Types of Pathology:
Branch I: Skin (Dermatologic)
Skin is the outermost layer of the body. The skin covers most parts of your body except for your head, hands, feet, genitals and eyes. Your skin consists mainly of dead cells called keratinocytes which are made up primarily of protein. Keratinocytes have many different functions including protecting your body from injury and disease.
They produce various hormones such as melanin and act as natural barrier against infection.
The skin contains two types of cells; those that make pigment and those that do not. Pigment cells are responsible for making color in the skin. These pigmented cells include melanocytes, eumelanins, phaeomelanosomes, leucocytoid dendrites and other cell types. Melanocytes produce melanin, which gives the skin its color.
Eumelanins are chemicals produced by eumelanoderms such as mollusks and crustaceans. Phaeomelanosomes contain enzymes that help break down food into smaller molecules so they can be absorbed through the skin’s surface. Leucocytoids are specialized cells found on hair follicles that secrete oil to keep hairs soft and pliable.
The skin also contains cells that do not produce pigment. These cells include Merkel cells, tactile hairs, Meissner’s corpuscles and Ruffini endings. Merkel cells are specialized cells found in the epidermis that help you sense light touch. Tactile hairs are specialized sensory cells found in the dermis that help you sense pain and temperature.
Meissner’s corpuscles are sensory receptors found in the dermis that detect changes in pressure. They are also sometimes called “end bulbs of Krause”. They are located in areas where you need to have the most sensitivity such as the fingertips and lips.
Ruffini endings are sensory receptors found in the subcutaneous layer of the skin that detect changes in temperature and pressure. These are also known as ” Slowly Conduction Fibers”. They are also sometimes called “Fine End Bulbs of Krause”. They are located in areas where you need to have the most sensitivity such as the fingers and lips.
There are two types of skin: hairy skin and glabrous skin. Hairy skin is also known as pilosebaceous skin. It is so named because it has both hairs and sebaceous glands. Most mammals have this type of skin.
It is thicker and has more nerve endings than glabrous skin. It also helps mammals sense their young and feel their offspring move inside the womb. Most mammals have this type of skin except for the hairless variety such as elephants, whales and hippopotamuses.
Glabrous skin is also known as “hairless skin”. It is so named because it has no hairs or sebaceous glands. Most reptiles, birds, amphibians and fish have this type of skin. It is much thinner and less sensitive than pilosebaceous skin.
This type of skin is usually devoid of hair, but some amphibians such as the common frog have both hair and glabrous skin.
The first layer of the skin is the epidermis. It is several layers of cells that protect your body. The top layer of the epidermis is called the stratum corneum, or simply the “horny layer”. It is this layer that you know as dry skin.
The stratum corneum contains dead cells filled with keratin. These cells are constantly being shed and replaced by new cells growing from below.
The stratum lucidum is a transparent layer sometimes found beneath the stratum granulosum in hairless skin, such as lips and palms.
The stratum granulosum is a layer of the epidermis that contains from 2 to 5 layers of cells. It is in this layer that you start to see keratin in the cells. This layer is sometimes called the “grainy layer”.
The stratum spinosum is a layer of the epidermis that contains from 4 to 6 layers of cells. This layer has small “spines” or “thorns” that help make the skin tough.
The stratum basale is a layer of the epidermis that contains from 2 to 4 layers of cells. It is in this layer that the cells are dividing and growing to produce new cells for the epidermis.
The dermis is a layer of skin beneath the epidermis that contains blood vessels, sweat glands, nerves, hair follicles and more. It also produces a fatty substance called “sebum” that helps keep the skin moist.
The hypodermis is a layer of fat beneath the dermis that helps insulate the body and provides support for the overlying skin.
The skin has three main functions: protection, regulation and sensation.
The skin protects your inner organs and body from the outside world. The skin stops pathogens and toxins from entering your body. The skin also stops you from losing too much water and vital nutrients through the process of evaporation.
The skin regulates the body’s temperature. When it is hot, the skin opens up blood vessels near the surface to allow heat to escape. When it is cold, the skin closes the blood vessels near the surface to keep the inner body warm.
The skin helps you sense the world around you. The skin contains special nerve endings that can feel heat, cold, pain, pressure and more. These nerve endings send messages to the brain so that you can feel things.
Skin diseases and disorders can be caused by genetics, infections, drugs, immunological disorders and even physical injury. Skin diseases are among the most common health problems today.
The skin is often exposed to the world, making it prone to all kinds of things. Sunlight causes the skin to age and can lead to skin cancer.
Tobacco smoke causes the skin to age, as the harmful chemicals in the smoke cause lines and wrinkles.
Skin diseases and disorders include:
Acne, Eczema, Herpes, HPV, Impetigo, Keloids, Moles, Pemphigus, Pityriasis Rosea, Scabies, Seborrheic Dermatitis, Skin Cancer, Warts.
Acne is a skin disease that causes pimples and blackheads to appear on the skin. It is most common in teenagers, but can also affect younger children and adults.
Eczema is a chronic (long-term) skin disease that causes the skin to become itchy, red and flakey. The main symptom is itchiness, which leads to the sufferer to scratch the area, making it worse.
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