Tissues and Organs

Tissues and Organs

• Tissues are groups of cells and intercellular substances working together in the body.
• Cells within a tissue share a common embryonic origin and morphological features, arranged in an orderly pattern.
• Tissues appear in more complex organisms.
• Tissues are organized into four broad categories: Epithelial, Connective, Muscle, and Nervous.
• Each tissue type has specific functions.
• Disruption of a tissue's structure can indicate injury or disease, diagnosable through histological analysis.

Tissue Types

• Epithelial: Cover exterior surfaces, line internal cavities/passageways, and form glands.
• Connective: Binds cells and organs, integrates/supports all body parts and provides protection.
• Muscle: Excitable, contracts for movement with skeletal (voluntary), smooth, and cardiac types.
• Nervous: Excitable, propagates electrochemical signals as nerve impulses.

Primary Tissues

• Vertebrate embryos are arranged with cells in layers, forming three primary germ layers.
• Those layers are: Ectoderm, Mesoderm, and Endoderm.
• These germ layers give rise to adult tissues.

Epithelial Tissue Characteristics

• Epithelial tissue consists of large sheets of cells covering body surfaces exposed to the outside world and lining the outside of the organs.
• It forms much of the glandular tissue.
• Endothelium is an epithelial type that lines hollow organs, blood vessels, and body cavities.
• Epithelial tissue is highly cellular with minimal extracellular space/material.
• Cells have apical (facing outside environment) and basal (facing body fluid) surfaces.
• It is nearly avascular and has a capability of rapid replacement.
• Epithelial tissue lines body surfaces, cavities, ducts, and tubes.
• One free surface faces a body fluid, while the other faces the environment.
• Cells are anchored to a basement membrane and assist with nutrition/waste exchange.

Epithelial Types

• Classification is based on cell arrangement (simple/single layer, stratified/many layers) and cell shape (squamous/flat, cuboidal/square, columnar/rectangular).
• Simple epithelium consists of a single layer of cells of any shape, lining body ducts, cavities, and tubes; function depends on cell shape.
• Stratified epithelium is made of multiple cell layers of varying shapes, at least two layers thick, functions in protection, and usually lines external body surfaces.

Glands

• These are secretory organs derived from epithelium.
• Exocrine glands have ducts or tubes, while endocrine glands are ductless.
• Sweat (water) and sebaceous (oil) glands are examples.

Connective Tissue

• Is the most abundant tissue in the body.
• Cells are scattered in an extracellular matrix that is its chief feature.
• The matrix is collagen/elastin fibers with polysaccharide ground substance.
• Connective tissue performs functions like transport, storage, cushioning, and protection.
• Components include cells, amorphous ground, and protein fibers.
• Categories include connective tissue proper (loose & dense), supportive connective tissue, and fluid connective tissue.
• Connective tissues proper vary in fiber arrangement.
• Supportive provide structure and strength.
• Fluid have specialized cells circulating in a watery fluid.

Blood

• Classified as a connective tissue, with blood cells arising in bone.
• Bone itself is connective tissue.
• "Tissue” consists of cells and "Connective" refers to the matrix.
• Serves as the body's transport medium with red cells, white cells, and platelets.
• Blood is dispersed in a fluid medium of plasma that is the connective matrix.

Bone

• Classified as connective tissue in both compact and spongy forms.
• Bone marrow gives rise to blood cells.
• Bone provides protection, support, and storage.
• It is composed of a solid medium that contains calcium phosphate matrix and organic osteoid.
• Bone has blood and nerve supply.

Muscle Tissue

• Characterized by properties that allow movement.
• Excitable in that properties respond to stimulus.
• Contractile, shortening and generating a pulling force.
• Voluntary muscle movement is under conscious control; involuntary is not.
• Muscle tissue includes skeletal (voluntary), smooth (involuntary), and cardiac (involuntary).
• It is made of arrays of contractile cells with striations, demanding ATP

Nervous Tissue

• Functions by detecting stimuli, integrating information, and relaying commands.
• Consists of excitable neurons and supporting neuroglial cells.
• The nervous system is highly metabolic, amitotic, and has extreme longevity.
• Neurons are basic units of nervous communication and the chief impulse-conducting cells.
• Neurons monitor information and issue commands, conducting it one way from dendrite to synaptic knob.
• Neuron parts include dendrites (extensions drawing impulses), cell body (control centre), axon (conducting portion), Node of Ranvier (exposed axon allowing speed), Schwann Cell (myelin-producing cell), Myelin Sheath (composed of fat for protection), and Synaptic Knobs (attaching to neurons or muscle).

Tissue Membranes

• Defined as thin cell layers or sheets that cover the outside of the body (skin), the organs (pericardium), internal passageways leading to the exterior (abdominal mesenteries), and lining moveable joint cavities.
• Two basic types: connective tissue membranes (synovial) and epithelial tissue membranes (mucous, serous, and cutaneous/skin).

Skin

• Part of the body’s integument.
• There are three layers: Epidermis, Dermis, and Hypodermis.
• The Epidermis is the outermost layer, serving as a waterproof barrier.
• The Dermis is a tough connective tissue including hair follicles, nervous tissue, and sweat/sebaceous glands.
• The Hypodermis is a deeper subcutaneous tissue with fat & connective tissue.
• The skin protects from injury, dehydration, UV radiation, and pathogens.
• It helps control temperature, receives external stimuli, and produces vitamin D.

Epidermis

• It is a stratified epithelium that grows from bottom upward.
• Keratinocytes are abundant cells, while melanocytes produce melanin pigment.

Dermis

• Dense connective tissue with many elastin and collagen fibers.
• Includes blood vessels, lymph vessels, and receptor endings of sensory nerves.

Glands

• Glands are derived from epidermal cells, controlled by sympathetic nerves.
• Sweat glands produce sweat to cool muscles.
• Oil glands secrete sebum to moisturize.

Hair

• Has its root embedded in skin, pushing cells above upward at root.
• A shaft of dead cells extends above the skin.

Organs

• These are groups of tissues performing a task and forming an organ,
• Organs form part of a larger system and are independently organised.
• E.g., The Heart-consisting of cardiac muscle, nerve supply, connective tissue, and epithelial lining.

Organ Systems

• Consists of two or more organs working together on a common task, interacting physically or chemically.
• E.g., Digestive System, the components are mouth, oesophagus, stomach, and intestines.

Major Organ Systems

• Integumentary, Muscular, Skeletal, Nervous, Endocrine, Lymphatic, Respiratory, Urinary, Circulatory, and Reproductive.

Major Body Cavities

• Cranial, Spinal, Thoracic, Abdominal, Pelvic.