A & P II - Chapter 26 - Fluid, Electrolyte & Acid-Base Balance

Extracellular Fluid

Blood plasma & Interstitial fluid

Intracellular fluid

In our cells (40% of our bodyweight)

Total body water

60% of our body weight

20% of body weight is

Extracellular fluid

80% of ECF

Interstitial fluid

20% of ECF

Plasma

Other types of Extracellular fluid

CSF, Serous fluid, lymph, synovial fluid

How are cells interstitial

Plasma membrane

How is blood plasma interstitial

Blood vessels

Plasma membrane allows for

Osmosis, diffusion, filtration & reabsorption

The plasma membrane is

Selectively permeable

Fluid balance happens when

Required amounts of water & solutes are present in body compartments in correct portions

Skeletal muscle can hold 

65% H20

Adipose can hold

20 % of H20

The net hydrostatic pressure will

force ions out of the blood

Function of the glomerulus

Filtration

Normally H2O loss =

H2O gain

Water intake ~

2500 mL/day

We recieve water from 

10% metabolism → Cell respiration, dehydration synthesis

30% foods 

60% beverages

Water loss should =

2500 mL

We lose water through

• 4% feces

• 8% sweat

• 28 % insensible loss

  • 60% urine

Thirst center is lockated in 

your hypothalamus

Responding to the thirst center

Increase of H2O

Drinking inhibits the

Thirst center

Dehydration is when 

• H20 loss > H20 gain

• 2% decrease in body mass due to fluid loss

Osmolarity

Solute amount in the water

ECF goes up when you are

dehydrated

Osmoreceptors

Detect increased osmolarity

When you take a drink of water,

Plasma increases, ECF decreases

Saliva production decreasing is coupled with

dehydration

When you have low blood plasma, 

you will have a decreased blood pressure

Dropping of plasma stimulates

• juxtolomedullar apparatus to release renin

• release of Angiotensin II

• Also stimulates the thirst center

ADH is produced in the

Hypothalamus and secreted from the posterior pituitary gland

ADH function

reduce loss of water in urine

High ADH = less loss

Low ADH = more loss

Osmoreceptors

release ADH

ADH targets

kidney ducts, leading to water reabsorption and reducing volume of urine

• decreasing osmolarity

An increase in Blood plasma

Means a decrease in urine

Increased plasma stimulates

the thirst center

Dehydration Symptoms

• Dry mouth

• Thirsty

• Dry skin

• Decrease in urine

• Prolonged weight loss

• Hypovolemic shock

As H20 enters the cells, the cells will shrink into ECF is known as 

cremation

Hypotonic Hydration Symptoms

• ECF is dilute with low Na (Hyponatremia)

• Nausea/Vomiting

• Muscle Cramps

• Cerebral Edema

• Disorientation

• Convulsions

When there is high Na in the cells,

osmosis will follow because water follows solute

Intake

Foods, fluids, metabolic reaction

Output

Sweat, feces, urine

Electrolytes are

the most abundant solutes in body fluids

mEg/L - expresses the ions and represents

1/1000th of a charge of a hydrogen moleMa

Major cation in ECF

Na

There is high concentrations of _ in the ECF

Na, Ca, Cl, HCO3-

Major cation in ICF

Potassium

Also high in

Mg, HPO4, SO4

The renin-Angiotensin-Aldosterone mechanism helps to

reabsorb sodium

Low sodium and high potassium triggers release of 

Renin and angiotensin

Aldosterone

Targets kidney tubules which has Na in blood and K gets secreted

65 % of sodium is stored in PCT and

25 is stored in Loop of Henle

ANP gets secreted in response to 

Atrial cells in response to stretching

ANP promotes

excretion of sodium

targets granular cells

• decreases renin and angiotensin

  • less water and decreased BP

  • less ADH

Changes in osmolarity = 

Changes in H20 levels and will impact water reabsorption

Potassium excretion will primarily occur through

urine

Increase in K signals

Adrenal Cortex

Aldosterone targets the kidney tubules which

INcreases Na which increases secretion

When Na is absorbed,

K will be excrted (High in ICF)

Calcium is higher in the

ECF

Calcium targets

The parathyroid glands to release PTH

When bone tissue gets broken down

it releases calcium in the blood

Calcium will get increasingly reabsorved in

the kidneys

Increase in Vitamin D, will increase that

Ca in Small Intestine

Chemical Acid Base Buffers

is the 1st line of defense

• will weaken acid/base but do not eliminate them

• Work immediately

Respiratory excretion is a

physiological buffer, CO2 and Hydrogen. will work within minutes

Renal Excretion is

• physiological

• eliminates excess acids

• can work between hours and days

Bicarbonate Buffer System

Mixture of strong and weak acids

HCO3- is

weak

H+ is

strong

Bicarb Buffer System will help to 

convert strong into weak

If you eliminate the strong acid,

It will help to regulate pH

Phosphate buffer system is important in

Urine and ICF

Protein Buffer Systems

Are amino acids, some side chains can be weak acids and bases

When pH drops,

it becomes more acidic

NH2 group

accepts hydrogen when pH falls

COOH group releases Hydrogen when

pH rises

When rate and depth increase,

it increases the amount of Co2

Renal Excretion can be

excreted as needed

Carbonic Anhydrase

Pumps bicarbonate into capillary which raises the pH

We release hydrogen

in urine

Secretion of Hydrogen is accompinted with

Retention of Hco3-

Acidosis & Alkolisis

When pH is imbalanced

Acidosis - drop

More acids & loss of bases

Alkalosis

Less acids and more bases

Respiratory Acidosis

• Accumulation of Co2

• Hypopnea

• Airway obstruction

  • Decreased gas exchange

Metabolic Acidosis

• Acumulate too much acids/loss of bases

• Kidney failure and ketones

• Diarrhea and vomiting

• too much alcohol and lactic acid

Metabolic Acidosis can lead to 

depression of the nervous system, coma and death

Respiratory Alkalosis

• Decrease of hydroden

• Excessive loss of Co2, decreases ions

• Hyperventilation

• Anxiety

• Fever

  • Poision

Metabolic Alkalosis

• Loss of acids through gastric drainage, vomiting & gastric secretion

• Too many antacids

• Nervousness/convulsions