Animal Tissues: Epithelial Tissue

• Levels of organization in organisms includes: cells, tissues, organs, organ system and body.

Types of Tissue

• A tissue is composed of specialized cells of the same type that perform a common function.
• There are four major types of tissues: epithelial, connective, muscular, and nervous.
• Epithelial tissue covers body surfaces and lines body cavities.
• Connective tissue binds and supports body parts.
• Muscular tissue moves the body and its parts.
• Nervous tissue receives stimuli and conducts nerve impulses.

Epithelial Tissue

• Tissue is a group of similar cells that perform a specific function.
• Epithelial tissues cover the body surface or line its cavities and tubes.
• Epithelium has a sheet-like structure with one side facing an internal body fluid or the outside environment.
• The other side of epithelium rests on a basement membrane, which is densely packed with proteins and polysaccharides that are not cells.

Types of Epithelium

• Simple epithelium is the thinnest type and consists of a single layer of cells, lining body cavities, tubes, and ducts.
• Example: chest cavity, tear ducts, and kidney tubes where urine is formed.
• Simple epithelium functions in diffusion, secretion, absorption, and filtration.
• Pseudo-stratified epithelium appears stratified but is a single layer, with nuclei not lining up.
• Most of these cells have cilia and line the throat, nasal passages, and reproductive tract where cilia sweep mucus.
• Stratified epithelium has more than one layer of cells and usually has a protective function.
• Tissues at the surface of the skin are exposed to nicks, bumps, and scrapes.
• Squamous epithelium is flattened and lines fine blood vessels.
• Cuboidal epithelium is cube-shaped and may secrete or absorb substances.
• Columnar epithelium is elongated.
• Each shape correlates with a given function.

Glands

• Glands make and release products such as saliva and mucus.
• Some glands consist of a single cell, while others are more complex.
• All glands develop from epithelial tissues and often stay connected to it.
• Mucus-secreting goblet cells are embedded in the epithelium lining the trachea and other tubes leading to the lungs.
• The stomach's epithelial lining contains gland cells that release mucus and digestive juices.

Types of Glands

• How their products reach the place where they are used:
• Exocrine glands release substances through ducts or tubes, such as mucus, saliva, oil, earwax, milk, and digestive juices.
• Endocrine glands release hormones that are released directly into surrounding fluid without using ducts or tubes.

Connective Tissue

• Bind, connect, and anchor body parts/organs/tissues.
• Provides support and protection for cells, tissues, and organs.
• Cells secrete fiber-like structural proteins and a ground substance of polysaccharides.
• These ingredients form a matrix around the cells.
• It can vary from hard to liquid, giving each connective tissue type its specialized properties.
• Types of connective tissue includes fibrous and special

Fibrous Connective Tissue

• Various types of fibrous connective tissues have cells and fibers in a matrix in different proportions, making each well-suited for its special function.
• Loose connective tissues have few fibers and cells loosely arranged in a jelly-like ground substance, making them flexible.
• They wrap many organs and support the skin.
• The reticular form provides a framework for soft organs like the liver, spleen, and lymph nodes.
• Dense connective tissue has more collagen fibers than loose connective tissues.
• It is less flexible but much stronger, supporting the skin's lower layer, the dermis.
• Wraps around muscles and organs that do not need stretching, like kidneys.
• Tendons connect muscles to bones.
• Ligaments connect bones to another bone at joints.
• Elastic connective tissue is a form of dense connective tissue.
• Most of the fibers consist of elastin, making the tissue elastic.
• It is found in organs needing to stretch, such as lungs, which expand and recoil as air moves in and out.

Specialized Connective Tissue

• Cartilage, bone, adipose tissues, and blood are considered specialized connective tissue.
• Cartilage is solid, pliable, like rubber, and not easily compressed.
• Its matrix is a blend of collagen and elastin fibers in a rubbery ground substance.
• It can withstand physical stress.
• Collagen-producing cells are trapped inside small cavities in the matrix.
• Hyaline cartilage is whitish and glistening, found at the end of bones to reduce friction in moveable joints, in the nose, windpipe, and ribs, and forms the early embryo skeleton.
• Elastic cartilage has both collagen and elastin fibers, found where flexible yet rigid structure is required, such as ear flaps.
• Fibrocartilage is packed with thick bundles of collagen fibers, can withstand a lot of pressure, and forms cushions in the joints, such as the knee and in the discs between the vertebrae in the spinal column.
• Bone tissue is the main tissue in the bones, consisting of collagen fibers, ground substance, and calcium salts, providing support, movement, and protection.
• Adipose tissue stores fat, mostly packed with fat droplets with little matrix between them, located beneath the skin providing insulation and cushioning.
• Blood is classified as a connective tissue.
• It transports materials, and contains a matrix of fluid plasma with proteins, blood cells, and cell fragments called platelets.

Muscle Tissue

• Muscle tissue cells contract or shorten when stimulated by an outside signal, causing movement in body parts, then relax and lengthen.
• Muscle tissues have long, cylindrical cells lined up in parallel, often called "Muscle fibers".
• Skeletal muscle attaches to bones and is unusual because cells have more than one nucleus.
• Skeletal muscle cells lined up in parallel bundles and look striated/striped.
• The bundles called fascicles are enclosed in a sheet of dense connective tissue, making up organs.
• Its movement or contraction is voluntary.
• Smooth muscle cells taper at both ends, are bundled inside a sheath of connective tissue, and are specialized for ongoing contractions, found in the walls of internal organs, including blood vessels, stomach, and intestines
• Its contractions are involuntary.
• Cardiac muscle is found only in the heart wall and its sole function is pumping blood.
• Special junctions fuse the plasma membranes of cardiac muscle cells.
• Communication junctions allow the cells to contract as a unit; when one cardiac cell contracts, those around it will too.

Nervous Tissue

• Nervous tissues make up the nervous system.
• Nervous tissue consists of neurons (nerve cells) and support cells.
• Tens of thousands of neurons occur in the brain and spinal cord and millions present throughout the body, making up the body's communication lines.
• Neurons carry signals called nerve impulses and contain a nucleus, cytoplasm, and nerve extensions/processes.
• Dendrites receive incoming messages.
• Axons conduct outgoing messages.
• Depending on the type of neuron, axons range from short to three to four feet long.
• Neuroglia, or support cells, make up 90 percent of the cells in the nervous system and were once thought to simply support neurons.
• In the central nervous system, glia help supply nutrients to neurons, provide physical support, and remove unwanted materials.
• Outside brain and spinal cord, glial cells provide insulation—a function that speeds nerve impulses through the body.

Cell Junctions

• Junctions between cells knit the cells firmly together, stop leaks, and serve as communication channels.
• Tight junctions stop leaks.
• Adhering junctions cement cells together.
• Gap junctions connect the cytoplasm of neighboring cells.

Tissue Membranes

• A membrane is a thin, sheet-like tissue covering that comes in two types: epithelial and connective tissue membranes.
• Epithelial membranes pair a sheet of epithelium with connective tissue, for example, mucosa.
• Membranes in joints consist only of connective tissue.

Types of Membranes

• Mucous membranes are specialized to excrete substances.
• Serous membranes are paired in sheets that secrete a fluid filling the space between them.
• Cutaneous membranes include skin.
• Synovial membranes secrete fluid that lubricates joints.

Organs

• Organs are a combination of two or more types of tissues that perform one or more functions.
• For example, the stomach contains all four tissue types.
• Its wall primarily consists of muscles and nerves to regulate muscle contractions to mix and move food.
• Connective tissues provide support.
• The stomach lining is epithelium.
• An organ system combines two or more organs working in a coordinated way to carry out specific functions.
• There are eleven organ systems make up the human body.
• The cranial cavity and spinal cavity house the central nervous system, including the brain and spinal cord.
• The heart and lungs reside in the thoracic cavity.
• The abdominal cavity holds the stomach, liver, pancreas, and other organs.
• The pelvic cavity holds reproductive organs, the bladder, and the rectum.
• In an organ system, two or more organs cooperate to carry out major body functions.
• Interaction between skeletal and muscular systems to allow movements.
• Blood in the cardiovascular system carries nutrients and other substances to cells and transport products and wastes away from cells. Respiratory system delivers oxygen from air to cardiovascular system and takes carbondioxide from it.

The Skin

• Integument is Latin for "to cover" and refers to the integumentary system.
• The integumentary system includes skin, hair, nails, oil, and sweat glands.
• Skin has the largest surface area of any organ and weighs about 9 pounds in an average-sized adult.
• It holds its shape through years of washing and stretching and protects from harmful solar radiations and microbes
• It also holds in moisture, fixes small cuts and burns, helps regulate body temperature, and signals the brain through sensory receptors about the external environment to detect stimuli.
• Skin makes cholecalciferol, a precursor of Vitamin D also known as (endocrine gland) that helps with the absorption of Calcium from food.
• Skin layers are made of the epidermis and dermis.
• The outer epidermis consists of stratified squamous epithelium, and sweet glands, oil glands, hair follicles and nails develop from it.
• The dermis lies under the epidermis and mainly consists of dense connective tissues.
• It contains elastic fibers that makes skin resilient.
• It has collagen fibers that make skin strong
• The epidermis and dermis form the cutaneous membrane.
• Under the dermis is the subcutaneous layer or hypodermis.
• This loose connective tissue anchors the skin, allows it to move, contains fats that insulate the body, and provide cushions to some body parts.

Cells of the Epidermis

• Keratinocytes make keratin, a tough, water-insoluble protein.
• Melanocytes produce melanin, a brown-black pigment that gives skin its color.
• Sweat glands develop from the epidermis, and the body has about 2.5 billion sweet glands.
• Sweat consist of 99% water, which contains dissolved salts, traces of ammonia, vitamin C and other substances.
• Oil glands (sebaceous glands) are everywhere except palms and soles of feet producing oil called sebum, softening and lubricating hair and skin, and killing harmful bacteria.
• Defensive cells like Langerhans cells or phagocytes consume bacteria and viruses, mobilizing the immune system.
• Granstein cells help control immune responses in the skin.
• Hair follicles are in the epidermis, a hair is created of mostly keratinized cells and scalp has around 100,000 hairs.

Dermis

• A yellow-orange pigment called carotene also contributes to skin color.
• Small blood vessels and sensitive nerve endings lace through the dermis.
• Hair follicles, sweat glands, and oil glands are also embedded here.
• Palms and soles of the feet have ridges that push up corresponding ridges on the epidermis called fingerprints.
• Fingerprints are determined by genes
• Pattern is different for each individual, even with identical twins.

Homeostasis

• Internal environment is a pool of extracellular fluid
• Trillions of body cells bathed in a fluid of about 15 liters or 4 gallons, called extracellular fluid, making the internal environment.
• Much of extracellular fluid is interstitial fluid, filling spaces between cells and tissues.
• Rest is blood plasma, the fluid portion of the blood.
• Substances constantly enter and leave interstitial fluid.
• As cells draw nutrients and expel metabolic waste product into it.
• Chemical traffic changes chemical makeup and volume of extracellular fluid.
• Drastic changes in chemical makeup have drastic changes on cellular activities.
• Homeostasis maintains stability in chemical makeup/volume of extracellular fluid.
• Maintaining homeostasis relies on body components working together.
• Each cell engages in metabolic activities for survival.
• Tissues perform activities contributing to the whole body's survival.
• Operations help keep extracellular fluid stable, resulting in homeostasis.

Homeostasis Interactions

• Homeostasis maintenance necessitates interaction of sensors, integrators, effectors.
• Three partners needed to maintain homeostasis.
• Sensory receptors are the cells/cell parts that detect a specific change and sends signals to brain
• Integrator: The brain is the control center where informations are pulled together in the selection of a response.
• Effectors are made up of the signals to muscles, glands or both to carry out the response.
• Receptors inform the brain about how things are operating, maintained as information in our bodies.

Set Point

• The conditions in the body shifts from set point and brain brings the body back within the proper range.
• Sends signals to effectors to bring back into balance.
• Is important in great many physiological.
• Mechanisms including that influence eating, breathing, thirst, and urination.

Feedback

• Negative feedback alters a condition to counteract a change.
• It's the primary control mechanism for maintaining homeostasis.
• Positive feedback intensifies a change from an original condition.
• Example: childbirth, but no major role in homeostasis

Homeostatic Feedback

• Maintains the body's temperature:
• Humans are endotherms, containing heat inside of themselves.
• Metabolic activity mainly controls the core temperature with loops.
• The body temperature maintained between 35-41 degrees C or 98.6 F.
• Homeostatic conditions adjust physiological responses for conserving or getting rid of heat.
• Control can be assisted by changing behavior.
• Changing cloths/switching on furnace or an air conditioner.

Temperature Regulation

• Metabolism produces heat, if that heat were to build up internally, core temperature Steady rises.
• Above 41degrees, enzymes become denatured and shut down.
• Enzymes activity decreases by half when body temperature drops by 10 F.
• Vasodilation eliminates heat.
• Body responses to heat stress includes hyperthermia, heat exhaustion and heat stroke.
• The body counteract the cold, which includes: Vasoconstriction, creation of insulating layer of air near the skin, shivering involuntary muscle contraction that produces heat, Nonshivering heat production that breaks down molecules.
• Hypothermia can be fatal - freezing destroys tissues, called frostbite.