Dermis: The second, inner layer of skin, that contains blood and lymph vessels, hair follicles, and glands. These glands produce sweat, which helps regulate body temperature, and sebum, an oily substance that helps keep the skin from drying out. Sweat and sebum reach the skin's surface through tiny openings called pores.
Hypodermis: the layer of tissue that lies immediately below the dermis of vertebrate skin. The hypodermis consists primarily of loose connective tissue and lobules of fat. It contains larger blood vessels and nerves than those found in the dermis. The Hypodermis is comprised of Areolar Tissue, (a type of connective tissue).
Epidermis: The upper or outer layer of the main layers of cells that make up the skin. The epidermis is mostly made up of flat, scale-like cells called squamous cells. Under the squamous cells are round cells called basal cells. The deepest part of the epidermis also contains melanocytes. These cells produce melanin, which gives the skin its color.
The Hypodermis is often referred to as subcutaneous tissue (from Latin subcutaneous, meaning "beneath the skin"), although this is ananatomically inaccurate term. The hypodermis is beneath dermis which is beneath epidermis. It is used mainly for fat storage.
Cells of the Epidermis
Produce a fibrous protein called keratin
Are formed in the lowest levels of the epidermis.
Pushed upward by the production of new cells beneath them.
Become dead and scale-like
Millions rub off everyday
The two types of epidermal cells we will be learning about in this class are Keratinocytes and Mealnocytes.
Synthesizes the pigment melanin
Can transfer melanin to keratinocytes
Protects skin from ultraviolet light.
Melanin: The pigment that gives human skin, hair, and eyes their color. Dark-skinned people have more melanin in their skin than light-skinned people have. Melanin is produced by cells called melanocytes.
Keratinocytes are the predominant cell type in the epidermis (the outermost layer of the skin), constituting 90% of the cells found there.
Stratum basale (germinativum): deepest layer of the epidermis,
undergoes rapid cell division. Connects with dermis.
Stratum spinosum: intermediate layer, contain spiny shaped
Stratum granulosum: cells are flattened, organelles are dying
Stratum lucidum: only found in palms and soles (“thick skin”)
Stratum corneum: outermost layer 20-30 cells thick of
dead keratinized cells.
* Average person shed 40 pounds of these cells
in their lifetime.
* Everything you see on a human is dead!
The Dermis is the layer of skin directly below the Epidermis.
The Dermis has characteristics that distinguish it from the epidermis:
made up of connective tissue
richly supplied with blood vessels
supplied with lymph vessels
has hair follicles,
glands, (both oil and sweat glands)
sensory receptors (nerve cells) that can sense pressure, heat and pain
ridges formed from the papillary layer can form finger prints.
Layers of the Epidermis
Characteristics of the Dermis
The ridges of the Dermal Papilliae form fingerprints
The Sebaceous Glands produce oils that prevent skin from drying out.
The Endocrine Glands produce sweat to cool down skin temperature.
The Hair Follicle anchors the hair root. Hairs can be raied or lowered to trap body heat by the pilli muscles.
The Dermis is filled with Sensory Receptors (nerve endings) to detect pressure, heat & pain.
Reticular layer of the dermis
Filled with dense irregular fibrous connective tissue
Matrix is filled with thick bundles of collagen fibers (give the skin strength)
Less dense regions are called lines of cleavage or tension lines; surgeons use these to make incisions because they heal quicker.
The lines of cleavage in the skin
Vitamin D Synthesis
Vitamin D synthesis- cholesterol in the skin is bombarded by sunlight and converted to vitamin D
Adequate vitamin D intake is important for
regulation of calcium and phosphorus absorption
maintenance of healthy bones and teeth
supplies a protective effect against multiple diseases and conditions such as
type 1 diabetes
Thermoregulation- skin contains sweat glands that secrete watery fluid, that when evaporated, cools the body.
Sensation- Skin contains sensory receptors that detect heat, cold, pressure, touch(x2), and pain.
Skin consists of three main layers:
1. Epidermis (epi-upon)
Composed of epithelial tissue (stratified squamous)
2. Dermis – underlies the epidermis
Tough leathery layer composed of fibrous connective tissue
Good supply of blood
3. Hypodermis (not considered skin)
Made of adipose and areolar tissue
Stores fat, anchors skin, protects against impact
Characteristics of skin:
Waterproof, stretchable, washable, self-repairing small cuts, rips and burns and guaranteed to last a lifetime; this is an amazing organ system!
Surface area of up to 2.2 square meters
7% of total body weight
Pliable yet tough
Excretion- Sweating is an important outlet for wastes
nitrogen containing compounds.
(similar wastes in urine)
Blood reservoir- blood will be moved from skin to muscles during strenuous activity.
(for shapes, edges,
and rough textures)
(for minimal skin depression)
Specialized skin cells called Langerhans’ cells act as macrophages (a cell type that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific to the surface of healthy body cells on its surface)
Skin is a Biological Barrier
Secretions have a low pH (acidic) which slows bacterial growth.
Human Defensin (an antibiotic that destroys bacteria) is produced by human skin
Skin is a Chemical Barrier
Physical barrier: very few substance are able to enter the skin.
Substances able to pass:
Lipid-soluble substances: oxygen, carbon dioxide, some vitamins
Oleoresins- poisons (poison ivy)
Organic solvents- dry-cleaning fluid, paint thinner
Salts of heavy metals- lead, mercury, nickel
Penetration enhancers- drug agents that help substances into the body.
Skin is a Physical Barrier
provides 3 types of barriers
Primary Function (Physiology) of Skin
The integumentary system is the organ system that protects the body from various kinds of damage, such as loss of water or abrasion from outside. The system comprises the skin and its appendages (including hair, scales, feathers, hooves, and nails).
This is material you need to know - there is no use in complaining about it. Memorize this material and be done.
"Bummer of a borthmark, Hal."