integument ( skin )

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SINGHBHUM HOMOEOPATHIC MEDICAL COLLEGE AND HOSPITAL DEPT. OF PHYSIOLOGY PRESENTS

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Structure, functions, glands and integuments of skin

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Page 1: Integument ( Skin )

SINGHBHUM HOMOEOPATHIC MEDICAL COLLEGE AND HOSPITAL

DEPT. OF PHYSIOLOGY

PRESENTS

Page 2: Integument ( Skin )

SKIN ( INTEGUMENT )

Skin is the largest organ of the body. It is not uniformly thick. At some places, it is thick and in some places, it is thin. The average thickness of the skin is about 1-2 mm. In the sole, palm and in the interscapular region, it is considerably thick, measuring about 5 mm. In other areas of the body, the skin is thin. It is thinnest over eyelids and penis measuring about 0.5 mm only.

Page 3: Integument ( Skin )

Skin is made up of two layers :1. Outer epidermis2. Inner dermis and sub - cutaneous loose connective

tissue contain lot of fat

Page 4: Integument ( Skin )

EPIDERMIS

The epidermis is the outer layer of the skin. It is formed by stratified epithelium, which consists of five layers :

1. Stratum corneum 2. Stratum lucidum 3. Stratum granulosum 4. Stratum spinosum 5. Stratum germinativum

Page 5: Integument ( Skin )

STRUCTURE OF EPIDERMIS

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The important features of epidermis is that, it does not have blood vessels. The nutrition is provided to epidermis by the capillaries of dermis.

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STRATUM CORNEUM

It is the most superficial layer of the skin. It is also known as horny layer. It is the outer most layer and consists of dead cells, which are called

corneocytes. These cells lose their nucleus due to pressure and become dead cells. The cytoplasm is flattened with fibrous protein known as keratin. Apart from this, these cells also contain phospholipids and glycogen.

Page 8: Integument ( Skin )

STRATUM LUCIDUM

It is made up of flattended epithelial cells. It is 3 to 5 cell deep. Many cells have degenerated nucleus and, in some cells, the nucleus is absent. As these cells exhibit shiny character, the layer looks like a homogeneous translucent zone. So, this layer is called stratum lucidum (Lucid = clear). The cytoplasm contains eleidin, which is precursor of keratin.

Page 9: Integument ( Skin )

STRATUM GRANULOSUM

It is a thin layer with 2 - 5 rows of flattened rhomboid cells. The cytoplasm contains granules of a protein called keratohyaline. The keratohyaline is the precursor of keratin.

Page 10: Integument ( Skin )

STRATUM SPINOSUM

This is a broad layer of variable thickness and is made up of polyhedral cells. The surface of these cells are apparently covered with minute spine which interdigited with similar spines of adjacent cells.

It is also known as prickle cell layer because the cells of this layer possess same spine like

protoplasmic projections.

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STRATUM GERMINATIVUM It is a thick layer made up of

polygonal cells superficial and columnar or cuboidal epithelial cells in the deeper parts. Here, new cells are constantly formed by mitotic division. The newly formed cells move continuously towards the stratum corneum. The stem cells, which give rise to new cells, are known as keratinocytes.

Another type of cells called melanocytes are scattered between the keratinocytes. The melanocytes produce the pigment called melanin. The colour of the skin depends upon melanin.

Page 12: Integument ( Skin )

From this layer, some projections called rete ridges extend down up to dermis. These projections provide anchoring and nutritional function.

Page 13: Integument ( Skin )

DERMIS

Dermis is the inner layer of the skin. It is a connective tissue layer made up of dense and stout collagen fibers, fibroblasts and histiocytes. The collagen fibers exhibit elastic property and are capable of storing or holding water. The collagen fibers contain the enzyme collagenase, which is responsible for wound healing. Dermis is made up of 2 layers :

1. Superficial papillary layer 2. Deeper reticular layer

Page 14: Integument ( Skin )

PAPILLARY LAYER

This layer projects into the epidermis. It contain blood vessels, lymphatics and nerve fibers. This layer also has some pigment containing cells known as chromatophores.

Dermal papillae are finger-like projections arising from the superficial papillary dermis. Each papilla contains a plexus of capillaries and lymphatics which are oriented perpendicular to the skin surface. The papillae are surrounded by rete ridges extending from the epidermis.

Page 15: Integument ( Skin )

RETICULAR LAYER

Reticular layer is made up of reticular and elastic fibers. These fibers are found around the hair bulbs, sweat glands and sebaceous glands. The reticular layer also contains mast cells, nerve endings, lymphatics, epidermal appendages and fibroblasts.

Immediately below the dermis, subcutaneous tissue is present. It is a loose connective tissue, which connects the skin with the internal surfaces of the body. It serves as an insulator to protect the body from excessive heat and cold of the environment. Lot of

smooth muscles called arrector Pilli are also found in skin around the hair follicles.

Page 16: Integument ( Skin )

GLANDS OF THE SKIN1. Sweat gland 2. Sebaceous

gland

Page 17: Integument ( Skin )

SWEAT GLAND

Sweat glands are simple, coiled, tubular glands for the secretion of sweat. These are found on all the body surface except margin of lips, glans penis and inner surface of prepuce.

Sweat glands are of two types : 1) Eccrine or, Merocrine sweat gland 2) Apocrine sweat gland

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ECCRINE SWEAT GLAND

Page 19: Integument ( Skin )

ECCRINE SWEAT GLANDThe eccrine sweat gland is a tubular coiled gland.

It consists of two parts-

A coiled portion lying deeper in dermis, which secretes the sweat.

A duct portion, which passes through dermis and epidermis and opens out through the sweat pore, distributed over the entire skin surface.

The coiled portion is formed by single layer of columnar or cuboidal epithelial cells, which are secretory in nature. The epithelial cells are interposed by the myoepithelial cells.

Page 20: Integument ( Skin )

Secretory activity of eccrine glands

Eccrine glands function throughout life since birth . These glands secrete a clear watery sweat . The secretion increase during increase in temperature and emotional condition . Eccrine gland play important role in regulating the body temperature by secreting sweat. Sweat contains water, sodium chloride, urea and lactic acid.

Page 21: Integument ( Skin )

Control of eccrine gland

Eccrine Glands are under nervous control and are supplied by sympathetic postganglionic nerve fiber, which secret acetylcholine (sympathetic cholinergic fibers). Stimulation by these nerves causes secretion of sweat.

Page 22: Integument ( Skin )

APOCRINE SWEAT GLAND

Page 23: Integument ( Skin )

APOCRINE SWEAT GLAND

The structure of apocrine glands is similar to that of eccrine glands. The coiled portion lies in deep dermis. But the duct opens into the hair follicle above the opening of the sebaceous gland. Apocrine gland are situated only in certain areas of the body like –Axilla, Areola, Pubis, Umbilicus.

Page 24: Integument ( Skin )

Secretory activity of apocrine gland

Apocrine sweat glands are non functional till puberty and starts functioning only at the time of puberty. In old age , the function of these glands declines . The secretion of the apocrine is viscid. At the time of the secretion , it is odorless. It’s acrid odor is due to bacterial activities. The apocrine gland do not play any role in temperature regulation like eccrine glands. .

Page 25: Integument ( Skin )

Composition of Sweat

The average composition of sweat is 0.5% solid and 99.5% water.

In solid –Sodium chloride – 0.2% to 0.5%Urea – 0.03%Potassium – 0.02% to 0.12%Calcium – 5mg%Lactic acid – 0.07%A trace of creatinine, amino acid, phosphorus and iron are also present.

Sp.gr. – 1.002 to 1.003 pH – 3.8 to 6.5

Page 26: Integument ( Skin )

Mechanism of Sweat secretion Stimulation of hypothalamus by excess heat causes sweating. The impulses from hypothalamus that cause sweating are transmitted in the autonomic pathway to the cord and then through the sympathetic out flow to the skin everywhere in the body.

The sweat glands are stimulated by sympathetic cholinergic nerve fibers. The sweat gland of the hands and feet do have some adrenergic nerve fibers. These glands can also be stimulated to some extent by epinephrine or, nor-epinephrine circulating in the blood. Local sweating in emotional state and sweating during exercise are adrenergic activities.

Page 27: Integument ( Skin )

A polypeptide, Bradykinin is believed to be liberated during sweat secretion. It causes dilatation of the cutaneous blood vessels and blood vessels supplying the sweat gland.When the rate of sweat secretion is very low, the sodium and chloride concentration of the sweat are also very low, because most of these ions reabsorbed before it reaches the surface of the skin.On the other hand, when the rate of secretion becomes progressively greater, the rate of sodium chloride reabsorption does not increase. So that then their concentration in the sweat usually rise.Sweating occurs at an environmental temperature of 29 C or more. Sweating occurs more quickly in hot and humid weather. Approximately 500ml to 1000ml sweat is secreted per hour in hot humid day.

Page 28: Integument ( Skin )

SEBACEOUS GLAND

Page 29: Integument ( Skin )

The sebaceous glands are compound alveolar glands, ovoid or spherical in shape and are situated at the neck of the hair follicle. Glands have connective tissue capsule. The alveoli of the glands are lined by stratified epithelial cells. Sometimes sebaceous glands are present but not communicate with hair follicle in some area like face, lips, nipples etc.

SEBACEOUS GLAND

Page 30: Integument ( Skin )

The sebaceous glands secrete an oily substance called sebum. Sebum is formed by the liquefaction of the alveolar cells and poured out through the ducts either via the hair follicle or directly into the exterior. Sebum contains free fatty acids, triglycerides, squalene, wax and paraffin. It protect the skin from fungal and bacterial infection. It also give smoothness to skin and hairs.

SEBUM

Page 31: Integument ( Skin )

Control of secretion of sebum

Sebaceous secretion is influenced by gonad hormones, both testosterone in male and progesterone in female. These hormones affect the secretion by affecting mitotic activities of the secretory cells. This is the reason why secretion of sebaceous glands increase during puberty, second half of menstruation and also during pregnancy. Contraction of arrector pilli helps in the expulsion of sebum.

Page 32: Integument ( Skin )

APPENDAGES OF SKIN

NAILS HAIRS

Page 33: Integument ( Skin )

Skin appendages are associated with the skin and serve a particular function. These are derived from the skin, and are usually adjacent to it.

In humans some of the more common skin appendages are hairs and nails.

APPENDAGES OF SKIN

Page 34: Integument ( Skin )

A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans. Fingernails and toenails are modified stratum corneum made of a tough protein called keratin. Average rate of growth in finger nails is about 1mm per week.

NAILS

Page 35: Integument ( Skin )

The nail plate or body of nail) is the actual nail, and like hair and skin, made of translucent hard keratin. In the nail it forms a strong flexible material made of several layers of dead, flattened cells. The plate appears pink because of the underlying capillaries.

The free margin (margo liber) or distal edge is the anterior margin of the nail plate corresponding to the abrasive or cutting edge of the nail.

STRUCTURE OF NAIL

The nail root is the base of the nail embedded underneath the skin. It originates from the actively growing tissue below, the matrix.

Page 36: Integument ( Skin )

STRUCTURE OF NAIL The matrix or, nail bed is the skin beneath the

nail plate upon which the nail rests. The part of the nail bed that extends beneath the nail root contains nerves, lymph and blood vessels.

The lunula (occasionally called simply "the moon") is the visible part of the matrix, the whitish crescent-shaped base of the visible nail. The lunula is largest in the thumb and often absent in the little finger.

The furrow between the nail fold and nail bed is called nail groove.

Page 37: Integument ( Skin )

Hair is an elastic, keratinized and thread like structure developed from the dermis.

The word "hair" often refers to two distinct structures:

• the part beneath the skin, called the hair follicle or when pulled from the skin, called the bulb. This organ is located in the dermis and maintains stem cells which re-grow the hair after it falls out.

• the shaft, which is the hard filamentous part that extends above the skin surface. A cross section of the hair shaft may be divided roughly into three zones :

HAIR

Page 38: Integument ( Skin )

STRUCTURE OF HAIR

Page 39: Integument ( Skin )

Hair fibers have a structure consisting of following layers from outside :

•the cuticle which consists of several layers of flat, thin cells laid out overlapping one another

•the cortex, which contains the keratin bundles in cell structures that remain roughly rod-like

•the medulla is the central portion consisting of two to three layers of cells. The cells are cubical in the root and cornified in the shaft.

Page 40: Integument ( Skin )

FUNCTIONS OF SKINProtective function – Intact skin protect our body from air, water and bacteria. It gives a protective covering to the delicate structures underneath it. Nails and sensory function of the skin also helps in the defense work. Melanin pigments offer protection against ultra violet light.Sensory function – Free nerve endings on the skin are sensitive to pain, touch, heat and cold, resulting in either voluntary or reflex activities.Secretory function – Sweat help in temperature regulation and sebum makes skin smooth.Heat regulatory function – Sweating and cutaneous blood flow help in temperature regulation.

Page 41: Integument ( Skin )

Excretory function – Through the secretion of glands of the skin – water, salt, fatty substances and urea are excreted.

Synthetic function – Sun’s ultra violet rays help in synthesis of natural vitamin D. skin can also manufacture melanin pigment.

Water balance – Skin serve a useful means in regulating water balance of the body by perspiration.

Absorption – Skin surface can absorb water, oil etc.

Storage function – Skin can store fat, salt, water, glucose etc.

Reflect nutritional status – The sign of dehydration, vitamin deficiency, age and malnutrition are manifested in the skin.