Cellular Structure and Tissue Types

Cellular Structure

• Cells are the fundamental units of life, exhibiting diverse structures and functions.
• The basic components of most cells include a plasma membrane, cytoplasm, and a nucleus.
• Plasma membranes are selectively permeable, regulating the passage of substances into and out of the cell.
• Cytoplasm encompasses the material between the nucleus and the plasma membrane; it consists largely of cytosol and organelles.
• Organelles are specialized structures within cells that carry out specific functions, like the mitochondria (energy production), ribosomes (protein synthesis), Golgi apparatus (protein modification), and endoplasmic reticulum (protein and lipid synthesis).

Tissue Types

• Tissues are groups of cells with similar structure and function, working together to perform specific tasks.
• Four primary types of tissues exist in animals: epithelial, connective, muscle, and nervous tissues.
• Epithelial tissue covers body surfaces, lines cavities, and forms glands, providing protection, secretion, and absorption.
• Connective tissue connects, supports, and separates different tissues and organs. Examples include bone, cartilage, blood, and adipose tissue.
• Muscle tissue contracts, enabling movement, and comes in three types: skeletal, smooth, and cardiac muscle.
• Nervous tissue transmits electrical signals throughout the body, enabling communication between different parts. It involves neurons and glial cells, for receiving, processing, and transmitting information.

Cell Membrane Structure

• The cell membrane is a phospholipid bilayer with embedded proteins and cholesterol.
• Phospholipids have a hydrophilic head and hydrophobic tails, creating a barrier that separates the intracellular and extracellular environments.
• Proteins in the membrane act as channels, pumps, receptors, or enzymes.
• Cholesterol helps maintain membrane fluidity and stability.

Cell Transport

• Cells transport materials across the membrane through various mechanisms including passive and active transport.
• Passive transport does not require energy and includes diffusion (movement of molecules from high to low concentration), osmosis (diffusion of water across a selectively permeable membrane), and facilitated diffusion (diffusion with the help of membrane proteins).
• Active transport requires energy (ATP) to move molecules against their concentration gradient. Examples include endocytosis (taking in materials) and exocytosis (releasing materials).

Cell Communication

• Cells communicate with each other through various signaling mechanisms.
• These mechanisms include direct contact, local signaling (e.g., paracrine and synaptic signaling), and long-distance signaling (e.g., hormonal signaling).
• Cell signaling involves a sequence of events, including signal reception, signal transduction, and cellular response.
• Receptor proteins on the cell surface recognize and bind to specific signaling molecules (ligands) to initiate intracellular responses.

Cellular Metabolism

• Cellular metabolism encompasses the chemical reactions that occur within cells to sustain life.
• These reactions involve energy production, biosynthesis, and waste removal.
• Cellular respiration is a key metabolic process that produces ATP, the cell's primary energy currency.
• Glycolysis, the Krebs cycle, and the electron transport chain are crucial steps in aerobic respiration.
• Fermentation occurs in the absence of oxygen.

Cellular Differentiation

• Stem cells are undifferentiated cells with the ability to develop into specialized cell types.
• Cellular differentiation is the process by which cells acquire specific structures and functions.
• This involves activation and deactivation of certain genes, leading to changes in gene expression patterns, impacting the cell's proteome.

Tissues and their organization

• Tissues such as epithelial and connective tissues may form specific structures like layers in organs.
• Organs are groups of different tissues working together to perform a specific function.
• Organs often have specific arrangements or layers for specialized functions. The precise arrangement and specific roles of the different tissue types within an organ are critical for its proper function.