acid/base

What are the two major fluid compartments of the body?

• Intracellular fluid (ICF)

• Extracellular fluid (ECF)

What is intracellular fluid (ICF)?

Fluid located inside cells.

Amount:
~25 L
~40% of body weight

What is extracellular fluid (ECF)?

Fluid located outside cells.

Amount:
✅ ~15 L
✅ ~20% of body weight

What are the two major components of extracellular fluid?

A:

• Plasma

• Interstitial fluid

What is plasma?

The fluid portion of blood.

Amount:
~3 L

What is interstitial fluid?

Fluid that surrounds and bathes body cells.

Amount:
~12 L

What is total body water volume?

~40 L

Approximately:
60% of body weight

What are nonelectrolytes?

Substances that do not carry an electrical charge.

Example:

• Glucose

What are electrolytes?

Substances that dissociate into charged ions.

Example:

NaCl → Na⁺ + Cl⁻

What does mEq/L measure?

The number of electrical charges in one liter of solution.

What are the major electrolytes in extracellular fluid?

High:

• Na⁺

• Cl⁻

What are the major electrolytes in intracellular fluid?

Low:

• Na⁺

• Cl⁻

(Cells contain more K⁺ instead.)

What determines movement between ECF and ICF?

The amount of NaCl in the extracellular fluid.

What direction does oxygen and glucose move?

Blood/interstitial fluid → cells

What direction does carbon dioxide and nitrogenous waste move?

Cells → extracellular fluid

Where does most water intake come from?

90%:

• Ingested water

10%:

• Metabolic water

What are the major routes of water loss?

• 60% urine

• 28% lungs/skin/mucosa

• 12% sweat/feces

What triggers thirst and ADH release?

Changes in:

• Plasma volume

• Osmolarity

What stimulates thirst?

↓ Plasma volume OR ↑ osmolarity

↓

Hypothalamic thirst center activated

↓

Feeling thirsty

What is dehydration?

Loss of water from the body.

Causes:

• Bleeding

• Burns

• Sweating

• Diuretics

What is hypotonic hydration?

Excess water or sodium imbalance causing overly diluted body fluids.

What is edema?

Accumulation of fluid in the interstitial space.

Why is sodium important?

Na⁺ is:

• 90% of solutes in ECF

• Most important extracellular electrolyte

Where is aldosterone released from?

adrenal cortex

What stimulates aldosterone release?

• Decreased blood pressure

• Decreased osmolarity of filtrate

• Sympathetic stimulation of juxtaglomerular cells

What does aldosterone do?

increase Na⁺ reabsorption in distal tubule

Water follows Na⁺ (if ADH allows water movement)

Where are baroreceptors located?

• Carotid arteries

• Aorta

What do baroreceptors detect?

Changes in blood vessel stretch caused by blood pressure changes.

What happens when blood pressure increases?

↑ BP
→ hypothalamus stimulation
→ ↓ sympathetic stimulation to kidneys
→ ↑ GFR
→ more water removed

What happens when blood pressure decreases?

↓ BP
→ ↓ GFR
→ water retained

Where is ADH released from?

posterior pituitary

What stimulates ADH release?

Osmoreceptors in hypothalamus.

What happens when ECF osmolarity increases?

↑ osmolarity

↓

↑ ADH

↓

Distal tubule becomes more permeable to water

↓

Less water lost in urine

What happens when ECF osmolarity decreases?

↓ ADH

↓

Less water reabsorbed

↓

More water released in urine

When is ANF released?

When blood pressure is high.

Released by:

• Heart atrial cells

What does ANF do?

↓ Blood pressure
↓ Blood volume

By inhibiting:

• Vasoconstriction

• Na⁺ retention

• Water retention

Why is potassium important?

K⁺ is the primary intracellular cation.

It affects:

• Resting membrane potential

• Neurons

• Cardiac muscle

Where is most potassium reabsorbed?

Proximal tubule.

How does the kidney regulate potassium levels?

By changing how much K⁺ is secreted into urine.

What happens when blood K⁺ is high?

↑ K⁺

→ ↑ K⁺ secretion into urine

What happens when blood K⁺ is low?

↓ K⁺

→ ↓ K⁺ secretion

→ more K⁺ reabsorbed

How does aldosterone affect potassium?

increase Aldosterone

→ ↑ Na⁺ reabsorption

→ ↑ K⁺ secretion

Where is most calcium stored?

Bone as calcium phosphate.

What are the major functions of calcium?

• Muscle and neuron signaling

• Blood clotting

• Heart rhythm

What is the main function of parathyroid hormone (PTH)?

Raises blood calcium levels.

What does PTH do to bone?

Causes release of Ca²⁺ and phosphate into blood.

What does PTH do to kidneys?

↑ Calcium reabsorption

↑ Phosphate excretion

What does PTH do to the small intestine?

Activates vitamin D, increasing calcium absorption.

When is calcitonin released?

When calcium levels are too high.

What does calcitonin do?

↓ Calcium release from bone

↑ Calcium phosphate formation in bone