Human Body Fluids and Homeostasis

Body Fluids

• Extracellular fluid (ECF) is the fluid environment outside the cells (1/3 of total body water).
• ECF contains ions, oxygen, nutrients, and waste products.
• Two components of ECF:
  • Plasma (inside blood cells)
  • Interstitial fluid (surrounding cells)
• Intracellular fluid (ICF) is the fluid contained within all body cells (2/3 of total body water).
• ICF is rich in potassium (K+) and has a lower sodium (Na+) concentration.
• ICF contains negatively charged proteins.

Balancing Internal and External Environments

• Cells continuously exchange nutrients and waste products with their surroundings.
• ICF is influenced by interstitial fluid, which is in turn affected by plasma, ultimately influenced by the organ systems it passes through.
• This dynamic interplay ensures a stable internal environment.
• Internal environment refers to the fluid surrounding cells (extracellular fluids)

Homeostasis

• Homeostasis refers to the maintenance of a relatively constant and stable internal environment, specifically the extracellular fluids.
• This stability is achieved through intricate physiological mechanisms, each organ's structure being designed for optimal functional performance.
  • Example: The chest cavity protects the heart and lungs, and its movement facilitates breathing.
• The body is structurally organized into a whole functional unit, enabling homeostasis.

Levels of Organization

• The body is organized into these levels:
  • Chemical level: Involves atoms and molecules; basic building blocks of life.
  • Cellular level: Cells are the fundamental living unit, performing essential life processes.
  • Tissue level: Tissues are groups of similar cells working together for a specific function.
  • Organ level: Organs are composed of two or more tissue types, coordinated for a specialized task.
  • Body system level: A group of related organs functioning together.
  • Organismic level: This refers to the whole human body, comprised of various organ systems.

Levels of Organization (Continued)

• Chemical Level Examples:
  • Atoms: Oxygen, nitrogen, carbon, hydrogen.
  • Molecules: Water, carbon dioxide, carbohydrates (CHO), proteins.
• Cellular Level Examples:
  • Muscle cells, nerve cells.
• Tissue Level Examples:
  • Epithelial tissue (covering), connective tissue (support), muscle tissue (movement), nervous tissue (communication).
• Organ Level Examples:
  • Skin, femur, heart, kidney.
  • Example: Stomach:
    • Epithelium: Lines the stomach’s inner surface.
    • Smooth muscle: Contributes to the stomach's wall.
    • Nervous tissue: Controls muscle contractions and glandular secretions.
    • Connective tissue: Binds all tissues together.
• Body System Level Examples:
  • Skeletal system, digestive system.
• Organismic level:
  • The human body.

Levels of Organization (Continued)

• The body has three openings to the external environment:
  • Respiratory system: Takes in oxygen and eliminates CO2.
  • Digestive system: Processes food and eliminates unabsorbed material.
  • Urinary system: Eliminates waste products from the body.

Body Fluids (Continued)

• Total body water is approximately 60% of the body weight in a healthy adult, but this percentage can vary with age and gender.
• Water content decreases with age; newborn's body is about 80% fluid.
• Women have a lower water content (50-55%) than men due to higher fat tissue percentage.
• Water's properties make it ideal for biological systems:
  • High specific heat: Regulates temperature.
  • Capillary action: Essential for processes like tear production and breastfeeding.
  • Excellent solvent: Enables dissolving and transport of ions (Na+, K+, Cl-).
  • Redox reactions: Involved in killing pathogens.

Cells

• The cell membrane allows passage of certain substances while restricting others.
• Lipid-soluble materials can cross the membrane, while water-soluble (lipid-insoluble) substances require channels.

Cell Membrane

• The cell membrane is primarily composed of phospholipids, which are amphipathic molecules.
• Phospholipid bilayer:
  • Hydrophilic (water-soluble) heads form the surfaces.
  • Hydrophobic (water-insoluble) tails form the interior.
• This structure makes the membrane permeable to lipid-soluble substances.

Movements into and Out of the Cell

• Passive (Physical) Processes:
  • Net movement down a concentration gradient, from high to low concentration.
  • Does not require energy (ATP).
  • Includes:
    • Simple diffusion
    • Facilitated diffusion
    • Osmosis (only for water)
• Active (Physiological) Processes:
  • Net movement against a concentration gradient, from low to high concentration.
  • Requires energy (ATP).
  • Includes:
    • Primary active transport
    • Secondary active transport
• Note: At equilibrium, the net movement is zero.
• Except for small, neutral molecules, most biologically relevant substances cannot readily pass through the cell membrane and require facilitated transport.

Simple Diffusion

• Cell membrane is permeable to:
  • Non-polar molecules (oxygen).
  • Lipid-soluble molecules (steroids).
  • Small polar covalent bonds (carbon dioxide).
  • Water (small size and lack of charge).
• Degree of diffusion depends on lipid solubility.
• Cell membrane is impermeable to:
  • Large polar molecules (glucose).
  • Charged inorganic ions (sodium).

Simple Diffusion (Continued)

• Substances pass through intermolecular spaces in the membrane (simple diffusion), primarily lipid-soluble substances and gases).
• This occurs whenever there is a concentration difference across the membrane (the membrane is permeable to the diffusing substance).
• Simple diffusion is an energy-independent process.

Facilitated Diffusion

• Facilitated diffusion involves the movement of lipid-insoluble or water-soluble substances across the cell membrane.
• It occurs down their concentration gradient with the assistance of membrane proteins.
• Substances transported by facilitated diffusion include:
  • Potassium (K+).
  • Sodium (Na+).
  • Calcium (Ca2+).
  • Glucose.
  • Amino acids.
  • Urea.
• Facilitated diffusion is also an energy-independent process.

Levels of Organization

• The human body is structurally organized into a whole functional unit, from the chemical to the organismic level.
• The organismic level is made up of 12 systems.
• Chemical level: comprises atoms and molecules, examples include Oxygen, Nitrogen, Carbon, hydrogen, water, CO2, CHO, and Proteins.
• Cellular level: the basic live organizational structure of the human body, the smallest unit that can perform life's necessary processes, examples include muscle cells and nerve cells.
• Tissue level: a group of similar cells (structure & specialized functions) that work together on one task, examples include epithelial, connective, muscle, and nerve tissues.
• Organ level: consists of two or more types of primary tissues that function together to perform a particular function or functions, examples include skin, femur, heart, kidney, stomach.
• Body System level: a collection of related organs with a common function, sometimes an organ is part of more than one system, examples include skeletal system and digestive system.
• Organismic level: the human (one living individual).

Body Fluids

• The total body water of a healthy adult is 60% of their body weight.
• Water content decreases with age, a newborn has about 80% fluid content, while a healthy female adult has 50-55%.
• Water's properties make it essential for the body:
  • Specific heat: water resists boiling and freezing, maintaining stable temperature.
  • Capillary action: aids in processes like tear production and breastfeeding.
  • Solvent: dissolves substances like Na+, K+, Cl- for transportation through channels.
  • Redox reactions: helps kill bugs through the production of “ROS.”

Homeostasis & Controls

• Homeostasis refers to the maintenance of a dynamic steady state in the internal environment.
• The internal environment remains relatively constant despite external changes.
• Homeostasis is crucial for cell survival and function.
• Each cell contributes to maintaining a stable internal environment.
• Factors Homeostatically Regulated:
  • Concentration of nutrients (glucose, O2, CO2, and waste products)
  • Concentration of water, salt, and other electrolytes
  • pH
  • Blood volume and pressure
  • Body temperature
• Success or failure to compensate for internal changes leads to:
  • Successful compensation: Homeostasis re-established.
  • Failure to compensate: Pathophysiology, illness, and potentially death.

Homeostatic Control Mechanisms

• These mechanisms involve three parts:
  • Receptor: provides information about the stimuli.
  • Control Center: Sets the ideal value for a specific factor (set point).
  • Effector: Responds to changes and corrects them.
• Negative Feedback Loops are central to Homeostasis:
  • Sensor: Monitors internal conditions and detects changes.
  • Integrating center: Receives and integrates information.
  • Effector: Responds to changes, restoring the condition to normal levels.

Cell Membrane

• The cell membrane is selectively permeable, allowing some substances to pass while blocking others.
• It is permeable to lipid-soluble substances, and impermeable to lipid-insoluble (water-soluble) substances, which need to pass through channels.
• The cell membrane's composition includes phospholipids, which are amphipathic molecules.
• The phospholipid bilayer has water-soluble heads that form surfaces (hydrophilic), and water-insoluble tails that form the interior (hydrophobic), creating a barrier.

Movement Into and Out of the Cell

• Passive processes: Movement down a concentration gradient (high to low), does not require ATP.
  • Simple diffusion
  • Facilitated diffusion
  • Osmosis (for water only)
• Active processes: Movement against a concentration gradient (low to high), needs energy.
  • Primary Active transport
  • Secondary Active transport

Simple Diffusion

• The movement of a substance from an area of high concentration to an area of low concentration, down the concentration gradient, without needing energy.

Secondary Active Transport

• Uses the energy stored in the concentration gradient of one molecule (typically Na+) to move another molecule, which can be in the same direction (co-transporter) or opposite direction (counter-transporter)

Membrane Resting Potential

• A constant potential difference across the resting cell membrane.
• This potential is crucial for the cell's ability to fire an action potential, typically around -70 mV.
• Neurons' basic signaling properties depend on changes in the resting potential.

Maintaining a Dynamic Steady State

• The internal environment of the body is relatively constant despite changes in the external environment.
• This stability is called homeostasis and is essential for cell survival and function.
• Homeostasis is achieved through dynamic regulation and adjustments within a narrow range.

Factors Homeostatically Regulated

• Concentration of nutrients: Glucose, oxygen (O2), carbon dioxide (CO2), and waste products.
• Concentration of water, salt, and other electrolytes.
• pH
• Blood volume and pressure.
• Body temperature.

Homeostasis & Controls

• Successful compensation: Homeostasis is reestablished through successful compensation.
• Failure to compensate: Leads to pathophysiology which manifests as illness or death.

Homeostatic Control Mechanisms

• These mechanisms monitor the internal environment and correct deviations.
• They are comprised of:
  • Receptor: Detects and provides information about the stimuli.
  • Control center: Determines the set point for the regulated factor.
  • Effector: Elicits responses that change conditions in the internal environment.

Homeostasis: Dynamic Stability

• Homeostasis is achieved through negative feedback loops.
• These loops involve:
  • Sensor: Detects changes in the internal environment.
  • Integrating center (controller): Receives and integrates information.
  • Effector: Responds to changes and returns conditions to normal levels.

Feedback Control

• Negative feedback: Initial change triggers a response that suppresses the initial change.
  • Examples: body temperature, blood pressure, and glucose regulation.
• Positive feedback: Initial change triggers a response that amplifies the initial change.
  • Examples: blood clotting, urination, LH surge before ovulation, sodium (Na+) inflow in nerve signals, uterine contraction during childbirth.

Feed-forward Control

• Anticipatory response to a change before feedback signals occur.
• Example: Shivering before diving into cold water, salivation in response to the smell of food.

Human Cell

• Humans are multicellular organisms with 50-100 trillion cells.
• Cells differentiate to specialize in specific functions.
• Cellular specialization is essential for maintaining the body's overall function.

Body Fluids

• Extracellular fluid (ECF): Fluid outside the cells (1/3 of total body water)
  • Contains ions, oxygen, nutrients, and waste products.
  • Two components:
    • Plasma: Fluid inside blood vessels.
    • Interstitial fluid: Fluid surrounding cells.
• Intracellular fluid (ICF): Fluid inside cells (2/3 of total body water)
  • Contains high potassium (K+) levels, low sodium (Na+), and negatively charged proteins.

Balancing Internal and External Environments

• Cells exchange nutrients and waste products with their surroundings.

• The flow of substances is interconnected between:

  • Intracellular fluid (ICF): Conditioned by interstitial fluid.
  • Interstitial fluid (ISF): Conditioned by plasma.
  • Plasma: Conditioned by the organ systems it passes through and the external environment.

• The internal environment is essentially the extracellular fluid.

Levels of Organization

• The human body is organized into multiple levels, starting with cells.
• Tissues are groups of similar cells that work together.
• Organs are composed of different tissues that work together to perform specific functions.
• An example of an organ is the stomach, which contains epithelial, smooth muscle, nervous, and connective tissues.
• Body systems are collections of related organs with a common function.
• For example, the digestive system is composed of the mouth, esophagus, stomach, small intestine, and large intestine.
• The human body is an organism, composed of all the body systems working together.

Body Fluids

• The total body water in a healthy adult is 60% of body weight.
• The body water content depends on age and gender, with newborns having a higher percentage of body water than adults.
• Water is important for several reasons.
  • It has a high specific heat, making it difficult to boil or freeze.
  • It exhibits capillary action, as seen in tears and breastfeeding.
  • It is an excellent solvent, allowing ions like Na+, K+, and Cl- to dissolve and pass through channels.
  • It is involved in redox reactions to kill bugs.

Negative Feedback

• Negative feedback mechanisms are used to maintain homeostasis in the body, where an initial change triggers a response that counteracts or reduces the change.
• An example is blood glucose regulation.
  • When blood glucose levels rise after eating, the pancreas releases insulin.
  • Insulin lowers blood glucose levels, bringing them back to normal.

Positive Feedback

• Positive feedback mechanisms amplify the initial change, resulting in an escalating, self-perpetuating response.
• These mechanisms are typically short-lived and do not require continuous adjustments.
• Examples include:
  • Blood clotting
  • Urination
  • LH (luteinizing hormone) increase before ovulation
  • Na+ inflow in the genesis of nerve signals
  • Contraction of the uterus during childbirth (parturition)

Feed-forward Control

• Feed-forward control involves anticipating a change and preparing the body for it.
• This proactive response occurs before feedback signals are received.
• Examples include:
  • Shivering before diving into cold water.
  • Salivation in response to smelling food.

Human Cell

• The human body is multicellular, containing trillions of cells.
• Cells specialize through a process called differentiation.
• Differentiation leads to variations in cell size and shape, reflecting their unique functions.

Basic Cell Functions

• Cells perform essential functions:
  • Obtaining nutrients and oxygen from the environment.
  • Performing chemical reactions to provide energy for the cell.
  • Eliminating CO2 and waste products.
  • Synthesizing cellular components, such as proteins.
  • Controlling the movement of materials into and out of the cell.
  • Sensing and responding to environmental changes.
  • Reproduction (except for nerve and muscle cells).

Specialized Cell Functions

• Each cell type has a specialized function.
• For example, white blood cells phagocytize foreign materials, while red blood cells transport oxygen.

Cell Membrane

• The cell membrane, or plasma membrane, is a thin and mechanically weak barrier surrounding each cell.
• It functions to:
  • Maintain cell integrity.
  • Control the movement of substances in and out of the cell (selective permeability).
  • Regulate cell-cell interactions.
  • Act as an interface between the cytoplasm and the extracellular milieu.

Cell Membrane Importance

• The cell membrane is crucial because it creates a barrier between the intracellular fluid (ICF) and the extracellular fluid (ECF).
• If the cell membrane ruptures, the cell dies.
• The cell membrane maintains concentration differences between the ICF and ECF, including:
  • Higher K+ concentration inside than outside.
  • Higher Na+ concentration outside than inside.
  • Higher Cl- concentration outside than inside.
  • Higher Ca++ concentration outside than inside.
  • Higher protein concentration inside than outside.
  • Slightly alkaline pH outside (7.4) and neutral pH inside (7).

Composition of the Cell Membrane

• The cell membrane is mainly composed of:
  • Proteins (55%)
  • Phospholipids (25%)
  • Cholesterol (13%)

Types of Membrane Transport

• Simple Diffusion:

  • Occurs directly through the cell membrane.
  • Permeable to non-polar molecules (O2), lipid-soluble molecules (steroids), small polar covalent bonds (CO2), and water (small size, lack of charge).
  • The degree of diffusion depends primarily on lipid solubility.
  • It is energy independent.

• Facilitated Diffusion:

  • Requires membrane proteins to transport substances across the membrane.
  • Transports lipid-insoluble or water-soluble substances down their concentration gradients.
  • Examples: K+, Na+, Ca2+, glucose, amino acids, urea.
  • It is energy independent.

• Active Transport:

  • Moves substances across a membrane against their concentration gradients, requiring energy.
  • Requires carrier proteins.
  • Includes primary and secondary active transport.

• Primary Active Transport:

  • Utilizes the direct breakdown of ATP or other high-energy compounds to power transport.
  • Examples: Na+/K+ pump, Ca++ active transport, active transport of H+ in gastric glands and kidneys, H+/K+ pump (proton pump in the stomach).

• Secondary Active Transport:

  • Derives energy indirectly from concentration gradients established by primary active transport.
  • Examples: Na+/Glucose co-transport in epithelial cells of the intestine.

Na+/K+ Pump

• The Na+/K+ pump is a primary active transport system found in all cells.
• It pumps three Na+ ions out of the cell and two K+ ions into the cell, maintaining a critical concentration gradient.
• This 3:2 ratio ensures that the cell remains electrically negative, crucial for various cellular processes.

Levels of Organization

• An organ is made up of two or more tissue types that work together
• A body system is a collection of organs that share a common function
• The organism is a living individual
• The human body has three openings to the external environment: the respiratory system, digestive system, and urinary system

Body Fluids

• Total water in a healthy adult is about 60% of body weight
• Women have less total body water than men because they have more fatty tissue
• Water's properties make it essential for life:
  • It has a high specific heat, so it's difficult to boil or freeze
  • It exhibits capillary action, which is important for tears and lactation
  • It's a good solvent, allowing for dissolution and transport of ions
  • It participates in redox reactions, which help kill pathogens.

Homeostasis

• The internal environment of the body is maintained within a narrow range despite external changes
• All organs are designed to contribute to the maintenance of homeostasis
• Factors regulated by homeostasis include:
  • Nutrient concentrations (glucose, oxygen, carbon dioxide, waste products)
  • Water, salt, and electrolyte concentrations
  • pH.
  • Blood volume and pressure
  • Body temperature

Homeostasis & Controls

• Successful compensation for internal changes leads to reestablishment of homeostasis
• Failure to compensate results in illness, pathophysiology, and ultimately death

Homeostatic Control Mechanisms

• These mechanisms monitor and correct changes in the internal environment
• They consist of three parts:
  • Receptor: detects changes in the internal environment
  • Control center: determines the set point for the regulated variable
  • Effector: elicits responses to alter the regulated variable

Regulation of Internal Constancy = Homeostasis

• Homeostasis is a dynamic process with fluctuations around a setpoint
• It relies on negative feedback loops:
  • A sensor detects changes in the internal environment
  • The integrating center (controller) receives and processes the information
  • The effector responds to changes in the internal environment

Feedback Control

• Feedback control can be positive or negative

Transported substance

• Facilitated diffusion is a type of passive transport that utilizes carrier proteins or channels
• Facilitated diffusion via carriers involves the binding of a substance to a carrier protein, which undergoes a conformational change to release the substance on the other side of the membrane
• Facilitated diffusion through channels allows free movement of specific ions or molecules through channel proteins
• Channels are selectively permeable and can be opened or closed by gated mechanisms, including voltage-gated channels and chemically-gated (ligand-gated) channels

Osmosis

• Osmosis refers to the movement of water across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration
• It's also the movement of water from a region of lower solute concentration to a region of higher solute concentration
• Osmosis is important at cellular level, causing cells to shrink or swell
• Osmosis also occurs at the tissue level, through epithelial cells in the digestive system and kidney, as well as through capillary walls.

Cell membrane Physiology

• Osmotic Pressure (OP) is the concentration of solutes inside a cell
• Humans cells have an osmotic pressure equivalent to 0.9% NaCl solution, referred to as "normal saline" or "physiologic saline"
• Hypotonic: OP of the extracellular fluid is less than the OP of the intracellular fluid, causing water to enter the cell
• Hypertonic: OP of the extracellular fluid is greater than the OP of the intracellular fluid, causing water to leave the cell
• Isotonic: OP of the extracellular fluid is equal to the OP of the intracellular fluid, resulting in a hydrostatic equilibrium of water.

Secondary Active Transport

• Involves the use of the energy stored in the concentration gradient of one substance to move another substance across the cell membrane
• Co-transporters move both substances in the same direction
• Counter-transporters move substances in opposite directions

Movements Into and Out of the Cell

• Active transport requires energy and specific membrane proteins
• Active transport enables the movement of substances against their concentration gradient
• Facilitated diffusion requires specific membrane proteins but does not require energy
• Simple diffusion does not require specific membrane proteins or energy
• The difference between facilitated diffusion and active transport lies in the direction of substance movement relative to the concentration gradient.

Membrane Resting Potential

• A constant potential difference across the resting cell membrane
• The cell's ability to fire an action potential is based on its ability to maintain the resting potential at ~ -70mV
• Changes in resting potential influence the signaling properties of neurons

Explore the essential functions of body fluids, including extracellular and intracellular fluid. This quiz delves into the components, balance, and significance of body fluids in maintaining homeostasis. Test your knowledge on how these fluids interact to create a stable internal environment.