Human Tissue Types and Organ System Functions

Classification of Human Tissue Types

Tissue: An integrated group of cells with a common function and structure.

Epithelial Tissues

• Pseudostratified Ciliated Columnar: Features a large cytoplasmic volume; functions in secretion and absorption (e.g., nasal passages).
• Cuboidal: Specialized for secretion; found in the epithelia of the kidney, salivary, and thyroid glands.
• Stratified Columnar: Lines the inner surface of the urethra.
• Stratified Squamous: Regenerates quickly at the base; protects against abrasion (e.g., vagina, anus, and esophagus).
• Simple Squamous Epithelium: Thin and leaky; facilitates exchange via diffusion (e.g., blood vessels and lung air sacs).
• Simple Columnar: Functions in the secretion of juices and absorption of nutrients (e.g., intestines).

Connective, Bone, and Nervous Tissues

Bone: Composed of the osteon, central canal, and matrix.

Loose Connective Tissue: Contains elastic fibers (long tubes), reticular fibers (small tubes), and collagenous fibers (large tubes). Includes fibroblasts (round structures) and macrophages (irregular points).

Cartilage: Contains chondrocytes and a liquid chondroitin matrix.

Nervous Tissue: Includes dendrites (terminations), the axon hillock (stalk), the myelin sheath (capsules), and terminal branches (synaptic).

Tisular, tisular, tisular.

Functions of the Integumentary System

The skin serves several vital functions:

• Regulates temperature through negative feedback.
• Acts as a sense organ and protects from physical and chemical damage.
• Produces Vitamin D for the absorption of calcium.

The Wound Healing Process

1. Clotting: Closes breaks in the skin, producing a clot and forming a scab to prevent bacteria from entering.
2. Defense: Vessels dilate to produce more white blood cells.
3. Replacement: Mitosis occurs to replace cells and fill the space.
4. Resolution: The scab falls off.

Aging: Sebaceous glands decrease oil production; skin loses elasticity faster with sun exposure.

Homeostasis and Major Organ Systems

Homeostasis: The steady-state physiological condition of the body.

• Digestive System: Food processing (ingestion, digestion, absorption, and elimination).
• Circulatory System: Vessels, heart, and blood; distributes nutrients.
• Respiratory System: Lungs and trachea; facilitates gas exchange.
• Immune and Lymphatic Systems: Bone marrow, nodes, thymus, and spleen; body defense.
• Excretory System: Kidneys, ureters, bladder, and urethra; disposal of metabolic waste and osmotic balance.
• Endocrine System: Pituitary and thyroid; coordination of body systems.
• Nervous System: Brain and spinal cord; coordination and detection of stimuli.
• Integumentary System: Skin and hair; protects against infection and drying out.

The Endocrine System and Hormonal Regulation

The endocrine system involves the production of hormones to induce changes in other locations.

Key Endocrine Glands

• Pituitary Gland: Secretes amino acid hormones; affects the adrenal, thyroid, ovaries, testes, and mammary glands. It stores hypothalamus hormones and growth hormones.
• Hypothalamus: Secretes amino acid hormones; controls the pituitary and synthesizes antidiuretic hormone and oxytocin.
• Parathyroid Gland: Secretes amino acid hormones (parathyroid hormone).
• Thyroid Gland: Secretes amino acid hormones (thyroxine and calcitonin).
• Adrenal Medulla: Secretes amino acid hormones (epinephrine and norepinephrine).
• Ovaries and Testes: Secrete steroid-based female and male sex hormones.
• Adrenal Cortex: Secretes steroid corticoids and aldosterone.

Mechanisms of Hormone Action

Steroid Hormones: Being lipid-soluble, they diffuse through the membrane, bind to a hormone receptor, and travel to the nucleus to activate the synthesis of mRNA and specific genes. The mRNA then moves from the nucleus to synthesize proteins.

Amino Acid and Peptide Hormones: These bind to receptors on the cell membrane; this action may open an ion channel or activate an inactive form of an enzyme. These enzymes can induce minor or major physiological changes.