Anatomy II - Chapter 25 "Fluid, electrolyte, and acid-base homeostasis""

body fluids

• interstitial fluid (ISF)

• cytosol

• blood

• lymph

• CSF

• fluids in serous cavities

• exo and endo crine secretions

*ECM = ISF and fibers

major functions of water in body’s fluids

1. transport of nutrients and waste products

2. functions as solvent for solutes in body

3. necessary for all chemical rxns

4. maintains blood volume

5. helps regulate body temp

total body water

• in standard man: 20-30yo, ~155 lbs → ~60% is water or 92.5 lbs = 42 L = 11 gal

• age, sex, weight, and adipose tissue impact total body water

age and total body water

infants have higher total body water (~65%)

individuals over 60 have a lower total body water (~50%, bc greater proportion of fat tissue)

sex and total body water

women have less body water bc they have more fat than men

(males = 60%, females = 50%)

weight/adipose tissue and total body water

obese ppl have less body water bc of the abundance of fat tissue

fat tissue vs muscle tissue and total body water

fat tissue is ~15% water

muscle tissue is ~70% water

more body fat = less body water (women, elderly, obese)

more muscle fat = more body water (men, youths, athletes)

distribution of H2O/fluid compartments

intracellular fluid compartment=ICF=inside cells (~60% or 26 L)

• cytosol

extracellular fluid compartment=ECF=outside cells (~40% or 16 L)

• ISF

• blood

• lymph

• CSF

• fluids in serous cavities

• exo and endo crine secretions

*ICF and ECF separated by cell membranes

**blood plasma and ISF separated by capillary walls

solute composition of ECF

major electrolyte is sodium

plasma has K+ and Ca2+

ISF only has K+

solute composition of ICF

major electrolyte is potassium

contains Na+ and Mg2+

2 major forces responsible for water movement WITHIN the ECF

movement btw the plasma and ISF is determined by:

1. hydrostatic pressure (HP)

2. osmotic pressure (OP)

exchanges btw plasma ad ISF occurs across capillary walls

*when plasma proteins are reduced or BP is increased, net filtration pressure changes and fluid movement across capillary increases, leads to edema (excess fluid build up in tissues)

water exchange BETWEEN ECF and ICF depends on?

movement btw the ISF and cytosol depends on

1. osmosis! (depends on osmotic gradient/pressure)

occurs across plasma membranes

ECF and ICF are usually in…

osmotic equilibrium meaning no net osmotic movement of water

*water moves btw cells and ISF bc osmotic gradient was created due to a change in SOLUTE concentration in the ISF

osmosis

passive transport

movement of water through a semipermeable membrane into a region of HIGHER solute concentration (water follows salt)

*if a cell is surrounded by hypertonic ISF to its cytosol water goes OUT (crenated/shriveled cell)

**if a cell is surrounded by hypotonic ISF to its cytosol water goes IN (swollen or lysed cells)

water balance

water gained each day is equal to water lost each day

organ systems involved in water balance

• digestive system: primary source of water gain/input

  • oral fluid intake

  • food

  • metabolism

• urinary system: primary route for water loss/output

  • urine

  • sweat

  • feces

  • lungs

metabolic water

water produced within body as a byproduct of metabolism (think back to krebs)

two major factors regulating water balance

1. thirst mechanism: controlled by hypothalamus

2. hormones

   • ADH (hypothalamus): antidiuretic stimulates H2O reabsorption

   • aldosterone (adrenal cortex): inc Na+ and H2O reabsorption

   • natriuretic peptides (cardiac muscle cells): dec Na+ and H2O reabsorption

*in summary: thirst and ADH

dehydration (water deficit)

1. excessive H2O loss from ECF → ECF rises (hypertonic) → cells lose H2O to ECF by osmosis (cells shrink)

2. vomiting, diarrhea, sweating, bleeding

3. dec input or inc output

*results in dry skin/mucosa, “tenting skin“, dec blood volume and BP, fatigue, death

**solution = rehydration

overhydration (water intoxication)

1. excessive H2O enters ECF → ECF concentration falls (hypotonic) → H2O moves into cell by osmosis (cells swell)

2. psychiatric disorders, IV infusions, renal failure

3. inc input or dec output

*results in cerebral edema, confusion and hallucinations, seizures, and coma/death

** solution = fluid restriction or diuretics

electrolytes

conduct electricity, when dissolved, separate into charged ions

(eg. HCl → H+ and Cl-)

electrolytes are obtained from

• foods

• beverages

• metabolic rxns

electrolytes are lost from

• urine (primary route)

• feces

• perspiration

electrolyte concentrations are kept constant in the blood due to what organ

kidneys

*heavy exercise, vomiting, diarrhea = electrolytes lost from body = must be replaced

most abundant ions in the ECF and ICF

Na+ in ECF and K+ in ICF

normal [K+] in ICF = 139 mEq/L and in ECF = 3.9 - 4.5 mEq/L

normal [Na+] in ICF = 10 mEq/L and in ECF = 140 mEq/L

main role of sodium and potassium in the body

sodium potassium pump, used to maintain voltages across cell membranes to carry electrical impulses

how are sodium ions and water balance related

sodium is the dominant ion in ECF and provides 90% of ECF osmotic concentration

• water balance determines sodium concentration NOT the other way around

*H2O movements causes changes in plasma (sodium dilution or concentration)

hypernatremia

hypertonic changes (>145 mEq/L)

1. loss of H2O (dehydration)

2. gain of Na+

water loss is the most common either from inadequate H2O intake or excessive diuretic use

sodium gain from wrong adminstration of hypertonic saline solution, or near drowning in salt water, or salt tablets

mortality rate is 45% across all ages but 79% in geriatric populations

hyponatremia

hypotonic changes (<135 mEq/L)

1. gain of H2O (overhydration)

2. loss of Na+

overhydration from excessive administration of fluids without Na+; water retention due to renal failure

isonatremia

isotonic changes

proportionate changes in water and sodium

1. proportional loss of H2O and Na+: hemorrhage and severe wound damage

2. proportional gain of H2O and Na+: administration of isotonic saline solution or increased aldosterone production → incr reabsorption of H2O and Na+ via kidney tubules

hyperkalemia

increased K+ level above 4.5 mEq/L

caused by:

• kidney failure

• cell trauma (burns, extensive surgeries)

• excessive salt substitutes

hypokalemia

decreased K+ levels below 3.5 mEq/L

caused by:

• overuse of diuretics (cause kidneys to excrete incr K+)

• diarrhea or vomiting or laxative abuse

• poor dietary intake

most common problems with electrolyte imbalance are caused by

imbalance btw gains and losses of Na+ ions

most dangerous problems with electrolytes imbalance are caused by

problems with potassium balance

definition of acid-base balance

body’s precise regulation of pH of it’s fluids, primarily blood

acid = release H+ atoms

base = accept H+ or release OH- ions

pH

concentration of H+ in solution

incr [H+] means decr pH (acidic)

decr [H+] means incr pH (basic)

normal range of blood pH

7.35-7.45

sources and types of acids (H+) in body

1. fixed acids

2. volatile acids

fixed acids

acids that do not leave solution; once produced they remain in body fluids until eliminated by kidneys

eg. aa, lactic acid, uric acid, nucleic acids

volatile acids

easily evaporated

acids that can leave the body and enter the atmosphere

eg. carbonic acid (CO2 + H2O ←→ H2CO3; H2CO3 ←→ H+ + HCO3-)

mechanisms regulating the pH level in the body

1. chemical buffer systems - act within a fraction of a second

   • bicarbonate buffer

   • phosphate buffer

   • protein buffer

2. respiratory centers - act within 1 - 3 mins

   • CO2 removal (incr CO2 means decr pH)

3. renal mechanisms - most potent but require time (hours to a day) to resist pH changes

chemical buffer systems extra

resist abrupt changes in blood pH by releasing H+ (acting as acids) when the pH rises and by binding H+ (acting as bases) when the pH drops

*protein buffers

types of pH imbalances

alkalosis = >7.45

acidosis = <7.35

acidosis

low pH or incr [H+]

dangerous bc H+ breaks chemical bonds, changes shape of complex molecules, disrupts plasma membranes, and impairs tissue functions

two classes of causes for acidosis/alkalosis

1. respiratory acid-base disorders

2. metabolic acid-base disorders

respiratory acid-base disorders

caused primarily by lung disorders and breathing problems

related to abnormal blood CO2 levels

metabolic acid-base disorders

caused by imbalance in the production of acids/bases and their excretions via kidneys

consumption of large amounts of Na+ (baking soda, bicarbonate, NaHCO3) could lead to metabolic alkalosis