The Integumentary System

Dr. V.P.C.Rajakaruna

MBBS (COLOMBO)

The Integumentary System

• Integument is skin

• Skin and its appendages make up the integumentary system

• A fatty layer (hypodermis) lies deep to it

• Two distinct regions– Epidermis– Dermis

Functions of skin

• Protection– Cushions and insulates and is waterproof– Protects from chemicals, heat, cold,

bacteria– Screens UV

• Synthesizes vitamin D with UV• Regulates body heat• Prevents unnecessary water loss• Sensory reception (nerve endings)

Epidermis

• Keratinized stratified squamous epithelium

• Four types of cells– Keratinocytes –produce keratin (tough fibrous

protein) which gives the protection– Melanocytes - make dark skin pigment

melanin – Merkel cells – associated with sensory nerve

endings – Langerhans cells – macrophage-like cells

• Layers (from deep to superficial)– Stratum basale or germinativum – single row of

cells attached to dermis, cells divide rapidly, ; youngest cells. 10% to 25% of cells in this layer are melanocytes which produce melanin which gives the dark skin color and protects from UV rays. Occasional Merkel cells also there.

– Stratum spinosum – keratinocytes contain spine like extensions; tonofilaments (bundles of protein) resist tension, Langerhans cells are there to provide protection against foreign particles

– Stratum granulosum – layers of flattened keratinocytes producing keratin (hair and nails made of it also), contain a water proofing glycolipid secreting into the extracellular space and is the major factor of slowing the water loss across the epidermis.

The plasma membranes of the cells thicken so that they become more resistant to destruction

Epidermis relies on capillaries in the underlying connective tissue (dermis) for its nutrients. Above stratum granulosum, epidermal cells are too far from the dermal capillaries, so they die, a completely normal occurrence

– Stratum lucidum – occurs in thick skin like on palms and soles but not in thin skin, keratinocytes

– Stratum corneum – horny layer (cells dead, many layers thick), both the keratin and the thickened plasma membranes of cells protects the skin against abrasion and penetration. Additionally, the glycolipid between its cells keep this layer waterproof.

( these cells are the dandruff shed from the scalp and the flakes that come off dry skin)

Epithelium: layers (on left) and cell types (on right)

Dermis• Strong, flexible connective tissue• Cells: fibroblasts, macrophages, mast cells, WBCs• Fiber types: collagen, elastic, reticular• Rich supply of nerves and vessels• Critical role in temperature regulation (the vessels)• Two layers

Papillary – 20%Superficial part, areolar connective tissue; includes dermal papillae

Reticular – 80%“reticulum” (network) of collagen and reticular fibers

*Dermis layers

*

*

*Dermal papillae

Fingerprints, palmprints, footprints

• Dermal papillae, finger like pegs that indent the overlying epidermis

• Elevate the overlying epidermis into epidermal ridges which are responsible for the finger, palm and foot prints

• Epidermal ridges increase friction and enhance the gripping ability of the hands and feet

• Patterns of ridges are genetically determined and unique to each person

The dermis is the receptive site for the pigment of tattoos

• When people touch an object leads to “sweat films” because of sweat pores are open in to epidermal ridges

• Collagen: strength and resilience• Elastic fibers: stretch-recoil

– Striae: stretch marks• Tension lines (or lines of cleavage)

– The direction the bundles

of fibers are directed

Flexion creases• Deep dermis is responsible• From continual folding

Reticular layer

Hypodermis

• “Hypodermis” (Gk) = below the skin

• “Subcutaneous” (Latin) = below the skin

• Also called “superficial fascia”“fascia” (Latin) =band; in anatomy: sheet of

connective tissue

• Fatty tissue which stores fat and anchors skin (areolar tissue and adipose tissue)

• Hypodermis also prevents the heat loss from the body

• The hypodermis markedly thicken with weight gain, but this thickening occurs in different body areas in the two sexes

• In females , subcutaneous fat accumulates first in thighs and breasts where as in males it first accumulates in the anterior abdomen as a “ beer belly “

Skin color

• Three skin pigments determine the skin color– Melanin: the most important, it passes from

melanocytes to keratinocytes in stratum basale of the epidermis

– Carotene: from carrots and yellow vegetables, it accumulates in the stratum corneum of the epidermis and in fat of the hypodermis

– Hemoglobin: the pink of light skin, in the capillaries of the dermis

Skin appendages

• Derived from epidermis but extend into dermis

• Include– Hair and hair follicles– Sebaceous (oil) glands– Sweat (sudoiferous) glands– Nails

Hair and hair folliclesDerived from epidermis and dermis

Everywhere but palms, soles, nipples, parts of genitalia

*“arrector pili” is smooth muscle*

Hair papilla is connective tissue________________

Hair bulb: epithelial cells surrounding papilla

Hair and hair follicles

• Complex structural units• Hair – long filaments• Hair follicle – tubular invaginations of the

epidermis from which the hair grows Hair• Flexible strand made of dead, keratinized

cells• Parts

– Root imbedded in skin– Shaft projecting above skin surface

• Three concentric layers– Medulla (core)– Cortex (surrounds medulla)– Cuticle (single layers, overlapping) is the most

heavily keratinized part of the hair, providing strenghth and keeping the inner layer tightly compacted

• Functions of hair– Warmth – less in man than other mammals– Sense light touch of the skin– Protection – scalp, eye, nose

Hair follicle

• Extend from the epidermal surface in to the dermis

• The deep end of the follicle is expanding to form a hair bulb

• A knot of sensory nerve endings wraps around each hair bulb to form a root hair plexus

• A nipple like bit of the dermis, the connective tissue papilla, protrudes into each hair bulb

• This papilla contains a knot of capillaries deliver substances that signal hair growth and supply nutrients to the growing hair

Types of hairVellus: fine, short hairs ( the body hair of children and women)Intermediate hairs Terminal: longer, coarser hair( every one’s scalp hair, at puberty appear in axillary and pubic regions in both sexes and on the face, chest, arms and legs of men. )

• Hair growth: averages 2 mm/week but varies among body regions and with sex and age– Active: growing– Resting phase then shed

On the scalp the hair follicle active for an average of 4 years, so individual hairs grow quite long before shedding. On the eye brows, by contrast, the follicles are active for only a few months, so the eye brows never grow very long

• Hair loss– Thinning – age relatedHair grows fastest from the teen years to the

forties. When hairs are no longer replaced as quickly as they are shed, the hair become thin. By age 60 to 65 both sexes usually experience some degree of balding.

– Male pattern baldnessGenetically determined, gender influenced

condition. Caused by a gene that is not expressed until adulthood, at which time it changes the response of hair follicles to androgens. Now the hairs respond to the androgens by increasingly shortening their growth cycles. The cycles become so short that many hairs never even emerge from their follicles before shedding.

• Hair color– Amount of melanin for black or brown; distinct

form of melanin for red– White: decreased melanin and air bubbles in

the medulla– Genetically determined though influenced by

hormones and environment

Sebaceous (oil) glands

• Entire body except palms and soles• Simple glands opens with a single duct• Central cells accumulate oily lipids until they

become engorged and burst apart.• This process is called holocrine secretion • Product is called sebum• Most sebaceous glands are associated with hair

follicles, emptying their sebum in to the upper third of the follicle

• From there, the sebum flows superficially to cover the skin

• In addition to making skin and hair greasy, sebum collects dirt, soften and lubricates the hair and skin, prevents hair from becoming brittle, and keeps the epidermis from cracking

• It also helps to slow water loss across the skin and to kill bacteria

• The secretion of sebum is stimulated by hormones, especially androgens.

• These sebaceous glands are relatively inactive during childhood but are activated in both sexes during puberty, when the production of androgens begins to rise

Sweat glands

• Entire skin surface except nipples and part of external genitalia

• Normally produce about 500 cc to 12 l/day! (is mostly water)

• Prevent overheating of the body, because its evaporation from the skin is a cooling process.

• Humans most efficient with cooling process via the sweat glands because of the less hairiness

• Produced in response to stress as well as heat• Sweat produce primarily as a filtrate of blood that

passes through the secretory cells of the sweat glands and released by exocytosis

• 99% of water, with some salts ( mostly sodium chloride) and traces of metabolic wastes ( urea, ammonia, uric acid)

• It is acidic, so it retards the growth of bacteria on the skin

Types of sweat glands

• Eccrine or merocrine– Most numerous– Produce true sweat: 99% water, some salts,

traces of waste– Most abundant on the palms, soles and fore

head– Open through pores

• Apocrine– Mostly confined to axillary, anal and genital

areas – Ducts open into hair follicles– Produce a special kind of sweat consisting of

fatty substances and proteins in addition to the components of true sweat

– Apocrine sweat is viscous and sometimes has a milky color

– This product starts out odorless, but when its organic molecules are decomposed by bacteria on the skin, it takes on a musky smell

– This is the basis of body odor

– Apocrine glands start function at puberty under the influence of androgens

– Activity increased by sexual foreplay and they enlarge and recede with the phases of a woman’s menstrual cycle.

• Modified apocrine glands– Ceruminous – secrete earwax– Mammary – secrete milk

Nails

• Consists of hard keratin• Corresponds to hooves and claws• Modification of the epidermis• Each nail has a distal free edge, a body

and a root• Nail rests on a bed of epidermis called nail

bed which contains the deeper layers of the epidermis

• Nail itself corresponds to the superficial keratinized layers

• Nails look pink because of the rich network of capillaries in the underlying dermis

• At the root and the proximal end of the nail body, the nail bed thickens to form nail matrix, the actively growing part of the nail

• The matrix is so thick that the pink dermis cannot show through it – Lunula

• The lateral and proximal borders of the nail are overlapped by skin folds called nail folds

CUTANEOUS SENSATIONS

CUTANEOUS SENSATIONS

• Cutaneous sensations include tactile (touch, pressure, vibration), thermal (hot, cold) and pain.

• The receptors for these sensations are located in the dermis or epidermis .

• These receptors are distributed across the body such that some areas are heavily populated (very sensitive) while other areas contain only a few receptors (poorly sensitive).

• The sensory receptors in the skin are:• cutaneous mechanoreceptors

– Ruffini's end organ (sustained pressure) – Meissner's corpuscle (changes in texture, slow

vibrations) – Pacinian corpuscle (deep pressure, fast vibrations) – Merkel's disc (sustained touch and pressure) – Free nerve endings

• thermoreceptor • nociceptor • chemoreceptor