CHAPTER 4: THE INTEGUMENTARY SYSTEM

OBJECTIVES- 1.Describe the regions of the skin and the hypodermis 2.Name two (2) main epidermal layers and describe their structure and function

1.Integument = skin 2.Skin and its appendages make up the integumentary system 3.A fatty layer called the hypodermis lies deep to it 4.Two distinct regions: a)Epidermis b)Dermis Structure of the Skin

FUNCTIONS OF SKIN (HOMEOSTASIS) 1.Protection: a)Cushions, insulates and is waterproof b)Protects from chemicals, heat, cold, bacteria c)Screens UV radiation (sun rays) 2.Synthesizes vitamin D (with UV) 3.Regulates body heat 4.Prevents unnecessary water loss 5.Sensory reception (nerve endings-cutaneous receptors)

EPIDERMIS 1.Thin outer layer 2.Made up of stratified squamous epithelium, divided into several layers 3.Important Cells: a)Keratinocytes – deepest, produce keratin (tough fibrous protein- protects and waterproofs) b)Melanocytes - make dark skin pigment (melanin) c)Merkel cells – associated with sensory nerve endings d)Langerhans cells – macrophage-like cells; related to white blood cells; destroy microbes and stimulate the immune system to react

EPIDERMAL LAYERS (FROM DEEP TO SUPERFICIAL) 1.Stratum Basale – a) single row of cells attached to dermis b) youngest cells w/rapid growth; new cell layers are pushed to the surface while old ones are sloughed off. c) location of Langerhans cells and melanocytes d) receives its nourishment from the dermis 2.Stratum Corneum – tough, uppermost part of the epidermis; hardening is caused by keratinization a) old cells, many layers thick, flake off (calluses) b) provides mechanical barrier against microbe invasion c) Keratin provides waterproof barrier

LAYERS (ON LEFT) AND CELL TYPES (ON RIGHT)

REMEMBER… Four basic types of tissue:  Epithelium – epidermis just discussed  Connective tissue - dermis  Muscle tissue  Nervous tissue

DERMIS 1.Strong, flexible connective tissue: your “hide” 2.Deeper, thicker region composed of dense irregular connective tissue 3.Fiber types: collagen and elastic 4.Collagen- offer resistance to overstretching and prevent the skin from being torn 5.Elastic- stretch to allow movement but maintain normal skin tension 6.Rich supply of nerves and vessels

* Dermis layers * * * Dermal papillae

Epidermis and dermis of (a) thick skin and (b) thin skin

HYPODERMIS 1.“Subcutaneous tissue” – Latin meaning “below the skin” 2.Underneath or below the dermis 3.Composed of loose connective tissue, including adipose 4.Fat= good source of energy and insulation 5.Gives the body a rounded appearance and provides protective padding 6.Excessive development of adipose= OBESITY

SKIN COLOR Three skin pigments 1.Melanin: the most important (protects skin from UV) 2.Carotene: comes from carrots and yellow veggies; gives skin yellowish tint 3.Hemoglobin: the pink of light skin (erythema = redness of skin) The number of melanocytes is the SAME for all individuals. Variation in skin color is due to the amount of melanin produced and its distribution.

ALBINISM- genetic condition where an organism cannot produce melanin