Part 2: Cardiovascular system

Why does high arterial blood pressure put additional strain on the heart?

- by increasing afterload. - When resistance in the arterioles is high, the myocardium must work harder to push the blood into the arteries.

Would you expect to find valves in the veins leading from the brain to the heart?

No. - Veins from the brain do not require valves because blood flow is aided by gravity.

Define bulk flow

mass movement of water or air as the result of pressure gradients

Describe the structure of capillary walls. How does capillary wall structure relate to capillary function? What are pericytes?

● Capillaries are the smallest vessels in the cardiovascular system. They and the post capillary venules are the site of EXCHANGE between the blood and the interstitial fluid. - To facilitate exchange of materials, capillaries lack smooth muscle and elastic or fibrous tissue reinforcement. Instead, their walls consist of a flat layer of endothelium, one cell thick, supported on an acellular matrix called the basal lamina. ● Many capillaries are closely associated with cells known as pericytes. In most tissues, these highly branched contractile cells surround the capillaries, forming a mesh-like outer layer between the capillary endothelium and the interstitial fluid. Pericytes contribute to the "tightness" of capillary permeability: the more pericytes, the less leaky the capillary endothelium. Cerebral capillaries, for example, are surrounded by pericytes and glial cells, and have tight junctions that create the blood-brain barrier. ● Pericytes secrete factors that influence capillary growth, and they can differentiate to become new endothelial or smooth muscle cells. Loss of pericytes around capillaries of the retina is a hallmark of the disease diabetic retinopathy, a leading cause of blindness.

Outline the mechanisms underlying the two typical causes of edema.

Edema is a sign that normal exchange between the circulatory system and the lymphatics has been disrupted. - Edema usually arises from one of two causes: (1) inadequate drainage of lymph or (2) blood capillary filtration that greatly exceeds capillary absorption.

List the types of catecholamine receptors and indicate their affinities for norepinephrine and epinephrine.

Epinephrine binds with alpha-receptors, reinforcing vasoconstriction. - However, a-receptors have a lower affinity for epinephrine and do not respond as strongly to it as they do to norepinephrine. - In addition, epinephrine binds to beta2-receptors, found on vascular smooth muscle of heart, liver, and skeletal muscle arterioles (fight or flight). - These receptors are not innervated and therefore respond primarily to circulating epinephrine. - Activation of vascular beta2-receptors by epinephrine causes vasodilation.

What types of exchange between the plasma and the interstitial fluid can take place at the capillary?

Exchange between the plasma and interstitial fluid takes place either by movement between endothelial cells (the paracellular pathway) or by movement through the cells (endothelial transport). - Smaller dissolved solutes and gases move by diffusion between or through the cells, depending on their lipid solubility. - Larger solutes and proteins move mostly by vesicular transport.

Precapillary sphincters provide ______________ control of blood flow.

LOCAL - In a tissue, blood flow into individual capillaries can be regulated by the precapillary sphincters. - When these small bands of smooth muscle at metarteriole-capillary junctions constrict, they restrict blood flow into the capillaries. - When the sphincters dilate, blood flow into the capillaries increases. - This mechanism provides an additional site for LOCAL control of blood flow.

Bulk flow moves fluid, proteins, and bacteria __________ (into or out of?) lymph capillaries.

Large gaps between cells allow fluid, interstitial proteins, and particulate matter such as bacteria to be swept into the lymph vessels by bulk flow.

What are the goals of local control of arteriolar resistance?

Local control of arteriolar resistance matches tissue blood flow to the metabolic needs of the tissue. - In the heart and skeletal muscle, these local controls often take precedence over reflex control by the central nervous system.

Where does lymph re-join the blood?

Lymph fluid empties into the venous circulation.

If blood flow into the arteries increases but there is no change in blood flow out of the arteries, MAP will __________ (increase or decrease?).

MAP will increase. - If flow in exceeds flow out, blood collects in the arteries, and MAP increases. - If flow out exceeds flow in, MAP falls.

Differentiate between essential (primary) hypertension and secondary hypertension

More than 90% of all patients with hypertension are considered to have essential (or primary) hypertension, with no clear-cut cause other than heredity. - Cardiac output is usually normal in these people, and their elevated blood pressure appears to be associated with increased peripheral resistance. - In the remaining 5-10% of hypertensive cases, the cause is more apparent, and the hypertension is considered to be secondary to an underlying pathology. - For instance, the cause might be an endocrine disorder that causes fluid retention.

- Diagram the reflex pathway for active hyperemia. - Diagram the reflex pathway for reactive hyperemia.

Schaubilder

What vessels make up the microcirculation? [How do metarterioles differ from arterioles? What is the function of metarterioles?]

Some arterioles branch into vessels known as metarterioles. True arterioles have a continuous smooth muscle layer, but the wall of a metarteriole is only partially surrounded by smooth muscle. - Blood flowing through metarterioles can take 1 of 2 paths: ● If muscle rings called precapillary sphincters are relaxed, blood flowing into a metarteriole is directed into adjoining capillary beds. ● If the precapillary sphincters are constricted, metarteriole blood bypasses the capillaries and goes directly to the venous circulation. In addition, metarterioles allow white blood cells to go directly from the arterial to the venous circulation.

Where are the two main receptors for blood pressure located? What is significant about these locations?

Stretch-sensitive mechanoreceptors known as baroreceptors are located in the walls of the carotid arteries and aorta, where they can monitor the pressure of blood flowing to the brain (carotid baroreceptors) and to the body (aortic baroreceptors).

What are the goals of autonomic reflex control of arteriolar resistance?

Sympathetic reflexes mediated by the CNS maintain mean arterial pressure and govern blood distribution for certain homeostatic needs, such as temperature regulation.

Paracrine Signals Influence Vascular Smooth Muscle:

tabelle mit chemical, physiol. role, source

Hypertension means chronically elevated blood pressure, with systolic pressures greater than __________ mm Hg or diastolic pressures greater than __________ mm Hg. For every 20/10 mm Hg increase in blood pressure over a baseline of 115/75, the risk for CVD __________.

- 130-140 mm Hg - 80- 90 mm Hg. - doubles

How do you explain the fact that stroke volume remains constant in hypertensive patients?

- Amazingly, stroke volume in hypertensive patients remains constant up to a mean blood pressure of about 200 mm Hg, despite the increasing amount of work that the ventricle must perform as blood pressure increases. - The cardiac muscle of the left ventricle responds to chronic high systemic resistance in the same way that skeletal muscle responds to a weight-lifting routine. - The heart muscle hypertrophies, increasing the size and strength of the muscle fibres.

Explain how the relative distribution of blood between the arterial and venous sides of the circulation can be an important factor in maintaining arterial blood pressure.

- Arteries are low-volume vessels that usually contain only about 11% of total blood volume at any one time. - Veins, in contrast, are high-volume vessels that hold about 60% of the circulating blood volume at any one time. - The VV. act as a volume reservoir for the circulatory system, holding blood that can be redistributed to the arteries if needed. - If arterial blood pressure falls, increased sympathetic activity constricts veins, decreasing their holding capacity. - Venous return sends blood to the heart, which according to the Frank-Starling law of the heart, pumps all the venous return out to the systemic side of the circulation. - Thus, constriction of the veins redistributes blood to the arterial side of the circulation and raises mean arterial pressure.

Compare stable plaques and vulnerable plaques, and describe their role in cardiovascular disease.

- Atherosclerosis is now considered to be an inflammatory process in which macrophages release enzymes that convert stable plaques to vulnerable plaques. - Stable plaques have thick fibrous caps that separate the lipid core from the blood and do not activate platelets. - Vulnerable plaques have thin fibrous caps that are more likely to rupture, exposing collagen and activating platelets that initiate a blood clot (thrombus). - If a clot blocks blood flow to the heart muscle, a heart attack, or myocardial infarction, results.

Define and contrast LDL-C with HDL-C. At normal levels, what is the function of LDL-C?

- HDL-C is the more desirable form of blood cholesterol because high levels of HDL are associated with lower risk of heart attacks. - LDL-C is sometimes called "bad" cholesterol because elevated plasma LDL-C levels are associated with coronary heart disease. - Normal levels of LDL-C are not bad, however, because LDL is necessary for cholesterol transport into cells.

What kinds of problems might result when blood pressure is too low? Too high?

- If blood pressure falls too low (hypotension), the driving force for blood flow is unable to overcome opposition by gravity. - In this instance, blood flow and oxygen supply to the brain are impaired, and the person may become dizzy or faint. - On the other hand, if blood pressure is chronically elevated (hypertension), high pressure on the walls of blood vessels may cause weakened areas to rupture and bleed into the tissues. - If a rupture occurs in the brain, it is called a cerebral haemorrhage and may cause the loss of neurological function (stroke). - If a weakened area ruptures in a major artery, rapid blood loss into the abdominal cavity causes blood pressure to fall below the critical minimum.

Distinguish between filtration and absorption in capillaries.

- If the direction of bulk flow is into the capillary, the fluid movement is called absorption. - If the direction of flow is out of the capillary, the fluid movement is known as filtration.

What effect will an increase in parasympathetic activity have on heart rate, force of contraction, and arteriolar diameter?

- Increased parasympathetic activity slows heart rate but has only a small effect on ventricular contraction. - Parasympathetic activity dilates arterioles.

What effect will an increase in sympathetic activity have on heart rate, force of contraction, and arteriolar diameter?

- Increased sympathetic activity increases heart rate at the SA node, shortens conduction time through the AV node, & enhances the force of myocardial contraction. - Sympathetic activity constricts arterioles.

What is lymph? What are lymph nodes?

- Once inside the lymphatics, this clear fluid is called simply lymph - At intervals along the way, vessels enter lymph nodes, bean-shaped nodules of tissue with a fibrous outer capsule and an internal collection of immunologically active cells, including lymphocytes and macrophages.

What creates the osmotic pressure gradient between the plasma and the interstitial fluid? What is colloid osmotic pressure (π)?

- Osmotic pressure is determined by solute concentration of a compartment. - The main solute difference between plasma and interstitial fluid is due to proteins, which are present in the plasma but mostly absent from interstitial fluid. - The osmotic pressure created by the presence of these proteins is known as colloid osmotic pressure (π), also called oncotic pressure. - Colloid osmotic pressure is not equivalent to the total osmotic pressure in a capillary. - It is simply a measure of the osmotic pressure created by proteins. - Because the capillary endothelium is freely permeable to ions and other solutes in the plasma and interstitial fluid, these other solutes do not contribute to the osmotic gradient.

Describe the physical characteristics of the aorta and major arteries.

- The aorta and major arteries are characterized by walls that are both stiff and springy. - Arteries have a thick smooth muscle layer and large amounts of elastic and fibrous connective tissue. - Because of the stiffness of the fibrous tissue, substantial amounts of energy are required to stretch the walls of an artery outward, but that energy can be stored by the stretched elastic fibres and released through elastic recoil.

What determines capillary density in a tissue? Which tissues have the highest capillary density?

- The capillary density in any given tissue is directly related to the metabolic activity of the tissue's cells. - Tissues with a higher metabolic rate require more oxygen and nutrients. - Those tissues have more capillaries per unit area. - Subcutaneous tissue and cartilage have the lowest capillary density. - Muscles and glands have the highest.

Compare the structure and function of continuous and fenestrated capillaries.

- The most common capillaries are continuous capillaries, whose endothelial cells are joined to one another with leaky junctions. - These capillaries are found in muscle, connective tissue, and neural tissue. - The continuous capillaries of the brain have evolved to form the blood-brain barrier, with tight junctions (protect neural tissue from toxins that may be present in blood). - Fenestrated capillaries have large pores that allow high volumes of fluid to pass rapidly between the plasma and interstitial fluid. - These capillaries are found primarily in the kidney and the intestine, where they are associated with absorptive transporting epithelia.

Outline the process of atherosclerotic plaque development.

1) LDL cholesterol accumulates between endothelium & connective tissue & is oxidized. 2) Macrophages ingest cholesterol & become foam cells 3) Smooth muscle cells attracted by macrophage cytokines, begin to divide and take up cholesterol. 4) lipid core accumulates beneath endothelium 5) fibrous scar tissue forms to wall off the lipid core 6) smooth muscle cells divide and contribute to thickening of the intima 7) calcification are deposited within the plaque 8) macrophages may release enzymes that dissolve collagen & convert stable plaques to unstable plaques 9) platelets that are exposed to collagen activate & initiate a blood clot

Give 3 examples of how other systems can influence cardiovascular function.

1) Respiratory System: If tissues require more oxygen, it is supplied by the cardiovascular system working in tandem with the respiratory system. Consequently, increases in breathing rate are usually accompanied by increases in cardiac output. 2) Blood pressure is also subject to modulation by higher brain centres, such as the hypothalamus and cerebral cortex. The hypothalamus mediates vascular responses involved in body temperature regulation and for the fight-or-flight response. Learned and emotional responses may originate in the cerebral cortex and be expressed by cardiovascular responses such as blushing and fainting. 3) Regulation of blood pressure in the cardiovascular system is closely tied to regulation of body fluid balance by the kidneys. Certain hormones secreted from the heart act on the kidneys, while hormones secreted from the kidneys act on the heart and blood vessels. Together, the heart and kidneys play a major role in maintaining homeostasis of body fluids.

What forces regulate capillary bulk flow?

2 forces regulate bulk flow in the capillaries. - One is hydrostatic pressure (lateral pressure component of blood flow that pushes fluid out through the capillary pores). - The other is osmotic pressure. These forces are sometimes called Starling forces.

Explain how blood elevated lipids and diabetes mellitus have both an uncontrollable genetic component and a modifiable lifestyle component.

2 risk factors for cardiovascular disease—diabetes mellitus and elevated blood lipids—have both an uncontrollable genetic component and a modifiable lifestyle component. - Diabetes mellitus is a metabolic disorder that puts a person at risk for developing coronary heart disease by contributing to the development of atherosclerosis ("hardening of the arteries"), in which fatty deposits form inside arterial blood vessels. - Elevated serum cholesterol and triglycerides also lead to atherosclerosis.

Which three tissues don't have traditional capillaries? What do they have? Why are these modified vessels necessary?

3 tissues— the bone marrow, the liver, and the spleen— do not have typical capillaries. - Instead they have modified vessels called sinusoids that are as much as five times wider than a capillary. - The sinusoid endothelium has fenestrations, and there may be gaps between the cells as well. - Sinusoids are found in locations where blood cells and plasma proteins need to cross the endothelium to enter the blood.

Define angiogenesis. Compare angiogenesis in children and in adults.

= The process by which new blood vessels develop, especially after birth. ● In children, blood vessel growth is necessary for normal development. ● In adults, angiogenesis takes place as wounds heal and as the uterine lining grows after menstruation. Angiogenesis also occurs with endurance exercise training, enhancing blood flow to the heart muscle and to skeletal muscles.

Explain why we say that hypertension represents failure of homeostasis.

A key feature of hypertension from all causes is adaptation of the carotid and aortic baroreceptors to higher pressure, with subsequent down-regulation of their activity. - Without input from the baroreceptors, the cardiovascular control centre interprets the high blood pressure as "normal," and no reflex reduction of pressure occurs.

Define systolic pressure and diastolic pressure. Provide average aortic systolic and diastolic values (with units).

Aortic pressure reaches an average high of 120 mm Hg during ventricular systole (systolic pressure), then falls steadily to a low of 80 mm Hg during ventricular diastole (diastolic pressure).

What property of artery walls plays a key role in the ability of arteries to sustain the driving pressure created by the heart?

As blood under pressure is ejected from the left ventricle, the aorta and arteries expand to accommodate it. - When the ventricle relaxes and the semilunar valve closes, the elastic arterial walls recoil, propelling the blood forward into smaller arteries and arterioles. - By sustaining the driving pressure for blood flow during ventricular relaxation, the arteries keep blood flowing continuously through the blood vessels.

What is atherosclerosis? Why is it considered an inflammatory process?

Atherosclerosis = "hardening of the arteries". - Atherosclerosis is now considered to be an inflammatory process, in which macrophages release enzymes that convert stable plaques to vulnerable plaques. - Stable plaques have thick fibrous caps that separate the lipid core from the blood and do not activate platelets. - Vulnerable plaques have thin fibrous caps that are more likely to rupture, exposing collagen and activating platelets that initiate a blood clot (thrombus). - If a clot blocks blood flow to the heart muscle, a heart attack, or myocardial infarction, results.

Create a map showing how the baroreceptor reflex would return homeostasis after a stimulus of increased blood pressure.

Baroreceptors increase their firing rate as blood pressure increases, activating the medullary cardiovascular control centre. In response, the cardiovascular control centre increases parasympathetic activity and decreases sympathetic activity to slow down the heart and dilate arterioles.

Explain mean arterial pressure (MAP). What formula is used to determine MAP?

Because arterial pressure is pulsatile, we use a single value—the mean arterial pressure (MAP)— to represent driving pressure. - Mean arterial pressure is estimated as diastolic pressure plus one-third of pulse pressure: MAP = diastolic P + 1>3 (systolic P - diastolic P)

When blood flow decreases through one set of arterioles, where does that blood go?

Blood is diverted from high-resistance arterioles to lower-resistance arterioles.

What mechanism maintains a continuous driving pressure for blood flow during ventricular contraction? (use the term pressure reservoir)

Blood leaving the left heart enters systemic arteries. - Pressure produced by contraction of the left ventricle is stored in the elastic walls of arteries and slowly released through elastic recoil. - This mechanism maintains a continuous driving pressure for blood flow during ventricular relaxation. - Therefore, the arteries are known as the pressure reservoir of the circulatory system.

How can low-pressure venous blood in the feet flow uphill against gravity to get back to the heart?

Blood return to the heart, known as venous return, is aided by valves, the skeletal muscle pump, and the respiratory pump. - When muscles such as those in the calf of the leg contract, they compress the veins, forcing blood upward past the valves.

Describe blood flow in the venous circulation (in terms of pulse pressure).

By the time blood reaches the veins, pressure has fallen because of friction, and a pressure wave no longer exists. - Venous blood flow is steady rather than pulsatile, pushed along by the continuous movement of blood out of the capillaries.

List some of the common treatments for hypertension.

Calcium entry into vascular smooth muscle and cardiac muscle can be decreased by a class of drugs known as calcium channel blockers. - These drugs bind to Ca+ channel proteins, making it less likely that the channels will open in response to depolarization. - With less Ca2+ entry, vascular smooth muscle dilates, while in the heart the depolarization rate of the SA node and the force of contraction decrease. - Other drugs used to treat hypertension include diuretics, which decrease blood volume, and beta-blocking drugs that target b1-receptors and decrease catecholamine stimulation of cardiac output. - 2 other groups of antihypertensive drugs, the ACE inhibitors and the angiotensin receptor blockers, act by decreasing the activity of angiotensin, a powerful vasoconstrictor substance.

Name two ways the cardiovascular system tries to compensate for a decrease in blood volume.

Cardiovascular compensation for decreased blood volume includes vasoconstriction and increased sympathetic stimulation of the heart to increase cardiac output. However, there are limits to the effectiveness of cardiovascular compensation.

Targeting angiogenesis for the therapeutic purposes - give two examples.

Cytokines that inhibit angiogenesis include angiostatin. - Scientists are currently testing these cytokines for treating cancer, to see if they can block angiogenesis and literally starve tumours to death. - Coronary heart disease, is a condition in which blood flow to the myocardium is decreased by fatty deposits that narrow the lumen of the coronary arteries. - In some individuals, new blood vessels develop spontaneously and form collateral circulation that supplements flow through the partially blocked artery. - Researchers are testing angiogenic cytokines to see if they can duplicate this natural process and induce angiogenesis to replace occluded vessels.

Where - within the CV system - is the site of variable resistance placed?

Downstream from the arteries, small vessels called arterioles create a high resistance outlet for arterial blood flow. - Arterioles direct distribution of blood flow to individual tissues by selectively constricting and dilating, so they are known as the site of variable resistance.

What happens to MAP if peripheral resistance increases?

Flow into arteries is unchanged, but flow out is decreased. - Blood again accumulates in the arteries, and the arterial pressure again increases.

What are the goals of hormonal control of arteriolar resistance?

Hormones—particularly those that regulate salt and water excretion by the kidneys—influence blood pressure by acting directly on the arterioles and by altering autonomic reflex control.

Hydrostatic pressure pushes water ___________ (into or out of?) capillaries. This pressure decreases along the length of the capillary as energy is lost to ______________.

Hydrostatic pressure pushes water out of the capillary. Capillary hydrostatic pressure (PH) decreases along the length of the capillary as energy is lost to friction.

How does hypertension contribute to atherosclerosis?

Hypertension is a risk factor for atherosclerosis because high pressure in the arteries damages the endothelial lining of the vessels and promotes the formation of atherosclerotic plaques. - In addition, high arterial blood pressure puts additional strain on the heart by increasing afterload. - When resistance in the arterioles is high, the myocardium must work harder to push the blood into the arteries.

Briefly describe how a blood clot can lead to myocardial infarction, arrhythmia, and potentially cardiac arrest or death.

If a clot blocks blood flow to the heart muscle, a heart attack, or myocardial infarction, results. - Blocked blood flow in a coronary artery cuts off the oxygen supply to myocardial cells supplied by that artery. - The oxygen-starved cells must then rely on anaerobic metabolism, which produces lactate. - As ATP production declines, the contractile cells are unable to pump Ca + out of the cell. - The unusually high Ca+ concentration in the cytosol closes gap junctions in the damaged cells. - Closure electrically isolates the damaged cells so that they no longer contract, and it forces action potentials to find an alternate route from cell to cell. - If the damaged area of myocardium is large, the disruption can lead to an irregular heartbeat (arrhythmia) and potentially result in cardiac arrest or death.

If blood flow through the systemic circulation is 5 L/min, what is blood flow through the pulmonary circulation?

If cardiac output is 5 L/min, blood flow through all the systemic capillaries is 5 L/min. - In the same manner, blood flow through the pulmonary side of the circulation is equal to blood flow through the systemic circulation.

What is congestive heart failure? How does it arise, and what are its effects on the body?

If cardiac output of the right heart remains normal while the output from the left side decreases, fluid collects in the lungs, creating pulmonary edema. - At this point, a detrimental positive feedback loop begins. - Oxygen exchange in the lungs diminishes because of the pulmonary edema, leading to less oxygen in the blood. - Lack of oxygen for aerobic metabolism further weakens the heart, and its pumping effectiveness diminishes even more. - Unless treated, this condition, known as congestive heart failure, eventually leads to death.

The formula given for calculating MAP applies to a typical resting heart rate of 60-80 beats/min. If heart rate increases, would the contribution of systolic pressure to mean arterial pressure decrease or increase, and would MAP decrease or increase? (map-mean arterial pressure)

If heart rate increases, the relative time spent in diastole decreases. In that case, the contribution of systolic pressure to mean arterial pressure increases, and MAP increases.

How do protein hormones and other essential proteins move out of the blood and into the interstitial fluid?

In most capillaries, larger molecules (including selected proteins) are transported across the endothelium by transcytosis. - The endothelial cell surface appears dotted with numerous caveolae and noncoated pits that become vesicles for transcytosis. - It appears that in some capillaries, chains of vesicles fuse to create open channels that extend across the endothelial cell.

A decrease in blood pressure results in __________________ (increased or decreased?) decrease sympathetic activity and __________________ (increased or decreased?) parasympathetic activity.

Increase, decrease

What is pulse pressure and how do you calculate it?

Pulse pressure, a measure of the strength of the pressure wave, is defined as systolic pressure minus diastolic pressure. - For example, in the aorta: 120 mm Hg - 80 mm Hg = 40 mm Hg pressure

Write the mathematical expression for the relationship between radius (r) and resistance (R).

R∝1/r4

Blood flow from arteries to arterioles is best described as _____________ (divergent or convergent?).

The arteries and arterioles are characterized by a divergent pattern of blood flow.

Which vessels are the main site of variable resistance in the systemic circulation? What property of these vessels permits them to change resistance?

The arterioles are the main site of variable resistance in the systemic circulation and contribute more than 60% of the total resistance to flow in the system. - Resistance in arterioles is variable because of the large amounts of smooth muscle in the arteriolar walls. - When the smooth muscle contracts or relaxes, the radius of the arterioles changes.

If you are monitoring the electrical activity of the sensory neurons linking these baroreceptors to the cardiovascular control centre, would you observe any electrical activity when a person's blood pressure is in the normal range? Are these receptors tonic or phasic?

The carotid and aortic baroreceptors are tonically active stretch receptors that fire action potentials continuously at normal blood pressures. - When increased blood pressure in the arteries stretches the baroreceptor membrane, the firing rate of the receptor increases. - If blood pressure falls, the firing rate of the receptor decreases

If you check the pulse in a person's carotid artery and left wrist at the same time, would the pressure waves occur simultaneously?

The carotid wave would arrive slightly ahead of the wrist wave because the distance from heart to carotid artery is shorter.

Why does blood pressure decrease as blood flows through the circulatory system?

The decrease in pressure occurs because energy is lost as a result of the resistance to flow offered by the vessels. Resistance to blood flow also results from friction between the blood cells.

For substances that diffuse freely across capillary walls, what factor is most important for determining the rate of diffusion?

The diffusion rate for dissolved solutes is determined primarily by the concentration gradient between the plasma and the interstitial fluid.

Why don't all tissues get equal blood flow at all times? At rest, which parts of the body receive most of the cardiac output?

The distribution of systemic blood varies according to the metabolic needs of individual organs. - Blood flow to individual organs is set to some degree by the number and size of arteries feeding the organ. - Usually, more than two-thirds of the cardiac output is routed to the digestive tract, liver, muscles, and kidneys.

Blood flow through individual arterioles depends on __________________.

The flow through individual arterioles depends on their RESISTANCE (R). - The higher the resistance in an arteriole,the lower the blood flow through it. - If an arteriole constricts and resistance increases, blood flow through that arteriole decreases. Flow arteriole ∝ 1/R arteriole

Which two systems of the body are responsible for homeostatic regulation of blood pressure?

The kidneys and the cardiovascular system

Compare the anatomy of the lymphatic system to that of the circulatory system.

The lymphatic system allows the one-way movement of interstitial fluid from the tissues into the circulation. - Blind-end lymph vessels (lymph capillaries) lie close to all blood capillaries except those in the kidney and central nervous system. - The smallest lymph vessels are composed of a single layer of flattened endothelium that is even thinner than the capillary endothelium. The walls of these tiny lymph vessels are anchored to the surrounding CT by fibres that hold the thin-walled vessels open. - Large gaps between cells allow fluid, interstitial proteins, and particulate matter such as bacteria to be swept into the lymph vessels by bulk flow

Name the factors that influence fluid flow through the lymphatics. (Does the lymph system have a pump like the heart?)

The lymphatic system has no single pump like the heart. - Lymph flow depends primarily on waves of contraction of smooth muscle in the walls of the larger lymph vessels. - Flow is aided by contractile fibres in the endothelial cells, by the one-way valves, and by external compression created by skeletal muscles.

Where in the brain is the main integrating centre for the regulation of cardiovascular function?

The main integrating centre is in the medulla oblongata. = Cardiovascular control centre

How is net fluid flow determined? Compare net fluid flow at the arterial end of a capillary with net fluid flow at the venous end.

The net pressure driving fluid flow across the capillary is determined by the difference between the hydrostatic pressure (PH) and the colloid osmotic pressure (π): Net pressure = PH - π A positive value for the net pressure indicates net filtration and a negative value indicates net absorption. ● At the arterial end, PH is greater than π, so the net pressure is 7 mm Hg of filtration pressure. ● At the venous end, π is greater than PH; the net pressure is -10 mm Hg (absorption).

Why is the venous circulation called the volume reservoir?

The veins act as a volume reservoir from which blood can be sent to the arterial side of the circulation if blood pressure falls too low.

Name the 3 systems with which the lymphatics interact, and briefly summarize the role of the lymphatics in each.

The vessels of the lymphatic system interact with three other physiological systems: the cardiovascular system, the digestive system, and the immune system. Functions of the lymphatic system include (1) returning fluid and proteins filtered out of the capillaries to the circulatory system, (2) picking up fat absorbed at the small intestine and moving it to the circulatory system (3) serving as a filter to help capture and destroy foreign pathogens.

Describe the layered composition of blood vessel walls. [use the term tunica intima]

The walls of blood vessels are composed of layers of smooth muscle, elastic connective tissue, and fibrous connective tissue. - The inner lining of all blood vessels is a thin layer of endothelium, a type of epithelium. - The endothelium & it´s adjacent elastic connective tissue together make up the tunica intima.

Is filtration in capillaries exactly equal to absorption? Explain.

There is net filtration at the arterial end and net absorption at the venous end. - If the point at which filtration equals absorption occurred in the middle of the capillary, there would be no net movement of fluid. - All volume that was filtered at the arterial end would be absorbed at the venous end. - However, filtration is usually greater than absorption, resulting in bulk flow of fluid out of the capillary into the interstitial space.

Tonic norepinephrine release onto ________ receptors creates myogenic tone. Vasodilation is accomplished by ______________ (increasing or decreasing?) release of norepinephrine.

Tonic discharge of norepinephrine from sympathetic neurons helps maintain myogenic tone of arterioles. - Norepinephrine binding to ALPHA-receptors on vascular smooth muscle causes vasoconstriction. - DECREASE (2. lücke)

True or false: The pulse is created by a wave of blood flowing through the arteries. Defend your answer.

True. - The rapid pressure increase that occurs when the left ventricle pushes blood into the aorta can be felt as a pulse, or pressure wave, transmitted through the fluid-filled arteries.

Define vasoconstriction and vasodilation, vascular smooth muscle tone.

Vasoconstriction narrows the diameter of the vessel lumen, and vasodilation widens it.In most blood vessels, smooth muscle cells maintain a state of partial contraction at all times, creating the condition known as muscle tone.

Compare the walls of veins with those of arteries.

Veins are more numerous than arteries and have a larger diameter. - As a result of their large volume, the veins hold more than half of the blood in the circulatory system, making them the volume reservoir of the circulatory system. - Veins lie closer to the surface of the body than arteries. - Veins have thinner walls than arteries, with less elastic tissue. - As a result, they expand easily when they fill with blood.

Explain how a sphygmomanometer and Korotkoff sounds can be used to estimate arterial pressure of the radial artery.

We estimate arterial blood pressure in the radial artery of the arm using a sphygmomanometer, an instrument consisting of an inflatable cuff and a pressure gauge. - The cuff encircles the upper arm and is inflated until it exerts pressure higher than the systolic pressure driving arterial blood. - When cuff pressure exceeds arterial pressure, blood flow into the lower arm stops. - Now pressure on the cuff is gradually released. When cuff pressure falls below systolic arterial blood pressure, blood begins to flow again. - As blood squeezes through the still compressed artery, a noise called a Korotkoff sound can be heard with each pressure wave. - Once the cuff pressure no longer compresses the artery, the sounds disappear. - The pressure at which a Korotkoff sound is 1st heard, represents the highest pressure in the artery and is recorded as the systolic pressure. - The point at which the Korotkoff sounds dis- appear is the lowest pressure in the artery & is recorded as the diastolic pressure.

Explain the relationship between total cross-sectional area and velocity of flow in the circulatory system. Specifically, how does the total cross-sectional area of capillaries compare to that of larger-diameter blood vessels, and what effect does this have on velocity in the different vessels?

What is total cross-sectional area? - Imagine circles representing cross sections of all the capillaries placed edge to edge, and you have it. - For the capillaries, those circles would cover an area much larger than the total cross-sectional areas of all the arteries and veins combined. - Therefore, because total cross-sectional area of the capillaries is so large, the velocity of flow through them is low. (↑cross section area: ↓velocity) - The fastest flow is in the relatively small-diameter arterial system. - The slowest flow is in the capillaries and venules, which collectively have the largest cross-sectional area. - The low velocity of flow through capillaries is a useful characteristic that allows enough time for diffusion to go to equilibrium.

If the volume of blood circulating through the system decreases, blood pressure _________ (increases or decreases?).

When blood volume decreases, blood pressure decreases.

When blood pressure in an arteriole increases, myogenic autoregulation causes the arteriole to _______________.

When smooth muscle fibres in the wall of the arteriole stretch because of increased blood pressure, the arteriole CONSTRICTS. (blood pressure ↑: constrict, blood pressure ↓: dilate)

What is orthostatic hypotension? Why does blood pressure initially fall when a person stands up after lying flat?

When you stand up, gravity causes blood to pool in the lower extremities. - This pooling creates an instantaneous decrease in venous return. - As a result, less blood is in the ventricles at the beginning of the next contraction. - Cardiac output falls from 5 L/min to 3 L/min, causing arterial blood pressure to decrease. - This decrease in blood pressure upon standing is known as orthostatic hypotension.

Fight-or-flight: a. vasodilation = epinephrine on _______ receptors (smooth muscle of heart, liver, skeletal muscle arterioles) b. vasoconstriction = epinephrine on _______ receptors (other arterioles)

a.) beta2-receptors b.) alpha-receptors

At any given moment, the total blood flow through all arterioles of the body = __________________.

always equals the CARDIAC OUTPUT

List controllable risk factors for cardiovascular disease.

cigarette smoking, obesity, sedentary lifestyle, and untreated hypertension.

List uncontrollable risk factors for cardiovascular disease.

sex, age, and a family history of early cardiovascular disease.