Mammals PDF

1 OUTLINE Subphylum Vertebrata – Mammalia 1. Introduction 2. Integument (a) General (b) Hair (c) Glands (d) Specializations...

1 OUTLINE Subphylum Vertebrata – Mammalia 1. Introduction 2. Integument (a) General (b) Hair (c) Glands (d) Specializations - Antlers & Horns 2 Mammals INTRODUCTION Subphylum: Vertebrata; Class: Osteichthyes Prototheria Subclasses Theria Metatheria Superorders Eutheria Order: 4 Orders ~20 Orders Monotremata (Marsupials) (Placentals) (Monotremes) Primates Rodentia - duck- Carnivora - echidna billed Cetacea platypus oviparous viviparous viviparous (egg-laying mammals) (pouched mammals) (placental mammals) 3 INTEGUMENT - GENERAL Sebaceous gland Hair Epidermis Dermis Arrector pili muscle hypodermis Sweat gland Hair follicle Nerve endings Fat 4 INTEGUMENT - GENERAL A. Epidermis - the epidermis is a stratified - outer region of the skin epithelium (layers of different cells) - epithelial cells of the epidermis are keratinocytes: (produce keratin) A Stratum corneum (Dead cells, keratin, form impermeable layer, limits water loss, can be sloughed off / replaced easily) Stratum Basale (undifferentiated cells; give rise to other epidermal layers) - specialized modifications of the epidermis (glands/hair follicles) also “housed” in dermis 5 INTEGUMENT - HAIR Functions of Hair 1. Insulation 2. Communication - raised hair can communicate warnings of anger or fear - controlled by arrector pili muscle contraction/relaxation 3. Sensation - provide tactile information from surroundings - often particularly long in nocturnal and burrowing mammals 4. Defense - spines of porcupines, hedgehogs etc. offer protection against predation 5. Camouflage - snowshoe hares, arctic foxes etc. molt according to season 6 INTEGUMENT - GLANDS - mammals have the greatest variety/type of glands in the integument - all are derivatives of the epidermis and fall into 4 categories; 1. Sweat Glands (i) Eccrine glands - not associated with hair follicles - function before puberty (human: begin to form at 4 months of gestation.) - secrete a watery fluid (primarly NaCl solution) (odourless). - involved in evaporative cooling - found in hairless regions of most mammals (e.g. foot pads) 7 INTEGUMENT - GLANDS - mammals have the greatest variety/type of glands in the integument - all are derivatives of the epidermis and fall into 4 categories; 1. Sweat Glands (ii) Apocrine glands - associated with hair follicles - begin to function at onset of sexual maturity - secrete a viscous fluid - appear to be functional in chemical communication?? - found in armpits, on and around genitalia etc. -When secretion contacts normal bacterial fauna on skin, odour develops. 8 INTEGUMENT - GLANDS 2. Sebaceous Glands - associated with hair follicles and found over entire body surface (in humans, abundant in scalp and face) - produce an oily secretion, sebum, that waterproofs & lubricates hair and skin - Overactive glands, or if duct becomes clogged results in Acne Sebaceous gland 9 INTEGUMENT - GLANDS 3. Scent glands - modified sebaceous glands or apocrine glands - secretions contain pheromones - used for communication (marking territory, warning, defense) Locations vary greatly Deer – face, chin, belly, inderdigital Wolves and Foxes – base of tail Dromedary – back of head Skunks – anal region 10 INTEGUMENT - GLANDS 4. Mammary Glands - occur in all female mammals and in males in a rudimentary form - produce and release milk to a suckling (lactation) - composed of numerous lobules, Lobules are clusters of alveoli that produce and secrete milk. - alveoli open into a duct that either opens: (a) directly to the surface (b) into a chamber (cistern) (c) through raised epidermal papilla 11 INTEGUMENT SPECIALIZATIONS True Horns Antlers - both formed by bony outgrowths of frontal bones of skull True Horns - keratinized sheaths of epidermis surrounding a core of bone and germinal epidermal layer - never shed or branch - grow continuously - found in both males and females Antlers - bone surrounded by a vascularized skin (velvet) - central beam from which branches arise 12 INTEGUMENT SPECIALIZATIONS Antlers - antlers grown & shed annually, typically found in males only - functional in social recognition, sexual display and jousting April May Late Summer