SB CARDIOVASCULAR SYSTEM PART 2

Explain why the alveoli normally do not fill with fluid.

Adjacent cells of the walls of the alveoli are bound so tightly together, that glucose, and sodium, potassium, and chloride ions cannot enter the alveoli. Since these substances remain in the interstitial space, the osmotic pressure in the interstitial space is higher than the of the alveoli. Therefore, any water that enters the alveoli is transported back into the interstitial space by osmosis.

How does venous circulation help maintain blood pressure when hemorrhaging causes blood loss?

After a hemorrhage, sympathetic stimulation of the muscle in the walls of veins causes vasoconstriction. This increases the amount of blood returned to the heart. More blood is now pumped out of the heart, which leads to an increase in blood pressure.

END-SYSTOLIC VOLUME (ESV)

After blood is ejected from the heart, come blood remains in the ventricle.

What causes a pulse in an artery?

A pulse is caused by the alternating pattern of expansion and recoil that occurs in the wall of an artery during a heartbeat. Ventricular contraction causes the walls of arteries to expand, as they receive blood from the ventricles. Ventricular relaxation then allows the arterial walls to recoil, due to a sudden decrease in blood pressure.

VENTRICULAR DIASTOLE

atrial pressure exceeds ventricular pressure, and the two atrioventricular (AV) valves open. A large portion of the blood flows passively from the atria into the ventricles through the open AV valves.

ATRIAL SYSTOLE

atrial pressure increases, and the rest of the atrial blood is pumped into the ventricles; this causes ventricular pressure to increase.

TUNICA INTERNA (INTIMA)

composed of a layer of simple squamous epithelium called ENDOTHELIUM

WALL OF AN ARTERY

consists of three distinct layers or tunics

ASCENDING AORTA

first part of the aorta

LUMEN

hollow space inside of an artery or arteriole, changes diameter (diameter = radius x 2) in response to the contraction (vasoconstriction) or relaxation (vasodilation) of smooth muscle within the artery/ arteriole wall.

LUMEN DIAMETER (Vasoconstriction)

lumen diameter and radius DECREASE causing an INCREASE in both PR and BP

LUMEN DIAMETER (Vasodilation)

lumen diameter and radius INCREASE causing a DECREASE in both PR and BP

BLOOD VESSELS

organs of the cardiovascular system; they form a closed circuit of tubes that carries blood from the heart to the body cells and back again

BRACHIOCEPHALIC TRUNK

supplies blood to the tissues of the upper limb and head; the first branch from the aortic arch and rises through the mediastinum to a point near the junction of the sternum and the right clavicle. Divides giving rise to the right common carotid artery and the right subclavian artery

AORTIC SINUS

swelling in the aortic wall, behind each cusp of the semilunar valve

CARDIAC OUTPUT (CO)

the amount (volume) of blood pumped by a single ventricle per minute Quantifies the amount of blood entering circulation Heart Rate (HR) x (multiplied by) Stroke Volume (SV) An increase in CO causes an increase in BP [Cardiac output (CO) = Stroke volume (SV) x Heart rate (HR)]

VISCOSITY

the difficulty with which the molecules of a fluid flow past one another. The greater the viscosity, the greater the resistance to flow. The greater the blood's resistance to flowing, the greater the force needed to move it through the vascular system, so blood pressure rises as blood viscosity increases and drops as blood viscosity decreases. Anemia may decrease viscosity and consequently lower blood pressure. Excess red blood cells (polycythemia) increase viscosity and blood pressure.

AFTERLOAD

the force that the ventricles must produce to open the semilunar valves to eject blood Increased arterial blood pressure (hypertension), especially the diastolic pressure, increases afterload and the heart must work harder to eject blood.

AORTA

the largest-diameter artery in the body from which all systemic arteries branch It extends upward from the left ventricle, arches over the heart to the left, and descends just anterior and to the left of the vertebral column.

SYSTOLIC PRESSURE

the maximum pressure achieved during ventricular contraction. When the ventricles contract (ventricular systole), their walls squeeze the blood inside their chambers and force the blood into the pulmonary trunk and aorta. As a result, the pressure in these arteries sharply increase.

TUNICA MEDIA

the middle layer makes up the bulk of the arterial wall; contains smooth muscle cells that encircle the tube, and a thick layer of elastic connective tissue

TUNICA EXTERNA

the outer layer is relatively thin and chiefly consists of connective tissue with irregular elastic and collagen fibers; attaches the artery to the surrounding tissues

AORTIC ROOT

the part of the aorta attached to the heart

CAPILLARIES

the smallest-diameter blood vessels, most often connect the smallest arterioles and the smallest venules extensions of the inner linings of arterioles in that their walls are endothelium - a single layer of squamous epithelial cells These thin walls form the semipermeable layer through which substances in the blood are exchanged for substances in the tissue fluid surrounding body cells.

CONTRACTILITY

the strength of a contraction at a given preload (EDV), is influenced by autonomic innervation and hormones (epinephrine, norepinephrine, thyroid hormones)

AORTIC ARCH

three major arteries originate from it: the brachiocephalic trunk, the left common carotid artery, and the left subclavian artery; have baroreceptors that detect changes in blood pressure

RIGHT COMMON CAROTID ARTERY

transports blood to the right side of the neck and head

VASOCONSTRICTION

INCREASES PR resulting in DECREASED blood flow

FLUID INTAKE

INCREASES blood volume (BV) and is largely dependent upon ingested water

CHANGES IN BLOOD VOLUME

If a hemorrhage reduces blood volume, blood pressure at first drops. If a transfusion restores normal blood volume, normal pressure may may be reestablished. If the fluid balance is upset, as happens in dehydration. Fluid replacement can reestablish normal blood volume and pressure.

Trace the path of blood through the pulmonary circuit form the right ventricle.

Blood flows from the right ventricle of the heart through the pulmonary valve into the pulmonary trunk, and then into the right and left pulmonary arteries, which enter the right and left lungs. The blood then flows into lobar branches of the pulmonary arteries, and into arterioles that continue into capillary networks associated with alveoli. While in the alveolar capillaries, the blood drops off CO2 and picks up O2; it then continues into the pulmonary venules. These venules merge with small veins, which merge with the larger right and left pulmonary veins. Blood from the pulmonary veins enters the left atrium of the heart.

CONTROL OF BLOOD PRESSURE

Blood pressure (BP) is determined by cardiac output (CO) and peripheral resistance (PR) according to this relationship: BP = CO x PR

How does blood volume affect blood pressure?

Blood pressure is directly proportional to blood volume. Factors that cause a decrease in blood volume, such as blood clots, also cause blood pressure to decrease. Any factor than increases blood volume will also increase blood pressure.

What is the relationship between peripheral resistance and blood pressure? Between blood viscosity and blood pressure?

Blood pressure is directly proportional to both peripheral resistance and blood viscosity. Peripheral resistance is the force of friction between the blood and the inner walls of blood vessels. When vasodilation occurs in arterioles, it its easier for blood flow from the arteries into the arterioles; this causes a decrease in peripheral resistance, which lowers the blood pressure. Blood viscosity measures how difficult it is for molecules in the blood to flow past each other. Great viscosity leads to greater resistance to flow, and higher blood pressure.

PULMONARY CIRCUIT

Consists of vessels that transport oxygen-poor blood from the right ventricle to the alveolar capillaries in the lungs, and vessels that transport oxygen-rich blood back to the left atrium Alveolar capillaries exert less pressure than those of the systemic circuit. Tightly joined epithelial cells of alveolar walls prevent most substances from entering the alveoli. Osmotic pressure rapidly draws water out of alveoli into the interstitial fluid, so alveoli do not fill with fluid.

VASODILATION

DECREASES PR which increases blood flow

FLUID OUTPUT

DECREASES blood volume (BV) and is the amount of water lost through sweating, respiration, and waste removal

How do respiratory movements affect venous blood flow?

During inspiration, when the diaphragm contracts downward, the abdominal pressure increases as the thoracic pressure decreases. Blood in the abdominal veins flows into the thoracic veins, where the pressure is lower. This helps to move blood back toward the heart.

BLOOD PRESSURE MEASUREMENTS

Measured using a sphygmomanometer or BP cuff The BP is inflated until blood flow through the brachial artery is temporarily stopped. The air from the cuff is slowly released as a practitioner listens through a stethoscope for pulse sounds. The normal resting blood pressure in adults is less than 120/80. The upper number indicates the systolic pressure in mm Hg, and the lower number indicates the diastolic pressure in mm Hg.

RADIAL PULSE RATE

Equal to the rate at which the left ventricle contracts, and for this reason, it can be used to determine heart rate A pulse can also reflect blood pressure, because an elevated pressure produces a pulse that feels strong and full, whereas a low pressure produces a pulse that is weak and easily compressed.

BLOOD VOLUME

Equals the sum of the formed elements and plasma volumes in the vascular system

Describe the effects of abnormal concentrations of potassium and calcium ions on the heart.

Excess blood potassium level decreases the heart rate and force of contraction, which may cause cardiac arrest. Deficient blood potassium may lead to an arrhythmia, a dangerous abnormal rhythm of the heart. Excess blood calcium increases the actions of the heart, and may extend the contractions. A deficiency of blood calcium decreases the action of the heart.

EXCHANGES IN THE CAPILLARIES

Gases, nutrients, and metabolic by-products are exchanged between the capillary blood and tissue fluid. Diffusion provides the most important means of transport. Diffusion pathways depend on lipid solubilities. Plasma proteins generally remain in the blood. Filtration, due to the hydrostatic pressure of blood, causes a net outward movement of fluid at the arteriolar end of the capillary. Colloid osmotic pressure causes a net inward of fluid at the venular end of the capillary. Some factors cause fluids to accumulate in the tissues. Transcytosis moves larger substances through the capillary wall.

VENOUS BLOOD FLOW

Not a direct result of heart action; it depends on skeletal muscle contraction, breathing movements, venoconstriction VENOCONSTRICTION can increase venous pressure and blood flow

Distinguish between systolic and diastolic blood pressure.

Systolic blood pressure is the maximum arterial pressure reached during ventricular systole (contraction). Diastolic pressure is the minimum pressure remaining in the arteries at the end of ventricular diastole (relaxation).

STROKE VOLUME (SV)

The amount of blood ejected from the ventricle per heartbeat EDV - (minus) ESV = (equals) SV

END-DIASTOLIC VOLUME (EDV)

The amount of blood that fills the ventricle during diastole The greater the EDV the greater the PRELOAD, or stretch on the heart wall, which INCREASES SV.

What is the largest artery of systemic circuit?

The aorta is the largest artery in the systemic circuit.

MEAN ARTERIAL PRESSURE

The average pressure in the arterial system represents the average force throughout the cardiac cycle driving blood to the tissues. Add the diastolic pressure to one-third of the pulse pressure (DP + 1/3 PP)

What is the function of the baroreceptors in the aortic arch and carotid sinuses?

The baroreceptors detect changes in blood pressure in the aorta and carotid arteries, and relay this information to the cardiac center in the medulla oblongata. A change in blood pressure evokes a response form the cardiac center, in order to bring the blood pressure back into normal range. A sympathetic response increases blood response, while a parasympathetic response decreases it.

In which blood vessel is arterial blood pressure commonly measured?

The brachial artery is most commonly used for measuring blood pressure.

What is the function of the smooth muscle in the arterial wall?

When the smooth muscle contracts, it decrease the diameter of the artery; this is called vasoconstriction. When the smooth muscle relaxes, it increase the diameter of the artery, this is called vasodilation. Changes in arterial diameter affect blood flow to various organs and blood pressure.

DIASTOLIC PRESSURE

When the ventricles relax (ventricular diastole), the arterial pressure drops, and the lowest pressure that remains in the arteries before the next ventricular contraction.

What factors stimulate venoconstriction?

Low venous pressure, blood loss, and low arterial blood pressure stimulate venoconstriction.

VEINS

Vessel that transports blood toward the heart Contain flaplike valves that open, allowing blood to the heart, but close to prevent flow in the opposite direction

ARTERIAL DIASTOLIC PRESSURE (DP)

Pulse sounds are no longer heard

How do skeletal muscles affect venous blood flow?

Skeletal muscles shorten and widen as they contract, squeezing local veins. As blood moves through the narrowed veins, venous valves prevent backflow. Since the blood can only move through open valves, it can travel in one direction, back toward the heart.

PULSE

Surge of blood pressure felt through the walls of arteries due to the contraction of the heart ventricles

RIGHT SUBCLAVIAN ARTERY

leads into the right arm Branches of the subclavian artery also supply blood to parts of the shoulder, neck, and head.

AORTIC BODIES

lie in the epithelial lining of the aortic arch; house chemoreceptors that sense blood pH and blood levels of oxygen and carbon dioxide

How do valves in the systemic veins assist in returning blood to the heart?

Valves in the veins are one-way valves, which prevent backflow of blood. As blood travels back toward the heart, especially from the upper and lower limbs, the valves allow the blood to travel only in one direction, upward toward the heart. This opposes the effects of gravity, which would tend to pull the blood downward toward the hands or feet.

What are the functions of veins and venules?

Veins and venules return blood to the heart and act as blood reservoirs.

How does the structure of a vein differ from that of an artery?

Veins consists of three layers, like arteries, but the walls of veins are thinner than those of arteries. The tunica media in veins is much thinner that that of arteries, and it contains less elastic connective tissue and smooth muscle. Also, many veins contain valves to prevent the backflow of blood; arteries do not have valves. Another difference is that the lumens of veins have greater diameters than those of arteries.

What is the function of the venous valves?

Venous valves are shaped so that they only open in one direction. They allow blood to flow toward the heart, and help prevent blood from flowing backward, and pooling in the veins. this is very important in the upper and lower lims, as the force of gravity tends to pull the blood downward, toward the hand or feet.

PERIPHERAL RESISTANCE (PR)

A force that opposes blood flow This occurs due to the friction between blood and the vessel wall and explains why blood moves fastest in the center of the vessel lumen and slowest at the vessel wall.

What is the function of a capillary?

A capillary exchanges substances, such as oxygen, carbon dioxide, and nutrients, between the blood and the tissue fluid that surrounds the cells.

VASOCONSTRICTION

A decrease in the diameter of blood vessels caused by contraction of smooth muscles in the vessel walls.

Describe the wall of an artery.

An artery consists of three layers. The tunica interna is the innermost layer, and consists of simple squamous epithelium, or endothelium, and an underlying layer of connective tissue containing collagen and elastic fibers. The tunica media is the thick middle layer; it consists of circular smooth muscle and elastic connective tissue. The tunica externa is the thin outermost layer; it consists of connective tissue.

How do changes in body temperature affect heart?

An increase in body temperature increases heart rate, and decrease in body temperature decreases heart rate.

What controls blood flow into the capillaries?

Blood flow into capillaries is regulated by precapillary sphincters, small bands of smooth muscle that wrap around the beginning of the capillaries. These sphincters constrict the capillaries as they contract, and dilate them as they relax.

How is cardiac output calculated?

Cardiac output is calculated by multiplying heart rate by stroke volume. CO = HR x SV.

Describe how the volume of blood returning to the heart and entering the ventricles affects cardiac output.

Cardiac output is limited by the volume of blood that us returning to the ventricles. The more blood that enters the ventricles, the more the myocardial cells of the ventricles stretch (preload). This leads to a greater force of ventricular contraction, a higher stroke volume, and a higher cardiac output. A lower volume of blood returning from the veins leads to a lower cardiac output.

How are cardiac output and blood pressure related?

Cardiac output is the amount of blood ejected from each ventricle per minute. Cardiac output = heart rate x stroke volume. Blood pressure is directly proportional to the cardiac output. An increase in stroke volume or heart rate causes the cardiac output to increase, which leads to an increase in blood pressure.

SYSTEMIC CIRCUIT

Composed of vessels that lead from the left ventricle to all body parts (including vessels supplying the heart itself) and back to the heart. It includes the aorta and its branches as well as the system of veins that return blood to the right atrium.

How is the structure of an arteriole different from that of an artery?

Larger arterioles have the same three layers as arteries, but they are thinner. As the arterioles become smaller, the tunica media and tunica externa become thinner. The smallest arterioles are composed only of an endothelium, and a small amount of smooth muscle and connective tissue.

CAPILLARY PERMEABILITY

Openings in capillary walls are thin slits between endothelial cells. The sizes of the capillary wall openings vary form tissue to tissue, with the smallest to largest openings being (in order): continuous capillaries, fenestrated capillaries, sinusoidal capillaries. Endothelial cells of brain capillaries are tightly fused, forming a blood-brain barrier.

BLOOD VESSEL LENGTH

PR increase over the time and distance blood travels through a blood vessel. NOTE: When an individual gains a large amount of weight, which requires additional blood vessel length, the individual suffers from both increased PR and higher BP.

How do parasympathetic and sympathetic impulses help control heart rate?

Parasympathetic fibers originating in the medulla oblongata connect mainly to the SA and AV nodes; their main effect is to decrease heart rate by lessening the activity of the SA node. Under resting conditions, the parasympathetic nervous system keeps the heart rate down to 60-80 beats/minute, lower than the inherent firing rate of the SA node, which is 100 beats/minute. Sympathetic neurons increase the heart rate by acting on the SA node, AV node, and ventricular myocardium.

REGULATION OF THE CARDIAC CYCLE

Physical exercise, body temperature, and concentration of various ions affect heart rate Branches of parasympathetic and sympathetic nerve fibers innervate the SA and AV nodes. (1) Parasympathetic impulses decrease heart action; sympathetic impulses increase heart action. (2) The cardiac center in the medulla oblongata regulates autonomic impulses to the heart.

PRESSURE AND VOLUME CHANGES DURING CARDIAC CYCLE

Pressure in chambers rises and falls in cycles Changes in pressure open and close the heart valves Volume in chambers increases during diastole and decreases during systole

CENTRAL VENOUS PRESSURE

Pressure in the right atrium Factors that influence it alter the flow of blood into the right atrium It affects pressure in the peripheral veins

CARDIAC CYCLE

The cardiac cycle is the sequence of contraction and relaxation of the heart chambers during a single heartbeat. The contraction of the heart chambers is called SYSTOLE and relaxation of the heart chambers is called DIASTOLE. The cycle begins with both the ATRIA and VENTRICLES in DIASTOLE. Both AV VALVES are OPEN while the PULMONARY and AORTIC SEMILUNAR VALVES are CLOSED. Blood flows in the RIGHT ATRIUM through the SUPERIOR and INFERIOR VENA CAVA. Blood flows from the LUNGS into the LEFT ATRIUM through the PULMONARY VEINS. Then blood moves from both ATRIA into the VENTRICLES through the OPEN ATRIAL VENTRICULAR VALVES. During atrial systole the ATRIA contract and force any remaining atrial blood into the VENTRICLES. The VENTRICLES are still in DIASTOLE, allowing them to expand and completely fill with blood. During ventricular systole the VENTRICLES contract. The ATRIAL VENTRICULAR VALVES CLOSE, preventing backflow or regurgitation of blood into the ATRIA. The PULMONARY SEMILUNAR VALVE OPENS and the RIGHT VENTRICLE expels blood into the PULMONARY ARTERIES to the LUNGS. Likewise, the AORTIC SEMILUNAR VALVE OPEN and the LEFT VENTRICLE expel blood into the AORTA and out to the rest of the body. After ventricular systole, the cardiac cycle begins again as both the atria and ventricles enter diastole to allow the heart to fill with blood. Normally this cycle repeats 60 to 100 times a minute.

PULSE PRESSURE (PP)

The difference between the systolic and diastolic pressures (SP-DP) is normally about 40 mm Hg

BLOOD PRESSURE (BP)

The force that blood exerts against the walls of blood vessels. BLOOD FLOW depends upon a BP gradient, with blood moving from a HIGHER pressure in the ARTERIES to a LOWER pressure in the VEINS. The pumping action of the heart is responsible for establishing this pressure gradient. Systolic / Diastolic (120/80 mmHg) Most commonly refers to pressure in arteries supplied by branches of the aorta (systemic arteries).

FRANK-STARLING LAW

The greater the length to which the cardiac muscle cells are stretched just before ventricular contraction, the greater the force with which they contract. During exercise venous blood returns more rapidly to the heart. The more blood that enters the heart from the veins, the greater the ventricular distension, the stronger the contraction, the greater the stroke volume, and the greater the cardiac output. The less blood that returns from the veins, the less the ventricle distends, the weaker the ventricular contraction, and the lesser the stroke volume and cardiac output. This mechanism helps ensure that the volume of blood discharged from the heart is equal to the volume entering its chambers.

VENULES

Vessel that transports blood from capillaries to a vein

ATERIAL SYSTOLIC PRESSURE (SP)

The pressure at which the first pulse sound is heard

Which nerves supply parasympathetic fibers to the heart? Which nerves supply sympathetic fibers?

The vagus nerves supply parasympathetic fibers to the heart. The accelerator nerves supply sympathetic fibers to the heart.

How does the vasomotor center control peripheral resistance?

The vasomotor center constantly transmits sympathetic impulses to the smooth muscle in the walls of arterioles. This keep the muscles in a state of partial, or tonic, contraction. This partial vasoconstriction keeps the peripheral resistance in the proper range to maintain normal blood pressure. The vasomotor center can increases sympathetic stimulation, to increase vasoconstriction, peripheral resistance, and blood pressure when necessary. It can also decreases sympathetic stimulation to decrease the blood pressure.

Describe a capillary wall.

The wall of a capillary consists only of endothelium, which is a layer of simple squamous epithelium. A capillary is a continuation of the inner layer of an arteriole.

Describe the pressure and volume changes in the atria and ventricles during a cardiac cycle.

When ventricular diastole begins, atrial pressure exceeds ventricular pressure, and the two atrioventricular (AV) valves open. A large portion of the blood flows passively from the atria into the ventricles through the open AV valves. In atrial systole, atrial pressure increases, and the rest of the atrial blood is pumped into the ventricles; this causes ventricular pressure to increase. During ventricular systole, ventricular pressure increases to the point that it is greater than atrial pressure; this causes the AV valves to close. At this time, the atria are in diastole, and blood is flowing from the venae cavae and the pulmonary veins into the atria. Also during ventricular systole, as soon as ventricular pressure is greater than that of the aorta and pulmonary trunk, the semilunar valves open, and blood flows from the ventricles into the large arteries. As blood leaves the ventricles, ventricular decreases to the point that it is lower than that of the aorta and pulmonary trunk; at this time the semilunar valves close.

VASODILATION

if vasomotor impulses are inhibited, the smooth muscle cells relax, and the diameter of the vessel increases

PRELOAD

increases stroke volume independently of sympathetic stimulation A blood enters the ventricles, myocardial cells in the ventricular walls are mechanically stretched.

ENDOTHELIUM

rest on a connective tissue membrane rich in elastic and collagen fibers The endothelial lining of an artery provides a smooth surface that allows blood cells and platelets to flow through without being damaged Help prevent blood clotting by secreting biochemicals that inhibit platelet aggregation May help regulate local blood flow by secreting substances that stimulate the dilation or constriction of blood vessels EXAMPLE: endothelium releases the gas nitric oxide, which relaxes the smooth muscle, resulting in an increased diameter, or vasodilation, of the vessel.

VENOUS WALLS

similar to arterial walls but are thinner and contain less muscle and elastic tissue

ARTERIOLE

small branch of an artery that communicates with a capillary network

ARTERIES

strong, elastic vessels adapted for transporting blood away from the heart under relatively high pressure

VENTRICULAR SYSTOLE

ventricular pressure increases to the point that it is greater than atrial pressure; this causes the AV valves to close. At this time, the atria are in diastole, and blood is flowing from the venae cavae and the pulmonary veins into the atria. Also, as soon as ventricular pressure is greater than that of the aorta and pulmonary trunk, the semilunar valves open, and blood flows from the ventricles into the large arteries. As blood leaves the ventricles, ventricular decreases to the point that it is lower than that of the aorta and pulmonary trunk; at this time the semilunar valves close.