pl rq 20. ch.42: 919-935

myeloid progenitors,

, produces all other white blood cells, red blood cells, and platelets

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

Note that arteries and veins are distinguished by the direction in which they carry blood, not by the O2 content or other characteristics of the blood they contain.

Arteries carry blood away from the heart toward capillaries, and veins return blood toward 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.*

arteries remain pressurized throughout entire cardiac cycle

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 (see Figure 42.10), blood continuously flows into arterioles and capillaries.

systolic pressure

Blood pressure in the arteries during contraction of the ventricles.

smallest blood vessel

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 an endothelium and a surrounding extracellular layer called the basal lamina.

differentiation of blood cells

Cell divisions of stem cells in bone marrow give rise to two specialized sets of cells. The lymphoid progenitor cells give rise to immune cells called lymphocytes, primarily B and T cells. The myeloid progenitor cells give rise to other immune cells, red blood cells (erythrocytes), and cell fragments called platelets.

Mammalian circulation

Contraction of 1 the right ventricle pumps blood to the lungs via 2 the pulmonary arteries. As the blood flows through 3 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 4 the left atrium of the heart. Next, the oxygen-rich blood flows into 5 the heart's left ventricle, which pumps the oxygen-rich blood out to body tissues through the systemic circuit. Blood leaves the left ventricle via 6 the aorta, which conveys blood to arteries leading throughout the body. The first branches leading from the aorta are the coronary arteries (not shown), which supply blood to the heart muscle itself. Then branches lead to 7 capillary beds in the head and arms (forelimbs). The aorta then descends into the abdomen, supplying oxygen-rich blood to arteries leading to 8 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. Capillaries rejoin, forming venules, which convey blood to veins. Oxygen-poor blood from the head, neck, and forelimbs is channeled into a large vein, 9 the superior vena cava. Another large vein, 10 the inferior vena cava, drains blood from the trunk and hind limbs. The two venae cavae empty their blood into 11 the right atrium, from which the oxygen-poor blood flows into the right ventricle.

heart attack / stroke

In atherosclerosis, thickening of an arterial wall by plaque formation can restrict blood flow through the artery. If a plaque ruptures, a thrombus can form, further restricting blood flow. Fragments of a ruptured plaque can also travel via the bloodstream and become lodged in other arteries. If the blockage is in an artery that supplies the heart or brain, the result could be a heart attack or stroke, respectively.

concept check 42.1 How is the flow of hemolymph through an open circulatory system similar to the flow of water through an outdoor fountain?

In both an open circulatory system and a fountain, fluid is pumped through a tube and then returns to the pump after collecting in a pool.

hearts of vertebrates contain

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

WHAT IF? Suppose that after you exercise regularly for several months, your resting heart rate decreases, but your cardiac output at rest is unchanged. Based on these observations, what other change in the function of your heart at rest likely occurred?

The heart, like any other muscle, becomes stronger through regular exercise. You would expect a stronger heart to have a greater stroke volume, which would allow for the decrease in heart rate.

lymph circulates within the

lymphatic system before draining into a pair of large veins of the cardiovascular system at the base of the neck. This joining of the lymphatic and cardiovascular systems completes the recovery of fluid lost from capillaries as well as the transfer of lipids from the small intestine to the blood

capillaries lack

smooth muscle

capillaries converge into

venules

systemic circuit

, begins with the left side of the heart pumping oxygen-enriched blood from the gas exchange tissues 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 circuit. blood pressure is often much higher in the

circulatory has three components:

- circulatory fluid - set of interconnecting vessels - muscular pump (<3)

gravity is a consideration

. Because blood pressure in veins is relatively low, valves inside the veins have an important function in maintaining the unidirectional flow of blood within these vessels. The return of blood to the heart is further enhanced by rhythmic contractions of smooth muscles in the walls of venules and veins and by the contraction of skeletal muscles during exercise

hemolymph passageway

. Contraction of the heart pumps the hemolymph through the circulatory vessels into interconnected sinuses, spaces surrounding the organs (Figure 42.3a). Within the sinuses, the hemolymph and body cells exchange gases and other chemicals. Relaxation of the heart draws hemolymph back in through pores, which have valves that close when the heart contracts. Body movements periodically squeeze the sinuses, helping circulate the hemolymph.

gastrovascular cavity

A central cavity with a single opening in the body of certain animals, including cnidarians and flatworms, that functions in both the digestion and distribution of nutrients.

open circulatory system

A circulatory system in which fluid called hemolymph bathes the tissues and organs directly and there is no distinction between the circulating fluid and the interstitial fluid.

cardiac cycle

A complete heartbeat consisting of contraction and relaxation of both atria and both ventricles

exchange of substances btwn the blood and intersitial fluid takes place across the thin endothelial walls of the capillaries :

A few macromolecules 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.

Heart murmur

A hissing sound that most often results from blood squirting backward through a leaky valve in the heart. Some people are born with heart murmurs. In others, the valves may be damaged as a result of infection

EPO (eryhtropoietin)

A hormone that stimulates the production of erythrocytes. It is secreted by the kidney when body tissues do not receive enough oxygen. Erythrocytes are the shortest-lived, circulating for only 120 days on average before being replaced. A feedback mechanism sensitive to O2 levels controls erythrocyte production

sickle cell disease

A recessively inherited human blood disorder in which a single nucleotide change in the a-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals. 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 frequently 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 their production rate. Short-term therapy includes replacement of erythrocytes by blood transfusion; long-term treatments are generally aimed at inhibiting aggregation of Hb

electrocardiogram

A record of the electrical impulses that travel through heart muscle during the cardiac cycle.

atrioventricular node

A region of specialized heart muscle tissue between the left and right atria where electrical impulses are delayed for about 0.1 second before spreading to both ventricles and causing them to contract.

If you had additional hearts distributed throughout your body, what would be one likely advantage and one likely disadvantage?

Additional hearts could be used to improve blood return from the legs. However, it might be difficult to coordinate the activity of multiple hearts and to maintain adequate blood flow to hearts far from the gas exchange organs.

Endothelium

All blood vessels contain a central lumen (cavity) lined with an endothelium, a single layer of flattened epithelial cells Like the polished surface of a copper pipe, the smooth endothelial layer minimizes resistance to fluid flow. Surrounding the endothelium are tissue layers that differ among capillaries, arteries, and veins, reflecting distinct adaptations to the particular functions of these vessels

Chambers A and B are separated by a membrane permeable to substance X. The concentration of X is 5% in A and 15% in B. The volume of A is three times that of B. Which of the following will occur?

Although diffusion is random, the result will be the net movement of X from B to A.

Four valves in the heart prevent backflow and keep blood moving in the correct direction

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 during ventricular systole. Pressure generated by the powerful contraction of the ventricles closes the AV valves, keeping blood from flowing back into the atria. Semilunar valves are located at the two exits of the heart: where the pulmonary artery leaves the right ventricle and where the aorta leaves the left 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 pulmonary artery and aorta closes the semilunar valves and prevents significant backflow.

hemoglobin

An iron-containing protein in red blood cells that reversibly binds oxygen. Mature mammalian erythrocytes lack nuclei. This unusual characteristic leaves more space in these tiny cells for hemoglobin, the iron-containing protein that transports Because each molecule of hemoglobin binds up to four molecules of O2, one erythrocyte can transport about 1 billion O2 molecules

O2 in erythrocytes

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.

jellies vs hydras

In a hydra, thin branches of the gastrovascular cavity extend into the animal's tentacles. In jellies and some other cnidarians, the gastrovascular cavity has a much more elaborate branching pattern... The mouth leads to an elaborate gastrovascular cavity that consists of radial canals leading to and from a circular canal. Ciliated cells lining the canals circulate fluid within the cavity.

The circulatory systems of amphibians, reptiles, and mammals have two circuits of blood flow, an arrangement called double circulation

In animals with double circulation, 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. Double circulation provides a vigorous flow of blood to the brain, muscles, and other organs because the heart repressurizes the blood after it passes through the capillary beds of the lungs or skin Some vertebrates with double circulation are intermittent breathers. For example, amphibians and many reptiles fill their lungs with air periodically, passing long periods either without gas exchange or by relying on another gas exchange tissue, typically the skin.A variety of adaptations found among intermittent breathers enable their circulatory systems to temporarily bypass the lungs in part or in whole Double circulation in birds and mammals, which for the most part breathe continuously, *differs from double circulation in other vertebrates* As shown for a panda in Figure 42.4c, the heart has 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. *Unlike amphibians and many reptiles, .... birds and mammals cannot vary blood flow to the lungs without varying blood flow throughout the body in parallel*.

pulmonary circuit

In one circuit, the right side of the heart pumps 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. In most vertebrates, including reptiles and mammals, this is called the pulmonary circuit) because gas exchange takes place in the lungs.

capillaries

Microscopic vessel through which exchanges take place between the blood and cells of the body thin, porous walls

In mammals, for example, ____ from inhaled air diffuses across only two layers of cells in the lungs before reaching the blood. The circulatory system then carries the oxygen-rich blood to all parts of the body. As the blood passes throughout the body tissues in tiny blood vessels, ___ in the blood diffuses only a short distance before entering the fluid that directly bathes the cells.

O2

how is blood flow in capillary beds altered?

One mechanism is constriction or dilation of the arterioles that supply capillary beds. A second mechanism involves precapillary sphincters, rings of smooth muscle located at the entrance to capillary beds The opening and closing of these muscular rings regulates and redirects the passage of blood into particular sets of capillaries. The signals regulating blood flow by these mechanisms include nerve impulses, hormones traveling throughout the bloodstream, and chemicals produced locally

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.

erthrocytes

Red blood cells that trasport oxygen from the lungs to the body and carbon dioxide from the cells to the lungs.

Physiological cues alter heart tempo by regulating the pacemaker function of the

SA node Two portions of the nervous system, the sympathetic and parasympathetic divisions, are largely responsible for this regulation. They function like the accelerator and brake in a car. For example, when you stand up and start walking, the sympathetic division speeds up your pacemaker. The resulting increase in heart rate provides the additional O2 needed by the muscles that are powering your activity. If you then sit down and relax, the parasympathetic division slows down your pacemaker, decreasing your heart rate and thus conserving energy. Hormones secreted into the blood also influence the pacemaker. -- epinephrine

blood flow in veins

Skeletal muscle contraction squeezes and constricts veins. Flaps of tissue within the veins act as one-way valves that keep blood moving only toward the heart. If you sit or stand too long, the lack of muscular activity may cause your feet to swell as blood pools in your veins

WHAT IF? Concept Check 42.1 The heart of a normally developing human fetus has a hole between the left and right atria. In some cases, this hole does not close completely before birth. If the hole weren't surgically corrected, how would it affect the O2 content of the blood entering the systemic circuit?

The O2 content would be abnormally low because some oxygen-depleted blood returned to the right atrium from the systemic circuit would mix with the oxygen-rich blood in the left atrium.

concept check 42.1 Three-chambered hearts with incomplete septa were once viewed as being less adapted to circulatory function than mammalian hearts. What advantage of such hearts did this viewpoint overlook?

The ability to shut off blood supply to the lungs when the animal is submerged

pacemaker of cells that regulates autorhythmic contractions

The answer lies in 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. impulses from the SA node spread rapidly within heart tissue. These impulses generate currents that can be measured when they reach the skin via body fluids 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 structures called bundle branches and Purkinje fibers.

lymph

The colorless fluid, derived from interstitial fluid, in the lymphatic system of vertebrates.

stroke

The death of nervous tissue in the brain, usually resulting 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. If a stroke results from arterial blockage by a thrombus, rapid administration of a clot-dissolving drug may help limit the damage.

Why is it important that the AV node delay the electrical impulse moving from the SA node and the atria to the ventricles?

The delay allows the atria to empty completely, filling ventricles fully before they contract.

net loss of fluid from capillaries

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.

listening to heart valves

The first heart sound ("lub") is created by the recoil of blood against the closed AV valves. The second sound ("dup") is due to the vibrations caused by closing of the semilunar valves.

What is the primary cause of the low velocity of blood flow in capillaries?

The large total cross-sectional area of the capillaries

Explain why blood has a higher O2 concentration in the pulmonary veins than in the venae cavae, which are also veins.

The pulmonary veins carry blood that has just passed through capillary beds in the lungs, where it accumulated O2. The venae cavae carry blood that has just passed through capillary beds in the rest of the body, where it lost O2 to the tissues.

pulse

The rhythmic bulging of the artery walls with each heartbeat.

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

This enormous increase in cross-sectional area results in a dramatic decrease in velocity from the arteries to the capillaries: Blood travels 500 times more slowly in the capillaries (about 0.1 cm/sec) than in the aorta (about 48 cm/sec).

If you trace the path of a molecule of carbon dioxide that starts in an arteriole in the right thumb and leaves the body in exhaled air, what is the minimum number of capillary beds the molecule encountered? Explain

Two capillary beds. The molecule of carbon dioxide would need to enter a capillary bed in the thumb before returning to the right atrium and ventricle, then travel to the lung and enter a capillary from which it could diffuse into an alveolus and be available to be exhaled.

Stroke occurs when _____. See Concept 42.4 (Page 935)

a blood clot enters the cerebral circulation, blocking an artery and causing the death of brain tissue

cholesterol

a steroid that is important for maintaining normal membrane fluidity in animal cells 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.

The open circulatory system of larger crustaceans, such as lobsters and crabs, includes a more extensive system of vessels as well as

accessory pump

edema

accumulation of lymph fluid

Partial blockage of the coronary arteries may cause occasional chest pain, a condition known as

angina pectoris

in contrast to capillaries, ______ and _____ have walls that consist of two layers of tissue surrounding the endothelium.

arteries and veins The outer layer is formed by connective tissue that contains elastic fibers, which allow the vessel to stretch and recoil, and collagen, which provides strength. The layer next to the endothelium contains smooth muscle and more elastic fibers.

three main types of blood vessels

arteries, veins, capillaries blood flows only one direction within each time

Homeostatic mechanisms regulate arterial blood pressure by altering the diameter of

arterioles

Within organs, arteries branch into

arterioles

Like dissolved ions, plasma proteins such as

as albumins act as buffers against pH changes and help maintain the osmotic balance between blood and interstitial fluid. and additional functions - immunoglobulins - Ab - apolipoproteins escort lipids - fibrinogens (clotting factor)

Lymph vessels, like veins, have valves that prevent the

backflow of fluid

heart rate

beats per minute

the fluid transported by an open circulatory system is continuous with the fluid that surrounds all of the body cells and thus has the same composition. In contrast, the fluid in a closed circulatory system can be much more specialized, as is the case for the blood of vertebrates.

blood composition

thrombus

blood vessel clot

Patterns of blood pressure and flow reflect the structure and arrangement of

blood vessels; To deliver oxygen and nutrients and remove wastes throughout the body, the vertebrate circulatory system relies on blood vessels that exhibit a close match of structure and function.

organic salts in the form of dissolved ions are an essential component of the blood. Some

buffer the blood, while others help maintaining osmotic balance

stem cell

can reproduce indefinitely, dividing mitotically to produce one daughter cell that remains a stem cell and another that adopts a specialized function. The stem cells that produce the cellular elements of blood cells are located in the red marrow inside bones, particularly the ribs, vertebrae, sternum, and pelvis. As they divide and self-renew, these stem cells give rise to two sets of progenitor cells with a more limited capacity for self-renewal

Arterioles convey blood to

capillaries

network of capillaries

capillary beds

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

Arteries

carry blood away from the heart to organs throughout the body

axolotl gills

carry out a process common to all organisms—the exchange of substances between body cells and the environment. Required resources, such as nutrients and oxygen (O2), enter the cytoplasm by crossing the plasma membrane. Waste products, such as carbon dioxide (CO2), exit the cell by crossing the same membrane

closed circulatory system

closed circulatory system A circulatory system in which blood is confined to vessels and is kept separate from the interstitial fluid. one or more hearts pump blood into large vessels that branch into smaller ones that infiltrate the tissues and organs. Chemical exchange occurs between the blood and the interstitial fluid, as well as between the interstitial fluid and body cells. Annelids (including earthworms), cephalopods (including squids and octopuses), and all vertebrates have closed circulatory systems.

key mechanical event in blood clotting response is

coagulation- , the conversion of the liquid components of blood into a solid—a blood clot. n the absence of injury, the coagulant, or sealant, circulates in an inactive form called fibrinogen. Blood clotting begins when injury exposes the proteins in a broken blood vessel wall to blood constituents. The exposed proteins attract platelets, which gather at the site of injury and release clotting factors. These clotting factors trigger a cascade of reactions leading to the formation of an active enzyme, thrombin, from an inactive form, prothrombin. Thrombin in turn converts fibrinogen to fibrin, which aggregates into threads that form the framework of the clot. Any 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

Much of the blood that enters the atria flows into the ventricles while all four heart chambers are relaxed. The remainder is transferred by contraction of the atria before the ventricles begin to

contract

A powerful four-chambered heart arose independently in the distinct ancestors of birds and mammals and thus reflects

convergent evolution

Artherosclerosis

damage or infection can roughen the lining and lead to atherosclerosis, the hardening of the arteries by accumulation of fatty deposits. Individuals with a high ratio of LDL to HDL are at substantially increased risk for atherosclerosis. In atherosclerosis, damage to the arterial lining results in inflammation, the body's reaction to injury. Leukocytes are attracted to the inflamed area 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. If the plaque ruptures, a thrombus can form in the artery (Figure 42.19), potentially triggering a heart attack or a stroke.

the relaxation phase is called

diastole

across the thin walls of capillaries,

dissolved gases and other chemicals are exchanged by diffusion between the blood and the interstitial fluid around the tissue cells. At their "downstream" end, capillaries converge into venules, and venules converge into veins, the vessels that carry blood back to the heart

lymph nodes

filter lymph Inside each lymph node is a honeycomb of connective tissue with spaces filled by white blood cells, which function in defense.

A ______ body optimizes exchange by increasing surface area and minimizing diffusion distances.

flat

Erythrocytes, leukocytes, and platelets all develop

from stem cells

cardiac muscle cells are electrically coupled through

gap junctions

pulmocutaneous circuit

gas exchange in frogs - gas exchange in capillaries in both lungs AND skin!

compared with atria, ventricles have

have thicker walls and contract much more forcefully—especially the left ventricle, which pumps blood throughout the body via the systemic circuit.

cardiovascular system

heart and blood vessels in vertebrates

cardiac output

heart rate x stroke volume

Blood flows from ____ pressure to ____ pressure

high to low

Cues from the nervous and endocrine systems regulate production of NO and endothelin in blood vessels, where their opposing activities provide ______ ______ of blood pressure

homeostatic regulation 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.

Natural selection has resulted in two basic adaptations that permit effective exchange for all of an animal's cells

i. One adaptation for efficient exchange is a simple body plan that places many or all cells in direct contact with the environment. Each cell can thus exchange materials directly with the surrounding medium. Such an arrangement is characteristic of certain invertebrates, including cnidarians and flatworms. ii. Animals that lack a simple body plan display an alternative adaptation for efficient exchange: a circulatory system. Such systems move fluid between each cell's immediate surroundings and the body tissues. As a result, exchange with the environment and exchange with body tissues both occur over very short distances.

What short-term changes in an animal's cardiovascular function might facilitate using skeletal muscles to escape from a dangerous situation?

increase in blood pressure and cardiac output combined with the diversion of more blood to the skeletal muscles would increase the capacity for action by increasing the rate of blood circulation and delivering more O2 and nutrients to the skeletal muscles.

capillary beds

infiltrate tissues, passing within a few cell diameters of every cell in the body.

blood pressure

is generally measured for an artery in the arm at the same height as the heart (Figure 42.11). 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.)

Fainting response

is triggered when the nervous system detects that the blood pressure in your brain is below the level needed to provide adequate blood flow. 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. For animals with very long necks, the blood pressure required to overcome gravity is particularly high.

advantage of open circulatory systems

lower hydrostatic pressures typically associated with open circulatory systems allow them to use less energy than closed systems. In some invertebrates, open circulatory systems serve additional functions. For example, spiders use the hydrostatic pressure of their open circulatory system to extend their legs.

fluid return by the

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 the proteins within it are recovered and returned to the blood via the lymphatic system Fluid diffuses into the lymphatic system via a network of tiny vessels intermingled with capillaries

movement of lymph

moves from peripheral tissues to heart --- 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.

heart attack

myocardial infarction s 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. The coronary arteries are small in diameter and therefore especially vulnerable to obstruction by atherosclerotic plaques or thrombi. Such blockage can destroy cardiac muscle quickly because the constantly beating heart muscle requires a steady supply of O2. If a large enough portion of the heart is affected, the heart will stop beating. Such cardiac arrest causes death if a heartbeat is not restored within minutes by cardiopulmonary resuscitation (CPR) or some other emergency procedure.

endotherms

need about ten times as much energy s equal-sized ectotherms.

As a property of enzymes, cooperativity refers to

one enzyme subunit altering the behavior of others.

Many blood proteins (and all blood cells) are too large to pass readily through the endothelium, so 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).

Plasma Dissolved in the plasma are ions and proteins that, together with the blood cells, function in

osmotic regulation, transport, and defense. 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. Serving all of these functions necessitates keeping plasma electrolytes within narrow concentration ranges.

SA node

pacemaker of the heart

Vertebrate blood is a connective tissue consisting of cells suspended in a liquid matrix called

plasma Plasma also contains many other substances (besides plasma proteins and dissolved ions) in transit, including nutrients, metabolic wastes, respiratory gases, and hormones. Plasma has a much higher protein concentration (bc capillaries aren't very permeable to proteins) than interstitial fluid, although the two fluids are otherwise similar.

serum

plasma without clotting factors

clotting involves a

positive feedback loop Initially, the clotting reactions convert only some of the prothrombin at the clot site to thrombin. However, thrombin itself stimulates the enzymatic cascade, leading to more conversion of prothrombin to thrombin and thus driving clotting to completion.

cellular respiration

produces CO2 and ATP.

lymphoid progenitors

produces lymphocytes.

diastole

relaxation phase of the heartbeat 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).

In sharks, rays, and bony fishes, blood travels through the body and returns to its starting point in a single circuit (loop), an arrangement called

single circulation in single circulation the blood flows under reduced pressure directly from the gas exchange organs to other organs. A circulatory system consisting of a single pump and circuit, in which blood passes from the sites of gas exchange to the rest of the body before returning to the heart These animals have a heart that consists of two chambers: an atrium and a ventricle. Blood entering the heart collects in the atrium before transfer to the ventricle. Contraction of the ventricle pumps blood to a capillary bed in 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. Following gas exchange in the capillary beds, blood enters veins and 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 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 ______ as it moves from arteries to arterioles to the much narrower capillaries.

slows

After passing through the capillaries, the blood speeds up as it enters the venules and veins, which have

smaller total cross-sectional areas.

The contraction phase of the cycle is called

systole

measurement of blood pressure with a sphygmomanometer

systolic/diastolic

advantage of closed circulatory systems

the benefits of closed circulatory systems include blood pressure high enough to enable the effective delivery of O2 and nutrients in 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

blood clotting

the process by which blood becomes thick and stops flowing, forming a solid cover over any place where your skin has been cut or broken.

veins

the vessels that carry blood back to the heart

stroke volume

the volume of blood pumped out by a ventricle with each heartbeat 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, the increased demand for O2 is met by an increase in cardiac output that can be as much as fivefold.

arterial walls

thick, strong, contain elastic fibers They can thus accommodate blood pumped at high pressure by the heart, bulging outward as blood enters and recoiling as the heart relaxes between contractions.

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: t/f?

true

Erythrocytes also lack mitochondria and generate their ATP exclusively by anaerobic metabolism: t/f?

true

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 : t/f?

true

The exchange of substances between the blood and interstitial fluid occurs only in capillaries because only there are the vessel walls thin enough to permit this exchange.: t/f?

true

Heart powers circulation by?

using metabolic energy to elevate the circulatory fluid's hydrostatic pressure, the pressure the fluid exerts on surrounding vessels. The fluid then flows through the vessels and back to the heart.

unlike arteries, veins contain

valves - maintain a unidirectional flow of blood despite the low blood pressure in these vessels.

If the smooth muscles in arteriole walls contract, the arterioles narrow, a process called

vascoconstriction Vasoconstriction increases blood pressure upstream in the arteries.

endothelin, a peptide, as the most potent inducer of

vasoconstriction

Researchers have identified nitric oxide (NO), a gas, as a major inducer of

vasodilation

When the smooth muscles relax, the arterioles undergo

vasoldilation an increase in diameter that causes blood pressure in the arteries to fall.

Arterial blood pressure is highest when the heart contracts during

ventricular systole

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.

leukocytes

white blood cells - Their function is to fight infections. Some are phagocytic, engulfing and digesting microorganisms and debris from the body's own dead cells *Unlike erythrocytes, leukocytes are also found outside the circulatory system, patrolling interstitial fluid and the lymphatic system.*