Cytology and Histology: Study Guide for ANP Exam 2

Cytology Part 2

The Cytoplasm

The cytoplasm is the cellular material located between the plasma membrane and the nucleus. It contains organelles, inclusions, and the cytosol.

• Organelles: Specialized structures within the cell that perform specific functions.

• Cellular Structures: Includes the cytoskeleton, centrosomes, and other non-membranous elements.

• Cellular Inclusions: Non-living substances found in the cytoplasm, such as glycogen granules, lipid droplets, and pigment granules.

Functions/Components of Major Organelles:

• Nucleus: Contains genetic material (DNA); controls cellular activities.

• Mitochondria: Site of ATP production via aerobic respiration.

• Ribosomes: Sites of protein synthesis; can be free or attached to rough ER.

• Rough Endoplasmic Reticulum (RER): Studded with ribosomes; synthesizes proteins for secretion or membrane insertion.

• Smooth Endoplasmic Reticulum (SER): Lacks ribosomes; synthesizes lipids, detoxifies chemicals, stores calcium ions.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes: Contain digestive enzymes; break down waste and cellular debris.

• Peroxisomes: Contain enzymes for detoxification and lipid metabolism.

• Cytoskeleton: Network of protein filaments (microfilaments, intermediate filaments, microtubules) that provide structural support and facilitate movement.

Cellular Extensions:

• Microvilli: Increase surface area for absorption (e.g., in intestinal cells).

• Cilia: Move substances across the cell surface (e.g., respiratory tract).

• Flagella: Propel the cell (e.g., sperm cell).

Cell Growth and Reproduction

Cells grow and reproduce through a regulated cycle known as the cell cycle, which includes interphase and the mitotic phase.

• Phases of the Cell Cycle:

  • G1 phase: Cell growth and normal functions.

  • S phase: DNA replication occurs.

  • G2 phase: Preparation for mitosis.

  • M phase (Mitosis): Division of the nucleus.

  • Cytokinesis: Division of the cytoplasm.

• DNA Replication: Occurs during the S phase of interphase.

• Mitosis vs. Cytokinesis:

  • Mitosis: Division of the nucleus into two identical nuclei.

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

Gene Expression and Protein Synthesis

Gene expression involves the process by which information from a gene is used to synthesize a functional gene product, usually a protein.

• The Genetic Code:

  • Consists of triplets of nucleotides (codons) in mRNA.

  • Each codon specifies a particular amino acid.

  • Made of four bases: adenine (A), cytosine (C), guanine (G), and uracil (U) in RNA.

• Transcription:

  • Process of copying DNA information into messenger RNA (mRNA).

  • Product: mRNA.

  • Steps: Initiation, elongation, termination.

  • Enzyme involved: RNA polymerase (synthesizes mRNA from DNA template).

• Translation:

  • Process of synthesizing a protein from mRNA template.

  • Product: Polypeptide (protein).

  • Steps: Initiation, elongation, termination.

  • Enzymes and molecules involved: Ribosomes, tRNA, aminoacyl-tRNA synthetase.

• Types of RNA:

  • mRNA (messenger RNA): Carries genetic code from DNA to ribosome.

  • tRNA (transfer RNA): Brings amino acids to ribosome during translation.

  • rRNA (ribosomal RNA): Structural and functional component of ribosomes.

Example: During translation, the codon AUG on mRNA codes for the amino acid methionine, which is always the first amino acid in a newly synthesized protein.

Histology

Epithelium

Epithelium is a tissue type that covers body surfaces, lines cavities, and forms glands.

• General Functions: Protection, absorption, filtration, excretion, secretion, and sensory reception.

• Characteristics: Cells closely packed, avascular, high regenerative capacity, polarity (apical and basal surfaces).

• Classification:

  • By layers: Simple (one layer), stratified (multiple layers).

  • By shape: Squamous (flat), cuboidal (cube-shaped), columnar (tall).

• Glands:

  • Exocrine glands: Secrete products into ducts (e.g., sweat glands).

  • Endocrine glands: Secrete hormones into the bloodstream (e.g., thyroid gland).

Connective Tissue

Connective tissue supports, protects, and binds other tissues together. It is the most abundant and widely distributed tissue type.

• General Functions: Support, protection, insulation, storage, and transport.

• Characteristics: Cells separated by extracellular matrix (ground substance and fibers), varying degrees of vascularity.

• Classification:

  • Connective tissue proper: Loose (areolar, adipose, reticular) and dense (regular, irregular, elastic).

  • Specialized connective tissues: Cartilage, bone, blood.

Muscle Tissue

Muscle tissue is specialized for contraction and movement.

• General Functions: Movement, posture maintenance, heat production.

• Characteristics: Excitability, contractility, extensibility, elasticity.

• Classification:

  • Skeletal muscle: Voluntary, striated, attached to bones.

  • Cardiac muscle: Involuntary, striated, found in heart.

  • Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

Nervous Tissue

Nervous tissue is responsible for transmitting electrical impulses throughout the body.

• General Functions: Communication, control, integration of body functions.

• Cell Types:

  • Neurons: Conduct electrical impulses.

  • Neuroglia (glial cells): Support, protect, and nourish neurons.

Body Membranes

Body membranes are thin layers of tissue that cover surfaces, line cavities, and divide spaces or organs.

• Cutaneous membrane: The skin; covers the body surface.

• Mucous membrane (mucosa): Lines body cavities open to the exterior (e.g., digestive, respiratory tracts); secretes mucus.

• Serous membrane (serosa): Lines closed body cavities (e.g., peritoneum, pleura, pericardium); secretes serous fluid.

Tissue Repair

Tissue repair is the process by which the body replaces damaged tissue. The process depends on the tissue type and the extent of injury.

• Steps in Tissue Repair:

  1. Inflammation: Damaged cells release chemicals; blood vessels dilate; white blood cells migrate to the area.

  2. Organization: Granulation tissue forms; new blood vessels develop.

  3. Regeneration and/or Fibrosis: Epithelial cells regenerate; connective tissue may form scar tissue (fibrosis).

• Repair by Tissue Type:

  • Epithelial tissue: Regenerates well.

  • Connective tissue: Varies; bone regenerates well, cartilage poorly.

  • Muscle tissue: Poor regeneration (skeletal muscle limited, cardiac and smooth muscle very limited).

  • Nervous tissue: Very limited regeneration in the central nervous system.

Example: A shallow skin wound heals primarily by regeneration of epithelial cells, while a deep wound may result in scar formation due to fibrosis.