Fluid Balance

What are the two main fluid compartments of the body?

Intracellular fluid (ICF) and extracellular fluid (ECF).

What is intracellular fluid (ICF)?

Fluid inside the body's cells.

What is extracellular fluid (ECF)?

Fluid outside the body's cells, including plasma and interstitial fluid (IF).

What is interstitial fluid (IF)?

 Fluid that surrounds and bathes the body's cells.

How does interstitial fluid (IF) differ from intracellular fluid (ICF)?

 IF is outside cells, while ICF is inside cells.

What are electrolytes?

Substances that dissociate into ions in water and can conduct electricity.

What is the major extracellular cation?

Sodium (Na⁺).

What is the major intracellular cation?

Potassium (K⁺).

Where is chloride (Cl⁻) more abundant?

Extracellular fluid (ECF).

What is osmosis?

The movement of water across a selectively permeable membrane toward the area with a higher solute concentration.

In osmosis, which way does water move?

Water moves toward the area with the higher solute concentration.

What happens to water when solute concentration increases in one compartment?

Water moves into that compartment.

What are the main sources of water for the body?

Beverages, food, and metabolic water produced during cellular metabolism.

What happens to ADH release when ECF osmolarity increases?

ADH release increases.

What happens to ADH release when ECF osmolarity decreases?

ADH release decreases.

Does an increase or decrease in osmolarity make us thirsty?

An increase in osmolarity makes us thirsty.

Where is fluid osmolarity detected in the brain?

 By osmoreceptors in the hypothalamus.

About what percentage increase in ECF osmolarity triggers thirst?

About a 2% increase.

What is the main driving force of water intake?

Thirst.

What is sensible water loss?

Water loss that can be easily measured, such as through urine, feces, and sweating.

What is insensible water loss?

Water loss that occurs without our conscious awareness, mainly through the skin and respiratory tract.

Why can we not live without water?

Water is essential for cellular reactions, transport, temperature regulation, and maintaining blood volume and homeostasis.

Approximately how long can a person survive without water?

Usually only a few days, depending on conditions.

What do hypothalamic osmoreceptors detect?

 Changes in ECF osmolarity.

What does high ECF osmolarity cause ADH to do?

Increase.

High ADH causes what type of urine?

Small amounts of concentrated urine.

What does low ECF osmolarity cause ADH to do?

Decrease

Low ADH causes what type of urine?

Large amounts of dilute urine.

What is dehydration?

A condition caused by excessive water loss from the body.

What happens to ECF osmolarity during dehydration?

ECF osmolarity increases.

During dehydration, water moves out of cells, causing cells to do what?

Shrink

What is hypotonic hydration?

Excessive water intake that causes ECF osmolarity to decrease.

What is another name for hypotonic hydration?

Water intoxication.

What happens to ECF osmolarity during hypotonic hydration?

It decreases.

What is hyponatremia?

An abnormally low sodium concentration in the blood.

What happens to cells during hypotonic hydration?

Water enters cells, causing them to swell.

How can severe hypotonic hydration be treated?

With hypertonic saline.

What is edema?

Excess fluid accumulation in the interstitial fluid (IF).

What can electrolyte deficiencies cause a person to crave?

Foods rich in the deficient mineral.

What is pica?

The craving and consumption of non-food substances.

What is the most abundant extracellular cation?

Sodium (Na⁺).

Why is sodium so important for fluid balance?

Sodium is the major extracellular solute and contributes significantly to osmotic pressure, affecting fluid movement and volume.

What cation contributes the most to ECF osmotic pressure?

Sodium (Na⁺).

How do changes in sodium concentration affect the body?

They affect fluid volumes in body compartments and can influence blood pressure.

Does the body have direct sodium sensors or receptors?

No. Sodium balance is controlled indirectly.

How is sodium balance indirectly controlled?

Changes in blood pressure or fluid volume trigger neural and hormonal mechanisms that regulate sodium.

What hormone is the key player in sodium regulation by the kidneys?

Aldosterone.

What triggers the release of aldosterone?

Angiotensin II.

What are the three major stimuli that trigger renin release?

Low blood pressure, decreased blood volume, and decreased sympathetic stimulation to the kidneys.

What is the sequence of the renin-angiotensin-aldosterone system (RAAS)?

Low BP → Renin → Angiotensin II → Aldosterone.

What does aldosterone do to sodium?

Increases sodium reabsorption by the kidneys.

What happens to water when sodium reabsorption increases?

Water follows sodium, increasing water reabsorption.

What is the overall effect of aldosterone on blood pressure?

It increases blood volume and blood pressure.

What does ANP do to blood pressure and blood volume?

ANP decreases blood volume and blood pressure by promoting sodium and water loss.

What do estrogen and progesterone generally do to water balance?

They can promote water and sodium retention, contributing to fluid retention.

Why is potassium (K⁺) important?

It is essential for normal nerve impulses, muscle contraction, and cardiac function.

What are hypokalemia and hyperkalemia?

 Hypokalemia is low blood potassium; hyperkalemia is high blood potassium.

Why are both hypokalemia and hyperkalemia potentially fatal?

Abnormal potassium levels can disrupt electrical activity in the heart and cause dangerous arrhythmias.

What happens to extracellular K⁺ during acidosis?

 Extracellular K⁺ increases as H⁺ moves into cells and K⁺ moves out.

Why is potassium important in our diet?

It is needed for normal nerve function, muscle contraction, and heart function.

What does aldosterone do to K⁺?

It increases potassium secretion into the urine, lowering blood K⁺ levels.

 In what form is most of the body's calcium found?

Stored in bones and teeth.

What hormone raises blood calcium levels?

 Parathyroid hormone (PTH).

What are the three ways PTH increases Ca²⁺ levels?

It increases bone resorption, increases calcium reabsorption by the kidneys, and indirectly increases intestinal calcium absorption by activating vitamin D.

What is extracellular Ca²⁺ important for?

Bone structure, blood clotting, muscle contraction, and normal nerve function.

What calcium imbalances can cause muscle tetany and heart arrhythmias?

Low calcium levels (hypocalcemia) can cause muscle tetany; both low and high calcium levels can contribute to abnormal heart rhythms.

What is hypocalcemia?

Abnormally low blood calcium levels.

What is hypercalcemia?

Abnormally high blood calcium levels.

What is the normal pH of arterial blood?

7.35-7.45

What is acidosis?

A condition in which blood pH falls below 7.35.

What is alkalosis?

A condition in which blood pH rises above 7.45.

What are the three body systems that regulate acid-base balance?

Chemical buffers, the respiratory system, and the kidneys.

Which acid-base defense system acts the fastest?

Chemical buffers.

Which acid-base defense system acts next?

The respiratory system

Which acid-base defense system takes the longest to act?

The kidneys

What is the bicarbonate buffer system made of?

Carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻).

What does H₂CO₃ do when blood pH is too high?

Releases H⁺, lowering pH.

What does HCO₃⁻ do when blood pH is too low?

Binds H⁺, raising pH.

Where is the bicarbonate buffer system especially important?

In the extracellular fluid (ECF)

Where are phosphate buffers primarily found?

Inside cells and in the kidneys.

What are protein buffers?

Proteins that can either accept or release H⁺ to help stabilize pH.

What does amphoteric mean?

Able to act as either an acid or a base.

How does the respiratory system regulate blood pH?

By adjusting the amount of CO₂ in the blood.

What is the chemical reaction involving CO₂ and bicarbonate?

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

What happens when CO₂ levels increase?

H⁺ increases, causing blood pH to decrease.

What happens when CO₂ levels decrease?

H⁺ decreases, causing blood pH to increase.

What do respiratory centers do when plasma H⁺ levels are high?

Increase ventilation to remove more CO₂.

What happens to the CO₂ reaction when ventilation increases?

The reaction shifts to the left, reducing H⁺ and raising pH.

What do respiratory centers do when plasma H⁺ levels are low?

Decrease ventilation, allowing CO₂ to accumulate.

What happens to the CO₂ reaction when ventilation decreases?

The reaction shifts to the right, increasing H⁺ and lowering pH.

What is hypoventilation?

Abnormally slow or shallow breathing that causes CO₂ to accumulate.

What condition can result from hypoventilation?

Respiratory acidosis.

What is hyperventilation?

Excessively rapid or deep breathing that removes too much CO₂.

What condition can result from hyperventilation?

Respiratory alkalosis.

What is the most important indicator of respiratory function for acid-base balance?

PCO₂ (partial pressure of carbon dioxide).

What happens to blood pH when CO₂ accumulates?

Blood pH decreases.

Respiratory acidosis is commonly caused by what?

Hypoventilation.

What is the normal range of PCO₂?

35–45 mmHg.

What causes metabolic acidosis?

Low HCO₃⁻ levels or an accumulation of nonvolatile acids.

What are some possible causes of metabolic acidosis?

Severe diarrhea, kidney failure, or excessive acid production.