Layman D. Biology Demystified: A Self-Teaching Guide

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Quiz

Refer to the text in this chapter if necessary. A good score is at least 8 correct

answers out of these 10 questions. The answers are listed in the back of this

book.

1. A synapse represents:

(a) A place where the tips of an axon almost touch a muscle ﬁber

(b) The major central region of a neuron

(d) A traveling wave of chemical excitation

2. _____ are masses of epithelial cells specialized for the function of

secretion:

(a) Blood vessels

(b) Hormones

(d) Glands

3. The mammary (MAH-mair-ee) glands within the female breasts are

most accurately classiﬁed as:

(a) Synapses

(b) Chemical messengers

(d) Exocrine glands

4. The phrase neuroendocrine system implies that:

(a) Some parts of the nervous system have no relationship to body

secretions

(b) There are just too darn many body structures and functions to

memorize!

functionally related

(d) Certain glands have unknown body functions that the brain can’t

understand

5. Antidiuretic hormone is actually produced and secreted by the:

(a) Posterior pituitary

(b) Anterior pituitary

(d) Hypothalamus

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6. TSH exerts a trophic eﬀect upon the _____ gland:

(a) Testis

(b) Thyroid

(d) Tonsil

7. Cortisol generally causes the blood glucose concentration to:

(a) Fall towards the lower limit of its normal range

(b) Stay relatively constant at all times

(d) Rise towards the upper limit of its normal range

8. Triggers ovulation (release of a mature ovum):

(a) GH

(b) ACTH

(d) LH

9. Epinephrine:

(a) Is exactly the same hormone as noradrenaline

(b) Typically causes a profound ‘‘relaxation response’’ and deep sleep

(d) Usually decreases the strength and rate of heart contractions

10. A ‘‘Second Messenger’’ is often required in the endocrine system, since:

(a) Most hormones don’t circulate far enough to reach tissue cells

(b) Metabolic action does not respond to hormone concentrations

(d) An error in interpreting the ‘‘First Messenger’’ frequently occurs

The Giraﬀe ORDER TABLE for Chapter 15

(Key Text Facts About Biological Order Within An Organism)

1. ____________________________________________________________

2. ____________________________________________________________

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278

3. ____________________________________________________________

4. ____________________________________________________________

5. ____________________________________________________________

The Dead Giraﬀe DISORDER TABLE for Chapter 15

(Key Text Facts About Biological Disorder Within An Organism)

1. ____________________________________________________________

2. ____________________________________________________________

3. ____________________________________________________________

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280

CHAPTER

Blood and the

Circulatory System

Chapter 15 included an overview of the neuroendocrine system. If you recall,

the endocrine glands (such as the thyroid) all secrete hormones directly into

the bloodstream. But the bloodstream, however, doesn’t carry the blood and

its hormones through the body in a straight line. Rather, it carries the blood

in a ‘‘little circle’’ (circul) (see Figure 16.1).

Chapter 16 thus discusses the circulatory (SIR-kyuh-luh-tor-ee) or cardio-

vascular (car-dee-oh-VAS-kyuh-lar) system. (This was ﬁrst mentioned in

Chapter 2 and Figure 2.4.) The circulatory (cardiovascular) system is an

organ system including the ‘‘heart’’ (cardi) and ‘‘little vessels’’ (vascul) that

carries the blood in a ‘‘little circle’’ that both begins and ends with the heart.

Along the way, the blood passes by the main body tissues. In so doing, the

blood delivers hormones, glucose, and various other nutrients to the main

body tissues. And, as it leaves, the blood picks up a number of waste pro-

ducts from the main body tissues.

1, Order

The Heart and Blood Vessels: The Pump and

Its Pipes

Glance back at Figure 16.1. You will see that if the heart represents a pump

for the blood, then the blood vessels represent the pipes carrying it! The

arteries (AR-ter-ees) are large-diameter vessels that always carry blood

away from the heart. Thus, the arteries immediately receive the blood

being pumped from the ventricles (VEN-trih-kls) – the ‘‘little belly’’-like

lower chambers on either side of the heart. Speciﬁcally, the right ventricle

(abbreviated as RV) pumps blood out into the common pulmonary (PULL-

mun-air-ee) artery (abbreviated as CPA), which in turn sends blood out

towards both ‘‘lungs’’ (pulmon). And the left ventricle (abbreviated as LV)

pumps blood out into the aortic (ay-OR-tik) arch. The aortic arch sends the

blood from the LV out towards the tissues of the major body systems (other

than the lungs) (See Figure 16.2, A).

As the major arteries (such as the common pulmonary artery and aortic

arch) travel farther from the heart, they branch into smaller arteries

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Fig. 16.1 An outline of the circulatory (cardiovascular) system.

(Figure 16.2, B). And these smaller arteries, in turn, branch into even smaller

arterioles (ar-TEER-ee-ohls) or ‘‘little arteries.’’ As the arterioles approach

the cells of the body tissues, they branch into the smallest blood vessels of all,

the capillaries (CAP-ih-lair-ees). Each capillary is very narrow (much like a

strand of hair). This characteristic is reﬂected in the translation of capillary,

which ‘‘pertains to a hair.’’

Since the wall of each capillary is only a single cell thick, nutrients and

waste products diﬀuse across the wall. Nutrients (such as oxygen, O

, and

glucose) diﬀuse out of the bloodstream, and into the tissue cells. And waste

products (such as carbon dioxide, CO

) diﬀuse out of the tissue cells, and into

the bloodstream.

After the capillaries run past the tissue cells, several of them merge

together to form the venules (VEN-yewls). The venules are the ‘‘little

veins,’’ in the sense that they connect the capillaries to the much larger

veins. The veins are all wide-diameter vessels that return blood towards the

heart.

Several of the largest veins return blood back to the atria (AY-tree-ah) –

the small ‘‘entrance rooms’’ (atri) or chambers located at the top of the heart.

Among the biggest sets of veins are the superior and inferior vena (VEE-nah)

cavae (KAY-veye), or ‘‘upper and lower cave veins.’’ The superior vena cava

(SVC) drains blood down into the right atrium (AY-tree-um), or RA, from

the area above the heart, while the inferior vena cava (IVC) returns blood up

into the right atrium from the entire region below the heart.

The four pulmonary veins, as their name suggests, return blood from the

lungs and empty it into the left atrium, LA.

THE SYSTEMIC AND PULMONARY CIRCULATIONS

For ease of study, the major vessels and heart chambers are often grouped

together into two connected circulations. The pulmonary or right-heart cir-

culation involves the circulation of blood to, through, and from the lungs.

The systemic (sis-TEM-ik) or left-heart circulation, in contrast, represents the

circulation of blood to, through, and from the tissues of all the major body

organ systems (except for the lungs). [Study suggestion: Review Figure 16.2.

From this diagram, which speciﬁc chamber of the heart begins the pulmonary

circulation? Which speciﬁc blood vessels end the pulmonary circulation?

What particular heart chamber begins the systemic circulation? What parti-

cular blood vessels end the systemic circulation?]

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2, Order

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Fig. 16.2 The major heart pumps and types of blood vessels. (A) The major chambers and

vessels attached to the heart. (B) Smaller blood vessels.

COMPARISON TO CIRCULATIONS IN OTHER VERTEBRATES

The four-chambered human heart (two upper atria, two lower ventricles) plus

a double circulation (pulmonary circulation plus systemic circulation) is pretty

typical of the heart and circulation found in both birds and other mammals.

Being endotherms (or homeotherms) that regulate their own internal body

temperature (Chapter 12), birds and mammals have a great need for energy

and oxygen to keep their body heat always at a fairly high level. A double

circulation plus powerful four-chambered heart provide both the required

force to pump a large volume of heated blood and a separate pulmonary

circulation that adds plenty of oxygen to the blood.

The pulmonary (right-heart) circulation in mammals, therefore, is specia-

lized for adding oxygen to the bloodstream. But the systemic (left-heart)

circulation specializes in extracting oxygen from the bloodstream and deli-

vering it to the tissues of the major organ systems. In the process, carbon

dioxide is picked up from the tissues.

The circulation in vertebrates that are heterotherms (poikilotherms), such

as ﬁsh, amphibians, and reptiles, is quite another matter. Fish have a two-

chambered heart with only a single circulation. Amphibians rely upon a

three-chambered heart (two atria, one ventricle) beating within their chests.

Reptiles, likewise, possess a three-chambered heart, with two atria and one

ventricle that is partially subdivided. Both amphibians and reptiles have

double circulations, but there is much less specialization of function of the

two circulations.

Internal Anatomy, Pacemaker Tissue, and

Valves of the Heart

The powerful four-chambered heart of humans and other mammals has a

complex internal anatomy (Figure 16.3). Consider, for example, the myocar-

dium (my-oh-CAR-dee-um) or ‘‘heart’’ (cardi) ‘‘muscle’’ (my). The cardiac

muscle ﬁbers of the myocardium are arranged in a fairly circular pattern

around the heart, so when they contract, they squeeze the blood out of the

heart chambers like a noose tightening around a bag. The blood from the

atria is pushed down into the ventricles, through a pair of one-way valves.

Not surprisingly, these valves are called the right and left atrioventricular (ay-

tree-oh-ven-TRIK-you-lar) valves. These two A-V (atrioventricular) valves

essentially act as one-way doors. They are actually ﬂaps of connective tissue

that are pushed open from above by blood in the atria.

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PACEMAKER TISSUE

The atria contract because they are excited by cardiac pacemaker cells. These

pacemaker cells are actually modiﬁed cardiac muscle ﬁbers that are self-excit-

ing. Sodium (Na

) and other charged particles are automatically let into the

pacemaker cells at a certain rate or rhythm. This happens because the proteins

in the membranes of the pacemaker cells tend to shift around, allowing ions to

enter and excite the pacemaker cells or ‘‘turn themselves on.’’

The main cardiac pacemaker area is called the sinoatrial (sigh-no-AY-tree-

al) or S-A node (NOAD). This region is called a node because it is somewhat

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Fig. 16.3 Some internal structures and functions of the heart.

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rounded, like a ‘‘knot.’’ The word sinoatrial indicates its anatomical location.

The S-A node lies in the outer wall of the right ‘‘atrium,’’ just below the

entrance of the superior vena cava – a major venous (VEE-nus) sinus (SIGH-

nus). (A sinus, in general, is a large vein that is shaped like a ‘‘hollow bay’’

[sin], holding a considerable volume of blood.)

As the primary cardiac pacemaker, the sinoatrial node excites itself ﬁrst.

The excitation then spreads from one cardiac muscle ﬁber to another, due to

the presence of intercalated (in-ter-KAY-lay-ted) discs between them. These

intercalated discs appear as thick dark lines when viewed through a com-

pound microscope. They are actually intercellular bridges ‘‘inserted between’’

(intercalat) adjacent cardiac muscle ﬁbers. Thus, when the S-A node ﬁres oﬀ

an action potential, this traveling wave of excitation moves from one cardiac

muscle ﬁber to another, across the intercalated discs connecting them end-to-

end. Eventually, both atria become excited and contract. And ﬁnally, both

ventricles become excited.

SEMILUNAR VALVES

After the ventricles are excited, their walls contract. The blood in the right

ventricle is pushed up into the common pulmonary artery through the right

semilunar (sem-eye-LOO-nar) valve. Likewise, the blood contained within the

left ventricle is pumped up into the aortic arch through the left semilunar

valve. Both of these valves get their names from the shapes of their ﬂaps,

which look like ‘‘partial or half ’’ (semi-) ‘‘moons’’ (lun). This is reﬂected in

their abbreviation, S-L.

Note back in Figure 16.3 that the myocardium is thicker in the walls of the

ventricles, compared to the atria. And observe that the myocardium is thick-

est of all in the wall of the left ventricle. [Study suggestion: Ask yourself,

‘‘Why is the myocardium thicker in the wall of the left ventricle, compared to

that of the right ventricle?’’ Hint: What happens to a skeletal muscle when

you repeatedly exercise it?]

The Cardiac Cycle

After the chambers of the heart are excited, they go into a state of systole

(SIS-toh-lee) or ‘‘contraction’’ and emptying. It is during systole that the

blood is pumped from each of the ventricles, and out into their major

arteries. After systole, comes diastole (die-AH-stoh-lee) or ‘‘relaxation’’ and

ﬁlling. While the atria are still contracting in systole, the ventricles below