Foundations of Anatomy & Physiology: Cells, Tissues, and the Integumentary System

Cell Theory and Cell Structure

Cell Theory

The Cell Theory is a fundamental concept in biology stating that all living things are composed of cells, and all cells arise from pre-existing cells.

• All living organisms are made up of one or more cells.

• Cells are the basic unit of structure and function in living things.

• All cells come from pre-existing cells by division.

Overview of Cell Structure

Cells contain specialized structures called organelles that perform distinct functions necessary for life.

• Nucleus: Contains genetic material (DNA); control center for cell activities.

• Mitochondria: Powerhouse of the cell; generates ATP through cellular respiration.

• Endoplasmic Reticulum (ER):

  • Rough ER: Protein synthesis (studded with ribosomes).

  • Smooth ER: Lipid metabolism.

• Golgi Apparatus: Packaging and modification of proteins.

• Lysosomes: Digestion of cellular waste.

• Plasma Membrane: Phospholipid bilayer controlling the movement of substances in and out of the cell.

Cell Division

Mitosis

Mitosis is the process by which a eukaryotic cell divides to produce two identical daughter cells. It is essential for growth, repair, and asexual reproduction in multicellular organisms.

• Occurs in somatic cells (non-reproductive cells).

• Produces two diploid daughter cells (same chromosome number as parent).

• Genetic variation does not change.

• Stages of mitosis (PMAT):

  • Prophase: Chromosomes condense, spindle fibers form.

  • Metaphase: Chromosomes align at the metaphase plate.

  • Anaphase: Sister chromatids are pulled apart.

  • Telophase: Nuclear membrane reforms, chromosomes decondense.

  • Cytokinesis: Cytoplasm divides, forming two cells.

Meiosis

Meiosis is a specialized form of cell division that produces gametes (sperm and egg), resulting in four haploid cells with genetic diversity.

• Occurs in germ cells (reproductive cells).

• Purpose: Sexual reproduction.

• Produces four haploid daughter cells (chromosome number halved).

• Involves two rounds of division: Meiosis I and Meiosis II.

• Increases genetic variation.

Comparison of Mitosis and Meiosis

Feature	Mitosis	Meiosis
Cell Type	Somatic	Germ
Daughter Cells	2 (diploid)	4 (haploid)
Genetic Variation	No change	Increased
Function	Growth, repair	Sexual reproduction

Cell Transport and Plasma Membrane Structure

Plasma Membrane Structure

• Phospholipid Bilayer: Composed of hydrophilic heads and hydrophobic tails.

• Proteins: Integral and peripheral proteins involved in transport and signaling.

• Cholesterol: Maintains membrane fluidity.

Transport Mechanisms

• Passive Transport (no energy required):

  • Simple Diffusion: Movement of small, non-polar molecules (e.g., O2, CO2).

  • Facilitated Diffusion: Movement through protein channels (e.g., glucose).

  • Osmosis: Diffusion of water across a selectively permeable membrane.

• Active Transport (requires energy):

  • Uses ATP to pump molecules against the concentration gradient (e.g., sodium-potassium pump).

  • Secondary Active Transport: Uses the energy of another molecule's gradient (e.g., sodium-glucose symport).

• Endocytosis: Cell engulfs particles to bring them into the cell.

• Exocytosis: Release of substances from the cell via vesicles.

Osmosis and Tonicity

• Isotonic Solution: Equal solute concentration inside and outside the cell; cell remains normal.

• Hypertonic Solution: Higher solute concentration outside the cell; water leaves the cell, causing it to shrink (crenate).

• Hypotonic Solution: Lower solute concentration outside the cell; water enters the cell, causing it to swell and possibly burst (lyse).

Classification of Tissues

Levels of Organization

• Chemicals → Organelles → Cells → Tissues → Organs → Organ Systems

Major Tissue Types

• Epithelial

• Connective

• Nervous

• Muscle

Epithelial Tissue

• Sheet of cells covering body surfaces or lining body cavities.

• Functions: Protection, absorption, secretion.

• Forms glands (endocrine and exocrine).

Connective Tissue

• Most abundant and widely distributed tissue type.

• Functions: Protect, support, insulate, bind other tissues.

• Types:

  • Connective tissue proper (loose and dense)

  • Cartilage

  • Bone

  • Blood

• Common origin: Derived from embryonic mesenchyme.

• Degrees of vascularity: Rich blood supply (except cartilage and dense connective tissue).

• Extracellular matrix: Nonliving material between cells.

Nervous Tissue

• Composed of neurons and supporting cells (neuroglia).

• Neurons: Highly specialized to receive stimuli and transmit electrical signals.

Muscle Tissue

• Specialized to contract and produce movement.

• Types:

  • Skeletal Muscle: Attached to skeleton, voluntary control.

  • Cardiac Muscle: Found only in the heart, involuntary control.

  • Smooth Muscle: Walls of hollow organs, involuntary control.

Integumentary System

Overview

The Integumentary System consists of the skin and its accessory structures. It protects the body, regulates temperature, and prevents water loss.

• Two main regions:

  • Epidermis: Composed of epithelial tissue.

  • Dermis: Underlying connective tissue.

Epidermis: Cell Types

• Keratinocytes: Most abundant; produce keratin for protection.

• Melanocytes: Produce melanin pigment for UV protection.

• Dendritic Cells: Immune response; arise from bone marrow.

• Tactile Epithelial Cells: Sensory touch receptors.

Dermis: Structure

• Papillary Dermis: Areolar connective tissue; forms fingerprints.

• Reticular Dermis: Dense irregular connective tissue; contains arteries, veins, sweat/sebaceous glands.

Accessory Organs of the Skin

• Nails

• Hair

• Cutaneous glands

Genetics

Genetics is the study of heredity and variation in organisms. It explains how traits are passed from parents to offspring through genes.

• Genes are segments of DNA that code for proteins.

• Genetic variation is essential for evolution and adaptation.