Human Anatomy & Physiology



Basic Anatomy & Physiology II Dr. L. Bacha

Chapter Outline (Marieb & Hoehn 6th ed)

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PART 1

BLOOD VESSEL STRUCTURE AND FUNCTION

(We already did “Blood Vessel Structure and Function” in Chapter 16 Outline on pages 8 and 9. Definitely go back and review it! (

Here is a little summary of the definition of arteries and veins, and the type of blood they carry:

| |ARTERIES |VEINS |

|direction blood is carried |away from the heart |toward the heart |

|type of blood carried in |oxygenated blood |deoxygenated blood |

|systemic circuit | | |

|type of blood carried in |deoxygenated blood |oxygenated blood |

|pulmonary circuit | | |

18.1 Most blood vessel walls have three layers

( Remember to go back to Chapter 16 Outline pages 8 and 9 and the structure of blood vessels!

18.2 Arteries are pressure reservoirs, distributing vessels, or resistance vessels

( list the three groups of arteries:

elastic arteries, muscular arteries, arterioles

Elastic Arteries

( thick-walled arteries near the heart

( name an example of an elastic artery:

the aorta & its major branches

( they contain a large amount of elastic connective tissue

( they are relatively inactive in vasoconstriction

( they are pressure reservoirs, expanding and recoiling as blood is ejected from the heart

Muscular Arteries

( deliver blood to specific body organs

( most named arteries studied in the anatomy laboratory are this type

( their tunica media contains more smooth muscle and less elastic tissue, so they are more active in vasoconstriction and are less distensible than elastic arteries

Arterioles

( arterioles are the smallest of the arteries

( do they contain smooth muscle cells? yes

( arterioles lead into capillaries, and arteriole diameter regulates blood flow into the capillary beds:

- when arterioles dilate, do you think more or less blood flows into capillaries? more

- when arterioles constrict, do you think more or less blood flows into capillaries? less

- arteriole diameter varies in response to what?

- changing neural, hormonal, and local chemical influences

18.3 Capillaries are exchange vessels

( capillaries are microscopic; they are the smallest blood vessels

( they are simply an endothelial tube, formed by simple squamous epithelial cells supported by a basement membrane

( what is the average diameter of a capillary? 8 – 10 micrometers

( the number of capillaries varies with the type and metabolic activity of body tissue

- most tissues have a rich capillary supply

- name two structures that are poorly vascularized:

tendons and ligaments

- where are capillaries absent?

cartilage, epithelia; cornea and lens of the eye

( given their location and thin walls, capillaries are ideally suited for their role, which is what?

- exchange of materials (gases, nutrients, hormones, and so on) between the blood and the interstitial fluid

Types of Capillaries

( list the three types of capillaries:

continuous, fenestrated, and sinusoid

( see Figure 18.3 to answer the following:

1. Continuous Capillaries

( continuous capillaries are the least permeable and the most common type

( they are abundant in what?

skin, muscles, lungs, CNS

( their endothelial cells form a continuous tube and are joined together by tight junctions

2. Fenestrated Capillaries

( the cell membranes of the endothelial cells have numerous large pores called fenestrations

( the fenestrations make them more permeable to fluids and solutes than continuous capillaries

( fenestrated capillaries occur in areas of what? (and give the examples)

active filtration (e.g., kidney) or absorption (e.g., small intestine) and areas of endocrine hormone secretion

3. Sinusoid Capillaries (Sinusoids)

( sinusoid capillaries are the most permeable and occur in limited locations

( sinusoid capillaries are found only in what organs?

- liver, bone marrow, spleen, adrenal medulla

( their basement membranes are incomplete

( they have larger lumens than other capillaries

( their endothelial cells are fenestrated and are not fitted tightly together, but rather have large clefts between them

( these structural adaptations allow large molecules and even blood cells to pass between the blood and surrounding tissues

Capillary Beds

( do capillaries function independently? no

( they tend to form interweaving networks called what? capillary beds

- blood flow through the capillary bed is regulated by the diameter of the arterioles and smooth muscle sphincters

( at any given moment, more or less blood may be flowing through a capillary bed; please read the examples given in the book and see Fig. 18.4.

18.4 Veins are blood reservoirs that return blood toward the heart

Venules

( capillaries unite to form venules; they are the smallest of the veins

Veins

( venules join to form veins

( how are the walls and lumens of veins different than those of corresponding arteries?

- walls are always thinner and their lumens are larger

( with their large lumens and thin walls, veins can accommodate what?

a fairly large volume of blood

Venous Valves

( veins have venous valves that prevent what?

blood from flowing backward in veins

PART 2

PHYSIOLOGY OF CIRCULATION

18.6 Blood flows from high to low pressure against resistance

Definition of Terms

Blood Flow

( define blood flow:

= the volume of blood flowing through a vessel, an organ, or the entire circulation in a given period (ml/min)

- under resting conditions, it is what?

relatively constant

- at any given moment, however, blood flow through individual body organs may vary widely according to their immediate needs

Blood Pressure (BP)

( define blood pressure (( from the glossary in the back of the textbook!):

the force exerted by blood against a unit area of the blood vessel walls

( unless stated otherwise, the term blood pressure means what?

- systemic arterial blood pressure in the largest arteries near the heart

( the term “ blood pressure” used here more specifically is for hydrostatic blood pressure (to distinguish it from osmotic blood pressure)

18.7 Blood pressure decreases as blood flows from arteries through capillaries and into veins

( blood flows through the blood vessels along what? - a pressure gradient

( blood is always moving from what to what? - higher to lower pressure areas

( what generates blood flow? -the pumping action of the heart

( examine Fig. 18.6 to answer the following:

- systemic blood pressure is highest in what vessel? - aorta

- systemic blood pressure is lowest in what vessel? - venae cavae

- which vessels offer the greatest resistance to blood flow? - arterioles

(clue: note the steepest drop in blood pressure shown on the graph!)

Arterial Blood Pressure

( arterial blood pressure reflects what two factors?

(1) how much the elastic arteries close to the heart can stretch

(their compliance or distensibility)

(2) the volume of blood forced into them at any time

( systolic arterial blood pressure = the pressure exerted by blood on the walls of arteries when the ventricles are contracting

( diastolic arterial blood pressure = the pressure exerted by blood on the walls of arteries at the end of relaxation of the ventricles

Clinical Monitoring of Circulatory Efficiency

( clinicians can assess the efficiency of a person’s circulation by measuring what?

pulse and blood pressure

( pulse, blood pressure, respiratory rate and body temperature are referred to collectively as what?

the body’s vital signs

Taking a Pulse

( define pulse (( from the glossary in the back of the book!):

= rhythmic expansion and recoil of arteries resulting from heart contractions; can be felt from outside the body

( because it is so accessible, what artery is routinely used (where it surfaces at the wrist) to take a pulse measurement? radial artery

( note the body sites where the pulse is most easily palpated in Fig. 18.7

( why are these pulse points also called pressure points?

- because they are compressed to stop blood flow into distal tissues during hemorrhage

Measuring Blood Pressure

( most often, systemic arterial blood pressure is measured indirectly in what artery?

- brachial artery of the arm

( what is the long name for a blood pressure cuff?

sphygmomanometer (“sphygmo” = pulse)

Capillary Blood Pressure

( look at Fig. 18.6; does capillary pressure increase, stay the same, or decrease as blood flows through capillaries? - decreases

Venous Blood Pressure

( the pressure in veins is too low to promote adequate venous return. Other mechanisms that aid in blood flow through veins and back to the heart are:

1. the presence of valves in veins – prevent backflow of blood

2. contracting skeletal muscles – help squeeze blood through nearby vessels

3. pressure changes created during respiration

4. sympathetic vasoconstriction

18.8 Blood pressure is regulated by short- and long-term controls

( maintaining blood pressure is critical for cardiovascular system homeostasis. Its regulation involves what three key variables?

cardiac output; peripheral resistance; blood volume

( mean arterial blood pressure varies directly with cardiac output, and blood volume, and peripheral resistance:

1. cardiac output

∙ blood pressure varies directly with cardiac output

∙ as we covered in Chapter 17, cardiac output is equal to stroke volume times heart rate

∙ so, factors that regulate stroke volume and heart rate influence cardiac output, and therefore blood pressure

2. blood volume

∙ blood pressure varies directly with blood volume

∙ knowing that blood pressure depends on the total volume of blood in the cardiovascular system:

- what effect do you think a decrease in blood volume (greater than 10% of the total) has on BP?

- causes a decrease in BP

- what effect do you think an increase in blood volume has on BP?

- causes an increase in BP

3. peripheral resistance

∙ peripheral resistance is a measure of the amount of friction blood encounters as

it passes through vessels; it is an opposition to blood flow

∙ blood pressure varies directly with peripheral resistance

∙ there are three important sources of peripheral resistance:

a. blood viscosity - related to the thickness of blood

b. total blood vessel length

- peripheral resistance (and therefore BP) varies directly with total blood vessel length

- what effect do you think an increase in blood vessel length has on BP?

- causes an increase in BP

c. blood vessel diameter

- peripheral resistance (and therefore BP) varies indirectly with blood vessel diameter

Blood viscosity and total blood vessel length typically remain fairly constant. Blood vessels diameter (mainly of arterioles) is variable and is the main means of short-term regulation of blood pressure moment to moment (by changing peripheral resistance).

Short term regulation of blood pressure is through changes in the diameter of arterioles; arterioles can dilate or constrict in response to nerve impulses (via the vasomotor center) and hormones:

Short-Term Regulation: Neural Controls (of Blood Pressure)

Vasomotor Center

( is a cluster of sympathetic neurons in the medulla oblongata that controls diameter of blood vessels

( continuous moderate impulses from the vasomotor center maintains arterioles in a constant state of moderate constriction, called vasomotor tone

( the vasomotor center can increase or decrease sympathetic impulses to arterioles to adjust blood pressure (BP):

( BP ( vasomotor center decreases ( ( blood vessel diameter ( ( peripheral resistance ( ( BP sympathetic impulses to arterioles (vasodilation)

( BP ( vasomotor center increases ( ( blood vessel diameter ( ( peripheral resistance ( ( BP sympathetic impulses to arterioles (vasoconstriction)

( the activity of the vasomotor center is modified by input from:

a. baroreceptors

- special sensory cells in some large arteries such as the aortic arch that detect changes in arterial blood pressure

b. chemoreceptors

- special sensory cells in the aortic arch and other large arteries that detect changes in blood levels of oxygen, carbon dioxide, and hydrogen ions (pH)

c. higher brain centers

- input from the cerebral cortex and hypothalamus can influence the vasomotor center

Short-Term Regulation: Hormonal Controls (p. 622)

( adrenal medulla hormones: epinephrine and norepinephrine

- increase cardiac output and promote vasoconstriction, which increases BP

( angiotensin II

- release of renin from the kidneys leads to the formation angiotensin II in the blood, which stimulates intense vasoconstriction, which increases BP

( Atrial natriuretic peptide

- this hormone is produced in the atria of the heart and released in response to high blood pressure - it also causes generalized vasodilation, which decreases BP

( Antidiuretic hormone (ADH)

- hormone produced by the hypothalamus and released from the posterior lobe of the pituitary

- stimulates the kidneys to conserve water, which increases blood volume and blood pressure

- also, in large amounts, causes intense vasoconstriction, which increases BP

( histamine and other chemicals released during inflammation

- potent vasodilators, which decrease BP

( alcohol

- inhibits release of ADH, depresses the vasomotor center, promotes vasodilation of the skin

Long-Term Regulation: Renal Mechanisms

( the kidneys maintain long-term blood pressure homeostasis by regulating blood volume

Homeostatic Imbalances in Blood Pressure

What are the normal systolic and diastolic blood pressure values for resting adults?

systolic pressure of less than 120 mm Hg and

diastolic pressure of less than 80 mm Hg

( define hypertension: = chronically elevated blood pressure

( define hypotension: = low blood pressure

18.10 Slow blood flow through capillaries promotes diffusion and bulk flow

Vasomotion

( is blood flow through capillary networks slow and intermittent? yes

Fluid Movements: Bulk Flow

- during bulk flow, fluid is forced out of the capillaries through clefts at the arterial end of the capillary bed, but most of it returns to what?

to the bloodstream at the venous end

( filtration is pressure-driven movement of fluids and solutes from blood capillaries into interstitial fluid

( reabsorption is pressure-driven movement of fluids and solutes from interstitial fluid into blood capillaries

( The Interplay between Filtration and Absorption during Bulk Flow

summary of the two main pressures involved during bulk flow:

(1) capillary hydrostatic pressure: is due to the pressure blood exerts on the blood vessel wall. This pressure tends to push fluid out of the capillary into the interstitial fluid (filtration)

(2) capillary osmotic pressure: is due to the presence of large molecules like plasma proteins in the blood; they are too big to pass thru capillaries and they exert an osmotic pressure that tends to draw interstitial fluid into the capillary (reabsorption)

net filtration pressure is the difference between the above 2 pressures

(interstitial fluid hydrostatic pressure and interstitial fluid colloid osmotic pressure are negligible and we are ignoring them)

Summary Of Bulk Fluid Flow (i.e., movement of fluids between blood capillaries and the surrounding interstitial fluid):

AT THE ARTERIAL END OF A BLOOD CAPILLARY:

1. The capillary hydrostatic pressure forces fluid from the blood, through the wall of the blood capillary, into the interstitial tissue.

2. The capillary osmotic pressure exerted by proteins (such as albumin) in the blood causes fluid to move from the interstitial tissue into the blood capillary.

3. The capillary hydrostatic pressure is greater than the capillary osmotic pressure, so that there is a net movement of fluid from the blood capillary into the interstitial tissue.

AT THE VENOUS END OF A BLOOD CAPILLARY:

4. The capillary hydrostatic pressure is lower, so that less fluid and ions are forced from the blood capillary into the interstitial tissue.

5. The capillary osmotic pressure is greater (because fluid moved out at the arterial end, leaving a higher concentration of nondiffusible proteins in the plasma).

6. There is a net movement of fluid from the interstitial tissue into the blood at the venous end of a blood capillary. (i.e., fluid is resorbed into the blood).

( Does all of the fluid that is filtered out of the blood capillary get reabsorbed?! no

( of the roughly 24 liters of fluid that moves out of the plasma and into the interstitial fluid each day, 20.4 liters is reabsorbed

( so, (are you good at math?) what percent of the fluid filtered out of blood capillaries is reabsorbed? 85%

( of the volume of fluid that leaves the blood at the arterial end of the capillary, only about 85% returns to the blood at the venous end of the capillary. The remaining 15% of fluid enters lymphatic capillaries, which are blind-ended vessels.

Lymph in the lymphatic capillaries is ultimately carried into subclavian veins, so that the fluid is eventually returned to the blood circulatory system. This maintains a balance in fluid exchange, so that normally there is no excess accumulation of interstitial fluid.

Edema (page 634)

PART 3

CIRCULATORY PATHWAYS: BLOOD VESSELS OF THE BODY

( read pages 634 to 635, and look at the Figures on those pages, for a review and summary of pulmonary and systemic circulation

( flip through the rest of the pages on circulation and be glad you don’t have to know all that stuff, but it’s there, just in case you need it in the future!

…………………………………………………………………………………………………………………………………………………………………

The flow chart below should help with some of the info in Chapters 17 and 18; enjoy!

THE END!

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OJQJ^JaJhê-UCJOJQJ^JaJ:jh3!35?B*CJ$OJblood pressure; you may as well, you’ll probably be doing it some day!

see page 616 of the textbook, where these terms are introduced

Define edema:

= an abnormal increase in the amount of interstitial fluid

( edema causes swelling

Edema occurs when something causes an imbalance in filtration and reabsorption:

( what if someone has hypoproteinemia (low protein in the blood, such as due to liver or kidney disease)…proteins exert an osmotic pressure in the blood, so there would be less capillary colloid osmotic pressure ( less fluid gets reabsorbed ( more remains in the interstitial fluid ( edema!

( what if someone has the larvae of a parasitic worm blocking their lymphatic capillaries

(as in the disease called “elephantiasis”) ( the 15% of the fluid would not be able to drain

into the lymphatic capillaries ( more remains in the interstitial fluid ( edema!

A capillary bed?!

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