Human Physiology: Water Balance and Functions

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Questions and Answers

What role does water play in facilitating digestion?

Water acts as a nutrient source.

Water neutralizes stomach acid.

Water promotes elimination of ingested food. (correct)

Water increases food absorption efficiency.

What is the primary consequence of failing to maintain extracellular fluid (ECF) volume?

Increased energy levels.

Enhanced nutrient absorption.

Impaired blood circulation. (correct)

Improved oxygen delivery.

What is the approximate urine osmolality for an individual on a normal diet?

900-1200 mOsm/kg water

400-500 mOsm/kg water

100-250 mOsm/kg water

500-850 mOsm/kg water (correct)

Which of the following factors primarily drives the thirst mechanism?

Increased plasma osmolality Signup and view all the answers

How much water is typically filtered by the kidneys each day?

130-180 liters Signup and view all the answers

What percentage of plasma volume is typically filtered by the kidneys at any given time?

10-20% Signup and view all the answers

What is insensible fluid loss?

Loss of water through evaporation from lungs and skin Signup and view all the answers

What happens to the majority of the glomerular filtrate in the kidneys?

It is reabsorbed back into the bloodstream. Signup and view all the answers

What is the primary role of aldosterone in the kidneys?

To promote sodium reabsorption Signup and view all the answers

What triggers the secretion of renin from the juxtaglomerular apparatus?

Reduction in renal artery blood flow Signup and view all the answers

What effect does angiotensin II have on blood vessels?

It causes vasoconstriction Signup and view all the answers

How does aldosterone affect potassium levels in the body?

Promotes potassium loss Signup and view all the answers

What substance is primarily converted to angiotensin I by renin?

Angiotensinogen Signup and view all the answers

What is one of the mechanisms that can lead to hyponatremia?

Excessive antidiuretic hormone secretion Signup and view all the answers

Where is angiotensin-converting enzyme (ACE) predominantly located?

In the lungs Signup and view all the answers

Which of the following is a function of atrial natriuretic peptide (ANP)?

Inhibits renin release Signup and view all the answers

Which of the following is NOT a common cause of hyponatremia?

Hypertensive crisis Signup and view all the answers

What is the typical range of osmolality in mOsm/Kg of water?

285 to 295 Signup and view all the answers

Which of the following statements is true about the dissociation of electrolytes in solution?

They dissociate into charged ions Signup and view all the answers

What is the recommended initial treatment for acute hyponatremia management?

Start 0.9% sodium chloride IV fluids Signup and view all the answers

What distinguishes hypovolemic hyponatremia from euvolemic and hypervolemic?

Decreased total body water Signup and view all the answers

What is the result of increased renin levels in the blood?

Production of angiotensin I Signup and view all the answers

Which electrolyte is most abundant in the extracellular fluid (ECF)?

Sodium (Na+) Signup and view all the answers

Which condition could lead to euvolemic hyponatremia?

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) Signup and view all the answers

What is the primary function of electrolytes in bodily fluids?

To produce nerve impulses and muscle contractions Signup and view all the answers

Which substance develops an electrical charge when dissolved in water?

Electrolytes Signup and view all the answers

How is the concentration of electrolytes typically expressed?

Milliequivalents per liter (mEq/L) Signup and view all the answers

Which mechanism increases salt and water excretion in the body?

Kinins Signup and view all the answers

What role does potassium (K+) play in the body?

It is essential for normal membrane excitability Signup and view all the answers

What effect does hypertonicity have on thirst?

Increases thirst sensation Signup and view all the answers

Which of the following solutions is considered hypertonic?

5% Sodium Chloride Signup and view all the answers

What is referred to as the osmolar gap?

The difference between calculated value and measured value Signup and view all the answers

What characterizes total body water deficiency or dehydration?

Thirst, dry skin, and low blood volume Signup and view all the answers

Which of the following solutes would invalidate an osmolality calculation?

Mannitol Signup and view all the answers

In a hypotonic solution, what is the relative concentration of solute and water?

More water and less solute Signup and view all the answers

What usually causes predominant water depletion leading to dehydration?

Negative water balance Signup and view all the answers

Which of the following is an example of an isotonic solution?

Normal Saline (0.9% Sodium Chloride) Signup and view all the answers

Study Notes

Water Function

Water regulates body temperature.
Water transports hormones, enzymes, platelets, and red and white blood cells.
Water acts as a solvent for electrolytes and non-electrolytes.
Water facilitates digestion and promotes the elimination of ingested food.
Water acts as a tissue lubricant.

Water Balance

Multicellular organisms require maintaining ECF volume to survive.
Humans deprived of fluids for a few days die from circulatory collapse.
Failure to maintain ECF volume causes impaired blood circulation, leading to tissue death.
Osmolality in the ECF and ICF is maintained between 285-295 mOsm/Kg H2O.
Normal urine osmolality is 500-850 mOsm/kg water.

Water Gain and Loss

Water gain occurs through drinking, oxidative processes, and disease conditions such as coma, vomiting, and diarrhea.
Water loss occurs through the kidneys as urine, the GIT in feces, and the lungs & skin as evaporative losses (insensible fluid loss).

Renal Water Excretion

The kidneys filter 130 – 180 liters of water daily as glomerular filtrate.
About 20% of the plasma volume passing through the glomerulus is filtered.
The entire plasma volume is filtered 60 times daily.
Only 1 to 2 liters are excreted as urine due to reabsorption in the proximal tubule and collection ducts under ADH influence.

Electrolytes

Electrolytes are substances that dissociate into ions when dissolved in solution.
These ions carry electrical currents.
Electrolytes are substances that develop an electrical charge when dissolved in water.
Electrolyte concentrations are expressed as mEq/L.

Electrolyte Types

Cations are positively charged electrolytes.
Anions are negatively charged electrolytes.
Water molecules surround dissociated ions, preventing the union of cations and anions.

Electrolyte Distribution

ECF Cations: Na+, K+, Ca+, Mg+
ECF Anions: Cl-, HCO3-, HPO4--, SO4--
ICF Cations: Na+, K+, Ca+, Mg+
ICF Anions: Cl-, HCO3-, HPO4- -, SO4--

Electrolyte Function

Electrolytes maintain osmotic pressure, contributing to water balance.
Sodium (Na+): The most abundant electrolyte in the ECF. It plays a crucial role in water balance.
Potassium (K+): Essential for normal membrane excitability for nerve impulses.
Chloride (Cl-): Regulates osmotic pressure and assists in acid-base balance.
Calcium (Ca2+): Promotes nerve impulses and muscle contraction/relaxation.
Magnesium (Mg2+): Involved in carbohydrate and protein metabolism, storage, and use of intracellular energy, and neural transmission. Essential for heart, nerves, and muscles.

Regulation of Sodium and Water Balance

Neural Mechanism - Thirst Mechanism: Influenced by ECF tonicity and blood volume.
Antidiuretic Hormone (ADH)/Vasopressin: Released in response to dehydration, increasing water reabsorption in the kidneys.
Renin-Angiotensin System (RAAS): Activated by decreased blood pressure or volume, leading to vasoconstriction and aldosterone release for sodium and water retention.
Aldosterone: A mineralocorticoid hormone that stimulates sodium reabsorption in the distal renal tubule, exchanging it for potassium or hydrogen ions.
Atrial Natriuretic Peptide (ANP): Released from the atrium in response to stretching, promoting sodium and water excretion, decreasing blood pressure and volume.
Kinins: Increase salt and water excretion.

Thirst Mechanism

The thirst center is stimulated when body water is lowered due to a lack of fluid intake, fluid losses through urine and feces, or obligatory losses.

Aldosterone

Aldosterone regulates sodium balance, controlling sodium loss in the distal tubule.
It affects sodium–potassium and sodium–hydrogen ion exchange across cell membranes.

Renin-Angiotensin-Aldosterone System (RAAS)

Renin is an enzyme secreted by the juxtaglomerular apparatus in response to decreased renal artery blood flow.
Renin converts angiotensinogen (released by the liver) into angiotensin I.
Angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II.

Actions of Angiotensin II

Angiotensin II causes vasoconstriction, maintaining blood pressure and altering glomerular filtration rate (GFR).
It stimulates aldosterone secretion, promoting sodium and water retention.
It stimulates the thirst center, promoting oral fluid intake.

Atrial Natriuretic Peptide (ANP)

ANP promotes sodium and water excretion, decreasing blood pressure and volume.

Osmolality

Osmolality is a measure of the number of solute particles per kilogram of water.
It is usually between 285 and 295 mOsm/Kg of water.
Osmolality can be measured by an osmometer.
The difference between the calculated and measured values is known as the osmolar gap.

Distribution of Sodium and Water Homeostasis

Isotonic solution: Equal concentrations of solute and water.
Hypertonic solution: More solute and less water.
Hypotonic solution: More water and less solute.
Examples of isotonic solutions: 0.9% sodium chloride solution (normal saline), Ringer’s solution, Lactated Ringer’s solution, 5% dextrose in water (D5W).
Examples of hypotonic solutions: 5% dextrose water, 2.5% dextrose water, 0.45% sodium chloride, 0.33% sodium chloride.
Examples of hypertonic solutions: 3% sodium chloride, 5% sodium chloride, whole blood, albumin, total parenteral nutrition, tube feedings, concentrated dextrose (>10%).

Disorders of Total Body Water and Sodium

Dehydration: Presents with thirst, dry skin and mucous membranes, loss of skin turgor, decreased urinary output, and circulatory disturbances.
TBW excess: Presents as peripheral edema, pulmonary edema, ascites, and circulatory overload with cardiac failure.
Serum Sodium (Na): Can be high, low, or normal, depending on body sodium content and other factors.

Causes of Total Body Water Deficiency

Negative water balance: Input less than output.
Losses related to dehydration: Profuse diaphoresis, vomiting, diarrhea, draining wounds, excessive blood loss, medication side effects, and renal disease.

Types of Dehydration

Predominant water depletion: Loss of water with minimal sodium loss.
Hypotonic fluid loss: Loss of water with some sodium loss.
Isotonic fluid loss: Loss of water and sodium in equal proportions.

Causes of Hyponatremia

Severe diarrhea, vomiting, drainage of GIT secretions, fistulas.
Excessive sweating.
Burns.
Renal diseases.
Adrenal insufficiency.
Diuretic therapy.
Osmotic diuresis (diabetes mellitus).
SIADH.
Excess fluid replacement with hypotonic solutions.
Psychogenic polydipsia.
Sick cell syndrome.
Artefactual hyponatremia due to IV fluid administration.

Types of Hyponatremia

Hypovolemic hyponatremia: Loss of both water and sodium. Most common type.
Euvolemic hyponatremia: Normal total body sodium levels with excess water.
Hypervolemic hyponatremia: Excess sodium and water with fluid overload and edema.

Management of Hyponatremia

Determine and treat the underlying cause.
Ensure good IV access.
Send blood work for laboratory analysis.
Begin IV fluid administration with 0.9%NS or lactated Ringer’s solution.

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Description

This quiz explores the essential functions of water in the human body, including its role in regulating temperature, transporting vital substances, and maintaining fluid balance. Additionally, it addresses how water gain and loss occur in various physiological processes, emphasizing the importance of hydration for survival. Test your understanding of these crucial concepts in human physiology.