Tissues: Types and Organization

Levels of Organization

• Tissues consist of cell groups working together in the body.
• Histology studies the appearance, function, and organization of tissues microscopically.
• Pathology studies changes occurring with disease.

Tissues Overview

• A tissue comprises cells performing a specific function.
• Histology examines tissue structure, organization and function.
• There are four primary tissue types in the human body.
• Pathology examines changes with tissue disease.

Tissue Types

• The body contains four types of tissue:
  • Epithelial: forms coverings, linings, and glands.
  • Connective: provides protection and support.
  • Muscle: provides movement.
  • Nervous: enables communication.

Tissue Features

• Extracellular matrix (ECM) exists outside of tissues.
• ECM's main components are collagen and proteoglycans.
• Collagen offers tough, protective protein fibers.
• Proteoglycans consist of negatively charged protein/carbohydrate molecules.
• Cellular connections attach cells to each other.
• Tight junctions prevent substance movement between cells.
• Desmosomes provide flexible connections allowing some movement.
• Gap junctions provide passageways that allow certain substance movement.

Cellular Connections

• Cells connect via tight junctions, desmosomes, and gap junctions:
  • Tight junctions fuse adjacent cell membranes.
  • Desmosomes provide strong, flexible connections between cells.
  • Hemidesmosomes connect cells to the ECM.
  • Gap junctions allow intercellular passageways.

Cellular Connection Locations

• Tight junctions exist in bladder and digestive tract epithelial tissues.
• Desmosomes and gap junctions can be found in cardiac muscle fibers.

Preparing Tissue for Examination

• Meticulous preparation of tissues is essential for examination.
• The appearance of a tissue is influenced by multiple factors like:
  • Plane of section.
  • Stain used.

Tissue Examination Prep

• A special blade cuts tissues.
• Tissues are cut into thin slices.
• The thin tissue slices are placed on slides.
• Tissues are stained before examination.
• Stains cause different colors and appearances.

Epithelial Tissue

• Epithelial tissues form coverings, linings, and glands.
• A basement membrane anchors epithelia to the ECM.
• Epithelia have two surfaces:
  • Basal surface: attached to the basement membrane.
  • Apical surface: exposed to the external environment or internal space.
• Epithelial tissues are avascular.
• Epithelial tissues are highly regenerative.

Epithelial Anatomy

• Epithelia are highly cellular and bound to a basement membrane.
• Epithelia are innervated and avascular.
• They are polar, featuring apical and basal surfaces.

Epithelial Cell Specializations

• Apical and basal membranes may have distinct tasks.
• Modifications to the apical surface include:
  • Cilia: move materials across the surface.
  • Microvilli: increase surface area.

Epithelia Cell Shapes and Layering

• Naming of epithelial tissue depends on cell shape and layering.
• Cell shape:
  • Squamous: flat.
  • Cuboidal: box-shaped.
  • Columnar: column-like.
• Number of Layers:
  • Simple: one layer.
  • Stratified: multiple layers.
  • Pseudostratified: appears multi-layered but is a single layer.

Unusual Epithelial

• Pseudostratified columnar epithelium may appear stratified.
• All cells touch the basement membrane, forming only a single layer.
• Transitional epithelium is stratified and its cells stretch/change shape.

Goblet Cells

• Goblet cells are common in simple, pseudostratified epithelia.
• They secrete mucus.

Stratified Epithelia

• Stratified epithelia contain more than one layer of cells.
• Basal layer cells are stem cells regenerating into apical layer cells.
• Basal and apical layer cells may differ in shape.
• Tissue naming depends on the shape of the cells in the apical layer.

Simple Squamous Epithelium

• Consists of a single layer of flat cells.
• Simple squamous epithelium is present in the air sacs of lungs, lining of heart, blood vessels, and lymphatic vessels.
• It facilitates material passage through diffusion and filtration.
• Additionally, it secretes lubricating substances.

Epithelial Types

• Simple cuboidal epithelium:
  • Kidney tubules are lined with it.
  • It secretes and absorbs substances such as Na+, K+, and glucose.
• Simple columnar epithelium:
  • Digestive and reproductive tracts are lined with it.
  • It secretes and absorbs various materials.
• Pseudostratified columnar epithelium:
  • Trachea and respiratory tract are lined with it.
  • it secretes and moves mucus.

Epithelial Types Continued

• Stratified squamous epithelium:
  • It lines the esophagus, mouth and vagina.
  • Protects against abrasion.
• Stratified cuboidal epithelium:
  • Found in sweat, salivary and mammary glands.
  • It secretes and protects.
• Stratified columnar epithelium:
  • It secretes and protects the male urethra and some gland ducts.

Transitional Epithelium

• Urinary organs like the bladder, urethra and ureters are lined with it.
• It enables these organs to expand/stretch.

Epithelial Glands

• Endocrine glands secrete hormones into the blood.
  • Examples include the thymus, pituitary, and adrenal glands.
  • They are ductless.
• Exocrine glands secrete substances locally through a duct.
  • Examples include sweat and digestive glands.
  • They secrete mucus, sweat, saliva, and breastmilk.

Exocrine Gland Structure

• Exocrine glands can be unicellular or multicellular:
  • Unicellular: single cells.
  • Multicellular: single layer of folding cells.
• Tubular glands form tubes.
• Acinar glands form pockets.
• Simple glands have one duct.
• Compound glands have multiple duct formats.

Exocrine Secretion

• Merocrine secretion is accomplished by exocytosis.
• Apocrine secretion's material accumulates near the gland's apical surface.
• Holocrine secretion destroys the entire gland cell, rupturing it.
• Serous glands produce watery secretions.
• Mucous glands produce watery to thick secretions.

Matching Activity Answers

• Squamous - Flat cells (B)
• Cuboidal - Cells shaped like a box (D)
• Simple - A tissue with one layer of cells (A)
• Transitional - Epithelia in the bladder (C)

Epithelial Tissue Example

• Twelve layers of tissue with box-shaped cells on the bottom, flat cells on top.
• This is stratified squamous epithelium.
• Multiple layers make it stratified, flat apical cells make it squamous.

Connective Tissue Overview

• Connective tissue has cells and an extracellular matrix (ECM).
• Cells rarely touch.
• The ECM contains ground substance and fibers.
• Ground substance separates fibers.
• Connective tissues are vascularized.

Connective Tissue Classification

• Connective tissues divide into three classes:
  • Connective tissue proper: areolar, adipose, reticular, dense regular, and dense irregular.
  • Supportive connective tissue: hyaline cartilage, fibrocartilage, elastic cartilage, compact and spongy bone.
  • Fluid connective tissue: blood and lymph.

Types of Connective Tissue

• Fibroblasts generate ECM fibers:
  • Collagen fibers are the strongest.
  • Elastic fibers provide elasticity.
  • Reticular fibers branch and support internal organs.
• Adipocytes store energy and provide cushioning.
• White blood cells provide immune function.
• Red blood cells carry gases.

Connective Tissue (1 of 2)

• Loose connective tissue (connective tissue proper)
  • Includes areolar and reticular tissues.
• Supportive connective tissue:
  • Includes hyaline cartilage, fibrocartilage and elastic cartilage.
• Fluid connective tissue is blood.

Connective Tissue (2 of 2)

• Connective tissue proper:
  • Dense regular and irregular tissues.
  • Adipose tissue.
• Supportive connective tissue is bone.
• Fluid connective tissue is lymph.

Connective Tissue Types

• Areolar connective tissue:
  • Subcutaneous layer.
  • Supports nearby tissues.
• Adipose tissue:
  • Subcutaneous layer.
  • It provides energy storage and cushioning.

Areolar Connective Tissue Location

• Areolar connective tissue is located under most epithelial layers.

Reticular Connective Tissue

• Reticular connective tissue provides a framework for internal organs.
• It is located in lymphatic tissues, spleen, and liver.

Dense Connective Tissues

• Dense regular connective tissue:
  • Forms tendons and ligaments.
• Dense irregular connective tissue:
  • Makes up the skin.

Dense Connective Tissue Features

• Dense irregular connective tissue is high in collagen fibers.
• Its fibers orient in every direction.
• It allows tissue to withstand force in any plane.
• Found in the dermis of the skin.

Collagen Fibers

• Dense regular connective tissue has a high number of collagen fibers.
• Its fibers are oriented parallel to each other.
• It allows tissue to withstand force in the fiber direction.
• It is found in ligaments and tendons.

Specific Cartilage Types

• Hyaline cartilage.
  • Located within joints, ribs.
  • It is the most abundant kind.
• Fibrocartilage.
  • Located in intervertebral discs.
  • It is the strongest kind.
• Elastic cartilage.
  • Located in external ear.
  • It is the most flexible kind.

Ribcage Mergence

• The ribcage mergers two supportive connective tissue forms.
• Bone makes up most of the ribcage
• Protection for lungs and heart.
• Cartilage allows the ribcage to expand when breathing.

Perichondrium

• Dense irregular connective tissue makes up the perichondrium.
• The perichondrium encapsulates cartilage within the body.

Damaged Cartilage

• Characteristic of cartilage results in improper healing after damage.
• Cartilage is avascular except for the perichondrium.
• Cartilage healing is slow or not at all with inadequate blood supply .

Bone Structure

• Bones are the most rigid connective tissue.
• Bones provide protection and support for internal organs.
• Compact bone is solid, with greater strength than spongy bone.
• Spongy bone's empty spaces have red bone marrow.

Fluid Connective Tissues

• Blood and lymph are fluid connective tissues.
• They transport cells and molecules.
• Blood contains erythrocytes, leukocytes, and platelets.
• Lymph is primarily acellular.

Lymph and Blood

• Lymph is fluid connective tissue.
• Lymph is mainly acellular.

Characteristics of Muscle Tissure

• Muscle tissue facilitates movement.
• It contracts upon stimuli and differs in location and control.
• Voluntary muscle are conscious with skeletal control.
• Involuntary muscle is unconscious with cardiac and smooth muscle.

Skeletal Muscle Function

• Skeletal muscles attach to bones.
• Skeletal muscles facilitates posture, movement and maintain posture.
• Striations are alternating light and dark band seen under a light microscope.
• Skeletal muscle is voluntarily controlled.
• Cells are multinucleated.

Cardiac Muscle

• Cardiac muscle resides in the heart walls
• it has striations, and is involuntarily controlled.
• Cells attach by intercalated discs.

Smooth Muscle

• Smooth muscle exsists within the internal organs.
• Associated with the digestive, respiratory, urinary, and reproductive systems.
• Lacks striations along with involuntary movement.

Muscle Tissue Capabilities In Infants

• Nervous system can control muscles regulating urination and defecation.

Muscle Tissure Functions

• Thermoregulation occurs via shivering.
• Shivering produces heat that increases body temperature.
• Muscles also aid in protection of internal organs.
• Muscles help with compression during blood circulation.

Overview of Nervous Tissue.

• Nervous tissue constitute peripheral and brain tissue
• Neurons communicate by conducting action potentials.
• Glial cells assist neuronal function.

Neurons and Action Potentials

• Neurons generate action potentials.
• Neuron anatomy includes dendrites, cell body, and axon.
• Dendrites are short, receiving branches.
• The cell body has the nucleus and organelles.
• The axon is a long projection sending action potentials.
• The synapse is the gap between a neuron, its target cell.

Types of Glial Cells

• Glial cells are various and associate with nerve tissue.
• They typically support functions as the production of myelin.
• Myelin enables rapid transmission and insulation functions as well.

Serous Membrane Function Correct

• Serous membranes function to reduce the friction inside the organs.

Tissue Membranes

• Mucous membranes exist in cavities exposed to the outside.
• Serous membranes line/surround organs inside body cavities.
• The cutaneous membrane covers the body.
• Synovial membranes line joints.

Mucous and Serous Membranes

• Mucous membranes lines body cavities exposed to outside environment.
  • Typically has goblet cells to secrete mucus.
  • Includes the digestive, urinary, respiratory, and reproductive tracts.
• Serous membranes cover/line internal organs.
  • Reduces friction.
  • Examples include: pericardium, pleura, and peritoneum.

Synovial, and Cuntaneous Membranes

• Cutaneous (skin) membrane is made of stratified squamous epithelium plus connected tissue.
  • Desiccation and pathogens are not common through membrane with the keratin barrier.
• Synovial membranes exsists in freely movable elbows, knees and hip joints.
  • Synovial cells make synovial fluids.
  • They nourish the cartilage at the joints.
  • Decreasing friction in joints that can move .

Healing, Aging & Tumors

• The body's initial response to damage is inflammation.
  • The damage starts repair and limits extended injury.
  • Acute inflammation happens quick.
  • Chronic inflammation can exsist long terms.
• Tissue aging changes
  • The rates of Mitosis become slower leading into tissue becoming damaged.
  • Loss of elastic fibers causes wrinkles and elastic structures.
• The scar tissue can make wound.
  • Damaged, rapid repair of tissues that include collagen fibers.
• Mutated cell tumors
  • Cancers create tumors and signals of cancer.
• The increase of density can increase the chances of increased cancer risk.