Introduction to Tissue Types

• Tissues are groups of similar cells performing a common function.
• The four tissue types are epithelial, connective, muscle, and nervous.

Epithelial Tissue

• Functions include protection, secretion, and absorption.
• It is avascular, lacking a direct blood supply.
• It is innervated, with neural receptors for pain, temperature, and pressure.

Epithelial Tissue Types

• Simple squamous epithelium is found in the lungs and lines blood vessels.
• Simple cuboidal epithelium lines kidney tubules, salivary gland ducts, the thyroid gland, and ovary surfaces.
• Simple columnar epithelium is present in the stomach, intestines, uterus, and other organs for absorption and secretion.
• Stratified squamous epithelium is in the epidermis, mouth lining, parts of the esophagus, and the vagina.
• Stratified cuboidal epithelium is located in salivary, sweat, and mammary glands.
• Stratified columnar epithelium is found in the eye, parts of the pharynx, anus, and male urethra.
• Transitional cell epithelium, found in the uterus and bladder, allows for contraction and stretching.
• Pseudostratified epithelium, ciliated, lines the trachea.

Other Epithelial Structures

• The basement membrane is a matrix that separates epithelium from connective tissue.
• Brush borders, such as those in the intestine, increase surface area with microvilli.

Glands

• These are collections of cells that secrete a product.
• Acini are secretory cells within glands.
• Endocrine glands secrete hormones directly into the bloodstream without ducts.
• Exocrine glands include simple (unbranched duct), compound (branched duct), tubular (tube-forming acini), and alveolar (sack-forming acini) types.

Gland Secretion Types

• Merocrine glands secrete products through exocytosis, such as the pancreas, salivary glands, and sweat glands.
• Holocrine glands release contents through cell disintegration, exemplified by oil glands.
• Apocrine glands release contents when a piece of the cell membrane ruptures.

Connective Tissue Characteristics

• Connective tissue supports, connects, insulates, and transports.
• Components include ground substance, fibers, cells, and adhesion proteins/cells.

Connective Tissue Components

• Ground substance is a gel of water, hyaluronic acid, and glycoproteins that holds connective tissue together.
• Fiber types include collagen, elastic, and reticular fibers.

Connective Tissue Cells

• Fibroblasts produce fiber and ground substance.
• Chondroblasts produce cartilage.
• Osteoblasts produce bone.
• Hemocytoblasts produce blood.
• Mast cells release histamine and heparin.
• Histamine is released by cells in response to injury, allergic, and inflammatory reactions.
• Heparin is an anticoagulant that prevents blood clots.
• Macrophages consume foreign debris.

Cell Adhesion Proteins

• Cell adhesion proteins attach or move things, exemplified by fibronectin.
• Fibronectin recruits cells or directs their movement based on secretions.

Connective Tissue Types

• Mesenchyme is embryonic connective tissue of the mesoderm.
• Areolar tissue provides loose packing, found in the skin and around organs, and is the most widely distributed connective tissue.
• Dense connective tissue is found in tendons, ligaments, skin, lymph nodes, spleen, and bone marrow.
• Adipose tissue is fat tissue located in the skin and around organs.
• Hyaline cartilage, also known as articular cartilage, covers bone ends and keeps the trachea open.
• Elastic cartilage is found in the external ear and epiglottis.
• Fibrocartilage is located in intervertebral discs and is a tough, strong tissue.
• Bone is the hard tissue that makes up the skeleton.
• Blood is liquid connective tissue of cells and molecules.

Muscle Tissue

• Muscle tissue is highly cellular and well-vascularized.
• It is responsible for body movements.

Muscle Tissue Types

• Skeletal muscle features light and dark banding and multiple nuclei, is under voluntary control, and functions in locomotion.
• Cardiac muscle is striated with one nucleus, branching structure, gap junctions, and is involuntary, functioning to pump blood.
• Smooth muscle has spindle-shaped cells, one nucleus, is in hollow organs, is under involuntary control, and aids in heat production.

Nervous Tissue

• These cells, with branches, transmit electrical signals and respond to stimuli.

Membranes

• Mucous membranes line body cavities open to the outside, such as the throat.
• Serous membranes line closed body cavities, such as the stomach.

Edema

• It is tissue swelling
• It can be pitting, leaving an indentation, or non-pitting.

Tissue Repair

• Tissue repair involves bleeding.
• Necrophils remove foreign debris.
• Mast cells release histamine.
• Capillaries leak fluid and proteins.
• A scab forms for cleaning.
• Immune cells move into the area.

Tissue Reformation

• Fibroblasts are immune cells.
• Normal cells result if enough are produced, otherwise fibroblasts create scar tissue.
• Granulation tissue is newly formed capillary tissue.
• Regeneration is the replacement of destroyed tissue with the same kind of tissue.
• Fibrosis occurs in the heart, lungs, and brain.
• It involves replacement with fibroblasts or scar tissue, not original tissue.

Tissue Abnormalities

• Adhesions are scar tissue strips that abnormally connect organs.
• Keloids are abnormal overgrowths of scar tissue during healing.
• Adenomas are benign tumors in gland tissue.

Integument

• Integument, including skin, hair, and nails.

Skin Functions

• These include protection/barrier against microbes, excretion, cooling and heat regulation.
• It provides neural sensors for pain and pressure and Vitamin synthesis.

Skin Layers

• The two major layers of skin are the epidermis and dermis.
• The hypodermis is not a skin layer.
• It is mostly fat.

Epidermis

• It contains keratinocytes, which produce keratin for waterproofing.
• Melanocytes produce melanin - a pigment that protects skin cell nuclei from sun damage.
• Monocytes in peripheral blood become tissue macrophages and consume foreign debris.

Epidermis Cells

• Special skin tissue cells are called Langerhans cells.
• Merkel cells are sensory nerve endings for touch reception.

Epidermis Layers (Outer to Inner)

• Corneum: dead cells with keratin
• Lucidum: clear keratin layer, hairless
• Granulosum: round keratin granules; cells die due to lack of blood supply
• Spinosum: thick keratinocyte bundles with keratin
• Basale: stem cells that undergo mitosis and push layers upward

Dermis

• The papillary and reticular layers connective tissue.
• It contains nerves, glands, receptors, and hair.
• Arrector pili muscles move hair.
• Dermal papillae create fingerprints.
• Striae are tears in the dermis from overstretching (stretch marks).
• Blisters are separations between the epidermis and dermis with fluid pockets.

Skin Pigments

• Melanin is a brownish-black pigment.
• Carotene is yellow/orange.
• Hemoglobin is pinkish.

Effects of sun exposure

• Sun exposure can cause skin cancer, DNA damage, elastine fiber clumping, and thick, spotty skin.

Skin Color Abnormalities

• Cyanosis: blue color
• Erythema: red color
• Pallor: increased pale, white, no blood flow
• Jaundice: yellow color

Skin Glands

• Eccrine glands are small sweat glands.
• Apocrine glands are large sweat glands
• Ceruminous glands secrete wax (e.g., ear wax).
• Sebaceous glands secrete oil.

Hair Glands

• The shaft projects from the skin.
• The root is embedded in the skin.
• The bulb is at the bottom of the root.
• New hair cells push the hair upwards
• Medulla: The inner center of hair and contains large cells and air spaces.
• Cortex: middle layer, flat cells
• Cuticle: outer layer of overlapping cells

Hair Abnormalities

• Alopecia is genetic hair loss, also caused by fever, surgery, trauma, or drugs.
• Minoxidil, originally for high blood pressure, may cause hair growth.
• Lanugo is delicate hair covering a fetus during months 5-6 of development.

Nail Structures

• Nail matrix cells produce hard keratin that makes up the nail.
• The cuticle is a thin skin fold overlapping the nail.
• The lunula is the white crescent over the nail.

Hypodermis

• The hypodermis is not a skin layer.
• It contains fat and blood vessels.
• It provides energy and cushions underlying organs.

Skin Burns

• 1st-degree burns affect the epidermis (sunburn).
• 2nd-degree burns affect the epidermis and dermis, with complete recovery and blisters.
• 3rd-degree burns destroy the epidermis and dermis, requiring grafts.

Other Conditions

• Boils are infected hair follicles or sebaceous glands that spread to the epidermis.

Tissues are groups of similar cells performing specific functions. There are four main tissue types: epithelial, connective, muscle, and nervous tissue. Epithelial tissue provides protection, secretion, and absorption without a direct blood supply but with neural receptors.