Integumentary System Flashcards
Integumentary System
The integumentary system is the outermost system of the body, comprising the skin, glands, hair, and nails. It covers and protects the body.
Skin
The skin acts as the first line of defense against external elements. It prevents bacteria from entering the body and retains water and heat. The skin consists of two primary regions:
Epidermis: The thin, outer layer.
Dermis: The thicker, inner layer.
Dermis
The dermis is a tough layer of fibrous connective tissue that is vascularized. It receives nutrients from the bloodstream.
Epidermis
The epidermis is made of epithelial tissue and is avascular, obtaining nutrients through diffusion from the dermis. Below the dermis is the subcutaneous layer, also known as the hypodermis, which is primarily composed of adipose tissue and anchors the skin to underlying structures.
Epidermis Layers
The epidermis is made of keratinized stratified squamous epithelium, consisting of four cell types in five layers:
Stratum Basale (Basal Layer):
The deepest layer, attached to the dermis.
Composed of a single row of cells, mostly keratinocytes, which rapidly divide to regenerate dead skin and produce keratin.
Contains melanocytes, which produce melanin, and tactile cells, which act as sensory receptors for touch.
Millions of dead keratinocytes rub off daily due to friction; the stratum basale ensures a new epidermis forms every few weeks.
Stratum Spinosum (Prickly Layer):
Several cell layers thick, featuring cells with a weblike system of intermediate filaments attached to desmosomes.
Contains dendritic cells, which ingest foreign substances and activate the immune system.
Stratum Granulosum (Granular Layer):
Four to six cell layers thick; keratinization begins in this layer as cells move upwards from the basal layer.
Cells fill with keratin as they die and flatten, while organelles disintegrate.
This process makes the cells tougher and scalier, enhancing protection.
Stratum Lucidum (Clear Layer):
Two to three cell layers thick, composed of dead keratinocytes that have become flat and clear.
Cells begin to aggregate into arrays called tonofilaments.
Stratum Corneum (Horny Layer):
The outermost section, twenty to thirty cell layers thick.
Cells are anucleated, with thick plasma membranes surrounding keratin, which protect the living cells within from external dangers.
Dermis Layers
The dermis is made of strong, flexible connective tissue, filled with nerves and blood vessels, and contains hair follicles. It has two sections:
Papillary Layer:
A thin layer made of areolar connective tissue and a loose network of collagen and elastic fibers.
Contains dermal papillae that project into the epidermis, containing tactile cells.
In areas of high friction, such as the hands, dermal papillae sit on dermal ridges, causing ridges in the epidermis to enhance gripping ability, forming unique fingerprints.
Reticular Layer:
Most of the dermis, made of dense, irregularly arranged fibrous connective tissue.
A network of blood vessels sits below this layer, just before the hypodermis.
Skin Color
Melanin, produced by melanocytes in the stratum basale, is a pigment that determines skin color and protects against ultraviolet radiation. Other pigments contributing to skin color include carotene (yellow-orange) and hemoglobin (red when oxygenated).
Skin Appendages
Skin appendages include hair, nails, and glands.
Hair
Hair consists of flexible strands made of dead, keratinized cells, specifically hard keratin, which is more durable than the soft keratin in the epidermis. Hair is produced by hair follicles, each with a root (where keratinization occurs) and a shaft (where keratinization is complete).
Hair Structure
Hair consists of three layers of cells:
Medulla: The innermost layer, containing large cells and soft keratin.
Cortex: Several layers of flattened cells.
Cuticle: A single layer of overlapping, highly keratinized cells.
Hair Follicle Structure
A hair follicle is a pocket that extends from the epidermis into the dermis, about four millimeters below the surface.
The deep end expands to form a hair bulb.
A bundle of nerve endings attaches to the bulb, acting as a receptor for hair bending.
A hair papilla protrudes into the bulb, supplying nutrients to the hair.
Follicle Wall Layers
Peripheral Connective Tissue Sheath: Derived from the dermis.
Glassy Membrane: Derived from the basal lamina.
Epithelial Root Sheath: Derived from the epidermis, with an external and internal part.
Actively dividing cells in the hair matrix push existing cells upwards, causing hair growth. Each follicle has an arrector pili, a small muscle bundle that contracts to pull the follicle, causing goose bumps.
Hair can be vellus (pale and fine) or terminal (darker and more coarse).
Nails
Nails are modifications of the epidermis, containing hard keratin, and consist of a free edge, a body, and a proximal root embedded in the skin. The nail sits on the nail bed and grows out of the nail matrix. Nail folds overlap the borders of the nail, with the eponychium extending onto the nail, and the hyponychium is at the edge of the finger.
Glands
The integumentary system includes various glands:
Sweat Glands (Sudoriferous Glands): About three million sweat glands are found on the skin. Two types exist:
Eccrine (Merocrine) Sweat Glands: The majority of sweat glands, consisting of a coiled tube in the dermis that secretes sweat (99% water, salts, and metabolic wastes) through a pore.
Apocrine Sweat Glands: Fewer in number, found only in certain areas, and secrete fat and protein components along with the normal mixture, contributing to body odor. Ceruminous glands (earwax) and mammary glands (breast milk) are types of apocrine glands.
Sebaceous Glands (Oil Glands): Branched alveolar glands that secrete sebum (oily lipids), which softens and lubricates hair and skin, slows water loss, and kills certain bacteria.
Function
The integumentary system acts as a barrier, separating the inside of the body from the outside environment. It repairs quickly, regulates body temperature, and responds to external stimuli.