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Cells of the epidermis

This micrograph of the epidermis shows stratum corneum as a rough, darkened layer. The next layer, the stratum granulosum, contains white cells with areas of black in their cytoplasm, equal in thickness to the stratum corneum. The third layer, the stratum spinosum, contains large, grayish cells. The stratum spinosum is the thickest layer, occupying half of the micrograph. A hair follicle is embedded in this layer, which is a round structure with black, concentric spots. The fourth layer is the stratum basalis, which contains grayish cells with clear, dark nuclei, similar in thickness to the stratum corneum. The dermis is the deepest layer, and is lightly-colored with interspersed gray cells. A cross-section of a capillary is visible within the dermis.
The cells in the different layers of the epidermis originate from basal cells located in the stratum basale, yet the cells of each layer are distinctively different. EM × 2700. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

View the University of Michigan WebScope at (External Link) to explore the tissue sample in greater detail. If you zoom on the cells at the outermost layer of this section of skin, what do you notice about the cells?

The keratinocytes in the stratum spinosum begin the synthesis of keratin and release a water-repelling glycolipid that helps prevent water loss from the body, making the skin relatively waterproof. As new keratinocytes are produced atop the stratum basale, the keratinocytes of the stratum spinosum are pushed into the stratum granulosum.

Stratum granulosum

The stratum granulosum    has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum. The cells (three to five layers deep) become flatter, their cell membranes thicken, and they generate large amounts of the proteins keratin, which is fibrous, and keratohyalin    , which accumulates as lamellar granules within the cells (see [link] ). These two proteins make up the bulk of the keratinocyte mass in the stratum granulosum and give the layer its grainy appearance. The nuclei and other cell organelles disintegrate as the cells die, leaving behind the keratin, keratohyalin, and cell membranes that will form the stratum lucidum, the stratum corneum, and the accessory structures of hair and nails.

Stratum lucidum

The stratum lucidum    is a smooth, seemingly translucent layer of the epidermis located just above the stratum granulosum and below the stratum corneum. This thin layer of cells is found only in the thick skin of the palms, soles, and digits. The keratinocytes that compose the stratum lucidum are dead and flattened (see [link] ). These cells are densely packed with eleiden    , a clear protein rich in lipids, derived from keratohyalin, which gives these cells their transparent (i.e., lucid) appearance and provides a barrier to water.

Stratum corneum

The stratum corneum    is the most superficial layer of the epidermis and is the layer exposed to the outside environment (see [link] ). The increased keratinization (also called cornification) of the cells in this layer gives it its name. There are usually 15 to 30 layers of cells in the stratum corneum. This dry, dead layer helps prevent the penetration of microbes and the dehydration of underlying tissues, and provides a mechanical protection against abrasion for the more delicate, underlying layers. Cells in this layer are shed periodically and are replaced by cells pushed up from the stratum granulosum (or stratum lucidum in the case of the palms and soles of feet). The entire layer is replaced during a period of about 4 weeks. Cosmetic procedures, such as microdermabrasion, help remove some of the dry, upper layer and aim to keep the skin looking “fresh” and healthy.

Questions & Answers

what are membranous epithelial tissues
Naa Reply
they are the lining and covering epithelial tissues which cover body surfaces and line cavities... they're grouped into simple and stratified according to the number of layers and squamous, cuboidal and columnar according to their shape
Ophelia
what is an acina
Nuella
the study of tissues is called
Scandy Reply
histology
Sirius
microscopic or histology anatomy
Shan
What specific types of biological macromolecules do living things require and why?
Marieland Reply
what is partial pressure?
Tariq Reply
it is the pressure exerted by mixture of gases...
Fatukasi
What is the Important of studying anatomy and philosophy
Michael Reply
because to know the mechanisms of our body
Tariq
how many region do we have in human body
nsofor Reply
head thorax abdomen and many kind of...
Shan
what is principal ponatine nucleas
Tariq
Human body can be divided into different regions on the basis of: 1. Systems: e.g. digestive system, respiratory system, excretory system etc.. 2. Parts: e.g. head, thorax, neck, upper limbs, lower limbs etc..
AMEL
we have 9 region in d human body
ZAINAB
what is systematic anatomy?
nsofor Reply
it is the anatomy or study of a certain body system for example the digestive system. or respiratory system.
Summer
It is a group of structure that work together to perform a unique function..
RAPHERA
describe the division of anatomy and physiology
Vissa Reply
the what and the how
Josh
anatomy is the structure. physiology is the function.
Gavin
what is homeostasis?
nsofor
the balance if everything in your body
Kare
is the tendency of the body to maintain the internal environment
Flora
It is the ability of systems and living organisms to adjust its internal environment
RAPHERA
how does a saggital plane look like and a frontal plane
susan Reply
saggital plane divides left and right.. frontal plane divides front and back.. I'm trying to upload a picture but idk how.
Pipiena
tnx sis
Angella
The sagittal plane is a vertical plane that divides the body into left and right anteriorly whilst the frontal plane divides the body into the posterior(back) and anterior(front) parts. They're all perpendicular to the transverse plane.
Sirius
what is a neurones?
Angella Reply
how many systems are there in human
Angella
It is a cell that specialized to conduct nerve impulse
RAPHERA
What is ovulation
Joy Reply
Ovulation is release of mature ovum from ovary
AMEL
what is physiology
Firdaus Reply
The study of how e body systems or structures function and interrelate with each other
Prettygal
what is the composition of the ground substance?
Nana Reply
large carbohydrates and proteins which is known as acid mucopolysacchrides
adam
thanks👍
Nana
you guy welcome
adam
Hi guys am new here
Nji
how does the negative feedback helps in maintaining body temperature at its normal range
dzreke
I need good sites that I can test myself on chapters 1,3,4,5. I have an exam tomorrow
Ana
please can you kindly share your questions here after the exams please
dzreke
What causes the banding pattern seen in the muscle fibril under the electron microscope
Nji
what organelles controls protein synthesis?
Katie Reply
Ribosome
AMEL
hmm...the ribosomes?
Fatukasi
ribosome
adam
Ribosome
Opara
Ribosome
Saifkhan
ribosome
DR
ribosome
ELIZABETH
are ribisomes made in the rRNA?
Lola
nop they are produced by cells of Nucleolus
adam
Is there anything about nerve and muscle physiology?
AMEL Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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