Cell Physiology, Anatomy, and Structure

Cell Physiology and Health Informatics

• Foundational knowledge of cell physiology can be applied to clinical scenarios in Health Informatics Practice

Cell Anatomy

• Cells are the structural units of all living things
• Cells are responsible for all of the biochemical activities that sustain life
• Cells are typically organized into three main regions: the nucleus, cytoplasm, and plasma membrane

The Cell

• The cell is the smallest structural and functional unit capable of carrying out life processes
• Cells serve as the fundamental building blocks of all multicellular organisms
• Functional activities of cells depend on specific structural properties

Overview of Cell Structure

• Most cells have three major subdivisions: plasma membrane, nucleus, and cytoplasm

Plasma Membrane

• The plasma membrane is a very thin membranous structure enclosing each cell
• It is mainly composed of lipid (fat) molecules and some proteins
• The plasma membrane separates the contents of a cell from its surroundings
• Proteins in the cell membrane selectively control the movement of molecules between the intracellular fluid (ICF) and extracellular fluid (ECF)

Cell Membrane Components

• Cholesterol: a lipid component that is incorporated into the cell membrane of animal cells
• Glycocalyx: is used for cell recognition so cells group together to form tissues
• Different varieties of membrane proteins:
  • Integral proteins: allow hydrophilic channel
  • Receptor proteins: for recognizing hormones
  • Carrier proteins: assist in transporting molecules across the membrane

Nucleus

• Contains the cell's genetic material, DNA
• It is surrounded by a double-layered membrane, the nuclear envelope, separating it from the rest of the cell
• The nuclear envelope contains nuclear pores allowing for the exchange of materials between the nucleus and the cytoplasm

Cytoplasm

• The cytoplasm is the region of the cell's interior not occupied by the nucleus
• Contains organelles, cytoskeleton, and cytosol
• Organelles are distinct, highly organized structures within the cell that perform specialized functions

Categories of Organelles

• Two categories: membranous and non-membranous
• A membranous organelle is a separate compartment within the cell enclosed by a membrane

Membranous Organelles

• The five main types include: endoplasmic reticulum, Golgi complex, lysosomes, peroxisomes, and mitochondria

Non-Membranous Organelles

• Non-membranous organelles are not surrounded by a membrane putting them in direct contact with the cytosol
• Examples include ribosomes and centrioles

Endoplasmic Reticulum (ER)

• The endoplasmic reticulum (ER) is a fluid-filled membranous system distributed throughout the cytosol
• It is primarily a protein- and lipid-producing factory
• There are two types of endoplasmic reticulum: Rough and Smooth

Rough Endoplasmic Reticulum

• Synthesizes proteins for secretion and membrane construction
• The outer surface of the rough ER membrane contains ribosomes, where protein synthesis takes place
• The membrane wall contains enzymes essential for the synthesis of lipids

Smooth Endoplasmic Reticulum

• Does not contain ribosomes, hence, it has a "smooth" appearance
• Primarily a central packaging and discharge site for molecules to be transported from ER

Golgi Complex

• Each Golgi complex consists of a stack of flattened sacs
• The sacs within each Golgi stack do not come into physical contact with one another
• Newly synthesized raw materials from the ER travel through vesicle formation through the layers of the Golgi stack
• During transit two important functions take place:
  • Raw materials are processed into finished products
  • The finished products are sorted and directed to their final destinations

Lysosomes

• Lysosomes are small, membrane-enclosed organelles that break down organic molecules
• They contain hydrolytic enzymes that are synthesized in the ER
• The enzymes catalyze hydrolysis, reactions that break down organic molecules using the addition of water at a bond site
• Lysosomes use enzymes to also break down cell debris and foreign material, e.g., bacteria, and viruses

Peroxisomes

• Peroxisomes are membranous organelles that degrade potentially toxic molecules
• They contain oxidative enzymes, including most of the cell's catalase
• Oxidative enzymes use oxygen (O2) to strip hydrogen from certain organic molecules
• The reaction helps to detoxify various waste products within the cell or foreign toxic compounds (alcohol)
• Hydrogen peroxide (H2O2) is formed within the peroxisome by molecular oxygen stripping hydrogen atoms
• Peroxisomes contain catalase; this enzyme decomposes potent H2O2 into harmless H2O and O2

Mitochondria

• Mitochondria are the energy organelles or "power plants" of the cell
• They extract energy from nutrients in food and transform it into a usable form for cell activities
• Mitochondria generate about 90% of the energy that cells need to survive and function

ATP Production

• Adenosine triphosphate (ATP) is used by the body for energy-dependent processes
• An ATP molecule consists of adenosine and three phosphate groups attached
• When the bond between one of the terminal phosphate groups and adenosine is split, energy is released
• Yielding adenosine diphosphate (ADP), inorganic phosphate (Pi) and energy
• ATP -> ADP + Pi + energy for use by cell

Uses of ATP

• Common uses: synthesis of new chemical compounds (e.g., protein synthesis), membrane transport (e.g., active transport), and mechanical work (e.g. heart muscles pumping blood)

Ribosomes

• Ribosomes carry out protein synthesis
• Ribosomes bring together all the components that participate in protein synthesis
• mRNA, tRNA, and amino acids – and provide the enzymes and energy required for linking the amino acids together
• Ribosomes exist either free in the cytosol or attached to the rough ER

Centrioles

• Centrioles are a pair of short cylindrical structures located near the center of the cell
• Centrioles form a mitotic spindle which directs the movement of chromosomes during cell division
• In some cells, centrioles form cilia and flagella, which are elongated, slender, motile structures