General Physiology and Homeostasis

General Physiology

• Physiology is the study of the functions of various organs and systems in the body.
• Physiology comes from the Greek words physis (nature) and logos (study).
• Physiology is the basis of medicine, and a Nobel Prize is awarded yearly in the field of physiology or medicine.

Homeostasis

• Maintaining a nearly constant internal environment within a narrow range of variables is homeostasis.
• Homeostasis comes from the Greek words homeo (the same) and stasis (standing).
• Examples include regulating temperature, body fluid volume, and blood sugar/blood pressure.

Mechanisms of Homeostasis

• Two main categories of regulatory mechanisms:
  • Intrinsic mechanism: Regulation by the organ itself.
    • Example: Nitric oxide (NO) produced by blood vessels (BVs) causing vasodilation (VD).
    • Example: Endothelin produced by blood vessels (BVs) causing vasoconstriction (VC).
  • Extrinsic mechanism: Regulation by the nervous system and endocrine systems.

Components of Homeostatic Control System

• Sensors: Receptors that detect changes and send information to the integrating center.
• Integrating center: Specific regions in the brain, spinal cord, or endocrine glands that detect changes from a set point.
• Effectors: Parts of the body that cause responses to correct deviations from the set point. Examples include muscles and glands.

Mechanism of Action of Homeostatic System

• Homeostasis is maintained through feedback signals.
• Negative feedback control: A mechanism that stops or reverses the direction of change.
  • Examples include: secretion of thyroxine, regulation of blood glucose, body temperature, water balance, and O2/CO2 balance.
• Positive feedback control: A mechanism that increases the intensity of the change in the same direction.
  • Examples include blood clotting, childbirth, milk lactation, WBC chemotaxis during immunity, and during ovulation (estrogen & LH surge).

Regulation of Blood Glucose Level

• After eating (increased blood glucose level), chemoreceptors send signals to the hypothalamus. This triggers beta-cells in the pancreas to secrete insulin, which increases glucose uptake by liver cells. Blood glucose levels decrease to normal.
• During fasting (decreased blood glucose level), chemoreceptors send signals to the hypothalamus, triggering alpha-cells in the pancreas to secrete glucagon. Glucagon increases glucose release from liver cells, thereby increasing blood glucose levels back to normal.

Body Fluids

• Total body water (TBW) varies based on age, gender, and degree of obesity.

Compartments of TBW

• Extracellular fluid (ECF) is about 20% of TBW, in a 70kg man it is 14 liters. ECF has 15% interstitial fluid and 5% plasma. The major cation is Sodium (Na+) and the major anions are Chloride (Cl-) and bicarbonate (HCO3-).
• Intracellular fluid (ICF) is about 40% of TBW, in a 70kg man it is 28 liters. The major cation is Potassium (K+) and the major anions are organic phosphates (ATP,ADP,AMP).

Osmolarity

• Osmolarity is the total number of osmotically active particles per liter of water.
• Osmolarity is dependent on the number of particles, not the type. -Normal plasma osmolarity is 290 – 300 mOsm/L.
• A solution containing 300 mOsm/L = Iso-osmotic solution
• A solution containing less than 300 mOsm/L = Hypo-osmotic solution
• A solution containing more than 300 mOsm/L = Hyper-osmotic solution

Osmotic Pressure

• The minimum pressure required to stop osmosis is equal to the osmotic pressure of the solution. -Calculating osmotic pressure, use van't Hoff's law (π = gCRT).

Tonicity

• Tonicity describes the effect of a solution on osmotic water movement, affecting cell volume.
• Isotonic solutions have the same effective osmolality (300 mOsm/L). Examples include 0.9% NaCl (normal saline) and 5% glucose.

Hypertonic Solution

• Hypertonic solutions have a higher osmolality than the body fluids (over 300 mOsm/L). Example: concentrations of saline greater than 0.9% sodium chloride or dextrose greater than 5%. Water moves out of the cells, causing cell shrinkage (crenation).

Hypotonic Solution

• Hypotonic solutions have a lower osmolality than the body fluids (under 300 mOsm/L). Example: concentrations of saline less than 0.9% or dextrose less than 5%. Water moves into the cells, causing swelling and cell rupture (hemolysis)

Transport of Molecules

• Transport according to carrier presence

  • Carrier-mediated transport (e.g., facilitated diffusion, active transport)
  • Non-carrier-mediated transport (e.g., simple diffusion, osmosis)

• Transport according to energy requirement

  • Passive transport (e.g., simple diffusion, facilitated diffusion, osmosis)
  • Active transport (e.g., primary active transport, secondary active transport)

Protein Channels/Ion Channels

• Ungated (leaky) channels: Continuously open.
• Gated channels: Open only under specific conditions (e.g., voltage-gated, ligand-gated).

Facilitated Diffusion

• Passive transport, no energy required
• Uses carrier proteins, more rapid than simple diffusion.
• Examples include transport of glucose and amino acids.

Active Transport

• Movement of substances against their concentration gradient.
• Requires energy (ATP).

Primary Active Transport

• Direct use of ATP.
• Examples include Na+/K+ pump and Ca2+ pump.

Secondary Active Transport

• Transport of one substance coupled with the movement of another substance (e.g., Na+/glucose cotransport). The energy comes from the electrochemical gradient.

Transport of Large Molecules (Vesicular Transport)

• Endocytosis (uptake):

  • Phagocytosis: Ingestion of solid particles.
  • Pinocytosis: Ingestion of fluid droplets.
  • Receptor-mediated pinocytosis: Selective uptake of specific molecules.

• Exocytosis (release):

  • Secretion of substances by cells.

Cell Communication

• Intercellular communication
  • Gap junctions: Allow exchange of chemical and electrical information.
  • Chemical messengers (ligands):
    • Neurotransmitters (neuron-to-neuron)
    • Hormones (endocrine glands to target cells)
    • Paracrines (local signaling)
    • Autocrines (affect the producing cell)
• Intracellular communication: Ligand binding to receptors triggers a response within the cell. Examples of receptor types:
  • Ligand-gated ion channels
  • G-protein coupled receptors
  • Enzyme-linked receptors
  • Intracellular receptors

Cell Physiology

• A cell is the basic unit of structure and function in living organisms.
• Cells have various functions, such as transporting oxygen to tissues and utilizing energy.
• Cells are composed of different components including plasma membrane, organelles, and cytoplasm

Protoplasm (cell)

• Cell composition is mainly water, electrolytes, proteins, lipids, and carbohydrates.
• The cell membrane:
  • Separates ECF from ICF.
  • Has a selective permeability.
• Structure: Proteins, lipids, and carbohydrates.

Membrane Proteins and Lipids

• Composition includes integral and peripheral proteins; transmembrane proteins involved in different functions, and lipids like phospholipids and cholesterol.
• Functions vary: include transport, enzymes, receptors, signaling, and cell adhesion.

Membrane Carbohydrates

• Carbohydrates (glycoproteins and glycolipids) are on the cell membrane outer surface.
• Functions include cell recognition, cell adhesion, and hormone receptor activity.

Cytoplasm

• The non-nuclear part inside the membrane.
• Includes the cytosol (jelly-like liquid) and organelles.
• Functions: chemical reaction and synthesis, and active transport of substances

Nucleus

• The cell's control center, containing the genetic material (DNA).
• Main function: Directing cell activities and controlling cell division.
• Composed of the nuclear envelope, nucleoplasm, and nucleolus

Endoplasmic Reticulum (ER)

• Connected to the nuclear membrane.
• Rough ER: Contains ribosomes; involved in protein synthesis and modification.
• Smooth ER: No ribosomes; synthesizes lipids and detoxifies substances.

Golgi Apparatus

• Processes, packages, and delivers proteins and lipids.

Lysosomes

• Cellular disposal system; contains digestive enzymes; involved in breaking down cellular debris and waste.

Mitochondria

• Site of cellular respiration and energy production (ATP).

Initiation of Apoptosis

• Programmed cellular death.

Storage of Calcium & Ammonia Detoxification

• Processes specific to the liver.

Explore the fundamentals of physiology, including the mechanisms behind homeostasis in the human body. This quiz covers essential concepts such as intrinsic and extrinsic regulatory mechanisms, providing insights into how our bodies maintain a stable internal environment. Perfect for students of biology and health sciences.