Introduction to Physiology and Fluid Balance

Introduction to Physiology and Fluid Balance

• Physiology is the study of the normal functioning of a living organism
• Physiology encompasses the chemical and functional processes within an organism
• It's an integrative science examining functions at various levels of organism complexity
• Physiology is the science of life
• Islamic medicine defines physiology as 'ilm umur tabi'iyyah', meaning the science of natural affairs
• Muslim physiology is based on the humoral theory, different from modern physiology
• The humoral theory proposes four major fluids (blood, phlegm, yellow bile, and black bile) dominate the human body
• Each humor is composed of heat, cold, dryness, and moisture
• Individual constitution is dictated by the dominating humor, influencing bodily functions, character, and intelligence

Learning Objectives

• Understanding the concept of physiology
• Explaining body fluid compartments
• Describing movement across membranes (passive transport, diffusion, mediated transport, facilitated diffusion, and active transport)
• Understanding the significance of water and solute balance in the body
• Describing the physiological regulation known as homeostasis

What is Physiology?

• The study of an organism's functions and how it works at different levels
• Focuses on the chemical and functional processes of living organisms
• Aristotle contributed to the study of the function of living organisms
• Hippocrates emphasized natural healing and connected physiology to medicine
• Physiology examines functions at multiple levels

From Oxford Dictionary

• Physiology is the study of homeostasis in living organisms and their parts
• Illustrates the hierarchical manner that physiology encompasses multiple levels of organization, from atoms to molecules, to organisms
• Physiology is the science of life

From Philosophy of Islamic Medicine

• Physiology is the science of natural affairs in Islamic medicine
• It focuses on the functioning of human body structures and organs
• Muslim physiology is based on the humoral theory, which differs in many respects from modern physiology

Humoral Physiology

• Four major fluids (blood, phlegm, yellow bile, and black bile) are central to this theory
• Each humor is composed of two elements (heat, cold, dryness, and moisture)
• Each individual's natural complexion/constitution is defined by one dominant humor, influencing bodily traits

Levels of Structural Organization and Body Systems

• Exploration of the human body ranges from atoms/molecules to the entire person
• 6 levels of organization:
  • Chemical (smallest - atoms and molecules)
  • Cellular (basic building blocks of life)
  • Tissue (groups of cells functioning together)
  • Organ (structures with specific functions)
  • System (composed of related organs working together)
  • Organismal (encompassing all levels for the survival of the whole person)

Chemical Level

• Atoms (C, H, O, N, P, Ca) are essential for life
• Molecules (DNA, glucose) are formed by combinations of atoms

Cellular Level

• Molecules combine to form cells which are the basic structural and functional unit of an organism
• Cells are composed of chemicals
• Examples include muscle, nerve, and epithelial cells

Tissue & Organ Level

• Tissues are groups of similar cells working together for a common cause
• Four types include epithelial, connective, muscle, and nervous
• Organs are structures made up of two or more tissue types with specific functions and identifiable shapes (e.g., stomach, skin, bones, heart, liver, lungs, brain)

System (Organ-System) Level

• Consists of related organs with a common function (e.g., digestive, endocrine)
• Examples include digestive, endocrine, nervous, respiratory, muscular, skeletal, circulatory, immune systems
• An organ can belong to multiple systems

The relationship between clinical manifestation, physiology, and molecular level interaction

• Clinical manifestations are explained by physiological processes, which in turn are governed by molecular interactions

Branches of Physiology

• Molecular physiology (individual molecules like proteins and DNA)
• Neurophysiology (nerve cells)
• Endocrinology (hormones and their control of body function)
• Cardiovascular physiology (heart and blood vessels)
• Immunology (body's defenses)
• Respiratory physiology (air passageways and lungs)
• Renal physiology (kidneys)
• Exercise physiology (muscle activity)
• Pathophysiology (disease and aging)

Membrane Permeability

• Describes how substances move through the plasma membrane; how permeable some substances are
• The plasma membrane is selectively permeable, permitting some substances (nonpolar, uncharged molecules) to cross more readily than others (ions, larger polar molecules).
• Transmembrane proteins (channels, carriers) increase membrane permeability to ions, and polar, uncharged molecules.
• Macromolecules (too large) cross only via endocytosis/exocytosis

Gradients Across The Plasma Membrane

• Concentration gradient - difference in chemical concentration between locations
• Electrical gradient - difference in electrical charges between regions
• Membrane potential - the charge difference across the membrane due to the uneven distribution of ions.
• Gradients drive substance movement

Transport Across The Plasma Membrane

• Essential for cellular life
• Substances enter/leave the cells - through passive or active transport
• Active transport (energy required, e.g., sodium-potassium pump)
• Passive transport (no energy required, e.g., diffusion)
• Vesicles (endocytosis, exocytosis)

Active Transport

• Primary active transport - energy obtained from ATP
• Secondary active transport - energy from an existing ionic gradient (e.g., sodium-gradient driven by primary active transport)

Primary Active Transport: Sodium-Potassium Pump

• Expels sodium and brings potassium into the cell; critical process; maintaining ion concentrations

Secondary Active Transport

• Involves a carrier protein
• Substances move in the same direction (symporter) or opposite directions (antiporter)

Transport in Vesicles

• Vesicles: Small, spherical sacs for transporting materials
• Function: transport materials between cellular structures, importing/exporting materials
• Endocytosis (enters the cell via plasma membrane vesicle formation)
• Exocytosis (exits via cell membrane vesicle fusion)

Distribution and Compartment of Body Fluids

• Cell membranes compartmentalize the body
• Body fluids exist in intracellular and extracellular compartments
• Intracellular fluid: fluid inside the cells
• Extracellular fluid (ECF): fluid outside the cells, consisting of interstitial fluid (between cells) and plasma (in blood vessels)

Body Fluid Compartments

• Body fluids comprise 50-60% of body mass for lean adults
• Intracellular fluid makes up about two-thirds of the body's water
• Extracellular fluid (ECF) comprises the remaining one-third
• Plasma and interstitial fluid make up ECF

Water and Electrolyte Balance: How It Is Important?

• Water balance is important for homeostasis
• Dehydration can lead to issues (e.g., reduced function, heart strain, headaches)
• Maintaining water/electrolyte levels is crucial

Fluid Movement Between Compartments

• Hydrostatic pressure and osmotic pressure drive fluid movement across cell membranes and capillaries
• Filtration (fluid exit from capillaries) and reabsorption (fluid re-enters capillaries)
• Surplus fluid is drained by the lymphatic system.

Homeostasis

• A state of internal balance among body systems
• Maintains stable internal conditions for survival.
• Body temperature, blood pressure, and blood sugar regulation are examples

Water Intoxication

• Occurs when the body absorbs water faster than the kidneys can excrete it
• Can result in severe complications like convulsions and coma

Intro: Water Intoxication

• Water intoxication (water poisoning/ dilutional hyponatremia)
• It's the potentially fatal disturbance in brain functions caused by electrolyte imbalance due to overhydration or consuming water rapidly exceeding the body's ability to excrete it
• It often occurs from overconsumption in a specific period of time without receiving essential nutrients

Regulation of Body Water Gain

• Primarily determined by water intake
• Dehydration: water loss is greater than gain, causing decrease in fluid volume and osmolarity
• Stimulates the thirst center in the hypothalamus which increases thirst to normalize body fluids

Regulation of Water and Solute Loss

• Elimination through urine
• Extent of urinary salt loss determines fluid volume
• Hormonal regulation (e.g., Angiotensin, ADH, ANP, and aldosterone) regulates sodium (Na+) and chloride (Cl-) reabsorption in kidneys, impacting water loss

Movement of Water Between Compartments

• Cells maintain similar intracellular and interstitial osmolarity
• Changes in interstitial fluid osmolarity (e.g., increase) will draw water from cells - causing shrinkage
• Osmolarity impacts fluid movement

Movement of Water: Osmolarity

• Water flows in/out of cells via osmosis across cell membranes, based on concentration differences

Water Intoxication

• Drinking water faster than kidneys excreting can lead to convulsions and coma
• Also known as water poisoning or dilutional hyponatremia

Intro: Water Intoxication

• Water intoxication (water poisoning/ dilutional hyponatremia)
• A hazardous disturbance in brain functions caused by electrolyte imbalance stemming from excessive hydration.
• It can be considered toxic
• Frequently occurs when water is consumed in large quantities without the proper intake of necessary nutrients.

Hyponatremia and Athletes

• Athletes are prone to hyponatremia (low sodium level in the blood)
• Caused by excessive sweating, poor electrolyte intake, and high water intake
• Exercise and/or sweating can significantly increase fluid loss, requiring adequate electrolyte intake with water consumption to lessen this effect

Electrolyte Imbalance

• Electrolyte imbalances caused by conditions such as diarrhea or vomiting lead to extracellular fluid depletion
• The conditions can influence water/electrolyte balance, necessitating medical intervention

Edema

• Edema is the accumulation of excess fluid in tissues.
• Can result from various factors, such as allergic reactions that cause capillary leakage

Other Examples

• Three common examples of homeostasis are body temperature, blood pressure, and blood sugar

### Additional information for study notes includes

• The roles of body systems in maintaining fluid and electrolyte balance
• The use of illustrations of fluid compartments
• Emphasis of the critical importance of fluid regulation in a person's health