Module 1: Tissue

PAS 250

Levels of Biological Organization

Molecules → Cells → Tissues → Organs → Organ Systems → Organism

Tissue

A group of similar cells working together to perform a common function

Four Primary Tissue Types

Epithelial, Connective, Muscle, Nervous

Epithelial Tissue – General

Densely packed, avascular sheets of cells with a free apical surface and attached basal surface; functions in protection, secretion, absorption, filtration, sensation

Basement Membrane

Thin extracellular layer that anchors epithelium to underlying connective tissue

Apical Surface

The free, exposed surface of an epithelial cell or tissue

Basolateral Surface

The side and bottom surfaces of an epithelial cell that contact neighbors and the basement membrane

Simple Epithelium

Single layer of cells from apical to basal surface

Stratified Epithelium

Two or more cell layers between apical and basal surfaces

Squamous Cell Shape

Thin, flattened cells

Cuboidal Cell Shape

Cube-shaped cells with centrally placed nuclei

Columnar Cell Shape

Tall, rectangular cells with oval nuclei

Simple Squamous Epithelium

One layer of flat cells; permits diffusion, filtration, absorption; lines alveoli, Bowman’s capsule, heart & vessels (endothelium), serous membranes (mesothelium)

Stratified Squamous Epithelium

Many layers of flattened cells; protects against abrasion; found in skin, mouth, esophagus, rectum, vagina

Simple Cuboidal Epithelium

Single layer of cube-like cells; secretion & absorption; located in kidney tubules, ducts of glands, ovarian surface

Stratified Cuboidal Epithelium

Two layers of cuboidal cells; rare; secretion; lines sweat gland ducts

Simple Columnar Epithelium

Single layer of tall cells, often with microvilli or goblet cells; absorption & secretion; lines digestive tract, gallbladder, uterine tubes

Stratified Columnar Epithelium

Multiple layers, apical cells columnar; secretion; large ducts of glands such as salivary glands

Pseudostratified Columnar Epithelium

Single disorganized layer appearing stratified; may have cilia & goblet cells; secretion & propulsion; lines upper respiratory tract, male urethra

Transitional Epithelium

Stratified tissue that stretches from cuboidal to squamous appearance; lines ureters, bladder, renal pelvis

Gland

One or more epithelial cells that produce secretions

Endocrine Gland

Ductless gland that releases hormones into surrounding tissue fluid and bloodstream

Exocrine Gland

Gland that releases secretions through ducts to body surface or lumen (e.g., sweat, oil, goblet cells)

Merocrine (Eccrine) Secretion

Exocytosis of vesicles from cell without loss of cytoplasm

Apocrine Secretion

Apical portion of cell breaks off releasing cytoplasmic content

Holocrine Secretion

Entire cell ruptures to release its secretions

Histology

The study of tissues using microscopic sections

Stem Cell

Multipotent precursor cell capable of differentiating into multiple cell types

Chemotaxis

Directed cell movement toward chemical signals during development or immune response

Contact Guidance

Cell migration directed by contact with extracellular matrix fibers

Adhesion (in development)

Process by which cells stick to each other or the extracellular matrix, maintaining tissue structure

Connective Tissue – General

Diverse tissue type consisting of cells surrounded by extracellular matrix; provides support, binding, storage, transport, immunity

Extracellular Matrix

Non-living material (ground substance + fibers) surrounding connective tissue cells

Ground Substance

Gel or fluid component of connective tissue matrix

Collagen Fiber

Strong, thick protein fiber providing tensile strength

Elastic Fiber

Thin, stretchy protein fiber allowing recoil

Reticular Fiber

Fine branching fiber forming supportive networks

Connective Tissue Proper – Loose

Areolar, Adipose, Reticular tissues with loosely arranged fibers

Connective Tissue Proper – Dense

Dense Regular, Dense Irregular, Elastic tissues with packed fibers

Areolar Connective Tissue

Loose CT with all fiber types; cushions organs, binds tissues, holds fluids; found under epithelia, around vessels & nerves

Adipose Tissue

Loose CT dominated by adipocytes; stores fat, insulates, cushions; located under skin, around organs, in abdomen & breasts

Reticular Connective Tissue

Loose CT with reticular fibers; forms soft skeleton (stroma) of spleen, lymph nodes, bone marrow, liver

Dense Regular Connective Tissue

Parallel collagen bundles; resists unidirectional stress; forms tendons & ligaments

Dense Irregular Connective Tissue

Random collagen bundles; resists multidirectional stress; dermis, joint capsules

Elastic Connective Tissue

Dense CT rich in elastic fibers; allows stretch & recoil; found in some ligaments, arterial walls, bronchial tubes

Supporting Connective Tissue

Cartilage and bone providing strong framework

Cartilage

Avascular supporting CT with chondrocytes in lacunae and firm matrix

Hyaline Cartilage

Most common cartilage; glassy matrix; supports, cushions; nose, trachea, costal cartilage, articular surfaces

Elastic Cartilage

Cartilage with abundant elastic fibers; flexible support; external ear, epiglottis

Fibrocartilage

Cartilage with thick collagen bundles; resists compression; intervertebral discs, pubic symphysis, menisci

Osseous Tissue (Bone)

Supportive CT with calcified matrix; osteocytes in lacunae; provides structure, protection, muscle attachment

Fluid Connective Tissue

Blood and lymph

Blood

Fluid CT with plasma matrix and formed elements (RBCs, WBCs, platelets); transports gases, nutrients, wastes; clotting

Lymph

Fluid CT in lymphatic system; returns tissue fluid to blood, immune surveillance

Myocyte

Contractile muscle cell containing actin & myosin

Skeletal Muscle

Voluntary, striated, multinucleate muscle attached to bones; long cylindrical fibers

Cardiac Muscle

Involuntary, striated muscle of the heart; branching cells with single nucleus and intercalated discs

Intercalated Disc

Specialized junction connecting cardiac muscle cells for synchronized contraction

Smooth Muscle

Involuntary, non-striated muscle with spindle-shaped cells and single central nucleus; in walls of organs & vessels

Nervous Tissue

Tissue specialized for electrical communication; found in brain, spinal cord, nerves

Neuron

Excitable cell that generates and conducts nerve impulses; consists of cell body, dendrites, axon

Neuroglia (Glial Cells)

Supportive nervous system cells that protect, insulate, and nourish neurons

Astrocyte

CNS glial cell that regulates extracellular environment and forms blood-brain barrier

Oligodendrocyte

CNS glial cell that forms myelin sheaths around axons

Ependymal Cell

CNS glial cell lining ventricles & central canal; produces cerebrospinal fluid

Microglia

CNS phagocytic glial cells providing immune defense

Schwann Cell

PNS glial cell that forms myelin around peripheral nerve fibers

Satellite Cell (PNS)

Glial cell surrounding neuron cell bodies in ganglia; regulates exchange

Organ

Structure composed of at least two tissue types performing a specific function

Organ System

Group of organs working together to accomplish common purpose

Embryonic Tissue Formation

Process where stem cells proliferate, migrate, adhere, and differentiate into specific tissues

Multipotency

Ability of a stem cell to develop into several different cell types

Asymmetric Division

Stem cell division yielding one stem cell and one differentiated daughter cell

Permeability (Epithelial Function)

Control of substance passage across epithelial barriers

Goblet Cell

Unicellular exocrine gland producing mucus within columnar epithelia