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Sensory Organs

Structural Anatomy

IrwanMRA

Content:Content: The Eye The Ear The Mouth Nose and Nasal Cavity The Skin

The Eye The eye is the organ of the sense of sight situated in the

orbital cavity and it is supplied by the optic nerve (2nd cranial nerve).

It is almost spherical in shape and is about 2.5 cm in diameter. The space between the eye and the orbital cavity is occupied by adipose tissue. The bony walls of the orbit and the fat help to protect the eye from injury.

Structurally the two eyes are separate but, unlike the ear, some of their activities are coordinated so that they function as a pair. It is possible to see with only one eye but three-dimensional vision is impaired when only one eye is used, especially in relation to the judgement of distance.

Structure

There are three layers of tissue in the walls of the eye. They are:

the outer fibrous layer: sciera and cornea

the middle vascular layer or uveal tract: choroid, ciliary body and iris

the inner nervous tissue layer: retina.

Structures inside the eyeball are the lens, aqueous fluid (humour) and vitreous body (humour).

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Fig. 8.8

Fig. 8-9

Fig. 8-10

Intrinsic Eye Muscles and their response to light

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Extraocular muscles of the eye

The eyeballs are moved by six extrinsic muscles,

attached at one end to the eyeball and at the other to

the walls of the orbital cavity. There are four straight

(rectus) muscles and two oblique muscles.

They are:

medial rectus

lateral rectus

superior rectus

inferior rectus

superior oblique

inferior oblique.

Fig. 8-20

Movement of the eyes to look in a particular direction is under voluntary control, but coordination

of movement, needed for convergence and

accommodation to near or distant vision, is under

autonomic (involuntary) control. Movements of the

eyes made by the action of these muscles are shown

in Table 8.1.

Nerve supply to the muscles of the eye Nerves shown in Table 8.1 supply the extrinsic muscles.

Tabel 8-1

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Accessory organs of the eye

The eye is a delicate organ which is protected by several structures :

eyebrows eyelids and eyelashes Lacrimal apparatus. For each eye this consists of:

lacrimal gland and its ducts 2 lacrirnal canaliculi I lacrimal sac I nasolacrimal duct.

Fig. 8-21 Fig. 8-22

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The Visual Pathway

VIDEO? CATARAC

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The Ear The ear can be divided into the external ear, the

middle ear, or tympanic cavity, and the internal ear, or labyrinth, the last containing the organs of hearing and of balance.

The ear is the organ of hearing. It is supplied by the 8th cranial nerve, i.e. the cochlear part of the vestibulocochlear nerve which is stimulated by vibrations caused by sound waves.

With the exception of the auricle (pinna), the structures that form the ear are encased within the petrous portion of the temporal bone.

Structure

The ear is divided into three distinct parts :

outer ear

middle ear (tympanic cavity)

inner ear.

Fig. 8-1

Outer ear

The outer ear consists of the auricle (pinna) and the external acoustic meatus.

The auricle (pinna)

External acoustic meatus (auditory canal)

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Pinna

Fig. 11-52 B

Cerumen

The purpose of wax: Repel water

Trap dust, sand particles, micro-organisms, and other debris

Moisturize epithelium in ear canal

Odor discourages insects

Antibiotic, antiviral, antifungal properties

Cleanse ear canal

Middle ear (tympanic cavity)

This is an irregular-shaped air-filled cavity within the petrous portion of the temporal bone.

The lateral wall of the middle ear is formed by the tympanic membrane.

The roof and floor are formed by the temporal bone.

The posterior wall is formed by the temporal bone

The medial wall is a thin layer of temporal bone oval window

round window

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Fig. 8-2

Auditory ossicles

These are three very small bones that extend across the middle ear from the tympanic membrane to the oval window

They form a series of movable joints with each other and with the medial wall of the cavity at the oval window.

They are named according to their shapes. The malleus.

The incus.

The stapes.

Middle Ear Structures

1- Malleus

2- Incus --Ossicles

3- Stapes

4- Tympanic Membrane (Eardrum)

5- Round Window

6- Eustachian Tube

Eustachian Tube

The eustachian tube connects the front wall of the middle ear with the nasopharynx

The eustachian tube also operates like a valve, which opens during swallowing and yawning This equalizes the pressure on either side of the

eardrum, which is necessary for optimal hearing. Without this function, a difference between the static

pressure in the middle ear and the outside pressure may develop, causing the eardrum to displace inward or outward

This reduces the efficiency of the middle ear and less acoustic energy will be transmitted to the inner ear.

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Inner ear

The inner (internal) ear or labyrinth (meaning maze) ear contains the organs of hearing and balance. It is generally described in two parts, the bony labyrinth and the membranous labyrinth.

Bony labyrinth

This is a cavity within the temporal bone lined with periosteum. It is larger than, and encloses, the membranous labyrinth of the same shape which fits into it, like a tube within a tube. Between the bony and membranous labyrinth there is a layer of watery fluid called perilymph and within the membranous labyrinth there is a similarly watery fluid, endolymph.

The bony labyrinth consists of: 1 vestibule

1 cochlea

3 semicircular canals.

The vestibule. This is the expanded part nearest the middle ear. It contains the oval and round windows in its lateral wall.

The cochlea. This resembles a snail s shell. It has a broad base where it is continuous with the vestibule and a narrow apex, and it spirals round a central bony column.

The semicircular canals. These are three tubes arranged so that one is situated in each of the three planes of space. They are continuous with the vestibule.

Membranous labyrinth

This contains endolymph and lies within its bony counterpart. It comprises:

the vestibule, which contains the utricle and saccule

the cochlea

three semicircular canals.

The cochlea

A cross-section of the cochlea contains three compartments:

the scala vestibuli

the scala media, or cochlear duct

the scala tympani.

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Fig. 8-6

Fig. 8-4 Fig. 8-5

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The ToungeThe tongue is a voluntary muscular structure which occupies the floor of the mouth. It is attached by its base to the hyoid bone and by a fold of its mucous membrane covering, called the frenulum, to the floor of the mouth.

The superior surface consists of stratified squamous epithelium, with numerous papillae (little projections), containing nerve endings of the sense of taste, sometimes called the taste buds.

There are three varieties of papillae

Fig. 12-12

Fig. 12-11

Vallate papillae, usually between 8 and 12 altogether, are arranged in an inverted V shape towards the base of the tongue. These are the largest of the papillae and are the most easily seen.

Fungiform papillae are situated mainly at the tip and the edges of the tongue and are more numerous than the vallate papillae.

Filiform papillae are the smallest of the three types. They are most numerous on the surface of the anterior two-thirds of the tongue.

Blood supply

The main arterial blood supply to the tongue is by the lingual branch of the external carotid artery. Venous drainage is by the lingual vein which joins the internal jugular vein.

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Saleh M. Al Salamah 45

Nerve supply

The nerves involved are:

the hypoglossal nerves (12th cranial nerves) which supply the voluntary muscle tissue

the lingual branch of the mandibular nerves which are the nerves of somatic (ordinary) sensation, i.e. pain, temperature and touch

the facial and glossopharyngeal nerves (7th and 9th cranial nerves) which are the nerves of the special sensation of taste.

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Why do the elders like to take in food with strong flavour?

Its too salty!

Do you know ?Because .

When you were a baby, you had taste buds, not only on your tongue, but on the sides and roof of your mouth. This means you were very sensitive to different foods.

As you grew, the taste buds began to disappear from the sides and roof of your mouth, leaving taste buds mostly on your tongue.

As you get older, your taste buds will become even less sensitive, so you will be more likely to eat foods that you thought were too strong as a child.

Remember

Spicy is not a taste. It is the sensation of pain in the tongue resulting fromthe destruction of taste buds by thehot food like chilly. It is spicy!

Also Note Taste is influence by olfactory sensation and nasal

congestion affect your taste. Tongue can detect other stimuli rather than taste

like temperature and Texture. In general, girls have more taste buds than boys.Flavor is a complex mixture of sensory input

composed of taste (Gustation), smell (olfaction) and the tactile sensation of food as it is being munched.

The receptors for alkaloids evolved to be the most sensitive in order to allow humans to detect plant poisons before they are eaten.

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Taste Disorders

Ageusia(complete loss of taste)

Dysgeusia(persistent abnormal taste)

What causes taste disorders?

Upper respiratory and middle ear infections Radiation therapy for cancers of the head and

neck Exposure to certain chemicals, such as

insecticides and some medications, including some common antibiotics and antihistamines

Head injury Some surgeries to the ear, nose, and throat

(e.g., third molarwisdom toothextraction and middle ear surgery)

Poor oral hygiene and dental problems

NOSE AND NASAL CAVITYPosition and structure

The nasal cavity is the first of the respiratory organs and consists of a large irregular cavity divided into two equal passages by a septum.

Nasal Cavity

The nasal cavity extends from the nostrils in front to the posterior nasal apertures or choanae behind

This is where the nose opens into the nasopharynx

The nasal vestibule is the area of the nasal cavity lying just inside the nostril

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Nasal Septum

The nasal cavity is divided into right and left halves by the nasal septum

The septum is made up of the septal cartilage, the vertical plate of the ethmoid, and the vomer

Walls of the Nasal Cavity Each half of the nasal cavity has a floor, a roof, a

lateral wall, and a medial or septal wall

The floor is formed by palatine process of the maxilla and the horizontal plate of the palatine bone

The roof is narrow and is formed anteriorly beneath the bridge of the nose by the nasal and frontal bones

In the middle by the cribriform plate of the ethmoid, located beneath the anterior cranial fossa

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Walls of the Nasal Cavity

Posteriorly by the downward sloping body of the sphenoid

The lateral wall has three projections of bone called the superior, middle, and inferior nasal conchae

The space below each concha is called a meatus

Sphenoethmoidal Recess

The sphenoethmoidal recess is a small area above the superior concha

It receives the opening of the sphenoid air sinus

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Superior Meatus

The superior meatus lies below the superior concha

It receives the openings of the posterior ethmoid sinuses

Middle Meatus

The middle meatus lies below the middle concha

It has a rounded swelling called the bulla ethmoidalis that is formed by the middle ethmoidal air sinuses, which open on its upper border

A curved opening, the hiatus semilunaris, lies just below the bulla

The anterior end of the hiatus leads into a funnel-shaped channel called the infundibulum, which is continuous with the frontal sinus

The maxillary sinus opens into the middle meatus through the hiatus semilunaris

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Inferior Meatus

The inferior meatus lies below the inferior concha

It receives the opening of the lower end of the nasolacrimal duct, which is guarded by a fold of mucous membrane

Medial Wall The medial wall is formed by the nasal septum

The upper part is formed by the vertical plate of the ethmoid and the vomer

The anterior part is formed by the septal cartilage

The septum rarely lies in the midline, thus increasing the size of one half of the nasal cavity and decreasing the size of the other

Mucous Membrane

The vestibule is lined with modified skin and has coarse hairs

The area above the superior concha is lined with olfactory mucous membrane and contains nerve endings sensitive to the reception of smell

The lower part of the nasal cavity is lined with respiratory mucous membrane

A large plexus of veins in the submucous connective tissue is present in the respiratory region

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Mucous Membrane

The presence of warm blood in the venous plexuses serves to heat up the inspired air as it enters the respiratory system

The presence of mucus on the surfaces of the conchae traps foreign particles and organisms in the inspired air

These particles are then swallowed and destroyed by gastric acid

Nerve Supply

The olfactory nerves from the olfactory mucous membrane ascend through the cribriform plate of the ethmoid bone to the olfactory bulbs

The nerves of ordinary sensation are branches of the ophthalmic division and the maxillary division of the trigeminal nerve

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Blood Supply

The arterial supply to the nasal cavity is from branches of the maxillary artery, one of the terminal branches of the external carotid artery

The most important branch is the sphenopalatine artery

The sphenopalatine artery anastomoses with the septal branch of the superior labial branch of the facial artery in the region of the vestibule

The submucous venous plexus is drained by veins that accompany the arteries

Lymph Drainage

The lymph vessels draining the vestibule end in the submandibular nodes

The remainder of the nasal cavity is drained by vessels that pass to the upper deep cervical nodes

Paranasal Sinuses The paranasal sinuses are cavities found in the interior of

the maxilla, frontal, sphenoid, and ethmoid bones

They are lined with mucoperiosteum and filled with air

They communicate with the nasal cavity through relatively small apertures

The maxillary and sphenoidal sinuses are present in a rudimentary form at birth

They enlarge appreciably after the eighth year and become fully formed in adolescence

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Drainage of Mucus

The mucus produced by the mucous membrane is moved into the nose by ciliary action of the columnar cells

Drainage of the mucus is also achieved by the siphon action created during the blowing of the nose

Function of Paranasal Sinuses

The function of the sinuses is to act as resonators to the voice

They also reduce the weight of the skull

When the apertures of the sinuses are blocked or they become filled with fluid, the quality of the voice is markedly changed

Maxillary SinusThe maxillary sinus is pyramidal in shape and located

within the body of the maxilla behind the skin of the cheek

The roof is formed by the floor of the orbit, and the floor is related to the roots of the premolars and molar teeth

The maxillary sinus opens into the middle meatus of the nose through the hiatus semilunaris

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Frontal Sinuses

The two frontal sinuses are contained within the frontal bone

They are separated from each other by a bony septum

Each sinus is roughly triangular, extending upward above the medial end of the eyebrow and backward into the medial part of the roof of the orbit

Sphenoidal Sinuses

The two sphenoidal sinuses lie within the body of the sphenoid bone

Each sinus opens into the sphenoethmoidal recess above the superior concha

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Ethmoid Sinuses

The ethmoidal sinuses are anterior, middle, and posterior and they are contained within the ethmoid bone between the nose and the orbit

They are separated from the latter by a thin plate of bone so that infection can readily spread from the sinuses into the orbit

Ethmoid Sinuses

The anterior sinuses open into the infundibulum

The middle sinuses open into the middle meatus, on or above the bulla ethmoidalis

The posterior sinuses open into the superior meatus

Integument System

Integument System Organs

Skin

Hair

Nails

Glands

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Integument System Functions

Protection Abrasion Infection UV light Dehydration

Thermal Regulation Insulation (fat keeps you warm) Cooling (sweating cools you down)

Sensory Reception Vitamin D Production Communication (raised eyebrows)

NOTEVitamin D is made in the dermis of the skin, after exposure to sunlight. Its function is to allow calcium to be absorbed from the foods you eat so your blood calcium levels are normal.

The Skin and the Hypodermis

Skin our largest organ Accounts for 7% of body weight

Divided into three distinct layers Epidermis (epi means above something)

Dermis

Hypodermis (hypo means deep to something)

Remember, the term SKIN refers to all three layers: epidermis, dermis, and hypodermis.

Skin Structure

Figure 5.1

EPIDERMIS

Primarily made up of keratinized stratified squamous epithelium

The EPIDERMIS is the layer that gives strength to the skin.

Varies in thickness from a few cells (eyelids) to dozens of cells thick (palms and soles of feet)

It does not have any vascularization (blood supply), so it relies on absorbing oxygen and nutrients from the blood vessels in the

dermis deep to it.

The nails are made in the epidermis.

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Layers of the Epidermis

Stratum corneum (most superficial layer of epidermis)

Stratum lucidum (only in thick skin)

Stratum granulosum

Stratum spinosum

Stratum basale (the deepest layer of epidermis)

Epidermal Cells and Layers of the Epidermis

Figure 5.3

STRATUM BASALE: has 4 types of cells

The cell type that makes the epidermis is aKERATINOCYTE

Keratin is a protein made by these cells. Keratin is waterproof and strong

MELANOCYTES produce MELANIN (dark brown pigment)

Everyone has the same number of melanocytes But they dont all make the same amount of pigment, so

people have different skin colors.

MERKEL CELLS: used as sensory receptors for the sense of light touch.

MACROPHAGES: ingest debris

STRATUM BASALE: This is the only layer of the epidermis where the cells

are dividing.

As new cells are made in the S. Basale, the older cells get pushed up and become the next layer (S. Spinosum)

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STRATUM SPINOSUM They are now attached to each other by desmosomes,

which are pointy/spiny (spinosum)

The cells are still alive, but they no longer divide in this layer

The stratum spinosum provides the strength to the epidermis

Also contains Langerhans cells, which are white blood cells that function in the immune response.

STRATUM GRANULOSUM As more new cells are made in the S. basale, the

S. spinosum layer is pushed up to become the S. granulosum layer.

The cells in the S. granulosum begin to die because they are now too far from nutrient source (in dermis).

The cells now have a grainy appearance, so this layer is called the stratum granulosum.

STRATUM CORNEUM

As more new cells are made in the S. basale, the cells are all pushed up again, and the S. granulosum layer becomes the S.

Corneum.

In this layer, the dead cells fill up with KERATIN. The cells lose their nucleus and fuse to squamous (flat) sheets,

which are shed from the surface in about 2 weeks. This process is

called desquamation.

The main difference between thick skin and thin skin relates to the thickness of the Stratum corneum.

It takes about 15-30 days for a cell to move from the stratum basale to the stratum corneum and another 2 weeks for it to shed

We lose half a million cells per hour; 1.5 grams a day That can be a major source of dust in the house Dust allergies are actually from the feces and saliva of dust mites

which eat the dead skin. One house has 3 million poops per day

from dust mites!

STRATUM LUCIDUM

This layer is only on the palms and soles

It is just deep to the S. corneum and superficial to the S. granulosum

This THIN layer provides protection from UV radiation.

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Conditions of the Epidermis

If you frequently rub one area of the skin, it stimulates cell division = callous

If you rub the skin too hard, the stratum basale tears away from the basement membrane, and causes a gap, which fills with fluid: BLISTER .

The epidermis then dies because its too far away from nutrients. Thats why the top of a blister dries up.

If the blisters are small (less than 5 mm in diameter), they are known as vesicles; if they are larger (greater than 5 mm in diameter), they are termed bullae.

Vesicles

Bullae Basal Cell carcinoma

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Reconstructive Surgery for Basal Cell Carcinoma

Vitilligo

An autoimmune disease of the skin

Destroys melanocytes, especially in areas of friction (eyelids, mouth, hands)

Causes depigmentation.

DERMIS:

1) PAPILLARY LAYER (Papillary = Pimple. Has bumps). This is the more superficial layer.

2) RETICULAR LAYER

Dermis

Figure 5.1

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Dermis

1) PAPILLARY LAYER (Papillary = Pimple. Has bumps)

The papillary layer of the dermis; LOOSE connective tissue.

Has ridges to increase surface area for contact with the epidermis

The papillary layer in the DERMIS is what forms our fingerprints.

Surgeons make incisions on the body based on the lines of cleavage of the skin formed by the papillary layer of the DERMIS

Nerve endings for heat, pain, cold, pressure and touch (Meissners corpuscles)

Skin lines of cleavage

Lines of cleavage Dermis

2) RETICULAR LAYER DENSE IRREGULAR Connective Tissue Gives the dermis its strength. Remember, the epidermis is the strongest layer of the

SKIN, but the reticular layer of the dermis is the strongest layer of the DERMIS.

This layer has lots of COLLAGEN and ELASTIN (elastic fibers)

The DERMIS is where most of the bodys collagen is found.

Stretch marks are caused from tiny tears in the collagen of the DERMIS.

Leather is made of this layer.

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Contains sebaceous and sweat glands, arrector pili muscle and hair follicle

Incisions made parallel to these lines during surgery wound heals faster

Pacinian corpuscles are distributed through the dermis and function as pressure receptors

Stretch marks and pregnancy due to breaks in collagen and elastic fibres

The dermis is also the area where all the glands of the body are located.

A transdermal patch (nicotine patch, etc) must diffuse all the way from the epidermis into the dermis to reach the blood vessels there.

The blood vessels in the dermis are what gives a pink color to Caucasian people.

Dermis

Pacinian Corpuscle: nerve receptors in the dermis for vibration and pressure

Meissner's Corpuscle: nerve receptors in the dermis for light touch

Dermis Conditions

What happens when you get cut? Bleed, then clot Macrophages eat foreign bodies and dead cells Fibroblasts lay down collagen to repair the wound.

If they produce more than normal, you get a SCAR.

If skin is cut with the grain, scar is not bad. Against the grain, the scar is worse.

Some people are more prone to scar tissue than others.

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Keloid Scars

Keloid Scars

Thick, red, sometimes painful scars

More common in African American, Native American, and Asian races

Treatment with cortisone injections

Keloid scar formers can get internal adhesions also

Keloid Scars

Dermis Conditions

Stretch Marks

Caused by sudden weight gain (pregnancy)

Expansion of skin, collagen fibers in the dermis separate = stretch marks.

HYPODERMIS :

Subcutaneous layer

This is the fat layer. It varies tremendously in thickness: Shins = thin; Buttocks = thick.

Functions

1) Stores fat

2) Cushions

3) Insulation from cold because of heat produced by blood vessels in this layer.

4) stabilizes the position of the skin in relation to underlying tissues

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Dermis

Figure 5.1

Hypodermis Conditions

Hypodermis is not connected to the muscle under it. Therefore, exercising muscle will not burn off fat only in that area. Fat is burned off equally over entire body. Losing 10 lbs is like loosing off whole body. More noticeable in face than in hips.

LIPOSUCTION

This is a surgical procedure where the patient has fat sucked out of the

hypodermis layer.

Liposuction is dangerous because hypodermis is very vascular, can bleed too

much.

BURNS

Three types:

FIRST DEGREE: Minor burn to the epidermis; sunburn

SECOND DEGREE: Dermis separates from epidermis; blister

THIRD DEGREE: Hypodermis is burned. (most severe type of burn)

2 and 3 burns over a large part of the body gives a survival chance proportional to the amount of skin left. 60% burn = 60% chance of dying.

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Estimating Burns Using the Rule of Nines

Figure 5.10a

Third Degree Burn

Why are deep burns so dangerous?

1) Infection

2) Dehydration: nothing to keep fluid in body. Therefore, they need a skin graft.

Skin grafts can be from a cadaver, animal, artificial, or from another part of the same persons body.

Skin grafts cause lots of scarring.

DECUBITUS ULCERS (bed sore)

Epidermis is destroyed, underlying tissue is exposed. How decubitus ulcers form: If youre sitting down, weight of the body presses against

blood vessels, no blood flow to skin of buttocks. In you, its ok, because youll be walking around again in a half hour. But if it goes on longer than a couple of hours because one cant move, tissues cant get oxygen. Ulcer forms, can get gangrene (tissue death).

It can also become systemic (bacteria enter the wound, travel in the blood), which can cause death. Whose fault is it? The nurses, for not moving the patient every couple of hours.

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Decubitus Ulcers

SKIN COLOR

Caused by four things:1) MELANIN : (dark brown pigment). More melanin, darker

the skin.2) CAROTENE : (a yellowish/orange pigment found only in

plants). Accumulates more in the skins of Asians and Native Americans.

3) SKIN THICKNESS : thinner skin see blood vessels, looks pinker

4) HEMOGLOBIN : The DERMIS contains the blood vessels that give Caucasians the pink color to the skin. Even veins are red because blood is red. But when you look at veins through the adipose layer (the hypodermis), they look blue.

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CYANOSIS: Bluish color to skin.

Caused by superficial blood vessel constriction in the dermis or lack of blood flow to skin

Occurs for two reasons:

1) Cold

2) Not enough oxygen in body to go around. The oxygen is conserved for the vital organs, so oxygen to skin and nails is shut down.

Cyanosis

TATTOOS Pigment is injected into the dermis. If the

needle is sterile, theres no health risk. However, the pigment diffuses with time.

What looks good in your 20s will look like a blob when youre 50.

Laser treatment is just burning the ink out of the dermis; may leave a scar. Depending on the color of the tattoo ink, it may only cause it to fade.

Laser Tattoo Removal

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Laser Tattoo Removal Laser Tattoo Removal

Hemangioma Hemangioma: enlargement of the lining

of blood vessels

Laser treatment works well

Strawberry Hemangioma

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Laser treatment of blood vessel

problems

HAIR

HAIR

There are about 2 million hairs on the body; 200,000 on the scalp.

Arrector pillae

Hair papillaHair matrix

Hair root

Longitudinal Section of Base of

Follicle

Figure 5.5c, d

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ARRECTOR PILLI: tiny muscles that make the hairs stand up during goosebumps.

HAIR PAPILLAE: what is destroyed by electrolysis, so hair wont grow back.

The HAIR MATRIX is the leading edge of the papillae. It is actually skin cells (keratinocytes) which are rapidly dividing. When they die, the new ones push them out, forming the hair. Hair is just dead skin cells. The HAIR ROOT is just the base of the hair.

The hair matrix is the part of the follicle that is the site of hair growth and the location of the melanocytes that determine hair color.

Hair that goes grey has lost its melanin pigment. Differences in uncut hair length result from both variations in

hair growth rate and duration of the hair growth cycle.

Head louse

Eyelash Mite Eyelash Mites

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Structures Associated With Hair Follicles

1. SEBACEOUS GLANDS1. Found all over the body

2. Produce sebum (oil that coats the hair and epidermis)When you wash it away, the skin gets dry. The best moisturizer

is lanolin, which is made from sheep sebum.

PIMPLES Some of the largest sebaceous glands are associated with

the smallest hairs (face).

Pimples begin when oil gland ducts (sebaceous glands) become blocked by viscous (thick) sebum and the gland swells.

The sebum in the gland is exposed to oxygen and turns black, called a blackhead.

The black part of a blackhead is oxidized sebum.

In puberty, there is an increase in hormones, and an increase in gland secretion, leading to pimples.

Pimple

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Sebaceous and Sweat Glands

Figure 5.1

2. NAILS

The EPIDERMIS gives rise to the nails.

The nails are made of keratin (no collagen or calcium)

Taking calcium wont make the nails any stronger because there is no calcium in keratinocytes.

At the nail matrix, there is rapid division of keratinocytes (cells that make keratin), and as they die, the skin moves up and creates the nail.

Structure of a Nail

Figure 5.9

The proximal nail fold creates the cuticle. The cuticle is called the eponychium. The white half-moon visible under the proximal part of a fingernail is the lunula.

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Glands Of The Skin

Two types:EccrineandApocrine

Eccrine Glands

Distributed almost all round the body

Secretory portion in hypodermis

Apocrine Glands

Arm pits and dark regions of nipple

Secretes fatty substances

These react to airYOU STINK

Sweat Glands

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Sebaceous and Sweat Glands

Figure 5.1 162

Sebaceous Glands

Located in the dermis

Lubrication and protection

Cluster of cells

Breakdown of inner cells in the cluster sebum formation

Connected to hair follicles

Sebum fight bacteria and fungi

Blackheads due to blocked glands

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Functions Of The Skin

Non-specific immunity (details to follow in later lectures)

[1] Protection

Anatomical barrier against infection

Melanin = screen out excess UV rays

When melanin is darkened by the tan transferred to outer skin layers(suntan) skin less sensitive to sunrays

Dark skin due to wider distribution of melanin beyond stratum basaleinto higher levels of epidermis

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[2] Thermoregulation

Control of heat production

Shivering

Skeletal muscle

Motor neurons

Control of heat loss

Skin vasocontriction and vasodilation

Skin blood vessels

Sympathetic nervous system

Control of heat loss

Sweating

Sweat glands

Sympathetic nervous system

Hypothalamic thermoregulatory integrating centre

Peripheral Thermoreceptors (Skin)

Skin temperature

10-Jan-15

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[3] Sensory Perception

Millions of nerve endings

Receptor for pain, heat and pressure

Therefore, maintain homeostasis

[4] Excretion

Excretion of lactic acid and sodium chloride

Urea (1 g nitrogenous waste eliminated through skin per hour)

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[5] Vitamin D Synthesis

Promotes absorption of calcium and phosphate through intestine

Active vitamin D

Modification by liver and kidney enzymes

Vitamin D3 (Cholecalciferol)

Vitamin D precursor (in skin)