Functions of the Skin –Protection (1 st line of defense) –Regulates body temp. –Conserves water inside body –Contains sensory receptors –Makes biochemicals –Excretion of wastes *Skin is the largest organ of the body
1. Epidermis Outer layer of skin cells Avascular- lacks blood vessels, fed by diffusion Acts as a mechanical barrier Made of many layers of cells Top cells dead Bottom layer alive- multiply and new cells are pushed upward (EX-”Ashiness” is caused by this layer of dead skin cells being very rough and raggedy. DUST you see around is made up of dead skin cells! )
Epidermis Keratinization- process where keratin develops in a cell, which hardens it, and makes the cell layer waterproof –Contains melonocytes- cells which contain the pigment melanin –Difference is skin color is due to % of melanin in the cell.( We all have the same # of cells, just produce a different amt. of melanin.) –Amt. of melanin increases with UV light exposure –Too much exposure=melanoma (skin cancer)
Review-Layers of Skin 1.Name the 3 layers of the skin. 2.What are the 5 layers of the epidermis from the outside of the body to the inside? 3.The top layer of the skin is the? 4.The layer that contains fat and thick blood vessels is _____________. 5.Which layer is avascular? 6.What layers have been burnt if a second degree burn occurs?
Accessory Organs of the Skin 1.Hair/hair follicles 2. Sebaceous glands 3. Nails 4. Sweat glands
Hair Structure –Found in Dermis of skin –Cells of hair follicle grow and develop in the blood vessels –As cells move upwards they become keratinized and die –Melanin – pigment that contributes to dark hair color
Arrector Pili –Smooth muscle attaches to follicle –Raises hairs –Response to fright or cold –Pulls hairs upright to create a layer of warm air on surface of skin
Functions of Hair –Protection –Sensory perception –Thermoregulation (insulation) -Minor role in humans (exception- Hypertrichosis)
Nail Function and Structure –Function- Protective covering on fingertip used for picking, scratching, grooming –Keratinized, stratifies squamous cells make nails hard –Nail root bed – area where new cells are formed
Sweat Glands –Sweat glands Found just about everywhere on body Dermis layer of skin Produce sweat aka perspiration –Water, salt, wastes (toxins), urea, and uric ac –Avg.- @500 mL/day, up to 12 L/day Function – cooling of the body, releasing scent, producing milk, ear wax
Sweat Gland Types Eccrine and Apocrine, two types are different in size and the age they become active –Eccrine- most numerous type, found all over the body particularly on the palms, soles of the feet, and forehead, exits pores –Apocrine is mostly the armpits. They end in hair follicles instead of or pores. modified- includes scent glands, mammary glands, ceruminous (produce ear wax), ciliary- eyelid
Checkpoint 1.What are accessory organs of the skin? 2.What is attached to each hair that produces oil? 3.Sweat glands are located in the ________. 4.What type of fluid is created by the sebaceous gland? 5.What is sweat made of? 6.What are functions of sweat?
The skin also helps control body temperature- Homeostasis! When you sweat, heat leaves the body through your pores. When the sweat hits the outer surface of the skin, it is cooled by the air. This lowers your body temperature.
Regulation of Body Temperature Normal body temp- 37 C, 98.6-98.8 F Controlled by hypothalamus of brain Amt. of heat produced is balance by the amt. of heat lost Cellular chemical rxns create heat Muscle contraction creates heat Homeostatic response when exposed to an increase in temp. or a decrease in temp.
Body has mechanisms to rid itself of excess heat- 1. Warmed blood reaches hypothalamus nerve impulses respond more blood sent to limbs flushed skin 2. Vasodilation- blood vessels dilate, skin releases heat 3. Activation of sweat glands- moisture allows more heat to be released Outcome- Overall temp. decreases
Mechanisms to save heat and create heat in response to cold- 1.Thermoreceptors send signals to hypothalamus 2.Vasoconstriction- blood vessels constrict to reduce heat loss more blood in core pale 3.Deactivation of sweat glands 4.If temp. is still too low, muscles will contract (shivering) to create heat Outcome- Increase in overall body and blood temp.
Table 5 - Hypothalamic Regulatory Center Structures When Body Cools When Body Warms Superficial blood vessels ConstrictsDilates Sweat glandsInactivatesActivates
Controlling body temperature Body temperature is controlled by the thermo-regulatory centere in the ________. It is kept at 37 0 C as this is the best temperature for __________ to work in. If the body becomes too hot then blood vessels _________ and sweat glands release ________. If the body is too ______ then blood vessels constrict and muscles start to __________. Words – sweat, enzymes, cold, dilate, shiver, brain
Checkpoint 1.What is the normal body temperature? 2.What part of the brain controls temp.? 3.How does the body respond to too much heat? 4.How does the body respond to cold temp.? 5.What type of muscle contracts to cause shivering? 6.What is the difference between vasoconstriction and vasodilation?
The “Birthday Suit” –Combination of 4 main tissues: Epithelial – outer layer Connective – underlies dermis Smooth Muscle – goose bumps Nervous – sensory receptors