Histology Lecture Notes PDF

THE CELL of macromolecules, such as amino acids and sugars, across membranes, either by themselves or linked to the Na pump. 2 major compartments: cytoplasm and th...

THE CELL of macromolecules, such as amino acids and sugars, across membranes, either by themselves or linked to the Na pump. 2 major compartments: cytoplasm and the nucleus -____-passageway for small ions, molecules, water across the plasma membrane in either direction (i.e., passive diffusion -______- recognition and localized binding of ligands (molecules Cytoplasm: organelles & inclusions in a cytoplasmic matrix that bind to the extracellular surface of the plasma membrane) in Gel like aqueous substance consisting of solutes , inorganic ions processes such ashormonal stimulation, coated-vesicle (Na, K, Ca2) and organic molecules such as intermediate endocytosis, and metabolites, carbohydrates,lipids, proteins, and RNAs. antibody reactions. -________- anchor the intracellular cytoskeleton to membranous: with plasma membrane that separates internal the extracellular matrix, example: INTEGRINS link cytoplasmic envt of organelle from cytoplasm actin filaments to an extracellular matrix protein (fibronectin). E.g. cell membrane, RER, SER, Golgi, endosomes, lysosomes, -_____- catalysts that play a variety of roles transport vesicles, mitochondria, peroxisomes, microtubules -STRUCTURAL non membranous: not surrounded by plasma membrane ______: are accumulations of material that is not metabolically CARBOHYDRATES: active. They are usually present in the cytosol only temporarily. _______ (cell coat) E.g crystals, pigment granules, lipids, glycogen, waste products located on the outer surface of the outer leaflet of the plasmalemma, varies in appearance (fuzziness) and thickness (up CELL MEMBRANE to 50 nm). 1. Composition. consists of polar oligosaccharide side chains The cell membrane , also known as the plasma membrane , is linked covalently to most proteins and some lipids (glycolipids) of the outer boundary of the cell. It separates the interior of the the plasmalemma. It also contains proteoglycans cell from the external environment and plays a crucial role in (glycosaminog lycans bound to integral proteins). maintaining the cell's integrity, controlling what enters and leaves 2. Function the cell, and facilitating communication between cells. The a. aids in attachment of some cells (e.g., fibroblasts but not structure and function of the cell membrane are essential for the epithelial cells) to extracellular matrix components. cell's survival and its interactions with the surrounding b. It binds antigens and enzymes to the cell surface. environment. c. It facilitates cell-cell recognition and interaction. d. It protects cells from injury by preventing contact with Structure of the Cell Membrane: inappropriate substances. The plasma membrane is approximately 7.5 nm thick and consists e. It assists T cells and antigen-presenting cells in aligning with of two leaflets, known as the lipid bilayer that houses associated each other in proper fashion integral and peripheral proteins. and aids in preventing inappropriate enzymatic cleavage of 1. The inner leaflet of the plasma membrane faces the cytoplasm, receptors and ligands. and the outer leaflet faces the extracellular environment. 2. When examined by transmission electron microscopy, the CELLULAR TRANSPORT plasma membrane displays a There are generally two classes of transport protein: trilaminar (unit membrane) structure. Substances that enter or leave the cell must traverse the plasma membrane. Phospholipid Bilayer: Some substances (fat-soluble and small, uncharged molecules) - The lipid bilayer is freely permeable to small, lipid-soluble, cross the plasma membrane by simple diffusion down their nonpolar molecules but is impermeable to charged ions. concentration gradient 1. Molecular structure. The lipid bilayer is composed of All other molecules large, polar or charged molecules require phospholipids, glycolipids, and cholesterol, of which, in most membrane transport proteins to provide them with individual cells, phospholipids constitute the highest percentage. passage across the plasma membrane. a. Phospholipids are amphipathic molecules, consisting of one polar (hydrophilic) head and two nonpolar (hydrophobic) fatty ________ acyl tails, one of which is usually unsaturated. small, water-soluble molecules. b. The two leaflets are not identical; instead the distribution of the They are highly selective, often transporting only one type various types of phospholipids is asymmetrical. of molecule. After binding to a molecule designated for (1) The _____of each molecule faces the membrane surface, transport, the carrier protein undergoes a series of whereas the ____ project into the interior of the membrane, conformational changes and releases the molecule on the other facing each other. side of the membrane (2) The tails of the two leaflets are mostly 16 to 18 carbon chain fatty acids, and they form weak noncovalent bonds that attach _______ the two leaflets to each other. made of transmembrane proteins with several membrane- Phospholipids: Negatively CHARGED- loves to interact with water spanning domains Phosphatidylcholine and Sphingosine -outer membrane that create hydrophilic channels through the plasma Phosphatidylserine and Phosphatidylethanolamine-inner membrane. membrane The primary mechanism for the movement of large molecules MEMBRANE PROTEINS into, out of, and within the cell is known as _________ This include integral proteins and peripheral proteins and, in most involves the formation of vesicles from the plasma membrane of cells, constitute approximately 50% of the plasma membrane one compartment, which then fuse with the membrane of composition. another compartment. Inside the cell, this process facilitates the 1. _______ are dissolved in the lipid bilayer. transfer of vesicle contents between compartments. a. _______ proteins span the entire thickness of the plasma membrane and may function as membrane receptors, enzymes, Vesicular transport involving the cell membrane can be further cell adhesion molecules, cell recognition proteins, molecules that categorized: function in message transduction, and transport proteins. - _____ refers to the processes by which substances are brought (1) Most ______ proteins are glycoproteins. into the cell through vesicular transport. (2) are amphipathic and contain hydrophilic and hydrophobic - ______ refers to the processes by which substances are amino acids, some of which interact with the hydrocarbon tails of transported out of the cell through vesicular transport. the membrane phospholipids. (3) are folded, so that they pass back and forth across ______ the plasmalemma; therefore, they are also known as multipass often referred to as "cell drinking," is a type of endocytosis where proteins. the cell takes in extracellular fluid and dissolved molecules. b. may also be anchored to the inner (or occasionally outer) 1. The cell membrane folds inward to form a pocket around a leaflet via fatty acyl or prenyl groups. small volume of extracellular fluid. 2. ________do not extend into the lipid bilayer. 2. Formation of vesicle: This pocket pinches off, creating a small a. These proteins are located on the cytoplasmic as well as on the vesicle that moves into the cell. extracellular aspects of the cell membrane. 3. Purpose: allows the cell to sample its environment and take in b. The outer leaflets of some cells possess covalently linked nutrients, such as sugars and amino acids, that are dissolved in glycolipids to which peripheral proteins are anchored; these the fluid. peripheral proteins thus project into the extracellular space. FUNCTION -______: transport actively, transport metabolic precursors _______: - Secretory Proteins: Released outside the cell (e.g., "cell eating," is a form of endocytosis where the cell engulfs large hormones, enzymes). particles, such as bacteria, cellular debris, or other solid - Membrane Proteins: Incorporated into the cell or organelle materials. membranes. 1. Particle recognition: The cell identifies a target (like a - Organelle Proteins: Sent to specific organelles like bacterium) using surface receptors. lysosomes. 2. Engulfment: The plasma membrane extends outward, 2. Protein Folding and Quality Control: forming ______ (arm-like projections) that surround the particle. post-translational modification and sequestration of 3. Vesicle formation: The membrane closes around the particle, proteins within the rER is the first step in the exportation forming a large vesicle called a _____. of proteins destined to leave the cell. 4. Digestion: The phagosome fuses with lysosomes, which - Inside the RER lumen, newly synthesized proteins are folded contain digestive enzymes that break down the engulfed into their correct shapes. material. - Chaperone proteins assist in folding, and incorrectly folded proteins are identified and degraded. ENDOSOMES 3. Addition of Modifications: storage and sorting stations inside the cell. After the cell "eats" - The RER modifies proteins by adding sugar or "drinks" (via endocytosis), the vesicles carrying materials (like groups (glycosylation), which helps in proper protein folding and nutrients or signaling molecules) fuse with endosomes. function. 4. Transport of Proteins: Functions - The RER packages properly folded proteins into transport 1. Sorting Materials: vesicles , which are sent to the Golgi apparatus for further - Endosomes decide where the materials should go: processing. - Recycle: Some things, like receptors, are sent back to the Importance of RER: cell membrane for reuse. - It is essential for producing and processing proteins that the cell - Breakdown: Other materials are sent to lysosomes, where uses for growth, communication, or defense. they are broken down into simpler parts. - It works closely with the Golgi apparatus and other organelles - Transport: Certain materials are delivered to other parts of to ensure proteins reach their correct destinations. the cell for use. SER 2. Types of Endosomes: The Smooth Endoplasmic Reticulum (SER) is a type of - _______ First stop after endocytosis; they sort and decide endoplasmic reticulum that lacks ribosomes on its surface, giving the next destination. it a smooth appearance under a microscope. Unlike the rough ER, - _______: Second stop, closer to lysosomes, where materials the SER is primarily involved in lipid metabolism, detoxification, are prepped for degradation. and calcium storage. Key Point Structure of SER: - _______ = near the cell membrane (first stop, for sorting). - Tubular Network: - _______ = deeper inside the cell (prepares materials for - The SER consists of a network of interconnected tubules and breakdown). sacs (_______), similar to the RER but without ribosomes. - ______ = final stage (materials are broken down and - It is often continuous with the rough ER but has distinct recycled). functions. Functions of SER: LYSOSOMES 1. Lipid and Steroid Synthesis: Lysosomes are membrane-bound compartments inside the cell - The SER synthesizes lipids like phospholipids and cholesterol, that function as its waste disposal and recycling centers. They which are essential for building cellular membranes. contain powerful enzymes that break down and digest unwanted - It also produces steroid hormones in specialized cells like those materials, such as damaged cell parts, bacteria, and large in the adrenal glands and gonads. molecules. 2. Detoxification: - The SER is involved in detoxifying harmful substances, such as Key Features of Lysosomes: drugs, alcohol, and metabolic byproducts, especially in liver cells. 1. Structure: - It uses enzymes to modify these compounds, making them - Lysosomes are small, spherical vesicles enclosed by a single water-soluble for excretion. membrane. 3. Calcium Storage and Release: - They contain digestive enzymes (like proteases and lipases) - The SER serves as a calcium reservoir, particularly in muscle that work in acidic conditions (pH ~5). cells, where it is referred to as the sarcoplasmic reticulum. 2. Functions: - It releases calcium ions during muscle contraction and - Breakdown of Materials: Lysosomes digest large molecules reabsorbs them for relaxation. (like proteins, lipids, and carbohydrates) into smaller, reusable 4. Carbohydrate Metabolism: components. - In liver cells, the SER plays a role in glycogen metabolism, - Recycling: The breakdown products, such as amino acids and particularly in breaking down glycogen into glucose sugars, are sent back to the cell for reuse. (glycogenolysis). - Defense: Lysosomes destroy harmful invaders like bacteria or Importance of SER: viruses engulfed by the cell during phagocytosis. - The SER is essential for lipid production in all cells, ensuring - Autophagy: They remove and recycle damaged or worn-out membrane maintenance and energy storage. organelles, keeping the cell healthy. - It helps the body detoxify harmful substances, making it 3. How They Form: especially important in liver cells. - Lysosomes originate from late endosomes. Enzymes needed - In muscle cells, it plays a critical role in calcium regulation , for their function are produced in the rough ER and processed in which is necessary for contraction. the Golgi apparatus before being sent to lysosomes. GOLGI BODIES RER The Golgi apparatus , also known as the Golgi The Rough Endoplasmic Reticulum (RER) is an organelle complex or Golgi body , is an organelle responsible involved in the synthesis and processing of proteins. It is called for processing, modifying, sorting, and packaging molecules like "rough" because its surface is studded with ribosomes , which proteins and lipids that are made in the cell. It acts as the cell’s give it a bumpy appearance under the microscope. post office , ensuring molecules are sent to the correct Structure of RER: destinations. 1. Membrane Network: Structure of the Golgi Apparatus: - The RER is made up of interconnected, flattened sacs or 1. Stack of Flattened Membranes: membranes called ______. - The Golgi consists of cisternae , which are flattened, - It is continuous with the ______ , which surrounds the cell membrane-bound sacs stacked on top of each other. nucleus. - The stacks have two faces: 2. Ribosome Attachment: ______ Located near the endoplasmic reticulum (ER); it receives - The ribosomes attached to its surface are the sites of protein molecules from the ER. synthesis. These ribosomes are responsible for making proteins _____ Faces the cell membrane; it packages and sends materials destined for secretion, membranes, or organelles. to their destinations. Functions of RER: 2. Associated Vesicles: 1. Protein Synthesis: - Vesicles surround the Golgi, carrying materials to and from the - Ribosomes on the RER synthesize proteins directly into its organelle. lumen. These proteins are: Functions of the Golgi Apparatus: 1. Modification of Proteins and Lipids:  - Molecules arriving from the ER are modified by the addition of Provide structural integrity and shape to the plasma carbohydrates (glycosylation) or phosphate groups membrane. (phosphorylation). 2. Intracellular Transport : - These modifications ensure that molecules are functional and Act as tracks for motor proteins like myosin. ready for transport. Facilitate movement of organelles and vesicles. 2. Sorting and Packaging: 3. Cell Motility : - After modification, the Golgi sorts molecules based on their Essential for processes such as _____ and ____ formation in destination: migrating cells. - Plasma membrane: For secretion or incorporation into the Play a key role in wound healing and immune cell movement. membrane. 4. Endocytosis and Exocytosis : - Lysosomes: For degradation. Aid in vesicle trafficking and membrane remodeling. - Other organelles: For specific cellular functions. 5. Cytokinesis : 3. Vesicle Formation: Form the contractile ring during the division of the cytoplasm in - Packaged molecules are enclosed in vesicles, which bud off mitosis from the Golgi and deliver materials to their targets. Introduction to Microtubules 4. Secretion: 1. Definition : - The Golgi plays a key role in exocytosis, where molecules like Microtubules are cylindrical, hollow structures (~___ nm in hormones or enzymes are secreted out of the cell. diameter) composed of ____ subunits. Importance of the Golgi Apparatus: Structure - It ensures that proteins and lipids are correctly modified, sorted, 1. Composition : and sent to their proper locations, preventing miscommunication Made of ____ and _____ dimers that polymerize into linear and errors in the cell. protofilaments. - Specialized cells, like those in glands (e.g., pancreas), rely heavily 13 protofilaments form the cylindrical wall of the microtubule. on the Golgi to secrete large amounts of enzymes or hormones. 2. Polarity : Microtubules are polar, with a plus end (fast growing) and MITOCHONDRIA a minus end (slow growing, often anchored at the microtubule The mitochondria are known as the powerhouses of the organizing center [MTOC]). cell because they produce the energy the cell needs to function. 3. Dynamic Instability : They are essential for energy metabolism and many other vital Microtubules undergo constant cycles of assembly and cellular processes. disassembly, regulated by GTP binding and hydrolysis Structure of Mitochondria: Functions 1. Double Membrane: 1. Intracellular Transport : - _____: Smooth and acts as a protective boundary. Act as tracks for motor proteins dynein (retrograde - _____: Folded into structures called ____ , which increase transport) and kinesin (anterograde transport). the surface area for energy production. Transport organelles, vesicles, and macromolecular complexes. 2. Matrix: 2. Mitotic Spindle Formation : - The space inside the inner membrane contains enzymes, Essential for chromosome segregation during mitosis and mitochondrial DNA, and ribosomes. meiosis. - This is where key biochemical reactions take place. 3. Structural Support : 3. Intermembrane Space: Provide shape and mechanical support to cells, particularly - The area between the inner and outer membranes, important neurons and ciliated cells. for certain steps in energy production. 4. Motility : Functions of Mitochondria: Facilitate the movement of cilia and flagella. 1. ATP Production (Cellular Respiration): 5. Organelle Positioning : - Mitochondria convert glucose and oxygen Anchor and position organelles like the Golgi apparatus and into ATP (adenosine triphosphate), the cell’s main energy endoplasmic reticulum currency, through a process called oxidative phosphorylation. - This process occurs in two main stages: Introduction to Intermediate Filaments - Krebs Cycle (in the matrix): Breaks down molecules into 1. Definition : smaller compounds, releasing energy. Intermediate filaments are cytoskeletal components with a - Electron Transport Chain (on the inner membrane): Uses diameter (~____ nm) between microfilaments and microtubules. energy to produce large amounts of ATP. Unlike actin filaments and microtubules, they are non 2. Regulation of Cell Death (Apoptosis): polar and provide mechanical support rather than acting as - Mitochondria help regulate programmed cell death by tracks for motor proteins. releasing proteins like cytochrome c, which trigger the process. 2. Unique Feature : 3. Calcium Storage and Signaling: Composed of diverse protein subunits, depending on cell type. - Mitochondria store calcium ions and release them as needed Structure for cellular signaling, muscle contraction, and other processes. 1. Basic Unit : 4. Heat Production: Composed of polypeptide monomers that assemble into - In specialized cells, mitochondria can generate heat instead of coiled coil dimers, then into tetramers, protofilaments, and ATP, a process important for maintaining body temperature. ultimately, rope like intermediate filaments. 5. Production of Biomolecules: 2. Lack of Polarity : - Mitochondria are involved in the synthesis of certain lipids and Tetramers are antiparallel and staggered, making IFs non other molecules necessary for cell function. polar. Importance of Mitochondria: Types of Intermediate Filaments - They provide the energy required for cellular activities like Intermediate filaments are classified based on their protein growth, division, and repair. composition and the cell types in which they are found: - Cells with high energy demands, such as muscle and nerve cells, 1. Class I and II: _____ : Found in epithelial cells. have more mitochondria. Provide strength to skin, hair, and nails. - Mitochondria have their own DNA , which means they can Example: Cytokeratins in stratified squamous epithelium. replicate independently and produce some of their own proteins. 2. Class III: ____ and Related Proteins : Introduction to Microfilaments Found in mesenchymal cells. 1. Definition : ____ : Most widely distributed IF in cells of mesenchymal Microfilaments are the thinnest components of the origin (e.g., fibroblasts). cytoskeleton, with a diameter of ~_____. ____ : Found in muscle cells; aligns sarcomeres. Composed primarily of _____ , a highly conserved and abundant _______ : Found in astrocytes and Schwann cells. protein in eukaryotic cells. 2. Location : 3. Class IV: ______ : Predominantly found in the cell cortex (just beneath the Found in neurons, providing structural support to axons. plasma membrane). 4. Class V: ______ : Structure Found in the nuclear envelope of all nucleated cells. 1. Composition : Form the nuclear lamina , supporting the inner nuclear Built from _____actin (__ actin) that polymerizes to form membrane. _____ actin ( __ actin ). 5. Class VI: _____and ______ Actin filaments are dynamic, with a fast growing “___” (barbed) end and a slower growing “___” (pointed) end Functions Functions 1. Mechanical Support : 1. Mechanical Support :  Provide tensile strength to cells and tissues, especially in high Inner membrane : Supported by the nuclear lamina , stress environments like skin and muscle. composed of intermediate filaments (lamins). 2. Scaffold for Cellular Structures : 2. Nuclear Pores : Stabilize organelles, such as the nucleus and desmosomes. Large protein complexes that span the nuclear envelope, 3. Nuclear Integrity : forming nuclear pore complexes (NPCs). Nuclear lamins maintain nuclear shape and play a role in Facilitate selective transport of molecules (e.g., mRNA, chromatin organization. ribosomal subunits, and proteins) between the nucleus and 4. Cell Cell and Cell ECM Connections : cytoplasm. Participate in forming desmosomes (cell cell junctions) 3. Nucleoplasm : and hemidesmosomes (cell ECM junctions) in epithelial cells. Gel like substance filling the nucleus, containing ions, enzymes, nucleotides, and chromatin. Histological Relevance 4. Chromatin : 1. Tissue Specific Markers : DNA protein complex organized into two forms: Intermediate filament proteins serve as diagnostic markers in _____ : Lightly stained, transcriptionally active regions. pathology: _____ : Densely stained, transcriptionally inactive regions. Cytokeratins for epithelial tumors (carcinomas). Visible distinction in histological sections, especially with H&E Vimentin for mesenchymal tumors (sarcomas). staining. GFAP for astrocytomas. 5. Nucleolus : 2. Visualization : Dense, basophilic region responsible for ribosome Immunohistochemistry (IHC) is commonly used to detect biogenesis. specific IFs in tissues. Composed of fibrillar centers (rRNA genes), dense fibrillar components (active transcription), and granular components Introduction to the Centrosome and Centrioles (ribosome assembly). 1. Definition : Functions of the Nucleus The centrosome is the major microtubule organizing center 1. Genetic Material Storage and Regulation : (MTOC) in animal cells, involved in organizing microtubules and Stores DNA in the form of chromatin. regulating cell cycle progression. Regulates gene expression through transcription and Each centrosome contains a pair of centrioles , cylindrical chromatin remodeling. structures composed of microtubules. 2. Ribosome Production : 2. Location : Synthesizes and assembles ribosomal RNA and ribosomal Found near the nucleus in non dividing cells and at spindle subunits in the nucleolus. poles during mitosis. 3. Cell Division : Structure of Centrosome and Centrioles Ensures faithful replication and segregation of genetic material 1. _____ : during mitosis and meiosis. Composed of two perpendicular centrioles surrounded by an 4. Nuclear Transport : amorphous protein matrix called the pericentriolar material Controls the import/export of molecules like transcription (PCM). factors, RNA, and ribosomal subunits via nuclear pores. The PCM contains proteins like γ tubulin , which nucleates microtubule growth. Histological Relevance 2. Centrioles : 1. Staining Characteristics : Cylindrical structures made of microtubule triplets arranged Stains basophilic due to the abundance of DNA and RNA. in a 9+0 pattern (nine triplets with no central microtubules). Euchromatin appears lightly stained, while heterochromatin is Dimensions: ~0.5 µm in length and ~0.2 µm in diameter. darker and condensed. 3. Centriolar Duplication : 2. Nucleolus Visibility : Occurs once per cell cycle during S phase. Prominent in cells actively producing proteins (e.g., neurons, New centrioles, or procentrioles , form perpendicular to the hepatocytes). existing ones. 3. Nuclear Shape : Functions Varies with cell type: 1. Microtubule Organization : Round in lymphocytes. Centrosomes nucleate and anchor microtubules, organizing Elongated in fibroblasts. the cell's cytoskeleton. Multilobed in neutrophils. Play a role in intracellular transport by directing microtubule dynamics. Introduction to Tissues 2. Role in Mitosis and Meiosis : 1. Definition : Form the spindle poles during mitosis/meiosis, ensuring Tissues are groups of structurally and functionally similar cells proper chromosome segregation. and their extracellular matrix (ECM) organized to perform specific The centrosome duplicates prior to mitosis to form the two functions. poles of the spindle apparatus. 2. Hierarchy : 3. Basal Body Formation : Cells → Tissues → Organs → Organ Systems → Organism. Centrioles act as templates for basal bodies, which 3. Primary Types : anchor cilia and flagella in epithelial and motile cells. Epithelial Tissue Connective Tissue Centrosome Cycle Muscle Tissue 1. Interphase : Nervous Tissue Centrosomes function as microtubule organizing centers (MTOCs). Overview of the Four Basic Tissue Types Centriole duplication begins in S phase. 1. Epithelial Tissue 2. Mitosis : General Characteristics : During prophase, centrosomes move to opposite poles of the Tightly packed cells with minimal ECM. cell. Avascular but innervated. Microtubules radiate from the centrosomes, forming the Attached to a basement membrane. mitotic spindle. Highly regenerative. Functions : Introduction to the Nucleus Protection (e.g., skin). 1. Definition : Absorption (e.g., intestinal lining). The nucleus is a membrane bound organelle that contains Secretion (e.g., glands). the cell’s genetic material (DNA). Sensory reception (e.g., taste buds). It regulates gene expression, cell division, and various Classification : metabolic activities. By layers : Simple (1 layer), stratified (>1 layer). 2. Location : By shape : Squamous (flat), cuboidal, columnar. Found in nearly all eukaryotic cells, with number, size, and Examples : shape varying depending on cell type and function. Simple squamous epithelium: Lining of blood vessels (endothelium). Structure of the Nucleus Stratified squamous epithelium: Skin epidermis. 1. Nuclear Envelope : Double membrane structure that encloses the nucleus. 2. Connective Tissue Outer membrane : Continuous with the rough endoplasmic General Characteristics : reticulum (RER) and may have ribosomes attached.  Cells dispersed within abundant extracellular matrix (ECM). ECM consists of fibers (collagen, elastin, reticular) and ground substance. Highly vascular (except cartilage). Functions : Support and structure (e.g., bone). Transport of nutrients (e.g., blood). Storage (e.g., adipose tissue). Protection (e.g., immune cells in connective tissue). Types : Loose connective tissue : Areolar, adipose, reticular. Dense connective tissue : Regular (e.g., tendons) and irregular (e.g., dermis). Specialized connective tissue : Bone, cartilage, blood. Examples : Hyaline cartilage: Found in the trachea. Compact bone: Provides structural support. 3. Muscle Tissue General Characteristics : Specialized for contraction, generating movement. Cells contain contractile proteins (actin and myosin). Functions : Locomotion (e.g., skeletal muscle). Propulsion of contents (e.g., smooth muscle in intestines). Pumping blood (e.g., cardiac muscle). Types : Skeletal muscle : Striated, voluntary, multinucleated. Cardiac muscle : Striated, involuntary, intercalated discs. Smooth muscle : Non striated, involuntary, spindle shaped cells. Examples : Skeletal muscle: Attached to bones. Smooth muscle: Walls of blood vessels. Cardiac muscle: Heart myocardium. 4. Nervous Tissue General Characteristics : Specialized for communication via electrical and chemical signals. Composed of neurons (excitable cells) and glial cells (support cells). Functions : Sensory input (e.g., detecting stimuli). Integration of information (e.g., processing in the brain). Motor output (e.g., activating muscles). Components : Neurons : Composed of a cell body, axon, and dendrites. Glial cells : Provide support, insulation, and nutrition (e.g., astrocytes, oligodendrocytes). Examples : Peripheral nerves: Transmit signals between the CNS and body. CNS: Brain and spinal cord. Histological Relevance 1. Epithelial Tissue : Easily identified by the arrangement of cells in layers with minimal ECM. 2. Connective Tissue : Recognized by its abundant ECM and scattered cells (e.g., fibroblasts, adipocytes). 3. Muscle Tissue : Striations in skeletal and cardiac muscle distinguish them from smooth muscle. 4. Nervous Tissue : Neurons with prominent nuclei and axonal/dendritic processes are key identifiers.