General Histology Lecture 10 Integumentary System 2 PDF

General Histology Lecture 10 Integumentary system 2 Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS  Lecture map Epidermis (continue) Thick versus thin skin Cells in epidermis Sensation in skin Mech...

General Histology Lecture 10 Integumentary system 2 Reference : Anthony L. MESCHER, Jonquiere's Basic Histology TEXT & ATLAS  Lecture map Epidermis (continue) Thick versus thin skin Cells in epidermis Sensation in skin Mechanoreceptors The Pilo-sebaceous Apparatus Glands of skin Layers of skin  Thick vs. Thin Skin Thick skin is present on palms and soles Epidermis has five cell layers + thick keratin layer. Hair follicles and sebaceous glands are NOT present. Thin skin is found everywhere else. Epidermis has no stratum lucidum, and the stratum granulosum and corneum are much thinner. May contain hair follicles and sebaceous glands. Melanin and skin color The number of melanocytes per unit area varies from one part of the body to another but is independent of race. Differences in skin color are due to differing numbers of melanin granules in melanocytes! Melanin granules accumulate above keratinocyte nuclei to protect genetic material from UV damage. Smart! Langerhans Cells and Merkel Cells Langerhans cells A type of macrophage. Arise in bone marrow, migrate to stratum spinosum. Eat stuff (like bugs), present antigen to T cells. Merkel cells Present in stratum basale. Function as touch receptors.  Lecture map Epidermis (continue) Thick versus thin skin Cells in epidermis Sensation in skin Mechanoreceptors The Pilo-sebaceous Apparatus Glands of skin  Mechanoreceptors Mechanoreceptors are a type of somatosensory receptors which relay extracellular stimulus to intracellular signal transduction through mechanically gated ion channels. The external stimuli are usually in the form of touch, pressure, stretching, sound waves, and motion. Mechanoreceptors are present in the superficial as well as the deeper layer of skin and near bone.  Mechanoreceptors These receptors are either encapsulated or un-encapsulated, and the free nerve endings are usually un-encapsulated dendrite. There are four major categories of tactile mechanoreceptors: 1) Meissner’s corpuscles 2) Pacinian corpuscles 3) Merkel’s disks 4) Ruffini endings  Mechanoreceptors 1. Meissner’s corpuscle Sensitive to light touch Consists of an unmyelinated axon meandering back and forth between flattened Schwann cells. 2. Pacinian corpuscle Sensitive to vibration and pressure. Consists of unmyelinated nerve terminal surrounded by layers of fibroblasts.  Mechanoreceptors 3. Merkel’s disks Un-encapsulated nerve endings in the epidermis. There is a high density in the fingertips, lips, and external genitalia. 4. Ruffini’s corpuscles Slow-adapting, encapsulated mechanoreceptors deep in the skin, ligaments, and tendons Ruffini corpuscles primarily sense skin stretching, movement, and finger position. Pacinian corpuscle: sensitive to vibration, pressure Meissner’s corpuscle: sensitive to light touch  The Pilosebaceous Apparatus Hairs: hair follicle and shaft Sebaceous glands and ducts: empty into hair follicle Arrector pili muscles: cause erection of hair shaft Hairs and sebaceous glands derive from ectoderm Pilosebaceous apparatus  The hair follicle is a tubular invagination of the epidermis extending deep into the dermis. The hair shaft arises from the base of the follicle. The dermal papilla The hair bulb is basically contains numerous just the base of the hair capillaries. It maintains follicle. the viability of the hair follicle. Main parts of the hair follicle  Skin glands Three types: sebaceous glands, eccrine (merocrine) sweat glands, and apocrine sweat glands. Arise from ectoderm. Secretory portion of glands resides in the dermis. Three different types of secretion: holocrine, merocrine, and apocrine. Types of glands  Sebaceous glands Present everywhere except palms and soles. Secretory portion: peripheral, flattened undifferentiated cells. Central cells are large with foamy cytoplasm containing lipids. Cells burst, releasing sebum (holocrine secretion). Duct empties into hair follicle. Become functional at puberty. Sebaceous gland Eccrine (Merocrine) Sweat Glands Secretory portion has three cell types: Clear cells (contain glycogen, produce a watery substance) Darker cells (produce a proteinaceous substance) Myoepithelial cells (surround gland) Duct is lined by simple cuboidal epithelium and opens onto skin surface.  Secretory cells: Clear Darker Myoepithelial cells Eccrine sweat glands and ducts  Apocrine Sweat Glands Located only in axilla, areola of breast, and anal canal. Have larger ducts and secretory units than eccrine sweat glands. Ducts open into hair follicles. Apocrine secretion is viscous and contains proteins, carbohydrates and lipids. Apocrine sweat glands