BIO 252 Anatomy and Physiology Module 8
AP 8– Fluid, Electrolyte, and Acid-Base Balance
8.1 – Body Fluids
Water
● Essential for life and is sometimes called a “nutrient”
○ It does not technically fit the definition of a nutrient because it does not provide energy
or structural molecules
○ But– it is still a necessary component for the body to function properly
Major Functions of Water
● Temperature regulation
○ Sweating and evaporation prevent overheating
● Cell Structure and Integrity
○ Major Component of cells, tissues, and organs
○ Maintains cell shape and supports cellular processes
● Nutrient Digestion and Absorption
○ Dissolves nutrients and transports them across the GI tract
● Waste Removal
○ Essential for urine formation and excretion of metabolic waste
● Lubrication
○ Reduces friction in joints and serous membranes
● Blood Volume and Blood Pressure
○ Major component of plasma affects perfusion of organs
● Solvent
○ Universal solvent allowing chemical reactions to occur
● Key Idea: without water, metabolism and homeostasis fail
Homeostasis and Solutions
● Homeostasis
○ Maintenance of stable internal conditions
○ Requires precise regulation of water and solute concentrations
● Solutions
○ Solvent
■ Substance doing the dissolving (water)
○ Solute
, ■ Substances being dissolved (ions, proteins,
nutrients) ● Electrolytes
○ Solutes that dissociate into ions and carry electrical
charge ○ Examples:
■ Sodium (Na+)
■ Potassium (K+)
■ Chloride (Cl-)
Osmosis Overview
● Osmosis
○ Movement of water across a semi-permeable membrane
■ Water moves from low solute concentration high solute concentration
● Osmotic Gradient
○ The difference in solute concentration across a semipermeable membrane
■ Causes water to move until equilibrium is reached
● Example:
○ If one side has more solutes, the water moves toward that side
Body Water Content Across the Lifespan
● The percentage of water in the body depends on body composition
○ Lean body mass (muscle mass) contains more water than adipose
tissue (fat) ■ Fat is hydrophobic
● The percent of body water changes with development
○ Because the relative amount of each type of tissue in the body changes over time
■ Each of these tissues contain different amounts of water
● Muscle & organs: high water content
● Fat: very low water content
● Bone: relatively low water content
■ As a person grows, the proportion of the body that is made up of muscle,
fat, bone, or tissue changes ● Average percentages:
○ Infants: ~ 75%
■ Low fat, low bone mass
○ Adult males: ~ 60%
■ Higher muscle mass
○ Adult females: ~ 50%
■ Higher fat content, less skeletal muscle mass
○ Elderly: lowest percentage (as low as ~ 45%)
■ Less muscle mass, decreased thirst, medications that eliminate fluid
● Water Content in Organs
○ Brain and kidneys highest (80–85%)
, ○ Teeth lowest (8–10%)
Fluid Compartments
● Substances in the body can be discussed in terms of their specific fluid
compartment
○ Fluid compartments are distinct spaces/locations within the cell where fluids are
contained
■ They are separate from other compartments by some form of physical barrier
● E.g. cell membranes or blood vessel walls ○ 2 main fluid compartments:
■ IFC
■ EFC
Analogy Body has millions of tiny water balloons (cells) floating in a bigger environment… IFC
(intracellular fluid) is the water inside the balloons and EFC (extracellular fluid) is the water outside the
balloon
● Plasma and interstitial fluid are also floating around the compartment of EFC
Intracellular Fluid Compartment
(IFC) ● Fluid inside the cells
○ The system that includes all the fluid enclosed in cells by their plasma membranes
● Makes up ~ 60% of total body water
○ In an average sized male ICF accounts for a little over 20 L of fluid
● Principal component of the cytosol/cytoplasm
● This fluid volume tends to be very stable
○ Very stable because the amount of water in living cells is closely regulated ■
If the amount of water in the cell falls too low:
● cell shrinks
● cytosol becomes too concentrated with solutes to carry on normal cellular activities ■ If
too much water enters the cell:
● the cell may burst and be destroyed (lysis)
Extracellular Fluid (ECF)
● Fluid located outside the cells
○ Surrounds all cells in the body
● Accounts for the other ~ 1/3rd ( or 33%) of total body water
● 2 Primary Constituents of ECF
○ Plasma (liquid portion of blood)
■ ~ 20% of the ECF is found in the plasma
● Plasma circulates through the body in blood vessels
● Plasma’s main role is transport, carrying a range of materials, including:
AP 8– Fluid, Electrolyte, and Acid-Base Balance
8.1 – Body Fluids
Water
● Essential for life and is sometimes called a “nutrient”
○ It does not technically fit the definition of a nutrient because it does not provide energy
or structural molecules
○ But– it is still a necessary component for the body to function properly
Major Functions of Water
● Temperature regulation
○ Sweating and evaporation prevent overheating
● Cell Structure and Integrity
○ Major Component of cells, tissues, and organs
○ Maintains cell shape and supports cellular processes
● Nutrient Digestion and Absorption
○ Dissolves nutrients and transports them across the GI tract
● Waste Removal
○ Essential for urine formation and excretion of metabolic waste
● Lubrication
○ Reduces friction in joints and serous membranes
● Blood Volume and Blood Pressure
○ Major component of plasma affects perfusion of organs
● Solvent
○ Universal solvent allowing chemical reactions to occur
● Key Idea: without water, metabolism and homeostasis fail
Homeostasis and Solutions
● Homeostasis
○ Maintenance of stable internal conditions
○ Requires precise regulation of water and solute concentrations
● Solutions
○ Solvent
■ Substance doing the dissolving (water)
○ Solute
, ■ Substances being dissolved (ions, proteins,
nutrients) ● Electrolytes
○ Solutes that dissociate into ions and carry electrical
charge ○ Examples:
■ Sodium (Na+)
■ Potassium (K+)
■ Chloride (Cl-)
Osmosis Overview
● Osmosis
○ Movement of water across a semi-permeable membrane
■ Water moves from low solute concentration high solute concentration
● Osmotic Gradient
○ The difference in solute concentration across a semipermeable membrane
■ Causes water to move until equilibrium is reached
● Example:
○ If one side has more solutes, the water moves toward that side
Body Water Content Across the Lifespan
● The percentage of water in the body depends on body composition
○ Lean body mass (muscle mass) contains more water than adipose
tissue (fat) ■ Fat is hydrophobic
● The percent of body water changes with development
○ Because the relative amount of each type of tissue in the body changes over time
■ Each of these tissues contain different amounts of water
● Muscle & organs: high water content
● Fat: very low water content
● Bone: relatively low water content
■ As a person grows, the proportion of the body that is made up of muscle,
fat, bone, or tissue changes ● Average percentages:
○ Infants: ~ 75%
■ Low fat, low bone mass
○ Adult males: ~ 60%
■ Higher muscle mass
○ Adult females: ~ 50%
■ Higher fat content, less skeletal muscle mass
○ Elderly: lowest percentage (as low as ~ 45%)
■ Less muscle mass, decreased thirst, medications that eliminate fluid
● Water Content in Organs
○ Brain and kidneys highest (80–85%)
, ○ Teeth lowest (8–10%)
Fluid Compartments
● Substances in the body can be discussed in terms of their specific fluid
compartment
○ Fluid compartments are distinct spaces/locations within the cell where fluids are
contained
■ They are separate from other compartments by some form of physical barrier
● E.g. cell membranes or blood vessel walls ○ 2 main fluid compartments:
■ IFC
■ EFC
Analogy Body has millions of tiny water balloons (cells) floating in a bigger environment… IFC
(intracellular fluid) is the water inside the balloons and EFC (extracellular fluid) is the water outside the
balloon
● Plasma and interstitial fluid are also floating around the compartment of EFC
Intracellular Fluid Compartment
(IFC) ● Fluid inside the cells
○ The system that includes all the fluid enclosed in cells by their plasma membranes
● Makes up ~ 60% of total body water
○ In an average sized male ICF accounts for a little over 20 L of fluid
● Principal component of the cytosol/cytoplasm
● This fluid volume tends to be very stable
○ Very stable because the amount of water in living cells is closely regulated ■
If the amount of water in the cell falls too low:
● cell shrinks
● cytosol becomes too concentrated with solutes to carry on normal cellular activities ■ If
too much water enters the cell:
● the cell may burst and be destroyed (lysis)
Extracellular Fluid (ECF)
● Fluid located outside the cells
○ Surrounds all cells in the body
● Accounts for the other ~ 1/3rd ( or 33%) of total body water
● 2 Primary Constituents of ECF
○ Plasma (liquid portion of blood)
■ ~ 20% of the ECF is found in the plasma
● Plasma circulates through the body in blood vessels
● Plasma’s main role is transport, carrying a range of materials, including:
