Developmental Biology PDF

DEVELOPMENTAL BIOLOGY BIOF7_LECTURE 1ST SEMESTER | LANI TABANGAY | MONDAY/FRIDAY (7:00-8:30) DEVELOPMENT OF INTEGUMENTARY SYSTEM LEARNING OUTCOMES A. Describe the development of epidermis, dermis, and the...

DEVELOPMENTAL BIOLOGY BIOF7_LECTURE 1ST SEMESTER | LANI TABANGAY | MONDAY/FRIDAY (7:00-8:30) DEVELOPMENT OF INTEGUMENTARY SYSTEM LEARNING OUTCOMES A. Describe the development of epidermis, dermis, and their associated structures. B. Identify conditions brought about by abnormal Proliferation of cells in the basal layer, a third, development of integumentary system intermediate zone is formed. Additional Information Why does hair hurts when pulled? The sharp pain might seem like it's coming from your hair itself, but it's actually coming from nerves in your scalp. A SKIN/INTEGUMENT Largest organ in the body and has a dual origin: (1) superficial layer, the epidermis, develops from the surface ectoderm. (2) deep layer, the dermis, develops from the underlying mesenchyme. Dermatology is the study of skin. End of the 4th month, the epidermis acquires its definitive arrangement and four layers can be distinguished. The horny layer, forming the tough scale-like surface of Additional Information the epidermis, made up of closely packed dead cells The layers of the epidermis, from deepest to most containing keratin. superficial, are the stratum basale, stratum The granular layer contains small keratohyalin granules spinosum, stratum granulosum, stratum lucidum, in its cells. and stratum corneum. The spinous layer consists of large polyhedral cells The dermis consists of two connective tissue layers: containing fine tonofibrils. the thinner, upper papillary layer, composed of loose The germinative layer or basal layer is responsible for connective tissue and responsible for fingerprints, and production of new cells. the thicker, deeper reticular layer, which is less The corium is the dermis. cellular and responsible for stretchmarks. Additional Information A1 EPIDERMIS Keratin is a protein that forms hair, nails, and the skin's outer layer, and it also makes hair waterproof. Tonofibrils are cytoplasmic structures that converge at the desmosomes and are anchored in the cytoskeleton. Cytoskeleton helps cells maintain their shape Initially, the embryo is covered by a single layer of and internal organization, and it also provides ectodermal cells. mechanical support that enables cells to carry out essential functions like division and movement. A1.1 SKIN PIGMENTATION End of the 2nd month, release of a layer of flattened cells, Melanoblasts originate from the neural crest and migrate the periderm, or epitrichium, laid down on the surface. through the stratum basale then differentiate to It serves as the coat body of the embryo. melanocytes. It is replaced continuously until the 21 st weeks of Melanosomes is the organelle present in the melanocyte gestation. that synthesize melanin. The shed periderm is found in the amniotic fluid. Melanin is a substance present in the skin that produces skin pigment. PAGE 1 ROSE MARIE ESTRADA | BIO-3A | MODULE 3  Hair consists of: A1.2 GROWTH FACTORS WHICH STIMULATE (1) the hair shaft, the part that sticks out from the THE DEVELOPMENT OF EPIDERMIS skin’s surface. (2) the root, a softened thickened bulb at the base of Transforming growth factor-α (TGF-α) the hair. o Made by stimulates their own division and acts as an (3) the follicle, a sac-like pit in the skin from which the autocrine growth factor. hair grows. o Autocrine is a signaling in which a cell produces a Each has three layers: substance that acts on itself, to regulate its own (1) the medulla at the center, which is soft. growth. (2) the cortex, which surrounds the medulla and is the Keratinocyte growth factor (KGF) main part of the hair. o Also known as fibroblast growth factor 7, is a (3) the cuticle, the hard outer layer that protects the paracrine factor produced by the fibroblasts of the shaft. underlying dermis. The matrix, a part of the hair follicle, is where matrix o Paracrine is a signaling where a cell produces a keratinocytes proliferate to form the hair shaft, while substance that acts on nearby cells. melanocytes mixed among these cells provide color to o It is received by the basal cells of the epidermis, the hair shaft. where it is thought to regulate their proliferation. A2 DERMIS B1 HAIR Derived from mesenchyme that has three sources: (1) lateral plate mesoderm supplying cells for dermis in the limbs and body wall. (2) paraxial mesoderm supplying cells for dermis in the back. (3) neural crest cells supplying cells for dermis in the face and neck. During the 3rd and 4th months, the corium forms many irregular papillary structures, the dermal papillae, which project upward into the epidermis. Contain a small capillary or sensory nerve ending. The second layer of the dermis, subcorium, contains a large amount of fatty tissue. Vernix caseosa or birthing custard o At birth, the skin is covered by a whitish paste formed by secretions from sebaceous glands and degenerated epidermal cells and hairs. o It protects the skin of the newborn against the macerating action of amniotic fluid. (A) Hairs begin development as solid epidermal proliferations from the generative layer that penetrates B HAIR FOLLICLE the underlying dermis. (B, C) At their terminal ends, hair buds invaginate to form hair papillae, which are rapidly filled with mesoderm containing in which blood vessels and nerve endings develop. (B, C) Soon, cells in the center of the hair buds become spindle-shaped and keratinized, forming the hair shaft, while peripheral cells become cuboidal, giving rise to the epithelial hair sheath. (C) Dermal root sheath is formed by the surrounding mesenchyme. (C) A small smooth muscle, the arrector pili, derived from mesenchyme, is typically attached to the dermal root sheath. (C) Continuous proliferation of epithelial cells at the base of the shaft pushes the hair upward, and by the end of the 3rd month, the first hairs appear on the surface in the region of the eyebrow and upper lip. (C) The first hair that appears, lanugo hair, is shed at about the time of birth and is later replaced by coarser hairs arising from new hair follicles. (C) Lanugo, the embryonic hair, is replaced by vellus (fine, thin hair) and terminal hair found on the scalp, axilla, and genitalia. (C) The epithelial wall of the hair follicle usually shows a small bud penetrating the surrounding mesoderm. PAGE 2 ROSE MARIE ESTRADA | BIO-3A | MODULE 3  (C) The epithelial wall of the hair follicle forms small buds D SWEAT GLANDS that penetrate the surrounding mesoderm, and cells from these buds give rise to sebaceous glands. Sweat glands are found across the entire surface of the (C) Cells from the central region of the gland degenerate, body and play a role in lubricating the skin, temperature forming a fat-like substance (sebum) secreted into the regulation, salt and water balance and are essential for hair follicle, and from there, it reaches the skin. the maintenance of normal physiology. Eccrine Glands o Most common and are found all over the surface of the body. B2 HAIR GROWTH OCCURS IN CYCLES CONSISTING OF THREE PHASES o They are most numerous on the palm of the hands and sole of the feet. Apocrine Glands Anagen (growth phase) o Common in armpits and groin area. o Cells of the germinative epithelium at the base of the follicle rapidly proliferate and differentiate to o Sweat from the apocrine glands does not evaporate as quickly and can lead to foul body odor. produce the lengthening hair fiber and layers of the o Apocrine sweat is often a result of emotional stress inner root sheath. or anxiety. Catagen (transitional phase) o The growth slows down and the follicle shrinks. Telogen (resting phase) D1 ECCRINE SWEAT GLANDS o Hairs do not grow and do not usually fall out and new hairs start to form in follicles that have just released Form in the skin over most parts of the body beginning as hairs during the catagen phase. buds from the germinative layer of the epidermis. Exogen (shedding phase) These buds grow into the dermis, and their end coils to o The extension of telogen stage and hair is shed form form the secretory parts of the glands. the scalp. Smooth muscle cells associated with the glands also develop from the epidermal buds. These glands function by merocrine mechanisms (exocytosis) and are involved in temperature control. D2 APOCRINE SWEAT GLANDS Develop anywhere there is body hair, including the face, axillae, and pubic region. Begin to develop during puberty and arise from the same epidermal buds that produce hair follicles. These sweat glands open onto hair follicles onto hair follicles instead of skin. C NAILS The sweat produced contains lipids, proteins, and pheromones, and odor is due to bacteria that break down The nail is composed of seven parts: these products. (1) nail plate is the hard keratinized structure that forms the visible part of the nail. These glands classified as apocrine because a portion of (2) nail folds (groove) is the skin surrounding and the secretory cells is shed and incorporated into the supporting the nail on three sides. secretion. (3) nail bed (sterile matrix) is the pinkish tissue underneath the nail plate. E MAMMARY GLANDS (4) germinal matrix is the base of the nail bed. (5) hyponychium is the skin beneath the free edge of the nail. (6) cuticle (eponychium) is the thin layer of tissue covering the base of the nail plate. (7) lunula is the half-moon-shaped area at the base of the nail, representing the visible part of the nail’s root. During week 10 of human development, the fetus develops its fingernails first, which are followed by the ten toenails (week 14), just as the arms and hands develop before the legs and feet. Originally, the nail fields appear at the tips of the digits and then migrate toward the dorsal surfaces. While the surrounding cells form the nail folds, keratinization of the proximal nail folds forms the nail plates. By week 32, the fingernails, and by week 36, toenails, reach the tips of the digits. Modified sweat glands and first appear as bilateral bands of thickened epidermis called the mammary lines and Often the stage of nail growth of a baby is utilized as an mammary ridges. indicator of the degree of prematurity. PAGE 3 ROSE MARIE ESTRADA | BIO-3A | MODULE 3  In a 7-week embryo, these lines extend on each side of the ABNORMALITIES OF HAIR DISTRIBUTION body from the base of the forelimb to the region of the F3 hindlimb. Congenital atrichia Although a major part of each mammary line disappears o Congenital atrichia is a rare genetic disorder caused shortly after it forms, a small portion in the thoracic by mutations in the human hairless (HR) gene on region persists and penetrates the underlying chromosome 8p22. mesenchyme. o It leads to the loss of scalp hair within the first six It forms 16 to 24 sprouts, which in turn give rise to small, months of life, with no regrowth afterward. solid buds. o It may also have sparse or absent eyebrow, eyelash, By the end of prenatal life, the epithelial sprouts are and body hair, with limited pubic and axillary hair canalized to form the lactiferous ducts, which initially growth. open into a small epithelial pit. Hypertrichosis Shortly after birth, the pit is transformed into the nipple o It is a condition characterized by excessive hair by proliferation of the underlying mesenchyme. growth, either localized or covering the entire body. At birth, lactiferous ducts have no alveoli and therefore o It results from an unusual abundance of hair follicles. no secretory apparatus. o The SOX3 gene, which plays a role in hair growth. At puberty, increased estrogen and progesterone stimulate branching from the ducts to form alveoli and secretory cells. F4 ABNORMALITIES OF MAMMARY GLAND Polythelia F CLINICAL CORRELATES o Formation of accessory nipple from the persistence of fragments of the mammary line. Polymastia Additional Information o It occurs when a remnant of the mammary line Genodermatosis refer to skin condition that is develops into a complete breast. associated with genetics. Inverted nipple o Lactiferous ducts open into the original epithelial pit that has failed to evert. F1 ABNORMALITIES OF MELANOCYTE FUNCTION Piebaldism o Rare inherited condition characterized by the absence of melanocytes in certain areas of the skin and hair, resulting in a white forelock. o Mutations of the c-Kit gene, which affects the differentiation and migration of melanoblasts from neural crest during the embryonic life. Waardenburg syndrome o Waardenburg syndrome is a genetic disorder caused by mutations in the PAX3 gene. o Characterized by distinctive features such as white patches of skin and hair, heterochromia irides, a square face, a wide nasal bridge, and often deafness. o These symptoms result from faulty migration or proliferation of neural crest cells. Albinism o Reduced or absence of pigmentation in the skin, hair, and eyes. o Abnormalities of melanin synthesis or processing. F2 KERATINIZATION DISORDERS Harlequin Type Ichthyosis o Excessive keratinization of the skin. o Infants with this condition, born prematurely with very hard, thick skin covering most of their bodies. o The skin forms large, diamond-shaped plates that are separated by deep cracks (fissures). o These skin abnormalities affect the shape of the eyelids, nose, mouth, and ears, and limit movement of the arms and legs. o Restricted movement of the chest can lead to breathing difficulties and respiratory failure in babies with harlequin ichthyosis. o Affected infants also have feeding problems. PAGE 4 ROSE MARIE ESTRADA | BIO-3A | MODULE 3