8

10

11

12

13

14 15

16

17

18

259

 1 Testis

 2 Interstitial (Leydig) cell

 3 Basement membrane

 4 Sertoli cell

 5 Spermatogonium

 6 Primary spermatocyte

 7 Secondary spermatocyte

 8 Spermatid

 9 Seminiferous tubule

10 Tunica albuginea

 11 Epididymis

12 Spermatic cord

Sagittal section of left testis

Medial view

Photomicrograph of testis

40x

The testes are oval-shaped organs about 2 inches (5 cm) long and 1 inch (2.5 cm) wide

that occupy the scrotal sac of a male. They are covered by a tough fi brous tunic and

wrapped in a serous sac that separates them from the external tissues that surround

Testes

them. Internally, the testes consist of numerous small compartments created by connective tissue bands that

project inward from the outer fi brous tunic. Each testicular compartment is occupied by a thin, highly coiled

seminiferous tubule. This thin tube is the site of sperm production. Situated between the tubules are the interstitial cells (of Leydig). It is these large interstitial cells that secrete the steroidal hormones in the testis.

1

2 3

3

4

5

6

7

8

9

9

10

11

11

12

3

3

4

10

3

260

In addition to the endocrine organs discussed

on the preceding pages, there are other endocrine tissues in the body. These include tisOther Endocrine Structures

Other organs with endocrine tissues

Stomach (upper left), kidney (upper right), heart (lower right),

placenta (lower left), and adipose tissue (center)

sues in the wall of the gastrointestinal tract that produce hormones such as gastrin and secretin, tissues in the kidney that

produce renin and erythropoietin, tissues in the atrium of the heart that produce atrial natriuretic peptide, tissues of the placenta that produce human chorionic gonadotropin, estrogens, and progesterone, and adipose tissue that produces leptin.

These hormones have a variety of functions, from stimulating the release of digestive enzymes, to raising blood pressure,

to decreasing blood pressure, to regulating reproductive cycles, and suppressing appetite.

261

16 Cardiovascular System

If you have ever planted a

 garden of signifi cant size, you have probably experienced the importance of an irrigation system. At its simplest, an irrigation system is

a network of channels or furrows that deliver needed water from

one main source to the roots of all the garden’s plants. Like an

irrigation system, the body’s blood vessels form an extensive

network of “irrigation channels” to deliver needed fl uid — in

this case the homeostatically maintained blood — to all the

body’s cells. In fact, this delivery system is probably the most

phenomenal irrigation network imaginable. Emanating

from a muscular pump, the heart, these vessels form an

 extensive system of tubular roadways that carry nourishing

blood away from the heart and toward the tissues. Th ey

then make a “U-turn” through small permeable, exchange

vessels, the capillaries, which feed all the body’s cells. Here,

life-supporting molecules, such as water, oxygen, glucose,

and amino acids are delivered to the cells, and the by-products

of cellular metabolism are picked up from the surrounding

tissue fl uid. Th e blood then fl ows back to the heart through

a series of return vessels, the veins, that parallel the delivery

vessels. Th is circular pattern of fl ow to and from the heart

constitutes the vascular (blood vessel) component of the

 cardiovascular (circulatory) system. Th is irrigation network

is so impressive, that if all the blood vessels of the body were

placed end-to-end they would extend 25,000 miles (96,500 km),

which is approximately two times the equatorial circumference

of the earth.

Th e irrigation network of blood vessels are of no value without

a pump. Th e heart is the dual, self-regulating pump that generates

the pressure to drive the blood through this impressive irrigation

network. It pumps the blood through two cycles — a pulmonary

cycle to pick up oxygen from the lungs and a systemic cycle to deliver

the oxygen to all the cells of the body. Soon aft er conception, and up

until death, the heart pumps blood. It averages approximately 70 beats

per minute, or about 3 billion contractions in an average lifetime.

Th e fi nal aspect of the cardiovascular system is the accessory drainage

network — the lymphatics. Th ese small vein-like vessels insure that the

cardiac return equals the cardiac output. Th is chapter will depict the anatomy

of this amazing muscular pump and the vascular and lymphatic roadways that

distribute the blood throughout the body.

Find more information

about the cardiovascular

system in

REAL ANATOMY

262

 1 Erythrocyte (red blood cell)

 2 Leukocyte - neutrophil (white blood cell)

 3 Leukocyte - monocyte (white blood cell)

 4 Thrombocyte (platelet)

 5 Blood plasma

Blood smear

700x

In the histology chapter we learned that the fl uid material we call blood has been historically classifi ed as

a connective tissue. This classifi cation was a result of the fact that, like other connective tissues, blood

has more extracellular matrix than cells. More recently, however, blood has been placed in a tissue catBlood

egory of its own — the hematolymphoid complex. The extracellular portion of the blood is a water solution that gives rise to

its liquid nature. Blood is closely related to other aqueous fl uids within the body, in fact most of the other body fl uids, such

as interstitial fl uid, lymph, cerebrospinal fl uid, and aqueous humor, arise from the blood. These extracellular fl uids are the

water environment that nourish, protect, and exchange with every cell of the body. This water environment is derived from

the blood, renewed by the blood, and returned to the blood. Dispersed in the blood plasma are the three groups of blood

cells — erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets). The blood smear below

depicts the three cell categories.

1

1

1

1

1 1

2

2

2

3

4

4

4

4

5

5

1

2

2

2

3

263

Heart

Posterior view

Heart

Anterior view

From its origin in the embryo as a simple pumping tube, the heart develops into a strong fi bromuscular

organ. During its development the original tubular pump is folded and subdivided into a four chambered

organ that has a pyramidal or conical form. It is approximately the size of a closed fi st and weighs

Heart

approximately 300 grams in males and a little less than this in females. For its small size, comprising only one half of one

percent of the total body mass, it is an important and functionally amazing organ. The wall of the heart consists of three

structural layers that each play signifi cant roles in its function as an effi cient pump. While the tissue makeup of this wall is

similar at any location in the heart, the thickness can vary considerably. Internally a septum and series of valves divide the heart

into four chambers through which the blood moves in a unidirectional fl ow. The chambers differ in structure and function, which

is primarily refl ected in the anatomy of their walls. Embedded within the walls of heart is a special electrical conduction system

that helps regulate its coordinated pumping action.

 1 Right atrium

 2 Left atrium

 3 Right ventricle

 4 Left ventricle

 5 Right auricle

 6 Left auricle

 7 Aorta

 8 Brachiocephalic artery

 9 Left common carotid artery

10 Left subclavian artery

 11 Pulmonary trunk

12 Right pulmonary artery

13 Left pulmonary artery

14 Ligamentum arteriosum

15 Superior vena cava

16 Inferior vena cava

17 Coronary sinus

18 Right coronary artery

19 Conus arteriosus branch

20 Marginal branch

21 Anterior interventricular artery

22 Lateral branches

23 Circumflex branch

24 Posterior interventricular artery

25 Anterior cardiac vein

26 Great cardiac vein

27 Posterior vein of left ventricle

28 Middle cardiac vein

29 Small cardiac vein

30 Right superior pulmonary vein

31 Right inferior pulmonary vein

32 Left superior pulmonary vein

33 Left inferior pulmonary vein

1

1

2

3

3

4

4

5 6

7

7

8

8 9

9

10

10

11

12

13

13

14

14

15

15

17 16

18

19

20

20

21

22

24

25

25

26

25

27

28

29

30

31

31

32

32

33

33

1

1

2

3

3

4

4

5 6

7

7

8

8 9

9

10

10

11

12

13

13

14

14

15

15

17 16

18

19

20

20

21

22

24

25

25

26

23

27

28

29

30

31

31

32

32

33

33

264

Dissection of heart and pericardial sac

Anterolateral view

Transverse section of heart comparing ventricle thickness

Inferior view, left ventricle at right

Dissected heart showing interior of chambers

Anterior view

Heart

 1 Parietal pericardium

 2 Fibrous pericardium

 3 Visceral pericardium

 4 Epicardium

 5 Myocardium

 6 Endocardium

 7 Right atrium

 8 Right auricle

 9 Interatrial septum

10 Fossa ovalis

 11 Crista terminalis

12 Valve of inferior vena cava

13 Pectinate muscle

14 Tricuspid valve

15 Chordae tendineae

16 Trabeculae carnae

17 Papillary muscle

18 Right ventricle

19 Pulmonary valve

20 Left atrium

21 Left auricle

22 Bicuspid valve

23 Left ventricle

24 Aortic valve

25 Apex

26 Aorta

27 Brachiocephalic artery

28 Left common carotid artery

29 Left subclavian artery

30 Pulmonary trunk

31 Left pulmonary artery

32 Ligamentum arteriosum

33 Anterior interventricular artery

34 Lateral branches of interventricular artery

35 Superior vena cava

36 Right coronary artery

37 Left coronary artery

38 Right pulmonary veins

39 Left pulmonary veins

40 Diaphragm

41 Lung

1

2 3

4

5

6

7

8

8

9 10

11

12

13

13

14

14

15

15

15

16

16

16

17

17

18

19 21

23

23

23

25

26

26

27 28

29

30

30

31

32

33 34

35

36

38

39

40

41

1

2 3

4

5

6

7

8

8

9 10

11

12

13

13

14

14

15

15

15

16

16

16

17

17

18

19 21

23

23

23

25

26

26

27 28

29

30

30

31

32

33 34

35

36

38

39

40

41

265

Dissection of heart revealing tricuspid valve

Anterior view

Heart dissection with atria and arteries removed

Superior view, anterior at top

Aortic valve

Superior view

7

9

13

13

14

14

15

16

17

18

19

20

22

24

24

36

37

7

9

13

13

14

14

15

16

17

18

19

20

22

24

24

36

37

266

Muscular artery

100x

Elastic lamellae of aorta

640x

Section of aorta — large elastic artery

100x

Like all tubes in the body, blood vessels have a basic pattern of design that involves

three structural tunics, or layers. The inner layer of the vessel is the tunica intima.

This consists of the luminal endothelium and a thin network of underlying elastic

Blood Vessels

connective tissue. The middle layer of the vessel is the tunica media, which consists of varying amounts of smooth muscle

and elastic connective tissue. Variations in the tunica media defi ne the different types of blood vessels. The outer layer, the

tunica externa, is a dense connective tissue outer coat. The designations — elastic arteries, muscular arteries, arterioles,

venules, and veins — are based on size differences and the differences in the vessels’ tunica media. Elastic arteries have

a thick elastic tunica media. Muscular arteries have a tunica media dominated by smooth muscle. Arterioles are tiny arteries

with a muscular tunica media. All the venous vessels have a thin, almost non-existent tunica media. The smallest blood

vessels, the capillaries, loose all the layers of their wall except the inner endothelium. These microscopic, thin walled tubes

become the exchange vessels of the system.

 1 Endothelium of tunica intima

 2 Internal elastic membrane of tunica intima

 3 Elastic lamellae of tunica media

 4 Smooth muscle cells of tunica media

 5 Connective tissue of tunica externa

 6 Red blood cells

 7 White blood cells

 8 Venous valves

 9 Nerve

10 Striated skeletal muscle

1

2

2

3

3

3

3

3

4

5

2

3

3

3

3

3

4

5

267

Arteriole

500x

Capillary

1000x

Neurovascular bundle — note thin-walled vein fi lled with red

blood cells (6) compared to thick-walled muscular arteries (4)

100x

Longitudinal section of vein showing valves

Anterior view

Transverse section of vein showing valves

Superior view

1

1

1

2

4

4

4

5

5

5

6

6

6

7

8 8

8

9

9

9

10

10

1

1

1

2

4

4

4

5

5

5

6

6

6

7

8 8

8

9

9

9

10

10

268

 1 Heart

 2 Pulmonary trunk

 3 Right pulmonary artery

 4 Left pulmonary artery

 5 Right superior pulmonary vein

 6 Right inferior pulmonary vein

 7 Left superior pulmonary vein

 8 Left inferior pulmonary vein

 9 Aorta

10 Right coronary artery

 11 Left coronary artery

12 Right common carotid artery

13 Right subclavian artery

14 Left common carotid artery

15 Left subclavian artery

Dissections of pulmonary trunk, arteries, and veins

Anterosuperior view below, anterior view above

The vascular system consists of two long circular loops of continuous

branched tubing that each begin and end with the heart. Leaving the

right ventricle and returning to the left atrium is the smaller pulmonary

Pulmonary Circuit

circulation. This circular loop courses through the lung tissues where its smallest vessels form an extensive interface with

the small air sacs of the lungs. This important interface is the site of exchange of O2

 and CO2

 between the blood and air.

16 Superior vena cava

17 Inferior vena cava

18 Trachea

19 Right principal bronchus

20 Left principal bronchus

21 Esophagus

22 Thyroid gland

23 Vagus nerve

24 Pulmonary plexus

25 Posterior vagal trunk

26 Esophageal plexus

27 Anterior vagal trunk

28 Anterior scalene muscle

29 Cricothyroid muscle

1

2

3

3

4

4

5

6

7

8

9

9

10

11

13 12 14

15

16

17

18

18

19 20

20

21

22

23 23

24

25 26

27

28

29

1

2

3

3

4

4

5

6

7

8

9

9

10

11