Epithelial Tissue Features

• A tissue constitutes a group of cells which usually have common embryonic origins
• Tissues function together in order to carry out specialized activities
• Four basic types of human body tissue are categorized according to their structure and function.
• Cells are held together in a number of ways to form tissues.
• Cell junctions, are points of contact between the plasma membrane.

Epithelial Tissue General Features

• Occurs as continuous sheets of cells that are densely packed.
• Epithelial tissue is avascular, having no blood vessels, but does have a nerve supply
• Epithelial tissue protects, secretes, absorbs, and excretes.
• Surface epithelium forms skin and some organs, inner lining of blood vessels, ducts, and body cavities.
• Portions of glands are made of glandular epithelium.
• Epithelial cells are attached to a basement membrane

Epithelial Cell Surface Qualities and Basement Membrane

• Epithelium anchors to connective tissue via the basement membrane
• Epithelium assists and is active in satellite cell activity located in muscle sections

Connective Tissue

• Bone Biology (Chapter 6) is reviewed in detail later in the term.
• It is composed of two basic elements which are cells, and protein fibers, or ground substance

Connective Tissue Proper Cells

• Reticular fibers made of collagen and glycoproteins provide blood vessel support
• They form branching networks around fat, smooth muscle, and nerve cells.
• Fibroblasts are large, flat cells which move through connective tissue, secreting fibers and ground substance.
• Collagen fibers are flexible bundles of the protein collagen, the most abundant protein in your body.
• Macrophages develop from monocytes, destroying bacteria and cell debris by phagocytosis.
• Elastic fibers are strong, stretchable fibers of the proteins elastin and fibrillin
• Elastic fibers are in skin, blood vessels, and lung tissue.
• Mast cells are abundant along blood vessels, producing histamine, which dilates small blood vessels to kill bacteria.
• Plasmocytes develop from B lymphocytes, attacking and neutralizing foreign substances by secreting antibodies.
• Adipocytes, store fat, and are found below the skin and around organs
• Eosinophils are white blood cells migrating to sites of parasitic infection and allergic responses.
• Neutrophils are white blood cells which migrate to sites of infection, destroying microbes by phagocytosis.
• Ground substance is the material between cells and fibers
• It supports cells and fibers, binds them together, and provides a medium for exchanging substances between blood and cells.
• Hyaluronic acid, chondroitin sulfate, and glucosamine are made of water and organic molecules

Connective Tissue Extracellular Matrix

• Fibers in the extracellular matrix provide strength and support to a tissue
• Collagen fibers are very strong, as found in cartilage and bone.
• Elastic fibers are strong and flexible as found in skin and lungs.

Main Classifications of Connective Tissue

• Mature examples include cartilage, bone, and blood
• Bone is covered in Chapter 6.
• Blood is covered in Chapter 19.

Cartilage

• Derived from cells whose primary role is production
• Cartilage consists of collagen fibers and a gel-like component of ground substance
• Strength is gained with the component and resilience for the ability to change shape and maintain structure is from chondroitin

Tissue Repair

• Tissue repair is the process that replaces worn, damaged, or dead cells.
• Epithelial cells are replaced by the division of stem or undifferentiated cells
• Not all connective tissue cells have the ability to repair.
• Muscle cells can perform limited repair and some nervous cells can have limited repair while others cannot
• Fibrosis is the replacement of cells with scar tissue

Nervous System

• Nervous tissue consists of neurons and neuroglia.
• Nerves consist of axons, connective tissue, and blood vessels located outside the CNS (central nervous system) & PNS (peripheral nervous system.)
• Sensory receptors monitor changes in the external and internal environment.

Neuron Structure Qualities

• Neurons possess "excitability."
• Neurons can respond to stimuli
• Neurons generate action potentials dependent on structure
• The cell body (soma) contains the nucleus and typical cell components.
• Dendrites act as the receiving portion.
• The axon sends signals to another neuron, gland, or muscle fiber, and does not contain rough endoplasmic reticulum.
• The axon terminal contains synaptic vesicles full of neurotransmitters involved in the action potential being relayed

Neuron Physiology

• Synapses are the sites of communication between 2 neurons, or a neuron and its effector cell.
• Sensory (Afferent) divisions convey messages into the CNS
• Motor (Efferent) divisions convey messages from the CNS

Nervous System Functions

• Detect changes through sensory receptors
• Sensory functions detect changes through sensory receptors that have the ability to detect touching a hot stove.
• Integrative functions analyze incoming sensory information, store aspects, and make decisions regarding behaviors appropriate to those aspects
• Motor funtions respond to stimuli, i.e. muscles & glands response to move a hand away quickly from a hot stove

Neuroglia

• They are non-excitable
• They do not transmit action potentials
• They repair by filling the spots which open up when neurons die.
• There are a total of 6 kinds of neuroglia, split among 4 in the CNS, 2 in the PNS
• Astrocytes protect neurons, maintain nutrient flow between them and capillaries, and help with the health of endothelial cells
• Oligodendrocytes help maintain structure as well forming/maintaining the myelin sheath
• Myelin is a lipid/protein cover insulates and speeds action potentials
• Ependymal cells monitor and produce cerebrospinal fluid
• Microglia clear cell debris/damage
• Satellite cells regulate nutrient exchange between neurons

Myelination

• Myelination is the process of forming a myelin sheath
• Myelin sheaths consist of up to 100 layers of insulating material
• Multiple sclerosis results in progressive myelin sheath destruction
• Factors affecting propagation speed include axon thickness, myelination level, temperature
• Thicker axons propagate action potential faster
• Myelin increases action potential speed
• Higher temperatures increase action potential speed

Electrical Qualities

• At resting, the membrane potential is negative
• At resting, the outside is also more positively charged than the inside.
• There is more Na+ outside and K+ inside.
• Channels and pump aid in transporting ions

Action Potential Qualities

• Threshold is reached at -55mV
• After threshold the interior is more positively charged than the outside.
• The voltage reaches +30mV inside.
• Depolarization results next.
• Calcium channels open, activating synaptic vesicles.
• These vesicles release acetylcholine, which stimulates muscles.
• Post-depolarization occurs soon after.
• Repolarization and potassium channel opening results in -90mV.
• Hyperpolarization prevents further firing due to abundance
• The neuron resets, and the process begins again.

Epithelial tissue is a basic type of human body tissue categorized by its structure and function. It occurs as continuous sheets of densely packed cells. It is avascular, lacks blood vessels, but possesses a nerve supply. Its main functions are to protect, secrete, absorb, and excrete.