Integumentary System Layers and Accessory Structures Study Notes

The Epidermis and Skin Strata

  • General Organization     * The epidermis is the most superficial region of the skin.     * It differentiates between thin skin and thick skin based on the presence of specific layers and the overall thickness of those layers.

  • Stratum Basale (Stratum Germ German)     * Names: Also referred to as the stratum basale or stratum germ German.     * Structure: It is the deepest layer of the epidermis, consisting of a single layer of cells (11 layer).     * Function: This layer contains mitotic stem cells (mitotic keratinocytes) that undergo continuous mitosis.     * Process: As these cells divide, they move toward the top of the skin. During this transit, they gradually die and are eventually sloughed off, necessitating constant replacement.

  • Stratum Spinosum     * Thickness: Consists of between 77 and 1010 layers of cells.     * Appearance: Named "spinosum" due to the spiny appearance the cells take on when fixed on a slide. This occurs because the cells burst during preparation, leaving behind prekeratin filaments.     * Internal Composition: This is the stage where intermediate filaments (prekeratin) begin to appear in the cytoplasm, leading to the production of keratin.     * Relative Size: It is the second thickest layer of the skin.

  • Stratum Granulosum     * Thickness: Composed of 33 to 55 layers of cells.     * Appearance: Very dark staining in histological sections. It appears as a distinct dark line.     * Cell Morphology: Cells in this layer begin to flatten out into a squamous shape as they move superficially.

  • Stratum Lucidum     * Occurence: Found only in thick skin; it is absent in thin skin.     * Structure: Consists of a single layer (11 layer) of dead cells.     * Visual Identification: Appears as a lighter/clearer layer on models and slides between the granulosum and corneum.

  • Stratum Corneum     * Most superficial layer of the skin.     * Thin Skin Composition: Contains 2020 to 3030 layers of dead cells.     * Thick Skin Composition: Contains 5050 to 7070 layers of dead cells.     * Composition: The cells are completely filled with Keratin, a protein providing waterproofing and protective properties.

The Dermis and its Sublayers

  • Structure and Tissue Type     * The dermis lies immediately underneath the epidermis.

  • Papillary Layer     * Position: The more superficial layer of the dermis.     * Composition: Composed primarily of areolar connective tissue.     * Dermal Papillae: These are hill-like structures or bumps located at the junction with the epidermis. Together, these bumps form the entire papillary layer.

  • Reticular Layer     * Position: The deeper layer of the dermis, located below the papillary area.     * Features: Contains larger blood vessels and deep sensory receptors.

Sensory Receptors and Nerve Structures

  • Tactile (Mesner's) Corpuscles     * Location: Found within the dermal papilla.     * Function: Responsible for the sensation of light touch.     * Identification: On models, they often appear as yellowish structures with small caps.

  • Free Nerve Endings     * Location: Found near the papillary layer.     * Identification: Nerve endings that do not have the specialized caps seen on corpuscles.

  • Vicinium (Lamellar/Pacinian) Corpuscles     * Location: Located deep in the dermis (reticular layer).     * Function: Specialized for detecting pressure and vibrations.     * Appearance: Distinct, large structures often representing an onion-like layered appearance on models.

  • Hair Follicle Receptors     * Structure: A network of yellow-coded nerve endings that wrap around the hair follicle.     * Function: Allows for the sensation of hair movement, such as when something is crawling on the skin.

Vascular Plexuses and Model Color Coding

  • Subpapillary Plexus     * Definition: A group or "plexus" of blood vessels located just below the papillary layer of the dermis.

  • Cutaneous Plexus     * Definition: A deeper network of blood vessels located within the reticular layer of the dermis.

  • Model Color Schemes     * Red: Oxygenated blood vessels (arteries or arterioles).     * Blue: Deoxygenated blood vessels (venules and veins).     * Purple: Represents capillary beds, where red and blue vessels connect.     * Yellow: Represents components of the nervous system, including nerve stringy endings and corpuscles.     * Green: Represents lymphatic vessels (though not visible on all models).

Cutaneous Glands

  • Sudoriferous Glands (Sweat Glands)     1. Equin (Eccrine/Merocrine) Glands         * Distribution: Found everywhere on the body (palms, arms, legs, face, scalp).         * Function: Thermoregulation (cooling the body).         * Triggers: Active during exercise, excitement, or embarrassment.         * Structure: Empties through a "sweat duct" to a "sweat pore" on the skin surface.     2. Apocrine Glands         * Distribution: Found in axillary (armpit) and anogenital regions.         * Activation: Become active at puberty.         * Nature of Secretion: Secretes sweat plus fatty substances. When bacteria consume these substances, it results in body odor.

  • Sebaceous Glands (Oil Glands)     * Association: Always associated with a hair follicle.     * Secretion: Produce Sebum, an oil-like substance.     * Function: Sebum lubricates and softens the hair and the skin surface.

The Arrecto Pili Muscle

  • Structure     * A band of smooth muscle that attaches the hair follicle to the epidermis.

  • Physiological Response     * Controlled by the sympathetic division of the autonomic nervous system (fight or flight).     * Contraction causes the hair to stand straight up and pulls the epidermis down, creating "goose bumps."

  • Biological Function     * In humans: No significant useful function due to lack of thick body hair.     * In animals (Example - Bluebird the dog):         * Helps conserve body heat by trapping warm air near the skin.         * Makes the animal look larger and more intimidating during a fight.

The Hypodermis

  • Location: Also called the subcutaneous layer, located below the dermis.

  • Composition: Composed of adipose tissue (fat).

  • Visual: On models, it appears as yellowish blobs or light-colored bubbles.

Hair Anatomy and Structure

  • Hair Shaft: The portion of the hair that protrudes from the surface of the skin.

  • Hair Root: The entire portion of the hair located underneath the surface of the skin.

  • Hair Bulb: The bulging bottom portion of the hair root.

  • Hair Papilla: A little bump or structure that comes up into the center of the hair bulb to provide nutrients.

  • Hair Matrix: A layer of cells directly surrounding the papilla responsible for hair growth.

  • Hair Follicle: The outer covering or sheath made of tissue that surrounds the hair root and shaft beneath the surface.

Questions & Discussion

  • Question: How can you tell where the stratum spinosum begins and ends on a slide?

  • Answer: The instructor identifies the stratum granulosum as the distinct dark line and the stratum basale as the single layer of cells at the bottom. The stratum spinosum is everything located in between those two markers.