Systemic Pathology VET 2133 PDF

SYSTEMIC PATHOLOGY VET 2133 1  Structure of the Integumentary System Normal Structure of the skin ▪The skin is considered the largest organ of the body ▪The skin has haired and hairless portion  The skin consist of the following components 1-EPIDERMIS...

SYSTEMIC PATHOLOGY VET 2133 1  Structure of the Integumentary System Normal Structure of the skin ▪The skin is considered the largest organ of the body ▪The skin has haired and hairless portion  The skin consist of the following components 1-EPIDERMIS 2-DERMIS composed of : composed of several cell types: fibers (collagen, reticulin, elastin), keratinocytes, Ground substance (glycosaminoglycans, melanocytes, proteoglycans), Langerhans cells, Cells (fibroblasts, mast cells, histiocytes, Merkel cells. smooth muscle), Vessels (blood, lymph), Nerves. 3 3-ADNEXA (APPENDAGES OF THE SKIN) 4-HYPODERMIS (SUBCUTIS) composed of : consists of : hair, lipocytes (panniculus adiposus, digital cushion), glands (sebaceous, apocrine, eccrine; also circumanal, tail, anal), fibers (collagen, elastin), claws / nails vessels, and hooves. nerves. 4 Skin Cells: ▪The keratinocytes: produce keratin ▪Melanocytes: Produce melanin pigment ▪Langerhans’ cells: immune protection of the skin ▪Merkel cells: Present in haired and hairless skin 5  General functions of the integumentary (Skin) system 1. Barriers Provides chemical barriers which reduces the growth rate of bacteria on its surface. physical barrier to prevents risks for dehydration (loss of water, and electrolytes) 2. Cutaneous sensation: Sensory perception such as touch, temperature, pressure, pain, itch 3. Body temperature regulation: Thermoregulation 4.Metabolic function: Production of vitamin D production of collagenase Immunoregulation Indicator of general health / internal disease. Storage: water, electrolytes, vitamins, fat, carbohydrates, proteins 5.Blood reservoir: The dermal vessels boost general circulation 6 ❑Response of skin to injury Portal of Entry into the Skin 8 Factors cause injury of the skin 1. External factors:Exogenous factors 2. Internal factors: Endogenous factors Histopathology and Complementary tests: biopsy, scraping, blood test often required to determine the etiology 9 ❖Gross morphology of skin lesions ❖ Gross morphology of skin lesions 1. Primary lesions: ✓ are the direct result of the underlying disease process ✓ most important diagnostically 2. Secondary lesions ✓ evolve from primary lesions (via self-trauma, altered keratinization, etc) ✓ less important diagnostically Primary Lesions Macule: area of altered skin color (discoloration), up to 1 cm in diameter lentigo = a benign heritable condition of hyperpigmentation; due to focal increase in number of melanocytes Papule: a small (< 1 cm diameter) circumscribed solid elevation of the skin Plaque: a larger, flat-topped solid elevation in the skin Papules and plaques on the trunk of a dog that developed a contact allergy to a shampoo. ©Paul Hanna Nodule: a circumscribed, solid elevation of skin, >1 cm, that usually extends into the deeper layers Many infectious agents and several immunologic conditions can cause nodular dermatitis in horses. Vesicle: well circumscribed, < 1 cm diameter, elevation of the epidermis, or below the dermal-epidermis filled with clear fluid Bulla: a large vesicle (blister) > 1 cm diameter, localized collection of fluid within epidermis Tumor: a large mass (neoplasia implied) that may involve any structure of the skin or subcutis Cyst: an epithelial lined cavity containing fluid or solid material Pustule: a small, circumscribed, pus filled elevation of the epidermis Abscess : small circumscribed accumulation of pus within epidermis or within follicle Wheal: a smooth, sharply circumscribed elevation of skin, due to dermal edema Wheals are most commonly seen with hypersensitivity (allergic) disorders in horses (above) and less frequently with dogs (left). Lesions that can be Primary or Secondary Scale - an accumulation of (flakes / dandruff) on the surface of skin Crust : an accumulation of dried exudate, blood / serum, scale or medications adhered to the skin surface. (1 or 2) can be primary (zinc-responsive dermatosis) or secondary (self-trauma, pyoderma, etc). Idiopathic photosensitization Comedo : a dilated hair follicle filled with cornified cells and sebaceous material (1 or 2) Comedones seen in dog with hyperadrenocorticism (Cushings) Abnormalities of hair Alopecia - loss of hair (1 or 2) Hypotrichosis (less hair than normal) / atrichia (absence) – failure to develop Effluvium / defluxion – excessive shedding (falling out) of the hair  Hypertrichosis (hirsutism) : more hair than normal Hirsutism due to pituitary adenoma of the pars intermedia in a horse Alteration in epidermal pigmentation consist of: 1. Hyperpigmentation: an increased production of melanin from existing melanocytes 2. Hypopigmentation: can be congenital or hereditary Is due to lack of melanocytes, failure of melanocytes to produce melanin 3. Pigmentation Incontinence: Loss of melanin pigment from the basal layer of the epidermis. Factors can affect melanin pigment production Melanocyte-stimulating hormone Age Inflammation Temperature genes 24 Hyperpigmentation Red (erythema) - inflammation / vasodilation Black - hypermelanosis (melanoderma) / melanotrichia 25 Hypopigmentation Leukoderma is due to decreased pigmentation of skin 26 Secondary Lesions Epidermal collarette: a circular rim of Ulcer: a break in the epidermis with exposure of keratin flakes following loss of the "roof" of the underlying dermis vesicle or pustule Excoriation: erosions or ulcers Scar: an area of fibrous tissue that has replaced caused by scratching, biting, or the damaged dermis and /or subcutis rubbing. Excoriation in a dog with sarcoptic mange Fissure: a linear cleavage of usually Lichenification: a thickening and thickened, inelastic skin hardening of the skin with exaggeration of the superficial markings Lichenification and alopecia in a bovine with sarcoptic mange