Chapter 5 b Appendages of the Skin Skin

Chapter 5 b Appendages of the Skin

Skin Appendages • Includes several derivatives of the epidermis • Sweat glands • Sebaceous (oil) glands • Nails • Hair follicles • Hair

Sweat Glands

Sweat glands • Widely distributed in skin • Also called sudoriferous glands – Sudor = Sweat • More than 2. 5 million person

Sweat glands • Different types – Prevent overheating of the body – Secrete cerumen (ear wax) – Secretion of milk

Sweat glands • Two main types: – Eccrine – Apocrine

Eccrine Sweat Glands • Eccrine glands • Most numerous, widely distributed – especially abundant on the palms, soles of feet, and the forehead

Eccrine Sweat Glands • Eccrine glands • Simple, coiled tubular gland – Secretory part lies coiled in the dermis – Open to skin surface by ducts (pores)

Sweat Composition • • • Mostly water (99%) Some salts (mostly Na. Cl) Vitamin C Antibodies Dermicidin (a microbe-killing protein) Lactic acid (attracts mosquitoes)

Sweat Composition • Traces of metabolic waste • Small amounts of some ingested drugs • Normally sweat is acidic • p. H between 4 -6

Sweat Function • Sweating is regulated by the sympathetic division of the autonomic nervous system • We have little control • Major role is to prevent overheating of the body • Excretes waste products • Acidic nature inhibits bacteria growth

Sweat Function – Heat induced sweating • helps dissipate excess heat • Prevents overheating of the body • Begins on the forehead – Emotionally induced sweating (Cold Sweats) • Brought on by fright, embarrassment, nervousness • Begins on palms, soles, armpits

Apocrine Sweat Glands • Found in the axillary (arm pit) and anogenital areas • Larger than eccrine glands • Ducts empty into hair follicles

Apocrine Sweat Gland • Secretion contains same component as sweat plus fatty substances and proteins • Odorless when secreted, but when decomposed by bacteria on skin, turns musky – basis of body odor • Sometimes has a milky or yellowish color

Apocrine Glands • Begins functioning at puberty • Becomes active during pain, stress, and sexual encounters • May be analogous to the sexual scent glands of animals

Other Sweat Glands types • Ceruminous glands – modified apocrine glands in external ear canal that secrete cerumen (earwax) – Deters insects and block entry of foreign material

Other Sweat Glands types – Mammary glands – specialized sweat glands that secrete milk – Considered part of the female reproductive system

Sebaceous (oil) glands ·Simple alveolar glands ·Found all over the body – except palms and soles of feet ·Small on body trunk and limbs, but large on face, neck, and upper chest

Sebaceous (oil) glands • • Produce oil (sebum) Lubricants and softens skin and hair Kills bacteria Most with ducts that empty into hair follicles • Glands are activated at puberty • Stimulated by hormones

Homeostatic Imbalances • When a sebaceous gland duct is blocked by accumulated sebum, it forms a • If whitehead material oxidizes and dries, it darkens to form a blackhead

Homeostatic Imbalances • Acne is an active inflammation of sebaceous glands – usually caused by a bacterial infection, often staphylococcus

Homeostatic Imbalances • Seborrhea (cradle cap) in infants – Caused by overactive sebaceous glands – Begins on the scalp as pink raised lesions that gradually become yellow to brown • Careful washing to remove excessive oil often helps

Nails

Nails • Scale-like modification of the epidermis • Clear protective covering on the dorsal surface of the distal part of a finger or toe (lacks pigment) • Correspond to the hooves or claws of other animals • Contains hard keratin (skin contains soft keratin)

Nails • Each nail has – a free edge – A body (visible attached portion) – A root (embedded in the skin) • Deeper layers of the epidermis extend beneath the nail as the nail bed • Thickened proximal portion of the nail bed, called the nail matrix responsible for nail growth

Nails • Nails appear pink because of capillaries in the underlying dermis • Region that lies over the matrix appears as a white crescent call the lunula • Proximal and lateral borders are overlapped by skin folds called nail folds

Nails • Proximal nail fold projects onto the nail body called the cuticle • Underneath the free edge is called the quick

Nail Structures · Free edge Figure 4. 9 · Body · Root of nail · Cuticle Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 4. 22

Hair

Hair Distribution • Millions of Hairs are distributed over the entire skin surface except – Palms, soles, lips, nipples and portions of the external genitalia

Hair Function • Functions of hair include: – Helping to maintain warmth (more so in other mammals) – Alerting the body to presence of insects on the skin (main function) – Guarding the scalp against physical trauma, heat loss, and sunlight

Hair Function • Functions of hair include: – Eyelashes shield the eyes – Nose hairs filter large particles like lint and insects from the air we breath

Structure of Hair • Filamentous and flexible strands of dead keratinized cells produced by hair follicles • Made up of the shaft projecting from the skin, and the root embedded in the skin • Contains hard keratin – which is tougher and more durable than soft keratin of the skin and does not flake off

Structure of Hair • If shaft is flat and ribbonlike in cross section, the hair is kinky or curly

Structure of Hair • If shaft is oval, hair is wavy

Structure of Hair • If shaft is round, hair is straight and tends to be course

· Produced by hair bulb Hair · Consists of hard keratinized epithelial cells · Melanocytes provide pigment for hair color Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 4. 7 c Slide 4. 18

Structure of Hair – 3 layers • 1. Medulla 2. Cortex 3. Cuticle • Medulla – Central core – Consists of large cells and air spaces – Absent in fine hairs

Structure of Hair – 3 layers • 1. Medulla 2. Cortex 3. Cuticle • Cortex – Bulky layer surrounding the medulla – Several layers of flattened cells

Structure of Hair – 3 layers • 1. Medulla 2. Cortex 3. Cuticle • Cuticle – Outermost layer – Single layer of overlapping cells

The hair shaft consists of a core called the medulla, a cortex, and an outermost cuticle Figure 5. 6 a

• Hair conditioners smooth out rough surface of cuticle to make hair look shiny • Cuticle tends to wear away at the tip of the hair shaft, allowing the keratin fibrils in cortex and medulla to frizz out, creating ‘split ends’

Color • Pigmented by melanocytes at the base of the hair • Gray or white hair results from decreased melanin production and from the replacement of melanin by air bubbles in the hair shaft

Hair Follicle • Root sheath extending from the epidermal surface into the dermis • Deep end is expanded forming a hair bulb • A knot of sensory nerve endings (a root hair plexus) wraps around each hair bulb • Bending a hair stimulates these endings, hence our hairs act as sensitive touch receptors

Hair Follicle Figure 5. 6 c

Associated Hair Structures · Hair follicle · Dermal and epidermal sheath surround hair root · Arrector pilli · Smooth muscle · Sebaceous gland Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 4. 7 a Slide 4. 20

Types of Hair • Vellus – pale, fine body hair found in children and the adult female • Terminal – coarse, long hair of scalp, eyebrows, axillary (armpit), and pubic regions

Hair Growth • Rate of hair growth – 2. 5 cm per week, but varies some with age and gender • Each follicle goes through growth cycles • Active stage – active growth, last from weeks to years • Regressive stage – Hair matrix cells die, hair bulb shrivels somewhat • Resting stage – lasts one to three months

Hair Growth • After resting stage, the matrix proliferates again and forms a new hair to replace the old one that has fallen out or will be pushed out by the new hair. • We lose about 90 scalp hairs daily • Follicles of eyebrows only stay active 3 to 4 months, which is why eyebrows are not as long as the hair on our heads

Hair Thinning & Baldness • Alopecia – hair thinning in both sexes (as we age) • True, or frank, baldness – Genetically determined and sex -influenced condition – Male pattern baldness is most common

• Other causes of hair loss or thinning – Fever, surgery, severe emotional trauma, drugs, protein-deficient diets • Hirsutism = excessive hairiness – In women may be the result of an adrenal gland or ovarian tumor

Rosacea • Usually on cheeks or nose • Begins as a sudden flushing of the skin that goes away • Then this flushing reoccurs, lasting longer each time • Eventually it becomes a persistent condition • Usually strikes between the ages of 30 to 50

Rosacea • Sometimes associated with heavy drinking – but not true • Alcohol does worsen the condition, but so does spicy foods, hot baths, and exposure to sun • Comedian W. C. Fields had this condition on his nose

Port Wine Stains • Blazing red birthmarks – Bright pink to purple blotches on the skin • Some Central American countries thought these were the mark of the devil • Gypsies believed they were signs of the mother’s guilt

Port Wine Stains • No known cause • Happens during fetal development • Laser therapy can remove, but is very costly

Tattoos • Using a needle to deposit pigment in the skin dermis • Originated around 8000 BC • Can be dangerous – Risk of allergic reaction and bloodborne infectious diseases such as hepatitis

Quiz Appendages of the Skin Next time! Complete study guide pages 106 -108