Chapter 42 Part 2

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

(a) How do the smooth muscles surrounding the arteries change during vasoconstriction and vasodilation, respectively?

The cross-sectional area increases from the arota to capillaries The number of capillaries is enormous, roughly 7 billion in a human body. Each artery conveys blood to so many capillaries that the total cross-sectional area is much greater in capillary beds than in arteries or another part of the circulatory system.

(a) How does the cross-sectional area of blood vessels change as you move from the aorta to capillaries?

Small solutes such as sugars, salts, and urea as well as for bulk flow of fluid into tissues driven by blook pressure within the capillaries diffuse from capillaries into the interstitial fluid. 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, so they remain in the capillaries. These dissolve proteins are responsible for much of the blood's osmotic pressure (pressure produced by the difference in solute concentration across a membrane).

(a) What diffuses from capillaries into the interstitial fluid? What diffuses from the interstitial fluid to the capillaries, and why?

At systolic pressure

(a) When is blood pressure in the arteries highest?

Fluids and small solutes are transported into the interstitial fluid from the blood pressure of the capillaries. Fluid moves from the interstitial fluid back into the bloodstream through osmotic pressure. There is a net loss of fluid in the capillaries.

(b) How are fluids and small solutes transported into the interstitial fluid? By what mechanism does fluid move from the interstitial fluid back into the bloodstream? Do capillaries experience a net gain or net loss of fluid?

Vasoconstriction causes an increase in blood pressure in upstream arteries Vasodilation causes a decrease in blood pressure in upstream arteries.

(b) How do vasoconstriction and vasodilation change blood pressure in upstream blood vessels?

The velocity decreases from the aorta to capillaries

(b) How does the velocity of blood change as you move from the aorta to the capillaries?

At diastolic pressure

(b) When is blood pressure in the arteries lowest?

The pressure decreases from the aorta to capillaries and continues to decrease from the capillaries to vena cavae.

(c) How does the blood pressure (defined as the force of liquid blood against the walls of the blood vessels) change as you move from the aorta to the capillaries? How about from the capillaries to the vena cavae?

The lost fluid and proteins within the capillaries are recovered and returned to the blood through the lymphatic system. Fluid diffuses into the lymphatic system via a network of tiny vessels intermingled with capillaries. The recovered fluid, called 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.

(c) What role does the lymphatic system play in maintaining the volume of blood?

Yes

(c) When the arteries are at their lowest pressure, is there still blood in the vessels?

No, because the artery is farther away from the heart and gravity causes changes in blood pressure. When you stand or sit, gravity draws blood down to your feet and impedes its upward return to the heart.

(d) If you took your blood pressure from an artery in your leg rather than in your arm, would it be reporting a pressure close to that of what's in the aorta? Why or why not?

Normally highest in the aorta and lowest in the venae cavae/ veins. Blood, like all fluids, flows from areas of higher pressure to areas of lower pressure. Contraction of a heat ventricle generates blood pressure, which exerts a force in all directions. The part of the force-directed lengthwise in an artery causes the blood to flow away from the heart, the site of the highest pressure.

(d) Where is blood pressure normally highest? Where is blood pressure normally lowest?

Once blood enters the millions of tiny arterioles and capillaries, the narrow diameter of these vessels generates substantial resistance to flow. By the time the blood enters the veins, this resistance has dissipated much of the pressure generated by the pumping heart.

(e) The book mentions the effect of resistance on the flow of blood as the main reason why blood pressure decreases as you move from the heart to the body. What aspect of blood vessels is the main contributor to this increased resistance?

Endothelium - A single layer of flattened epithelial cells. This smooth layer minimizes resistance to fluid flow. Capillaries Have very thin walls, which consist of just an endothelium and a surrounding extra cellular layer called the basal lamina. 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. Arteries Have walls that consist of two layers of tissues surrounding the endothelium. The outer layer is formed by connective tissue that contains elastic fibers, allowing the vessel to stretch and recoil, and collagen, which provides strength. The layer next to the endothelium contains smooth muscle and more elastic fibers. Walls are thick, strong, and elastic. Can accommodate blood pumped at high pressure by the heart, bulging outward as blood enters and recoiling as the heart relaxes between contractions. The behavior of the wall has an essential role in maintaining blood pressure and flow to capillaries. Veins Have walls that consist of two layers of tissues surrounding the endothelium. The outer layer is formed by connective tissue that contains elastic fibers, allowing the vessel to stretch and recoil, and collagen, which provides strength. The layer next to the endothelium contains smooth muscle and more elastic fibers. Because veins convey blood back to the heart at a lower pressure, they do not require thick walls. Veins contain valves that maintain a unidirectional flow of blood despite the low blood pressure in these vessels.

1. Examine Figure 42.9. What types of tissues make up capillaries, arteries, and veins? What mechanical properties do these tissues give to arteries and veins?

partial pressure

1. Fill in the blanks: In general, gases move from an area of high __ to an area of low __.

In the Bone Marrow

11. Where in the body can you find the stem cells that give rise to many blood cell types arise? (You are not responsible for the information in Figure 42.17.)

Platelets adhere to collagen fibers in the connective tissue and release a substance that makes nearby platelets sticky. The platelets form a plug that provides immediate protection against blood loss Unless the break is very small, the plug is reinforced by a fibrin clot. These clotting actors 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. Initially, the clotting reactions convert only some of the prothrombin at the clot site to thrombi. Thrombin however itself stimulates the enzymatic cascade, leading to more conversion of prothrombin to thrombin and thus driving clotting to completes.

12. Examine Figure 42.18. What happens when there is damage to the epithelium of a blood vessel? When does this process stop?

Individuals with high LDL to HDL have an increased risk of this. Damage causes inflammation. Leukocytes are attracted to the inflamed area and begin to take up lipids, including cholesterol. A fatty deposit, called plaque, grows steadily, incorporating fibrous connective tissue and additional cholesterol. - If the plaque ruptures, a thrombus can form in the artery, potentially triggering a heart attack or stroke. If a large enough portion of the heart is affected, the heart will stop beating.

14. How does a plaque form in atherosclerosis? When does the formation of this plaque become deadly?

The concentrations of O2 in the air and in the ater differ substantially because O2 is much less soluble in water than in air. Also, the warmer and saltier the water is, the less dissolved O2 it can hold. Air is much less dense and less viscous than water, so it is easier to move and to force through small passageways. Water's lower O2 content, greater density, and greater viscosity mean that aquatic animals such as fishes and lobsters must expend considerable energy to carry out gas exchange.

2. Why is air a better medium for oxygen exchange compared to water?

Surface Area - The movement of O2 and CO2 across respiratory surfaces takes place by diffusion. The rate of diffusion is proportional to the surface area across which it occurs and inversely proportional to the square of the distance through which molecules must move.

3. What property of the body do most organisms try to maximize in order to maximize the amount of gas exchange that can take place with air or water? (Think back to Ch. 40)

Arterial blood pressure is highest when the heart contracts during ventricular systole. The pressure at this time is called systolic pressure Each ventricular contraction causes a spike in blood pressure that stretches the walls of the arteries. The pressure surge is partly due to the narrow openings of arterioles impeding the exit of nlood from the arteries. When the heart contracts, blood enters the arteries faster than it can leave, and the vessels stretch to a wider diameter from the rise in pressure During diastole, the elastic walls of the arteries snap back. 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. Arteries remain pressurized through the cardiac cycle, therefore blood continuously flows into arterioles and capillaries.

3. When blood is pushed from the ventricles into the aorta and arteries, how does the force of the entering fluid change the shape of these vessels? What happens to the fluid in these vessels right after the contraction of the ventricle ceases?

- To initiate ventilation, most gill-bearing animals either move their gills through the water or move water over their gills. - Gills have a total surface area much greater than that of the rest of the body's exterior. - Countercurrent exchange that results in a partial pressure gradient that favors the diffusion of O2 from water to blood along the entire length of the capillary.

4. What is ventilation, and how do non-terrestrial animals make it happen? Consult Figure 42.21.

Insects Tracheal System - A network of air tubes that brack throughout the body. The largest tubes, called tracheae, open to the outside. Brings air within a very short distance of virtually every body cell in an insect, the efficient exchange of O2 and CO2 does not require the participation of the animal's open circulatory system. Mammals All depend entirely on the lungs for gas exchange. Branching ducts convey air to the lungs which are located in the thoracic cavity, enclosed by the ribs and diaphragm.

5. How is the respiratory surface area maximized in insects? How about in mammals?

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.

6. Examine Figure 42.12. What specialization do veins have that help them overcome the effect of gravity on blood flow?

Tracheal systems are branched throughout the insect body and lungs are localized respiratory organs.

7. What is the difference between a lung and a tracheal system?

Precapillary sphincters regulate the passage of blood into capillary beds. The opening and closing of these muscular rings regulate and redirects the passage of blood into particular sets of capillaries.

7. What structure is responsible for mediating the diameter of capillaries, thereby allowing or restricting blood flow?

The capillaries are webbed around the alveoli. Oxygen in the air entering the alveoli dissolves in the moist film ling their inner surfaces and rapidly diffuses across the epithelium into a web of capillaries that surrounds each alveolus.

9. Describe how capillaries are organized around alveoli.

Tracheal System

A network of air tubes that brack throughout the body. The largest tubes, called tracheae, open to the outside. Brings air within a very short distance of virtually every body cell in an insect, the efficient exchange of O2 and CO2 does not require the participation of the animal's open circulatory system. Mammals

Alveoli

Air savs clustered at the tips of the tiniest bronchioles. Gas exchange occurs here. In humans, the surface area of this is 50 times that of skin. If too much particulate matter reaches this, the defenses (white blood cells) can be overwhelmed, leading to inflammation and irreversible damage.

Bronchi

Branches of the trachea, that lead to each lung.

Thrombus

Clots that form within a blood vessel, blocking the flow of blood.

Surfactant (Surface-active agent)

Coats the alveoli and reduces surface tension.

Plasma

Connective tissue consisting of cells suspended in a liquid matrix. Dissolved within it are ions and proteins that, together with the blood cells, function in osmotic regulation, transport, and defense.

Heart attack (Myocardial Infarction)

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. 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

Low-Density Lipoprotein (LDL)

Delivers cholesterol to cells for membrane production.

Bronchioles

Finer and finer tubes of the bronchi brank within the lung.

Hypertension

High blood pressure that is yet another contributor to a heart attack or stroke.

The cross-sectional area decreases from capillaries to the vena cave.

How does the cross-sectional area of blood vessels change as you move from capillaries to the vena cavae?

The velocity increases as you move from capillaries to venae cavae.

How does the velocity of blood flow change as you move from capillaries to the vena cavae?

Cellular elements (cells and cell fragments) occupy about 45% of the volume of blood. The remainder is plasma.

How much of the blood is plasma vs. cellular elements?

Ventilation

Movement of the respiratory medium over the respiratory surface. Maintains the partial pressure gradients of O2 and CO2 across the gill that are necessary for gas exchange.

High-density Lipoprotein (HDL)

Scavenges excess cholesterol for return to the liver.

Stroke

The death of nervous tissue in the brain due to lack of O2. usually results from rupture or blockage of arteries in the head.

Countercurrent exchange

The exchange of a substance or heat between two fluids flowing in opposite directions,

Atherosclerosis

The hardening of the arteries by the accumulation of fatty deposits. A key player in the development is cholesterol, a steroid that is important for maintaining normal membrane fluidity in animal cells.

Partial Pressure

The pressure exerted by a particular gas in a mixture of gases.

Larynx

The upper part of the respiratory tract. Moves upward and tips the epiglottis over the glottis, which is the opening of the trachea, or windpipe when eating to allow food to go down the esophagus.

Leukocytes (white blood cells) = Defense and immunity Platelets = Blood clotting Erythrocytes (Red Blood Cells) - Transport of O2 and some CO2

What are the three classes of cells in blood? What do these classes of cells do?