Cell Biology

Resting Membrane Potential

The resting membrane potential is the electrical potential difference across the plasma membrane of a cell when it is not actively sending signals. It is essential for the function of excitable cells such as neurons and muscle cells.

• Ions involved: Mainly sodium (Na+), potassium (K+), and chloride (Cl-).

• Maintenance: The sodium-potassium pump (Na+/K+ ATPase) actively transports 3 Na+ out and 2 K+ into the cell, maintaining the gradient.

• Equation: The Nernst equation can be used to calculate equilibrium potential for each ion:

• Example: Neurons typically have a resting membrane potential of about -70 mV.

Functions of Organelles

Cell organelles perform specialized functions necessary for cell survival and activity.

• Mitochondria: Site of ATP production via cellular respiration.

• Ribosomes: Responsible for protein synthesis.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids.

• Lysosomes: Contain digestive enzymes for breaking down waste.

• Example: Muscle cells have many mitochondria due to high energy demand.

Cell Growth and Reproduction

Cells grow and reproduce through the cell cycle, which includes DNA replication and cell division.

• DNA Replication: Occurs during the S phase of the cell cycle, prior to cell division.

• Mitosis vs. Cytokinesis:

  • Mitosis: Division of the nucleus.

  • Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

• Example: Skin cells undergo mitosis to replace lost or damaged cells.

Protein Synthesis

Protein synthesis involves transcription and translation, processes that convert genetic information into functional proteins.

• Transcription: DNA is used as a template to synthesize messenger RNA (mRNA) in the nucleus.

• Translation: mRNA is decoded by ribosomes in the cytoplasm to assemble amino acids into a polypeptide chain.

• Products: mRNA (transcription), polypeptide/protein (translation).

• Steps:

  1. Initiation: RNA polymerase binds to the DNA's promoter region and unwinds the DNA helix

  2. Elongation: RNA polymerase moving along the DNA template strand, synthesizing a complementary RNA molecule by adding nucleotides to the 3' end of the growing chain

  3. Termination: RNA polymerase stops RNA chain elongation and detaches from the DNA template when it encounters a specific termination signal.

  4. Types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal). Each plays a specific role in protein synthesis.

• Example: Hemoglobin is synthesized in red blood cell precursors via these processes.

Histology

Definition of Tissue

Tissue is a group of similar cells that perform a specific function.

• Four basic types: Epithelial, connective, muscle, and nervous tissue.

Epithelial Tissue

Epithelial tissue covers body surfaces, lines cavities, and forms glands.

• Functions/Characteristics: Protection, absorption, secretion, filtration; cells are tightly packed with minimal extracellular matrix.

• Classification: Based on cell shape (squamous, cuboidal, columnar) and number of layers (simple, stratified).

• Types of Glands: Exocrine (secrete into ducts), endocrine (secrete into blood).

• Example: Skin surface is covered by stratified squamous epithelium.

Connective Tissue

Connective tissue supports, binds, and protects organs.

• Functions/Characteristics: Provides structural support, stores energy, connects tissues; contains cells, fibers, and ground substance.

• Classification: Loose (areolar, adipose), dense (regular, irregular), cartilage, bone, blood.

• Example: Tendons are composed of dense regular connective tissue.

Nervous Tissue

Nervous tissue is specialized for communication via electrical and chemical signals.

• Functions/Characteristics: Detects stimuli, transmits impulses, processes information.

• Cell Types: Neurons (conduct impulses), neuroglia (support neurons).

• Example: Brain and spinal cord are composed of nervous tissue.

Membranes

Body membranes cover surfaces, line cavities, and form protective sheets around organs.

• Types:

  • Cutaneous: Skin; protects body surface.

  • Mucous: Lines cavities open to exterior (e.g., digestive tract); secretes mucus.

  • Serous: Lines closed cavities (e.g., thoracic, abdominal); secretes serous fluid.

• Example: The peritoneum is a serous membrane lining the abdominal cavity.

Tissue Repair

Tissue repair restores structure and function after injury.

• Process: Involves inflammation, proliferation, and remodeling.

• Different tissue types: Epithelial tissues regenerate well; connective tissues vary; nervous tissue has limited repair.

• Example: Skin heals by regeneration and scar formation.

Integumentary System

Epidermis

The epidermis is the outermost layer of the skin, providing protection.

• Cell Types: Keratinocytes (main cell), melanocytes (produce pigment), Langerhans cells (immune), Merkel cells (sensory).

• Layers:

  1. Stratum basale (deepest; cell division)

  2. Stratum spinosum (strength, flexibility)

  3. Stratum granulosum (keratin formation)

  4. Stratum lucidum (only in thick skin)

  5. Stratum corneum (outermost; dead cells)

• Example: Palms and soles have a prominent stratum lucidum.

Dermis

The dermis lies beneath the epidermis and provides strength and elasticity.

• Functions/Characteristics: Contains collagen and elastin fibers, blood vessels, nerves, hair follicles, and glands.

• Layers:

  1. Papillary layer (superficial; loose connective tissue)

  2. Reticular layer (deep; dense irregular connective tissue)

• Example: The dermal papillae form fingerprints.

Pigments Involved in Skin Color

Skin color is determined by three main pigments.

Hair

Hair protects, senses, and regulates temperature.

• Characteristics: Composed of keratinized cells; grows from follicles in the dermis.

• Functions: Protection (scalp, eyes), sensation, thermoregulation.

• Example: Eyelashes protect eyes from debris.

Nails

Nails are protective coverings on the fingers and toes.

• Characteristics: Hard plates of keratinized cells.

• Functions: Protect distal phalanges, aid in grasping.

• Example: Fingernails help manipulate small objects.

Glands

Skin contains several types of glands with distinct functions.

• Types:

  • Sudoriferous (sweat) glands: Eccrine (thermoregulation), apocrine (odor, puberty).

  • Sebaceous (oil) glands: Secrete sebum to lubricate skin and hair.

• Example: Eccrine glands are abundant on palms and soles.

Skin Cancer

Skin cancer is the uncontrolled growth of abnormal skin cells.

• General Terms: Tumor, malignancy, metastasis.

• Types:

  1. Basal cell carcinoma (most common, least dangerous)

  2. Squamous cell carcinoma (can metastasize)

  3. Melanoma (most dangerous, arises from melanocytes)

• Example: Melanoma often appears as a dark, irregular mole.

Burns

Burns are injuries to the skin caused by heat, chemicals, electricity, or radiation.

Additional info: These notes expand on the original bullet points with academic context, definitions, and examples for clarity and completeness.