integumentry system Flashcards
Epithelial membranes
(also called covering and lining membranes) include:
Cutaneous membrane (skin): The outer covering of the body, consisting of keratinized stratified squamous epithelium (epidermis) and an underlying connective tissue layer (dermis)
Mucous membranes (mucosa): Line body cavities that open to the exterior, such as the respiratory, digestive, and urinary tracts. These membranes secrete mucus for lubrication and protection.
Serous membranes (serosa): Line body cavities that do not open to the exterior, such as the pleura (lungs), pericardium (heart), and peritoneum (abdominal organs). They produce serous fluid to reduce friction between organs.
These membranes are not just epithelial; they consist of:
Epithelial layer
and Underlying connective tissue layer
ehich means there simple organs
Cutaneous membrane (skin)
Skin (Cutaneous Membrane):
Epidermis: The outer layer made of flat, layered cells (stratified squamous epithelium). Think of it as the “brick wall” of your skin.
Dermis: The inner layer made of tough, tangled fibers (dense irregular connective tissue). Imagine it as the “support mesh” under the bricks.
Key Difference:
Unlike the moist membranes lining your internal organs, your skin is
Mucous membrane (mucosa)
Mucous membranes are moist linings that cover body surfaces which open to the outside. They have two main parts:
Epithelium: The outer cell layer that varies depending on where it’s located.
Lamina propria: A loose, supportive connective tissue layer beneath the epithelium.
These membranes are found in areas like the nose, mouth, lungs, and digestive tract.
Serous membranes (or serosa
Tissue Layers:
Simple Squamous Epithelium: A single, thin layer of flat cells.
Areolar Connective Tissue: A loose, supportive tissue underneath.
Location:
These membranes, known as serous membranes, line the closed cavities of the ventral body (for example, the lining around the lungs, heart, and abdominal organs). They differ from mucous membranes, which line cavities that open to the exterior.
Synovial membranes
Composition:
Made solely of loose areolar connective tissue
They do not have epithelial cells
Where They Are Found:
They line the fibrous capsules around joints
They cover bursae (small, fluid-filled sacs)
They wrap around tendon sheaths
Function:
They provide a smooth surface
They secrete a lubricating fluid (synovial fluid)
This fluid helps cushion and reduce friction between moving parts (like a tendon sliding over a bone)
skin
Essential Function:
Maintains the body’s boundary by keeping water and valuable molecules inside and unwanted substances (like excess water) outside.
Allows you to swim for hours without becoming waterlogged.
Structural Features:
The skin is pliable yet tough, which allows it to withstand constant external damage.
Protects against bacteria and prevents water and heat loss.
Importance: Without skin, we would be vulnerable to infections and lose critical body fluids, making it essential for survival.
skin and heat
Heat Regulation:
The capillary network and sweat glands help regulate heat loss from the body, controlled by the nervous system.
Excretory Role:
The skin acts as a mini-excretory system, losing urea, salts, and water when we sweat.
Chemical Production:
The skin produces proteins important for immunity.
It synthesizes vitamin D: Modified cholesterol molecules in the skin are converted to vitamin D when exposed to sunlight.
Protection:
The skin secretes an acid mantle (acidic secretions) that helps protect against bacterial invasion.
epidermis and dermis
Epidermis:
Made of stratified squamous epithelium.
Capable of becoming hard and tough.
Dermis:
Mostly made of dense irregular connective tissue.
Firmly connected to the epidermis and is tear-resistant.
Blister Formation:
If the epidermis and dermis separate (due to burns or friction, like from a poorly fitting shoe), interstitial fluid can accumulate between the layers, forming a blister.
subcutaneous tissue (hypodermis):
Location: It lies beneath the dermis, but it is not considered part of the skin.
Composition: Primarily made up of adipose (fat) tissue.
Functions:
Anchors the skin to underlying organs.
Stores nutrients.
Acts as a shock absorber.
Insulates deeper tissues from extreme temperature changes.
Body Shape: The subcutaneous tissue is also responsible for the curves typically seen in women, as it stores fat in certain areas more than in men.
epidermis
Keratinocytes (keratin-producing cells) make up most of the epidermis.
Keratinization: Keratinocytes produce keratin, a fibrous protein that makes the epidermis tough and protective.
Cell Connection:
Keratinocytes are connected by desmosomes, which help hold them together.
Avascular:
The epidermis has no blood supply of its own, which is why shaving doesn’t cause bleeding (you’re only cutting through cell layers, not blood vessels).
Epidermal Layers (Strata):
The epidermis consists of up to five layers:
Stratum basale (innermost layer)
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin like palms and soles)
Stratum corneum (outermost layer)
Each layer has multiple rows of cells, with the topmost layers being more flattened and filled with keratin.
stratum basale
Location:
The stratum basale is the deepest layer of the epidermis, located closest to the dermis.
It is connected to the dermis by a wavy border (like corrugated cardboard).
Nutrient Supply:
This layer contains the most nourished cells in the epidermis because nutrients from the dermis reach them first.
Cell Division:
Stem cells in the stratum basale are constantly dividing and producing millions of new cells daily. This is why it’s also called the stratum germinativum (germinating layer).
Some new cells continue to divide, maintaining the population of stem cells, while others start to move up to become part of the upper epidermal layers.
Movement of Cells:
As cells move away from the dermis, they pass through the stratum spinosum and stratum granulosum.
As they travel upward, they become flatter and more keratinized (filled with keratin).
stratum lucidum
Formation:
As cells move out of the stratum granulosum, they die and form the stratum lucidum.
Location:
The stratum lucidum is only found in areas of thick skin—specifically the palms of the hands and soles of the feet.
It is absent in thinner skin (like the skin on your arms and face).
Cell Changes:
In the stratum lucidum, cells accumulate keratin and secrete a water-repellent glycolipid into the extracellular space.
As the cells move further from the dermis, they become increasingly deprived of nutrients and oxygen (because the skin is avascular), which leads to their death.
stratum corneum,
Structure:
The stratum corneum is 20 to 30 cell layers thick, making up about three-quarters of the epidermal thickness.
It consists of dead, shingle-like cells that are completely filled with keratin. These cells are called cornified or horny cells.
Function:
This layer acts as a durable “overcoat” for the body, protecting the deeper cells from:
The harsh external environment.
Water loss.
Biological, chemical, and physical assaults.
Shedding:
The stratum corneum rubs off slowly and steadily as dandruff.
The average person sheds about 18 kg (40 lb) of these flakes over their lifetime, which become a food source for dust mites in homes and bed linens.
Regeneration:
The stratum corneum is continuously replaced by new cells produced by the division of stratum basale cells.
We get a completely new epidermis every 25 to 45 days.
Melanin:
A pigment responsible for skin color, ranging from yellow to brown to black.
Melanocytes:
Melanin is produced by melanocytes, special spider-shaped cells.
These cells are mostly found in the stratum basale (the deepest layer of the epidermis).
Freckles and Moles:
Freckles and moles appear where melanin is concentrated in one spot.
So, melanin gives the skin its color and helps protect against UV radiation, and its concentration in certain areas can result in freckles or moles.
Epidermal Dendritic Cells:
These are important immune system “sentries”.
They help alert and activate immune cells in response to threats like bacterial or viral invasion.
Merkel Cells:
Located at the epidermal-dermal junction.
Associated with sensory nerve endings, acting as touch receptors known as Merkel discs.
Dermis
The dermis is your “hide.” It is a strong, stretchy envelope that helps to bind the body together. When you purchase leather goods (bags, belts, shoes), you are buying the treated dermis of animals.
papillary layer
Structure:
The papillary layer is the superficial region of the dermis.
It has peg-like projections called dermal papillae, which indent the epidermis above.
Functions:
Capillary loops within the dermal papillae provide nutrients to the epidermis.
Pain receptors (free nerve endings) and touch receptors are located in the dermal papillae.
Special Features on the Palms and Soles:
On the palms and soles, the papillae form looped and whorled ridges on the epidermal surface, which:
Increase friction.
Enhance gripping ability of the fingers and toes.
Genetic Determination:
Papillary patterns are genetically determined, which is why everyone has unique fingerprints.
Fingerprints:
The ridges on the fingertips are equipped with sweat pores, leaving behind fingerprints on objects we touch.
reticular layer
is the deepest skin layer. It contains dense irregular connective tissue, as well as blood vessels, sweat and oil glands, and deep pressure receptors called lamellar corpuscles.
cutaneous sensory receptors
The skin contains various sensory receptors that are part of the nervous system, helping us detect stimuli from the external environment. These include:
Touch receptors.
Pressure receptors.
Temperature receptors (heat and cold).
Pain receptors.
These receptors give us important information about our surroundings, such as detecting heat, cold, or even the tickle of a bug on our skin.
Phagocytes:
The dermis also contains phagocytes, which are immune cells that help prevent microbes from penetrating deeper into the body.
These cells act as a defense mechanism to stop harmful microorganisms that have breached the epidermis.
Collagen Fibers:
Provide the toughness and strength of the dermis.
Attract and bind water, helping to hydrate the skin.
Elastic Fibers:
Give the skin its elasticity, allowing it to stretch and return to its original shape when we’re young.
Aging and Skin Changes:
As we age, the number of collagen and elastic fibers decreases.
The subcutaneous tissue also loses fat.
These changes result in loss of elasticity, causing the skin to sag and wrinkle.
So, the collagen and elastic fibers are key to the skin’s strength, hydration, and flexibility, but as we age, their decline contributes to the visible signs of aging.
blood vessels in the dermis:
Blood Supply:
The dermis is richly supplied with blood vessels, which play a key role in regulating body temperature.
When Body Temperature is High:
The capillaries in the dermis dilate (engorge with blood) when the body is too hot.
This causes the skin to become reddened and warm as heat radiates from the skin surface, helping to cool the body down.
When Body Temperature is Low:
In cooler conditions, the body conserves heat by temporarily bypassing the dermal capillaries.
This helps maintain a higher internal body temperature, keeping warmth in.
