Animal Tissues Overview

Animal Tissues

• Animal tissues are groups of cells with similar structures and functions.
• Four primary tissue types in animals are: epithelial, connective, muscle, and nervous.

Epithelial Tissues

• Epithelial tissues cover body surfaces, line body cavities, and form glands.
• Characteristics include tightly packed cells, a free surface, and a basement membrane.
• Types: simple squamous, simple cuboidal, simple columnar, pseudostratified columnar, stratified squamous, stratified cuboidal, and transitional epithelium

Connective Tissues

• Connective tissues support, connect, and separate different types of tissues and organs.
• Characteristics include specialized cells embedded within an extracellular matrix.
• Types: loose connective, dense connective, adipose, cartilage, and bone.

Muscle Tissues

• Muscle tissues contract to produce movement.
• Types: skeletal, smooth, and cardiac.

Nervous Tissue

• Nervous tissue transmits nerve impulses throughout the body.
• Components include neurons and neuroglia.

Simple Squamous Epithelium

• Location: air sacs of lungs, lining of heart, blood vessels, lymphatic vessels
• Function: allows materials to pass through by diffusion and filtration; secretes lubricating substance

Simple Cuboidal Epithelium

• Location: ducts and secretory portions of small glands, in kidney tubules
• Function: secretes and absorbs

Simple Columnar Epithelium

• Location: uterine tubes, and uterus; digestive tract, bladder (ciliated and nonciliated)
• Function: absorbs; secretes mucus and enzymes

Pseudostratified Columnar Epithelium

• Location: trachea and much of the upper respiratory tract
• Function: secretes mucus; ciliated tissue moves mucus

Stratified Squamous Epithelium

• Location: esophagus, mouth, and vagina
• Function: protects against abrasion

Stratified Cuboidal Epithelium

• Location: sweat glands, salivary glands, mammary glands.
• Function: protective tissue

Stratified Columnar Epithelium

• Location: male urethra and ducts of some glands.
• Function: secretes and protects

Transitional Epithelium

• Location: bladder, urethra, and ureters
• Function: allows urinary organs to expand and stretch

Skeletal Muscle

• Features: striated, tubular, multi-nucleated, voluntary, attached to skeleton
• Location: attached to skeleton
• Histology: detailed image of skeletal muscle fibers presented

Smooth Muscle

• Features: non-striated, spindle-shaped, uninucleated, involuntary, covering walls of internal organs
• Location: covering walls of internal organs
• Histology: detailed image of smooth muscle fibers presented

Cardiac Muscle

• Features: striated, branched, uninucleated, involuntary, covering walls of the heart
• Location: covering walls of the heart
• Histology: detailed image of cardiac muscle fibers presented

Bone Tissue

• Dynamic and elastic
• Organic and inorganic components
• Organic components: cells and extracellular matrix (amorphous substance, type I collagen)
• Inorganic components: minerals (calcium, magnesium phosphates, Na, Mn, K citrates)
• Organic component: 35% dry weight; provides strength and elasticity
• Inorganic component: 65% dry weight; provides consistency and hardness
• Structure and function change due to age, diet, and individual conditions

Cells of Bone Tissue

• Osteoprogenitor cells: responsible for development of new bone tissue
• Osteoblasts: precursors for osteocytes; produce organic matrix (osteoid) and inorganic matrix, produce collagen, osteocalcin, osteopontin and bone sialoprotein.
• Osteocytes: trapped osteoblasts; maintain extracellular matrix of bone
• Osteoclasts: not from osteoblasts; destroy and remodel bone tissue, have multiple nuclei.
• Role of Osteoclasts: erosion of bone matrix forming resorption bays
• Microenvironment: acidified through enzymes (lysosomal and non-lysosomal), proteases, phosphatase, and metalloproteinase

Loose Connective Tissue

• Characterized by numerous different cells and a scarcely dense amorphous substance lacking in fibers.

Reticular Connective Tissue

• Packed with reticular fibers (type III collagen)
• Isolate muscle fibers, nerve fibers, surround adipocytes
• Forms connective stroma of lymphatic organs and large glands (both exocrine and endocrine)
• Reticular fibers appear first during embryonic connective tissue transformation, then replaced by collagen fibers

Elastic Connective Tissue

• Composed of non-birefringent fibers (different from collagen fibers)
• Formed by elastin, amorphous substance, and fibrillin
• Organized in parallel or scattered fibers
• Found in ligaments, tendons, epiglottis, external ear, urinary bladder
• Contains elastin and forms elastic membranes

Dense Connective Tissue

• Marked by multiple type I collagen fibers in bundles
• Can be parallel, crossed, or interwoven
• Fewer cells compared to loose connective tissue
• Dense and loose connective tissues do not have precise borders

Adipose Tissue

• Composed of adipocytes
• Two types: white (unilocular) and brown (multilocular)
• White adipocytes: single large lipid droplet, nucleus eccentric. Function: energy storage, insulation, cushioning, protection.
• Brown adipocytes: multiple lipid droplets, nucleus central. Function: energy production (especially heat), more abundant in newborns.

Cartilage

• Specialized connective tissue formed by chondroblasts and chondrocytes
• Surrounded by a jelly-like extracellular matrix with fibers
• Lacks blood vessels; nourishment through matrix permeability
• Surrounded by perichondrium (except in joints)
• Chondroblasts in lacunae; create isogenous groups
• Types: hyaline, fibrocartilage, elastic cartilage based on matrix characteristics

Hyaline Cartilage

• Most common cartilage in mammals
• Chondrocytes in lacunae/depressions
• Isogenous groups (clusters) in mature cartilage, more numerous in deeper zones
• Avascular, generally surrounded by perichondrium
• Matrix lacks fibers, contains proteoglycans (higher in territorial matrix)

Elastic Cartilage

• Low extracellular substance, lacking amorphous component
• Abundant elastic fibers, interconnected network surrounding chondrocytes
• Lacks isogenous groups
• Avascular, surrounded by perichondrium

Blood

• Red fluid circulating in closed system of channels (blood vessels)
• Derived from mesenchyma, corpuscular part (RBC, WBC, platelets), and liquid part (plasma)
• Function: transport oxygen, hormones.

Erythrocytes (RBC)

• Small, rich in hemoglobin (responsible for red color)
• Bind oxygen in lungs, transport to tissues
• Lose nucleus during maturation
• Biconcave shape for increased surface area

Platelets

• Created in bone marrow from megakaryocytes
• Small, round/elongated, anucleate
• Important role in blood clotting

Leukocytes (WBC)

• Nuclei visible, can be granular or agranular
• Various types based on appearance and function in immune system

Granular Leukocytes (e.g., neutrophils, eosinophils, basophils)

• Distinguishable by granules, differ in staining
• Play roles in immune responses, allergy reactions, etc.

Agranular Leukocytes (e.g., lymphocytes, monocytes)

• Lack granules, differentiate based on size, shape
• Lymphocytes: part of immune system (B cells, T cells)
• Monocytes: differentiate into macrophages in tissues

Nervous Tissue

• Neurons: Transmit nerve impulses; consist of cell body (soma), dendrites (receive impulses), axons (transmit impulses)
• Neuroglia: supporting cells; maintain proliferative capacity in contrast to neurons

Neuroglial Cells

• Oligodendrocytes/Schwann cells: form myelin sheaths surrounding axons in CNS/PNS respectively. Multiple layers for complete myelin sheath.
• Astrocytes: star-shaped, physical support for neurons, create blood-brain barrier
• Microglia: phagocytic cells, immune protection of CNS
• Ependymal cells: line brain ventricles, central canal, choroid plexuses; aid in cerebrospinal fluid production
• Ganglia: clusters of neuron cell bodies in peripheral nervous system (sensory or autonomic)