Stratum spinosum - Prickle cell layer - Functions of stratum spinosum

Home   ›   Know your skin   ›   Epidermis   ›   Functions of stratum spinosum (Prickle cell layer)
Stratum spinosum or prickle cell layer of the epidermis has the vital function of Keratinization. Prickle cell layer is the fourth tier from the exterior and is situated between stratum granulosum and germinativum (basale).

The basale and spinosum keratinocytes are together denoted as Malpighian layer. This prickle tier ranges between 5-10 keratinocytes in thickness and the keratinocytes are modified basal keratinocytes having large nuclei which contain very prominent nucleoli.

Keratinization process begins in stratum spinosum. The large pale staining nuclei of prickle layer, function actively to synthesize cytokeratin, a type of fibrillar protein. Cytokeratin builds up within the keratinocytes and aggregate together to form tonofibrils. These tonofibrils form desmosomes which radiate from the keratinocytes forming points of intracellular connections between adjacent prickle keratinocytes. However it is to be noted that there is no continuity of cytoplasm through the 'prickles' of adjacent spinosum keratinocytes.

The name spinosum denotes the prickle or spiny appearance of the keratinocytes due to the radiating desmosomes. This net-like prickle tier provides protection to the underlying tissues. This net-like spinosum also gives some elasticity and flexibility to the epidermis. The prickle cells tier is thicker in areas of skin subject to frequent abrasion such as palms and soles.

One of the important function of the spinosum keratinocytes is the production of lamellar bodies having polar lipids, free sterols, phospholipids and enzymes. Bipolar lipids are produced and retained by these prickle keratinocytes, whose function is prevention of loss of moisture from the skin.

This spinosum layer contains Langerhans cells which are macrophages with the function of protection against pathogens. Langerhans macrophages contain Birbeck granules also known as Birbeck bodies, which are rod shaped with a striated appearance. Birbeck granules function in receptor-mediated endocytosis and phagocytosis. The origin of Langerhans cells is in the bone marrow and they migrate to this prickle region of epidermis. As these polyhedral spinosum keratinocytes approach the granulosum tier they get gradually flattened. Mitosis (cell division function), which occurs continuously in the basale epidermis is nearly absent in these spinosum keratinocytes.

Illustration of Prickle cell layer (stratum spinosum)

Layers of epidermal skin
stratum spinosum (Prickle cell layer)

Like the keratinocytes of basale region, spinosum keratinocytes are also susceptible to mutations caused by sunlight and can become malignant. Prickle cell carcinoma is found in fair-skinned individuals who have a history of longer term sun exposure.

Related topics:

1. Stratum basale of epidermal skin.
2. Function of the stratum corneum.
3. Structure of dermis.
4. Papillary dermis.
5. Reticular dermis.

Interesting topics:

1. Function of hypodermis.
2. Skin sensitive to touch.
3. Different type of face skin.
4. Main functions of human skin.
5. Know your skin.
6. Nourishing skin with fruits and vegetables.
7. Small itchy water blisters on hands and feet.
8. Cosmetic laser treatments - Types of cosmetic lasers.
9. What are salmon patches? - Nevus simplex birthmarks on babies.
10. What is a hemangioma? - What are the causes of hemangioma?

Reference:

• Harding, C. R. (2004), The stratum corneum: structure and function in health and disease. Dermatologic Therapy, 17: 6–15. doi: 10.1111/j.1396-0296.2004.04S1001.x

1.Image source:
http://en.wikipedia.org/wiki/File:Epidermal_layers.png
Author: Mikael Häggström, based on work by Wbensmith
License: CC BY-SA 3.0
2.Image source:
http://en.wikipedia.org/wiki/File:Prickle_cell.JPG
Author: Sandy G Phillips-Long
License: CC BY-SA 3.0
Current topic: Functions of stratum spinosum (Prickle cell layer).

Basal cell layer of epidermal skin - Stratum basale (germinativum)

Home > Know your skin > Epidermis > Basal cell layer of epidermis

Basal cell layer of skin (aka stratum basale or germinativum) is the lowermost sublayer of epidermis. This layer of basal cells is made up of one row of constantly dividing columnar or cubical undifferentiated keratinocytes.

This region is separated from the lower dermis by basement membrane and is attached to the basement membrane through hemidesmosomes.

Structure of basal cell layer

Stratum basale is usually one keratinocyte deep with melanocytes and Langerhans or immune cells dispersed in between. These melanocytes synthesize melanin pigment, giving color and hue to the skin and the hair. The amount of melanin produced though predetermined genetically, is affected by sun exposure levels leading to increase or decrease in production. The Merkel nerve endings (neuroectodermal origin) which have tactile or touch sensation function are also dispersed in this germinativum epidermis. As this basal stratum is in close contact with dermis, it is nurtured with oxygen and nutrients by dermis by diffusion process.

Functions of basal cell layer

Basal cell (stratum basale)
layers in epidermal skin

High degree of mitosis or cell proliferation activity is found in this basal region and hence the name 'germinativum' (germinating). This cuboid keratinocyte divides into two daughter keratinocytes and the upper keratinocyte migrates towards outer epidermal layers undergoing progressive transformation called keratinisation. After moving into stratum spinosum, these keratinocytes change shape and become polygonal and start synthesizing keratin. Keratinocytes produce more and more keratin and eventually undergo programmed death (apoptosis). In humans, it is estimated that basal stratum turnover from epidermal proliferation units to desquamation every 40–56 days.

The lower basal daughter keratinocyte remains in the stratum basale and undergoes growth and maturation for the next mitosis. As the stratum cornium is continuously sloughed off, the mitosis and replacement activity at basal region should continuously go on. The proliferation and differentiation of basal epidermal region is regulated by Vitamin D3 (cholecalciferol).

Any chemical, physical, physiological, radiological or pathgenic disturbance of this cell proliferation activity at basal germinativum brings about dermal ailments.

Related topics:

1. Function of the stratum corneum.
2. Dermis layers - Structure of dermis.
3. Papillary dermis.
4. Reticular dermis.
5. Function of hypodermis.

Interesting topics:

1. Skin sensitive to touch.
2. Different type of facial skin.
3. Main functions of human skin.
4. Know your skin.
5. Nourishing skin with fruits and vegetables.
6. Small itchy water blisters on hands and feet.
7. Cosmetic laser treatments - Types of cosmetic lasers.
8. What are salmon patches? - Nevus simplex birthmarks on babies.
9. What is a hemangioma? - What are the causes of hemangioma?
10. Hemangioma treatments - Hemangioma removal.

Reference:
Harding, C. R. (2004), The stratum corneum: structure and function in health and disease. Dermatologic Therapy, 17: 6–15. doi: 10.1111/j.1396-0296.2004.04S1001.x
Image source:
http://en.wikipedia.org/wiki/File:Epidermal_layers.png
Author:Mikael Häggström, based on work by Wbensmith
License: CC BY-SA 3.0
Current topic: Basal layer cells of epidermal skin.