42 Flashcards

1
Q

time it takes for a substance to diffuse from one place to another

A

proportional to the square of the distance.
t = (x^2)/2D
(x = distance; D = diffusion coeff)

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2
Q

animals that lack a distinct circulatory

system

A
  • In animals with a gastrovascular cavity, fluid bathes both
    the inner and outer tissue layers, facilitating exchange of
    gases and cellular waste. Only the cells lining the cavity have
    direct access to nutrients released by
    digestion. However, because the body
    wall is a mere two cells thick, nutrients
    need diffuse only a short distance to
    reach the cells of the outer tissue layer
  • Planarians and most other flatworms also survive without a circulatory system. Their combination of a
    gastrovascular cavity and a flat body is
    well suited for exchange with the environment (Figure 42.2b). A flat body optimizes diffusional exchange by increasing surface area
    and minimizing diffusion distances.
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3
Q

For animals with many cell layers,

A

diffusion
distances are too great for adequate exchange of nutrients
and wastes by a gastrovascular cavity. In these organisms, a
circulatory system minimizes the distances that substances
must diffuse to enter or leave a cell.

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4
Q

A circulatory system has three basic components:

A

a circulatory
fluid, a set of interconnecting vessels, and a muscular pump,
the heart

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5
Q

heart

A

powers circulation by using metabolic energy to elevate the hydrostatic pressure of the circulatory fluid,
which then flows through the vessels and back to the heart.

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6
Q

open circulatory system

A

Arthropods and most molluscs have an open circulatory
system, in which the circulatory fluid bathes the organs directly (Figure 42.3a).
- In these animals, the circulatory fluid,
called hemolymph, is also the interstitial fluid that bathes
body cells.
- Contraction of one or more hearts pumps the
hemolymph through the circulatory vessels into interconnected sinuses, spaces surrounding the organs. Within the sinuses, chemical exchange occurs between the hemolymph
and body cells. Relaxation of the heart draws hemolymph back in through pores, which are equipped with valves that
close when the heart contracts. Body movements help circulate the hemolymph by periodically squeezing the sinuses.
- The open circulatory system of larger crustaceans, such as
lobsters and crabs, includes a more extensive system of vessels as well as an accessory pump.

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7
Q

closed circulatory system

A
  • Annelids (including earthworms),
    cephalopods (including squids and octopuses), and all vertebrates have closed circulatory systems
  • a circulatory fluid
    called blood is confined to vessels and is distinct from the
    interstitial fluid (Figure 42.3b). One or more hearts pump
    blood into large vessels that branch into smaller ones that infiltrate the organs. Chemical exchange occurs between the
    blood and the interstitial fluid, as well as between the interstitial fluid and body cells
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8
Q

advantage of open circ

A

The lower hydrostatic pressures associated with open circulatory systems make them less costly
than closed systems in terms of energy expenditure.
- In some
invertebrates, open circulatory systems serve additional functions. For example, spiders use the hydrostatic pressure generated by their open circulatory system to extend their legs.

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9
Q

advantages of closed circ

A

The benefits of closed circulatory systems include relatively
high blood pressures, which enable the effective delivery of O2
and nutrients to the cells of larger and more active animals.
Among the molluscs, for instance, closed circulatory systems
are found in the largest and most active species, the squids and
octopuses.
- Closed systems are also particularly well suited to
regulating the distribution of blood to different organs

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10
Q

cardiovascular system

A

The closed circulatory system of humans and other vertebrates
is often called the cardiovascular system. Blood circulates
to and from the heart through an amazingly extensive network of vessels: The total length of blood vessels in an average
human adult is twice Earth’s circumference at the equator!

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11
Q

arteries

A

Arteries carry blood away from the heart to organs
throughout the body. Within organs, arteries branch into
arterioles, small vessels that convey blood to the capillaries.

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12
Q

capillaries

A

Capillaries are microscopic vessels with very thin, porous
walls. Networks of these vessels, called capillary beds, infiltrate every tissue, passing within a few cell diameters of every
cell in the body. Across the thin walls of capillaries, chemicals, including dissolved gases, are exchanged by diffusion
between the blood and the interstitial fluid around the tissue
cells. At their “downstream” end, capillaries converge into
venules.

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13
Q

veins

A

venules converge into veins, the vessels that

carry blood back to the heart.

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14
Q

Arteries and veins are distinguished by

A

the direction in
which they carry blood, not by the O2 content or other characteristics of the blood they contain. Arteries carry blood
from the heart toward capillaries, and veins return blood to
the heart from capillaries.
- The only exceptions are the portal
veins, which carry blood between pairs of capillary beds. The
hepatic portal vein, for example, carries blood from capillary
beds in the digestive system to capillary beds in the liver. From the liver, blood passes into the hepatic
veins, which conduct blood toward the heart.

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15
Q

The hearts of all vertebrates contain two or more muscular

chambers:

A

The chambers that receive blood entering the
heart are called atria (singular, atrium). The chambers responsible for pumping blood out of the heart are called
ventricles.

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16
Q

single circ

A

In bony fishes, rays, and sharks, the heart consists of two chambers: an atrium and a ventricle. The blood passes through the
heart once in each complete circuit, an arrangement called
single circulation (Figure 42.4a). Blood entering the heart
collects in the atrium before transfer to the ventricle. Contraction of the ventricle pumps blood to the gills, where there is a
net diffusion of O2 into the blood and of CO2 out of the blood.
As blood leaves the gills, the capillaries converge into a vessel
that carries oxygen-rich blood to capillary beds throughout the
body. Blood then returns to the heart.
- In single circulation, blood that leaves the heart passes
through two capillary beds before returning to the heart.
When blood flows through a capillary bed, blood pressure
drops substantially. The
drop in blood pressure in the gills limits the rate of blood
flow in the rest of the animal’s body. As the animal swims,
however, the contraction and relaxation of its muscles help
accelerate the relatively sluggish pace of circulation.
- (blood flows under reduced pressure directly from the gas exchange organs to other organs)

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17
Q

double circ

A

The circulatory systems of amphibians, reptiles, and mammals
have two circuits, an arrangement called double circulation
(Figure 42.4b). The pumps for the two circuits are combined
into a single organ, the heart. Having both pumps within a
single heart simplifies coordination of the pumping cycles.
- One pump, the right side of the heart, delivers oxygen-poor
blood to the capillary beds of the gas exchange tissues, where
there is a net movement of O2 into the blood and of CO2 out of
the blood.
- This part of the circulation is called a pulmonary
circuit if the capillary beds involved are all in the lungs, as in
reptiles and mammals.
- It is called a pulmocutaneous circuit
if it includes capillaries in both the lungs and the skin, as in
many amphibians.
- After the oxygen-enriched blood leaves the gas exchange tissues, it enters the other pump, the left side of the heart. Contraction of the heart propels this blood to capillary beds in
organs and tissues throughout the body. Following the exchange of O2 and CO2, as well as nutrients and waste products, the now oxygen-poor blood returns to the heart, completing
the systemic circuit.
- Double circulation provides a vigorous flow of blood to
the brain, muscles, and other organs because the heart repressurizes the blood destined for these tissues after it passes
through the capillary beds of the lungs or skin. Indeed, blood
pressure is often much higher in the systemic circuit than in
the gas exchange circuit.

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18
Q

double circ in amphibians

A
  • have a heart
    with three chambers: two atria and one
    ventricle.
  • A ridge within the ventricle diverts most (about 90%) of the oxygen-poor
    blood from the right atrium into the pulmocutaneous circuit and most of the oxygen-rich blood from the left atrium into the
    systemic circuit.
  • When underwater, a frog
    adjusts its circulation, for the most part
    shutting off blood flow to its temporarily
    ineffective lungs. Blood flow continues to
    the skin, which acts as the sole site of gas
    exchange while the frog is submerged.
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19
Q

double circ in reptiles (except birds)

A

turtles, snakes, lizards:
- 3 chambered heart: an incomplete septum
partially divides the single ventricle into
separate right and left chambers.
- Two
major arteries, called aortas, lead to the
systemic circulation.

- In alligators, caimans, and other
crocodilians, the ventricles are divided
by a complete septum (not shown), but
the pulmonary and systemic circuits connect where the arteries exit the heart.
This connection enables arterial valves
to shunt blood flow away from the lungs
temporarily, such as when the animal is
underwater.
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20
Q

double circ in mammals and birds

A
  • two atria
    and two completely divided ventricles. The
    left side of the heart receives and pumps
    only oxygen-rich blood, while the right
    side receives and pumps only oxygen-poor
    blood.
  • As
    endotherms, mammals and birds use about
    ten times as much energy as equal-sized
    ectotherms. Their circulatory systems therefore need to deliver about ten times as
    much fuel and O2 to their tissues (and remove ten times as much CO2 and other
    wastes).
  • This large traffic of substances is
    made possible by separate and independently powered systemic and pulmonary
    circuits and by large hearts that pump the
    necessary volume of blood.
  • A powerful
    four-chambered heart arose independently
    in the distinct ancestors of mammals and
    birds and thus reflects convergent evolution
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21
Q

plasma

A

Vertebrate blood is a connective tissue consisting of cells suspended in a liquid matrix called plasma. Dissolved in the
plasma are ions and proteins that, together with the blood
cells, function in osmotic regulation, transport, and defense.
Separating the components of blood using a centrifuge reveals that cellular elements (cells and cell fragments) occupy
about 45% of the volume of blood (Figure 42.17). The remainder is plasma.

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22
Q

electrolytes

A

Among the many solutes in plasma are inorganic salts in the
form of dissolved ions, sometimes referred to as blood electrolytes (see Figure 42.17).
- Although plasma is about 90%
water, the dissolved salts are an essential component of the
blood.
- Some of these ions buffer the blood, which in humans
normally has a pH of 7.4.
- Salts are also important in maintaining the osmotic balance of the blood.
- In addition, the concentration of ions in plasma directly affects the composition of the interstitial fluid, where many of these ions have a vital role
in muscle and nerve activity.
- To serve all of these functions,
plasma electrolytes must be kept within narrow concentration
ranges

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23
Q

plasma proteins

A

Plasma proteins act as buffers against pH changes, help
maintain the osmotic balance between blood and interstitial
fluid, and contribute to the blood’s viscosity (thickness). Particular plasma proteins have additional functions.
- The immunoglobulins, or antibodies, help combat viruses and
other foreign agents that invade the body.
- Others are escorts for lipids, which are insoluble in water
and can travel in blood only when bound to proteins.
- A
third group of plasma proteins are clotting factors that help
plug leaks when blood vessels are injured.

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24
Q

plasma vs interstitial fluid

A

Plasma has a much higher protein concentration than interstitial fluid, although the two fluids are otherwise similar. (Capillary walls, remember, are not very permeable to proteins.)

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25
Blood contains two classes of cells:
red blood cells, which transport O2, and white blood cells, which function in defense (see Figure 42.17). Also suspended in blood plasma are platelets, fragments of cells that are involved in the clotting process.
26
erythrocytes
Red blood cells, or erythrocytes, are by far the most numerous blood cells. Each microliter (μL, or mm3) of human blood contains 5–6 million red cells, and there are about 25 trillion of these cells in the body’s 5 L of blood. - Their main function is O2 transport, and their structure is closely related to this function. Human erythrocytes are small disks (7–8 μm in diameter) that are biconcave—thinner in the center than at the edges. This shape increases surface area, enhancing the rate of diffusion of O2 across their plasma membranes. - Despite its small size, an erythrocyte contains about 250 million molecules of hemoglobin. Because each molecule of hemoglobin binds up to four molecules of O2, one erythrocyte can transport about a billion O2 molecules.
27
Mature mammalian erythrocytes lack
nuclei. This unusual characteristic leaves more space in these tiny cells for hemoglobin, the iron-containing protein that transports O2 (see Figure 5.20). Erythrocytes also lack mitochondria and generate their ATP exclusively by anaerobic metabolism. Oxygen transport would be less efficient if erythrocytes were aerobic and consumed some of the O2 they carry
28
erythrocytes and O2 diffusion
As erythrocytes pass through the capillary beds of lungs, gills, or other respiratory organs, O2 diffuses into the erythrocytes and binds to hemoglobin. In the systemic capillaries, O2 dissociates from hemoglobin and diffuses into body cells.
29
sickle cell disease
- an abnormal form of hemoglobin (HbS) polymerizes into aggregates. Because the concentration of hemoglobin in erythrocytes is so high, these aggregates are large enough to distort the erythrocyte into an elongated, curved shape that resembles a sickle. - Sickle-cell disease significantly impairs the function of the circulatory system. Sickled cells often lodge in arterioles and capillaries, preventing delivery of O2 and nutrients and removal of CO2 and wastes. Blood vessel blockage and resulting organ swelling often result in severe pain. In addition, sickled cells frequently rupture, reducing the number of red blood cells available for transporting O2. The average life span of a sickled erythrocyte is only 20 days—one-sixth that of a normal erythrocyte. The rate of erythrocyte loss outstrips the replacement capacity of the bone marrow.
30
siclke cell treatment
Short-term therapy includes replacement of erythrocytes by blood transfusion; long-term treatments are generally aimed at inhibiting aggregation of HbS
31
leukocytes
The blood contains five major types of white blood cells, or leukocytes. Their function is to fight infections. - Unlike erythrocytes, leukocytes are also found outside the circulatory system, patrolling both interstitial fluid and the lymphatic system.
32
platelets
Platelets are pinched-off cytoplasmic fragments of specialized bone marrow cells. They are about 2–3 μm in diameter and have no nuclei. Platelets serve both structural and molecular functions in blood clotting.
33
hemophiila
Any genetic mutation that blocks a step in the clotting process can cause hemophilia, a disease characterized by excessive bleeding and bruising from even minor cuts and bumps
34
blood clotting
- A break in a blood vessel wall exposes proteins that attract platelets and initiate coagulation, the conversion of liquid components of blood to a solid clot. - The coagulant, or sealant, circulates in an inactive form called fibrinogen. - In response to a broken blood vessel, platelets release clotting factors that trigger reactions leading to the formation of thrombin, an enzyme that converts fibrinogen to fibrin. - Newly formed fibrin aggregates into threads that form the framework of the clot. - Thrombin also activates a factor that catalyzes the formation of more thrombin, driving clotting to completion through positive feedback
35
anticlotting
Anticlotting factors in the blood normally prevent spontaneous clotting in the absence of injury. Sometimes, however, clots form within a blood vessel, blocking the flow of blood. Such a clot is called a thrombus.
36
stem cells
Erythrocytes, leukocytes, and platelets all develop from a common source: multipotent stem cells that are dedicated to replenishing the body’s blood cell populations (Figure 42.19). The stem cells that produce blood cells are located in the red marrow of bones, particularly the ribs, vertebrae, sternum, and pelvis. Multipotent stem cells are so named because they have the ability to form multiple types of cells—in this case, the myeloid and lymphoid cell lineages. When a stem cell divides, one daughter cell remains a stem cell while the other takes on a specialized function.
37
differentiation of blood cells
stem cells --> lymphoid and myeloid stem cells lymphoid --> lymphocytes (B and T cells) myeloid --> erythrocytes, neutrophils, basophils, monocytes, platelets, eosinophils
38
Throughout a person’s life, erythrocytes, leukocytes, and | platelets arising from stem cell divisions replace the worn-out cellular elements of blood.
Erythrocytes, for example, circulate for only 120 days on average before being replaced; the old cells are consumed by phagocytic cells in the liver and spleen. The production of new erythrocytes involves recycling of materials, such as the use of iron scavenged from old erythrocytes in new hemoglobin molecules
39
EPO
A negative-feedback mechanism, sensitive to the amount of O2 reaching the body’s tissues via the blood, controls erythrocyte production. If the tissues do not receive enough O2, the kidneys synthesize and secrete a hormone called erythropoietin (EPO) that stimulates erythrocyte production. If the blood is delivering more O2 than the tissues can use, the level of EPO falls and erythrocyte production slows. Physicians use synthetic EPO to treat people with health problems such as anemia, a condition of lower-than-normal erythrocyte or hemoglobin levels that lowers the oxygen-carrying capacity of the blood.
40
blood doping
Some athletes inject themselves with EPO to increase their erythrocyte levels, although this practice, a form of blood doping, has been banned by the International Olympic Committee and other sports organizations.
41
cardiovascular disease
- disorders of the heart and blood vessels - Cholesterol metabolism plays a central role in cardiovascular disease. The presence of this steroid in animal cell membranes helps maintain normal membrane fluidity. - Another factor in cardiovascular disease is inflammation, the body’s reaction to injury. Tissue damage leads to recruitment of two types of circulating immune cells, macrophages and leukocytes. Signals released by these cells trigger a flow of fluid out of blood vessels at the site of injury, resulting in the tissue swelling characteristic of inflammation. Although inflammation is often a normal and healthy response to injury, it can significantly disrupt circulatory function.
42
LDL/HDL
- Cholesterol travels in blood plasma mainly in particles that consist of thousands of cholesterol molecules and other lipids bound to a protein. - One type of particle—low-density lipoprotein (LDL)—delivers cholesterol to cells for membrane production. - Another type—high-density lipoprotein (HDL)—scavenges excess cholesterol for return to the liver. - Individuals with a high ratio of LDL to HDL are at substantially increased risk for heart disease.
43
atherosclerosis
- Circulating cholesterol and inflammation can act together to produce a cardiovascular disease called atherosclerosis, the hardening of the arteries by accumulation of fatty deposits - Healthy arteries have a smooth inner lining that reduces resistance to blood flow. Damage or infection can roughen the lining and lead to inflammation. - Leukocytes are attracted to the damaged lining and begin to take up lipids, including cholesterol. - A fatty deposit, called a plaque, grows steadily, incorporating fibrous connective tissue and additional cholesterol. - As the plaque grows, the walls of the artery become thick and stiff, and the obstruction of the artery increases.
44
heart attack
- one result of untreated atherosclerosis - A heart attack, also called a myocardial infarction, is the damage or death of cardiac muscle tissue resulting from blockage of one or more coronary arteries, which supply oxygen-rich blood to the heart muscle. - Because the coronary arteries are small in diameter, they are especially vulnerable to obstruction. Such blockage can destroy cardiac muscle quickly because the constantly beating heart muscle cannot survive long without O2. - If the heart stops beating, the victim may nevertheless survive if a heartbeat is restored by cardiopulmonary resuscitation (CPR) or some other emergency procedure within a few minutes of the attack.
45
stroke
- one result of untreated atherosclerosis - A stroke is the death of nervous tissue in the brain due to a lack of O2. - Strokes usually result from rupture or blockage of arteries in the head. - The effects of a stroke and the individual’s chance of survival depend on the extent and location of the damaged brain tissue. - Rapid administration of a clot-dissolving drug may reduce the effects of a stroke or heart attack
46
atherosclerosis warning signs
- Although atherosclerosis often isn’t detected until critical blood flow is disrupted, there can be warning signs. - Partial blockage of the coronary arteries may cause occasional chest pain, a condition known as angina pectoris. The pain is most likely to be felt when the heart is laboring hard during physical or emotional stress, and it signals that part of the heart is not receiving enough O2. - An obstructed coronary artery may be treated surgically, either by inserting a metal mesh tube called a stent to expand the artery or by transplanting a healthy blood vessel from the chest or a limb to bypass the blockage.
47
hypertension
- Hypertension (high blood pressure) is yet another contributor to heart attack and stroke as well as other health problems. - According to one hypothesis, chronic high blood pressure damages the endothelium that lines the arteries, promoting plaque formation. - The usual definition of hypertension in adults is a systolic pressure above 140 mm Hg or a diastolic pressure above 90 mm Hg. - Fortunately, hypertension is simple to diagnose and can usually be controlled by dietary changes, exercise, medication, or a combination of these approaches.
48
cardiovascular dsease risk factors
- Although the tendency to develop particular cardiovascular diseases is inherited, it is also strongly influenced by lifestyle. - Smoking and consumption of certain processed vegetable oils called trans fats increase the ratio of LDL to HDL, raising the risk of cardiovascular disease. - In contrast, exercise decreases the LDL/HDL ratio.
49
cardiovascular disease treatment: cholesterol
Many individuals at high risk | are now treated with drugs called statins, which lower LDL levels and thereby reduce the risk of heart attacks.
50
cardiovascular disease treatment: inflammation
- The recognition that inflammation plays a central role in atherosclerosis and thrombus formation is also changing the treatment of cardiovascular disease. - For example, aspirin, which inhibits the inflammatory response, has been found to help prevent the recurrence of heart attacks and stroke. - Researchers have also focused on C-reactive protein (CRP), which is produced by the liver and found in the blood during episodes of acute inflammation. Like a high level of LDL cholesterol, the presence of significant amounts of CRP in blood is a useful risk indicator for cardiovascular disease
51
endothelium
Blood vessels contain a central lumen (cavity) lined with an endothelium, a single layer of flattened epithelial cells. - The smooth surface of the endothelium minimizes resistance to the flow of blood. - Surrounding the endothelium are layers of tissue that differ in capillaries, arteries, and veins, reflecting the specialized functions of these vessels
52
capillary structure
Capillaries are the smallest blood vessels, having a diameter only slightly greater than that of a red blood cell. - Capillaries also have very thin walls, which consist of just the endothelium and its basal lamina. This structural organization facilitates the exchange of substances between the blood in capillaries and the interstitial fluid.
53
artery and vein structure
- Both arteries and veins have two layers of tissue surrounding the endothelium: an outer layer of connective tissue containing elastic fibers, which allow the vessel to stretch and recoil, and a middle layer containing smooth muscle and more elastic fibers. - The walls of arteries are thick and strong, accommodating blood pumped at high pressure by the heart. Arterial walls also have an elastic recoil that helps maintain blood pressure and flow to capillaries when the heart relaxes between contractions. Signals from the nervous system and hormones circulating in the blood act on the smooth muscle in arteries and arterioles, dilating or constricting these vessels and thus controlling blood flow to different parts of the body. - Because veins convey blood back to the heart at a lower pressure, they do not require thick walls. For a given blood vessel diameter, a vein has a wall only about a third as thick as that of an artery. Valves inside the veins maintain a unidirectional flow of blood despite the low blood pressure.
54
blood slows as it moves from arteries to arterioles to capillaries. Why?
- The reason is that the number of capillaries is enormous. Each artery conveys blood to so many capillaries that the total cross-sectional area is much greater in capillary beds than in the arteries or any other part of the circulatory system. - The result is a dramatic decrease in velocity from the arteries to the capillaries: Blood travels 500 times slower in the capillaries (about 0.1 cm/sec) than in the aorta (about 48 cm/sec).
55
reduced velocity of blood flow in capillaries
The reduced velocity of blood flow in capillaries is essential to the function of the circulatory system. - The exchange of substances between the blood and interstitial fluid occurs only in capillaries because only capillaries have walls thin enough to permit this transfer. Diffusion, however, is not instantaneous. The slower flow of blood through capillaries is thus necessary to provide time for exchange to occur. - After passing through the capillaries, the blood speeds up as it enters the venules and veins, which have smaller total cross-sectional areas than the capillaries.
56
blood pressure
- Blood, like all fluids, flows from areas of higher pressure to areas of lower pressure. - Contraction of a heart ventricle generates blood pressure, which exerts a force in all directions. - The force directed lengthwise in an artery causes the blood to flow away from the heart, the site of highest pressure. - The force exerted against the elastic wall of an artery stretches the wall, and the recoil of arterial walls plays a critical role in maintaining blood pressure, and hence blood flow, throughout the cardiac cycle. - Once the blood enters the millions of tiny arterioles and capillaries, the narrow diameter of these vessels generates substantial resistance to flow. This resistance dissipates much of the pressure generated by the pumping heart by the time the blood enters the veins.
57
systolic pressure
Arterial blood pressure is highest when the heart contracts during ventricular systole. The pressure at this time is called systolic pressure (see Figure 42.11). - The spikes in blood pressure caused by the powerful contractions of the ventricles stretch the arteries.
58
pulse
By placing your fingers on the inside of your wrist, you can feel a pulse—the rhythmic bulging of the artery walls with each heartbeat. - The surge of pressure is partly due to the narrow openings of arterioles impeding the exit of blood from the arteries. - Thus, when the heart contracts, blood enters the arteries faster than it can leave, and the vessels stretch from the rise in pressure.
59
diastolic pressure
During diastole, the elastic walls of the arteries snap back. As a consequence, there is a lower but still substantial blood pressure when the ventricles are relaxed (diastolic pressure). - Before enough blood has flowed into the arterioles to completely relieve pressure in the arteries, the heart contracts again. - Because the arteries remain pressurized throughout the cardiac cycle, blood continuously flows into arterioles and capillaries.
60
BP changes
Changes in arterial blood pressure are not limited to the oscillation during each cardiac cycle. Blood pressure also fluctuates on a longer time scale in response to signals that change the state of smooth muscles in arteriole walls. For example, physical or emotional stress can trigger nervous and hormonal responses that cause smooth muscles in arteriole walls to contract or relax.
61
vasoconstriction/dilation
- when smooth muscles in arteriole walls contract, the arterioles narrow, a process called vasoconstriction. Narrowing of the arterioles increases blood pressure upstream in the arteries. - When the smooth muscles relax, the arterioles undergo vasodilation, an increase in diameter that causes blood pressure in the arteries to fall. - Vasoconstriction and vasodilation are often coupled to changes in cardiac output that also affect blood pressure. This coordination of regulatory mechanisms maintains adequate blood flow as the body’s demands on the circulatory system change. - During heavy exercise, for example, the arterioles in working muscles dilate, causing a greater flow of oxygen-rich blood to the muscles. By itself, this increased flow to the muscles would cause a drop in blood pressure (and therefore blood flow) in the body as a whole. However, cardiac output increases at the same time, maintaining blood pressure and supporting the necessary increase in blood flow
62
signaling molecules
- Researchers have identified a gas, nitric oxide (NO), as a major inducer of vasodilation and a peptide, endothelin, as the most potent inducer of vasoconstriction. Both produced in blood vessels in response to cues from the nervous and endocrine systems. - Each kind of molecule binds to a specific receptor, activating a signal transduction pathway that alters smooth muscle contraction and thus changes blood vessel diameter.
63
normal BP
For a healthy 20-year-old human at rest, arterial blood pressure in the systemic circuit is typically about 120 millimeters of mercury (mm Hg) at systole and 70 mm Hg at diastole, expressed as 120/70. (Arterial blood pressure in the pulmonary circuit is six to ten times lower.)
64
how is BP measured?
Blood pressure is generally measured for an artery in the arm at the same height as the heart.
65
BP and gravity
``` - Gravity has a significant effect on blood pressure. When you are standing, for example, your head is roughly 0.35 m higher than your chest, and the arterial blood pressure in your brain is about 27 mm Hg less than that near your heart. - If the blood pressure in your brain is too low to provide adequate blood flow, you will likely faint. By causing your body to collapse to the ground, fainting effectively places your head at the level of your heart, quickly increasing blood flow to your brain. ```
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gravity and veins
Gravity is also a consideration for blood flow in veins, especially those in the legs. Although blood pressure in veins is relatively low, several mechanisms assist the return of venous blood to the heart. - First, rhythmic contractions of smooth muscles in the walls of venules and veins aid in the movement of the blood. - Second, and more important, the contraction of skeletal muscles during exercise squeezes blood through the veins toward the heart. - Third, the change in pressure within the thoracic (chest) cavity during inhalation causes the venae cavae and other large veins near the heart to expand and fill with blood.
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why is it that exercising heavily immediately after | eating a big meal may cause indigestion?
- blood flow to the skin is regulated to help control body temperature, and blood supply to the digestive tract increases after a meal. - During strenuous exercise, blood is diverted from the digestive tract and supplied more generously to skeletal muscles and skin.
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empty capillaries
- At any given time, only about 5–10% of the body’s capillaries have blood flowing through them. However, each tissue has many capillaries, so every part of the body is supplied with blood at all times. - Capillaries in the brain, heart, kidneys, and liver are usually filled to capacity, but at many other sites the blood supply varies over time as blood is diverted from one destination to another
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capillaries lack ___
smooth muscle
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Given that capillaries lack smooth muscle, how is blood | flow in capillary beds altered?
- One mechanism involves contraction of the smooth muscle in the wall of an arteriole, which reduces the vessel’s diameter and decreases blood flow to the adjoining capillary beds. When the smooth muscle relaxes, the arterioles dilate, allowing blood to enter the capillaries. - The other mechanism involves the action of precapillary sphincters, rings of smooth muscle located at the entrance to capillary beds. The signals that regulate blood flow include nerve impulses, hormones traveling throughout the bloodstream, and chemicals produced locally.
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histamine
the chemical histamine released by cells at a wound site causes smooth muscle relaxation, dilating blood vessels and increasing blood flow. The dilated vessels also give disease-fighting white blood cells greater access to invading microorganisms.
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where does exchange of substances take place?
the critical exchange of substances between the blood and interstitial fluid takes place across the thin endothelial walls of the capillaries.
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how does exchange of substances take place?
- Some substances are carried across the endothelium in vesicles that form on one side by endocytosis and release their contents on the opposite side by exocytosis. - Small molecules, such as O2 and CO2, simply diffuse across the endothelial cells or, in some tissues, through microscopic pores in the capillary wall. - These openings also provide the route for transport of small solutes such as sugars, salts, and urea, as well as for bulk flow of fluid into tissues driven by blood pressure within the capillary.
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Two opposing forces control the movement of fluid between the capillaries and the surrounding tissues:
- Blood pressure tends to drive fluid out of the capillaries, and the presence of blood proteins tends to pull fluid back. - Many blood proteins (and all blood cells) are too large to pass readily through the endothelium, and they remain in the capillaries. These dissolved proteins are responsible for much of the blood’s osmotic pressure (the pressure produced by the difference in solute concentration across a membrane). - The difference in osmotic pressure between the blood and the interstitial fluid opposes fluid movement out of the capillaries. - On average, blood pressure is greater than the opposing forces, leading to a net loss of fluid from capillaries. The net loss is generally greatest at the arterial end of these vessels, where blood pressure is highest.
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lymphatic system
Each day, the adult human body loses approximately 4–8 L of fluid from capillaries to the surrounding tissues. There is also some leakage of blood proteins, even though the capillary wall is not very permeable to large molecules. - The lost fluid and proteins return to the blood via the lymphatic system, which includes a network of tiny vessels intermingled among capillaries of the cardiovascular system.
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lymph
- After entering the lymphatic system by diffusion, the fluid lost by capillaries is called lymph; its composition is about the same as that of interstitial fluid. - The lymphatic system drains into large veins of the circulatory system at the base of the neck. - The joining of the lymphatic and circulatory systems functions in the transfer of lipids from the small intestine to the blood.
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movement of lymph
- The movement of lymph from peripheral tissues to the heart relies on much the same mechanisms that assist blood flow in veins. - Lymph vessels, like veins, have valves that prevent the backflow of fluid. Rhythmic contractions of the vessel walls help draw fluid into the small lymphatic vessels. - In addition, skeletal muscle contractions play a role in moving lymph.
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lymphatic disorders
- Disorders that interfere with the lymphatic system highlight its role in maintaining proper fluid distribution in the body. Disruptions in the movement of lymph often cause edema, swelling resulting from the excessive accumulation of fluid in tissues. - Severe blockage of lymph flow, as occurs when certain parasitic worms lodge in lymph vessels, results in extremely swollen limbs or other body parts, a condition known as elephantiasis.
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lymph nodes
- Along a lymph vessel are organs called lymph nodes. - By filtering the lymph and by housing cells that attack viruses and bacteria, lymph nodes play an important role in the body’s defense. - Inside each lymph node is a honeycomb of connective tissue with spaces filled by white blood cells. When the body is fighting an infection, these cells multiply rapidly, and the lymph nodes become swollen and tender (which is why your doctor may check for swollen lymph nodes in your neck, armpits, or groin when you feel sick). - Because lymph nodes have filtering and surveillance functions, doctors may examine the lymph nodes of cancer patients to detect the spread of diseased cells.
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In recent years, evidence has surfaced demonstrating that | the lymphatic system also plays a role in
harmful immune responses, such as those responsible for asthma. Because of these and other findings, the lymphatic system, largely ignored until the 1990s, has become a very active and promising area of biomedical research.
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human heart: location, size, composition
Located behind the sternum (breastbone), the human heart is | about the size of a clenched fist and consists mostly of cardiac muscle
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atria
The two atria have relatively thin walls and serve as collection chambers for blood returning to the heart from the lungs or other body tissues. - Much of the blood that enters the atria flows into the ventricles while all heart chambers are relaxed. - The remainder is transferred by contraction of the atria before the ventricles begin to contract.
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ventricles
- The ventricles have thicker walls and contract much more forcefully than the atria—especially the left ventricle, which pumps blood to all body organs through the systemic circuit. - Although the left ventricle contracts with greater force than the right ventricle, it pumps the same volume of blood as the right ventricle during each contraction.
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cardiac cycle
- The heart contracts and relaxes in a rhythmic cycle. When it contracts, it pumps blood; when it relaxes, its chambers fill with blood. - One complete sequence of pumping and filling is referred to as the cardiac cycle. - The contraction phase of the cycle is called systole, and the relaxation phase is called diastole
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cardiac output
The volume of blood each ventricle pumps per minute is the cardiac output. - Two factors determine cardiac output: - the rate of contraction, or heart rate (number of beats per minute), and the - stroke volume, the amount of blood pumped by a ventricle in a single contraction.
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average stroke volume
- The average stroke volume in humans is about 70 mL. - Multiplying this stroke volume by a resting heart rate of 72 beats per minute yields a cardiac output of 5 L/min—about equal to the total volume of blood in the human body. - During heavy exercise, cardiac output increases as much as fivefold.
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valves
Four valves in the heart prevent backflow and keep blood moving in the correct direction (see Figures 42.7 and 42.8). Made of flaps of connective tissue, the valves open when pushed from one side and close when pushed from the other.
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AV valve
- An atrioventricular (AV) valve lies between each atrium and ventricle. - The AV valves are anchored by strong fibers that prevent them from turning inside out. - Pressure generated by the powerful contraction of the ventricles closes the AV valves, keeping blood from flowing back into the atria.
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semilunar valves
- Semilunar valves are located at the two exits of the heart: where the aorta leaves the left ventricle and where the pulmonary artery leaves the right ventricle. - These valves are pushed open by the pressure generated during contraction of the ventricles. - When the ventricles relax, blood pressure built up in the aorta closes the semilunar valves and prevents significant backflow.
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valve sounds
You can follow the closing of the two sets of heart valves either with a stethoscope or by pressing your ear tightly against the chest of a friend. - The sound pattern is “lub-dup, lub-dup, lub-dup.” - The first heart sound (“lub”) is created by the recoil of blood against the closed AV valves. - The second sound (“dup”) is produced by the recoil of blood against the closed semilunar valves
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heart murmur
If blood squirts backward through a defective valve, it may produce an abnormal sound called a heart murmur. - Some people are born with heart murmurs; in others, the valves may be damaged by infection (from rheumatic fever, for instance). - When a valve defect is severe enough to endanger health, surgeons may implant a mechanical replacement valve. However, not all heart murmurs are caused by a defect, and most valve defects do not reduce the efficiency of blood flow enough to warrant surgery
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SA node
- In vertebrates, the heartbeat originates in the heart itself. - Some cardiac muscle cells are autorhythmic, meaning they contract and relax repeatedly without any signal from the nervous system. You can even see these rhythmic contractions in tissue that has been removed from the heart and placed in a dish in the laboratory! - Because each of these cells has its own intrinsic contraction rhythm, their contractions are coordinated in the intact heart by a group of autorhythmic cells located in the wall of the right atrium, near where the superior vena cava enters the heart. This cluster of cells is called the sinoatrial (SA) node, or pacemaker, and it sets the rate and timing at which all cardiac muscle cells contract.
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EKG
- The SA node generates electrical impulses much like those produced by nerve cells. - Because cardiac muscle cells are electrically coupled through gap junctions, impulses from the SA node spread rapidly within heart tissue. - In addition, these impulses generate currents that are conducted to the skin via body fluids. In an electrocardiogram (ECG or, often, EKG, from the German spelling), these currents are recorded by electrodes placed on the skin. - The resulting graph of current against time has a characteristic shape that represents the stages in the cardiac cycle
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sympathetic/parasympathetic nervous system
- Physiological cues alter heart tempo by regulating the SA node. Two portions of the nervous system, the sympathetic and parasympathetic divisions, are largely responsible for this regulation. - The sympathetic division speeds up the pacemaker, and the parasympathetic division slows it down. - when you stand up and start walking, the sympathetic division increases your heart rate, an adaptation that enables your circulatory system to provide the additional O2 needed by the muscles that are powering your activity. - If you then sit down and relax, the parasympathetic division decreases your heart rate, an adaptation that conserves energy
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node impulses
- Impulses from the SA node first spread rapidly through the walls of the atria, causing both atria to contract in unison. - During atrial contraction, the impulses originating at the SA node reach other autorhythmic cells located in the wall between the left and right atria. These cells form a relay point called the atrioventricular (AV) node. - Here the impulses are delayed for about 0.1 second before spreading to the heart apex. This delay allows the atria to empty completely before the ventricles contract. - Then the signals from the AV node are conducted to the heart apex and throughout the ventricular walls by specialized muscle fibers called bundle branches and Purkinje fibers.
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circulation: getting fresh O2
Contraction of the right ventricle pumps blood to the lungs via the pulmonary arteries. - As the blood flows through capillary beds in the left and right lungs, it loads O2 and unloads CO2. - Oxygen-rich blood returns from the lungs via the pulmonary veins to the left atrium of the heart.
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circulation: pumping O2-rich blood out
- Next, the oxygen-rich blood flows into the heart’s left ventricle, which pumps the oxygenrich blood out to body tissues through the systemic circuit. - Blood leaves the left ventricle via the aorta, which conveys blood to arteries leading throughout the body. - The first branches leading from the aorta are the coronary arteries, which supply blood to the heart muscle itself. - Then branches lead to capillary beds in the head and arms (forelimbs). - The aorta then descends into the abdomen, supplying oxygen-rich blood to arteries leading to capillary beds in the abdominal organs and legs (hind limbs). - Within the capillaries, there is a net diffusion of O2 from the blood to the tissues and of CO2 (produced by cellular respiration) into the blood.
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circulation: getting O2-poor blood back to heart
- Capillaries rejoin, forming venules, which convey blood to veins. - Oxygen-poor blood from the head, neck, and forelimbs is channeled into a large vein, the superior vena cava. - Another large vein, the inferior vena cava, drains blood from the trunk and hind limbs. - The two venae cavae empty their blood into the right atrium, from which the oxygen-poor blood flows into the right ventricle