Cell Biology

Basic Cell Processes

The cell is the fundamental unit of life, carrying out essential processes to maintain homeostasis and support organismal function. Understanding these processes is crucial for studying anatomy and physiology.

• Metabolism: The sum of all chemical reactions in the cell, including anabolic (building up) and catabolic (breaking down) pathways.

• Redox Reactions: Chemical reactions involving the transfer of electrons, important in energy production.

• Transport: Movement of substances across cell membranes, including passive (diffusion, osmosis) and active (requiring energy) mechanisms.

• Communication: Cells communicate via chemical signals, such as hormones and neurotransmitters.

• Cellular Respiration: The process by which cells produce ATP from nutrients, primarily glucose.

Key Terms: phospholipid bilayer, mitochondria, cytoplasm, ATP, Na+/K+ pump, diffusion, osmosis, facilitated diffusion, secondary active transport, endocytosis, exocytosis.

Organelles and Their Functions

Organelles are specialized structures within cells that perform distinct functions necessary for cell survival and activity.

• Membrane-bound Organelles: Include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and peroxisomes.

• Non-membrane-bound Organelles: Include ribosomes, cytoskeleton (microtubules, filaments), and centrioles.

• Genetic Control: DNA (chromatin/chromosomes) regulates protein synthesis via transcription (DNA to mRNA) and translation (mRNA to protein).

Key Terms: ribosome, tRNA, mRNA, rRNA, genetic code, protein synthesis, cell cycle, interphase, G1, S, G2, DNA synthesis, mitosis, cytokinesis.

Tissues

Histology and Tissue Types

Tissues are groups of cells with similar structure and function. Histology is the study of tissues, which are classified into four main types.

• Epithelial Tissue: Covers body surfaces and lines cavities; functions in protection, absorption, and secretion.

• Connective Tissue: Supports, binds, and protects organs; includes bone, cartilage, adipose, and blood.

• Muscle Tissue: Responsible for movement; includes skeletal, cardiac, and smooth muscle.

• Nervous Tissue: Conducts electrical impulses; includes neurons and glial cells.

Key Terms: extracellular matrix (ECM), collagen fibers, elastic fibers, reticular fibers, GAGs (glycosaminoglycans), cell junctions (tight, desmosomes, gap).

Classification and Functions of Epithelial Tissue

Epithelial tissues are classified by cell shape (squamous, cuboidal, columnar) and number of layers (simple, stratified).

• Simple Epithelium: Single layer; functions in absorption and filtration.

• Stratified Epithelium: Multiple layers; functions in protection.

Example: Simple squamous epithelium lines blood vessels; stratified squamous epithelium forms the skin's outer layer.

Integumentary System

Structure and Function

The integumentary system includes the skin, hair, nails, and associated glands. It serves as the body's first line of defense and plays roles in protection, sensation, and thermoregulation.

• Epidermis: Outermost layer; composed of keratinized stratified squamous epithelium.

• Dermis: Middle layer; contains connective tissue, blood vessels, nerves, and glands.

• Accessory Structures: Hair follicles, sebaceous (oil) glands, sweat glands, nails.

Key Terms: keratin, melanin, melanocyte, papilla, arrector pili muscle, tactile cells, Merkel cells, Langerhans cells.

Functions and Clinical Relevance

• Protection: Prevents entry of pathogens and minimizes water loss.

• Sensation: Contains sensory receptors for touch, pain, and temperature.

• Thermoregulation: Sweat glands and blood vessels regulate body temperature.

• Clinical Conditions: Burns (classified by degree), skin cancers (basal cell, squamous cell, melanoma), acne, psoriasis.

Example: Melanin produced by melanocytes protects against UV radiation.

Skeletal System

Structure and Composition

The skeletal system provides support, protection, and movement. It consists of bones, cartilage, and associated connective tissues.

• Bone Tissue: Composed of osteocytes, osteoblasts, and osteoclasts; matrix contains collagen and hydroxyapatite.

• Cartilage: Types include hyaline, elastic, and fibrocartilage; provides flexibility and cushioning.

• Bone Marrow: Site of hematopoiesis (blood cell formation).

Key Terms: periosteum, endosteum, Sharpey's fibers, diaphysis, epiphysis, red marrow, yellow marrow.

Bone Growth and Development

Bones grow and remodel throughout life via two main processes: intramembranous ossification (flat bones) and endochondral ossification (long bones).

• Intramembranous Ossification: Bone develops directly from mesenchymal tissue.

• Endochondral Ossification: Bone replaces a cartilage model.

Example: The femur develops via endochondral ossification; the skull bones via intramembranous ossification.

Hormonal Regulation of Bone

Bone metabolism is regulated by hormones such as parathyroid hormone (PTH), calcitonin, and vitamin D.

• PTH: Increases blood calcium by stimulating osteoclasts.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

• Vitamin D: Promotes calcium absorption in the gut.

Equation:

Types of Fractures

Fractures are classified based on their characteristics and severity.

Summary Table: Major Tissue Types

Additional info: These notes provide a concise overview of foundational topics in Anatomy & Physiology, including cell biology, tissue classification, integumentary system, and skeletal system. For deeper study, refer to textbook chapters and laboratory manuals.