Chapter 5: The Integumentary System

Vitamin D Synthesis

1. The synthesis of Vitamin D begins in the skin with the formation of a pre-curser molecule, cholecaliferol, we need to have some skin exposed to the sunlight. We are required to increase calcium absorption from food. 2. Cholesterol in the dermal blood is converted to a Vitamin D. pre-cursor 3. The pre-cursor model is transported through the blood to the liver and the kidney. 4. Converted to calcitrol (active Vitamin D) 5. Vitamin D stimulates the absorption of Ca ions from ingested foods in the intestine 6. This final step increases Calcium levels in the blood

5. Stratum corneum

25-30 layers of flat, dead keratinocytes and is the thickest part of the skin containing keratin. Lamellar section (lipids) between the cell waterproofs this layer. Secreted from the lamellary ranulosum.

3. Stratum granulosome

3-5 layers of flattened keratohyalin (protein) and lamented granules. Lamented granules release a lipid-rich, water-repellant secretion. There's a transition layer between living cells below and dead cells above.

Melanin

A black pigment which is produced by melanocytes. The number of melanocytes are the same to all people, but differences occur in the amount of melanin it produces by the varying skin tones. UV light exposure increases melanin production with a tan. Moles are benign as a result of overgrowing melanocytes.

Vitamin D

A group of closely related compounds

Special functions of the skin

A major body temperature regulator and keeps it at 37.5 C as much as possible in order to function properly. At a normal body temperature, conditions are optimal for enzymatic activity in the body. Body core (organs in skull, thoracic & abdominal cavities), the temperature is relatively constant. Shell (skin) temperature can fluctuate, exposing to the external environment.

2. Stratum Spinosum

A more complex cell and consists of 8-10 layers of irregularly shaped keratinocytes. Cells contain many intermediate filaments and are joined by desmosomes, withstanding of stress. Contains Langerhans cell and projections of melanocytes.

Cuticle

A single layer of cells which overlap one another from below.

1. Papillary region

A small part of the dermis, consisting of only 1/5. Has areola connective tissue, which attaches to the underlying skin. Dermal papillae at the junction with the epidermis, resulting in fingerprints. These papillae contain capillaries, free nerve endings, and Meissner's corpuscles.

Sebaceous glands

Actively related to puberty because these glans are activated during puberty. Simple branched alveolar glands connected to our hair follicles. Produces and secretes an oily substance called ___________. It softens and lubricates the hair and the skin. It inhibits the growth of certain bacterias on the skin.

Dandruff

An excess of keratinized cells, shedding from the scalp. Loss of skin cells and get stuck in the hair.

Hair growth

An interesting process and tends to vary depending on hair type. Each hair follicle goes through the growth cycle.

3. Lungerhans cells (dendritic cells)

Cells that arise from the dead bone marrow and migrate to the epidermis and are also involved in immune responses.

Sweat

Composed of water, ions, urea, uric acid, ammonia, amino acids, glucose, and lactic acids. Regulates our body temperature and has a small hole for the elimination of wastes.

2. Melanocytes

Consist of 8% of the cell and are spider-shaped epithelial cells. Secretes and transfers the pigment melanin to keratinocytes. Found near the bottom layer of the surface and their cell projections extend between the keratinocytes. The exposure of UV rays can be detrimental, tanning.

1. Keratinocytes

Consist of most of the cell and produces keratin (fibrous proteins). It protects the skin and underlying tissues from heat, microbes, and chemicals. Surface cells die and only contain keratin.

Hair shaft and root structure

Consists of 3 concentric rings of dead keratinized cells

Medulla

Core of the large cells, irregularly shaped shaped cells in 2-3 rows.

Skin

Covers the surface of the body and has an impact on our social interactions. Protects our body against dehydration, impact on friction and injuries, mold and bacterial invasion, protection from UV rays and damage, acts as a receptor for organs, regulated body temperature, secretes wastes, and synthesizes vitamin D.

Nail root

Embedded in the fold of the skin

Hair bulb

Expanded base of the follicle and the hair papilla protrudes into this. Contains capillaries, contains layers of cells (matrix) division and production of cells.

Arector pili muscle

Extends from the dermis to the hair follicle and makes your hair stand when you're cold or frightened. Most hairs have a smooth muscle attached to the follicle and smooth muscles are attached to them. There are also sensory nerve endings around the bulb.

Free edge

Extends over the digit

Collagen fibers

Give our skin its elasticity. Tough fibrous bands of protein collagen and provide high strength

Nails

Hard, keratinized epidermal cells

2. Apocrine sweat gland

Larger sweat glands and empty into the hair follicles

Hemoglobin

Locate in red blood cells and gives skin the pinkish color as blood moves through the capillaries.

Hypodermis

Located underneath of the dermis

Hair pigment

Made by melanocytes at the base of the hair follicle and is transferred to the cortex and medulla cells.

Growth stage

Matrix cells divide and the hair actively grows

Regression stage

Matrix cells stop dividing and the hair stops growing.

3 pigments of the skin

Melanin Carotene Hemoglobin

Hypodermis

Not a part of the skin, it attaches to the underlying tissues and organs.

Resting stage

Nothing happens. After the resting stage, old hair roots fall out of the follicle and a new hair begins to grow.

Hair

Present on most skin surfaces and provides touch sensations in certain areas. It insulates, protects, and shields us from the sunlight.

4. Stratum lucidium

Present only in thick skin (fingertips, palms, soles) and wouldn't have this layer on the eyelids. 3-5 layers of clear, flat dead keratinocytes.

Hair shaft

Protrudes from our skin and the root is embedded in our skin

Elastic fibers

Recoiling properties, thin, dark lines allowing the fibers to stretch and recoil

Cortex

Several layers of flattened cells and is the bulk of the hair.

1. Merocrine (encrine) sweat glands

Simple, coiled tubular glands emptying into a pore (palms, soles, foreheads). Functions from birth and onwards.

Meissner's corpuscles

Specialized nerve endings which consist of collagen and recoiling elastic fibers. To respond to light touch receptors.

Dermis

The connective tissues with fibroblasts, adipocytes, macrophages, mast cells, and embedded with fibers. Contains blood vessels, hair follicles, glands, and nerves which are all vascularized.

1. Stratum Basale (stratum germinal)

The deepest layer and is attached to the dermis by a wavy border. Consists of a single row of cuboidal/ columnar keratinocytes. (elongated, cube-shaped) Constantly goes through mitosis, producing new cells. Contains both melanocytes and merkel cells.

Albinism

The inherited inability to produce melanin

Dermis

The inner, thicker layer of the skin and is vascularized.

4. Merkel cells

The least numerous cells. Contact sensory neurons and function in touch sensations. It is located in the deep epidermis and varies in thickness depending on the location in the body.

Epidermis

The outer, thin layer of the skin, composed of keratinized stratified squamous epithelium, and contains four major cell types and 5 cell layers.

Vitiligo

The partial or complete loss of melanocytes from patches of skin

2. Reticular region

The thick, lower part of the dermis and consists of a dense, irregular connective tissue. Dense because there's lots and are randomly disbursed. Collagen fibers strengthen the skin and resiliency to bind water to keep skin hydrated. Elastic fibers provide stretch and recoil properties when we pinch our skin, it goes back down.

Nail body

The visible portion of the nail

Carotene

The yellow-orange pigment found in the stratum corneum and adipose tissue of the dermis and subcutaneous layer.

Follicle

Tube-like pocketing of epidermis that extends into the dermis.

Pacinian corpuscles

a specialized type nerve receptor. Functions in deep touch sensations.

Stretch marks

can appear if the skin is over-stretched because the skin stretches to a certain extent.

Matrix cells

divide mitotically as hair grows and actively grows new layers

Keratinization

the accumulation of more and more protective keratin and occurs as cells move from the deepest layer to the surface layer.