- There are three major regions of the skin, epidermis, dermis and hypodermis. Each of the three regions have a distinctive structure and function.
- Infective agents favor specific regions of the skin and exploit those regions.
- Learn to regard the great diversity of visual symptoms associated with different pathogens.
- Epidermis has 5 layers of cells, each layer forming a “stratum”. The layers of the epidermis include: Stratum Corneum, Stratum Lucidum, Stratum Granulosum and Stratum Spinosum.
- Dermis has two distinct layers:
- Papillary layer with bumps called papillae
- Reticular layer under the papillae layer
- Blood vessels in the dermis do not enter the epidermis. Nutrients and wastes of the epidermis move by diffusion between the layers. The papillae increase the contact surface area between the epidermis and dermis this enhances adhesion between the layers as well as diffusion of nutrients and wastes.
- Hypodermis Structure: Lies under the dermis, is not part of the skin, connects the skin to underlying tissues and stores energy.
- Sweat and sebaceous glands are the two primary glands of the skin. Both glands create their secretions within the dermis then dump them onto the surface of the skin. The skins surface is typically covered with salt that is left aft sweat evaporates and sebum. Sebum is an oily lipid secreted by sebaceous glands in the dermis. Chemicals in sweat and sebum are antimicrobial
- Although the sweat is formed in the deepest coiled portion of the sweat gland, the tube that lead to the surface of the skin actively refines the concentrations of ions and that will ultimately reach the surface. In the case of cystic fibrosis, the function of ion channels has been altered and therefore also the concentration of ions that appear in the sweat.
- There are four nerve sensors in the skin. Of which only one is located in the epidermis and is called the merkel cell.
- Bacterial Infections Described: Acne, Rocky Mountain Spotted Fever, Impetigo, Necrotizing Fasciitis (Flesh Eating Bacteria), Cat Scratch Fever, Cutaneous Anthrax, and Pseudomonas.
- Viral Infections of the Skin: Poxviruses, Herpes, Warts, Rubella, Rubeola, Chicken Pox, Shingles and Varicella-zoster.
- Fungal infections of the skin are categorized by the regions of the body they infect. The categories of Mycoses: Superficial, Cutaneous, Subcutaneious and Systemic (affecting internal organ systems).
- The Protozoa infection, Leishmaniasis is profiled as an example of this type of infection.
- Basic Eye Structure:
- The cornea is the first structure crossed as light enters the eye; it offers the greatest degree of bending of the light. Next the light passes through the iris which through the motions of two muscles, a sphincter and a dilator, controls the amount of light that enters the eye. Next the light passes through the lens of the eye which controls the fine focusing of the eye. Interesting, when the focusing muscles of the lens relax, the eye focuses on close objects. The light exits the lens, transits the clear jelly-like vitreous humor to strike the optically active retina where the energy of the photons will be converted into neural signals. The neural signals are conducted to the brain via the optic nerve (CN II). The sclera is very tough fibrous exterior structure which is the site of attachment for all of the muscles that move the eye. One can imagine that the sclera is pretty special, because it must not change shape when the muscle attached to it move the eye.
- Aqueous humor is produced in the posterior compartment and drained away by the canal of Schlemm in the anterior compartment. Blockage of this canal cause blindness. Excessive pressure from the aqueous humor damages the tissues. This is called glaucoma. It is a very serious condition !!!
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