SKIN MAMMARY GLANDS By Dr Mujahid Khan Skin

SKIN & MAMMARY GLANDS By: Dr. Mujahid Khan

Skin Ø The skin is a membranous protective covering of the body Ø Is a complex organ system Ø It consists of two layers derived from two different germ layers Ø Ectoderm and mesoderm

Skin Ø The epidermis is a superficial epithelial tissue Ø It is derived from surface ectoderm Ø The dermis is a deeper layer composed of dense irregularly arranged connective tissue Ø It is derived from mesoderm Ø The meshwork of embryonic connective tissue derived from mesoderm Ø It forms the connective tissues in the dermis

Skin Ø Skin structures vary from one part of the body to another Ø The skin of eyelids is thin and soft and has fine hairs Ø The skin of eyebrows is thick and has coarse hairs Ø The embryonic skin at 4 -5 weeks consists of a single layer of surface ectoderm overlying the mesenchyme

Epidermis Ø During the first and second trimester, epidermal growth occurs in stages and result in an increase in epidermal thickness Ø Primordial of the epidermis is the layer of surface ectodermal cells Ø These cells proliferate and form a layer of squamous epithelium called periderm and a basal germinative layer

Epidermis Ø The cells of periderm continually undergo keratinization and desquamation and are replaced by cells arising from basal layer Ø The exfoliated peridermal cells form part of the white greasy substance called vernix caseosa which covers the fetal skin Ø Vernix caseosa protects the developing skin from constant exposure to amniotic fluid with its urine content during the fetal period Ø Vernix also facilitates birth of the fetus because of its slippery nature

Epidermis Ø The basal layer of the epidermis becomes the stratum germinativum Ø It produces new cells that are displaced into the layer superficial to it Ø By 11 weeks, the cells from stratum germinativum have formed an intermediate layer Ø Replacement of peridermal cells continues until about 21 weeks

Epidermis Ø Thereafter the periderm disappears and the stratum corneum forms Ø Proliferation of cells in the stratum germinativum also forms epidermal ridges which extend into the developing dermis Ø Epidermal ridges produce grooves on the surface of the palms and soles including digits Ø The type of pattern is determined genetically and constitute the basis for examining fingerprints

Dermatoglyphics Ø Abnormal chromosome complements affect the development of ridge patterns Ø Infants with Down syndrome have distinctive patterns on their hands and feet that are of diagnostic value

Epidermis Ø Late in the embryonic period the neural crest cells migrate into the mesenchyme of the developing dermis and differentiate into melanoblasts Ø Later these cells migrate to the dermoepidermal junction and differentiate into melanocytes Ø The differentiation of melanoblasts into melanocytes involves the formation of pigment granules

Epidermis Ø Melanocytes appear in the developing skin at 40 – 50 days, immediately after the migration of neural crest cells Ø In white races, the cell bodies of melanocytes are usually confined to basal layers of the epidermis Ø Melanocytes begin producing melanin before birth and distribute it to the epidermal cells

Epidermis Ø Pigment formation can be observed prenatally in the epidermis of dark-skinned races Ø There is a little evidence of such activity in lightskinned fetuses Ø Increased amount of melanin are produced in response to ultraviolet light Ø The relative content of melanin in the melanocytes accounts for the different colors of skin

Thick Skin Ø It covers the palms and soles and lacks Ø Hair follicles Ø Arrector muscles Ø Sebaceous glands Ø But it has sweat glands

Thin Skin Ø It covers most of the rest of the body and contains Ø Hair follicles Ø Arrector muscles of hairs Ø Sebaceous glands Ø Sweat glands

Dermis Ø The dermis develops from mesenchyme, derived from the mesoderm underlying the surface ectoderm Ø Most of the mesenchyme that differentiates into the connective tissue of the dermis originates from the somatic layer of lateral mesoderm Ø Some of it is derived from the dermatomes of the somites

Dermis Ø By 11 weeks the mesenchymal cells have begun to produce collagenous and elastic connective tissue fibers Ø As the epidermal ridges form, the dermis projects into the epidermis forming dermal ridges that interdigitate with the epidermal ridges Ø Capillary loops develop in some of these ridges and provide nourishment for the epidermis

Dermis Ø Sensory nerve endings form in other ridges Ø The developing afferent nerve fibers play an important role in the spatial and temporal sequence of dermal ridge formation Ø Blood vessels in the dermis begin as simple, endothelium-lined structures that differentiate from mesenchyme Ø As the skin grow, new capillaries grow out from the primordial vessels

Dermis Ø Such capillary-like vessels have been observed in the dermis by the end of 5 th week Ø Some capillaries acquire muscular coats through differentiation of myoblasts developing in the surrounding mesenchyme and become arterioles and arteries Ø Others become venules and veins Ø By the end of 1 st trimester, the major vascular organization of the fetal dermis is established

Sebaceous Glands Ø Most sebaceous glands develop as buds from the sides of developing epithelial root sheaths of hair follicles Ø The glandular buds grow into the surrounding embryonic connective tissue and branch to form the primordia of several alveoli and their associated ducts Ø The central cells of alveoli break down forming an oily secretion called sebum

Sebaceous Glands Ø Sebum is released into the hair follicle and passes to the surface of the skin Ø In skin it mixes with desquamated peridermal cells to form vernix caseosa Ø Sebaceous glands independent of hair follicles develop in a similar manner to buds from the epidermis

Sweat Glands Ø Eccrine sweat glands are located in the skin throughout most of the body Ø They develop as epidermal down growths into the underlying mesenchyme Ø As bud elongates, its end coils to form the primordium of the secretory part of the gland Ø The epithelial attachment of the developing gland to the epidermis forms the primordium of the duct

Sweat Glands Ø The central cells of the primordial ducts degenerate, forming the lumen Ø Peripheral cells of the secretory part of the gland differentiate into myoepithelial and secretory cells Ø Myoepithelial cells are thought to be specialized smooth muscle cells that assist to expel sweat from the glands Ø Eccrine sweat glands begin to function shortly after birth

Sweat Glands Ø The distribution of large apocrine sweat glands in humans is mostly confined to axilla, pubic and perineal regions and areola of the nipples Ø They develop from the stratum germinativum of the epidermis that give rise to hair follicles Ø The ducts of these glands do not open into the skin surface Ø They open into the upper part of hair follicles superficial to the opening of sebaceous glands Ø They secrete during puberty

Mammary Glands Ø They are a modified and highly specialized type of sweat glands Ø Mammary buds begin to develop during the 6 th week as a solid downgrowths of the epidermis into the underlying mesenchyme Ø These changes occur due to the inductive influence from the mesenchyme Ø The mammary buds develop as downgrowths from thickened mammary crest or ridges

Mammary Glands Ø Mammary crest are thickened strips of ectoderm extending from the axillary to the inguinal regions Ø The mammary crests appear during the 4 th week but normally persist in humans only in pectoral area Ø Each primary bud soon gives rise to several secondary mammary buds that develop into lactiferous ducts and their branches

Mammary Glands Ø Canalization of these buds is induced by placental sex hormones entering the fetal circulation Ø By the term, 15 to 20 lactiferous ducts are formed Ø The fibrous connective tissue and fat of the mammary gland develop from the surrounding mesenchyme

Mammary Glands Ø During the late fetal period the epidermis at the site of origin of the mammary gland becomes depressed forming a shallow pit Ø The nipples are poorly formed and depressed in newborn infants Ø Soon after birth the nipples usually rise from the mammary pits Ø The smooth muscle fibers of the nipple and areola differentiate from surrounding mesenchymal cells

Mammary Glands Ø The rudimentary mammary glands of newborn males and females are identical Ø Some secretion, often called witch’s milk may be produced Ø This is caused by maternal hormones passing through the placental membrane into the fetal circulation Ø Only main lactiferous ducts are formed at birth and mammary glands remain underdeveloped until puberty

Mammary Glands Ø In females the breasts enlarge rapidly during puberty due to development of mammary glands and accumulation of fat Ø Growth of the duct system also occurs because of the raised levels of circulating estrogens Ø Progestogens, prolactin, corticoids and growth hormone also play a role Ø If pregnancy occurs, the mammary glands complete their development owing to the raised estrogen and progesterone level

Mammary Glands Ø The intralobular ducts undergo rapid development forming buds that become alveoli Ø The breasts become hemispherical in shape largely because of fat deposition Ø Full development occurs at about 20 years

Gynecomastia Ø It refers to excessive development of the male mammary tissue Ø The rudimentary mammary glands in males normally undergo no postnatal development Ø It occurs in most newborn males because of stimulation of the glandular tissue by maternal sex hormones Ø The effect disappears in few weeks

Gynecomastia Ø During midpuberty about two-thirds of boys develop varying degree of hyperplasia of breasts Ø The subareolar hyperplasia may persist for a few months to 2 years Ø A decreased ratio of testosterone to estradiol is found in boys with gynecomastia Ø About 80% of males with Klinefelter syndrome have gynecomastia

Polythelia Ø An extra nipple occurs in about 1% of females Ø It usually develops just inferior to the normal breast Ø It is also relatively common in males Ø Often they are mistaken for moles Ø Less commonly they appear in the axillary or abdominal regions of females Ø In these positions the nipples develop from extra mammary buds that develop along the mammary crests

Polythelia Ø It usually becomes obvious in women when pregnancy occurs Ø About one-third of affected persons have two extra nipples Ø Supernumerary mammary tissue very rarely occurs in a location other than along the course of the mammary crests Ø It probably develops from tissue that was displaced from these crests

Inverted Nipples Ø Sometimes nipples fail to elevate above the skin surface Ø They remain in their newborn location Ø Inverted nipples may make breast feeding of an infant difficult Ø A special exercise can be used to prepare the nipple for feeding an infant