Name: hair follicles and their skin functions
Uploaded: 2025-05-22T09:05:56.000Z
Duration: 1 min 16 s
Channel: JoVE

K12 Standards

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Ohio’s Learning Standards and Model Curriculum

9-12

Human Anatomy and Physiology

Support And Motion

Integumentary System

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Accessory Structures of the Skin: Hair and Hair Follicles

Hairs are cylindrical and flexible cellular structures present on the skin.
The visible part of hair seen on the skin surface is its shaft, while its root is below the epidermis.
A transverse section of hair root or shaft mainly shows three concentric layers. The central core &#8212; medulla &#8212; consists of large irregular cells. The intermediate layer &#8212; the cortex&#8212;has several layers of elongated cells. The outermost layer &#8212; the cuticle &#8212; has a single layer of heavily keratinized flat cells.
The hair root is surrounded by the hair follicle, which is made up of epidermal cells and the cellular matrix.
The base of each follicle has a hair bulb wrapped by sensory nerve endings called hair follicle receptors.
In a longitudinal section, the hair bulb shows all the layers of the hair root and the hair follicle.
Deep into the hair bulb is the nipple-shaped hair papilla, whose capillaries nourish the hair.
Above the papilla lies the hair matrix &#8212; the germinal cells &#8212; responsible for the formation and growth of new hair.

accessory structures of the skin: hair and hair follicles

Hair and hair follicles are integral components of the integumentary system. Hair is a filamentous structure composed mainly of a protein called keratin. It is found on the surface of the skin throughout the body, except for areas such as the palms of the hands and soles of the feet.
Hair is a keratinous filament growing out of the epidermis. It is primarily made of dead, keratinized cells. Hair strands originate at the epidermal penetration called the hair follicle. The hair shaft is the part of the hair not anchored to the follicle, and much of this is exposed at the skin&#39;s surface. The rest of the hair, anchored in the follicle, lies below the skin&#39;s surface and is referred to as the hair root. The hair root ends deep in the dermis at the hair bulb and includes a layer of mitotically active basal cells called the hair matrix. The hair bulb surrounds the hair papilla, which is made of connective tissue and contains blood capillaries and nerve endings from the dermis.
The hair follicle is teardrop shaped. Its enlarged base, the hair bulb, is embedded in the hypodermis. The outermost layer of the follicle is the epidermis, which invaginates from the skin surface to envelop the follicle. Within the epidermis is the outer root sheath, which is only present on the hair bulb. It does not extend up the shaft of the hair. Within the outer root sheath is the inner root sheath. The inner root sheath extends about half of the way up the hair shaft, ending midway through the dermis. The hair matrix is the innermost layer. The hair matrix surrounds the bottom of the hair shaft, where it is embedded within the hair bulb. The hair shaft contains three layers: the outermost cuticle, a middle layer called the cortex, and an innermost layer called the medulla.
Hair serves a variety of functions, including protection, sensory input, thermoregulation, and communication. For example, hair on the head protects the skull from the sun. The hair in the nose, ears, and around the eyes (eyelashes) defends the body by trapping and excluding dust particles that may contain allergens and microbes. The hair of the eyebrows prevents sweat and other particles from dripping into and bothering the eyes. Hair also has a sensory function due to sensory innervation by a hair root plexus surrounding the base of each hair follicle. Hair is extremely sensitive to air movement or other disturbances in the environment, much more so than the skin surface. This feature is also useful for the detection of the presence of insects or other potentially damaging substances on the skin surface. Each hair root is connected to a smooth muscle called the arrector pili that contracts in response to nerve signals from the sympathetic nervous system, making the external hair shaft &#34;stand up.&#34; The primary purpose of this is to trap a layer of air to add insulation. This is visible in humans as goose bumps and even more obvious in animals, such as when a frightened cat raises its fur.
This text is adapted from <a href="https://openstax.org/books/anatomy-and-physiology/pages/5-2-accessory-structures-of-the-skin?query=hair&amp;target=%7B%22index%22%3A0%2C%22type%22%3A%22search%22%7D#fs-id1539274">Openstax, Anatomy and Physiology 2e, Section 5.2: Accessary structures of the skin</a><a href="https://openstax.org/books/anatomy-and-physiology/pages/5-2-accessory-structures-of-the-skin?query=hair&amp;target=%7B%22index%22%3A0%2C%22type%22%3A%22search%22%7D#fs-id1539274">.</a>

Hair and hair follicles are integral components of the integumentary system. Hair is a filamentous structure composed mainly of a protein called keratin. ...

Education

JoVE Core

Anatomy and Physiology

Unit 1

The Integumentary System

KEY TERMS AND CONCEPTS

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 dermis, the root ends at the hair bulb. The bulb contains the hair matrix, a layer of basal cells that divide quickly.

The hair bulb surrounds the hair papilla. This papilla is connective tissue that contains blood capillaries and nerve endings from the dermis. The hair follicle has a teardrop shape, and its enlarged base, the hair bulb, sits in the hypodermis. The outer layer of the follicle comes from the epidermis and folds inward to wrap around the hair.

Inside the follicle are the outer root sheath and the inner root sheath. The outer root sheath is found only on the hair bulb and does not extend up the hair shaft. The inner root sheath extends about halfway up the shaft and ends midway through the dermis. The innermost layer is the hair matrix, which surrounds the bottom of the hair shaft in the bulb. The hair shaft itself has three layers: the cuticle, cortex, and medulla.

Hair has several functions. It helps protect the body, provides sensory input, helps with thermoregulation, and can support communication. Hair on the head helps shield the skull from the sun. Hair in the nose, ears, and around the eyes traps dust particles that may carry allergens and microbes. Eyebrows help keep sweat and other particles from dripping into the eyes.

Hair also has a sensory role. A hair root plexus surrounds the base of each follicle and gives the hair sensitivity to air movement and other disturbances. This makes hair more responsive than the skin surface and helps detect insects or other potentially harmful substances on the skin. Each hair root is connected to a smooth muscle called the arrector pili. When the sympathetic nervous system signals it, the muscle contracts and makes the hair shaft stand up.

This reaction helps trap a layer of air for insulation. In humans, it appears as goose bumps. It is also easy to see in animals, such as when a frightened cat raises its fur.

Hair Follicles and Their Skin Functions

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,...

cells of the epidermis

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...

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.

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

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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

Explore hair follicles, hair shaft layers, and the ways hair protects, senses, and helps insulate the body, from eyebrows to goose bumps.

Hair Follicles and Their Skin Functions | 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.

Alabama Course of Study Science

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From Molecules to Organisms: Structures and Processes

9-12.HA.1.2

Florida Department of Education

High School

Life Science

SC.912.L.14

SC.912.L.14.51

Introduction to the Integumentary System

The integumentary system is the organ system that comprises the skin and its associated structures. It is the largest system in the human body and plays a ...

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 ...

Layers of the Epidermis

The epidermis, the outermost layer of the skin, is composed of several distinct layers. From deep to superficial, the layers of the epidermis are as ...

Papillary Dermis

Dermis
The dermis might be considered the &#34;core&#34; of the integumentary system, as distinct from the epidermis and hypodermis. It contains blood and ...

Reticular Dermis

The papillary and reticular dermis are the two layers of the dermis. They are made of connective tissue with fibers of collagen extending from one to the ...

Hypodermis

The hypodermis (the subcutaneous layer or superficial fascia) is present directly below the dermis. It connects the skin to the underlying fascia (fibrous ...

Pigmentation

The color of the skin is influenced by a number of pigments, including melanin, carotene, and hemoglobin. Recall that melanin is produced by cells called ...

Changes in Skin Color: Clinical Perspectives

The first thing a clinician sees is the skin, so the examination of the skin should be part of any thorough physical examination. Most skin disorders are ...

Accessory Structures of the Skin: Hair Growth and Types

Hair growth begins with the production of keratinocytes by the basal cells of the hair bulb. As new cells are deposited at the hair bulb, the hair shaft ...

Accessory Structures of the Skin: Nails

Nails are one of the important accessory structures of the skin. They are hard, protective structures that cover the dorsal surface of the distal ...

Accessory Structures of the Skin: Sweat Glands

Sweat glands or sudoriferous glands are one of the important accessory structures of the skin. They are small, coiled tubular structures located in the ...

Accessory Structures of the Skin: Sebaceous Glands

A sebaceous gland is a type of oil gland found almost all over the skin ( except palms and soles) and helps lubricate and waterproof the skin and hair. ...

Sensory Functions of the Skin

The skin is the largest organ of the human body and plays a crucial role in our sensory perception. It contains a vast network of sensory receptors that ...

Role of Skin in Vitamin D Synthesis

The skin plays a crucial role in the synthesis of vitamin D, a vital nutrient for various physiological processes in the body. Vitamin D is unique because ...

Skin Diseases and Disorders

Skin is the first line of defense and encounters a variety of microbes. Some pathogenic strains are often the cause of a broad range of infections of the ...

Skin Cancer

Skin cancer is a type of cancer that occurs when there is an abnormal growth of skin cells, usually triggered by damage to the DNA within the skin cells. ...

Burn Injuries

Burn injuries occur when the skin and underlying tissues are damaged due to exposure to heat, electricity, chemicals, radiation, or friction. They can ...

Integumentary System

Content elaboration: The integumentary system consists of skin and accessory structures. The skin is composed of three layers: the epidermis, the dermis and the hypodermis (subcutaneous layer). The accessory structures can include sweat glands, sebaceous glands, arrector pili muscles, hair follicles and nails. Skin functions include protection, temperature regulation, excretion and sensory perception. These occur through the processes of perspiration, skin production and shedding, vitamin D synthesis and repair. Homeostatic imbalances are explored. These include, but are not limited to, burns, skin cancer, anhidrosis, acne, eczema or scleroderma. Investigations are used to understand and explain the integumentary system in a variety of inquiry and design scenarios that can incorporate evolutionary concepts, scientific reasoning, comparative analysis, communication skills and real-world applications.

Introduction to the Skeletal System

The skeletal system is the central framework of the body, consisting of different connective tissues: bones, cartilage, tendons, and ligaments.
Components ...

The Functions of the Skeletal System

The most apparent functions of the skeletal system are support, protection, and movement. However, bone tissue also performs several other critical ...

Classification of Bones

The bones of the human skeletal system are of varied shapes, sizes, and functions. They can be classified based on their shape and function into four ...

Gross Anatomy of Bone

The two main features of a long bone are the diaphysis and the epiphysis.
The diaphysis is the tubular shaft that runs between the proximal and distal ...

Compact Bone

Most bones contain compact and spongy osseous tissue, but their distribution and concentration vary based on the bone&#39;s overall function.
Compact ...

Spongy Bone

All bones comprise an outer layer of compact bone, and an interior made up of spongy bone tissue, also called cancellous or trabecular bone. In long ...

Bone Markings

Bones have various surface features that help form joints and attach to other soft tissues. Depending on the function, bone markings are categorized into ...

Bone Cells and Tissue

Bones contain a relatively small number of cells entrenched in a matrix of organic and inorganic components. Although bone cells compose only a small ...

The Bone Matrix

Bone contains a relatively small number of cells entrenched in a matrix of collagen fibers that provide an adherent surface for inorganic salt ...

Blood and Nerve Supply to the Bones

Bones are dynamic organs that require a rich supply of oxygen and nutrients. Around 5% to 10% of the cardiac output supplies blood to the bones. A typical ...

bone-formation-by-intramembranous-ossification

Bone Formation by Intramembranous Ossification

Intramembranous ossification is one of the two processes involved in the development of bones within an embryo. The flat bones of the face, most of the ...

bone-formation-by-endochondral-ossification

Bone Formation by Endochondral Ossification

Bone formation, or ossification, begins around the sixth to seventh week of embryonic development. Most bones develop from a cartilaginous template ...

Bone Remodeling and Repair

Fractures: Bone Repair

Treatment for a fracture is based on the type of break, the bone affected, and the patient&#39;s age.
Minor fractures with no bone displacement are ...

Bone Disorders

Aging and its effect on bone remodeling is the most common cause of bone disorders. In young and healthy people, bone deposition and resorption happen at ...

Essential Minerals for Bone Health

The minerals contained in all of the food we consume are essential for our organ systems. However, certain essential minerals, such as calcium, ...

role-of-vitamins-in-maintaining-bone-health

Role of Vitamins in Maintaining Bone Health

The growth and maintenance of bone are regulated by a combination of nutritional factors, including vitamins, such as vitamin A, B12, C, D, and K.
Vitamin ...

Hormones and Bone Tissue

The endocrine system produces and secretes hormones, which interact with the skeletal system. These hormones control bone growth, maintain bone once it is ...

Skeleton and Calcium Homeostasis

Calcium is not only the most abundant mineral in bone but also the most abundant mineral in the human body. Calcium ions are needed for bone ...

Overview of the Axial Skeleton

The skeleton is subdivided into two major divisions&#8212;the axial skeleton and the appendicular skeleton. The axial skeleton forms the vertical, central ...

Overview of the Skull

The cranium (skull) is the skeletal structure of the head that supports the face and protects the brain. It is subdivided into the facial bones and the ...

cranial-bones-superior-and-posterior-view

Cranial Bones: Superior and Posterior View

The superior view of the cranium shows the frontal and paired parietal bones.
The frontal bone is the single bone that forms the forehead. At its anterior ...

Cranial Bones: Lateral View

The lateral view of the cranium is dominated by temporal, sphenoid, and ethmoid bones.
The temporal bone forms the lower lateral side of the skull. The ...

Sutures of the Skull

The human skull is composed of several bones that come together to protect the brain and support the structures of the face. The junctions where these ...

The Hyoid Bone

The hyoid bone is a small U-shaped bone located in the upper neck at the level of the inferior mandible, with its tips pointing posteriorly. It does not ...

The Auditory Ossicles

The auditory ossicles of the middle ear transmit sounds from the air as vibrations to the fluid-filled cochlea. The auditory ossicles consist of two ...

Vertebral Column: Regions and Curvature

The vertebral column or spine is a flexible column that supports the head, neck, and body and&#160; allows for their movements. It also protects the ...

General Structure of a Vertebra

A typical vertebra, with the exception of the sacrum and coccyx, consists of a body, a vertebral arch, and seven different projections termed processes. ...

The Thoracic Cage: Sternum

The thoracic or rib cage forms the body&#39;s thorax (chest) portion. Its primary function in the body is to protect vital organs in the thoracic cavity, ...

The Thoracic Cage: Ribs

Ribs are curved, flattened bones forming the thoracic cavity wall with the thoracic muscles. There are 12 pairs of thoracic ribs. The posterior ends of ...

Structural Joints: Fibrous Joints

Fibrous joints are a type of joint where the bones are connected by fibrous connective tissue. These joints provide stability and minimal to no movement ...

Bones of the Upper Limb: Humerus

The upper limb consists of the arm, forearm, wrist, and hand bones. The humerus is the single bone of the upper arm region. Proximally, it has a large, ...

Structural Joints: Cartilaginous Joints

As the name indicates, at a cartilaginous joint, the adjacent bones are united by cartilage, a tough but flexible type of connective tissue. Unlike ...

Bones of the Upper Limb: Ulna

The ulna and radius are parallel bones of the antebrachium or the forearm. The ulna lies medially and consists of a bony tip called the olecranon process ...

Structural Joints: Synovial Joints

Synovial joints are the most common type of joint in the body. A key structural characteristic for a synovial joint is the presence of a joint cavity. ...

Bones of the Upper Limb: Radius

The radius is longer of the two bones that make up the human antebrachium or forearm. At the proximal end, the radius articulates with the capitulum of ...

Skeletal System

Content elaboration: The skeletal system is composed of bones, cartilage, joints and ligaments. Bones make up most of the skeleton. There are four main cell types that compose bone tissue, each with a specific function: osteogenic cells, osteocytes, osteoblasts and osteoclasts. The microscopic anatomy of compact bone includes osteons. Bones are classified by their shape. The structure of a typical long bone can be explored. Specific bones of the skeleton can be studied by their subdivisions: the axial skeleton and the appendicular skeleton. Cartilage is found in areas of the nose, ears, ribs and joints. Joints can be classified by structure or by function. The general structure of synovial joints may be explored. Ligaments connect bone to bone, stabilizing joints. The skeletal system provides support for the human body, protects soft organs, allows for movement due to attachment of muscles, stores minerals and fat and forms blood cells. Processes of the skeletal system include hematopoiesis, ossification and bone growth and remodeling. A comparison of male to female, juvenile to adult or human to other vertebrate skeletons may be explored. Homeostatic imbalances are explored. These include, but are not limited to, osteoporosis, malnutrition, fractures, anterior cruciate ligament (ACL) injuries and arthritis. Investigations are used to understand and explain the skeletal system in a variety of inquiry and design scenarios that can incorporate evolutionary concepts, scientific reasoning, comparative analysis, communication skills and real-world applications.

Skeletal System

Hair Follicles and Their Skin Functions

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