Animal Tissue Types: Epithelial, Connective, and More

Structural Organization in Animals

• A tissue is a group of similar cells with a common structure, function, and origin.
• Coelenterates are the first animals to possess tissues.
• Cells within a tissue may vary in structure and function but share a similar origin.
• Histology is the study of tissues.
• The term "histology" was coined by Mayer, and the concept of tissue was introduced by Bichat.
• Animal tissues are classified into four types based on structure and function, as described by Bichat.

Types of Animal Tissues

• Epithelial Tissues: Originate from all three germ layers (endodermal, mesodermal & ectodermal), form coverings and linings, and are protective.
• Connective Tissue: Originates from the mesoderm, connects and supports body organs and transports them..
• Muscular Tissue: Originates from the mesoderm and aids in locomotion and movement.
• Neural Tissue: Originates from the ectoderm and is responsible for generating and conducting nerve impulses.

Epithelial Tissue

• Origin may be ectodermal (epidermis [skin]), mesodermal (mesothelium [outer/inner linings]), or endodermal (lining of gut).
• Epithelial tissue develops during embryonic development.
• It exhibits regeneration and is typically found growing on connective tissues.
• Epithelial tissue faces either body fluid or the external environment, forming a covering or lining.
• Epithelial tissue cells are compactly arranged with minimal matrix.
• There is no intercellular space between epithelial cells, making it avascular.
• Epithelial cells rest on the basement membrane, which is highly permeable and has a free (apical) surface.
• Epithelial cells secrete the basal lamina and connective tissue secretes the fibrous lamina to form a basement membrane
• The connective tissue supplies nutrients to the epithelial tissue across this membrane.
• The basement membrane helps in adhesion and support of epithelial cells and also acts as a selective filter.

Classification of Epithelial Tissue

• Simple Epithelium: Consists of a single layer of cells.
• Compound Epithelium: Consists of multiple layers of cells.
• Simple Squamous: Single layer, flat cells, forming diffusion boundaries and filtration.
• Can be called pavement or tesselated membrane
• Found in alveoli of lungs (pneumocyte cells), Bowman's capsule of kidney (podocytes), mesothelium lining the coelom (peritoneum), pericardium (heart wall), pleura (lungs), and endothelium lining blood and lymph vessels, and the thin segment of the loop of Henle in the nephron.
• Simple Cuboidal: Cube-like cells resting on a basement membrane with centrally placed nuclei, secretion/ absorption/excretion.
• Some modifications include Brush Bordered Cuboidal Epithelium and Ciliated Cuboidal Epithelium
• Germinal Epithelium-(gonads; testes/ovaries); Thick segment of Loop of Henle
• Collecting ducts DCT (distal), Ducts of glands (salivary/pancreatic)

Modification of Cuboidal Epithelium

• Brush Bordered: Protoplasmic extensions (microvilli) on the free surface increase surface area for absorption; e.g., PCT (Proximal Convoluted Tubule) where 80% of absorption occurs.
• Ciliated Cuboidal Epithelium: Possesses motile cilia (kinocilia).
• Simple Columnar Epithelium: Single layer of tall, pillar-like cells with elongated nuclei at the base, aiding absorption and secretion in stomach/intestine/gallbladder linings.

Modifications of Columnar Epithelium

• Brush Bordered epithelum has microvilli and is found in samll intestine for max absorption
• Ciliated epitheleium contains cilia
• Location of ciliated version = respiratory bronchioles

Glandular Epithelium

• Columnar or cuboidal cells specialized for secretion
• Produce and release secretary products
• Unicellular Glands possess a single-celled chamber: goblet cells in the alimentary canal lining.
• Multicellular Glands are cell clusters e.g. salivary glands
• Endocrine Glands are ductless and secrete hormones directly into body fluids (e.g., pituitary/thyroid/adrenal glands).
• Exocrine Glands possess ducts and secrete products like ear wax/oils/milk/saliva/digestive enzymes (e.g., mammary/digestive glands, ceruminous (earwax) glands and goblet cells).
• Heterocrine Glands (Mixed): both exocrine and endocrine, like the pancreas, testes, and ovaries.

Compound Epithelium

• Multi-layered, limited role in secretion and absorption to act as protection
• Non-Stretchable epithelia = stratified. Epithelia stretchable = transitional [urothelium in ureters/bladder and proximal urethra].

Stratified Epithelium Types

• Stratified Squamous version can be keratinized/ non-keratinized (moist)
• Stratified Cuboidal version has larger duct glands
• Ciliated version is columnar conjunctions
• Cuboidal is found in cavities

Cellular Junctions

• Structural and functional links between individual tissue cells, prevalent in epithelial tissue.
• Tight Junctions (Zona occludens): Formed by plasma membrane fusion, preventing substance leakage across tissue.
• Adhering Junctions (Desmosomes): facilitate holding of cells together
• Gap Junctions: aid cell communication and chemical exchange between cells

Connective Tissue

• Most abundant and widely distributed in complex animals, linking and supporting other tissues and organs are.
• Mesodermally originated
• Intercellular matrix is abundant.
• Made of fibroblast cells that make the matrix protein, plasma and immune cells

Cell and Fiber Description

• Fibroblast: Cells that form fibers that are the matrix
• Macrophage: Type of WBC, large cell derived from monocyte, phagocytosis
• Plasma cll = cell similar to "B" lymphocytes, produces antibodies
• Mast Cell: Similar to Basophils, makes Heparin (anticoagulant), Serotonin (neutransmitter), Histamin (vasodilator, for allergic reactions] -Collagen are the main fibre in a cell and allow flexability -Elastin fibres allow elasticity -Reticular fibres allow elasticity
• Mesenchymal Cell: Secreates protein and builds matrixes
• Mucoplysaccharides make up the around substance and have hyaluronic acid as a modifider
• Desnity depeds of matrix and fibre present

Connective Tissue Types

• Loose Connective Tissue: More matrix, fewer fibers.
• Areolar Connective Tissue provides support to epithelium, present beneath the skin.
• Adipose Connective Tissue has adipocytes and Blubber to mantain body's insulation.
• Dense Connective Tissue has less matrix, more fibres.
• fibres in regular rows and is found in tendons/ligaments; can be skin/connects bone
• Specialized CT = Skeletal, Fluid
• The skeletons cells hold solid matrix
• Fluid version has blood and other lymphatic vessels

Cartilage

• Solid and pliable, resisting compression from matrix containing chondrin (proteinaceous compound).

• Avascular Cells called Chondrocytes is the matrix material, mainting the call as the cells ate chondroblast & chondroclast.

• Elastin Fiber & collagen fibres can connect cells

• Lacunae aids with the maintanace material

• Perichondrium = outer membranes

• Hyaline Cartilage

• Elastin Cartilage

• Fibrous Cartilage

Bone

• Osteon = bone system
• Head, Epiphysis (end), Shaft/Diopysis
• Volkmann (horizontal) and Haversian are horizontal canals
• Osteicytes = where bone cells are store
• Periosteum= endo and outer most layer of system
• Matrix has organic components (protein: ossin) & inorganic components.
  • inorganic components- Calcium compounds contribute towards hardness (Calcium carbonate (10%), Calcium phosphate (85%), Calcium hydroxide (5%)
• Only collagen fibers are present.
• 3 Cells are present in 3 matrix versions to create an osteoblast/cyte/clast.
• Matrix, Fibres (only collagen), specialized cells called chondrocytes.

Fluid Connective Tissue - Blood

• A fluid connective tissue consisting of a matrix that flows and suspended cells.
• 55% of the blood contains plasma (aqueous suspension of cell) and 45% is cell
• Plasma is light yellow/ pale yellow in nature, is mostly h2o & proteins and is formed of other material ie glucose lipid, amino, serum proteins of albumin.
• Other chemicals in the cell for regular and balance like clotting proteins, fibronigen

Formed Elements [45%]

• Contain all the "cyto" cells.
• RBCs or Erythrocytes = Enucliared membrane used to carry oxygen cells
• WBCs or Lucocytes creates a immune membrane or system made of granulocytes and agranulocytes
• Granulocytes are white blood cells for clotting of the blood
• Platelelts are a granulocyte as well
• Lymph = fluid used in system
• Lymph is what makes of a person's immune system by being filtered and re-collect back into the viens.

Muscular Tissue

• Of mesodermal origin. Exhibits:
• Excitability = respond to stimulus
• Contractility = contract and relax
• Extensibility = stretch
• Muscle tissues consist of myofibrils which are the contractile protein.
• Structural & functional unit is the "Sarcomere"

Muscle Tissues Types

• Skeletal Muscle is Striated in appearance, cylindrical/ unbranched/ multinucleated, and voluntary:
• has Sarcolemma and Sarcoplum as cells
• Smooth Muscles are Visceral, Unstriped, involuntary
• Only located visceral organs
• Cardiac Muscle is striated, cylindrical, branched, uninucleated, with intercalated discs to form junctions, involuntary
• Both Smooth and Cardiac versions are tapered

Nervous Tissue

• Derives from the ectoderm and is made of nervous systems
• Contains Neuron, axon, and other dendrilas is the basic form
• Has a Cell is Single and long
• Has Nissuls granula & Sheaths made to proteins
• Contains unipolar/bipolar versions when un-matured
• Multipolar cell is the version in Cerebral Cortex
• Neuron has motor and Sensory and some mix neurons.

2 Types present in nervous tissue

• Neuron (above)

• Neuroglia which compativly store more in the nervous tissue

• Supportive form with astrocyte cells that provider nuturment

• Oligodendroglia Cells are secreater cells that secret schwann cells

• Micogrea cells are phagocytic and againsy outside cells

• Secretoy cells release and Epyndenal are ciliated calls.

• Tissues grouped together for form organ systems, all which share complex traits of functions.