Handout - Tissues PDF

I. Introduction to Tissues II. Classification of Tissues Four Basic Types of Tissues 1. Epithelial Tissue Functions - Classification by Layers: - Simple Epithelium - Stratified Epithelium - Classification by Cell Shape: - Squamous - Cuboidal - Columnar - Specialize...

I. Introduction to Tissues II. Classification of Tissues Four Basic Types of Tissues 1. Epithelial Tissue Functions - Classification by Layers: - Simple Epithelium - Stratified Epithelium - Classification by Cell Shape: - Squamous - Cuboidal - Columnar - Specialized Epithelium 2. Connective Tissue - Functions - Components - Types - Loose Connective Tissue - Dense Connective Tissue 3. Muscle Tissue - Functions - Types - Skeletal Muscle - Cardiac Muscle - Smooth Muscle 4. Nervous Tissue  - Functions - Components - Neurons - Neuroglia III. Epithelial Tissue: In-Depth - Membrane Junctions - Glandular Epithelium - Surface Specializations IV. Connective Tissue - Extracellular Matrix - Cartilage and Bone - Blood as a Connective Tissue V. Muscle Tissue - Structure of Muscle Tissue - Skeletal Muscle - Cardiac Muscle - Smooth Muscle - Muscle Contraction Mechanism VI. Nervous Tissue - Neuron Structure - Types of Neurons - Neuroglia Types VII. Tissue Repair and Regeneration - Process of Tissue Repair: - Inflammation - Organization - Regeneration and fibrosis - Factors Affecting Tissue Repair VIII. Clinical Considerations - Tissue Pathology - Tissue Engineering ____________________________________________________________________________ I. Introduction to Tissues Definition: Tissues are groups of similar cells that work together to perform a specific function. Histology: The study of tissues, which provides insights into how tissues contribute to the structure and function of organs and the body as a whole. Pathology: The study of changes that occur during the disease condition Extracellular Matrix: support network that surrounds cells in a tissue. This is varying according to the type of cell or tissue present. For example, bone tissues contain a solid ECM while the blood contains a liquid ECM. The matrix consists of the following substances”: o Collagen: most abundant protein in the body; create long and tough fibers. Tough and protective; leather-like o Proteoglycans: large negatively charged molecules that comprise both protein and carbohydrate. The negative charge attracts sodium and water to the ECM to create a gel-like consistency. o ECM is vital to the health of the cells and the tissues, its composition affects nutrition, gene expression and growth factors  Cellular connections: Allow varying degrees of interaction between cells o Tight junctions: fuses two neighboring cells together so tight that there is no extracellular space which blocks any form of movement. This is commonly seen in the intestines as the cells should be close and tight to prevent bacteria from sliding in. o Gap junction: Forms and intracellular passageway between the membranes of adjacent cells to facilitate the movement of small molecules and ions. These junctions allow electrical and metabolic coupling. o Desmosomes: A.K.A Anchor junctions. They provide strong and flexible connections between cells. Allow some degree of movement. Anchors two cells between each other ▪ Hemidesmosomes: This anchor junction on the other hand provides anchoring between the cell and the ECM instead. II. Classification of Tissues The human body is composed of four basic types of tissues: 1. Epithelial Tissue: covers exterior surfaces o Features: Highly cellular, polar, avascular, innervated, adhered to base o Functions: ▪ Protects underlying structures ▪ Absorbs substances ▪ Filters particles ▪ Secretes substances such as hormones and enzymes. o Background ▪ Endothelium vs Epithelium 1. Endothelium: Endo means inside. Not allowed to touch bacteria 2. Epithelium: Epi means upon/over/above. Connected to outside ▪ Polarity of Tissues: This means the tissue has two sides 1. Apical: side exposed to the environment  2. Basal: side that faces the ECM a. Basement Membrane: specialized ECM that anchors basal epithelium. Consists of two layers: lamina lucida which contains both proteoglycans and collagen and lamina densa which is full of tough collagen fibers o Classification by Cell Shape: ▪ Squamous: Flat, scale-like cells. ▪ Cuboidal: Cube-shaped cells. ▪ Columnar: Tall, column-like cells. o Classification by Layers: ▪ Simple Epithelium: Single cell layer, allowing for absorption, secretion, and filtration. 1. Simple squamous: fried egg appearance, present in rapid passage of chemical compounds e.g alveoli, kidney tubules, capillaries 2. Simple cuboidal: found in places of transport e.g gland ducts 3. Simple columnar: elongated, found in the bases of cells, active in absorption and secretion. Digestive system and respiratory tract. Often have cilia and microvilli. ▪ Stratified Epithelium: Multiple layers, providing protection in areas of high abrasion. 1. Stratified squamous: most abundant in the body, usually found in areas that are dry since it is modified to help retain moisture. Apical cells or dead cells that are filled with the protein keratin. 2. Stratified cuboidal: salivary glands, sweat glands, mammary glands 3. Stratified columnar epithelium: Male urethra ▪ Pseudostratified epithelium: pseudo means false, this type looks like it has multiple layers but really contains only one. Only columnar epithelia are considered under this category  1. Goblet cells: unicellular exocrine gland that release mucus 2. Specialized Epithelium: o Glandular Epithelium: Involved in secretion; includes endocrine (hormone- secreting) and exocrine (secreting substances onto body surfaces) glands. ▪ A gland is a structure that synthesizes and secretes chemicals. Most glands are composed of groups of epithelial cells, but some are unicellular. 1. Endocrine: releases hormones, ductless 2. Exocrine: varying structures; acinar(pockets) and tubular(tubes) a. Merocrine: most common type, exocrine secretion. Releases serous (watery) and mucus secretions b. Apocrine: secretion accumulates in the apical side e.g sweat glands of axilla and genital area c. Holocrine: rupture and destruction of the glandular cell o Transitional Epithelium: Found in the bladder, able to stretch and recoil. This type is able to transform from any shape and go back to its original shape Connective Tissue Functions: o Provides support o Binds tissues together o Protects organs o Stores energy (fat) o Transports substances (blood). Components: o Cells: Include fibroblasts (produce fibers), macrophages (immune response), adipocytes (fat storage), etc.  o Extracellular Matrix (ECM): Composed of ground substance and fibers (collagen, elastic, reticular) that provide structural support. o Fibroblasts produces three types of fibers ▪ Collagen fibers are flexible but also have great tensile strength, resists stretching ▪ Elastic fibers contain elastin. For stretching and compression, returns to original shape ▪ Reticular fibers are formed form collagen subunits, narrow and branching. Found in organs ▪ All of these are embedded in the ground substance/extracellular matrix Types: o Loose Connective Tissue: absorbs shocks and bind tissues together, allows diffusion of water, salt, and nutrient ▪ Areolar: Supports and binds other tissues. Loosely woven web appearance ▪ Adipose: Stores fat, insulates, and protects organs. ▪ White: yellow appearance, for lipid storage and insulation ▪ Brown: found in infants, releases heat instead of ATP ▪ Reticular: Provides a framework for lymphatic organs. Mesh like appearance o Dense Connective Tissue: MORE COLLAGEN FIBERS ▪ Dense Regular: Parallel collagen fibers, found in tendons and ligaments. ELASTIN ▪ Dense Irregular: Collagen fibers arranged in various directions, found in the dermis. ▪ Elastic: Allows for stretching, found in arteries. o Specialized Connective Tissue: Supportive connective tissues. For posture ▪ Cartilage: Provides flexible support, Avascular and semisolid material that offers both structure and some flexibility. E.g. Ribcage ▪ The matrix of the cartilage is composed of polysaccharides called chondroitin sulfate and cartilage cells called chondrocytes. These cells sit within small spaces called the lacunae. ▪ The perichondrium is a supportive dense irregular connective tissue that encapsulates the cartilage. ▪ Types of Cartilage: ▪ Hyaline: Smooth appearance with no visible fibers, most common type of cartilage. Short and dispersed fibers ▪ Commonly seen in the ribcage and during the fetal period since it can form bone if the chondrocytes differentiate to become bone cells ▪ Elastic cartilage: Least common type of cartilage, contains collagen and proteoglycans. ▪ Commonly seen in ear lobes and external ear ▪ Fibrocartilage: Many visible collagen fibers. Found in weight bearing parts of the body since it has the ability to absorb pressure. ▪ Commonly seen in the knee joints and the vertebrae of the spine ▪ Bone: Provides rigid support and stores minerals. ▪ Provides protection to internal organs e.g Cranium, Ribcage, Vertebra ▪ The bone is rigid due to the deposition of Calcium and mineral crystals. The ECM of the bone consists of three cells: ▪ Osteocytes ▪ Osteoblasts ▪ Osteoclasts  o Fluid connective tissue: Its function is to distribute materials and nutrients throughout the body ▪ Blood: Transports nutrients, gases, and waste products. Also called as Fluid Connective Tissue. ▪ The cells circulate in a liquid form of extracellular matrix called the plasma. It contains only monomers of proteins ▪ Formed elements of the blood (components) 1. Erythrocytes: RBC, carries hemoglobin and oxygen 2. Leukocytes: WBC, fights against infection 3. Platelets: for coagulation ▪ Lymph: another form of Fluid connective tissue. This fluid does not have its own resident cells unlike blood. It is a fluid collected from excess interstitial fluid. It is mostly acellular. ▪ Lymphatic capillaries are extremely permeable and drains fluid straight into the bloodstream ____________________________________________________________________________________ Muscle Tissue Functions: Produces movement, maintains posture, and generates heat. Types: o Skeletal Muscle: Voluntary control, striated, attached to bones for movement. Also called as skeletal fibers. Their number remains relatively constant throughout life ▪ Are capable of hypertrophy but are not capable of mitosis due to their multiple nuclei. Their appearance is very long due to myoblasts that fuse to form each fiber. Arranged in bundles and surrounded by connective tissue. ▪ Striations or linings are seen due to the arrangement of the contractile proteins actin and myosin o Cardiac Muscle: Involuntary control, striated, found only in the heart, contains intercalated discs.  ▪ Also known as cardiomyocytes: smaller and has a single nucleus ▪ Intercalated discs connect each cardiomyocyte through desmosomes and gap junctions. With this the cells create a mechanical and electrical union allowing a synchronized movement throughout the muscle, in this case the heart. o Smooth Muscle: Involuntary control, non-striated, found in the walls of hollow organs (e.g., intestines, blood vessels). Nervous Tissue: make up the brain, spinal cord, and peripheral nerves. Functions: o Responsible for communication ▪ The nerves communicate by way of electrochemical impulses called action potentials ▪ Action potentials are released by the result of chemical signaling between molecules o Coordination o Control within the body. Components: o Neurons: The primary cells that conduct electrical impulses. o Neuroglia: Support cells that protect and assist neurons. ▪ Glia is Greek for “glue” ▪ Are incapable of sending signals but they help neurons function ▪ They outnumber neurons nine to one Neuron Structure: o Dendrites: Receive signals from other neurons or sensory receptors. ▪ Shorter ▪ Receives signals towards the brain o Axon: Transmits electrical impulses away from the cell body to other neurons, muscles, or glands.  ▪ Longer ▪ Sends signals away from the brain ▪ Wrapped in an insulating jacket called myelin which functions to speed up impulses ▪ Synapse is a terminal that receives the electrical impulses o Cell Body (Soma): Contains the nucleus and organelles, integrating incoming signals and generating outgoing signals. Types of Neurons: o Sensory Neurons: Transmit sensory information from receptors to the central nervous system (CNS). o Motor Neurons: Convey signals from the CNS to muscles or glands to elicit a response. o Interneurons: Connect neurons within the CNS and integrate sensory input with motor output. Neuroglia (Glial Cells): o Astrocytes: Provide structural support, maintain the blood-brain barrier, and regulate ion balance. o Oligodendrocytes: Form the myelin sheath in the CNS, which insulates axons and speeds up signal transmission. o Microglia: Act as the immune defense in the CNS by engulfing pathogens and dead cells. o Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord, producing and circulating cerebrospinal fluid. Tissue Membranes: also called as membrane Mucous Membrane: composites of connective and epithelial tissues e.g. body cavities that open to the outside Serous Membrane: found in cavities that do not open to the outside, named according to location e.g. pericardium Cutaneous Membrane: stratified squamous epithelial membrane resting on top of connective tissue, IT IS FULL OF KERATIN Synovial Membrane: connective tissue found in joints Tissue Repair and Regeneration Tissue repair and regeneration are vital processes that restore tissue integrity and function after injury. This section covers the mechanisms involved in healing, the types of repair, and the factors that influence the outcome. 1. Overview of Tissue Repair Definition: Tissue repair refers to the process of restoring tissue structure and function after damage. It involves two primary mechanisms: regeneration and fibrosis (scar formation). 2. Stages of Tissue Repair Tissue repair typically occurs in three overlapping stages: 1. Inflammation: o Initiation: The body's immediate response to injury, which helps to prevent further damage and sets the stage for healing. o Key Events: ▪ Vascular Changes: Blood vessels dilate, increasing blood flow to the injured area. ▪ Chemical Mediators: Release of histamine, prostaglandins, and cytokines, which attract immune cells to the site of injury. ▪ Phagocytosis: White blood cells, particularly neutrophils and macrophages, engulf and remove dead cells, pathogens, and debris. o Signs of Inflammation: Redness, heat, swelling, pain, and loss of function. 2. Organization (Granulation Tissue Formation): o Definition: The process where the initial framework for healing is established. o Granulation Tissue: ▪ Formation: New capillaries grow into the wound area, providing necessary nutrients and oxygen.  ▪ Fibroblasts: These cells migrate into the area, producing collagen fibers that help to stabilize the wound. ▪ Appearance: Granulation tissue is pink and soft, often described as having a granular texture due to the presence of capillaries. o Purpose: This tissue acts as a scaffold for the subsequent regeneration of the epithelium or the formation of scar tissue. 3. Regeneration and Fibrosis: o Regeneration: ▪ Definition: The replacement of damaged tissue with the same type of cells, restoring normal structure and function. ▪ Conditions: Regeneration occurs when the cells involved are capable of proliferation and the basement membrane remains intact. ▪ Examples: Skin, liver, and epithelial cells have a high capacity for regeneration. o Fibrosis (Scar Formation): ▪ Definition: The replacement of damaged tissue with fibrous connective tissue (scar tissue), which does not restore normal function but provides structural stability. ▪ When It Occurs: Fibrosis is common when the damage is severe, the basement membrane is disrupted, or the tissue involved has limited regenerative capacity. ▪ Outcome: Scar tissue is composed of dense collagen fibers and may lead to reduced elasticity and function of the affected area. 3. Factors Affecting Tissue Repair Several factors influence the efficiency and outcome of tissue repair: Nutritional Status: o Protein Intake: Essential for the synthesis of collagen and other proteins involved in repair. o Vitamins:  ▪ Vitamin C: Necessary for collagen synthesis. ▪ Vitamin A: Supports epithelial cell proliferation. ▪ Zinc: Plays a role in DNA synthesis and cell division. Blood Supply: o Oxygen Delivery: Adequate blood flow is critical for delivering oxygen and nutrients to the healing tissue. o Angiogenesis: The formation of new blood vessels within the granulation tissue ensures a continued supply of nutrients. Infection: o Delays Healing: Infection can prolong the inflammatory phase and damage newly formed tissue. o Management: Appropriate wound care and antibiotics are necessary to prevent or treat infections. Age: o Younger Individuals: Generally have a faster and more efficient healing process due to higher cell proliferation rates. o Older Adults: May experience slower healing due to reduced cellular function and circulation. Chronic Conditions: o Diabetes: Can impair wound healing due to poor circulation and immune function. o Immunosuppression: Conditions or treatments that weaken the immune system can delay the healing process. Wound Type and Severity: o Clean Wounds: Typically heal faster with less scarring. o Complicated Wounds: Larger or deeper wounds, or those with foreign bodies, take longer to heal and may result in more significant scarring. 4. Clinical Considerations in Tissue Repair  Keloids: o Definition: An overgrowth of scar tissue that extends beyond the original wound boundary, often raised and thick. o Treatment: May include corticosteroid injections, laser therapy, or surgical removal, although recurrence is common. Contractures: o Definition: Permanent tightening of the skin, muscles, tendons, or ligaments, often occurring after severe burns. o Impact: Can restrict movement and function in the affected area. o Management: Physical therapy, surgery, and the use of pressure garments can help reduce contractures. Chronic Wounds: o Definition: Wounds that fail to progress through the normal stages of healing, often remaining in the inflammatory phase. o Examples: Diabetic ulcers, pressure sores. o Treatment: May include advanced wound care techniques, such as negative pressure wound therapy, growth factor application, and hyperbaric oxygen therapy. Tissue Engineering and Regenerative Medicine: o Advances: The field is exploring ways to enhance tissue repair, including the use of stem cells, biomaterials, and bioengineered tissues. o Potential: These approaches aim to regenerate damaged tissues with minimal scarring and restore normal function.