THE DERMIS OF THE SKIN

The dermis is the layer of the skin beneath the epidermis. It  makes up about 90% of the skin's thickness. It has:

• Blood vessels
• Hair follicles - This is the tube that surrounds the hair and nourishes it.
• Lymphatic vessels - These drain the lymph in the skin. The lymph contains cells that fight infections. 
• Sebaceous glands - These glands produce sebum. This is the oily substance that lubricates the skin and keeps it waterproof. It keeps the skin smooth and supple. It also helps to fight off bacteria and fungal infections.
• Sweat glands - Produce sweat. There are two types: Apocrine and Eccrine sweat glands. Apocrine sweat glands are found in the armpit and pubic areas. They produce milky sweat that can encourage bacteria growth. Eccrine sweat glands are found in the other parts of the body. 
• Nerve endings - These include touch, pain, pressurs and temperature sensors.
• Collagen and Elastic fibers - These are connective tissues that help to keep the skin tough and elastic.

The dermis consist of two layers. The upper layer is called the papillary dermis and the lower one is called reticular dermis. The papillary layer is thinner than the reticular layer. The papillary layer contains a lot of blood vessels that help to nourish the epidermis and to regulate the body's temperature. The reticular layer has collagen fibers arranged parallel to the skin to help in stretching and maintenance of the strength of the skin. It supports the hair follicles, sweat and sebaceous glands. 

THE LAYERS OF THE EPIDERMIS OF THE SKIN

The epidermis of the skin refers to the topmost layer. It is composed of five layers. From the surface to the deep layers, the names are:

1. Stratum corneum
2. Stratum lucidum
3. Stratum granulosum
4. Stratum spinosum
5. Stratum basale or germinativum

STRATUM CORNEUM
This layer consists of dead cells with a hard protein envelope. These cells contain keratin surrounded by lipid. It is a tough water resistant layer. They are flat, anucleated  and cornified cells.

STRATUM LUCIDUM
This layer consists of dead cells containing dispersed keratohyalin granules. This layer is found in thick thick skins only such as the palm and soles.

STRATUM GRANULOSUM
This layer consists of cells that contain keratohyalin granules and lamellar bodies that have released lipids. They, therefore, look granular. The cells are covered by hard protein. They are polygonal cells with basophylic granules.

STRATUM SPINOSUM
This layer consists of cells that are accumulating keratin fibers and lamellar bodies. The are cuboidal like cells and desmosomes in between.

STRATUM BASALE
The cells in this layer undergo mitosis (cell division) to reproduce the top layers. The are columnar- like cells. The keratinocytes arise from this layer.They produce keratin. Keratin makes our skin tough. It provides protection from microorganisms, physical harm, and chemical irritation.  


Here is a diagram illustrating the layers.

COMPREHENSIVE OVERVIEW OF ANATOMY AND PHYSIOLOGY

This is a great website with a comprehensive overview of anatomy and physiology. Click this link to visit the site.

In future, this website will also become a good resource to you in your medical practice. It gives you insight into various medical conditions and their treatments.