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Even under normal circumstances, slightly more fl uid is fi ltered out of the capillaries into

the interstitial fl uid than is reabsorbed from the interstitial fl uid back into the plasma. On

average, the net fi ltration pressure starts at 11 mm Hg at the beginning of the capillary,

Lymphatics

whereas the net reabsorption pressure only reaches 9 mm Hg by the vessel’s end. Because of this pressure differential more

fl uid is fi ltered out of the fi rst half of the capillary than is reabsorbed in its last half. If this extra fi ltered fl uid were not drained

away, the consequence of this unbalanced exchange would be accumulation of excess interstitial fl uid, or edema. To circumvent this potentially disastrous problem, a system of accessory drainage vessels, the lymphatic vessels, evolved in vertebrate

animals. This lymphatic system of vessels consists of an extensive network of one-way tubes that provide an accessory route

through which fl uid is returned from the interstitial fl uid to the blood to keep the cardiac output and return equal.

Dissection of lymphatic vessels and nodes in the thigh

Anterior view

 1 Superficial inguinal lymph node

 2 Afferent lymphatic vessels

 3 Efferent lymphatic vessels

 4 Great saphenous vein

 5 Femoral vein

 6 Femoral artery

 7 Spermatic cord

 8 Penis

 9 Sartorius muscle

10 Rectus femoris muscle

 11 Femoral nerve

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REAL ANATOMY

Th e respiratory system consists of a

network of passageways that begin at the openings into the nose and mouth

and terminate in about 600 million microscopic air spaces within the substance

of the lungs. Th e passageways are typically divided into upper respiratory passageways and lower respiratory passageways. Th e upper respiratory tract consists

of the nose, the nasal cavity and associatied sinuses, and the pharynx. While

the mouth is typically included in the digestive system, it can also serve as a

passageway for air entering the respiratory system. Th e lower respiratory

tract consists of the larynx, trachea, and the bronchial and alveolar

tubes that form a large, branching network of passageways within the

lungs. Th is branching bronchial tree within each lung begins as a

large, fi nger-sized tube called the main or principal bronchus

and terminates in the lungs as the microscopic air sacs

called alveoli.

Like other systems that form an environmental

 exchange surface with the cardiovascular system,

the respiratory system forms an extensive surface

area in contact with the capillaries. It is estimated

that the surface area of the small dead-end air

sacs in  the lungs is about the size of a tennis

court. Th is extensive interface is essential for

the exchange of oxygen and carbon dioxide

between the inhaled air and the blood. If

body cells are deprived of oxygen, they cannot function and they die as a result. So the

 acquisition of oxygen through the respiratory passageways and its subsequent

exchange with the capillary blood is an

important function of the respiratory

system.

In addition to gas exchange, the

portion of the respiratory passageways

referred to as the larynx is responsible

for generating the sound waves that we

manipulate into voice. Internal folds in

the lining of the larynx, the vocal folds,

vibrate as air passes upward from the

lungs to produce the vibrations. For

this reason the larynx is oft en referred

to as the voice box.

17 Respiratory System

Find

pper Respiratory Tract

Sagittal section of head

Medial view

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Frontal section of head

Anterior view

 1 Nasal cavity

 2 Superior nasal concha

 3 Middle nasal concha

 4 Inferior nasal concha

 5 Torus tuberius

 6 Frontal sinus

 7 Ethmoid air cell

 8 Sphenoidal sinus

 9 Hard palate

10 Oral cavity

 11 Soft palate

12 Nasopharynx

13 Oropharynx

14 Laryngopharynx

15 Epiglottis

16 Tongue

17 Frontal lobe

18 Parietal lobe

19 Occipital lobe

20 Corpus callosum

21 Lateral ventricle

22 Pons

23 Cerebellum

24 Fourth ventricle

25 Medulla oblongata

26 Nasal septum

27 Maxillary sinus

28 Temporalis

29 Masseter

30 Mandible

31 Orbit

32 Intervertebral disc

33 Vertebral body

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The lower respiratory tract Lower Respiratory Tract arises as an outgrowth of

Lower respiratory tract and lungs in situ

Anterior view

the tubular gut during embryonic development. This anterior outgrowth of the gut tube begins at the

larynx (voice box), which is the upper expanded portion of the lower respiratory tract. It continues

from the neck into the thorax as the trachea (windpipe), and forms a large branching network of

tubes that enter the lungs, the bronchial tree. The pages that follow show the tubular organs and

histology of the lower respiratory tract.

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Dissection of lower respiratory tract and lungs in situ

Anterior view

 1 Thyroid cartilage of larynx

 2 Cricoid cartilage of larynx

 3 Trachea

 4 Main (primary) bronchus

 5 Right lung

 6 Left lung

 7 Bronchial tree

 8 Thyroid gland

 9 Common carotid artery

10 Subclavian artery

 11 Vagus nerve

12 Esophagus

13 Aorta

14 Pulmonary artery

15 Pulmonary vein

16 Inferior vena cava

17 Diaphragm

18 Stomach

19 Phrenic nerve

20 Rib

21 Intercostal muscle

22 Anterior scalene muscle

23 Thyrohyoid muscle

24 Cricothyroid muscle

25 Spleen

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Larynx

Laryngeal cartilages

Anterior view

Laryngeal cartilages

Posterior view

Laryngeal cartilages

Superior view

The entrance to the trachea is an expanded region called the larynx, or

voice box. A series of large cartilages form the walls of this region. The

soft tissue lining of the laryngeal cartilages folds into the larynx to form the vocal folds, fl aps of

tissue that lie across the opening of the larynx. Within the edges of the vocal folds are the vocal

cords, two bands of elastic tissue that can be stretched and positioned in different shapes by

laryngeal cartilages and muscles. As air is moved past the taut vocal cords, they vibrate to

produce the many different sounds of speech. During swallowing, the vocal cords assume a

function not related to speech; they are brought into tight apposition to each other to close off

the rima glottidis, the entrance to the lower larynx and trachea.

 1 Epiglottis

 2 Thyroid cartilage

 3 Thyroid tubercle (Adam’s apple)

 4 Superior cornu

 5 Inferior cornu

 6 Cricothyroid membrane

 7 Cricoid cartilage

 8 Arytenoid cartilage

 9 Corniculate cartilage

10 Trachea

 11 Vocal fold

12 Vocal ligament

13 Rima glottidis

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Trachea and Bronchial Tree

Photomicrograph of tracheal wall

100x

Dissection of lower

respiratory tract

Anterior view

The trachea, “windpipe,” is the conduction tube that

transports the air to and from the lungs. It is reinforced by U-shaped cartilages.The trachea branches

into two tubes called bronchi that enter the lungs. Each bronchus serves as the trunk of a highly

branched, tree-like network of bronchial tubes that become progressively narrower, shorter, and more

numerous as they spread throughout the tissues of the lung. These small tubes eventually terminate as

the small, dead-end air sacs called alveoli, the principal site of gas exchange between air and blood.

 1 Epiglottis

 2 Thyroid cartilage

 3 Cricoid cartilage

 4 Trachea

 5 Right main (primary) bronchus

 6 Left main (primary) bronchus

 7 Lobar (secondary) bronchus

 8 Segmental (tertiary) bronchus

 9 Bronchiole

10 Fibromuscular membrane

 11 Tracheal ring

12 Hyaline cartilage of tracheal ring

13 Tunica mucosa (pseudostratified)

14 Tela submucosa (areolar ct)

15 Tunica adventitia (dense ct)

16 Bronchiole cartilage (hyaline)

17 Alveolar spaces

18 Vein with red blood cells (rbc)

19 Pulmonary vein with rbcs

Section of trachea

Anterolateral view

Photomicrograph of alveoli and

small bronchial tube

100x

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