Layman D. Biology Demystified: A Self-Teaching Guide

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wandering macrophages (mostly derived from monocytes). It is therefore an

important helper in phagocytosis of foreign invaders, such as bacteria, as well

as devouring fragments of broken erythrocytes.

The Tonsils: ‘‘Little Almonds’’ In the Back of

Our Throat

In addition to full-blown lymphatic organs, there are smaller masses of lym-

phatic tissue scattered here and there around the body. Prominent among

these are the tonsils (TAHN-sils). The tonsils are literally ‘‘little almonds’’

(tonsils) – oval, somewhat almond-shaped clusters of lymphatic tissue – lying

in the back of the throat (Figure 17.4).

In humans, there are ﬁve tonsils. The pharyngeal (fah-RIN-jee-al) tonsil is

the single uppermost mass, located in the portion of the pharynx (FAIR-inks)

or ‘‘throat’’ just behind the nose. The pharyngeal tonsil is also called the

adenoids (AD-uh-noyds), because it is rather big and ‘‘gland’’ (aden) ‘‘like’’

(-oid).

The two palatine (PAL-ah-tyn) tonsils, as their name indicates, are a pair of

tonsils lying on either side of the throat, just below the palate (PAL-aht) or

‘‘roof of the mouth.’’ Finally, there is a pair of lingual (LING-gwal) tonsils,

attached way back at the base of the ‘‘tongue’’ (lingu).

CHAPTER 17 Immune/Lymphatic Systems 307

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Fig. 17.4 The tonsils: ‘‘Little almonds’’ tucked away in our throats. (A) Frontal view.

(B) Side view.

TONSILLITIS

Since they are composed of lymphatic tissue, these ﬁve tonsils play minor

roles in body defense. They contain lymphocytes and macrophages that pha-

gocytose foreign invaders entering the nose, mouth, or throat. These invaders

naturally include various airborne bacteria and viruses.

Sometimes, however, the lymphatic tissue of the tonsils becomes over-

whelmed by a huge number of bacteria or viruses. In such cases, tonsillitis

(tahn-sihl-EYE-tis) may result. Tonsillitis is ‘‘an inﬂammation and swelling

of ’’ (-itis) the tonsils. This inﬂammation may be accompanied by a danger-

ously high fever. The operation of tonsillectomy (tahn-sihl-EK-toh-mee) or

‘‘removal of ’’ (-ectomy) the tonsils is then frequently performed.

[Study suggestion: Using your growing knowledge, write a single term that

literally means, ‘‘inﬂammation of the adenoids.’’ Why do you think that a

person aﬄicted with this condition might have trouble breathing?]

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. Immunity literally translates to mean:

(a) ‘‘Soreness of the back’’

(b) ‘‘A condition of not serving’’

(d) ‘‘Guards of protection’’

2. The word, lymph, derives its name from what speciﬁc characteristic?

(a) Dark red color of the ﬂuid

(b) Clear, watery ﬂuid contents

(d) Milky, murky sludge

3. The lymph is mainly created due to the process of:

(a) Simple diﬀusion

(b) Phagocytosis

(d) Pressure-driven ﬁltration

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1, Disorder

4. The ultimate destination of all lymph:

(a) Small masses of lymphatic tissue

(b) Extremely large lymph veins

(d) Blood-containing veins

5. Act as scouts that ﬁrst chemically detect and signal the presence of a

foreign invader:

(a) Plasma cells

(b) Thymic lymphocytes

(d) B-lymphocytes

6. A bone marrow lymphocyte:

(a) Readily diﬀerentiates into a plasma cell

(b) Is a major producer of antibodies

(d) Basically is identical to an erythrocyte

7. Amoeba-like cells that are active in achieving immunity:

(a) B-lymphocytes

(b) Plasma cells

(d) Wandering macrophages

8. An endocrine gland that secretes thymosin:

(a) Spleen

(b) Pancreas

(d) Thyroid

9. Both the spleen and red bone marrow are involved in the functions of:

(a) Hematopoiesis, recycling of old erythrocytes, and phagocytosis

(b) Antigen–antibody reactions, only

(d) Body movement and support of the vertebral column

10. The type of tonsil also known as the adenoids:

(a) Lingual

(b) Palatine

(d) Pharyngeal

CHAPTER 17 Immune/Lymphatic Systems 309

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The Giraﬀe ORDER TABLE for Chapter 17

(Key Text Facts About Biological Order Within An Organism)

1. ____________________________________________________________

2. ____________________________________________________________

3. ____________________________________________________________

4. ____________________________________________________________

The Dead Giraﬀe DISORDER TABLE for Chapter 17

(Key Text Facts About Biological Disorder Within An Organism)

1. ____________________________________________________________

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311

CHAPTER

The Respiratory

System: Breath of

Life

Chapter 17 talked about the lymphatic system and its circulation. But

Chapter 17, which deals with the respiratory (RES-pir-ah-tor-ee) system,

has much more in common with the cardiovascular or blood circulatory

system.

Respiration versus Ventilation

Respiration literally means ‘‘the act of ’’ (-tion) ‘‘breathing’’ (spir) ‘‘again’’

(re-). In actual usage, however, respiration is the process of gas exchange

between two or more body compartments. Consider, for example, external

respiration in mammals (Figure 18.1). External respiration is gas exchange

(such as that of O

gas and CO

gas) that occurs between the blood in the

pulmonary capillaries and the air within the alveoli (al-VEE-oh-lie). In mam-

mals, each alveolus (al-VEE-oh-lus) is a ‘‘little cavity’’ (alveol) or microscopic

air sac within the lung.

Internal respiration, in contrast, is gas exchange that occurs between the

blood in the systemic capillaries and the ﬂuid within the tissue cells. Internal

respiration, then, is the way mammalian cells acquire oxygen and give oﬀ

carbon dioxide.

During breathing, air is inhaled from the atmosphere, and it enters the

millions of alveoli within the lungs. We know that breathing, itself, involves

pulmonary functions: that is, those ‘‘pertaining to’’ (-ary) the ‘‘lungs’’

(pulmon). An appropriate term here is ventilation (ven-tih-LAY-shun), the

‘‘process of ’’ (-tion) ‘‘fanning or blowing’’ (ventil). A ventilation system in a

large building, for example, blows stale air out, and sucks fresh air in. A

similar situation exists for the lungs. Therefore, pulmonary ventilation is the

sucking of air into the lungs, followed by the blowing of air out of the

lungs.

INSPIRATION VERSUS EXPIRATION

The technical terms concerning pulmonary ventilation are inspiration (IN-

spir-ay-shun) on the one hand, expiration (EKS-pir-ay-shun) on the other

hand. Inspiration is the process of sucking air into the lungs, while expiration

is the process of blowing air out of the lungs.

Summarizing these relationships, we can say that:

PULMONARY VENTILATION ¼ INSPIRATION þ EXPIRATION

while

RESPIRATION ¼ The Process of Gas Exchange between Various

Body Compartments

Pulmonary ventilation is the way that the body takes in fresh air (by

inspiration) and gets rid of stale air (by expiration). And respiration (external

and internal) is the means by which O

and CO

are exchanged between

various compartments while the air is within the body.

These very basic inter-relationships are diagrammed for humans and other

mammals within Figure 18.1.

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1, Order

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Fish Gills: Respiration and Ventilation through

the Water

Land-dwelling animals – mammals, birds, reptiles, and amphibians – use air

as a means for both respiration and ventilation. And associated with this

characteristic, they have developed lungs, which inﬂate and deﬂate with air.

Aqueous (water-dwelling) animals, such as ﬁsh, however, ventilate water

through their mouths (Figure 18.2). The water passes through the pharynx

(throat), and then out across a set of curved gill arches. The gill arches consist

of a series of thin, thread-like gill ﬁlaments. Thin plates on the surfaces of the

gill ﬁlaments serve as the actual points of respiration (gas exchange). Water

passes through the narrow gaps between the plates and moves in a single

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Fig. 18.1 Respiration versus ventilation within humans.

1, Web

direction, out towards the edge of the operculum (oh-PER-kyuh-lum) or gill

‘‘cover.’’

As the water passes, O

molecules diﬀuse out of the water, and into tiny

blood capillaries. Simultaneously, CO

molecules diﬀuse out of the ﬁsh’s

bloodstream, and into the water. This mechanism for gas exchange is very

eﬀective. A limiting problem, however, is that the gill arches are very soft and

tend to easily collapse. There is also no defense mechanism to protect gill

arches in ﬁsh from dehydration. [Study suggestion: Ask yourself the following

question: ‘‘So, why can’t most ﬁsh just use their gills and extract O

from the

air? Why can’t most ﬁsh breathe outside of the water?’’ Use the preceding

hints in your reading to help you.]

The Path of Airflow in Humans

‘‘When humans take in air by inspiration, what is the sequence of body

structures through which the air passes?’’ the curious-minded reader might

well ask. The answer is depicted within Figure 18.3.

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Fig. 18.2 Fish gills: Extracting oxygen from the water.

THE UPPER RESPIRATORY PATHWAY

Lying above both lungs is the upper respiratory pathway. This pathway begins

with two cavities – the nasal (NAY-sal) cavity and the oral (OR-al) cavity.

The nasal cavity lies within the ‘‘nose’’ (nas), while the oral cavity is

situated behind the ‘‘mouth’’ (or). These are the ﬁrst two body structures

that inhaled air usually enters. From both of these cavities, the air goes back

into the pharynx (throat).

Situated at the lower end of the pharynx, one sees the larynx (LAIR-inks).

The larynx or ‘‘voice box’’ is a box-shaped collection of cartilage plates held

together by dense ﬁbrous connective tissue. Like the bow of a ship, the

laryngeal (lah-RIN-jee-al) prominence is a projection of cartilage sticking

out from the front of the voice box. Stretched across the interior of the larynx

are the two vocal (VOH-kal) cords. The vocal cords are two straps of highly

elastic connective tissue, which vibrate with the passage of air through the

larynx. These vibrations create the ‘‘voice’’ (voc) sounds.

The glottis (GLAHT-is) is the name of the tapered, ‘‘tongue’’ (glott)-

shaped opening between the two vocal cords. Closely related to the glottis

is the epiglottis (EH-pih-glaht-is). The epiglottis is a highly ﬂexible ﬂap of

cartilage literally located ‘‘upon’’ (epi-) the glottis. The epiglottis thus serves

as a ﬂexible lid over the top of the larynx or voice box. When a person

swallows, the food or liquid normally pushes the epiglottis shut. This usually

prevents food or liquid from entering the larynx and the rest of the respira-

tory pathway.

Below the larynx is the trachea (TRAY-kee-ah) or main ‘‘windpipe.’’ The

trachea is stiﬀ and noncollapsible, due to the presence of horseshoes of

cartilage within its walls.

THE LOWER RESPIRATORY PATHWAY

As the trachea branches, the lower respiratory pathway is created. The right

and left primary bronchi (BRAHN-kigh), the ﬁrst branches, then enter the

two lungs. The primary bronchi just keep branching. Eventually, a set of

bronchioles (BRAHN-kee-ohls) or ‘‘little bronchi’’ emerges. Much like an

inverted (upside down) tree, the respiratory tree thus consists of a succession

of ever-smaller and more numerous branches – the larynx, trachea, bronchi,

and bronchioles.

At the furthest tips of the bronchioles, hang clusters of thousands of

alveoli. (Picture the many olives suspended from the branches of an

inverted olive tree.) Each alveolus is essentially a collapsible, extremely

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thin-walled air sac. It is across the walls of the alveoli, and their close

neighbors, the pulmonary capillaries, that external respiration occurs. By

this means, remember, oxygen contained in the inhaled air ﬁnally enters the

bloodstream.

[Study suggestion: Look very carefully at Figure 18.3. Which structure

mentioned in this section do you think represents the so-called ‘‘Adam’s

apple’’ in males? Why?]

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Fig. 18.3 The respiratory tree.