skin

The Integumentary System “Cont’d”

presented by : Khaled Alkhodari

Subcutaneous Tissue

The subcutaneous tissue layer consists of loose connective tissue that binds the skin loosely to the subjacent organs

The hypodermis often contains fat cells that vary in number according to the area of the body and vary in size according to nutritional state.

Dr. Sami Zaqout IUG

Vessels of The Skin

The connective tissue of the skin contains a rich network of bloodand lymphatic vessels.

The arterial vessels that nourish the skin form two plexuses: One is located between the papillary and reticular layers “subpapillary

plexus” One is located between the dermis and the subcutaneous tissue.

Veins are disposed in three plexuses: Two in the position described for arterial vessels Third in the middle of the dermis.

Lymphatic vessels begin as closed sacs in the papillae of the dermis and converge to form two plexuses, as described for the arterial vessels.

Dr. Sami Zaqout IUG

Skin Sensorial Receptors

Numerous free nerve endings found in the epidermis, hair follicles, and cutaneous glands.Free nerve endings are sensitive to:Touch-pressureTactile receptionhigh and low temperaturesPainItching

Dr. Sami Zaqout IUG

Skin Sensorial Receptors

encapsulated receptors , respond rapidly to stimuli on the skin. The expanded ending includes:

Ruffini endings Encapsulated ending includes:

Pacini corpuscles (lamellated) Meissner corpuscles Krause corpuscles.

The expanded and encapsulated receptors respond to tactile stimuli, functioning as mechanoreceptors.

Pacini corpuscles and Ruffini endings are also found in the connective tissue of organs located deep in the body, where they probably are sensitive to movements of internal organs and to pressure of one organ over another.

Dr. Sami Zaqout IUG

coarse touch, pressure

temperatures , pain ,itching, tactile receptors.

detect movements of the hairs.

sense lowfrequency vibrations.

Subcutaneous layer

stretch or twisting in the skin.

a.Epidermal free endings. b.Merkel’s c.Pacinian. d.Krause’s end bulb e.Meissner’s. f.Ruffini’s

sustained light touch +object’s texture.

Lighttouch\low-frequencydeform their shape. numerous in figertips,palms,soles ,decline slowly in number after puberty.

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In your opinion; which layer forms the epidermal water barrier???494

Hairs

Hairs are elongated keratinized structures derived from invaginations of epidermal epithelium.

Hairs are found everywhere on the body except on the palms, soles, lips, glans penis, clitoris, and labia minora.

Hairs grow discontinuously and have periods of growth (anagen) followed by periods of rest (catagen and telogen) .

Dr. Sami Zaqout IUG

Hairs

Each hair arises from an epidermal invagination, the hair follicle

Has a terminal dilatation calleda hair bulb.

At the base of the hair bulb, a dermal (hair) papilla can be observed.

The epidermal cells covering this dermal papilla form the hair root that produces and is continuous with the hair shaft, which protrudes beyond the skin.

Dr. Sami Zaqout IUG

Hairs

Dr. Sami Zaqout IUG

The cells of the central region of the root at the apex of the dermal papilla produce large, vacuolated, and moderately keratinized cells that form the hair medulla.

Root cells multiply and differentiate into heavily keratinized, compactly grouped fusiform cells that form the hair cortex.

Farther toward the periphery are the cells that produce the hair cuticle.

Hairs

Dr. Sami Zaqout IUG

The outermost cells give rise to the internal root sheath, which completely surrounds the initial part of the hair shaft.

Disappear above the level of thesebaceous glands.

The external root sheath is continuous with epidermal cells and, near the surface, shows all the layers of epidermis.

external root sheath covers the internal sheath and extends all the way to theepidermis, where it is continuous with the basal and spinous layers.

Near the dermal papilla. , the external root sheath is thinner and is composed of cells corresponding to the stratum germinativum of the epidermis

Hairs

Dr. Sami Zaqout IUG

Separating the hair follicle from the dermis is a noncellular hyaline layer, the glassy membrane which results from a thickening of the basal lamina.

The dermis that surrounds the follicle is denser, forming a sheath of connective tissue.

What’s the hair follicle??

Hairs

Arrector pili muscles are disposed in an oblique direction, and their contraction results in the erection of the hair shaft to a more upright position.

Contraction of arrector pili muscles also causes a depression in the skin where the muscles attach to the dermis.

Hair color is created by the activity of melanocytes located between the papilla and the epithelial cells of the hair root.

Dr. Sami Zaqout IUG

keratinization processes differencesbetween the epidermis and hair

1. The epidermis produces relatively soft keratinized outer layers of dead cells that adhere slightly to the skin and desquamate continuously.The opposite occurs in the hair, which has a hard and compact keratinized structure.

2. Although keratinization in the epidermis occurs continuously and over the entire surface.It is intermittent (cyclic manner) in the hair and occurs only in the hair root.

3. In the epidermis the differentiation of all cells in the samedirection gives rise to the final keratinized layer.Cells in the hair root differentiate into various cell types that differ in ultrastructure, histochemical characteristics, and function.

Dr. Sami Zaqout IUG

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• Cells in which regions of the hair follicle are directly responsible for the growth of hair?

• Which layer is the largest & responsible for the texture +elasticity + color of the hair ???

Epithelial cells surrounding the dermal papilla are collectively referred as the hair matrix. Matrix cells represent the proliferative (germinative) layer of the hair follicle

Nails

Nails are plates of keratinized epithelial cells on the dorsal surface of each distal phalanx.

The proximal part of the nail, hidden in the nail groove, is the nail root.

The epithelium of the fold of skin covering the nail root consists of the usual layers of cells.

The stratum corneum of this epithelium forms the eponychium, or cuticle.

Dr. Sami Zaqout IUG

Nails The nail plate, which corresponds

to the stratum corneum of the skin, rests on a bed of epidermis called the nail bed.

Only the stratum basale and the stratum spinosum are present in the nail bed.

Nail plate epithelium arises from the nail matrix.

The proximal end of the matrix extends deep to the nail root.

The distal end of the plate becomes free of the nail bed and is worn away or cut off.

**The crescent-shaped white area near the root of the nail,the lunula, partially keratinized+ opaque Dr. Sami Zaqout

IUG

Sebaceous Glands

Sebaceous glands are embedded in the dermis over most of the body surface.

Not found in the glabrous skin of the palms and soles.

Acinar glands that usually have several acini opening into a short duct.

This duct usually ends in theupper portion of a hair follicle.

In certain regions, such as the glans penis, glans clitoridis, and lips, it opens directly onto the epidermal surface.

Dr. Sami Zaqout IUG

Sebaceous Glands

The acini consist of a basal layer of undifferentiated flattened epithelial cells that rests on the basal lamina.

These cells proliferate and differentiate, filling the acini with rounded cells containing increasing amounts of fat droplets in their cytoplasm.

Their nuclei gradually shrink, and the cells simultaneously become filled with fat droplets and burst (Holocrine gland) ?

يذكرنا مين

The product of this process issebum.

Dr. Sami Zaqout IUG

Holo Mero Apo

Acne

The flow of sebum iscontinuous

Disturbance in the normal secretion and flow of sebum is one of the reasons for the development of acne, a chronic inflammation of obstructed sebaceous glands.

It occurs mainly during puberty.

Dr. Sami Zaqout IUG

Sweat Glands

Sweat glands are widely distributed in the skin except for certain regions, such as the glans penis.

The merocrine sweat glands are simple, coiled tubular glands whose ducts open at the skin surface.

Their ducts do not divide, and their diameter is thinner than that of the secretory portion.

The secretory part of the glandis embedded in the dermis;

Dr. Sami Zaqout IUG

Sweat Glands

Dark cells: Pyramidal cells that line

most of the luminal surface of this portion of the gland.

Their basal surface does nottouch the basal lamina.

Secretory granules containing glycoproteins are abundant in their apical cytoplasm.

Clear cells: Devoid of secretory granules Their basal plasmalemma has

the numerous invaginations characteristic of cells involved in transepithelial salt and fluid transport.

The ducts are lined with stratified cuboidal epithelium.

Dr. Sami Zaqout IUG

This micrograph shows myoepithelial cells (My) and two distinctive gland cell types, dark cells (D) and clear cells (C). The apical portion of the dark cell is broad; it faces the lumen (L) of the gland and contains numerous secretory granules. The dashed linemarks the boundary of one dark cell. The clear cell is more removed from the lumen of the gland. Its base rests on the myoepithelial cells or directly on the basal lamina. Most of the free surface of the clear cell faces an intercellular canaliculus (IC). Clear cells contain numerous mitochondria, extensive infoldings of the plasma membrane, and large numbers of electron-dense glycogen inclusions. 5,600

Sweat Glands

Apocrine gland is present in the axillary, and perineal regions+ functional at puberty.

Much larger merocrine sweat glands. ??it’s very wide lumen

Embedded in the dermis and hypodermis

Their ducts open into hair follicles +composed of a single cell type.

Produce a viscous secretion that is initially odorless but may acquirea distinctive odor as a result of bacterial decomposition.

Innervated by adrenergic nerve endings, whereas eccrine glands receive cholinergic fibers.

THE QUESTION is: is this gland an APOCRINE gland ??!!Dr. Sami Zaqout IUG

Junqueira's Basic Histology Text and Atlas , 13th Edition 2013, p380.

Differences between thick skin and thin skin

Dr. Sami Zaqout IUG

Thick or non hairy skin Thin or hairy skin

1.Present in the palms, soles, lateral surfaces and the tips of fingers and toes.

2. The epidermis is thick and is

formed of:a) Thick Malpighian layer.b) Thick granular layer.c) Presence of Lucidum layer.d) Very thick horny layer.

1. Present in the other body areas.

2. The epidermis is thin and is formed of:

a) Thin Malpighian layer.b) Very thin granular layer.c) No lucidum layer.d) Very thin horny layer.

Differences between thick skin and thin skin

Dr. Sami Zaqout IUG

Thick or non hairy skin Thin or hairy skin

3. No hair follicles.4. No sebaceous glands.

5. No arrector pili muscles.

6. Presence of ridges andfurrows on the surface.

7. Regular dermal papillae

3. Presence of hair follicles.4. Presence of sebaceous

glands.5. Presence of arrector

pili muscles.6. Presence of less ridges

and less furrows on the surface.

7. Irregular dermal papillae.

Tumors of the Skin

In adults, one-third of all tumors are of the skin.

Most of these tumors derive from: Basal cells: Basal cell carcinomas

Squamous cells of the stratum spinosum:

Squamous cell carcinomas

Melanocytes: Melanomas

Dr. Sami Zaqout IUG

Tumors of the Skin

basal cell carcinomas and squamous cell carcinomas, can be diagnosed and excised early and consequently are rarely lethal.

Skin tumors show an increased incidence in fair-skinned individuals residing in regions with high amounts of solar radiation.

Dr. Sami Zaqout IUG

Tumors of the Skin

Malignant melanoma is aninvasive tumor of melanocytes.

Dividing rapidly, malignantly transformed melanocytes penetrate the basal lamina, enter the dermis, and invade the blood and lymphatic vessels to gain wide distribution throughout the body.

Dr. Sami Zaqout IUG

Thank you for listening

Histology A Text and Atlas With Correlated Cell and Molecular Biology 7th ed 2016 ; p509

Wheater's Functional Histology 6th ed 2014 ;p180

BRS 7th ed 2015 , p 261