Histology Notes PDF

# Histology - Study of the microscopic structure of tissues. - Provides insights into the function and pathology of cells and tissues by allowing one to observe their detailed structure and how they interact within the body. ## Through the examination of tissue samples under a microscope, we can i...

# Histology - Study of the microscopic structure of tissues. - Provides insights into the function and pathology of cells and tissues by allowing one to observe their detailed structure and how they interact within the body. ## Through the examination of tissue samples under a microscope, we can identify: - Normal tissue architecture. - Detect abnormalities that may indicate disease, such as inflammation, cancer, or degenerative conditions. ## This understanding is crucial for: - Diagnosing diseases. - Guiding treatments. - Conducting research into cellular and tissue functions. ## Branches of Histology - **General Histology:** Study of the structure and function of tissues. - **Special Histology:** Focuses on the microscopic structure of organs. - **Pathological Histology:** Examines discarded tissue. ## Basic Tissue Types 1. **Epithelial Tissue** - Covers body surfaces and lines cavities. 2. **Connective Tissue** - Supports, binds, and protects organs. 3. **Muscle Tissue** - Responsible for movement. 4. **Nervous Tissue** - Controls and coordinates body activities. ## Epithelial Tissue - **Types:** Simple, stratified, pseudostratified, transitional. - **Functions:** Protection, secretion, absorption, and filtration. ## Connective Tissue. - **Types:** Loose, dense, cartilage, bone, blood. - **Functions:** Provides support, stores energy, and transports materials. ## Muscle Tissue - **Types:** Skeletal, cardiac, smooth. - **Functions:** Movement, posture, and heat production. ### Skeletal Muscle - Main features: Fiber striated, tubular, and multinucleated. - Voluntary. - Usually attached to the skeleton. - **Location:** Covering the wall of internal organs (attached to skeleton). ### Smooth Muscle - **Type of cell:** - Fibers: non-striated, spindle-shaped and uninucleated. - Involuntary. - **Location:** Covering the wall of internal organs (not attached to skeleton). ### Cardiac Muscle - **Type of cell:** - Fibers: striated, branched, unbranched. - Involuntary. - **Location:** Only covering walls of the heart. ## Nervous Tissue - **Components:** Neurons and neuroglia. - **Functions:** Transmits electrical signals, processes information. ### Neurons - The primary functional units of the nervous system. - They are responsible for transmitting electrical impulses and processing information. - Neurons communicate with other neurons, muscles, and glands, enabling sensation, movement, thought, and many other functions. ### Structure: - **Cell Body (Soma):** Contains the nucleus and most of the cell's organelles. - **Dendrites:** Branch-like structures that receive signals from other neurons. - **Axon:** A long, slender projection that transmits impulses away from the cell body to other neurons or effector cells. ### Neuroglia (Glial Cells) - **Function:** - Supportive cells in the nervous system. - Do not transmit electrical impulses like neurons. - Play crucial roles in maintaining the environment around neurons, providing support, protection, and nutrients, and assisting in signal transmission. #### Types and Functions: - **Astrocytes:** Provide structural support, regulate blood flow, maintain the blood-brain barrier, and regulate the chemical environment around neurons. - **Oligodendrocytes (CNS) and Schwann Cells (PNS):** Produce the myelin sheath, which insulates axons and speeds up electrical signal transmission. - **Microglia:** Act as the immune cells of the central nervous system, protecting neurons by engulfing pathogens and debris. - **Ependymal Cells:** Line the ventricles of the brain and the central canal of the spinal cord, involved in producing and circulating cerebrospinal fluid. ## Histological Techniques - **Fixation:** Preserves tissue structure. - **Staining:** Enhances contrast (hematoxylin and eosin). - **Microscopy:** Light microscopy, electron microscopy. ### Microscopy in Histology #### Light Microscopy - Uses visible light that passes through or reflects off a specimen to magnify and view it. - Can magnify objects up to about 1000-1500 times their actual size, with a resolution of about 200 nanometers (nm). - **Types:** Bright field, dark field, phase contrast, fluorescence microscopy, coch - **Applications:** Commonly used in histology, biology, and medical labs to observe cells, tissues, and microorganisms. Useful for routine examinations such as identifying cell structures and diagnosing diseases. #### Electron Microscopy - Uses a beam of electrons instead of light to achieve much higher magnification and resolution - Can achieve resolution as fine as 0.1 nanometers, allowing for visualization of much smaller structures such as organelles within cells and even individual molecules. - **Types:** Transmission Electron Microscopy (TEM), which provides detailed images of internal structures, and Scanning Electron Microscopy (SEM), which gives three-dimensional images of surfaces. #### Applications: - Used in advanced research, material science, and pathology to study cell ultrastructure, viruses, and nanomaterials in great detail. ## Applications of Histology - **Medical Diagnosis:** Identifying diseases at the cellular level. - **Research:** Understanding tissue function and development. - **Forensic Science:** Analyzing tissue samples in criminal investigations. ## Epithelial Tissue - A group of similar cells that work together to perform a specific function. - Fundamental building blocks of organs and are essential for understanding the structure and function of the body. ## The Four Basic Tissue Types 1. **Epithelial Tissue:** Covers body surfaces, lines cavities, and forms glands. 2. **Connective Tissue:** Provides support and structure, connects tissues and organs. 3. **Muscle Tissue:** Facilitates movement through contraction. 4. **Nervous Tissue:** Transmits signals and processes information. ## Three Germ Layers 1. **Ectoderm:** - Outermost germ layer. - *Epidermis:* Skin and associated structures (hair, nails) - *Nervous System:* Brain, spinal cord, peripheral nerves. - *Specialized Sensory Organs:* Eyes, ears. - **Examples:** - Epidermal Tissue: Stratified squamous epithelium. - Nervous Tissue: Neurons and glial cells. 2. **Mesoderm:** - Middle germ layer. - *Musculoskeletal System:* Muscle, bones, cartilage. - *Circulatory System:* Blood vessels, heart. - *Connective Tissues:* Tendons, ligaments, adipose tissue. - **Examples:** - Skeletal Muscle Tissue: Striated muscle fibers. - Bone Tissue: Osteocytes within a calcified matrix. - Blood: Red blood cells, white blood cells. 3. **Endoderm:** - Innermost germ layer. - *Gastrointestinal Tract:* Lining of the stomach, intestines. - *Respiratory System:* Lining of the lungs, trachea. - *Glandular Epithelium:* Liver, pancreas. - **Examples:** - Simple Columnar Epithelium: Lining of the small intestine. - Glandular Tissue: Hepatocytes in the liver. ## Epithelial Tissue: One of the Four Basic Tissue Types - Covers body surfaces and lining cavities. ### Characteristics: - **Cellularity:** Composed of closely packed cells with minimal extracellular matrix. - **Polarity:** Distinct apical and basal surfaces. - **Basement Membrane:** A supportive structure anchoring epithelial cells to underlying connective tissue. - **Avascularity:** Lack blood vessels, with nutrients supplied through diffusion. - **Regeneration:** High capacity for renewal and repair. ### Functions of Epithelial Tissue: - **Protection:** Forms a barrier to protect underlying tissues from mechanical damage, pathogens, and dehydration. - **Example:** Epidermis of the skin. - **Absorption:** Absorbs nutrients and substances. - **Example:** Intestinal lining. - **Secretion:** Secretes substances such as enzymes, hormones, and mucus. - **Example:** Glandular epithelium in the pancreas. - **Filtration:** Filters blood in organs like the kidneys. - **Example:** Glomeruli in kidneys. - **Sensation:** Contains sensory receptors for various stimuli - **Example:** Olfactory epithelium in the nasal cavity. ## Classification of Epithelial Tissue: #### By Cell Shape: 1. **Squamous:** Flat, scale-like cells. 2. **Cuboidal:** Cube-shaped cells. 3. **Columnar:** Tall, column-like cells. #### By Cell Layers: 1. **Simple Epithelium:** Single layer of cells. 2. **Stratified Epithelium:** Multiple layers of cells. #### Special Epithelial Types: 1. **Pseudostratified Epithelium:** Appears layered but is actually a single layer with varying cell heights. 2. **Transitional Epithelium:** Specialized for stretching (e.g., bladder). ## Simple Squamous Epithelium - **Location:** Alveoli of lungs, lining of blood vessels (endothelium), and serous membranes (mesothelium). - **Function:** Diffusion, filtration, and secretion. ## Simple Cuboidal Epithelium - **Location:** Kidney tubules, ducts of glands. - **Function:** Secretion and absorption. ## Simple Columnar Epithelium - **Location:** Lining of the gastrointestinal tract, gallbladder. - **Function:** Absorption, secretion of mucus, and enzymes. ## Stratified Squamous Epithelium - **Keratinized:** Found in the epidermis of the skin. - **Non-Keratinized:** Found in the lining of the mouth, esophagus, and vagina. - **Function:** Protection against abrasion, pathogens, and chemical attack. ## Stratified Cuboidal Epithelium - **Location:** Ducts of sweat glands, mammary glands. - **Function:** Protection and secretion. ## Stratified Columnar Epithelium - **Location:** Rare, found in the male urethra and large ducts of some glands. - **Function:** Protection and secretion. ## Specialized Epithelia ### Pseudostratified Columnar Epithelium - **Location:** Respiratory tract (trachea, bronchi). - **Function:** Secretion of mucus, propulsion by ciliary action. ### Transitional Epithelium - **Location:** Urinary bladder, ureters. - **Function:** Permits expansion and recoil after stretching. ## Functional Significance - **Protective Role:** Stratified epithelia provide a durable layer of defense in areas subject to wear and tear. - **Absorption and Secretory Functions:** Simple epithelia with fewer layers, are adapted for efficient absorption and secretion. - **Adaptation to Function:** The structure of epithelial tissue is closely related to its function in different organs. ## Histological Features - **Basement Membrane:** A thin, fibrous layer that anchors epithelial tissue to underlying connective tissue. - **Intercellular Junctions:** - **Tight Junctions:** Prevent leakage between cells. - **Desmosomes:** Provide mechanical strength between cells. - **Gap Junctions:** Allow communication between cells. - **Polarity:** Apical surface faces the lumen or external environment; basal surface faces the underlying connective tissue. ## Clinical Relevance - **Carcinomas:** Cancers arising from epithelial cells. - **Examples:** Squamous cell carcinoma and adenocarcinoma. - **Cyst Formation:** Occurs when epithelial cells form sac-like cavities filled with fluid or semi-solid material. - **Barrier Dysfunction:** Conditions like psoriasis involve abnormal epithelial cell proliferation. - **Infections:** Respiratory and urinary infections often involve epithelial tissue. ## Microscopic Study of Tissues - **Biopsy:** Removal of tissue for diagnostic purposes. - **Autopsy:** Examination of organs of a dead body to determine cause of death. ## Connective Tissue - It supports, connects, or separates different types of tissue and organs. ### Functions: - **Structural Support:** - **Protection of Organs:** - **Transportation of Fluids (Blood, Lymph):** - **Energy Storage (Adipose Tissue):** - **Defense (Immune Response):** ### Composition of Connective Tissue: #### Cells: 1. **Fibroblasts:** Produce fibers and ground substance. 2. **Macrophages:** Phagocytic cells, part of immune defense. 3. **Adipocytes:** Store fat. 4. **Mast Cells:** Mediate allergic reactions. 5. **Plasma Cells:** Produce antibodies. #### Extracellular Matrix: - **Fibers:** - **Collagen Fibers:** Provide strength. - **Elastic Fibers:** Provide elasticity. - **Reticular Fibers:** Form supportive networks. - **Ground Substance:** - Proteoglycans, glycosaminoglycans (GAGs), and glycoproteins facilitate the diffusion of nutrients and waste. ### Classification of Connective Tissue: #### Connective Tissue Proper 1. **Loose Connective Tissue:** Areolar, adipose, reticular. 2. **Dense Connective Tissue:** Dense regular, dense irregular, elastic. #### Specialized Connective Tissue 1. **Cartilage:** Hyaline, elastic, fibrocartilage. 2. **Bone:** Compact bone, spongy bone. 3. **Blood:** Fluid connective tissue. 4. **Lymph:** Interstitial fluid involved in immune response. #### Loose Connective Tissue - **Areolar Tissue:** - **Function:** Provides elasticity, strength, and support. - **Location:** Beneath epithelial tissue, around blood vessels. - **Histology:** Contains collagen and elastic fibers, fibroblasts, macrophages. - **Adipose Tissue:** - **Function:** Stores energy, insulates, and cushions organs. - **Location:** Subcutaneous tissue, around organs. - **Histology:** Large fat droplets, nucleus pushed to the side. - **Reticular Tissue:** - **Function:** Supports the framework of lymphatic organs. - **Location:** Lymph nodes, bone marrow. - **Histology:** Reticular fibers and white blood cells. #### Dense Connective Tissue: - **Dense Regular:** - **Function:** Provides tensile strength. - **Location:** Tendons, ligaments. - **Histology:** Parallel collagen fibers with fibroblasts. - **Dense Irregular:** - **Function:** Provides strength in multiple directions. - **Location:** Dermis of skin, capsules of organs. - **Histology:** Irregularly arranged collagen fibers. - **Elastic Connective Tissue:** - **Function:** Allows stretch and recoil. - **Location:** Walls of large arteries, bronchial tubes. - **Histology:** Dense elastic fibers. #### Specialized Connective Tissue (Cartilage) - **Hyaline Cartilage:** - **Function:** Provides support with flexibility. - **Location:** Nose, trachea, larynx, ends of long bones. - **Histology:** Chondrocytes in lacunae, glassy matrix. - **Elastic Cartilage:** - **Function:** Maintains shape while allowing flexibility. - **Location:** External ear, epiglottis. - **Histology:** Many elastic fibers in matrix. - **Fibrocartilage:** - **Function:** Absorbs compressive shock. - **Location:** Intervertebral discs, pubic symphysis. - **Histology:** Thick collagen fibers. #### Specialized Connective Tissue (Bone) - **Compact Bone:** - **Function:** Supports and protects, stores calcium. - **Location:** Outer layer of bone. - **Histology:** Osteons, concentric lamellae, central canal. - **Spongy Bone:** - **Function:** Lightweight support, bone marrow. - **Location:** Inside bones. - **Histology:** Trabeculae with red or yellow marrow. #### Special Connective Tissue (Blood) - **Function:** Transports oxygen, nutrients, waste, and immune cells. - **Components:** - **RBC:** Oxygen transport. - **WBC:** Immunity. - **Platelets:** Clotting. - **Plasma:** Carries dissolved substances. ## Lymph - Interstitial fluid involved in immune responses. - **Definition:** Lymph is a clear, interstitial fluid that circulates in the lymphatic system, playing a crucial role in immune responses. - **Composition:** Contains lymphocytes (a type of white blood cells), proteins, and waste products. - **Function:** - Transports immune cells to sites of infection or injury. - Helps in the removal of toxins, waste, and pathogens from tissues. - Maintains fluid balance between blood and tissues. - **Histology:** Composed of lymphatic vessels, lymph nodes, and lymphatic organs (like the spleen and tonsils). - **Histo Physiology of Connective Tissue:** - **Structural Function:** Supports epithelial tissue and organs, binds tissues together. - **Defense Mechanism:** Contains immune cells (macrophages, lymphocytes), fights infections and repairs damaged tissues. - **Storage Function:** Stores energy (adipose tissue), stores minerals (bone tissue). ## Repair and Healing - Fibroblasts play a crucial role in wound healing. - Collagen deposition aids in tissue repair. ## Clinical Correlates ### Connective Tissue Disorders: - **Marfan Syndrome:** Genetic disorder affecting elastic fibers. - **Osteogenesis Imperfecta:** Defect in collagen production, leading to brittle bones. - **Ehlers-Danlos Syndrome:** Hyperelastic skin and hypermobile joints due to abnormal collagen. ## Nervous Tissue - **Overview of the Nervous System:** - Allows the body to adapt and respond to both internal and external stimuli. - Responsible for controlling and integrating organ systems. ### Central Nervous System (CNS): - Brain and spinal cord. ### Peripheral Nervous System (PNS): - Cranial, spinal, and peripheral nerves. ### Central Nervous System - **Composed of the brain and spinal cord.** - The CNS is enclosed within the **cranial cavity** (brain) and the **spinal canal** (spinal cord). - It processes information and determines responses. ### Peripheral Nervous System - Includes cranial, spinal, and peripheral nerves that transmit signals between the CNS and the rest of the body. - Functions to relay sensory and motor information. - **Structure of the CNS:** - **Brain:** The command center for sensory information and motor control. - **Spinal Cord:** Connects the brain to the peripheral nervous system, facilitates reflex actions. #### Regions of the Brain: - **Cerebrum:** Responsible for higher brain functions (thinking, memory, sensory processing). - **Cerebellum:** Coordinates voluntary movements and balance. - **Brainstem:** Controls vital functions (breathing, heart rate, and signal relays between the brain and spinal cord). #### Divisions of the Brain: - **Cerebrum:** Divided into left and right hemispheres. - **Lobes:** - **Frontal:** Executive functions, decision-making. - **Parietal:** Sensory processing. - **Temporal:** Hearing, memory. - **Occipital:** Vision. - **Cerebellum:** - **Function:** Maintains posture, balance, and coordination of voluntary movements. - **Structure:** Contains a cortex and deep nuclei. - **Brainstem:** - **Components:** Midbrain, pons, medulla oblongata. - **Functions:** - **Medulla:** Control autonomic function (heart rate, breathing). - **Pons:** Relay signals and regulates sleep. #### Spinal Cord Structure: - **Segments:** Divided into cervical, thoracic, lumbar, sacral, and coccygeal regions. - **Gray Matter:** H-shaped structure containing neuron cell bodies. - **White Matter:** Contains myelinated axons organized into tracts. #### Function of the Spinal Cord: - **Conduit:** Transmits signals between the brain and the body. - **Reflex Actions:** Mediates reflexes independently of the brain. ### Meninges - **Definition:** Protective membranes covering the CNS. #### Layers: - **Dura Mater:** Outer tough layer. - **Arachnoid Mater:** Middle layer with a web-like structure. - **Pia Mater:** Inner layer adhering to the brain and spinal cord. ### Cerebrospinal Fluid (CSF) - **Function:** Cushions the CNS, removes waste, and provides nutrients. - **Production:** Formed in the ventricles of the brain and circulates in the subarachnoid space. ### Blood-Brain Barrier - **Definition:** A selective permeability barrier protecting the brain from harmful substances. - **Importance:** Maintains the brain's environment and homeostasis. ## Components of Nerve Tissue - **Neurons:** The functional cells that generate and transmit electrical impulses. - **Neuroglia:** Supporting cells that protect, nourish, and support neurons. ### Neurons - Specialized cells responsible for receiving stimuli and transmitting signals. - **Each neuron consists of:** - **Cell Body (Soma):** Contains the nucleus and most of the cytoplasm, serving as the metabolic center of the cell. - **Dendrites:** Receive signals and axons transmit them to other neurons or effectors. ### Synapses - Specialized junctions through which neurons communicate with each other or with other types of cells, such as muscle cells or glandular cells. - They play a crucial role in transmitting signals across the nervous system. #### Key Components: 1. **Presynaptic Neuron:** The neuron that sends the signal. It contains synaptic vesicles filled with neurotransmitters. 2. **Postsynaptic Neuron:** The neuron that receives the signal. It has receptors that bind to the neurotransmitters released from the presynaptic neuron. 3. **Synaptic Cleft:** The small gap between the presynaptic and postsynaptic neurons where neurotransmitters are released. ### Types of Neurons in the CNS - **Motor Neurons:** Transmit signals to muscles. - **Sensory Neurons:** Relay information from sensory receptors. - **Interneurons:** Process and integrate information. ### Neuroglia or Glial Cells - Non-neuronal cells in the nervous system that support, nourish, and protect neurons. #### Functions: - **Support:** Provide structural support to neurons. - **Protection:** Shield neurons from pathogens and injury. - **Nutrition:** Supply nutrients and oxygen to neurons. - **Maintenance:** Help maintain the extracellular environment and remove waste. #### Neuroglia in the CNS - **Types:** - **Astrocytes:** Support neurons and maintain the blood-brain barrier. - **Oligodendrocytes:** Produce myelin sheaths for axons. - **Microglia:** Act as immune cells within the CNS. - **Ependymal Cells:** Line the ventricles and produce CSF. ## Peripheral Nervous System (PNS) - Consists of all the nerves outside the central nervous system (CNS) that connect the CNS to the limbs and organs. - Transmits sensory information to the CNS and carries motor commands from the CNS to the body. ### Components of the PNS: - **Cranial Nerves:** 12 pairs of nerves that emerge directly from the brain. - **Spinal Nerves:** 31 pairs of nerves that emerge from the spinal cord. - **Peripheral Nerves:** Branches that extend to the limbs and organs. ## Functional Divisions of the PNS - **Somatic Nervous System:** Controls voluntary movement by innervating skeletal muscles. - **Autonomic Nervous System:** Controls involuntary functions (heart rate, digestion). ### Somatic Nervous System - **Components:** - **Sensory (Afferent) Neurons:** Relay sensory information to the CNS. - **Motor (Efferent) Neurons:** Convey commands from the CNS to skeletal muscles. - **Functions:** Responsible for voluntary movements and reflex actions. ### Autonomic Nervous System - **Subdivisions:** - **Sympathetic Division:** Prepares the body for "fight or flight" response. - **Parasympathetic Division:** Promotes "rest and digest" activities. - **Enteric Division:** Manages gastrointestinal function independently. ### Peripheral Nerves: - Bundles of axons wrapped in connective tissue. - **Types:** Sensory, motor, and mixed nerves. - **Function:** Relay signals between the CNS and peripheral organs. #### Cranial Nerves: - 12 pairs with various functions (sensory, motor). - **Olfactory (I):** Sensory (smell). - **Optic (II):** Sensory (vision). - **Oculomotor (III):** Motor (eye movement, pupil constriction). - **Trochlear (IV):** Motor (eye movement). - **Trigeminal (V):** Mixed: Sensory from the face; motor for mastication. - **Abducens (VI):** Motor (eye movement). - **Facial (VII):** Mixed: Facial expressions, taste, salivary glands). - **Vestibulocochlear (VIII):** Sensory (hearing and balance). - **Glossopharyngeal (IX):** Mixed: Taste, swallowing, salivation. - **Vagus (X):** Mixed (autonomic functions of the heart, lungs, and digestive tract). - **Accessory (XI):** Motor (shoulder and neck movement). - **Hypoglossal (XII):** Motor (tongue movement). #### Spinal Nerves: - Each spinal nerve has a dorsal (sensory) and ventral (motor) root. - **Function:** Relay signals between the spinal cord and the body. ## Types of Neuroglia in the PNS 1. **Schwann Cells:** - **Function:** Produce myelin sheaths for peripheral nerves. - **Role in Repair:** Aid in the regeneration of damaged peripheral nerves. 2. **Satellite Cells:** - **Location:** Surround neuron cell bodies in ganglia. - **Function:** Provide support and nutrition to peripheral neurons). ## Clinical Correlates ### Parkinson's Disease - First described by James Parkinson in 1817. - Originally termed "shaking palsy". - **Neurodegeneration:** Characterized by the loss of dopamine-producing neurons in the substantia nigra. - **Lewy Bodies:** Abnormal protein aggregates that develop in the brains of affected individuals. - **Dopamine:** - A neurotransmitter, a chemical messenger in the brain that plays several important roles in both the central nervous system and peripheral nervous system. - Key points about Dopamine: - **Neurotransmission:** Dopamine transmits signals between nerve cells, facilitating communication within the brain. - **Reward and Motivation:** It is crucial for the brain's reward system, influencing pleasure, motivation, and reinforcement of behaviors. - **Movement Control:** Dopamine is essential for coordinating smooth and controlled movements. It helps regulate motor functions and is involved in the initiation and execution of movement. - **Mood Regulation:** It affects mood and emotional responses, with imbalances linked to conditions such as depression and anxiety. #### Symptoms of Parkinson's Disease: - **Motor Symptoms:** - **Tremors:** Resting tremors (slight rhythmic involuntary movements). - **Bradykinesia:** (Slowness of movement). - **Rigidity:** (Muscle stiffness). - **Postural Instability:** (Balance issues). - **Non-Motor Symptoms:** - **Depression and anxiety.** - **Sleep disturbance.** - **Cognitive impairment.** ### Guillain-Barré Syndrome (GBS) - An acute condition affecting the PNS, often triggered by an infection. - Leads to rapid muscle weakness and paralysis. - Due to demyelination of peripheral nerves. ### Chronic Inflammatory Demyelinating Polyneuropathy (CIDP) - A chronic condition similar to GBS but occurring over a longer timeframe. - Can cause progressive weakness and sensory loss. ### Acute Disseminated Encephalomyelitis (ADEM) - A brief but intense inflammatory demyelinating condition often following a viral infection or vaccination. - Primarily affects children. ### Guillain-Barré Syndrome - A rare process in the central nervous system (CNS) characterized by the proliferation and activation of glial cells, primarily astrocytes in response to injury, inflammation, or disease. ### Alzheimer's Disease - A progressive neurodegenerative disorder characterized by the gradual decline of cognitive functions, including memory, reasoning, and the ability to perform daily activities. #### Clinical Symptoms: - **Cognitive Decline:** Memory loss, particularly short-term memory, difficulty in problem-solving, and planning. - **Behavioral Change:** Mood swings, depression, anxiety, and changes in personality. - **Loss of Daily Function:** Difficulty performing familiar tasks, disorientation in time and space. ## Muscle Tissue ### Skeletal Muscle - **Structure:** - **Striated Appearance:** Skeletal muscle fibers have a distinct banded pattern due to the organization of myofilaments (actin and myosin). - **Multinucleated:** Each fiber contains multiple nuclei, located at the periphery of the cell. - **Voluntary Control:** Controlled by the somatic nervous system, allowing for conscious movement. - **Function:** - **Movement:** Responsible for voluntary movements of the skeleton (walking, lifting). - **Posture Maintenance:** Help maintain body posture and stabilize joints. - **Heat Production:** Generates heat through muscle contractions, aiding in thermoregulation. - **Location:** Attached to bones throughout the body, forming the bulk of the muscular system. ### Smooth Muscle - **Structure:** - **Non-Striated Appearance:** Smooth muscle fibers lack the striations characteristic of skeletal muscle. - **Spindle-Shaped Cells:** Each fiber is a single, spindle-shaped cell with a single central nucleus. - **Involuntary Control:** Regulated by the autonomic nervous system and hormones, operating without conscious control. - **Function:** - **Involuntary Movements:** Control movements in internal organs, such as peristalsis in the digestive tract and vasoconstriction/dilation in blood vessels. - **Regulation:** Helps regulate the diameter of blood vessels and the movement of substances through hollow organs. - **Location:** Found in the walls of hollow organs (intestines, blood vessels, bladder) and in the respiratory tract. ### Cardiac Muscle - **Structure:** - **Striated Muscle:** Cardiac muscle also has striations, similar to skeletal muscle, due to the arrangement of actin and myosin. - **Branched Cells:** Cardiac fibers are branched and interconnected, forming a network. - **Single Central Nuclei:** Typically contain one or two nuclei usually centrally located. - **Involuntary Control:** Regulated by the autonomic nervous system and specialized pacemaker cells. - **Function:** - **Pumping Blood:** Responsible for the rhythmic contractions of the heart, which pump blood throughout the body. - **Automaticity:** Capable of initiating its own contractions without external nerve stimulation. - **Location:** Exclusively found in the heart, forming the myocardium (heart muscle). ### Body Location of Muscle Tissue: * **Skeletal:** Attached to bone or for some facial muscle, to skin. * **Cardiac:** Wall of the heart. * **Smooth:** Mostly in walls of hollow visceral organs (other than the heart). ### Characteristics of Muscle Tissue: - **Cell Shape and Appearance:** - **Skeletal:** Single, very long, cylindrical, multinucleated cells with very obvious striations. - **Cardiac:** Branching chains of cells; uninucleate; striations; intercalated discs. - **Smooth:** Spindle, fusiform, uninucleated, no striations. - **Connective Tissue Components:** - **Skeletal:** Epimysium, perimysium, and endomysium. - **Cardiac:** Endomysium attached to the fibrous skeleton of the heart. - **Smooth:** Endomysium. - **Regulation of Contraction:** - **Skeletal:** Voluntary, via nervous system control. - **Cardiac:** Involuntary; the heart has a pacemaker; also nervous system control; hormones, chemicals, stretch. - **Smooth:** Involuntary; nervous system control; hormones, chemicals, stretch. - **Speed of Contraction:** - **Skeletal:** Slow to fast. - **Cardiac:** Slow. - **Smooth:** Very slow. - **Rhythmic Contraction:** - **Skeletal:** No. - **Cardiac:** Yes. - **Smooth:** Yes, in some. ## Discoveries in Cell Biology 1. **Robert Hooke (1665)** - Observed a thin slice of cork with a microscope. - "Little boxes" - First to discover the cell. - Coined the term "cell". 2. **Anton van Leeuwenhoek (1675)** - The first person to observe living cells (bacteria and protozoa). - "Father of Microscopy." - "Father of Microbiology" ## The Cell Theory - All living things are composed of one or more cells. - Cells are organism's basic units of structure and function. - Cells come only from existing cells. ### 3.1. Matthias Schleiden (1838) - "All plants are composed of cells." - Embryonic plant arises from a single cell. - Declared that the cell is the basic building block of all plant matter. ### 3.2. Theodor Schwann (1839) - "All animals are composed of cells." - Examined notochordal tissue and tissues from pig embryos. - All living things are composed of cells and cell products. ### Classification of Cells in terms of five types of highly differentiated cellular tissues: 1. **Cells that are independent and separate (blood cells).** 2. **Cells thar are independent but compacted together in layers (skin, fingernails, feathers).** 3. **Ceils whose connecting walls have coalesced (cartilage, bone, tooth enamel).** 4. **Elongated cells forming fibers (tendons and ligaments).** 5. **Cells formed by the fusion of walls and cavities (muscles: tendons, and nerves).** ### 3.3. Rudolf Virchow (1855) - "Cells come only from other cells." - "The study of disease at the cellular level." - *Omnis cellula e cellula.* ## Cell Diversity 1. **Size:** - Eukaryotic cells: 2 - 10 µm (e.g., bacteria). - Longest cell: Giraffe nerve cells - 2mm - Biggest cell: Ostrich egg - 5 inches long and wide, 3 pounds. 2. **Shape:** - Cells differ widely in shape. - Cuboidal or spherical. 3. **Internal Organization:** - Nucleus, organelles. - Prokaryotic, eukaryotic. ## Prokaryotes vs. Eukaryotes: | Feature | Prokaryotes | Eukaryotes | |----------------|-----------------|----------------| | Nucleus | No | Yes | | Membrane-Bound Organelles | No | Yes | | Size | 1-10 µm | 10-50 µm | | When Evolved | 3.5 billion years ago | 1.5 billion years ago | | Cytoplasm | Yes | Yes | | Cell Membrane | Yes | Yes | | Cell Wall | Some do | Yes | | Ribosomes | Yes | Yes | | DNA | Circular free floating | Chromosomes in nucleus | | Examples | Bacteria | Plants, fungi, animals, and protists | ## Cell: The Basic Structural and Functional Unit of All Living Organisms. **Functions:** 1. **Metabolism:** Chemical reactions that provide energy. 2. **Growth:** Increase in cell size and number. 3. **Reproduction:** Cell division to produce new cells. 4. **Response to Stimuli:** Cells can respond to environmental changes. 5. **Homeostasis:** Maintenance of a stable internal environment. ## Cell - **Protoplasm:** Main and karyoplasm. - **Most eukaryotic cells have three main components:** - **Plasma membrane:** - Phospholipid bilayer with protein that function as channel markers and receptors. - Contains cholesterol. - Consists of integral membrane proteins and peripheral membrane proteins. - **Functions:** - Form selective barrier between the cytoplasm and the external environment. - Regulating cell-cell interactions. - Recognition, via receptors, antigens, and foreign cells as well as altered cells. - Establishing transport systems for specific molecules. - **Membrane Transport:** - **Endocytosis:** Performs the uptake and transfer of molecules and solutes across the cell membrane into the cell interior. - **Exocytosis:** Release of material from the cell cytoplasm across the cell membrane. - **Pinocytosis:** Cell ingests small molecules of extracellular fluid. - **Phagocytosis:** Ingestion of large particles by cells. - **Receptor-Mediated End