Skin histology

00:00 / 00:00


Skin histology

USMLE® Step 1 questions

0 / 1 complete


USMLE® Step 1 style questions USMLE

of complete

A group of dermatologists is studying the layers of skin under a microscope. They discovered that the epidermal layer of the skin has sub-layers that make up the epidermis. The structure labeled A in the histological image below represents which of the following layers of the skin?  


The skin covers and helps protect the body from its environment.

It’s also known as the integument, which is part of the integumentary system.

The integumentary system also consists of structures that are derivatives of the skin, such as nails, hair, and glands within the skin, like sweat glands.

The skin can be split into two general types: thick skin and thin skin.

Thick skin has a much thicker outer layer of epidermis that helps to protect the body in places where it’s regularly exposed to slightly harsher physical conditions.

That’s why it’s typically found in places such as the palms of the hands and soles of the feet.

Thick skin can also be differentiated from thin skin because it doesn’t have hair follicles or oil-producing glands called sebaceous glands.

It does still contain sweat glands though.

The overall thickness is often more than 5mm, whereas thin skin is typically only between 1-2mm thick.

Thin skin has all the same structures as thick skin except it has a thinner epidermis and additional structures such as hair follicles and sebaceous glands.

If we compare histologic images of thick skin and thin skin at low magnification, we can see the three main layers that make up the skin.

At the top of the image is the surface epidermal layer or epidermis that’s significantly thicker in thick skin.

Hair follicles are only found in thin skin, and as we can see in this image, they’re located in the middle layer called the dermis or dermal layer.

The third and deepest layer is called the hypodermis, which consists mainly of adipose and loose connective tissue, although this image of thick skin doesn’t include the hypodermis.

Now, if we look at just the epidermis, there are sub-layers that make up the epidermis.

Starting from the base of the skin is the stratum basalis, spinosum, granulosum, lucidum, and corneum at the surface.

The Stratum Lucidum can only be seen histologically in very thick skin.

If we take a closer look at the epidermis of both thick skin and thin skin, we can see that the stratum basalis is only a single-layer of cuboidal or columnar germ cells.

These cells are attached to a basement membrane that’s normally too thin to see under the microscope.


The skin is the largest organ of the body, and has many important functions in physiology. It protects the body from infections, helps in thermoregulation, and contains nerve receptors that detect pain, sensation, and pressure. The skin is composed of three main layers: the epidermis, the dermis, and the subcutaneous tissue.

The epidermis is the outermost layer and is composed mainly of keratinocytes, which produce the protein keratin that helps protect the skin from damage. The epidermis also contains melanocytes, which produce the pigment melanin that gives the skin its color, and Langerhans cells that play a role in the immune response.

The dermis is the layer beneath the epidermis and is composed of connective tissue, blood vessels, and various types of cells, which give the skin its strength and elasticity. The dermis also contains nerve endings, sweat glands, and hair follicles. The third and deepest layer is called the hypodermis, and consists mainly of adipose and loose connective tissue that helps cushion and insulate the body. It also contains blood vessels and nerves that supply the skin and underlying tissues.


Copyright © 2023 Elsevier, its licensors, and contributors. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

Cookies are used by this site.

USMLE® is a joint program of the Federation of State Medical Boards (FSMB) and the National Board of Medical Examiners (NBME). COMLEX-USA® is a registered trademark of The National Board of Osteopathic Medical Examiners, Inc. NCLEX-RN® is a registered trademark of the National Council of State Boards of Nursing, Inc. Test names and other trademarks are the property of the respective trademark holders. None of the trademark holders are endorsed by nor affiliated with Osmosis or this website.