• See Chapters 6, General and Oral Pathology: nervous system pathology; 9, Pharmacology: drugs and nervous system; 14, Pain Management: nerve anatomy and physiology.

A. CNS: composed of the brain and spinal cord (Figures 3-6 and 3-7):

1. Within the brain, covered by meninges: outermost layer (dura mater), middle layer (arachnoid), and innermost layer (pia mater); subarachnoid space between arachnoid and pia mater contains blood vessels and cerebrospinal fluid.

2. Components of the brain:

a. Cerebrum: largest portion, divided into two hemispheres by longitudinal fissure; connected by band of white fibers, corpus callosum, responsible for higher level thought processes (i.e., what we need to channel during the case study portions of NDHBE):

(1) Outer surface is cerebral cortex, composed of gray matter and marked by gyri (raised folds) and sulci (grooves, furrows).

(2) Each hemisphere has frontal, parietal, occipital, temporal lobe, insula; primary somatosensory area is in parietal, primary somatomotor area is in frontal, visual cortex is in occipital, auditory and olfactory areas are in temporal, taste is in parietal.

b. Diencephalon: surrounded by cerebrum; includes thalamus, hypothalamus, pituitary gland:

(1) Thalamus: serves as relay station for sensory impulses that travel to cerebral cortex; hypothalamus plays MAIN role in maintaining homeostasis (body’s thermostat).

(2) Brainstem: between diencephalon and spinal cord; consists of midbrain, pons, medulla oblongata; midbrain: contains voluntary motor tracts and visual and auditory reflex centers; pons: contains the pneumo-taxic and apneustic areas that help regulate breathing movements; medulla oblongata: contains ascending and descending tracts and vital cardiac, vasomotor, and respiratory centers.

c. Cerebellum: second largest portion; motor area that coordinates skeletal muscle activity; maintains muscle tone, posture, balance.

3. Spinal cord: continuation of medulla oblongata and extends from foramen magnum to first lumbar vertebra; acts as conduction pathway and reflex center:

a. Ascending tracts: conduct sensory impulses to brain.

b. Descending tracts: carry motor impulses from brain to effectors.

B. PNS includes all cranial and spinal nerves:

1. Consists of afferent (sensory) division and efferent (motor) division; efferent division includes somatic nervous system (SNS), which enables voluntary control over skeletal muscle contraction, and autonomic nervous system (ANS), which regulates smooth and cardiac muscle contraction and glandular activity.

2. Components: bundles of nerve fibers (axons and dendrites), 12 pairs of cranial nerves that emerge from inferior surface (caudal) of brain (see next section).

3. Spinal nerves contain both sensory and motor fibers; 31 pairs emerge from spinal cord and are grouped according to origin; in all but thoracic region, MAIN portions of nerves form complex networks called plexuses (cervical, brachial, lumbar, sacral); nerves emerge from plexuses to supply specific regions.

4. Autonomic nervous system (ANS) is a visceral efferent system part of PNS; innervates smooth muscle, cardiac muscle, and glands; has two divisions, with MOST organs being innervated by BOTH to maintain homeostasis:

a. Sympathetic division (thoracolumbar division) (SANS) is energy-expending system that is MOST active when body is in emergencies or stressful conditions; MOST postganglionic neurons release norepinephrine.

b. Parasympathetic division (craniosacral division) (PANS) is energy-conserving system that is MOST active when the body is in normal relaxed condition; MOST postganglionic neurons release acetylcholine.

Figure 3-6 Brain.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Figure 3-7 Brain and spinal cord.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Cranial Nerves

Cranial nerves are part of the PNS; designated by both number and Roman numerals I through XII, as well as specific name (Figure 3-8). Include 12 pairs that are connected to the brain at its base and pass through the skull by way of fissures and foramina; may be either afferent or efferent or have both types.

• See Chapters 4, Head, Neck, and Dental Anatomy: fifth (trigeminal) and seventh (facial); 6, General and Oral Pathology, and 16, Special Needs Patient Care: neurological disorders.

A. First (I) (olfactory): afferent for smell from the nasal mucosa to the brain, enters skull through perforations in cribriform plate of ethmoid to join olfactory bulb in brain.

B. Second (II) (optic): afferent for vision from retina to brain, enters skull through optic canal of sphenoid, where right and left optic nerves join at the optic chasm and where many fibers cross to the opposite side before continuing into the brain as optic tracts. Glaucoma results from damage to this nerve.

C. Third (III) (oculomotor): efferent to eye muscles, carries preganglionic parasympathetic fibers to ciliary ganglion near the eyeball and postganglionic fibers innervate muscles inside the eyeball; located in lateral wall of cavernous sinus and then exits skull through superior orbital fissure on its way to the orbit; strabismus (lack of eye coordination, “cross-eyed”) can occur with damage.

D. Fourth (IV) (trochlear): efferent to one eye muscle (superior oblique) for proprioception; runs in lateral wall of cavernous sinus and exits skull through the superior orbital fissure on its way to the orbit.

E. Fifth (V) (trigeminal): efferent for muscles of mastication and for other cranial muscles; afferent for ALL of oral cavity, including teeth and portions of tongue, and for MOST of facial skin; trigeminal neuralgia is a neural lesion involving afferent nerves to the face.

1. Trigeminal ganglion (semilunar, gasserian) is on anterior surface of petrous portion of temporal bone; largest cranial nerve; has two roots: sensory and motor:

a. Sensory root has three divisions: ophthalmic, maxillary, mandibular; each enters skull in different location in sphenoid:

(1) Ophthalmic division: provides sensation for upper face and scalp; enters through superior orbital fissure (SOF).

(2) Maxillary division: provides sensation for middle face; enters by way of foramen rotundum.

(3) Mandibular division: provides sensation for lower face and sensory for anterior one third of tongue; enters by way of foramen ovale.

b. Motor root accompanies mandibular division of the sensory root and also exits skull through foramen ovale.

F. Sixth (VI) (abducens): efferent to one of the eyeball muscles (lateral rectus); exits skull through superior orbital fissure on its way to the orbit; runs through cavernous sinus; often is FIRST nerve affected by sinus infection.

G. Seventh (VII) (facial): efferent for muscles of facial expression, for preganglionic parasympathetic innervation of lacrimal, and for submandibular and sublingual; afferent for skin behind the ear, for taste sensation, and for the body of the tongue:

1. Leaves cranial cavity by passing through internal acoustic meatus; leads to facial canal inside temporal bone; exits the skull by way of stylomastoid foramen.

2. Nerve lesions include permanent or transient facial paralysis, loss of movement of muscles of facial expression caused by injury to nerve or Bell’s palsy (BOTH motor and sensory deficit).

H. Eighth (VIII) (vestibulocochlear): afferent for hearing and balance; enters cranial cavity through internal acoustic meatus.

I. Ninth (IX) (glossopharyngeal): efferent for pharyngeal muscle (stylopharyngeal) and preganglionic parasympathetic innervation for parotid; afferent for pharynx (swallowing), taste, and general sensation from base of tongue (posterior one third of tongue).

1. Passes through skull by way of jugular foramen and tympanic branch; has sensory fibers for middle ear and preganglionic parasympathetic fibers for parotid; arises within the gland and reenters the skull.

2. After supplying ear, parasympathetic fibers leave skull through foramen ovale as lesser petrosal nerve; these preganglionic fibers then end in otic ganglion, located near mandibular division of trigeminal.

J. Tenth (X) (vagus): longest nerve in body; efferent for muscles of soft palate, pharynx, and larynx and for parasympathetic fibers to many major body organs, including thymus, heart, stomach; afferent for skin around ear and for taste sensation of the epiglottis; passes through skull by way of the jugular foramen; originates in brainstem and terminates in transverse colon.

K. Eleventh (XI) (accessory): efferent for trapezius and sternocleidomastoid, as well as muscles of soft palate and pharynx; ONLY partly a cranial nerve; consists of two roots: one arising from brain and one from spinal cord; exits skull through jugular foramen.

L. Twelfth (XII) (hypoglossal): efferent for intrinsic and extrinsic muscles of tongue; exits skull through hypoglossal canal; tongue is ONLY organ in the body with own cranial nerve; damage, such as by cerebrovascular accident (CVA, stroke), can result in deviation of tongue to one side.

Figure 3-8 Cranial nerves.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Sense Organs

Sense organs include the widely distributed general senses and localized special senses of taste, smell, vision, hearing, equilibrium.

• See Chapter 4, Head, Neck, and Dental Anatomy: lacrimal gland.

A. General senses: widely distributed in the body; include touch, pressure, proprioception, thermoreception, pain:

1. Touch and pressure: free nerve endings, Meissner’s corpuscles, pacinian corpuscles.

2. Proprioception (sense of position or orientation): Golgi tendon organs and muscle spindles.

3. Thermoreception (temperature changes): thermoreceptors are free nerve endings; some are sensitive to heat, others to cold; extremes in temperature stimulate pain receptors.

4. Pain (nociceptors): free nerve endings that are stimulated by tissue damage.

B. Gustatory (taste) and olfactory (smell) are localized special senses, closely related, complementary:

1. Taste buds are located on the lingual papillae on the dorsal surface of tongue; salty, sweet, sour, bitter are four taste sensations (possibly savory is another) (see Chapter 4, Head, Neck, and Dental Anatomy).

2. Seventh cranial nerve (facial): transmits taste impulses from anterior two thirds of tongue’s body, and ninth cranial nerve (glossopharyngeal) transmits impulses from posterior one third of tongue’s root; impulses are interpreted in parietal lobe of brain.

3. Receptors for smell: located in olfactory epithelium of nasal cavity; first cranial nerve (olfactory) transmits impulses from olfactory epithelium; impulses are perceived as odors in temporal lobe of brain.

C. Visual sense is a localized special sense:

1. Protective features of eye: eyebrows, eyelids, and eyelashes (cilia) protect from foreign particles and irritants; lacrimal glands produce antibacterial tears that moisten, cleanse, protect.

2. Structure of eyeball: sclera (white) and cornea (clear): outermost fibrous layer; iris: middle vascular layer that regulates pupil size; retina: innermost neural layer and contains visual receptors (Figure 3-9).

3. Refraction (bending of light rays): necessary to focus light rays on retina; in normal relaxed eye, refractive media are sufficient to focus light rays from 20 or more feet on retina; closer objects require accommodation to focus, which involves change in shape of lens, convergence of eyes, constriction of pupil.

4. Photoreceptors are rods for vision in dim light and cones for color and acuity in bright light; cones are concentrated in fovea centralis and rods are located peripherally in retina; visual pathway begins with impulses that are triggered by chemical reactions in rods and cones that are transmitted to second cranial nerve (optic).

5. There is 25% crossover of visual fields between right (o.d.) and left eye (o.s.).

D. Auditory sense is a localized special sense (Figure 3-10):

1. Regions of ear include outer ear (auricle and external auditory meatus), ending at tympanic membrane; middle ear, containing auditory ossicles (malleus, incus, stapes); inner ear, containing vestibule, semicircular canals, cochlea.

2. Receptors for hearing: located in organ of Corti in cochlea.

3. Sound waves cause tympanic membrane vibrations, which are transmitted to inner ear by ossicles; organ of Corti moves and hairs bend, triggering impulses transmitted by eighth cranial nerve (vestibulocochlear) to brain, where impulses are interpreted as sound.

E. Sense of equilibrium is a localized special sense:

1. Receptors are located in vestibule and semicircular canals of inner ear.

2. As fluids in inner ear move relative to gravity, hairs bend, triggering impulses transmitted to eighth cranial nerve (vestibulocochlear); brain interprets impulses in terms of acceleration and position.

Figure 3-9 Anatomy of the eye.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Figure 3-10 External ear.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

CLINICAL STUDY

Age	68 YRS	SCENARIO
Sex	Male Female	The dental hygienist calls to remind the patient that she is due for her 3-month recall appointment. The patient says that she has just been diagnosed with an eye disease that has permanently narrowed her fi eld of vision. She does not like the drops prescribed and wonders why she should take them.
Height	5′5″
Weight	145 LBS
BP	118/74
Chief Complaint	“How am I going to get to the appointment?”
Medical History	Osteoarthritis in both hands and neck Removal of gallstones Basal cell carcinoma of the lip Past history of smoking

Current Medications Ibuprofen p.r.n. Social History Retired grade school teacher

1. What has happened to the patient’s eyesight? What is the reason for it?

2. How does this affect her eyesight? To what drug is she referring, and should she take it?

3. What type of test did she have? How often should persons at risk have the test?

4. What factors would reduce the effectiveness of oral care in the dental office for this patient?

1. The patient probably has glaucoma, a group of eye diseases of second (II) cranial nerve (optic), which involves loss of retinal ganglion cells in characteristic pattern of optic neuropathy. Raised intraocular pressure (ocular hypertension) is significant risk factor, as well as female gender, age, family history, race (African-American or Asian), diabetes mellitus (DM). Unstable ocular blood flow could be involved in pathogenesis; may be related to hypertension (high blood pressure). This information should be added to patient’s health history.

2. Involves loss of visual field that often occurs gradually and may not be recognized until advanced. Once lost, the visual field can never be recovered. Glaucoma is second leading cause of blindness in United States. If increased intraocular pressure (above 20 mm Hg) is present, can be lowered with drugs, usually eye drops, or surgery if severe. Major reason for vision loss is poor compliance with drugs and follow-up visits. One type of drop medication is pilocarpine, a nonselective muscarinic receptor agonist in the parasympathetic nervous system, which relieves the symptoms by decreasing intraocular pressure (also available in weekly time-released inserts). This drug is also given in intraoral form (Salagen) for non-drug-induced xerostomia. Any new medications should be added to patient’s drug history.

3. The patient had a dilated eye examination to check nerve. Includes measurements of intraocular pressure via tonometry, changes in size or shape of eye, and retinal examination of nerve to look for visible damage; if damage is suspected, formal visual field test is performed. Those at risk are advised to have the test at least once a year.

4. For visually impaired, not being able to see objects in path or to view instructions or procedures being done.

Endocrine system consists of endocrine glands (release product into bloodstream) and hormones produced (Figure 3-11). Acts with nervous system to regulate body activities to maintain homeostasis. Nervous system acts through electrical impulses and uses a neurotransmitter, and effects are MORE localized and of LESS duration; endocrine system acts through a chemical messenger called a hormone, and effects are MORE generalized and of MORE duration.

Figure 3-11 Endocrine glands.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Endocrine glands are ductless; secretions flow directly into blood, which carries the hormones to appropriate region (exocrine glands release product to the body surface). Exert effects on specific target organs by attaching to receptor sites, causing some type of reaction in organ.

A. Chemical classes of hormones:

1. Proteins and polypeptides: long chains of amino acids; class includes MOST of hormones NOT listed below.

2. Amines: derivatives of amino acids; class includes epinephrine, norepinephrine, thyroxine.

3. Steroids: derivatives of cholesterol, lipid; class includes sex hormones and adrenal cortex hormones.

B. Mechanism of hormone action: react with specific receptor sites on or in cells; cells with appropriate receptors make up the target tissues.

1. Protein hormones react with receptors on the cell membrane; amines and steroids react with receptors in the cytoplasm or nucleus.

2. MOST action is regulated by negative feedback, with some positive feedback; stimulus may be other hormones, substances in the blood, or direct neural stimulation.

C. Endocrine glands and related hormones:

1. Anterior pituitary (adenohypophysis): growth hormone (GH), adrenocorticotropic hormone (ACTH), thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin.

2. Intermediate pituitary (pars intermedius): melanocyte-stimulating hormone (MSH).

3. Posterior pituitary (neurohypophysis): antidiuretic hormone (ADH) and oxytocin.

4. Thyroid gland: thyroxine, triiodothyronine (iodinated amino acids), calcitonin; parathyroid gland: parathyroid (PTH) (see Chapter 4, Head, Neck, and Dental Anatomy).

5. Adrenal (suprarenal) cortex: mineralocorticoids (aldosterone), glucocorticoids (cortisol), sex steroids; adrenal (suprarenal) medulla: epinephrine and norepinephrine.

6. Pancreas (islets of Langerhans): insulin and glucagon.

7. Testes: androgens (testosterone); ovaries: estrogen and progesterone.

Cardiovascular System

Cardiovascular system (CVS) includes blood, heart, and blood vessels.

• See Chapters 8, Microbiology and Immunology: immunology of the blood; 9, Pharmacology: drugs that affect CVS.

A. Blood (liquid connective tissue):

1. Composition: MOSTLY plasma at ~55% of blood volume; formed elements compose ~45% of volume.

2. Plasma: MAINLY water; also contains plasma proteins, nutrients, gases, electrolytes, nitrogenous waste compounds.

3. Formed elements in blood:

a. Erythrocytes (red blood cells [RBCs]): biconcave disks without nuclei that contain hemoglobin, transport oxygen (O₂) and carbon dioxide (CO₂).

b. Leukocytes (white blood cells [WBCs] ): have nuclei and do NOT have hemoglobin; five types include neutrophils (polymorphonuclear leukocytes [PMNs], MOST numerous), monocytes, lymphocytes, eosinophils, basophils; provide defense against disease, mediate inflammatory reactions. See Table 3-1 for more information.

(1) Lymphocytes: second MOST common leukocytes; three types: B cells, T cells, NK (natural killer) cells.

(a) B cells: mature in bone marrow and gut-associated lymphoid tissue such as lymph nodes.

(b) T cells: mature in thymus.

(c) NK cells: mature in bone marrow, large cells involved in first line of defense against tumor cells or virally infected cells by killing them; thus are NOT considered part of immune response.

(2) Cytokines: chemical mediators of immune response; produced by B and T cells.

(3) B cells divide during immune response to form plasma cells:

(a) Plasma cell: round cell with a single round nucleus (cartwheel appearance).

(b) Once mature, plasma cells produce antibody (immunoglobulin [Ig]).

(d) Two types of IgA: serum and secretory.

(e) Thrombocytes (platelets), small fragments of cells, aid in blood clotting.

4. Blood types (ABO and Rh):

a. ABO blood types are based on agglutinogens (antigens) and agglutinins (antibodies).

b. In transfusion reactions, recipient’s agglutinins react with donor’s agglutinogens; type AB is universal recipient; type O is universal donor.

c. Example: people with Rh+ blood have Rh agglutinogens; those with Rh− blood do NOT; neither type has anti-Rh agglutinins; exposure to Rh+ blood causes an Rh− individual to develop anti-Rh agglutinins, and subsequent exposures may result in transfusion reaction.

B. Heart: muscle that pumps the blood, with two thirds on the left of the sternum; enclosed in fibrous pericardial sac lined with serous membrane (Figure 3-12):

1. Heart wall: outermost layer of epicardium; thickest middle layer of myocardium composed of cardiac muscle; innermost layer of endocardium.

2. Four chambers: atria are thin-walled receiving chambers (superior); ventricles are thick-walled pumping chambers (inferior).

3. Right atrium: receives O₂-poor blood from systemic circulation through inferior and superior venae cavae; left atrium receives O₂-rich blood from lungs through pulmonary veins; the ONLY veins that carry oxygenated blood.

4. Right ventricle: pumps blood to lungs through pulmonary trunk; left ventricle pumps blood to systemic circulation through aorta.

5. Four heart valves: maintain unidirectional flow of blood by opening and closing depending on the difference in pressure on each side.

a. Atrioventricular valves: between atria and ventricles; tricuspid valve is on right and bicuspid (mitral) valve is on left.

b. Semilunar valves: at exits from heart; pulmonary semilunar valve regulates flow from right ventricle into pulmonary trunk; aortic semilunar valve is between left ventricle and ascending aorta.

6. Purkinje fibers: in inner ventricular walls; conduct electrical impulse that enables heart to contract in coordinated fashion; work with sinoatrial node (SA node, has inherent rhythmicity) and atrioventricular node (AV node, bundle of His) to control heart rate.

C. Blood vessels:

1. Arteries: carry blood away from heart; thicker muscular walls than veins:

a. Radial artery, located on thumb side of wrist, palpated by two fingers of clinician to obtain radial pulse so as to measure heart rate in conscious adults; in unconscious adults, common carotid artery in neck palpated on ONLY one side by emergency personnel.

b. Arterioles: small arteries that branch off larger artery; connect with capillary beds.

c. Capillary beds: form connection between arteries and veins; site for exchange of materials between blood and cells.

2. Veins: carry blood toward heart; walls are thinner and have valves to prevent backflow of blood (EXCEPT for emissary veins of face):

a. Veins are BEST point of access to bloodstream, permitting withdrawal of blood specimens (venipuncture) for testing purposes and intravenous (IV) delivery of fluid, electrolytes, nutrition, drugs by needle or catheter.

b. Venules: smaller veins; drain the capillaries of a tissue area and then join larger veins.

c. Venous sinuses: blood-filled spaces between two layers of tissue.

3. Anastomosis: communication (joining) of one blood vessel with another by connecting channel.

4. Plexus: network of blood vessels (usually veins).

5. Pressure of circulating blood decreases as blood moves through arteries, arterioles, capillaries, venules, veins; blood pressure refers to arterial pressure in larger arteries.

D. Circulatory pathways (Figure 3-13):

1. Pulmonary circulation: transports O₂-poor blood from right ventricle through pulmonary arteries to lungs, where blood picks up new O₂ supply; then pulmonary veins return O₂-rich blood to left atrium.

2. Systemic circulation: carries O₂-rich blood from left ventricle through systemic arteries to capillaries in the tissues of the body for O₂ and CO₂ exchange; systemic veins transport O₂-poor blood containing CO₂ from capillaries to superior and inferior venae cavae and then into right atrium.

3. Hepatic portal circulation: carries venous blood from digestive system to liver, filters through sinusoids, and then enters hepatic veins to inferior vena cava (IVC).

Table 3-1 Blood cells and related tissue cells

Table 3-2 Known immunoglobulins (antibodies)

Immunoglobulin	Description
IgA	Has two subgroups: serous in blood and secretory in saliva and other secretions; aids in defense against proliferation of microorganisms in body fluids
IgE	Involved in hypersensitivity reactions, since can bind to mast cells and basophils and bring about release of bioactive substances such as histamine
IgD	Functions in activation of B-cell lymphocytes.
IgG	Major antibody in blood serum; can pass placental barrier and forms first passive immunity for newborn
IgM	Involved in early immune responses owing to involvement with IgD in activation of B-cell lymphocytes

Figure 3-12 Internal view of the heart.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Figure 3-13 Circulatory pathways.

(From Applegate EJ: The anatomy and physiology learning system, ed 3, Philadelphia, 2006, Saunders/Elsevier.)

Lymphatic System

Lymphatic system is composed of lymph, lymphatic organs, lymphatic vessels. Functions to return excess interstitial fluid to the blood, absorb fats and fat-soluble vitamins from digestive system, provide defense against invading microorganisms and disease. Lymph is interstitial fluid that has entered lymph vessels.

• See Chapters 4, Head, Neck, and Dental Anatomy: nodes, tonsils; 6, General and Oral Pathology: lymphadenopathy.

A. Lymphatic organs include lymph nodes, tonsils, spleen, thymus (Figure 3-14):

1. Lymph nodes: dense mass of lymphocytes separated by spaces called sinuses; filters and cleanses lymph before enters blood; periphery of node contains B cells, and germinal center contains T cells:

a. Nodes cluster in three areas: inguinal nodes cluster in groin, axillary nodes in armpit, and cervical nodes in neck; NO nodes exist in CNS; must be enlarged (lymphadenopathy) to be palpated.

b. Tonsil: aggregate of lymphatic tissue that provides protection against pathogens that enter through nose, mouth, and throat; pharyngeal (adenoids) are located in nasopharynx; palatine are located in oropharynx; lingual are located at posterior portion of tongue.

2. Spleen: large masses of lymphocytes and macrophages supported by reticular fibrous framework; SIMILAR to lymph node but is larger and filters blood instead of lymph, also acts as reservoir for blood; contains red and white pulp.

3. Thymus: processes and matures T-cell lymphocytes, involved in defense against pathogens; also produces hormone thymosin; involutes (shrinks) with aging.

B. Lymphatic vessels carry fluid from interstitial spaces and return it to subclavian veins, where it becomes part of blood plasma:

1. Vessels have thin walls and valves; small lymphatic vessels merge to form larger ones until there are two MAIN ducts that empty into subclavian veins.

2. Afferent lymph flows into node; efferent lymph flows out (area of hilum).

3. Lymphatic ducts: larger lymphatic vessels; drain smaller vessels, then empty into venous system; right lymphatic duct drains upper right quadrant of body, and thoracic duct drains remainder of body.

Figure 3-14 Lymph organs.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

CLINICAL STUDY

Age	23 YRS	SCENARIO
Sex	Male Female	During an extraoral examination, a hard fi xed mass, approximately 6 mm wide by 36 mm long by 6 mm deep, is noted on the right side of the neck; enlargement is clearly visible but no discomfort is noted when it is palpated. Other enlarged areas have been detected by the patient in his armpit and groin areas on same side. He states that he feels fi ne, although he tires easily. Intraoral exam shows poor oral hygiene and moderate gingivitis but no evidence of caries, only decalcifi cation.
Height	6′2″
Weight	185 LBS
BP	112/69
Chief Complaint	“There is a swelling on my neck that has been there for 6 months and is getting larger.”
Medical History	Broken kneecap at age 8
Current Medications	None
Social History	Real estate lawyer Drinks diet colas to keep awake

1. What could the enlargement along the right side of the patient’s neck possibly be?

2. What would cause such a severe enlargement on his neck?

3. Identify the treatment planning procedures that should be completed.

1. Enlargement along right side of neck is most likely either a tumor or an enlarged cervical lymph node (lymphadenopathy) along sternocleidomastoid (SCM) muscle of right side.

2. If involving the lymph nodes, such severe enlargement is indicative of severe infection (local or systemic) or malignancy (cancer). Severe infection should be painful; lack of pain is prognostically threatening and points to its being an early malignancy.

3. Treatment planning procedures should include thorough intraoral examination for possible causes of swelling (e.g., pulpal infection, periodontal infection) and panoramic radiograph (shows entire jaw areas). If no evidence suggests dental causative factors, oral prophylaxis should be rescheduled until patient has seen his physician. Imperative that he seek immediate medical consult. (Later, Hodgkin’s lymphoma, a cancer of lymph nodes, was diagnosed in this patient.)

Respiratory System

Respiratory system includes the upper and lower respiratory tracts and the lungs (Figure 3-15). It functions to move gases to and from exchange surfaces, where diffusion can occur. Defends body against pathogens, permits speech, helps regulate acid-base balance in body.

A. Upper respiratory tract:

1. Nose (nasal cavity): warms, moistens, and filters air; opens to outside through external nares and in to pharynx through internal nares; separated from oral cavity by palate.

2. Pharynx (throat): passageway for air; divided into nasopharynx, oropharynx, laryngopharynx; opening from oral cavity into oropharynx is the fauces.

3. Larynx (voice box): formed by nine cartilages that are connected by muscles and ligaments:

a. Three largest cartilages are thyroid, cricoid, epiglottis.

b. Vocal folds (cords): present in central region; air passing through vibrates vocal folds to produce sound. Hoarseness indicates inflammation or possibly cancer if chronic.

Figure 3-15 Respiratory tract.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Digestive System

Digestive system includes gastrointestinal (alimentary) tract (GIT; includes oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus) and accessory organs (liver, gallbladder, pancreas) (Figure 3-16). Embryologically and physiologically, the mouth is the beginning of GIT. Functions include ingestion, mechanical digestion, chemical digestion, secretion, mixing and propelling movements, absorption, elimination of waste products, immunological functions (e.g., secretory IgA).

• See Chapter 4, Head, Neck, and Dental Anatomy: oral cavity structure.

A. Pharynx (throat): muscles in wall contract during deglutition (swallowing) to propel food along passageway into esophagus, then into stomach.

B. Esophagus: carries liquids and solids from pharynx to stomach:

1. Located posterior to trachea and anterior to vertebral column; passes through diaphragm, enters cardiac region of stomach.

2. Lower esophageal (cardiac) sphincter: controls passage of food from esophagus into stomach.

C. Stomach: involved in temporary storage of ingested food, maceration and mixing of ingested materials, secretion of enzymes that begin breaking chemical bonds (digestion), production of intrinsic factor, absorption of fluoride (IMPORTANT with toxicity):

1. Located in upper left quadrant of abdomen, anterior to spleen; divided into fundus, cardiac region, body, pyloric region.

2. Mucosal lining has folds (wrinkles) called rugae, which increase surface area for absorption, and glandular cells; parietal cells secrete hormone gastrin that stimulates gastric acid production (hydrochloric acid) and intrinsic factor (necessary for the absorption of vitamin B₁₂); also causes chief cells to secrete pepsinogen, which then is converted to pepsin by acids.

3. Chyme: semifluid mixture of ingested food, liquids, and gastric juice that passes through pyloric sphincter into small intestine; pH of contents as low as 2.

D. Small intestine: extends from pyloric sphincter to ileocecal valve; materials require ~5 hours to pass through and into the large intestine; divided into duodenum (MOST enzymes), jejunum, ileum:

1. Glandular cells in mucosa produce peptidase, which acts on proteins; maltase, sucrose, and lactase, which act on disaccharides; lipase, which acts on neutral fats.

2. Produces two hormones, secretin and cholecystokinin; secretin stimulates pancreas to produce fluid rich in bicarbonates; cholecystokinin stimulates gallbladder to secrete bile and stimulates pancreas to secrete digestive enzymes.

E. Large intestine: divided into cecum, colon, rectum, anal canal; MAIN functions are to absorb water, electrolytes, and vitamins; compact feces; and store fecal material before defecation:

1. Cecum: short region inferior to ileocecal valve; vermiform appendix is attached to cecum.

2. Rectum and anal canal: terminal portions of digestive system.

F. Accessory organs:

1. Pancreas: extends from duodenum to spleen:

a. Composed MAINLY of exocrine cells, which produce enzymes amylase, trypsin, peptidase, lipase; pancreatic enzymes are carried to duodenum by pancreatic duct (of Wirsung).

b. Endocrine cells (islets of Langerhans) produce insulin and glucagon.

2. Liver: largest visceral organ; located in upper right quadrant of abdomen:

a. Lobule consists of hepatocytes arranged like spokes of a wheel around central vein and separated by sinusoids.

b. Blood is brought to liver by portal vein and hepatic artery, flows through sinusoids into central vein and then into hepatic veins.

c. Functions include production of bile (yellow color from bilirubin, breakdown of hemoglobin), production of plasma proteins, detoxification of harmful substances, filtering of blood, nutrient metabolism, immunological response via Kupffer cells.

3. Gallbladder: attached to visceral surface of liver by cystic duct; joins hepatic duct to form common bile duct; empties into duodenum; functions to store, concentrate, secrete bile produced by liver. Contracts in response to cholecystokinin, hormone secreted by duodenum.

Figure 3-16 Organs of the digestive system.

(From Fehrenbach MJ, ed: Dental anatomy coloring book, St. Louis, 2008, Saunders/Elsevier.)

Urinary System

Urinary system consists of kidneys, ureters, urinary bladder, urethra (Figure 3-17). Functions to rid wastes, regulate fluid volume, maintain electrolyte concentrations, control blood pH, secrete renin and erythropoietin responsible for long-term maintenance of blood pressure.