries blood away from the heart. A person's BP is usually expressed in terms of the systolic pressure over diastolic pressure
(mmHg), for example 140/90.
Physiology
There are many physical factors that influence arterial pressure. Each of these may in turn be influenced by physiological factors, such
as diet, exercise, disease, drugs or alcohol,stress, obesity, and so-forth.
Some physical factors are:

15. Rate of pumping.
In the circulatory system, this rate is called heart rate, the rate at which blood (the fluid) is pumped by the heart. The volume of blood
flow from the heart is called the cardiac output which is the heart rate (the rate of contraction) multiplied by the stroke volume (the
amount of blood pumped out from the heart with each contraction). The higher the heart rate, the higher the mean arterial pressure,
assuming no reduction in stroke volume or central venous return.
Volume of fluid or blood volume
The amount of blood that is present in the body. The more blood present in the body, the higher the rate of blood returns to the heart
and the resulting cardiac output. There is some relationship between dietary salt intake and increased blood volume, potentially
resulting in higher arterial pressure, though this varies with the individual and is highly dependent on autonomic nervous system
response and the renin-angiotensin system
Resistance
In the circulatory system, this is the resistance of the blood vessels. The higher the resistance, the higher the arterial pressure
upstream from the resistance to blood flow. Resistance is related to vessel radius (the larger the radius, the lower the resistance),
vessel length (the longer the vessel, the higher the resistance), blood viscosity, as well as the smoothness of the blood vessel walls.
Smoothness is reduced by the build up of fatty deposits on the arterial walls. Substances called vasoconstrictors can reduce the size of
blood vessels, thereby increasing BP. Vasodilators (such as nitroglycerin) increase the size of blood vessels, thereby decreasing

16. arterial pressure. Resistance, and its relation to volumetric flow rate (Q) and pressure difference between the two ends of a vessel are
described by Poiseuille's Law.
Viscosity
Thickness of the fluid. If the blood gets thicker, the result is an increase in arterial pressure. Certain medical conditions can change
the viscosity of the blood. For instance, anemia (low red blood cell concentration), reduces viscosity, whereas increased red blood cell
concentration increases viscosity. It had been thought that aspirin and related "blood thinner" drugs decreased the viscosity of blood,
but instead studies found]
that they act by reducing the tendency of the blood to clot.
In practice, each individual's autonomic nervous system responds to and regulates all these interacting factors so that, although the
above issues are important, the actual arterial pressure response of a given individual varies widely because of both split-second and
slow-moving responses of the nervous system and end organs. These responses are very effective in changing the variables and
resulting BP from moment to moment.
Moreover, blood pressure is the result of cardiac output increased by peripheral resistance: blood pressure = cardiac
output X peripheral resistance. As a result, an abnormal change in blood pressure is often an indication of a problem affecting the
heart's output, the blood vessels' resistance, or both. Thus, knowing the patient's blood pressure is critical to assess any pathology
related to output and resistance.
Regulation of blood pressure
The endogenous regulation of arterial pressure is not completely understood, but the following mechanisms of regulating arterial
pressure have been well-characterized:

17.  Baroreceptor reflex: Baroreceptors in the high pressure receptor zones (mainly in the aortic arch and carotid sinus) detect
changes in arterial pressure. These baroreceptors send signals ultimately to the medulla of the brain stem, specifically to
the Rostral ventrolateral medulla (RVLM). The medulla, by way of the autonomic nervous system, adjusts the mean arterial
pressure by altering both the force and speed of the heart's contractions, as well as the total peripheral resistance. The most
important arterial baroreceptors are located in the left and right carotid sinuses and in the aortic arch.
 Renin-angiotensin system (RAS): This system is generally known for its long-term adjustment of arterial pressure. This system
allows the kidney to compensate for loss in blood volume or drops in arterial pressure by activating an
endogenous vasoconstrictor known as angiotensin II.
 Aldosterone release: This steroid hormone is released from the adrenal cortex in response to angiotensin II or high
serum potassium levels. Aldosterone stimulates sodium retention and potassium excretion by the kidneys. Since sodium is the
main ion that determines the amount of fluid in the blood vessels by osmosis, aldosterone will increase fluid retention, and
indirectly, arterial pressure.
 Baroreceptors in low pressure receptor zones (mainly in the venae cavae and the pulmonary veins, and in the atria) result in
feedback by regulating the secretion of antidiuretic hormone (ADH/Vasopressin), renin and aldosterone. The resultant increase
in blood volume results an increased cardiac output by the Frank–Starling law of the heart, in turn increasing arterial blood
pressure.
These different mechanisms are not necessarily independent of each other, as indicated by the link between the RAS and aldosterone
release. Currently, the RAS is targeted pharmacologically by ACE inhibitors and angiotensin II receptor antagonists. The aldosterone
system is directly targeted by spironolactone, an aldosterone antagonist. The fluid retention may be targeted by diuretics; the

18. antihypertensive effect of diuretics is due to its effect on blood volume. Generally, the baroreceptor reflex is not targeted
in hypertension because if blocked, individuals may suffer from orthostatic hypotension and fainting.
The Kidney
One of the functions of the kidney is to monitor blood pressure and take corrective action if it should drop. The kidney does this by
secreting the protease

19. Renin.
• Renin acts on angiotensinogen, a plasma peptide, splitting off a fragment containing 10 amino acids called
• angiotensin I.
• angiotensin I is cleaved by a peptidase secreted by blood vessels called angiotensin converting enzyme (ACE) — producing
• angiotensin II, which contains 8 amino acids.
• angiotensin II
o constricts the walls of arterioles closing down capillary beds;
o stimulates the proximal tubules in the kidney to reabsorb sodium ions;
o stimulates the adrenal cortex to release aldosterone. Aldosterone causes the kidneys to reclaim still more sodium and
thus water [Discussion].
o increases the strength of the heartbeat;
o stimulates the pituitary to release the vasopressin.
All of these actions, which are mediated by its binding to G-protein-coupled receptors on the target cells, lead to an increase in
blood pressure.

20. Measurement of blood pressure
Arterial pressure is most commonly measured via a sphygmomanometer, which historically used the height of a column of mercury to
reflect the circulating pressure. BP values are generally reported in millimetres of mercury (mmHg), though aneroid and electronic
devices do not use mercury.
For each heartbeat, BP varies between systolic and diastolic pressures. Systolic pressure is peak pressure in the arteries, which occurs
near the end of the cardiac cycle when the ventricles are contracting. Diastolic pressure is minimum pressure in the arteries, which
occurs near the beginning of the cardiac cycle when the ventricles are filled with blood. An example of normal measured values for a
resting, healthy adult human is 120 mmHg systolic and 80 mmHg diastolic (written as 120/80 mmHg.
Systolic and diastolic arterial BPs are not static but undergo natural variations from one heartbeat to another and throughout the day
(in acircadian rhythm). They also change in response to stress, nutritional factors, drugs, disease, exercise, and momentarily from
standing up. Sometimes the variations are large. Hypertension refers to arterial pressure being abnormally high, as opposed
to hypotension, when it is abnormally low. Along with body temperature, respiratory rate, and pulse rate, BP is one of the four main
vital signs routinely monitored by medical professionals and healthcare providers.
Measuring pressure invasively, by penetrating the arterial wall to take the measurement, is much less common and usually restricted to
a hospital setting.
Many fluctuations in blood flow occur as a result of alterations in signals the circulatory system receives from the nervous system. As
depicted by the solid arrows in The former directs what is frequently called the ‘fight-flight’ response, and the latter directs what has
been called the ‘relaxation response.’ Although initially it was thought that these two systems were interconnected (as sympathetic

21. nervous system activity increases, parasympathetic activity decreases), it is now known that they can operate independently. In this
regard, sympathetic and parasympathetic influences can work simultaneously to affect the target organs in the body.
The sympathetic nervous system employs two distinct neural systems that affect blood pressure, known as the alpha-adrenergic and
beta-adrenergic systems. The alpha-adrenergic neurotransmitters and receptor systems affect blood vessels by causing them to
constrict, whereas the beta-adrenergic system affects both the heart and the blood vessels. Beta-adrenergic activity leads to increased
heart pumping action (increased heart rate) as well as vasodilation of blood vessels.
Neural influences
This combination of neural influences represents an adaptive response, as the increased blood flow caused by the increase in heart rate
needs more space in the vasculature in order for blood pressure to be properly regulated. The parasympathetic nervous system
influences only the heart via the vagal nerve, which results in slowed heart rate.
In sum, these components of the autonomic nervous system interact to regulate blood pressure with the aim of keeping it within
adaptive limits. During the type of exercise described above, heart rate will increase accompanied by vasodilation of the blood vessels
in the leg muscles mediated by the beta-adrenergic system. This response pattern permits increased delivery of oxygen to the leg
muscles without a concomitant alteration in local diastolic blood pressure. At the same time, blood flow to the gastrointestinal system
is likely reduced via vasoconstriction, as digestion is not an important use of the body’s resources during a bout of exercise.
The normal mean blood pressure is about 100 mm Hg. If for some reason the pressure level falls significantly below the mean level, it
triggers a cascade of nervous reflexes that promotes contraction in the large venous reservoirs, and increases both the rate and force of
cardiac contractions as well as induces a general constriction of small arteries (arterioles) throughout the body. Therefore, more blood

22. is made available in the arterial tree. The substance released by the nervous system in the smooth muscle cells of the blood vessel
walls is norepinephrine, a vasoconstrictor (vessel-constricting chemical).
However, if the causes leading to such low blood pressure persist and are no longer beneficial, other regulatory systems are activated,
such as the secretion of pressure-controlling hormones. For instance, the kidneys control arterial pressure inducing changes in the
volume of extra cellular fluids through the renin-angiotensin system. Renin is an enzyme released by the kidneys when the blood
pressure is dangerously low. Renin helps to increase blood pressure through several ways. It promotes the release of angiotensin I, a
mild vasoconstrictor, by entering the blood circulation. Angiotensin I is then enzymatically processed to become angiotensin II, a
powerful vasoconstrictor that acts mainly on the small arterioles, and in a lesser way on veins. Arteriolar constriction increases the
total vascular peripheral resistance, what elevates blood pressure in the arteries and the mild venal constriction helps the return of the
blood to the heart. Angiotensin II also inhibits the elimination of sodium and water by the kidneys, thus augmenting the volume of
extra cellular fluid. Even small elevations in the volume of extra cellular fluid can induce a blood pressure increase. Whereas the
vasoconstriction by angiotensin II lasts for just a few minutes, the elevation of extra cellular fluid

24. Figure 1.2, the brain communicates with various organs in the circulatory system through the autonomic nervous system. This system
is comprised of two separate systems called the sympathetic nervous system and the parasympathetic nervous system.
Hormonal control of blood pressure
The normal mean blood pressure is about 100 mm Hg. If for some reason the pressure level falls significantly below the mean level, it
triggers a cascade of nervous reflexes that promotes contraction in the large venous reservoirs, and increases both the rate and force of
cardiac contractions as well as induces a general constriction of small arteries (arterioles) throughout the body. Therefore, more blood
is made available in the arterial tree. The substance released by the nervous system in the smooth muscle cells of the blood vessel
walls is norepinephrine, a vasoconstrictor (vessel-constricting chemical).
However, if the causes leading to such low blood pressure persist and are no longer beneficial, other regulatory systems are activated,
such as the secretion of pressure-controlling hormones. For instance, the kidneys control arterial pressure inducing changes in the
volume of extra cellular fluids through the renin-angiotensin system. Renin is an enzyme released by the kidneys when the blood
pressure is dangerously low. Renin helps to increase blood pressure through several ways. It promotes the release of angiotensin I, a
mild vasoconstrictor, by entering the blood circulation. Angiotensin I is then enzymatically processed to become angiotensin II, a
powerful vasoconstrictor that acts mainly on the small arterioles, and in a lesser way on veins. Arteriolar constriction increases the
total vascular peripheral resistance, what elevates blood pressure in the arteries and the mild venal constriction helps the return of the
blood to the heart. Angiotensin II also inhibits the elimination of sodium and water by the kidneys, thus augmenting the volume of
extra cellular fluid. Even small elevations in the volume of extra cellular fluid can induce a blood pressure increase. Whereas the
vasoconstriction by angiotensin II lasts for just a few minutes, the elevation of extra cellular fluid

25. volume lasts for several hours or days, and is, therefore, the major
effect in pressure elevation by the renin-angiotensin system. A
smaller quantity of renin remains in the renal system where it
elicits other regulatory functions.
Another pressure-controlling hormone, vasopressin, is secreted by
the posterior pituitary gland, and also increases water reabsorption
by the kidneys, and in turn, causes constriction of the blood
vessels, thus elevating blood pressure. ADH (antidiuretic
hormone), also secreted by the posterior pituitary, promotes the
renal water reabsorption and vasoconstriction, increasing blood
pressure. Aldosterone, secreted by the cortex of adrenal glands, is
a hormone activated by angiotensin II that also increases sodium
reabsorption and the elimination of potassium, which increases
blood pressure as well. It also increases extra cellular fluid
volume.
Arterial pressure is also regulated by vasodilator substances, such
as bradykinin, acetylcholine, mineral ions, and endogenous nitric
oxide, carbon dioxide and hydrogen gases. Bradykinin promotes
arteriolar dilatation and increased capillary permeability. Mineral

26. ions that induce vasodilatation are potassium and magnesium.
High intake of salt in the diet causes an increase in the volume of
extra cellular fluid that ultimately leads to an increase in blood
pressure above normal levels (i.e., hypertension). Although some
cases of chronic high blood pressure are due to hereditary traits, a
sodium-rich diet through childhood and young adulthood may
also lead to chronic hypertension during later life. Hypertension,
in turn, may lead to blood vessel ruptures in the brain, or strokes
(cerebral infarct). Hypertension causes progressive destruction of
the kidneys through successive ruptures of vessels in this organ,
which leads to renal failure, an increased level of urea in the
blood (uremia), and ultimately death.
Blood pressure measurements are usually done in millimeters of
mercury (mm Hg) with a mercury manometer used for this
purpose. The mercury manometer measures the force of blood
against any unit area of the vessel wall. However, it is only useful
for measuring stable pressures. When it is necessary to monitor
unstable blood pressure, oscillating rapidly, electronic pressure
transducers are utilized. These instruments convert pressure into

27. electrical signals that are recorded at high speed.
Local Control in the Capillary Beds
• Nitric oxide (NO) is a potent dilator of arteries and arterioles.
o When the endothelial cells that line these vessels are stimulated, they synthesize nitric oxide. It quickly diffuses into the
muscular walls of the vessels causing them to relax.
o In addition, as the hemoglobin in red blood cells releases its O2 in actively-respiring tissues, the lowered pH [Link]
causes it to also release NO which helps dilate the vessels to meet the increased need of the tissue.
Nitroglycerine, which is often prescribed to reduce the pain of angina, does so by generating nitric oxide, which relaxes the
walls of the arteries and arterioles. The prescription drug sildenafil citrate("Viagra") does the safor vessels supplying blood to
the penis. The effects of these two drugs are additive and using them together could precipitate a dangerous drop in blood
pressure.
• Cells where infection or other damage is occurring release substances like histamine that dilate the arterioles and thus increase
blood flow in the area.

28. • In most of the body, the flow of blood through a capillary is controlled by the arteriole supplying it. In the brain, however,
another mechanism participates. The degree of contraction of pericytes, cells that surround the capillary, also adjusts the flow
of blood through the capillary. The changes in brain activity seen by such imaging procedures as fMRI and PET scans are
probably influenced by pericyte activity.
IN HEART
A rise in blood pressure stretches the atria of the heart. This triggers the release of atrial natriuretic peptide (ANP). ANP is a peptide
of 28 amino acids. ANP lowers blood pressure by:
• relaxing arterioles
• inhibiting the secretion of renin and aldosterone
• inhibiting the reabsorption of sodium ions in the collecting ducts of the kidneys.
The effects on the kidney reduce the reabsorption of water by them thus increasing the flow of urine and the amount of sodium
excreted in it (These actions give ANP its name: natrium = sodium; uresis = urinate). The net effect of these actions is to reduce blood
pressure by reducing the volume of blood volume in the system.

29. The Lymphatic System
Lymphoid organs:
1. spleen - is made up of masses of lymphoid tissue which are located around terminal branches of the circulation,
2. thymus - is made up of 2 lateral lobes, which are enclosed in a capsule. Each lateral lobe is made up of many smaller lobules
and
3. lymph nodes - Lymph nodes are located throughout the body and serve as filters for tissue fluid.
Lymph fluid: is made up of:
1. Fluid from the intestines containing proteins and fats,
2. A few red blood cells and
3. Many lymphocytes. Lymph (originally tissue fluid) is collected in the lymphatic vessels and ultimately transported back into
the systemic circulation by the pressure in the tissue, skeletal muscle activity and a series of one-way valves
When tissue fluid enters the small blind-ended lymphatic capillaries that form a network between the cells it becomes lymph.
Lymph is a clear watery fluid that is very similar to blood plasma except that it contains large numbers of white blood cells,
mostly lymphocytes. It also contains protein, cellular debris, foreign particles and bacteria. Lymph that comes from the intestines also
contains many fat globules following the absorption of fat from the digested food into the lymphatics (lacteals) of the villi. From the
lymph capillaries the lymph flows into larger tubes called lymphatic vessels. These carry the lymph back to join the blood circulation.

30. •
Lymphatic vessels
Lymphatic vessels have several similarities to veins. Both are thin walled and return fluid to the right hand side of the heart. The
movement of the fluid in both is brought about by the contraction of the muscles that surround them and both have valves to prevent
backflow. One important difference is that lymph passes through at least one lymph node or gland before it reaches the blood system.
These filter out used cell parts, cancer cells and bacteria and help defend the body from infection.
Lymph nodes are of various sizes and shapes and found throughout the body and the more important ones are shown in diagram 10.3.
They consist of lymph tissue surrounded by a fibrous sheath. Lymph flows into them through a number of incoming vessels. It then
trickles through small channels where white cells called macrophages (derived from monocytes) remove the bacteria and debris by

31. engulfing and digesting them. The lymph then leaves the lymph nodes through outgoing vessels to continue its journey towards the
heart where it rejoins the blood circulation.

32. As well as filtering the lymph, lymph nodes produce the white cells known as lymphocytes. Lymphocytes are also produced by
the thymus, spleen and bone marrow. There are two kinds of lymphocyte. The first attach invading micro organisms directly while
others produce antibodies that circulate in the blood and attack them.
The function of the lymphatic system can therefore be summarized as transport and defense. It is important for returning the fluid and
proteins that have escaped from the blood capillaries to the blood system and is also responsible for picking up the products of fat
digestion in the small intestine. Its other essential function is as part of the immune system, defending the body against infection.

33. Problems with lymph nodes and the lymphatic system
During infection of the body the lymph nodes often become swollen and tender because of their increased activity. This is what causes
the swollen ‘glands’ in your neck during throat infections, mumps and tonsillitis. Sometimes the bacteria multiply in the lymph node
and cause inflammation. Cancer cells may also be carried to the lymph nodes and then transported to other parts of the body where
they may multiply to form a secondary growth or metastasis. The lymphatic system may therefore contribute to the spread of cancer.
Inactivity of the muscles surrounding the lymphatic vessels or blockage of these vessels causes tissue fluid to ‘back up’ in the tissues
resulting in swelling or oedema.
Other Organs Of The Lymphatic System
The spleen is an important part of the lymphatic system. It is a deep red organ situated in the abdomen caudal to the stomach (see
diagram 10.3). It is composed of two different types of tissue. The first type makes and stores lymphocytes, the cells of the immune
system. The second type of tissue destroys worn out red blood cells, breaking down the haemoglobin into iron, which is recycled, and
waste products that are excreted. The spleen also stores red blood cells. When severe blood loss occurs, it contracts and releases them
into the circulation.
The thymus is a large pink organ lying just under the sternum (breastbone) just cranial to the heart (see diagram 10.1). It has an
important function processing lymphocytes so they are capable of recognising and attacking foreign invaders like bacteria.
Other lymph organs are the bone marrow of the long bones where lymphocytes are produced and lymph nodules, which are like tiny
lymph nodes. Large clusters of these are found in the wall of the small intestine (called Peyer’s Patches) and in the tonsils

34. ECG
The ECG is the most commonly performed cardiac test. This is because the ECG is a useful screening tool for a variety of cardiac
abnormalities; ECG machines are readily available in most medical facilities; and the test is simple to perform, risk-free and
inexpensive.
How is the ECG performed?
You will lie on an examination table, and 10 electrodes (or leads) are attached to your arms, legs, and chest. The electrodes detect the
electrical impulses generated by your heart, and transmit them to the ECG machine. The ECG machine produces a graph (the ECG
tracing) of those cardiac electrical impulses. The electrodes are then removed. The test takes less than 5 minutes to perform.
What information can be gained from the ECG?
From the ECG tracing, the following information can be determined:
• the heart rate
• the heart rhythm
• whether there are “conduction abnormalities” (abnormalities in how the electrical impulse spreads across the heart)
• whether there has been a prior heart attack
• whether there may be coronary artery disease
• whether the heart muscle has become abnormally thickened

35. All of these features are potentially important. If the ECG indicates a heart attack or possible coronary artery disease, further testing is
often done to completely define the nature of the problem and decide on the optimal therapy. (These tests often include astress
test and/or cardiac catheterization.) If the heart muscle is thickened, anechocardiogram is often ordered to look for possible valvular
heart disease or other structural abnormalities. Changes in the electrical pattern on the ECG may give clues to the cause of syncopee
(fainting), or may indicate underlying cardiac disease.
What are the limitations of the ECG?
• The ECG reveals the heart rate and rhythm only during the time that the ECG is taken. If intermittent cardiac rhythm
abnormalities are present, the ECG is likely to miss them. Ambulatory monitoring is needed to record transient arrhythmias.
• The ECG can often be normal or nearly normal in patients with undiagnosed coronary artery disease or other forms of heart
disease (false negative results.)
• Many "abnormalities" that appear on the ECG turn out to have no medical significance after a thorough evaluation is done
(false positive results).

36. The above sequence of events creates an action potential in all atrial fibers followed
by an action potential in all ventricle fibers. This synchronous electrical activity in so
many myocardial cells produces large currents that can be detected using electrodes
placed on the skin. The characteristic recording of the electrical activity of the heart
during the cardiac cycle is called the electrocardiogram or ECG (see illustration).
Cardiac action potentials are different from those recorded from nerves and skeletal
muscle. They are composed of three phases: a rapid depolarization, a plateau
depolarization (which is pronounced in ventricular fibers), and a repolarization back
to resting membrane potential. The components of the ECG can be correlated with
the electrical activity of the atrial and ventricle fibers such that:
• The P-wave is produced by atrial depolarization
• The QRS complex is produced by atrial repolarization and ventricular depolarization
• The T-wave is produced by ventricular repolarization.
There are two sets of heart valves, one between the atria and the ventricles (the AV valves) and the other between the ventricles and
the artery (the semilunar valves). In the relaxed heart, the AV valves are open and blood passes from the veins through the atria to the
ventricles. At this point the high arterial pressure keeps the semilunar valves closed. Ventricular contraction increases the pressure of
the blood in the ventricle and closes the AV valves, producing the Lubsound. The ventricular pressure increases until it is greater than
the arterial pressure, the semilunar valves open and blood flows into the artery. The myocardium then relaxes, the ventricular pressure
declines and the semilunar valves close, producing the Dup sound.
The Electrocardiogram (ECG)

37. Cardiac electrophysiology is the science of elucidating, diagnosing, and treating the electrical activities of the heart. The term is
usually used to describe studies of such phenomena by invasive (intracardiac) catheter recording of spontaneous activity as well as of
cardiac responses to programmed electrical stimulation (PES). These studies are performed to assess complexarrhythmias, elucidate
symptoms, evaluate abnormal electrocardiograms, assess risk of developing arrhythmias in the future, and design treatment. These
procedures increasingly include therapeutic methods (typically radiofrequency ablation) in addition to diagnostic and prognostic
procedures. Other therapeutic modalities employed in this field include antiarrhythmic drug therapy and implantation
of pacemakers and automatic implantable cardioverter-defibrillators (AICD)

38. The cardiac electrophysiology study (EPS) typically measures the response of the injured or cardiomyopathic myocardium to PES on
specific pharmacological regimens in order to assess the likelihood that the regimen will successfully prevent potentially fatal
sustained ventricular tachycardia (VT) or ventricular fibrillation VF (VF) in the future.
An electrophysiology (EP) study is a test that records the electrical activity and the electrical pathways of your heart. This test is used
to help determine the cause of your heart rhythm disturbance and the best treatment for you. During the EP study, your doctor will
safely reproduce your abnormal heart rhythm and then may give you different medications to see which one controls it best or to
determine the best procedure or device to treat your heart rhythm.
Each heartbeat generates a "complex" consisting of 3 parts:
The "P" wave represents the electrical impulse traveling across the atria of the heart. Abnormalities of the P wave, therefore, reflect
abnormalities of the right and/or left atrium.

39. The QRS complex represents the electrical impulse as it travels across the ventricles. Abnormalities of the QRS are often seen when
there has been prior damage to the ventricular muscle, such as in a prior myocardial infarction (heart attack.)
The "T" wave represents the recovery period of the ventricular muscle after it has been stimulated.
The portion of the ECG between the QRS complex and the T wave is called the ST segment. Abnormalities of the ST segment and the
T waves are often seen when the heart muscle is ischemic - that is, when it is not getting enough oxygen, usually because there is a
blockage in a coronary artery.