Chapter 4 Notes
Integumentary System/Cutaneous Membrane
It covers the entire body, a surface area of 20.8 square feet! It is the largest organ of
the body. 7% of your total body weight!
Functions:
Sensory Interface: the skin is the interface between the outside World and the internal
milieu. Therefore, it communicates intricately with the nervous system to ensure the body
maintains homeostasis.
The skin contains many sensory receptors responsible for detecting temperature,
pressure, pain etc.
protection: cushions & insulates deeper body organs, protects from bumps, scrapes,
chemicals & invading organisms.
Epidermis is water proof (reduce loss or gain of water)
Body temp. regulation: capillary networks & sweat glands regulate heat loss.
Excretion: excretes urea, salts, water
Produces vitamin D: epidermal cells use UV to create this vitamin which is necessary for
Ca+2 absorption.
1. Layers: Epidermis (stratified Squamous epithelium, keratinized)
Dermis (dense irreg) Hypodermis/ subcutaneous (adipose)
Epidermial ridge (friction ridge)- hands, soles, = fingerprints & footprints
Dermal papillae: increase surface area of dermis contact with epidermis= diffusion
of gasses.
Epidermal Layers: basale, spinosum, granulosum, lucidum (palms & soles only),
corneum
1. Stratum Basale- Also called germinativum because it’s the “germ” layer. Germ=
reproduction
New cells- active mitosis 15-30 days to go from bottom to top
Melanocytes: produce melanin (several forms: yellow, red, brown & black)
a) Function of melanin: block UVB radiation, protects cells from DNA damage &
UV radiation can break down folic acid (B vitamin) so melanin also prevents
breakdown of folic acid.
b) Exposure to radiation stimulates melanocytes to produce more melanin=
tanning.
b) Evolution of skin color based on balance btwn UVB damage & Vit. D production.
Skin Color is determined by: type of melanin, amount of melanin
melanin is eventually digested & broken down. Dark skinned people’s skin
has slow or no digestion of melanin so it remains in skin.
Other coloration factors: carotene= yellow, blood=red , thickness of corneum
eg) your palms & soles of feet are always lighter than thin skin
Eg) cyanosis: blue coloration of skin due to lack of oxygenated blood.
Merkel cells (hairless areas (touch when compressed)
Stratum Spinosum “spines”are exposed desmosomes (tight junctions) is artifact due to
shrinkage when skin is fixed.
Thickest living layer- several layers thick. Some mitosis
Cells tied together with protein to form sheets
Langerhan’s cells (dendritic cells), some melanocytes
Stratum Granulosum Still have nucleus
Cells undergo apoptosis, fill with lipid rich substance (water proof)
This layer increases keratin with friction: callus.
Stratum lucidum -Thick skin only: clear appearance b/c no nuclei or organelles. Dead
Composition is exactly the same as stratum corneum. A transition zone between
Stratum corneum - 25-30 layers of flat dead cells. Most numerous# of cells in this layer.
Keratinocytes- keratin (tough, fibrous protein). millions of keratinocytes slough off
everyday. In areas of increased friction, rubs off faster.
Dermis:
Papillary layer
Upper 20% areolar CT
Dermal papillae= increases surface area between epidermis & dermis.
Papillary plexus: branching network of capillaries which supply epidermal cells
Reticular layer
Dense irregular CT
Hypodermis/Subcutaneous layer
Mainly consists of adipose. For histology: very light staining layer
Thermoregulation, protection, padding
The sensory receptors in the skin are:
cutaneous mechanoreceptors
Ruffini's end organ (sustained pressure)
Meissner's corpuscle (changes in texture, slow vibrations)
Pacinian corpuscle (deep pressure, fast vibrations)
Merkel's disc (sustained touch and pressure)
Free nerve endings (light touch)
Thermoreceptor (temperature)
Nociceptor (noxious sensations)
Chemoreceptor (sensitivity to chemicals)
Accessory Structures: Hair and nails
Hair is found all over body except palms, soles, lips, nipples, & external reproductive
organs.
Hair is formed from epidermal tissue, but located in dermis of skin.
Hair follicle: entire structure that generates hair:
Bulb: epithelial cells that create hair.(around papilla – CT with blood supply)
Root: from bulb to where hair is organized
Shaft - The majority extends beyond the skin.
Certain hair follicle cells continuously divide producing new cells that form a hair.
As these cells are pushed farther away from the dermis, loose nourishment, become
keratinized & die. The part of hair in the dermis is called the root.
Hair Structure:
Medulla: contains soft keratin- flexible
Cortex: hard keratin- rigid
Cuticle: thin, tough outer layer of hard keratin
Sebaceous gland -Produces sebum, an oil that is slightly acidic. Empties into the hair root.
Sebum provides lubrication for hair & skin. Also inhibits microbes due to low pH.
Arrector pili muscle:
Root hair plexus: nerve fibers at base of each hair follicle to feel movement of each hair.
Nails:
Keratinized cells
Lunule: contains nail matrix- where nail grows from
•
Glands
Sebaceous – secrete oil directly into hair shaft – hairy areas
•
Sweat glands – two types: merocrine and apocrine. Both are myoepithelial
– Merocrine also called eccrine
• Most numerous in palms and soles
• Common sweat gland
• Used for thermoregulation and excretion of toxins
– Apocrine
• Release their secretions into hair follicles in the armpits, around the
nipples and groin areas
Others:
Mammary - milk
Ceruminous – ear wax