Cell Structure, Function, and Division: Human Cytology and Cancer

Cytology

The study of cells.

Different cell types in the human body

~260 different cell types.

Total cells in the human body

About 10-50 trillion.

Three major structural parts of the cell

Cell membrane (plasma membrane), Nucleus, Cytoplasm.

Structure of the cell membrane

Phospholipid bilayer with embedded proteins and cholesterol molecules.

Functions of receptor proteins

Receive signals and trigger responses in the cell.

Integral proteins

Proteins that form pores, channels, and carriers in the cell membrane.

Cellular Adhesion Molecules (CAMs)

Proteins that allow cells to stick together.

Selectin

Coats WBCs, slowing them down and allowing them to stick to capillary walls.

Integrin

Allows one cell to stick to another cell or tissue.

Intercellular junctions

Structures that connect cells to each other.

Tight junctions

Fuse adjacent cell membranes.

Desmosomes

'Spot welds' that hold cells together.

Gap junctions

Tubular structures that allow small molecules to pass between adjacent cells.

Function of the cell membrane

Regulates passage of materials in and out of the cell (selectively permeable).

Molecules passing easily through the hydrophobic region

Lipid-soluble substances (oxygen, carbon dioxide, steroids, lipids).

Molecules having difficulty passing through

Water-soluble molecules (amino acids, sugars, proteins, nucleic acids, ions).

Role of cholesterol in the membrane

Stabilizes the membrane and keeps it flexible.

Diffusion

Movement of molecules from high to low concentration.

Facilitated diffusion

Movement from high to low concentration using a carrier protein.

Osmosis

Movement of water from high to low concentration through a selectively permeable membrane.

Isotonic solution

Equal solute concentration inside and outside the cell.

Hypertonic solution

Higher solute concentration outside → water leaves cell → cell shrinks.

Hypotonic solution

Lower solute concentration outside → water enters cell → cell swells.

Filtration

Movement of a substance through a membrane by hydrostatic pressure.

Active transport

Movement from low to high concentration using carrier proteins and ATP.

Endocytosis

Process by which large molecules enter the cell inside vesicles.

Phagocytosis

"cell eating" solids.

Pinocytosis

"cell drinking" liquids.

Exocytosis

Process by which large molecules exit the cell via vesicles.

Nuclear envelope

Double membrane of phospholipids and proteins; regulates movement between nucleus and cytoplasm.

Chromatin

Long, thin strands of DNA and protein; regulate activity and store hereditary info.

Nucleolus

Dense body of RNA, protein, and condensed chromatin; synthesizes ribosomes.

Membranous organelles

Rough ER, Smooth ER, Golgi apparatus, vesicles, vacuoles, lysosomes, peroxisomes.

Non-membranous organelles

Ribosomes, centrosome (centrioles), microfilaments, microtubules, cilia, flagella.

Purposes of cell division

Growth, replacement of dead cells, tissue repair, reproduction.

Mitosis + cytokinesis

Same chromosome number (somatic cells).

Meiosis + cytokinesis

Chromosome number reduced by half (sex cells).

Interphase

Time between cell divisions; DNA replication and centriole duplication occur; chromatin is visible.

Prophase

Chromatin condenses to chromosomes, nuclear membrane fragments, spindle fibers appear, centrioles move to opposite poles.

Metaphase

Chromosomes line up along equator; spindle fibers attach to centromeres.

Anaphase

Sister chromatids separate and move to opposite poles.

Telophase

Cytokinesis occurs; chromosomes uncoil to chromatin; nuclear membrane reforms; two daughter cells form.

Cell differentiation

Process by which cells develop specialized structures and functions.

Stem cells

Cells that can divide and differentiate into other types.

Embryonic stem cells

Derived from fertilized egg; can form any cell type.

Adult stem cells

Undifferentiated cells in tissues/organs; can renew and specialize into some types; also found in umbilical cord & amniotic fluid.

Tumor

A group of newly dividing cells.

Benign tumors

Remain at original site.

Malignant tumors

Spread to other sites.

Cancer

Condition of unregulated cell growth.

Characteristics of cancer cells

Metastasis, hyperplasia, dedifferentiation, invasiveness, angiogenesis.

Causes of aging

Decreased ability to replace dead/worn out cells.

Progeria

Genetic disease causing accelerated aging.