Physiology

Introduction to Cell Physiology

  • Course Details:

    • Course Name: Introduction to Cell Physiology

    • Instructor: Professor Charles Hayfron-Benjamin

    • Departments: Department of Physiology, UGMS; Department of Anesthesia and Intensive Care, UGMC/KBTH

    • Date: January 2025

Lecture 1: Homeostasis

What is Physiology?

  • Definition:

    • Physiology is the scientific study of the physical and chemical mechanisms responsible for the origin, development, and progression of life.

  • Human Physiology:

    • The scientific study of specific characteristics/functions and mechanisms of the human body.

  • Importance:

    • Physiology is considered a basic science course and is essential for understanding medicine.

  • Scope:

    • Encompasses all levels from cells to tissues to organs to organ systems to integrated function of the body.

The Cell

  • Basic Unit of Life:

    • Cells are the structural and functional units of life.

  • Cell Types and Functions:

    • Each cell type is specialized to perform specific functions.

    • Red Blood Cells (RBCs):

      • Approximately 25 trillion; contain hemoglobin to transport oxygen from lungs to tissues.

    • Neurons:

      • Approximately 35 billion; transmit signals using electrical and chemical processes.

  • Extracellular Fluid (ECF):

    • Cells function optimally when the ECF is maintained within normal limits (normal pH, concentrations of gases, glucose, ions, amino acids, fatty substances).

Homeostasis

  • Definition:

    • Homeostasis is the maintenance of nearly constant conditions in the internal environment, a term coined by Walter Cannon in 1929.

  • Functions:

    • All organs and tissues perform functions to maintain these constant conditions critical for normal functioning.

  • Integrated Actions:

    • Requires cooperation of cells, tissues, organs, along with various control systems (nervous, hormonal, and local) contributing to homeostasis and health.

  • Disease Implications:

    • Disease is viewed as a state of disrupted homeostasis, although homeostatic processes continue to maintain vital functions under pathological conditions.

Feedback Mechanisms

Negative Feedback

  • Mechanism:

    • A physiological response that counteracts a deviation from a set point, returning the body to homeostasis.

    • E.g., A thermostat turns off a heater when a set temperature is reached.

  • Examples in Humans:

    • Regulation of body temperature (sweating, shivering)

    • Blood glucose control (insulin secretion)

    • Blood pressure regulation

    • Blood pH regulation.

Positive Feedback

  • Mechanism:

    • A deviation leads to further changes that move the system away from the normal range.

    • E.g., Fruit ripening via ethylene gas release.

  • Normal Usage:

    • Positive feedback is functional when there is a clear endpoint.

  • Examples in Humans:

    • Regulation during childbirth (uterine contractions), blood clotting, lactation.

Body Water and Fluid Compartments

Total Body Water (TBW)

  • Proportion of Body Weight:

    • Approximately 60% of body weight

  • Compartments:

    • Intracellular Fluid (ICF): Roughly 40% of body weight (2/3 of TBW)

    • Extracellular Fluid (ECF): Approximately 20% of body weight (1/3 of TBW)

    • Intravascular space: 6% of body weight.

    • Na+ Concentration: 140 mmol/l

    • K+ Concentration: 4 mmol/l

  • Age and Sex Impact:

    • Total body water varies with age and body composition; generally higher in males due to lower adipose tissue percentage.

Body Water Composition by Age

Category

Composition (%)

Fetus

70-80%

Infant

75%

Baby at Birth

60%

Normal Adult

50-60%

Elderly

45-50%

Total Body Water Distribution

  • Composition Differences: - Highest in infants, lowest in elderly due to increasing adipose tissue.

Intracellular and Extracellular Fluid Composition

  • Intracellular Fluid (ICF):

    • Major cations: K+, Mg2+.

    • Major anions: Proteins, organic phosphates (AMP, ADP, ATP).

  • Extracellular Fluid (ECF):

    • Major cations: Na+, Ca2+.

    • Major anions: Cl-, HCO3-.

    • ECF carries nutrients essential for cells like oxygen and glucose.

Acid-Base Balance

Acid Definitions

  • Arrhenius Acids: Liberate excess H3O+ in solution.

  • Brønsted–Lowry Acids: Proton donors.

  • Lewis Acids: Electron pair acceptors.

Importance of Acid-Base Regulation

  • Optimal pH: Maintains stable pH at 7.40 (normal range: 7.35-7.45).

    • Essential for enzyme function, with small pH fluctuations leading to enzyme denaturation.

  • Consequences of Imbalance:

  • Poor vascular tone, myocardial pump failure, increased arrhythmia risk, muscle weakness, delirium/coma, impaired respiration.

Mechanisms of Acid Production and Elimination

  • Net Formation vs. Excretion: Net acid production equals net acid elimination.

  • Elimination Methods:

    • Pulmonary: Excretion of CO2 (volatile acid).

    • Renal: Excretion of non-volatile/fixed acids.

Volatile vs Non-Volatile Acids

  • Volatile Acids:

    • CO2 from aerobic metabolism; combines with water to form H2CO3, dissociating into H+ and HCO3-.

    • Production rate: ~200 ml/min.

  • Non-Volatile Acids:

    • Such as sulfuric acid (protein breakdown) and phosphoric acid (phospholipid breakdown).

    • Production rate: 40-60 mmoles/day.

Contribution of Lungs and Kidneys to Acid-Base Balance

  • Lungs: Control CO2 excretion via alveolar ventilation alteration.

    • Hyperventilation: Increases CO2 excretion, creating an alkaline environment.

    • Hypoventilation: Reduces CO2 excretion, leading to acid retention.

  • Kidneys: Mechanisms include H+ excretion regulation and bicarbonate handling.

    • In acidosis, bicarbonate is retained; in alkalosis, bicarbonate is excreted.

Buffers and Their Role

  • Function: Substances that can reversibly bind H+.

  • Extracellular Buffers: HCO3-/CO2, HPO4^2-/H2PO4−, proteins.

  • Intracellular Buffers: Organic phosphates, hemoglobin.

Summary: Acid-Base Balance

  • Imbalances:

    • Respiratory vs. metabolic issues with compensatory mechanisms.

    • Respiratory imbalances corrected by kidneys; metabolic issues corrected by lungs.

Lecture 3: Cell Membranes and Membrane Transport

Overview of the Cell

  • Structure: Basic unit of life; consists of eukaryotic and prokaryotic cells.

  • Eukaryotic Cells: Contain membrane-bound organelles and nucleus (humans are eukaryotic).

  • Prokaryotic Cells: Lack membrane-bound nucleus/organelles; found in bacteria.

Organelles

  • Mitochondria:

    • Energy generation sites; ATP production.

    • Structure: Double lipid membrane bound.

  • Endoplasmic Reticulum:

    • Rough ER: Synthesis of secretory proteins.

    • Smooth ER: Steroid synthesis, detoxification.

  • Golgi Apparatus: Protein distribution center from ER to cell membrane, lysosomes, secretory vesicles.

  • Lysosomes: Contain digestive enzymes, play a role in cellular metabolism.

Cell Membrane Structure and Function

  • Composition:

    • Major components: Lipids, membrane proteins, and intercellular connections.

    • Lipid Bilayer: Composed of a glycerol backbone with hydrophilic heads and hydrophobic fatty acid tails, forming a bilayer.

Membrane Proteins

  • Types:

    • Integral Proteins: Embedded within membrane (ion channels, transport proteins, receptors).

    • Peripheral Proteins: Attain location outside membrane, not covalently bonded.

Ion Movement Across Cell Membranes

  • Transport Mechanisms:

    • Simple diffusion, facilitated diffusion (carrier-mediated), and various forms of active transport.

Special Transport Systems

  • Symport (Cotransport): Transport of two or more solutes in the same direction.

    • Example: Na+-glucose transport.

  • Antiport (Countertransport): Transport of two solutes in opposite directions.

    • Example: Chloride/bicarbonate transport in RBCs.

Summary of Membrane Transport

  • Key Points:

    • Primary active transport uses ATP directly.

    • Secondary active transport is tied to Na+/K+ gradients.

  • Na+/K+ Pump:

    • Essential for maintaining concentration gradients across the cell membrane.

Conclusion

  • Understanding cell physiology is crucial for insights into health and disease, serving as a foundational element in medical education.

Final Notes

  • Following completion of foundational knowledge in cell physiology, students should be prepared to engage in more complex topics regarding body systems and their interrelations, paving the way for advanced studies in medicine.

  • Ethical Consideration:

    • Students are encouraged to adhere to principles of integrity and respect in all academic and professional endeavors, as emphasized by moral teachings incorporated in the course materials.