Ch. 26 Anatomy Exam 3 - Fluid, Electrolyte, and Acid-Base Balance

Body Fluids

water and dissolved solutes in the body

What does the body regulate to maintain homeostasis?

The volume and composition of the body fluids

Intracellular Fluid (ICF)

Fluid INSIDE cells, about 2/3 total body fluids

Extracellular Fluid (ECF)

Fluid OUTSIDE cells, about 1/3 total body fluids

How many ECF compartments are there?

2

Plasma

Fluid component of blood

Interstitial fluid (IF)

Fluid in spaces between cells, includes lymph, CSF, serous fluid, synovial fluid, digestive tract secretions.

Extracellular Fluid Volume

volume = 15 L

20% of body weight

Plasma Fluid Volume

volume = 3 L

Interstitial Fluid Volume

volume = 12 L

20% of ECF

Intracellular Fluid Volume

volume = 25 L

40% of body weight

Total body water volume

Volume = 40 L

60% of body weight

Intracellular fluid (ICF) + Interstitial fluid (IF) + Plasma = total body water

Composition of Body Fluids

Water and solutes (60% of body)

Solutes consist of :

- Electrolytes

- Nonelectrolytes

Electrolytes

substances that dissociate and release ions in solution

Ex: salts, acids, and bases

Nonelectrolytes

Substances that do not dissociate, do not release ions in solution

Ex: glucose, urea, creatinine, lipids

Why do electrolytes have a greater effect on fluid movements than nonelectrolytes?

Electrolytes dissociate and release more particles in solution

Osmolarity equation

Osmolarity = # of solute particles / 1L per water

Na+

- High plasma (part of ECF)

- High IF (part of ECF)

- Low ICF

K+

- Low plasma (part of ECF)

- Low IF (part of ECF)

- High ICF

Protein

- Medium plasma (part of ECF)

- Low IF (part of ECF)

- High ICF

Fluid movement

continuous intermixing of body fluids in different compartments

About 2.5 liters of water

gained and lost per day

Water gain per day

- metabolism 10%

- foods 30%

- Beverages 60%

water loss per day

- feces 4%

- sweat 8%

- Insensible loss via skin and lungs 38%

- urine 60%

most body fluids are isotonic

300 mOsmolar

if water loss > water gain

Dehydration occurs (osmolarity increases)

if water gain > water loss

Excess water in body (osmolarity decreases)

hypertonic

greater than 300

hypotonic

less than 300

consequences of dehydration

osmolarity increases, cells shrink

consequences of water gain

osmolarity decreases, cells swell

The thirst center is located in

the hypothalamus which contains osmoreceptors

Osmoreceptors

sensors that detect osmolarity

Thirst center responses that correct for dehydration

- Induces thirst - response that corrects the imbalance

- Releases ADH (hormone) - increases water reabsorption

when osmolarity is too high

dehydration occurs

thirst center responses that correct for an excess of water (imbalance - osmolarity is too low)

- inhibits thirst

- inhibits ADH release (facilitates water reabsorption)

Na+ is

regulated by tubular reabsorption

tubular reabsorption

how much is reabsorbed to blood

High BP (too much sodium) (imbalance), high blood volume triggers ANP release ---> decreases Na+ reabsorption

Results in lower BP and blood volume

most abundant ion in ICF

Na+

Low BP (too little sodium) (imbalance), low blood volume triggers Aldosterone release ---> increases Na+ reabsorption

Results in higher BP and blood volume

Aldosterone

A hormone that regulates the body's salt and water balance which is crucial for maintaining blood pressure and blood volume

Atrial Natriuretic Peptide (ANP)

A hormone, secreted by the heart, that normally reduces blood pressure, inhibits drinking, and promotes the excretion of water and salt at the kidneys.

K+ is regulated by

tubular secretion

Tubular secretion

The process where substances are transported from the blood into the renal tubules to be excreted in urine. Eliminates waste products, toxins, and excess ions.

High blood K+ (imbalance)

triggers an increase in secretion of K+ into urine, results in lowering the blood K+

Low blood K+ (imbalance)

inhibits secretion of K+ into urine, results in conserving the K+ in blood

pH

a measure of the H+ ion concentration in solution

More acidic, More H+

<7 pH

Less acidic, Less H+, More Basic

>7 pH

Neutral pH

7

Arterial plasma

7.4 pH - slightly basic

Venous plasma and IF

7.35 pH - slightly basic

ICF

7.0 - Neutral

pH imbalances of arterial plasma

- pH > 7.45 called Alkalosis

- pH < 7.35 called Physiological Acidosis

Alkalosis

ph > 7.45 - too basic, alkaline, too few H+

Physiological Acidosis

pH < 7.35 - too acidic, too many H+

There are 3 mechanisms to regulate acid base balance of the blood

- Buffers (short term)

- Respiratory compensation (short term)

- Renal compensation (long term)

Buffers

weak acids or weak bases which minimize changes in pH

Acids

substances that release H+ ions in solution

Bases

substances that remove H+ ions from solution

What type of acid completely dissociates into its ions?

Strong acids.

What type of acid does not dissociate completely?

Weak acids.

Weak acids:

- carbonic acid (H2CO3)

- dihydrogen phosphate (H2PO4-1)

Weak bases:

- Bicarbonate (HCO3-1)

- Monohydrogen phosphate (HPO4-2)

Acidic amino acids:

aspartic acid, glutamic acid

Basic amino acids:

lysine, arginine, histidine

generalized structure of all amino acids

R group

How buffers work to correct for pH imbalances:

- if pH is too low (too many H+), the weak base removes H+ from solutions, results in raising the pH

- if pH is too high (too few H+), the weak acid releases H+ into solution, results in lowering the pH

if pH is too low (too many H+)

the weak base removes H+ from solutions, results in raising the pH

if pH is too high (too few H+)

the weak acid releases H+ into solution, results in lowering the pH

Respiratory Compensation

corrects blood pH imbalances by changing breathing

if blood pH <7.35, respiratory compensation by hyperventilation

results in raising pH of blood (respiratory compensation)

if blood pH >7.45, respiratory compensation by slow, shallow breathing

results in lowering the pH of blood

Renal compensation

kidneys correct for pH imbalances long term

if imbalances is acidosis, then the kidneys compensate by reabsorbing more bicarbonate

results in raising blood pH

reabsorption =

= raises blood pH

if imbalance is alkalosis, then the kidneys compensate by reabsorbing more H+ ions

results in lowering the pH of blood

which fluid has the highest protein concentration?

- Intracellular fluid

What are the 2 responses of the body that correct for dehydration?

- the thirst mechanism (promoting water intake)

- the increased secretion of antidiuretic hormone (ADH) (promoting water retention by the kidneys).

Give 3 examples of amino acids having a basic R group:

1. lysine

2. arginine

3. histidine

How does breathing change to compensate for acidosis?

The body begins to breathe faster and deeper, a process called hyperventilation.

What specific chemical reaction does carbonic anhydrase catalyze?

CO2+H2O⇌H2CO3⇌HCO3−+H+

What is the main difference in composition between the plasma and the IF?

 

The plasma has more proteins than the IF.

Which fluid contains 2/3 of the total fluids in the body?

ICF

Where is the thirst center located?

hypothalamus 

Which buffer works mainly in the ICF?

phosphate buffer

Which fluid has a pH of 7.0?

ICF

Which helps to regulate the pH of arterial blood?

 

carbonic-acid-bicarbonate buffer

Approximately how much water is lost per day from the body through the urine?

1500 ml

Which hormone regulates water balance?

ADH

 

what are the 2 responses of the body that correct for dehydration

• release of ADH —> increases water reabsorption

• release of aldosterone —> increases Na+ reabsorption

give 3 examples of amino acids having a basic R group

• Lysine

• arginine

• Histadine

how does breathing change to compensate for acidosis 

you breathe faster and deeper to blow off CO2 

what is different about the way the kidneys regulate Na+ and K+ in the body

• the kidneys reabsorb sodium (Na+)

• the kidneys secrete potassium (K+) into the filtrate

what specific chemical reaction does carbonic anhydrase catalyze 

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻
(Converts CO₂ and water into carbonic acid → bicarbonate + H⁺)

How do we regulate and correct fluid imbalances

• by adjusting water intake, output, and electrolyte levels

• when we lose too much water, the body releases ADH which makes the kidneys save water and aldosterone which makes the kidneys save sodium

• if we have too much water, the body decreases ADH so the kidneys release more water in urine

• the thirst center makes us drink more when fluid levels drop

• the kidneys, hormones, and thirst mechanism work together to keep the amount of water and electrolytes stable