Smooth & Cardiac Muscle Physiology

• A tissue is a group of cells with a common embryonic origin.
• Tissues function together to perform specialized activities.
• Tissues can be hard (bone), semisolid (fat), or liquid (blood).
• Histology is the study of tissues.
• Pathologists are specialized in laboratory studies of cells and tissues for diagnoses.

Four Types of Tissues

• Epithelial tissue: covers body surfaces, lines hollow organs and body cavities, ducts, and forms glands.
• Connective tissue: protects, supports, and binds organs, stores energy as flat, and provides immunity.
• Muscular tissue: generates the physical force needed to make body structures move and generate body heat.
• Nervous tissue: detects changes in the body and responds by generating nerve impulses.
• Body tissues develop from three primary germ layers: ectoderm, endoderm, and mesoderm.
• Epithelial tissues develop from all three germ layers.
• Connective tissue and most muscle tissues derive from the mesoderm.
• Nervous tissue develops from the ectoderm.
• Van Leeuwenhoek was the first to use a histological stain to color specimens using saffron.
• Joseph von Gerlach introduced carmine mixed with gelatin as a histological stain.

Epithelial Tissue

• The sheets of cells cover exterior surfaces of the body.
• Epithelial tissue lines internal cavities and passageways.
• Epithelial tissue forms certain glands.
• Epithelial tissues provide the body's first line of protection against wear and tear (physical, chemical, and biological).
• Epithelium cells act as gatekeepers of the body.
• Epithelium cells control permeability and allow selective transfer of materials across a physical barrier.
• All substances that enter the body must cross an epithelium.
• Epithelial tissue consists of cells arranged in continuous sheets in either single or multiple layers. Characteristics include:
• Cells are closely packed and held tightly together.
• Covers and lines the body.
• Has a free surface.
• There are three major functions:
• Acts as a selective barrier that regulates the movement of materials in and out of the body.
• Serves as secretory surfaces that release products onto the free surface.
• Provides protective surfaces against the environment.
• The epithelial cells can be seen to have:
• Apical Surface
• Lateral Surfaces
• Basal Surface

Connective Tissue

• Binds cells and organs of the body together.
• functions in the protection, support, and integration of all parts of the body.
• Functions of connective tissue are:
• Support and connect other tissues.
• Protection.
• Defense against microorganisms via specialized cells.
• Transport of fluid, nutrients, waste, and chemical messengers via fluid connective tissues like blood and lymph.
• Storage and thermal insulation via adipose cells storing fat.

Muscle Tissue

• Excitable tissue responds to stimulation and contracts to provide movement.
• Three major types of muscle tissue are: skeletal, smooth, and cardiac.
• Skeletal muscle:
• Histology: Long cylindrical fiber, striated, many peripherally located nuclei.
• Function: Voluntary movement, produces heat, and protects organs.
• Location: Attached to bones and around entrance points to the body (e.g., mouth, anus).
• Cardiac muscle:
• Histology: Short, branched, striated, single central nucleus.
• Function: Contracts to pump blood.
• Location: Heart.
• Smooth muscle:
• Histology: Short, spindle-shaped, no evident striation, single nucleus in each fiber.
• Function: Involuntary movement, moves food, involuntary control of respiration, moves secretions, and regulates blood flow in arteries by contraction.
• Location: Walls of major organs and passageways.
• Skeletal and cardiac muscle have a striated appearance.
• Cardiac and smooth muscle cells generally have a single nucleus.
• Skeletal muscle fibers are multinucleated.

Nervous Tissue

• Excitable tissue allows the propagation of electrochemical signals in the form of nerve impulses that communicate between different regions of the body.
• Functions of nervous tissue are:
• Neurons propagate information via electrochemical impulses called action potentials, which are biochemically linked to the release of chemical signals.
• Neuroglia play an essential role in supporting neurons and modulating their information propagation.

Cell Junctions

• These are contact points between the plasma membranes of tissue cells.
• There are 5 common types: tight junctions, adherens junctions, desmosomes, hemidesmosomes, and gap junctions.
• In tight junctions, web-like strands of transmembrane proteins fuse cells together.
• Tight junctions seal off passageways between adjacent cells,
• These are common in epithelial tissues of the stomach, intestines, and urinary bladder.
• They help to retard the passage of substances between cells and leaking into the blood or tissues.
• Tight junctions forms when the extracellular surfaces of two adjacent plasma membranes join together so that no extracellular space remains between them
• Adherens junctions contain a dense layer of proteins called plaque.
• Adherens junctions resist separation of cells during contractile activities
• They are located inside the plasma membrane attached to both membrane proteins and microfilaments of the cytoskeleton.
• Transmembrane glycoproteins called cadherins insert into the plaque and join cells
• In epithelial cells, adhesion belts encircle the cell.
• Desmosomes contain plaque and cadherins extending into the intercellular space to attach adjacent cells together.
• Desmosome plaque attaches to intermediate filaments that contain the protein keratin.
• Prevent epidermal cells from separating under tension.
• Desmosomes consist of a region between two adjacent cells where the apposed plasma membranes are separated by about 20 nm.
• Desmosomes are characterized by accumulations of protein known as "dense plaques" along the cytoplasmic surface of the plasma membrane.
• Cadherins are proteins that extend from the cell into the extracellular space, where they link up and bind with cadherins from an adjacent cell.
• Hemidesmosomes resemble half of a desmosome.
• Unlike desmosomes, theses do not link adjacent cells.
• They anchor cells to the basement membrane.
• Contain transmembrane glycoprotein integrin attaching to intermediate filaments and laminin present in the basement membrane.
• Gap junctions connect neighboring cells via connexons.
• Connexons are tiny fluid-filled tunnels.
• These junctions contain membrane proteins called connexins.
• Plasma membranes of gap junctions are separated by a very narrow intercellular gap (space) for communication.
• Ions, nutrients, waste, chemical and electrical signals travel through the connexons from one cell to another.
• These consist of protein channels linking the cytosols of adjacent cells.
• Many cell types possess gap junctions, including heart muscle cells, for the transmission of electrical activity.

Smooth Muscle Types

• Single-Units: Innervation is restricted to only a few cells in the tissue, and electrical activity is conducted from cell to cell throughout the tissue by 'Gap-Junctions' between the cells
• Single-Unit Smooth Muscle is synchronous electrical and mechanical activity is why all muscle tissue responds to stimulation like the heart muscle
• MultiUnit: Has no direct connection between each cell, and muscle responds independently
• Some multiunit smooth muscles have no or few gap junctions cells responds independently and works as seperate units
• Cardiac muscle combines properties of both skeletal and smooth muscle
• Adjacent cells are joined end to end structures called intercalated disks, which are the same as the desmosomes found in the cells and the myofibrils are attached.

Cardiac Muscle

• Found within are the intercalated disks are gap junctions like those in single-unit smooth muscle and act like a syncytium

Explore the physiology of smooth and cardiac muscle. Questions cover electrical activity, structural features like gap junctions and intercalated discs, and the impact of these structures on muscle function and communication.