Skin Anatomy PDF

Skin 1  Skin Skin is considered an organ because it consists of different tissues that are joined to perform a specific activity. – One of the largest organs in the body. – Average adult - 3,000 in2 (2 m2) and weighs about 4.5-5 kg (10-11 lbs.). Rough...

Skin 1  Skin Skin is considered an organ because it consists of different tissues that are joined to perform a specific activity. – One of the largest organs in the body. – Average adult - 3,000 in2 (2 m2) and weighs about 4.5-5 kg (10-11 lbs.). Roughly 16% of body weight. 2  Skin Structure of Skin: – 1. EPIDERMIS - outer, thinner portion, composed of EPITHELIUM (Epithelial tissue). – 2. DERMIS - inner, thicker, connective tissue part. – Beneath the dermis is a second connective tissue layer rich in adipose tissue called the HYPODERMIS. – Appendages of the skin develop from epidermis and therefore are of epithelial 3 4 5 6 7 8 9  Epidermis The epidermis is composed of keratinized stratified squamous epithelium and contains 4 principal types of cells: – 1. KERATINOCYTES - about 90% of the epidermis. Contain KERATIN - waterproofs and protects skin. – 2. MELANOCYTES - contains MELANIN, a pigment which contributes to skin color. 10 11 12 13 14 15 Melanocytes 16 17 18  Epidermis 3. LANGERHANS CELLS - involved in the immune response. – Clear antigens from the integument. – Found in hair follicles, lymph nodes, and glandular ducts. 4. MERKEL CELL – believed to function in the sensation of TOUCH. 19 20 21  Epidermis The epithelium lacks blood and lymph vessels. – Receives oxygen and nutrients via diffusion from the dermis. Epidermis does contain sensory nerve endings. – However, the bulk of integumentary innervation occurs in the dermis. 22 23 24  Epidermis – 1. STRATUM BASALE - a single layer of columnar cells, capable of CONTINUED CELL DIVISION. As these cells multiply, they push up toward the surface and become part of the more superficial layers. – 2. STRATUM SPINOSUM - 8 to 10 rows of polyhedral (many-sided) cells that fit closely together. “spinosum” – prickly Beginning of keratin deposition. 25 26 27 28 29  Epidermis 3. STRATUM GRANULOSUM - 2 or 3 rows of flattened cells with nuclei that are in various stages of degeneration. – Highest rate of kerainization. – No mitotic activity in this layer or any superficial to it. 30 31 32 33  Epidermis 4. STRATUM LUCIDUM - Pronounced in the thick skin of the palms/soles. Consists of 3-4 rows of clear, flat, dead cells. – “lucid” - clear 34 35  Epidermis 5. STRATUM CORNEUM - 25-30 rows of flat, dead cells containing keratin. – The stratum corneum is continuously shed and replaced. – It functions as a barrier against light and heat waves, bacteria, and chemicals. – Thickness varies based on the degree of mechanical abuse. 36 37 38 39 40 41 42  Dermis The dermis is composed of connective tissue containing collagenous and elastic fibers. Many blood vessels, nerves, glands, and hair follicles are also present. The upper region of the dermis is called the PAPILLARY REGION - its surface is greatly increased by small fingerlike projections called DERMAL PAPILLAE. 43 44 45  Dermis Papillary layer – Most superficial, just below the epidermis. – 20% of dermis – Loose connective tissue. Reticular layer – Deeper portion of the dermis, just above hypodermis. – 80% of dermis – Dense irregular connective tissue. 46 47 48 49  Dermis Some dermal papillae contain MEISSNER’S CORPUSCLES - nerve endings sensitive to light TOUCH. The dermis also contains nerve endings called PACINIAN CORPUSCLES, sensitive to deep PRESSURE. 50 51 52 53 54 55 56 57 58 59 60  Hypodermis Layer of loose connective tissue, rich in adipocytes, located immediately deep to the skin. – Panniculus adiposis – massively infiltrated with adipocytes. – Panniculus carnosus – contains sheets of skeletal muscle. Well developed in mammals except humans. In humans, mostly made up of platysma muscle in the anterior neck. 61 62 63 64 65  Hypodermis Varies in thickness throughout the body in response to nutritional levels. Connected to underlying structures such as the deep fascia, aponeuroses, or periosteum. Functions: – Provides support for the above lying skin. – Stores fat – Cushions and insulates the body. 66  Epidermal Derivatives Some structures that are derived from embryonic epidermis - hair, glands, nails – perform functions that are necessary and often vital. Ex. Hair and nails protect the body and sweat glands help regulate body temperature. 67  Hair HAIRS = PILI – Filamentous strands of fused keratinocytes projecting from the surface of the skin. – Located in FOLLICLES. Epidermal invaginations into the dermis and/or hypodermis. – Growths of the epidermis that are variously distributed over the body. – Primary function is PROTECTION. 68 69 70 71  Hair Hair Structure – At the base of the hair follicle is an indentation of highly vascularized connective tissue known as the dermal papillae. If this is destroyed, the hair cannot be replaced. – Keratin of hair is different than keratin of epidermis. (hard keratin). 72 73 74 75 76  Hair Hair Structure – Each hair consists of a column of dead, keratinized cells compressed together. – SHAFT - superficial portion, most projects above the surface of the skin. – ROOT - part of the hair deep to the surface. Penetrates into the dermis, possibly into the subcutaneous layer. 77 78  Hair Hair Structure – The Shaft and Root have 3 main parts: MEDULLA - inner portion. CORTEX - middle, forms the major part of the shaft. CUTICLE - outermost layers, consists of a single layer of thin, flat cells. 79 80 81 82  Hair Hair Structure – Surrounding the ROOT is the HAIR FOLLICLE which is made up of 2 layers: EXTERNAL ROOT SHEATH – downward continuation of the EPIDERMIS. INTERNAL ROOT SHEATH – At the base of each hair follicle is an enlarged BULB. It contains blood vessels that nourish growing hair. 83 84 85 86 87 88  Hair SEBACEOUS (oil) GLANDS and bundles of smooth muscle are associated with hairs. Smooth muscle called ARRECTOR PILI muscles are associated with hairs. – These may contract and make hair “stand on end”. – When this muscle contracts it may also result in “goosebumps” because skin around the shaft forms slight elevations. 89 90 91 92 Arrector Pili Muscle 93 94 95  Nails Nails are plates of tightly packed, keratinized cells of the epidermis. Nails consist of: – NAIL BODY - the visible part. – FREE EDGE - part that may extend past the distal end of the digit. – NAIL ROOT - portion that is buried in a fold of skin. 96 97 98 99  Nails Why do nails appear pink? – Because of the blood flowing to underlying capillaries in the dermis. – At the proximal end of the nail, it appears white because there is no underlying vascular supply. This is called the LUNULA. 100 101  Nails EPONYCHIUM = CUTICLE – A narrow band of epidermis that extends from the margin of the nail wall. The epithelium deep to the nail root is called the NAIL MATRIX. 102 Nail 103 104 105 106  Sudoriferous Glands Sweat Glands – Eccrine – Most numerous and widely distributed. – Absent in only a few areas Lips, glans penis, glans clitoris, labia minora and beneath nails. – Highest density in palms and soles of feet. – Primary function is thermoregulation and slightly in removal of wastes. 107 108 109 110 111  Sudoriferous Glands Sweat Glands – Eccrine – Simple coiled tubular glands – Shallow and Deep Eccrine Glands Based on where secretory part is located. – Duct is composed of two layered stratified cuboidal epithelium. – Secretory part is composed of pyramidal shaped cells. 112 Sebaceous Gland Sweat Gland 113 114 115  Sudoriferous Glands Sweat Glands – Apocrine – Much less widely distributed. – Primarily in the axillary and perianal areas. – Associated with hair follicles. – Become active with the onset of puberty. – Much larger lumen. 116 117  Sudoriferous Glands Sweat Glands – Apocrine – Also coiled tubular glands. – Secretory portion is much larger than in eccrine glands. – Duct will run parallel to a hair follicle. – Typically will open into the hair follicle above the opening point of a sebaceous gland. 118 119 120  Sudoriferous Glands Sweat Glands – Apocrine – Duct is two layered stratified cuboidal epithelium. – Secretory portion is composed of a single layer of cuboidal or columnar shaped cells resting on a basement membrane. – Product is secreted by merocrine, apocrine, and holocrine mechanisms. – Thermoregulation, removal of wastes, and may play a role in release of 121 122  Sudoriferous Glands Sweat Glands – Apocrine – Specialized apocrine glands Ceruminous glands – lining the external auditory canal. – Produce cerumen – ear wax. Mammary glands 123 124  Sebaceous Glands Sebaceous glands are widely distributed, found on all body surfaces except for the soles and palms. – Simple branched acinar glands. – Duct is stratified squamous epithelium, keritanized. Continuous with epithelium of the epidermis and/or hair follicle. 125 126 Sebaceous Gland Sweat Gland 127  Sebaceous Glands Secretory portion consists of acinar cells in various stages of differentiation. – As lipid amount increases in cells, they die. – Holocrine secretion. – Product is sebum. May lubricate and soften hairs and prevent them from drying out. May also contain some pheromones. 128 129 130 131 132 133 134 135