Each cell has a specialization that works to keep your body in homeostasis.
The body has six different stages of complexity:
- Chemical
- Cellular
- Tissues
- Organs
- Organ System
- The full body
Groups of similar cells come together to perform a common function. The most basic are tissues. When multiple tissues come together, they will form organs.
The type of tissue defines its function.
Four different types of tissues:
- Nervous tissue: control and communication
- Muscle tissues: movement
- Epithelial tissues cover and protect the body.
- Connective tissues provide support.
Nervous tissue forms the nervous system, which involves the central nervous system (brain and spine) and then the peripheral nervous system.
Nervous tissues have two jobs. Which are to sense stimuli and then send electrical impulses, often in response to those stimuli.
The tissue is split into two different cells. Which are neurons and glial cells.
Each neuron is made up of a cell body (soma), dendrites, and an axon. The cell body contains the nucleus and mitochondria. It controls all of the things necessary for the life of the cell. Dendrites are where the neuron listens for information. The axon is where the neuron transmits information.
Glial cells will support the neurons. They will provide support, insulation, and protection. It also allows them to be tethered to blood vessels.
Muscle tissues can contract and move. Muscle tissue is well vascularized, so it has a lot of blood coming and going.
There are three types of muscle tissue:
- Skeletal muscle tissue attaches all of your bones to your skeleton. Work voluntarily (running, eating, etc.).
- Long multinucleate parallel cells, striations (fine black lines running perpendicular to the fibers)
- Cardiac muscle tissue works involuntary (the heart beats on its own). It is only found in the heart, and it helps your heart propel blood through your body.
- Cells divide and converge, one nucleus per cell, striated, with intercalated disks.
- Smooth muscle tissue lines most of the blood vessels and hollow organs. Like the ones on your digestive tract.
- Short tapered cells, built without striations
There are two different types of epithelial tissue:
- Proper epithelium covers and lines your outer and inner body.
- The glandular epithelium forms your glands and secretes hormones and other substances.
The primary epithelium protects your whole body inside and out. When pushed, the epithelium will act similarly to when a balloon is pressed in. It does this to protect your deeper layers of tissues from injury or infection.
All epithelial tissues are avascular. They instead rely on the connective tissue around them.
Avascular: not associated with or supplied by blood vessels
Epithelial tissues are determined by their shape and layering. There are three different shapes.
- Squamous cells have fast absorption and diffusion, making thin membranes (flat).
- Cuboidal cells absorb nutrients and produce secretions. (cube shape)
- Columnar cells absorb nutrients and produce secretions (column shape).
The shape of each kind of epithelial cell correlates with its functions.
In places where you lose more cells, there are typically more squamous cells. Cells take resources to make, so the “expendable” ones are found in places like your skin and mouth.
Types of layering:
- Simple epithelium: one layer of cells
- Stratified: multiple layers set on top of each other, like bricks
- Pseudostratified: Most just one layer. Cells with different shapes and sizes
You could name an epithelial tissue as a “simple squamous epithelium”. It mentions the layers and the type of cell.
Squamous cells are flat, and there needs to be a lot of them to form a layer that can offer any protection.
Epithelial tissue regenerates really quickly.
All epithelial cells are polar. This means that they have distinct sides. There is an apical side, which is usually facing away from the organ it’s protecting. Then, the basal side is tightly attached to the basement membrane, which anchors it to the connective tissue.
The boundaries that the cells form aren’t absolute. They are selectively permeable. Allowing for some level of absorption, filtration, and excretion of substances.
Small intestines: allow you to absorb nutrients through diffusion and active transport.
The glandular epithelium forms two different kinds of glands:
- Endocrine glands secrete hormones right into your bloodstream or to nearby cells.
- Exocrine glands secrete their juice into tubes or ducts that lead to the outside of the body.
Connective tissue is everywhere in the body. Its distribution is varied throughout the body. There is a lot on the skin, but a lot less on the brain.
There are four different types of connective tissues.
- Proper connective tissue that supports your skin and ligaments
- Cartilage connective tissue
- Bone connective tissue
- Blood connective tissue
Some responsibilities of connective tissue:
- Binding and supporting
- Protecting
- Insulating
- Storing reserve fluid and energy
- Transporting substances within the body
- Movement
Fat is a type of proper connective tissue that provides insulation and fuel storage.
Your bones, tendons,and cartilage bind, support, and protect your organs and give you a skeleton so you can move with purpose.
All connective tissues have three factors in common that set them apart from other tissue types.
- They all develop from mesenchyme, a loose embryonic tissue. Connective tissues are more flexible.
- Connective tissues also have different degrees of vascularity, or blood flow. Most cartilage is avascular, while other types of connective tissue, like your skin, have a lot of blood.
- All connective tissues are mostly composed of nonliving material called the extracellular matrix.
The extracellular matrix is like jello. Your cells kind of just float around inside of it. The extracellular matrix is made of two components. The ground substance is a watery, rubbery, unstructured material that fills the space between cells. They protect the cells and are very flexible.
The anchors of this framework are proteins called proteoglycans. Each proteoglycan stretches out starchy stands called glycosaminoglycans (Gags).
Fibers provide support and structure to the otherwise shapeless ground substance. There are multiple different types of fibers.
- Collagen fibers are the strongest and most abundant type of fiber.
- Elastic fibers form a branching framework. Stretch and recoil like rubber bands. Found in places like your skin, lungs, and blood vessels
- Reticular fibers are short, finer collagen fibers. Sponge-like networks Cradle and support organs
Cells of connective tissue can be classified as either mature (suffix-cyte) or immature (suffix is always blast).
All blast cells are still in the process of dividing and replicating themselves to become stem cells. Blast cells have the specialized function of secreting the ground substance and fibers that form their unique matrix.
Chondroblasts: the blast cells of cartilage (which make spongy tissue that forms your nose, ears, and joints).
Osteoblasts: The blast cells of bone
The cyte cells maintain the health of the matrix. Sometimes these mature cells can go back to their immature state if they need to repair or generate a new matrix.
Macrophages (immune functions): eat bacteria, foreign materials, and even your own dead cells.
No matter how different a tendon, bone, or hunk of fat may appear, they are indeed very closely related.
The most diverse type is the connective tissue proper.
- Connective tissue proper (elastic)
- Loose: areolar, reticular, adipose
- Dense, regular, irregular, elastic
Loose connective tissues have fewer fibers, more cells, and more ground substance.
Areolar tissue is the most common loose connective tissue. Found under your epithelial tissue and wrapped around your organs. It looks like it has a lot of open space.
Adipose tissue is your fat tissue. Mostly cells. Stores lipids (adipocytes) for later use and insulates the body against heat loss. Someone’s weight is like 18% of this tissue.
Reticular tissue is like areolar tissue but with a woven mess of reticular fibers rather than collagen and elastin fibers. It provides a soft internal framework for the spleen, lymph nodes, and bone marrow, and it supports a lot of developing blood cells.
Your reticular tissue is what holds your blood in place in many of your organs.
All loose connective tissue properly has an airy feeling, and fibers are far apart.
Dense connective regular tissue proper is full of tight bundles of collagen all running parallel. You find this tissue in your tendons (which connect muscle to bone) or in your ligaments (which connect bone to bone).
If they are not stacked neatly in rows, they form irregular tissue. Their fibers are thicker. These tissues are found in places where there might be tension exerted in a lot of different directions.
You will find dense elastic connective tissue in places like your joints, which need more flexibility than rigidity.
Connective tissue proper is the most diverse group in this tissue family.
Cartilage does not have any blood or nerves. Stands up against both tension and compression.
Hyaline cartilage is the most common type. It provides pliable support. Keep your nose perky and connect your ribs to the sternum. It is hard to see the collagen fibers.
Elastic cartilage is similar to hyaline but with more elastic fibers. Like in your ear.
Fibrocartilage is dominated by thick fibers of collagen. Good at withstanding lots of pressure. Located in places like your knee joints.
Spongy bone tissue is typically found in the heads of long bones. This spongy tissue is strong but porous. It uses the extra room to store bone marrow.
Compact bone tissue is quite dense, with no visible spaces. It forms the external layer of your bones and stores calcium for bone cells to make more tissue.
In this case, the ground substance is your blood plasma, which has protein fibers floating around it.
Your blood’s main job is to transport cells, nutrients, hormones, wastes, etc. Most of your blood cells are erythrocytes (they carry around oxygen and carbon dioxide; they are red blood cells). There are also larger infections fighting white blood cells (leukocytes). Platelets are the small cell fragments needed for blood clotting (make sure you don’t get destroyed by a paper cut).
The blood doesn’t have fibers, but it doesn’t have a lot of protein dissolved in the plasma. The proteins will form fiber-like structures when your blood needs to clot.
Your skin protects your body against infection and extreme temperatures, maintains your balance of fluids, and even synthesizes vitamin D for your own personal use.
Integumentary System:
- Hair
- Nails
- Sweat
- Oil glands
- Skin
Your skin has three layers. Each with their own jobs.
The epidermis is the only part of the skin that you can see. It is made of stratified squamous tissues.
The dermis is just below, and it is where most of the work that the skin does gets done. It will sweat, circulate blood, and detect feelings.
At the bottom, there is the hypodermis. Which is mostly composed of fatty tissue.
The bulk of your epidermis is made up of keratinocytes. Keratinocytes are the building blocks of the tough, fibrous protein keratin.
There is another epidermal cell called a melanocyte. It synthesizes melanin, which gives skin color. Every person, pale or dark, usually has the same amount of melanocytes.
Since the epidermis is your outward protection, it also has a lot of immunity functions.
Langerhans cells are ingesting the unwanted invaders.
Merkel cells combine with nerve endings to create a sensory receptor for touch.
In some places, you have more layers of epidermis than others. Your thick skin is tougher stuff and can be found in places like your palms.
The layers of the epidermis
The first is the stratum corneum, which is made up of about 20–30 sheets of dead keratinocytes. This is the layer that usually comes off.
Stratum lucidum contains two of three rows of clear, flat, dead keratinocytes. This is only found in thick skin.
Stratum granulosum. Contains living keratinocytes, which are forming keratin.
The epidermis is avascular. All the oxygen and nutrients that its cells need have to come from the dermis below.
Epidermal cells are the youngest at the bottom. They move toward the surface of your skin as they mature.
Stratum spinosum: extremely young cells
Stratum basale, which is just a single layer of columnar cells. This is where most of the new cell products happen. It’s also the part of your epidermis that connects your skin to the dermis.
The ultraviolet radiation in sunlight can damage the epidermis, causing elastic fibers to clump up.
Dermis contains collagen and elastin fibers. Full of nerve fibers and blood vessels.
The dermis is broken up into three different layers.
The papillary layer, which is made up of areolar connective tissue, It also has dermal papillae that create friction ridges that switch pressure through to the epidermis to help our fingers and feet grip surfaces (your fingerprints).
Under that layer is the reticular layer, which makes up 80% of the dermis. Made up of dense, irregular connective tissue.
Hypodermis: made up of adipose connective tissue. It provides insulation, energy storage, shock absorption, and helps anchor the skin.
Your integumentary system provides some of the following:
- Protection
- Sensation
- Blood storage
- Temperature regulation
- Vitamin D synthesis
- Excretion
The first and most vital purpose of your integumentary system is to act as a protective barrier.
The system is also vital to how you sense the world around you.
Your skin has a lot of structures that are part of your nervous system. They are called cutaneous sensory receptors (corpuscles). They receive stimuli from the outside environment and send them to your brain. Register all the sensations you associate with touch.
Tactical corpuscles: when something is touching you, like a tag on a shirt
Lamellar corpuscles: for feeling pressure
Hair follicles: being able to feel a breeze
Your integumentary system also plays a role in the excretion of waste.
About 5 percent of your entire blood volume is retained in your skin at any given time.
When you’re exercising, your blood and sweat glands work together to regulate the temperature of your body.
A human sweats a lot, but sometimes you can’t see it. This type of sweat is called insensible perspiration. Noticeable sweat is called sensible perspiration.
When it colds, your dermal blood vessels will contract, sending the blood to your organs instead (vasoconstriction). Once things warm back up, those blood vessels relax, allowing blood to come back to the dermis.
Changes in the color of your skin can indicate a number of homeostatic imbalances.
Cyanosis (blue skin)
- May indicate heart failure.
- Poor circulation
- Severe respiratory issues
Jaundice (yellow skin):
- May indicate a liver disorder
Erythema (red skin)
- Fever
- Inflammation
- Allergy
Melanin is there to protect our skins from the sun. So, in places where there is more sunlight, they tend to have darker skin.
The integumentary system also includes your skin appendages. Which are your hair, nails, sweat glands, and oil glands?
Your hair seems to have two parts. The shaft, which is where the keratinization is complete, The root is where the keratinization is still happening. The bottom of each follicle is young and fresh.
You’ve got up to three million tiny sudoriferous, or sweat glands, distributed throughout your body.
Sweat secrets come in two different types. Eccrine glands and apocrine glands
Eccrine sweat glands are more common. They are found in your palms, forehead, and foot soles. Start from the dermis and open into a pore on the surface of your skin.
For apocrine glands, you only have about 2000 of them, and they start cooking around puberty, emptying into hair follicles around your armpits and groin.
Mammary glands secrete milk.
Ceruminous Glands: Which secrete cerumen or earwax?
Sebaceous glands (oil glands) are found everywhere but in thick skin. Their ducts are small on your limbs but they are big on your face,neck, and upper chest. Most sebaceous glands secrete their sebum (oily substance) into hair follicles.
Their primary goal is to soften and lubricate your skin and hair. They also help to slow water loss from the skin in dry environments.
All of your thoughts,actions, and emotions can be boiled down into three principal functions.
- Sensory input
- Integration
- Motor output
After there is sensory input, your nervous system processes that input and decides what should be done about it. Deciding what to do about it is called integration.
The motor output is the response that occurs when your nervous system activates certain parts of your body.
The central nervous system is your brain and spinal cord (the main control center). Your peripheral system is composed of all the nerves that branch off from the brain. It allows your central nervous system to communicate with the rest of the body.
Since the PNS is how the CNS talks to the rest of the body, its relationship has to go both ways. The PNS can be broken up in two ways. The sensor division (afferent) picks up sensory stimuli. The motor division (efferent) sends directions from your brain to muscles and glands.
The motor division also includes the somatic (voluntary) nervous system, which rules your skeletal muscle movements. It also controls the autonomic (involuntary) nervous system, which keeps your heart beating, your lungs breathing, and your stomach churning.
The autonomic nervous system also has subdivisions of its own. It has a sympathetic division, which gets the body fired up. It also has the parasympathetic division, which relaxes the body.
Glial cell types provide support, nutrition, insulation, and help with signal transmission in the nervous system.