The Integumentary System

Summary

Professor Dave's video delves into the integumentary system, the body's outermost layer. It comprises the skin, hair, nails, and various glands, serving as a protective barrier. The skin, an organ with two main layers—the epidermis and dermis—functions as a first defense against environmental threats. The epidermis, made of keratinized cells, renews itself every few weeks. The dermis, rich in nerves and blood vessels, supports the skin. Hair and nails, made of keratin, offer additional protection. Glands like sweat and sebaceous contribute to temperature regulation and skin health, highlighting the integumentary system's multifaceted role in maintaining homeostasis.

Takeaways

• 🧬 The integumentary system is the outermost system of the body, consisting of the skin, its derivatives like glands, hair, and nails.
• 🛡️ The skin serves as the first line of defense, protecting against environmental elements, bacteria, and preventing water loss while retaining heat.
• 🔍 The skin is structured into two main regions: the epidermis, a thin outer layer, and the dermis, a thicker, inner layer.
• 🌱 The epidermis is avascular and receives nutrients by diffusion from the dermis, while the dermis is vascularized and receives nutrients from the bloodstream.
• 🔑 The stratum basale, the deepest layer of the epidermis, contains keratinocytes that continuously divide to regenerate the skin and produce keratin.
• 🌈 Melanocytes in the stratum basale produce melanin, contributing to skin color and offering protection from ultraviolet radiation.
• 💧 The dermis contains hair follicles, nerves, and blood vessels, and is divided into the papillary layer and the reticular layer.
• 🦠 Dermal ridges and papillae enhance the skin's grip and tactile sensitivity, with fingerprints being a result of these structures.
• 💇 Hair is made of keratinized cells and serves protective functions; it grows from hair follicles which have a complex structure including a hair bulb and matrix.
• 💧 Sweat glands help regulate body temperature and excrete waste, while sebaceous glands produce sebum to lubricate the skin and hair.
• 🌀 The integumentary system plays a crucial role in maintaining homeostasis by acting as a barrier, aiding in temperature regulation, and interacting with the external environment.

Q & A

What is the integumentary system and what does it consist of?

The integumentary system is the outermost system of the body, consisting of the skin, hair, nails, and various glands. It serves as a protective barrier and has functions such as temperature regulation and sensation.

What are the two main regions of the skin and their functions?

The skin is divided into the epidermis and the dermis. The epidermis is the thin outer layer made of epithelial tissue that acts as a barrier, while the dermis is the thicker inner layer of connective tissue that provides structural support and houses blood vessels and nerves.

How does the epidermis obtain nutrients since it is avascular?

The epidermis gets nutrients by diffusion through the tissue fluid from the dermis, as it lacks its own blood supply.

What is the function of the stratum basale in the epidermis?

The stratum basale is the deepest layer of the epidermis where cells, primarily keratinocytes, divide rapidly to regenerate dead skin and produce keratin.

What are melanocytes and what role do they play in the skin?

Melanocytes are cells in the stratum basale that produce melanin, a pigment that determines skin color and protects the skin from ultraviolet radiation.

Describe the structure of a hair follicle and its role in hair growth.

A hair follicle is a pocket that extends from the epidermis into the dermis, containing a hair bulb with nerve endings and a hair papilla that supplies nutrients for hair growth. The hair matrix within the follicle is where cells divide, pushing the hair upwards and causing it to grow.

What is the difference between eccrine and apocrine sweat glands?

Eccrine sweat glands are more numerous and secrete a watery sweat primarily composed of water, salts, and metabolic wastes. Apocrine sweat glands are fewer, found in specific areas, and secrete a sweat that contains fat and protein components, which contribute to body odor.

How does the structure of nails relate to their function?

Nails are made of hard keratin, providing them with strength and durability. They have a free edge for scratching or picking up objects, a body that covers the nail bed, and a proximal root embedded in the skin, all of which facilitate their protective and functional roles.

What is the purpose of the arrector pili muscles associated with hair follicles?

The arrector pili muscles can contract, causing the hair follicle to stand up and the skin to dimple, creating goose bumps. This response can be triggered by cold temperatures or fear and serves as a way to trap heat or signal potential threats in more fur-covered mammals.

What are the primary functions of the integumentary system?

The integumentary system serves as a barrier to protect the body from external threats, regulates body temperature, allows for the sensation of touch, and has the ability to repair quickly.

Outlines

00:00

🌟 Overview of the Integumentary System

Professor Dave introduces the integumentary system, which is the outermost system of the human body, consisting of the skin and its derivatives like hair, nails, and certain glands. The skin serves as a protective barrier, preventing bacteria from entering and maintaining the body's water and heat balance. The structure of the skin is explored, highlighting the epidermis, a thin outer layer, and the dermis, a thicker inner layer. The subcutaneous layer, or hypodermis, anchors the skin to underlying structures. The epidermis is further divided into layers with specific functions, such as the stratum basale for cell regeneration and the stratum corneum for protection. The role of melanocytes in skin color and protection from UV radiation is also discussed.

05:00

🔍 Deep Dive into Skin Structure and Hair

This section delves deeper into the structure of the skin, focusing on the dermis which contains hair follicles, nerves, and blood vessels. The dermis is divided into the papillary layer, involved in touch sensation and fingerprint formation, and the reticular layer, which provides strength and flexibility. The discussion moves on to hair, explaining that it is made of keratinized cells and serves protective functions. Hair structure is detailed, including the medulla, cortex, and cuticle, and the process of hair growth from the hair follicle is described. The role of the arrector pili muscle in creating goosebumps is also mentioned.

10:02

💧 Functions of Skin Appendages and Glands

The final paragraph covers the remaining components of the integumentary system, including nails and various glands. Nails are described as hard keratin structures that protect the fingertips and aid in manipulation. The structure of a nail, including the free edge, body, and root, is outlined. The integumentary system's glands are explored, with a focus on sweat glands, which regulate temperature and excrete waste, and sebaceous glands, which produce sebum to lubricate the skin. The paragraph concludes by summarizing the integumentary system's role as a barrier, its repair capabilities, and its functions in temperature regulation and external stimuli response.

Keywords

💡Integumentary System

The integumentary system is the outermost system of the human body, primarily composed of the skin, hair, nails, and various glands. It serves as the body's first line of defense against environmental factors, protecting internal organs and regulating body temperature. In the video, the integumentary system is introduced as the starting point for exploring the body's systems, highlighting its crucial role in maintaining overall health and homeostasis.

💡Epidermis

The epidermis is the thin, outermost layer of the skin, made up of epithelial tissue. It is avascular, meaning it lacks blood vessels, and relies on diffusion from the underlying dermis for nutrients. The epidermis is composed of several layers, including the stratum basale, which contains cells that continuously divide to regenerate the skin. The video explains that the epidermis is essential for protection and is composed of keratinized cells that provide a barrier against external threats.

💡Dermis

The dermis is the thicker, inner layer of the skin, located beneath the epidermis. It is a tough layer of fibrous connective tissue that is vascularized, meaning it contains blood vessels that supply nutrients to the skin. The dermis contains hair follicles, nerves, and blood vessels, and is divided into the papillary and reticular layers. The video describes the dermis as being responsible for the skin's strength and elasticity, as well as its sensory functions.

💡Keratinocytes

Keratinocytes are the predominant cell type found in the stratum basale of the epidermis. They are responsible for the production of keratin, a protein that provides structural support to the skin. The video emphasizes that these cells are constantly dividing and pushing new cells upward, which is essential for skin regeneration and the constant renewal of the epidermis.

💡Melanocytes

Melanocytes are specialized cells in the skin that produce melanin, a pigment molecule responsible for the color of the skin and for protecting it from ultraviolet radiation. The video mentions that melanocytes are found in the stratum basale and play a role in determining skin color, alongside other pigments like carotene and hemoglobin.

💡Hair Follicles

Hair follicles are the structures from which hair grows. They consist of a root, where keratinization occurs, and a shaft, which is the part of the hair that extends above the skin surface. The video explains that hair follicles are part of the integumentary system and are responsible for hair growth, with the hair itself being composed of keratinized cells.

💡Sweat Glands

Sweat glands, also known as sudoriferous glands, are exocrine glands found throughout the skin that produce sweat. The video distinguishes between two types of sweat glands: eccrine, which are more numerous and secrete a watery sweat, and apocrine, which are fewer and secrete a sweat that contains fat and protein components. Sweat glands play a role in thermoregulation and excretion of waste products.

💡Sebaceous Glands

Sebaceous glands, or oil glands, are glands that secrete sebum, an oily substance that lubricates and softens the skin and hair. The video mentions that these glands are part of the integumentary system and help to prevent water loss and inhibit the growth of certain bacteria on the skin.

💡Nails

Nails are hard, protective structures found at the tips of fingers and toes, made of a form of keratin called hard keratin. The video explains that nails are part of the integumentary system and serve a protective function, with the nail growing from a region called the nail matrix.

💡Stratum Corneum

The stratum corneum is the outermost layer of the epidermis, composed of dead, keratinized cells that have lost their nuclei. The video describes this layer as providing a critical barrier against environmental factors, such as pathogens and water loss, while also being part of the skin's protective mechanism.

Highlights

The integumentary system is the outermost system of the body, consisting of the skin and its derivatives.

Skin acts as the first line of defense, keeping bacteria out and maintaining body water and heat.

The skin is composed of the epidermis and dermis, with the latter being vascularized and the former avascular.

The epidermis is made of keratinized stratified squamous epithelium with four different cell types in five layers.

The stratum basale is the deepest layer of the epidermis, containing rapidly dividing keratinocytes.

Melanocytes in the stratum basale produce melanin, affecting skin color and UV protection.

The stratum spinosum is characterized by cells with a weblike system of intermediate filaments.

The stratum granulosum is where keratinization begins, and cells fill with keratin as they die.

The stratum lucidum is a clear layer of dead keratinocytes that are beginning to form tonofilaments.

The stratum corneum is the outermost, dead cell layer that protects the living cells inside.

The dermis is made of connective tissue, containing nerves and blood vessels, and is where hair follicles begin.

The papillary layer of the dermis contains dermal papillae that enhance tactile sensation.

Dermal ridges in areas of high friction, like the hands, contribute to grip and form fingerprints.

The reticular layer is the main part of the dermis, made of dense fibrous connective tissue.

Hair is a flexible strand of dead keratinized cells, produced by hair follicles with a root and a shaft.

Hair follicles contain a hair bulb with nerve endings that respond to hair bending.

Arrector pili muscles can cause goose bumps by contracting and pulling hair follicles.

Nails are made of hard keratin and serve as tools for scratching or picking up objects.

Sweat glands, including eccrine and apocrine types, are responsible for sweat production and body temperature regulation.

Sebaceous glands secrete sebum to lubricate hair and skin, slowing water loss and providing antimicrobial properties.

The integumentary system serves as a barrier, regulates body temperature, and responds to external stimuli.

Transcripts

It’s Professor Dave, let’s look at the integumentary system.

With some basics covered regarding two of the types of tissue in the human body, we

are ready to start looking at some of the different systems found in the body, and we

are going to start with the outermost system, which is called the integumentary system.

This is made up of the skin that covers and protects all your other body parts, as well

as its derivatives, like certain glands, as well as hair and nails.

Let’s look at the structure and function of these components now.

The skin is a remarkable organ, acting as the first line of defense from the elements

that surround us.

It keeps bacteria out, and water and heat in, so let’s check out the structure of skin.

Our skin is made of two regions, a thin outer layer, which is the epidermis, and a thicker

inner layer, called the dermis.

The dermis, which is a tough layer of fibrous connective tissue, is vascularized, getting

its nutrients from the bloodstream.

The epidermis, which is made of epithelial tissue, is avascular, so it gets nutrients

by diffusion through the tissue fluid from the dermis.

In addition, below the dermis is the subcutaneous layer, also called the hypodermis.

This is made predominately of adipose tissue, and it anchors the skin to other structures below.

Now let’s zoom in on the epidermis, the thin outer layer of the skin.

This is made of keratinized stratified squamous epithelium, made of four different cell types

in five layers.

The deepest layer, the one attached to the dermis, is called the stratum basale, meaning

basal layer.

This is made of a single row of cells, most of which are called keratinocytes.

These are rapidly dividing all the time, pushing new cells up into the layers above, to help

regenerate dead skin, and producing lots of keratin as they do so.

This is necessary because millions of dead keratinocytes rub off your skin every day,

due to friction, and even more from your hands and feet, so these constantly dividing cells

in the stratum basale ensure that a new epidermis forms every few weeks, so that we always have

our skin intact.

This layer also contains melanocytes, which produce melanin, and tactile cells, which

act as the sensory receptor for touch.

Above this is the stratum spinosum, meaning prickly layer.

This section is several layers of cells thick, and is full of cells with a weblike system

of intermediate filaments attached to desmosomes.

They look kind of spiky, so they are sometimes called prickly cells.

Here we can also find dendritic cells, which ingest foreign substances and activate the

immune system, which we will talk about later.

Next is the stratum granulosum, or granular layer.

This is four to six cell layers thick, and in this section, keratinization begins as

cells continue to move their way upwards from the basal layer.

This is when the cells get far enough from the dermal capillaries below to receive sufficient

nutrients, so the cells fill up with keratin as they die, and they flatten while the organelles

disintegrate.

This makes the cell tougher and scalier, which allows for the outer layers to better protect

the body.

Above this is the stratum lucidum, or the clear layer.

This is two or three cell layers thick, made of dead keratinocytes that have become flat

and clear.

This is where they begin to aggregate into arrays called tonofilaments.

And lastly, there is the stratum corneum, or horny layer.

This outermost section is twenty to thirty cell layers thick, and all of these cells

are anucleated, meaning the nucleus has disintegrated.

So it’s incredible to think that all the cells covering the outside of your body are

actually dead, but they are dead in a specialized way, with thick plasma membranes surrounding

lots of keratin.

These dead cells protect all the living ones inside from all the outside dangers.

With the epidermis covered, let’s go a little deeper and talk about the dermis.

This is made of strong and flexible connective tissue, and is full of nerves and blood vessels.

This is also where hair follicles begin.

The dermis has two sections, the papillary layer, and the reticular layer.

Descending from the epidermis we enter the papillary layer, which is very thin, made

of areolar connective tissue and a loose network of collagen and elastic fibers.

This leaves room for defensive cells to patrol the area for bacteria that may have made it

through the skin.

The word papillary refers to the projections from the surface of this layer, which are

called dermal papillae, that stick out into the epidermis above.

These contain lots of tactile cells as described previously.

In areas where there is lots of friction, like the hands, these papillae sit on mounds

called dermal ridges, which cause ridges in the epidermis as well, which are meant to

enhance the gripping ability of the fingers, and they are visible as the lines on our fingertips

that make our unique fingerprints.

Below this papillary layer sits the reticular layer, which is most of the dermis, and it

is made of dense fibrous connective tissue that is arranged irregularly.

A network of blood vessels sits below this, just before the hypodermis.

What else can we say about the skin?

We mentioned that the stratum basale also contains melanocytes, which produce melanin.

This is a pigment molecule, and this is one of the components of the skin that determines

its color, and protects the skin from ultraviolet radiation.

The other pigments responsible for skin color are carotene, which is yellow-orange, and

hemoglobin, which is red when oxygenated.

We will discuss this molecule in more depth later in the series.

That wraps things up for the skin, so let’s just briefly touch on the other components

of the integumentary system, which are called skin appendages.

First, there is hair.

Of course most of us have lots of hair on our heads, but there is also hair all over

the body, including eyelashes and nose hairs, and these all have specific protective functions.

So what is a hair made of exactly?

As it turns out, a hair is a flexible strand made largely of dead, keratinized cells.

This is hard keratin, which is a bit different from the soft keratin found in cells of the

epidermis, which makes them more durable, and not as flaky.

Hairs are produced by hair follicles.

These possess a root, which is the part deep inside the follicle where keratinization is

happening, and a shaft, the part closer to the surface of the skin and then extending

outside the body, where keratinization is complete.

The hair itself consists of three layers of cells.

The innermost is the medulla, containing large cells and soft keratin.

Next is the cortex, which is several layers of flattened cells.

And lastly there is the cuticle, which is a single layer of overlapping cells, the most

keratinized cells in the hair.

As for the follicle the hair sits in, this also has some structure to it.

In general, a hair follicle is a pocket that folds down from the surface of the epidermis

down into the dermis, about four millimeters below the surface.

The deep end then expands slightly to form a hair bulb.

A bundle of nerve endings attach to the bulb and act as a receptor, responding to any bending

of the hair and alerting the brain in case an insect is there, or something of the like.

A little bit of dermal tissue called a hair papilla protrudes into the bulb, which supplies

signals and nutrients to the hair so it can grow.

The wall of each follicle has a few layers.

The outermost is the peripheral connective tissue sheath, derived from the dermis.

Next is the glassy membrane, derived from the basal lamina.

And then there is the innermost epithelial root sheath, derived from the epidermis.

This last section has an external part and an internal part, which thins as it approaches

the bulb.

The cells that actively divide are found in the hair matrix, which push existing cells

upwards as they divide, causing the hair to grow.

In addition, each follicle has an arrector pili.

This is a small bundle of muscle cells that can contract and pull the follicle in such

a way that the surface of the skin dimples out, producing what we refer to as goose bumps,

when cold or afraid.

Our body hair is pretty sparse so this no longer serves much purpose, but for much furrier

mammals it is an important defense mechanism for trapping heat and intimidating enemies.

Hair can either be vellus hair, which is pale and fine, or terminal hair, which is darker

and more coarse, like hair of the eyebrows and scalp.

The nails found on our fingers and toes are also part of the integumentary system.

These are products of a modification of the epidermis.

Just like with hair, in contrast to the soft keratin of the skin, nails contain hard keratin,

making them great tools for scratching or picking up objects.

Each nail has a free edge, which is the very tip, then a body, which is most of what we

see, and then a proximal root, which is embedded in the skin.

The part of the epidermis the nail sits on is called the nail bed, and the nail grows

out of the nail matrix, which pushes the nail outwards across the nail bed as these cells

divide.

There are also skin folds overlapping the borders of the nail which are called nail

folds, sitting on the lateral and proximal borders, and the latter extends onto the nail

as the eponychium.

At the edge of the finger is the hyponychium, where dirt tends to collect.

The last part of the integumentary system we must mention is the vast collection of

glands that can be found.

First up are the sweat glands, also known as sudoriferous glands.

These are found almost everywhere on the surface of the skin, totalling up to around three

million.

There are two types of sweat glands.

The first is called eccrine, or merocrine sweat glands.

Most of them are of this type, and it consists of a coiled tube.

Secretion occurs in the dermis, and the resulting fluid, or sweat, travels through the tube

towards a funnel-shaped opening called a pore.

Sweat is ninety-nine percent water, but it contains some salts and metabolic wastes,

among other things.

Sweat is also secreted by apocrine sweat glands, which are far fewer, found only in certain

areas, and secrete fat and protein components along with the normal mixture, which is the

cause of body odor.

Ceruminous glands and mammary glands are also types of apocrine glands, which produce earwax

and breast milk.

Beyond sweat glands there are sebaceous glands, also known as oil glands.

These are branched alveolar glands that secrete sebum, which is made of oily lipids.

This will soften and lubricate hair and skin, slowing water loss and killing certain bacteria.

So that covers the basics of the integumentary system, which consists of skin, hair, nails,

and glands.

This system acts a barrier, separating what’s outside of us from what’s inside of us.

It has the ability to repair quickly, regulate body temperature, and respond to stimuli outside

of the body, among other things.

Now that we have this system covered, let’s head inside the body and check out the rest.