Cytology and Histology Overview

Cytology and Histology

• Cytology is the study of cells
• Histology is the study of tissues
• An organism is made up of systems
• A system is made up of organs
• An organ is made up of tissues
• A tissue is made up of identical cells
• Cells are the basic units of living things

Levels of structural complexity

• Living beings are organized into different levels of complexity
• Organism - a set of systems
• System - a set of organs
• Organ - a set of tissues
• Tissue - a set of identical cells

Cytology: Cell Biology

• Cytology, also known as cell biology, studies the cell
• Morphology: form and structure of cells
• Study of cell life, continuity, and function
• Chemical composition: components and molecules of cells

Atoms, Molecules, and Compounds

• All matter is made of atoms
• An element contains only one type of atom
• A compound contains two or more types of atoms combined
• There are 92 naturally occurring elements
• Living tissues are primarily composed of carbon, hydrogen, oxygen, and nitrogen
• Other elements are present in smaller amounts (approx 4%)
• Examples of these elements include sodium, potassium, calcium, and phosphorus

Atomic Structure

• Atoms are mostly empty space with a central nucleus containing protons and neutrons
• Electrons orbit the nucleus
• Neutrons have no electrical charge
• Protons have a positive charge
• Electrons have a negative charge
• Atoms have equal numbers of protons and electrons, leading to a neutral charge
• Protons and neutrons have roughly the same mass, but electrons are much less massive

Subatomic Particles

• Protons: 1 unit of mass, 1 positive charge
• Neutrons: 1 unit of mass, 0 charge
• Electrons: negligible mass, 1 negative charge

Molecules and Compounds

• Molecules consist of two or more atoms chemically combined
• Atoms in a molecule can be the same element (e.g., O2) or different elements (e.g., H2O)
• Compounds contain two or more different elements
• Organic compounds contain carbon and hydrogen
• Inorganic compounds do not contain carbon and hydrogen

Covalent and Ionic Bonds

• Chemical bonds form when atoms join together
• Covalent bonds occur when atoms share electrons
• Ionic bonds occur when electrons are transferred between atoms
• Water molecules are held together by covalent bonds

Electrolytes

• An ionic compound dissolved in water is called an electrolyte
• Electrolytes conduct electricity in solution
• When NaCl dissolves in water, the ionic bond breaks, and the Na+ and Cl- ions separate
• Ions can have a positive or negative charge based on whether they've gained or lost electrons

Acids, Bases, and pH

• pH measures the concentration of hydrogen ions in a fluid
• pH is a measure of acidity or alkalinity
• Living cells are very sensitive to changes in pH
• Biochemical processes continually produce or consume hydrogen ions

pH values of body fluids

• The pH of body fluids needs to be tightly controlled
• Normal pH ranges vary for different body fluids
• Chemical buffers in fluid help maintain stable pH

Chemical constituents of the cell

• Inorganic molecules form small molecules held together by ionic bonds
• Inorganic molecules are essential to the functions of the body, e.g. CO2
• Organic molecules are molecules containing carbon compounds
• Macromolecules are large molecules for the organism
• Organic molecules are covalently bonded

Inorganic Compounds: Water

• Water is the most abundant substance in cells
• Water is more prevalent in plants (80%) than animals (65%)
• The amount of water varies between different tissues (e.g., liver vs. skeleton)
• Water is essential for cellular metabolism
• Water is a natural solvent for certain molecules
• Facilitates reactions
• Provides a suspending medium

Inorganic Compounds: Mineral Salts

• Mineral salts exist in two forms:
  • Insoluble: These salts form rigid structures, for example in cell walls
  • Ionized: They dissociate into ions like Na+, K+, Ca2+, and Mg2+
• Ions are vital for various bodily functions, and their concentrations in cells are generally stable
• Regulation is done through specific mechanisms
• Involved in chemical reactions

Organic Compounds: Carbohydrates

• Carbohydrates are composed of carbon, hydrogen, and oxygen
• When two sugar molecules combine a water molecule is expelled
• A glycosidic bond forms
• Glucose is a monosaccharide and the preferred fuel source in cells
• Blood glucose level is regulated/maintained

Organic Compounds: Amino Acids & Proteins

• Amino acids contain carbon, hydrogen, oxygen, and nitrogen (and sometimes sulfur)
• 20 amino acids are used for protein synthesis in humans
• Amino acids have a common structure with an amino group (NH2), a carboxyl group (COOH), a hydrogen atom, and a variable side chain

Organic Compounds: Lipids

• Lipids are diverse, hydrophobic group of substances
• Mainly composed of carbon, hydrogen, and oxygen, sometimes with nitrogen or phosphorus
• Important lipid types include phospholipids (important in cell membranes), fats/triglycerides (stored as energy) prostaglandins
• Lipids also include important hormones produced in gonads & adrenal glands, and steroids like cholesterol

Organic Compounds: Nucleotides

• Nucleic acids are major components of cells
• Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are comprised of nucleotides
• Adenosine triphosphate (ATP) is a nucleotide with a high energy bond

Organic Compounds: Enzymes

• Enzymes are proteins that act as catalysts for biochemical reactions
• Enzymes speed up reactions without being changed themselves
• They are specific, binding to particular substrates at an active site
• After the reaction, products release and enzymes are ready for use again
• Enzyme action can be sensitive to environmental factors like temperature and pH
• Anabolic reactions combine substances; catabolic reactions break them down