Name: epidermis layers and cell turnover
Uploaded: 2023-06-23T15:38:47.000Z
Duration: 1 min 24 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-1

Cells of the Epidermis

The epidermis, the topmost layer of the skin, consists of four major cell types&#8212;keratinocytes, melanocytes, dendritic cells, and Merkel cells.
Keratinocytes form most of the epidermis. They produce a protein called keratin - a tough, fibrous protein that protects the skin and underlying tissue.
In response to the epidermal growth factors, the newly produced keratinocytes continuously push the older cells toward the skin surface.
By the time they reach the skin surface, keratinocytes die due to the lack of dermal blood supply and are replaced by new cells rendering a renewed epidermis every 25 to 45 days.
Melanocytes are spider-shaped cells found deep inside the epidermis. They produce melanin pigment, which is transferred to nearby keratinocytes through their processes. Melanin protects the nucleus of keratinocytes from the damaging effects of UV radiation.
Dendritic cells are star-shaped cells dispersed in the epidermis. They can ingest microorganisms and activate immune responses.
Merkel cells at the junction of the dermis and epidermis are linked to disc-like nerve endings forming the sensory receptor for touch.

cells of the epidermis

The epidermis is made of four or five layers of epithelial cells, depending on its location in the body. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. 
The cells in all these layers except the stratum basale are called keratinocytes, a type of cell that manufactures and stores the protein keratin. The keratinocytes in the stratum corneum are dead and regularly slough away, being replaced by cells from the deeper layers.
The stratum basale is a single layer of cells primarily made of basal cells. A basal cell is a cuboidal-shaped stem cell that is a precursor of the keratinocytes of the epidermis. All keratinocytes are produced from this single layer of cells, constantly going through mitosis to produce new cells. As new cells are formed, the existing cells are pushed superficially away from the stratum basale. Two other cell types are found dispersed among the basal cells in the stratum basale. The first is a Merkel cell, which functions as a receptor and is responsible for stimulating sensory nerves that the brain perceives as touch. These cells are especially abundant on the surfaces of the hands and feet. The second is a melanocyte, a cell that produces the pigment melanin. Melanin gives hair and skin their color and helps protect the living cells of the epidermis from ultraviolet (UV) radiation damage.
The stratum spinosum is composed of eight to ten layers of keratinocytes formed due to cell division in the stratum basale. Interspersed among the keratinocytes of this layer is a type of dendritic cell called the Langerhans cell, which functions as a macrophage by engulfing bacteria, foreign particles, and damaged cells in this layer. 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.
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, and their cell membranes thicken, generating large amounts of the proteins keratin, which is fibrous, and keratohyalin, which accumulates as lamellar granules within the cells. 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 next two layers of the epidermis - the stratum lucidum, and the stratum corneum.
The keratinocytes that compose the stratum lucidum are dead and flattened. These cells are densely packed with eleidin, a clear protein derived from keratohyalin, giving these cells a transparent (i.e., lucid) appearance.
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 in about four weeks. Cosmetic procedures, such as microdermabrasion, help remove some dry upper layers and keep the skin looking &#34;fresh&#34; and healthy.
This text is adapted from <a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/5-1-layers-of-the-skin">Openstax, Anatomy and Physiology 2e, Section 5.1: Layers of the Skin</a>

The epidermis is made of four or five layers of epithelial cells, depending on its location in the body. From deep to superficial, these layers are the ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

The Integumentary System

KEY TERMS AND CONCEPTS

epidermis layers and cell turnover

The epidermis is the outer skin layer and is built from four or five layers of epithelial cells, depending on where it is found in the body. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. Most of the cells in these layers are keratinocytes, which make and store keratin, a protective protein.

The stratum basale is a single cell layer made mostly of basal cells. A basal cell is a cuboidal stem cell that gives rise to the keratinocytes of the epidermis. These cells divide by mitosis to form new keratinocytes, and the newer cells push older cells toward the surface. Two other cell types are found among the basal cells. Merkel cells act as receptors that help stimulate sensory nerves for touch, especially on the hands and feet. Melanocytes make melanin, the pigment that gives hair and skin color and helps protect living epidermal cells from UV radiation damage.

Above this layer is the stratum spinosum, which usually has eight to ten layers of keratinocytes made by cell division in the stratum basale. Langerhans cells are scattered through this layer. They are dendritic cells that act like macrophages by engulfing bacteria, foreign particles, and damaged cells. Keratinocytes here begin making keratin and release a water-repelling glycolipid. This helps limit water loss and makes the skin relatively waterproof.

As more new keratinocytes are made, the cells move into the stratum granulosum. This layer has three to five layers of cells and looks grainy because the keratinocytes keep changing as they move upward. The cells flatten, their membranes thicken, and they produce large amounts of keratin and keratohyalin. Keratin is fibrous, and keratohyalin collects as lamellar granules inside the cells. Together, these materials make up most of the cell mass in this layer. The nuclei and other organelles then break down as the cells die, leaving keratin, keratohyalin, and cell membranes for the upper layers.

The next layers are the stratum lucidum and the stratum corneum. The keratinocytes in the stratum lucidum are dead and flattened, and they contain eleidin, a clear protein made from keratohyalin. This gives the layer a transparent, or lucid, look. These cells are shed from time to time and replaced by cells pushed up from the stratum granulosum, or from the stratum lucidum in the palms and soles of the feet. The entire layer is replaced in about four weeks. Cosmetic treatments such as microdermabrasion remove some of the dry outer layers and can help skin look fresh and healthy.

Epidermis Layers and Cell Turnover

introduction to the integumentary system

Layers and Functions of Skin

The integumentary system includes the skin and its associated structures. It is the largest organ system in the human body. It helps protect the body and maintain homeostasis, which means keeping internal conditions stable. Skin has three main layers: the epidermis, dermis, and hypodermis, also called subcutaneous tissue. The epidermis is the outermost layer. It forms a protective barrier against bacteria, UV radiation, and chemicals. It also contains melanocytes, the cells that make melanin,...

The epidermis is the outer skin layer and is built from four or five layers of epithelial cells, depending on where it is found in the body. From deep to superficial, these layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. Most of the cells in these layers are keratinocytes, which make and store keratin, a protective protein. The stratum basale is a single cell layer made mostly of basal cells. A basal cell is a cuboidal stem cell that...

layers of the epidermis

Epidermis Cell Renewal and Skin Protection

The epidermis is the outermost layer of skin, and it is built to protect the body. It contains several distinct layers that change as cells move upward. From the deepest layer to the surface, these layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum basale, also called the stratum germinativum, is the deepest layer of the epidermis. It has a single layer of actively dividing basal cells, or basal keratinocytes. These cells keep...

papillary dermis

Papillary Layer of the Dermis

The papillary layer is the outer part of the dermis. It is made of loose, areolar connective tissue, so its collagen and elastin fibers form a loose mesh. This layer sits next to the epidermis and helps show how the skin is organized into distinct layers. The papillary layer projects into the stratum basale of the epidermis. These finger-like extensions are called dermal papillae. Inside this layer are fibroblasts, a small number of adipocytes, and many small blood vessels. It also contains...

reticular dermis

Reticular Dermis and Skin Support

The reticular dermis is the thicker inner layer of the dermis. It lies beneath the papillary layer, and both layers are made of connective tissue. Collagen fibers extend from one layer to the other, so the border between them is not very clear. The papillary layer includes the dermal papillae that extend into the epidermis. Below that, the reticular layer is made of dense, irregular connective tissue. It has a tight meshwork of fibers, which gives it a net-like, or reticulated, appearance. <br...

hypodermis

Hypodermis and Body Fat Storage

The hypodermis is the layer beneath the dermis. It is also called the subcutaneous layer or superficial fascia. It links the skin to the fascia, which is fibrous tissue over the bones and muscles. The border between the hypodermis and dermis can be hard to see, and the hypodermis is not strictly part of the skin. The hypodermis contains loose areolar connective tissue and adipose tissue. Adipose tissue is fat tissue, and its cells are called adipocytes. This layer stores much of the body fat...

pigmentation

How Skin Gets Its Color

Skin color comes from melanin, carotene, and hemoglobin. Melanin is made by melanocytes, which are scattered through the stratum basale of the epidermis. The pigment moves to keratinocytes through melanosomes, which help carry the color into the skin cells. Melanin appears in two main forms. Eumelanin gives black and brown color, while pheomelanin gives red color. People with darker skin make more melanin than people with pale skin. Sun exposure changes melanin production. UV rays from the...

changes in skin color: clinical perspectives

changes-in-skin-color-clinical-perspectives

Skin Color Changes as Health Clues

Skin color changes can be an important clue about health. A careful skin exam is part of a full physical examination. Most skin disorders are harmless, but some, including melanoma, can be fatal if they are not treated. Two visible disorders, albinism and vitiligo, change the color of the skin and its accessory organs. Albinism is a genetic disorder that affects the color of the skin, hair, and eyes. It happens when melanocytes, the cells that make melanin, cannot produce enough or any melanin.

accessory structures of the skin: hair and hair follicles

accessory-structures-of-the-skin-hair-and-hair-follicles

Hair Follicles and Their Skin Functions

Hair and hair follicles are accessory structures of the skin. Hair is a keratin-filled filament that grows from the epidermis. It is mainly made of dead, keratinized cells. Hair is found on most body surfaces, but not on areas such as the palms of the hands and the soles of the feet. Each hair strand begins in a hair follicle, which is an epidermal opening that extends into the skin. The part above the skin surface is the hair shaft. The part below the surface is the hair root. Deep in the...

accessory structures of the skin: hair growth and types

accessory-structures-of-the-skin-hair-growth-and-types

Hair Growth Cycle and Pigment Basics

Hair is an accessory structure of the skin that grows from a hair bulb inside a follicle. Basal cells in the hair bulb make keratinocytes, and new cells are added there as the hair shaft is pushed upward toward the surface. As the cells move up, keratinization finishes, and the visible part of the hair becomes a dead structure made mostly of keratin. Because only the surface of the hair is cut or shaved, these methods do not damage the hair structure. Most chemical hair removers also work only...

accessory structures of the skin: nails

Nail Structure and Function in the Skin

Nails are hard accessory structures of the skin on the tips of fingers and toes. They cover the dorsal surface of the distal phalanges. Nails are made of specialized keratinized cells. They help protect the fingertips and toes, support sensation, and aid manual dexterity. The nail plate is the visible part of the nail that extends beyond the fingertips or toes. It is hard and translucent, but it often looks pink because blood vessels underneath show through. The nail plate is made of layers of...

accessory structures of the skin: sweat glands

accessory-structures-of-the-skin-sweat-glands

How Sweat Glands Help Cool the Body

Sweat glands help the body control temperature and remove waste. These sudoriferous glands are small, coiled tubes in the dermis, which is the middle layer of the skin. They release sweat, a watery fluid that supports homeostasis, the body’s stable internal balance. Sweat glands are classified as merocrine glands. In merocrine secretion, the gland releases its product by exocytosis through a duct, and the gland cells stay intact. This process allows sweat to move out of the gland without...

accessory structures of the skin: sebaceous glands

accessory-structures-of-the-skin-sebaceous-glands

Sebum, Acne, and Sebaceous Glands

Sebaceous glands are oil glands in the skin that release sebum. They are found almost everywhere on the body, except on the palms and soles. Most of them are linked to hair follicles, where they help keep the skin and hair lubricated and waterproofed. These glands make a lipid-rich mixture called sebum and release it onto the skin surface. Sebum softens the dry, dead cells of the stratum corneum, the outer keratinized layer of the skin, and helps keep that layer pliable. Sebaceous glands are...

sensory functions of the skin

Skin Receptors and the Sense of Touch

The skin is the largest organ of the human body, and it helps us sense touch, temperature, and pain. It contains many sensory receptors that detect physical, biological, and environmental cues. These signals help protect the body and guide fast responses. Skin receptors are grouped into two main categories: capsulated and non-capsulated. The non-capsulated receptors are mainly pain receptors. The capsulated receptors respond to specific kinds of stimuli, such as pressure, vibration, and...

role of skin in vitamin d synthesis

How Sunlight Triggers Vitamin D in Skin

The skin helps make vitamin D when it is exposed to sunlight. UVB radiation from the sun, with wavelengths of 290 to 315 nm, starts a chemical reaction in the skin. This makes vitamin D unique because it can be synthesized in the body through the skin. In this process, UVB rays are absorbed by the skin and convert 7-dehydrocholesterol, also called provitamin D3, into previtamin D3. Previtamin D3 then changes quickly into vitamin D3, also known as cholecalciferol. Once vitamin D3 forms, it...

skin diseases and disorders

Common Skin Infections and Their Causes

Skin infections often start when microbes affect the body’s first line of defense. Many skin conditions can affect people of all ages. They may come from genetic factors, infections, autoimmune reactions, environmental factors, or lifestyle choices. Many of the most common skin infections are caused by gram-positive Staphylococcus spp. and Streptococcus spp. However, many skin problems are not linked to just one pathogen. Opportunistic pathogens can infect skin wounds, and similar symptoms may...

skin cancer

Skin Cancer Signs and Treatments

Skin cancer develops when skin cells grow in an abnormal way because their DNA has been damaged. Ultraviolet, or UV, radiation from the sun and from tanning beds is the main cause. The number of skin cancer cases continues to rise, and it is the most common type of cancer worldwide. Basal cell carcinoma, or BCC, is the most common form and makes up about 80% of cases. It usually appears on skin that gets a lot of sun, such as the face, scalp, neck, and hands. A BCC may look like a small raised...

burn injuries

Burn Severity, Healing, and Care

Burn injuries damage the skin and the tissues below it. They can result from heat, electricity, chemicals, radiation, or friction. These injuries range from minor superficial burns to deep burns that can be life-threatening. Severe burns can kill skin cells and cause a major loss of fluid. That fluid loss can lead to dehydration, electrolyte imbalance, and failure of the kidneys and circulatory system. Burn patients often receive intravenous fluids to replace water loss and intravenous...

key terms and concepts

Learn how epidermis layers renew from basal cells to dead surface cells, plus the roles of keratinocytes, melanocytes, Merkel cells, and Langerhans cells.

Epidermis Layers and Cell Turnover | JoVE K12

anatomy and physiology

JoVE Core Anatomy and Physiology showcases the anatomical and physiological details of the human body in comprehensive, clear, and engaging video animations. This collection of lessons focuses on the structures, components, functions, and requirements of the human body. It is complemented by scientist-in-action videos that demonstrate the application of this knowledge in real-world medical and research settings.

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Ohio’s Learning Standards and Model Curriculum

9-12

Human Anatomy and Physiology

Support And Motion

Integumentary System

Alabama Course of Study Science

From Molecules to Organisms: Structures and Processes

9-12.HA.1.2

Florida Department of Education

Life Science

SC.912.L.14

SC.912.L.14.51

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HS-LS1-2

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HS-LS1-3

Epidermis Layers and Cell Turnover

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