Chapters 18 and 19 Cardiovascular system and blood vessels

Venous portion -

Peripheral veins merge and eventually return blood to either the inferior vena cava or superior vena cava, which returns blood to the heart. For details, see the flowchart in Figure 19.26

stroke volume:

(SV) volume of blood pumped out by one ventricle with one beat

risk factors involved in heart disease:

-Congestive heart failure -Coronary atherosclerosis -Persistent high blood pressure -Multiple myocardial infarcts -Dilated cardiomyopathy

Neural controls of blood vessels are directed primarily at:

1. altering blood distribution 2. maintaining adequate systemic blood pressure Under conditions of low blood volume, all vessels except those supplying the heart and brain are constricted.

The main factors influencing blood pressure are:

1. cardiac output 2. peripheral resistance 3. blood volume blood pressure = cardiac output X peripheral resistance Cardiac output (ml/min) = stroke volume (ml/beat) X heart rate (beats/min) Cardiac output is about 5.5L/min

The kidneys act directly and indirectly to regulate arterial pressure and provide long-term mechanism of blood pressure control:

1. direct - control water retention 2. indirect - release renin which results in the formation of angiotensin, a powerful vasoconstrictor.

Blood flowing through a terminal arteriole may take one of two routes:

1. through the true capillaries 2. through the shunt Blood flowing through true capillaries exchanges with tissue cells, whereas blood flowing through shunts bypasses the tissue cells. blood flowing into the true capillaries is regulated by vasomotor nerve fibers and local chemical conditions. The capillary beds may be flooded with blood or almost completely bypassed.

heart wall:

3 layers: outer epicardium(same as visceral pericardium) , middle myocardium(cardiac muscle , bulk of heart, layer that contracts its branching layers are connective tissue called fibrous skelteon of heart ), and inner endocardium(sheet of endothelium on inner heart surface, slick and reduces friction due to blood flow , is continuous with endothelium of blood vessels.) The heart has its own blood supply via coronary arteries.

heart chambers:

4 chambers(receives blood to heart, contract minimally and thin walled.): 2 superior atria (atrium and singular) 2 inferior ventricles separated by interatrial septum or interventricular septum external to atria are auricles that increase the atrial volume somewhat. Interatrial septum has a shallow depression , fossa ovalis is spot where opening(formen ovale) existed in fetal heart .

blood enters left atrium by:

4 pulmonary veins that transport blood from lungs back to the heart .

maintenance of systemic blood pressure:

Any fluid driven by a pump through a circuit of closed channels operates under pressure, and the nearer the fluid is to the pump, the greater the pressure. Blood flows through the blood vessels along a pressure gradient from high to low. Pressure results when flow is opposed by resistance. As the left ventricle contracts and expels blood into the aorta, it stretches the elastic walls of the aorta causing aortic pressure to reach its peak-the systolic arterial blood pressure and averages about 120 mm Hg. During diastole which occurs during ventricular relaxation, closure of the semilunar valve prevents blood flowing back into the heart, and the walls of the aorta recoil, maintaining continuous pressure on the reducing blood volume. During this time, aortic pressure drops to its lowest level (diastolic pressure). The difference between the systolic and diastolic pressures is the pulse pressure. It is felt as a throbbing pulsation in an artery during systole as the elastic arteries are expanded by the blood being forced into them by ventricular contraction.

Systemic Circuit -

Arterial portion - Aorta (largest artery in the body) is named by regions (ascending aorta, aortic arch, thoracic aorta, abdominal aorta. Branches off the aorta go to all body regions. For details, see the flowchart in Figure 19.21a.

general structure of arterial system:

Arteries can be divided into three groups: 1. elastic arteries 2. muscular arteries 3. Arterioles

autoregulation of localized blood flow:

Automatic adjustment of blood flow to each tissue in proportion to its requirements at any point in time. Regulated by conditions and is independent of systemic factors. Since mean arterial pressure is identical throughout the body, changes in blood flow through individual organs are controlled by modifying the diameter of local arterioles feeding the capillaries. Thus organs regulate their own blood flow by varying resistance of their arterioles. Local physical factors are also important autoregulatory stimuli. Vascular smooth muscle responds directly to passive stretch and causes vasoconstriction. Reduced stretch promotes vasodilation. Such responses to changing volume entering an arteriole are called myogenic responses. Generally both chemical and physical factors determine the final autoregulatory response of a tissue. Autoregulation in the brain, heart, and kidneys is extraordinarily efficient. Adequate perfusion is maintained even in the face of fluctuating mean arterial pressure. The number of vessels in the region increases, and the existing vessels enlarge. This is common in the heart when a coronary vessel is partially occluded; it occurs throughout the body in people who live in high-altitude areas.

structure and function of heart valves:

Blood flows through the heart in one direction. This one-way flow is enforced by 4 heart valves: one pair of atrioventricular valves(tri and bi cuspid) and one pair of semilunar valves(pulmonary and aortic ), which open and close in response to differing blood pressures on their two sides. The aortic and pulmonary semilunar valves guard the bases of the large arteries issuing from the ventricles and prevent backflow into the associated ventricles. Each of the semilunar valves has three pocket-like cusps. When the ventricles contract, the pressure in the ventricles are greater than the pressure in the aorta and pulmonary arteries and the valves are forced open. The blood exits the ventricle. When the ventricles relax and the blood begins to flow backward toward the heart, it fills the cusps and effectively closes the valves. In valvular stenosis (narrowing) the valves become stiff and the heart must contract more forcibly than normal.

structure and function of the venous system:

Blood is carried from the capillary beds toward the heart by veins. vessels increase in diameter, and their walls gradually thicken as they progress from venules to the larger and larger veins. Veins are usually collapsed, and their lumens appear slit-like in routine tissue preparations. The tunica media tends to be thin and there is little smooth muscle or elastin. In the vena cava, the tunica adventitia is further thickened by longitudinal bands of smooth muscle. With their large lumens and thin walls, veins can accommodate large blood volume. Up to 65% of the body's total blood supply is found in the veins. veins are normally only partially filled with blood.Blood pressure within the veins is low and some special adaptations that help return blood to the heart .The large diameter lumens are one structural adaptation. Another is the presence of valves that prevent blood from flowing backward. Valves are most abundant in the veins of the limbs. They are absent in veins of the ventral body cavity.

function of vascular system:

Blood is forced into the large arteries leaving its ventricles. It then moves into successively smaller arteries, finally reaching their smallest branches, the arterioles, which feed into the capillary beds of body organs and tissues. Blood draining from the capillaries is collected by venules-( small veins that merge to form larger veins that ultimately empty into the great veins converging on the heart. )

Ventricular filling (mid-to-late diastole) -

Blood returning from the circulation flows through the atria and the open AV valves into the ventricles. Following atrial depolarization (P wave), the atria contract to propel residual blood out of the atria and into the ventricles. Ventricles now have the maximal volume of blood.

capillary structure:

Capillaries are the smallest blood vessels. Their thin walls consist of a thin tunica intima.The average capillary length is 1 mm and the average lumen diameter is 8-1 0 μm just large enough for RBC's to slip through. capillaries are ideally suited for their role in exchange of materials between the blood and interstitial fluid. Structurally, capillaries are classified as: 1. continuous 2. Fenestrated Continuous capillaries are abundant in the skin and muscles. They are continuous in the sense that their endothelial cells provide an uninterrupted lining.

capillary function:

Capillaries do not function independently; they tend to form interweaving networks called capillary beds. In most body regions, a capillary bed consists of two types of vessels: 1. vascular shunt (metarteriole-thoroughfare channel) 2. true capillary

blood flow through capillaries:

Capillaries: blood flow is slow and intermittent, rather than steady (vasomotion), and reflects the "on-off' opening and closing of the precapillary sphincters. Fluid movements: fluid (water + solutes) is forced out of the capillaries through the clefts at the arterial end of the bed, but most is returned at the venous end. In theory, blood pressure -- which forces fluid out of the capillaries -is opposed by hydrostatic pressure of the interstitial fluid (back pressure).

Hepatic portal system -

Carries nutrient-rich blood from the digestive organs to the liver where it can be processed before going to the rest of the body. Capillary beds of the intestines -mesenteric veins -hepatic portal vein (also receives input from splenic vein) -liver (sinusoidal capillaries) -hepatic veins -inferior vena cava

Circulatory shock:

Condition in which blood vessels are inadequately filled and blood cannot circulate normally. If this condition persists, cell death and organ damage occurs.

blood flow in special areas:

Each organ has special functions revealed in its pattern of autoregulation.

orthostatic hypotension -

Elderly people are prone, temporary low blood pressure and dizziness when they rise suddenly from a reclining or sitting position. Blood pools in the lower extremities.

effects of exercise on the cardiovascular system:

In response to regular exercise, the heart adapts to the increased demand by increasing in size and becoming a more efficient and more powerful pump. Also it clears fatty deposits from blood vessels walls, retarding atherosclerosis and coronary heart disease.

Hypotension:

Low blood pressure; systolic pressure below 100mm Hg. reflects individual variations and is no cause for concern. Often associated with long life and old age free of illness.

control of blood pressure:

Maintaining a steady flow of blood is vital for proper organ function. Blood pressure is regulated by neural, chemical and renal controls.

Pulmonary Circuit -

Pulmonary trunk rt/lt pulmonary arteries lobar arteries pulmonary capillaries pulmonary veins

The heart

Pump that circulates blood via blood vessels. Size of fist and located in thorax in mediastenum cavity. Tips slightly to the left.

factors that affect it (CO):

The Cardiac Output increases when (SV)stroke volume increases or the HR increases or both. The critical factor controlling SV is preload (the degree to which cardiac muscle cells are stretched just before they contract). Stretching cardiac muscle cells leads to increases in contractile force. A slow heartbeat gives more time for ventricular filling. Exercise speeds venous return to the heart. SV can also be affected by increasing contractility (via hormones thyroxine, epinephrine). Afterload (back pressure on the semilunar valves by arterial blood) can be a factor in SV in hypertensive individuals because this pressure must be overcome for ventricles to eject blood

principal events of the cardiac cycle:

The cardiac cycle is the blood flow through the heart during one complete heartbeat.

coronary circulation:

The cells of the heart receive no nutrients or oxygen from the blood flowing through the heart. Their blood supply provided right and left coronary arteries. coronary arteries branch and supply routes for blood delivery. there is a backup system when these arteries become occluded. Full occlusion of a coronary artery leads to tissue death and heart attack. After passing through the capillary beds of the myocardium, the cardiac veins join together forming an enlarged vessel-the coronary sinus, which empties into the right atrium.

pathways of blood through the heart:

The heart is 2 side-by-side pumps with separate blood circuit. receives blood returning to the heart from body and sends it through lungs. In lungs the blood gives up waste carbon dioxide and takes on oxygen.

unique aspects of fetal circulation

The interatrial septum in the fetal heart is incomplete. The foramen ovale connects the two atria and allows blood entering the right heart to bypass the pulmonary circuit and the collapsed, non-functional fetal lungs. Another bypass, the ductus arteriosus connects the pulmonary trunk and aorta. The ductus venosus largely bypasses the liver. The umbilical vein and arteries circulate the blood between the fetal circulation and the placenta where gas and nutrient exchanges occur with the mother's blood.

intrinsic conduction system of the heart and how it relates to an electrocardiogram:

The intrinsic conduction system consists of noncontractile (non-muscular) cardiac cells specialized to initiate and distribute impulses throughout the heart, it depolarizes and contracts orderly manner. The heart has autorhythmic cells that have an unstable resting potential; these cells continuously depolarize until reaching a threshold and initiating an action potential. These electrical events are based on the flow of ions (sodium, potassium, and calcium) across the cell membranes.

pathways of blood through the heart:systemic circulation pump

The left side of the heart , receives oxygenated blood from the lungs and pumps it to body tissues via the arteries. longer/thicker and encounters 5 times as much friction.

sounds of the heart and their clinical significance:

The normal heartbeat produces two sounds : (lub-dup)- -Thefirst sound happens when the AV valves close. -The second sound occurs as the semilunar valves close. Each lub-dup is separated by a pause which indicates heart relaxation. . (incompetent)-If a valve fails to close completely a swishing sound is heard. (stenosis)-If a valve fails to open completely it restricts blood flow through the valve .

pathways of blood through the heart: pulmonary circuit pump

The right side of the heart ,pumps deoxygenated blood to the lungs. short/thinner and low-pressure.

true capillary

The terminal arteriole feeding the bed leads into a metarteriole which is continuous with the thorough fare channel. The channel joins the postcapillary venule that drains the bed. Typically, a cuff of smooth muscle (precapillary sphincter), surrounds the root of each true capillary at the metarteriole and acts as a valve to regulate the flow of blood into the capillary.

the structure of vessel walls

The three vessel types vary in length, diameter, and the relative thickness and tissue makeup of their walls. The walls of all blood vessels EXCEPT the capillaries are composed of three distinct layers, or tunics. The tunics surround lumen. The inner most tunic contacts with the blood- tunica intima. It contains the endothelium that lines the lumen of the vessel, and its cells fit together, forming a slick surface minimizing friction. The middle layer-tunica media, consists mostly of circularly arranged smooth muscle cells and elastic fibers. Since small changes in blood vessel diameter greatly influence blood flow and blood pressure, the activities of the tunica media are critical in regulating circulatory dynamics. The tunica media is usually the bulkiest layer in arteries. The outer most layer is the tunica adventitia and is composed of loosely woven collagen fibers that protect the vessel and anchor it to surrounding structures.

physiology of blood flow:

The velocity of blood flow changes as blood travels through the systemic circulation. It is fastest in the aorta and other large arteries and slowest in the capillaries. Velocity is inversely related to the cross-sectional areaof the vessel to be filled. Blood flows fastest where the total cross-sectional area is least. As the arterial system continues to branch the total cross-sectional area of the vascular bed increases, and velocity of blood flow declines proportionally.

general structure of vascular system:

There are three types of blood vessels: 1. arteries 2. capillaries 3. veins

vessels

There is about 60,000 miles of within the adult body.

Isovolumetric relaxation (early diastole) -

This phase following the T wave, is when the ventricles relax. The blood remaining in the chambers is called the end systolic volume. The falling pressure in the ventricles causes the blood in the large arteries to flow back,which closes the semilunar valves. During the time of ventricular contraction, the atria have been in relaxation and refilling with blood. When the ventricles finish contracting the pressure in the atria is now greater than in the ventricles, and the AV valves reopen.

Hypertension:

Transient elevations occur as normal adaptations during fever, physical exercise, and emotional upset. Although hypertension is usually asymptomatic for the first 10-20 years, it slowly strains the heart and damages the arteries (silent killer). defined physiologically as a condition of sustained elevated arterial pressure of 140/90 or higher. As a general rule, elevated diastolic pressures are more significant medically, because they always indicate progressive occlusion and/or hardening of the arterial tree. About 90% of hypertensive people have "primary or essential" hypertension which cannot be assigned to specific organic cause. Factors such as diet, obesity, heredity, race, and stress are believed to be involved. Clinical signs usually appear after the age of 40. Dietary factors :high sodium, saturated fat,and cholesterol and deficiencies in certain metal ions (potassium, calcium, magnesium). Factors that most accurately predict risk are the seventy of blood pressure elevation, blood cholesterol levels, cigarette smoking, presence of diabetes mellitus, and stress levels.

The sympathetic nervous system(BP)

enervates the smooth muscle layer of blood vessels (arterioles) via- a potent vasoconstrictor.

structure and function of vascular anastomoses:

Where vascular channels unite or interconnect, they form anastomoses. Most organs receive blood from more than one arterial branch, and nearby arteries supplying the same territory often merge, forming arterial anastomoses, which permits free communication between vessels involved and provide alternate pathways for blood to reach a given body region. Arterial anastomoses are abundant in abdominal organs and around joints, where active movement may hinder blood flow through one channel. Veins interconnect much more freely than arteries, and as a result, occlusion of venous channels rarelyblocks blood flow or leads to tissue death.

lumen

a central blood-containing space

Chronic hypertension is

a common and dangerous disease that warns of 'increased peripheral resistance.

The sinoatrial (SA) node:

a small mass of cells in the right atrium that spontaneously depolarize (initiate a contraction) about 75 times a minute. the pacemaker of theheart. The rate of contraction can be altered by the sympathetic nervous system,hormones, and electrolytes depolarization wave spreads by gap junctions throughout atria and reaches the atrioventricular (AV) node . There is a 0.1 sec delay to give the atria time to contract before theventricles contract. The delay happens because the fibers are smaller & fewer gap junctions. After this step the impulses speed up again.

Secondary hypertension

accounts for 10% of cases, is due to identifiable disorders-arteriosclerosis, and endocrine disorders such as hyperthyroidism and Cushing's disease. Treatment is directed at the underlying disorder.

Arteries and veins

act simply as conduits for blood. Only the capillaries come into intimate contact with tissue cells and directly serve cellular needs.

cardiac output

amount of blood pumped out by each ventricle in 1 minute. product of heart rate (HR) and stroke volume .

veins

are blood reservoir

arteries

are conduits

capillaries

are exchange sites

Baroreceptors (BP)

are mechanoreceptors that detect changes in arterial pressure.located in the carotidsinuses and the aortic arch & in nearly every large artery of the neck and thorax. When pressure rises and stretches these receptors, they send signals to the vasomotor center resulting in vasodilation and decline in pressure.

papillary muscles

are projecting and stalk-like and play a role in valve function.

arterioles

are resistance vessels

Ventricular systole -

atria relaxes, the ventricles begin contracting, the AV valves close; the ventricles are now in the isovolumetric contraction phase. Then the semilunar valves open, and blood is expelled from the ventricles to the aorta and pulmonary trunk (ventricular ejection phase)

When arterioles constrict blood :

backs up in the arteries and blood pressure increases. Blood pressure varies directly with the amount of blood in the vascular system. Blood volume varies with age and gender and is usually maintained at about 5 liters in adults.

heart

is the pump

Lungs:(Blood Flow)

blood flow through the lungs is unusual in many ways. The pathway is short, and the arteries and arterioles are similar to veins and venules in structure (thin walls, large lumens). There is little resistance to blood flow, and less pressure is needed. Arterial pressure in the pulmonary circulation is much lower (about 25/10 versus 120/80). The autoregulatory mechanism is exactly opposite that seen in most tissues (low oxygen causes vasoconstriction). When the air sacs of the lungs are flooded with oxygen-rich air, the pulmonary capillaries become flushed with blood and ready to receive the oxygen. If the air sacs are blocked, the oxygen content in those areas will be low, and blood will largely bypass those areas.

Vascular shock :

blood volume is normal and constant. Poor circulation results from extreme vasodilation that leads to an abnormal expansion of the vascular bed. The huge drop in peripheral resistance is revealed by rapidly falling blood pressure. The most common causes are loss of vasomotor tone due to failure of autonomic nervous system regulation and septicemia.

Primary hypertension

cannot be cured. Most can be controlled by diet, losing weight, and antihypertensive drugs.

Blood vessel diameter

changes often , important factor in altering peripheral resistance. Fluid close to the walls of a channel is slowed by friction as it passes along the wall-fluid in the center of the channel flows more freely and faster. smaller the tube=greater the friction because relatively more fluid contacts the tube walls. Because arterioles are small diameter vessels and can enlarge or constrict in response to neural and chemical controls, they are the major determinants of peripheral resistance.

forms of circulatory shock:

circulatory shock, hypovolemic shock, vascular shock, and cardiogenic shock

Coronary atherosclerosis -

clogging of coronary vessels with fatty buildup, impairs blood and oxygen delivery to cardiac cells

Blood pressure in the elastic arteries

close to the heart reflects two factors: 1. how much those arteries can be stretched 2. the volume of blood forced into them at any time . Blood pressure changes in a regular fashion in the elastic arteries near the heart, and blood flow within them is pulsatile.

Persistent hypertension is

common in obese people because of the total length of their blood vessels is relatively greater than that in thinner people.

Purkinje fibers:

complete the pathway to the apex and then turn superior to depolarize the contractile cells of both ventricles, which spread throughout the ventricles via gap junctions between cells. The ventricles then contract from inferior to superior forcing blood into arteries (pulmonary and aorta).

An electrocardiogram (ECG, EKG):

composite of all the action potentials generated by the intrinsic conduction system. It is made possible because the electrical currents generated in and transmitted through the heart spread throughout the body and can be detected. Atrial depolarization( by the SA node) - P wave. atrial depolarization complete, impulse is delayed at the AV node. Ventricular depolarization begins at the apex-QRS complex. During this time atrial repolarization occurs (restoration of ion distribution allowing another depolarization event) the wave is not visible, being drowned out by the large QRS wave. Ventricular depolarization is completed. Ventricular repolarization begins at the apex-T wave. After the T wave, ventricular repolarization is complete

Congestive heart failure -

condition where pumping efficiency (CO) of the heart is so low that blood circulation is inadequate to meet tissue needs

Systole:

contraction period of heart (forcing blood out of its chambers)

The nervous system (BP)

controls blood pressure and distribution by altering the diameter of arterioles.

Osmotic pressure:

created by the presence in a fluid of large nondiffusible molecules, such as plasma proteins. Such substances draw water toward them. Osmotic pressure does not vary form one end of the capillary bed to the other. At any point along a capillary, fluids will leave the capillary if net hydrostatic pressure is greater than net osmotic pressure, and fluids will enter if net osmotic pressure exceeds net hydrostatic pressure.

Multiple myocardial infarcts -

decreases pumping efficiency because dead heart cells are replaced by scar tissue

Function of arterial system Muscular arteries, (distributing arteries):

deliver blood to specific body organs and account for most of the named arteries. Their diameter ranges from that of a little finger to that of a pencil lead. They have the thickest tunica media of all vessels. Their tunica media contains smooth muscle and less elastic tissue. more active in vasoconstriction and are less distensible.

Fenestrated capillaries

essentially similar to the continuous variety except that some of the endothelialcells are riddled with oval pores/fenestrations (windows). The fenestrations are usually covered by a very delicate membrane , so this variety has greater permeability to fluids and small solutes. They are found where active capillary absorption occurs, (such as in the small intestines, and in endocrine organs) which allow hormones to gain rapid entry into the blood. Fenestrated capillaries with perpetually open pores occur in the kidneys, where rapid filtration is essential. Highly modified, leaky capillaries (sinusoids) connect the arterioles and venules in the liver, bone marrow, lymphoid tissues, and some endocrine glands.

Skeletal muscles:(blood flow)

extremely changeable, varies with the degree of muscle activity. Resting skeletal muscles receive about 1 liter of blood per minute, and only about 25% of their capillaries are open. During this time, myogenic and general neural mechanisms predominate. When muscles become active, blood flow increases in direct proportion to their greater metabolic activity (active or exercise hyperemia). During vigorous exertion, blood flow can increase tenfold or more, and virtually all capillaries are open. Autoregulation occurs almost entirely in response to the decreased oxygen concentration. Systemic adjustments occur to ensure that more blood reaches the muscles. Vasoconstriction of vessels in the digestive viscera and skin diverts blood away from these areas temporarily.

Hydrostatic pressure:

force exerted by fluid pressing against a wall. In capillaries, hydrostatic pressure is the same as capillary blood pressure -- pressure of blood against the capillary wall. Capillary hydrostatic pressure is also called filtration pressure because it forces fluids through the capillary walls. Hydrostatic forces dominate at the arterial end while osmotic forces dominated at the venous end. Thus, net fluid flows out of the circulation at the arterial ends of the capillary beds and into the blood stream at the venous end. More fluid enters the tissue spaces than is returned to the blood. This fluid and any leaked proteins are picked up by the lymphatic vessels

Blood Vessels

form the closed delivery system that begins and ends at the heart. They are dynamic structures that pulsate, constrict, and relax, and even proliferate.

Function of arterial system Arterioles:

have a lumen smaller than 0. 3 mm , smallest of the arterial vessels. The largest of the arterioles exhibit all three tunics, but the tunica media is chiefly smooth muscle with few elastic fibers. Blood flow into the capillary beds determined by alterations in arteriole diameter in response to changing neural stimuli and local chemical influences. When arterioles constrict the tissues served are largely bypassed. When arterioles dilate, blood flow into the local capillaries increases .

Dilated cardiomyopathy -

heart enlargement; ventricles stretch and have decreased contractility

Abnormal heart sounds:

heart murmurs-Unobstructed blood flows silently. If theres obstructions, the turbulence generates heart murmurs.

Systemic blood pressure

highest in the aorta and declines throughout the length of the pathway to finally reach 0mm Hg in the right atrium. The steepest change in pressure occurs in the arterioles, which offer the greatest resistance to blood flow. So long as a pressure gradient exits, blood flow continues until it completes the circuit back to the heart.

variations from normal blood pressure

hypotension and hypertension

The net result of autoregulation is:

immediate vasodilation of the arterioles serving the capillary beds of needy tissues, and blood flow to the area is temporarily increased. This is accompanied by relaxation of precapillary sphincters allowing blood to surge through the true capillaries.

covering of heart :

in order: double walled pericardium--> outer fibrous pericardium( protects heart and anchors to surrounding structures: diaphram , sternum, and great vessels)--> outer serous pericardium(parietal pericardium:fused to outer fibrous peri.)--> serous fluid(prevents friction damage as heart contracts)--> inner serous pericardium(visceral pericardium:covers hearts external surface)--> heart wall--> heart

Hypercalcemia (affects HR)

increases heart irritability, can lead to spastic heart contraction.

Too much sodium(affects HR)

inhibits transport of calcium, thus blocking heart contraction.

Excess potassium (affects HR)

interferes with depolarization and may lead to heart block and cardiac arrest.

The activity of the vascular smooth muscle

is regulated by vasomotor fibers of the sympathetic system. Depending on the needs of the body, the vasomotor fibers can cause either vasoconstriction or vasodilation.

Venous blood pressure

is steady and changes very little during the cardiac cycle.

Sinusoids

large, irregularly shaped lumens, and are usually fenestrated. These modifications allow large molecules to pass between blood and surrounding tissues. Blood flows sluggishly through the sinusoid channels, allowing time for it to be processed or modified in various ways (absorbing nutrients, removing and destroying microbes).

Function of arterial system Elastic arteries

large, thick-walled vessels near the heart( ex.aorta and its major branches.) largest and most elastic in arterial system . Their large-diameter lumen allows them to serve as low-resistance conduits. The elastic arteries contain more elastin than any other vessel type. The abundance of elastin enables these arteries to withstand and smooth out large pressure fluctuations by expanding when the heart forces blood into them, and then recoiling to propel blood onward into the circulation when the heart relaxes. The alternating expansion and recoil of elastic arteries during each cardiac cycle creates a pressure wave called a pulse. The arterial pulse rate reflects heart rate.

The atrioventricular valves (AV):

located at the junctions of the atria and theyre respective ventricles and prevent backflow into the atria when ventricles are contracting. The right AV valve, the tricuspid, has 3 valve flaps/cusps. The left AV valve/mitral valve, the bicuspid, has two. Attached to AV valve flaps are tiny white collagen cords -chordae tendineae ("heart strings") that anchor the cusps to the papillary muscles protruding from the ventricular walls. When heart is relaxed, the AV valve flaps hang open. Blood flows through the atria into the ventricles. When the ventricles contract, pressure rises in the ventricle and forces blood against the valve flaps- closing the valve. The chordae tendineae and papillary muscles anchor the valve flaps in the closed position. If the cusps where not anchored in this manner, they would be blown upward into the atria.

atrioventricular (AV) node:

located in the inferior portion of the interatrial septum. the nerve fibers spread the depolarization wave through the atrioventricular bundle (bundle of His) . the AV bundle splits into right and left bundle branches which continue down the interventricular septum.

atrioventricular bundle(bundle of His):

located in the interventricular septum.

vessel length

longer the vessel= greater resistance. Since viscosity and vessel length are normally unchanging, these factors are constant.

Chronic hypotension

may hint at poor nutrition because the poorly nourished are often anemic and have inadequate levels of plasma proteins.

regulation of heart rate:

most important influences on heart rate are from autonomic nervous system. When the sympathetic nervous system is activated, norepinephrine is released causing the heart to beat faster and to contract more forcibly. Activation of the parasympathetic division opposes the sympathetic effects and reduces heart rate via the release of acetylcholine. Hormones such as epinephrine produces the same effects as norepinephrine. Thyroxine causes a slower but more sustained increase in heart rate when it is released in large quantities. Reduced blood levels of ionic calcium depress the heart. Other factors including age, gender, exercise, and body temperature also influence heart rate.

Heart:(blood flow)

movement of blood through the smaller vessels of the heart is influenced by aortic pressure and the pumping activity of the ventricles. When the ventricles contract, the coronary vessels are compressed, and blood flow stops. As the heart relaxes, the high aortic pressure forces blood through the circulation. Under resting conditions, blood flow through the heart is about 250ml/min. During strenuous exercise, the coronary vessels dilated in response to a local accumulation of ADP and carbon dioxide, and blood flow can increase 3 to 4 times. This increased blood flow is important because cardiac cells use as much as 65% of the oxygen carried to them in blood under resting conditions (most other tissue use 25%). Increased blood flow is the only way to make sufficient oxygen available

Cardiogenic shock, or pump failure :

occurs when the heart is so inefficient that it cannot sustain adequate circulation. It's usually cause is myocardial damage from numerous myocardial infarcts.

Peripheral resistance is

opposition to flow ,measure of the amount of friction the blood encounters passing through the vessels. Most friction is encountered in the peripheral circulation. There are three important sources of resistance: 1. blood viscosity 2. vessel length 3. vessel diameter

inferior ventricles:

pumps blood out of heart . The right ventricle pumps blood to pulmonary arteries carriying blood to the lungs. left ventricle ejects blood into aorta carrying blood to the body. Marking the internal ventricle walls are irregular muscle ridges called trabeculae carneae.

Venules

range are about 8-100μm in diameter, and are formed when capillaries unite. The smallest venules (postcapillaryvenules) consist entirely of endothelium around which a few fibroblasts congregate. The venules are extremely porous, and inflammatory fluid and WBC's move easily from the blood stream through their walls. Venules join to form veins, which usually have three distinct tunics, but their walls are always thinner and their lumens larger than those of corresponding arteries.

diastole:

relaxation period of heart (allowing its chambers to refill with blood)

Blood viscosity is

resistance to flow and related to the thickness/stickiness of a fluid. greater the viscosity, =less easily molecules pass one another.

blood enters the right atrium via three veins:

returns blood from body regions: superior vena cava- superior to diaphram inferior vena cava-inferior to diaphram coronary sinus-collects blood draining from myocardium

vascular shunt (metarteriole-thoroughfare channel) -

short vessel connects the arteriole and venule at opposite ends of the capillary bed.

Blood flow is

the actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given period of time. For the entire vascular system, blood flow is = to cardiac output.

Blood pressure is

the force per unit area exerted on the wall of a blood vessel by blood.Differences in pressure within the vascular system provide force that keeps blood moving through the system. The term blood pressure means- systemic arterial blood pressure in the largest arteries near the heart. in terms of millimeters of mercury.

Persistent high blood pressure -

the heart must work harder to pump the blood against the pressure exerted by arterial blood

Prolonged hypertension is

the major cause of heart failure, vascular disease, renal failure and strokes.Because the heart has to work harder, the myocardium enlarges, the heart weakens and its walls become flabby. The vessels also develop small tears 'in the endothelium and accelerate the progress of atherosclerosis. As the vessels become increasingly blocked, blood flow to the tissues becomes inadequate, and vascular complications of vessels 'in the brain, retinas heart and kidneys begin to appear.

Hypovolemic shock :

the most common form of shock. It results from large-scale blood loss such as might follow acute hemorrhage, severe vomiting or diarrhea, or extensive bums. If blood volume drops rapidly, heart rate increases, creating a weak, "thready" pulse. Intense vasoconstriction alsooccurs moving blood away from blood reservoirs into the major circulatory channels. Blood pressure is stable at first, but eventually drops if blood volume loss continues. The key to management is fluid replacement as quickly as possible.

Blood vessel diameter changes

the most important influence on pressure and blood flow patterns. Very small changes in diameter can produce substantial changes in resistance and blood pressure, because resistance varies inversely with the fourth power of vessel radius. if the radius of a vessel is doubled=resistance is then 1/16 as much

Brain:(blood flow)

total blood flow to the brain averages about 750 ml/min and is maintained at relatively constant levels. Cerebral blood flow is regulated by one of the most precise autoregulatory systems in the body and is tailored to local neuronal need. Brain tissue is exceptionally sensitive to declining pH and increased carbon dioxide. Oxygen deficits are much less potent stimulus for autoregulation. Greatly excessive carbon dioxide levels abolish autoregulatory mechanisms and severely depress brain activity. The brain also has myogenic mechanisms that protect it from possible damaging changes in blood pressure. Fainting occurs when mean arterial pressure falls below 60 mm Hg and cerebral edema is the usual result of pressures over 160mm Hg.