Integumentary System. Integumentary System

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Evan Erick Jackson
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1 Integumentary system consists of the the skin and specialized organs Skin is the largest organ of the body. Integument contains several organs fingernails (or claws), hairs and feathers sebaceous, sweat and oil glands Sensory organs 1 Functions Containment -- Prevents loss of body fluid. Protection -- Resists abrasion and penetration, and blocks the entry of foreign material. Immunological defense -- Immune cells defend against pathogens Wound healing -- regenerating after damage. Sensation -- several modalities of tactile information; variety of receptors. Thermoregulation -- Controls the transfer of heat Communication -- Visual and pheromonal signals 2

2 Two layers: 1- Epidermis: outer layer of the skin; consists of stratified squamous epithelium. 2-Dermis: inner layer of the skin; generally composed of dense irregular CT. Root word: derm:= skin Hypodermic layer hypo: under; hypodermic: under the skin Not part of the skin itself. Composed of loose (areolar) CT Can be fibrous or adipose 3 Epidermis: general features Primarily protective; tough, relatively impermeable, and regenerative Keratinized stratified squamous epithelium Keratinocyte: main cell type. Quality of the epidermis changes in different body regions Thick: up to 1.5 mm Palms and soles of feet No hair follicles and sebaceous glands. well-developed stratum corneum. Thin: 0.5mm over most of the body Only a few cell layers. Can be a thin as 0.1 mm; eyelids 4

3 Epidermal basal surface is very irregular with dermal papillae projecting up some papillae may be obliquely or cross-sectioned Creates firm attachment to the dermis 5 Layers of the epidermis Stratum corneum (C). Cells of the cornified layer are dead, eventually sloughed off. Stratum granulosum (G). Cells accumulate keratohyalin; darkly stained granules. Diagnostic for keratinized stratified squamous epithelium. Stratum spinosum (S). Prickle-cells ; linked together by desmosomes ( spines"). Cells pushed up by new cells below Stratum basale / stratum germinativum (B). Attached to the BM by hemidesmosomes. Basal cell divides; daughters migrates upward 6

4 Layers of the epidermis lumen 7 Mostly keratinocytes Have numerous desmosomes. Extend between keratinocytes. Intercellular space; nutrients diffusion from dermis into epidermis. Stratum basale keratinocytes can undergo mitosis. Pushes cells through the stratum spinosum. Keratinocytes near the lumenal surface; contain intracellular keratin and secrete a waxy material into the intercellular space visible in the stratum granulosum, Keratinocytes seal off the intercellular channels; eventually die and form the stratum corneum,. Surface cells are sloughed off. Epidermis above the basal layer is replaced within two weeks. 8

5 Melanocytes Manufacture the pigment melanin. Small cells, usually in or near the stratum basale. Thin cytoplasmic processes (not visible with H&E)) extend between nearby keratinocytes Transfer melanosomes (melanin granules) into keratinocytes. Most pigment-containing cells in the epidermis are keratinocytes not melanocytes. 9 Dermis Consists of dense fibrous CT and fibroblasts Main component is collagen. Can recognize two regions Papillary layer Next to the epidermis consists of small, fine collagen fibers. named after dermal papillae Reticular layer beneath the papillary layer consists of larger, coarsely textured collagen fibers lots of reticular fibers (not visible) 10

6 Dermis Dermis has several functions. Mechanical support; collagen and elastic fibers Dermal GS allows diffusion of nutrients and wastes to and from integumentary organs Immune defense Capable of response to injury; inflammation, then tissue repair. Integumentary organs are present; sweat glands, hair follicles blood vessels and nerve endings. Dermis transitions into hypodermis no sharp distinct boundary. 11 Vascularization moderate to moderately high immediately under the epidermis. epidermis is more metabolically active than the dermis, has a higher need for 0 2, nutrients, etc. Major role of the sub-epidermal vascularization Thermoregulation regulating body heat loss via control of blood flow through that capillary bed. tissues of the skin can survive low blood flow for hours for conservation of body heat 12

7 Special structures: Sweat glands Simple tubular glands. Secretory portion is in the dermis; formed into a tangle of tubes. Comprised of a simple cuboidal epithelium, with myoepithelial cells expel sweat by contraction ducts extends through the dermis and the epidermis. consists of two-layered stratified cuboidal epithelium. usually stained more intensely than those of the secretory portion of the tubule. 13 Special structures: Sweat glands Thermoregulation. Influence water and ion balance. Primary function for sweating is evaporative cooling Also involved in salt reabsorption and regulation. 14

8 15 Special structures: Sweat glands Two types of sweat glands Eccrine Most common sweat glands Secrete onto epidermal surface Large numbers in palms and soles Produce a clear, odorless sweat; mostly water and NaCl Starts in dermis Apocrine Eccrine sweat gland Axillary, pubic, and perianal regions. Gland starts in subcutaneous fat Secrete into hair follicles. Secrete an oily (and eventually smelly) compound that acts as a pheromone, in most mammals. Apocrine sweat gland 16

9 Hair follicles Tubular invaginations of epidermis stratified squamous epithelium. Similar pattern of cell growth and change as in the epidermis. Produces a shaft of dead keratinized cells. Pilosebaceous apparatus Follicle + sebaceous glands + nerve endings + smooth muscle 17 Histological components of hair follicle External root sheath (ERS) epidermal tube; full length of follicle; 2-3 cells thick; very small cuboidal. External C.T. sheath (ECT) thin layer of dense CT; around external root sheath and hair bulb. Internal root sheath (IRS) epidermal layer next to external root sheath, in deeper part of follicle only; cells larger than those of external root sheath. IRS ERS ECT ECT ERS Hair Hair IRS 18

10 Hair bulb cup-shaped end of epidermal part inner wall cells produce the hair by mitosis Melanocytes typically abundant melanin granules are released into the epithelial cells and incorporated into the hair shaft Cells of deeper part of the hair follicle are alive near skin surface, cells die hair extending out from the skin surface is dead cells only. 19 Hair typically has two regions differing in cell size and arrangement, and in thickness: Hair shaft (medulla) inner part of hair; composed of larger cells Hair cuticle (cortex) outer part of hair--usually relatively thin 20

11 Sebaceous gland Sebaceous gland is an epithelial extension off side of upper part of the hair follicle. Produces and secretes an oil: sebum provides softness to the stratum corneum Oil is secreted to the lumen of the hair follicle; coats and waterproofs the hair. Epithelial cells are very large and moderately eosinophilic; granular cytoplasm. 21 Erector pili (pilium: hair) Very small, thin smooth muscle origin is at the basement membrane of the epidermis insertion is on the external CT sheath of the hair bulb. Function elevates the angle of hair follicle and hair shaft extending out from surface of epidermis 22

12 Two main functions or purposes system relatively vestigial in humans Increased thermal insulation by fur layer, for conserving body heat thermoregulation (probably the fundamental function). Erector pili contraction in human skin due to exposure to cold produces "goose bumps". Increasing fur thickness increases apparent size of body for social signaling in social interactions 23 Sensory nerve endings variety of modalities pressure, vibration, heat, cold, itch, pain Meissner's corpuscles encapsulated endings in dermal papillae, common in palmar and plantar skin, especially in fingertips. Pacinian corpuscles located deeper in dermis simple nerve endings encapsulated by multilamellar, ovoid structures small onions Respond to deep pressure. Meissner's corpuscles 24

Two main classes: Epithelial Connective (synovial) Epithelial. Cutaneous Mucous Serous

Two main classes: Epithelial Connective (synovial) Epithelial Cutaneous Mucous Serous Epithelial Membranes = sheet of epithelia + connective tissue base 1. Cutaneous membrane: outer skin layer (stratified