Cellular Physiology

Cellular Physiology

• Cellular physiology is the study of how individual cells function.
• Cells are the basic structural and functional unit of living tissue.
• Tissues are an aggregation of multiple cells, held together by intercellular supporting structures.
• There are over 200 different types of human cells.
• The human body contains approximately 35-40 trillion cells.
• Form follows function means that each cell is specifically adapted to perform one or a few particular functions.
• Cell types vary greatly, but all cells have certain common characteristics.

Objectives

• Review foundational concepts of cellular physiology.
• Examine cellular transport mechanisms.
• Analyze application of cellular physiology principles.

Cell Structure and Function

• Cells are the basic structural and functional unit of life.
• Cells have various components: nucleus, cytoplasm, and plasma/cell membrane.
• Cells have complex internal structures which include: centrioles, chromosomes, DNA, rough and smooth endoplasmic reticulum, Golgi apparatus, ribosomes, microtubules, microfilaments, lysosomes, mitochondrion, nucleus, nucleolus.
• Water makes up 70-85% of the cell.
• Ions are crucial for cellular reactions and control.
• Proteins (10-20% of cell mass) are structural and functional (enzymes).
• Lipids are fat-soluble substances.
• Carbohydrates play roles in cell nutrition and structural formation.
• Microorganisms live in the human body and outnumber human cells by a significant amount.

Cell Structure Review

• The levels of organization in the body go from cells to tissues, to organs to systems.
• Cells form tissues, tissues form organs, organs make up systems, systems work together as a whole organism.

Application

• Mitochondria are sites of oxidative phosphorylation and ATP synthesis, providing cellular energy.
• Sarcoplasmic reticulum (skeletal muscle endoplasmic reticulum) regulates calcium, controlling muscle contraction/relaxation.
• Ribosomes translate RNA to proteins, which are essential for many cellular functions.

Cellular Functions

• Barrier and transport: the plasma membrane acts as a selective barrier. -Digestion: breakdown and removal of unwanted materials within the cell. -Signaling: communication and response to signals from the environment (chemicals in the extracellular fluid). -Migration: capacity of cells to move within the body (immune and tissue forming). -Metabolism: sum of anabolic (formation and maintenance) and catabolic (breakdown) processes. -Cell division (mitosis & meiosis): formation of new cells. -Cell death (apoptosis): planned/programmed cellular death.

Digestion by the Cell

• Cells need nutrients to live and grow.
• Most substances enter cells by diffusion or active transport
• Endocytosis and exocytosis are methods of transport.

Autophagy & Recycling

• Lysosomes play crucial roles in recycling cellular components.
• Autophagy is the process by which cells eat their own obsolete organelles and large proteins.

Energy Extraction

• Nutrients like glucose, fatty acids, and amino acids are used to produce energy in the form of ATP.
• This process occurs in mitochondria.

Cellular Locomotion

• There are two main types of cellular locomotion outside of muscle contractions:

1. Ameboid movement: Entire cells move (e.g., WBCs).
2. Ciliary movement: Cilia on cell surfaces (e.g., respiratory airways).

Cellular Transport

• Movement of substances across the cell membrane (into/out).
• Essential for cell function and homeostasis.
• Used for action potentials.

Transport of Substances Through Cellular Membranes

• Intracellular fluid exchanges with extracellular fluid. -Most fluid is intracellular. -The extracellular fluid is constantly moving and contains vital nutrients and ions for cell function.

Extracellular Fluid

• Fluid is transported through the body via blood and exchange between blood vessels and tissues.

Cellular Transport (Classification)

• Cellular transport is categorized as active (needs energy) or passive (no energy).
• Active transport is further classified by use of energy (primary/secondary).
• Vesicles are involved in endocytosis (into) and exocytosis (out).
• Substances move through membranes via diffusion (simple or facilitated) or osmosis (water movement).

Passive Transport

• Molecules move freely.
• Movements are driven by electrochemical gradients (differences in concentration or charge).

Active Transport

• Molecules are moved against electrochemical gradients.
• Cells spend energy to move molecules.

Electrochemical Gradient

• A gradient of electrochemical potential determines how molecules move across the plasma membrane.
• There are chemical (difference in solute concentration) and electrical (difference in charge) components of the electrochemical gradient.

Diffusion

• Molecules move from high to low concentration areas spontaneously.

Types of Cellular Transport

• Simple Diffusion: movement of molecules or water down a concentration gradient without assistance.
• Facilitated Diffusion: molecules or water move with the help of protein channels.
• Osmosis: movement of water down a concentration gradient with concentration of solute (or absence) as the driver.

Membrane Transport Proteins

• Proteins facilitate the movement of molecules across membranes.
• Includes aquaporins, ion channels (voltage & ligand-gated), solute carriers (uni, co, symporters, antiporters).

ATP-Dependent Transporters

• Involved in primary active transport.
• Example: Na+/K+ -ATPase transports 3 sodium ions out and 2 potassium ions in.

Vesicular Transport

• Endocytosis and exocytosis are used to move large molecules or groups of molecules across membranes and into or out of the cell.
• Exocytosis is used to move molecules OUT of a cell.
• Endocytosis is used to move molecules INTO a cell.

Membrane Transport Proteins

• Aquaporins: facilitate water movement (osmosis) that may be regulated by hormones
• Ion Channels: selective or non-selective; gated to open or close based on signals.
• Example: voltage gated channels respond to membrane potential; ligand-gated channels respond to a chemical binding.

Extracellular Edema

• Excess fluid accumulation in extracellular spaces.
• Causes are abnormal plasma leakage to interstitial spaces and/or lymphatic failure to return fluid from the interstitium to the blood.

Health Condition- Diabetes Mellitus (DM2)

• A metabolic disorder characterized by high blood glucose due to insufficient insulin secretion, insulin resistance, and inadequate glucagon suppression.
• Impacts normal cellular transport, especially glucose uptake.

Skeletal Muscle & Glucose Homeostasis

• Skeletal muscle plays a vital role in maintaining blood glucose levels, especially post-meal.
• GLUT4 is crucial for glucose uptake into cells and is increased via aerobic training.

Insulin Response

• Insulin is a hormone that regulates blood glucose levels; in a healthy response, insulin triggers a chain of events that lead to increasing glucose uptake.
• In DMII, insulin receptors do not function to the same degree or not at all.

Role of Physical Therapists

• Regular aerobic training increases GLUT4 transport in skeletal muscle, which helps reduce hyperglycemia.