L13 physiology

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Questions and Answers

What percentage of body weight is typically composed of water in healthy females?

60%

55% (correct)

50%

65%

Which fluid compartment contains two-thirds of total body water?

Extracellular fluid

Intracellular fluid (correct)

Interstitial fluid

Transcellular fluid

What is the primary cation found in extracellular fluid (ECF)?

Ca++

K+

Cl-

Na+ (correct)

Which of the following mechanisms does not contribute to the regulation of water loss by the kidneys?

Blood glucose regulation Signup and view all the answers

What is the effect of the pressure-volume control system in the kidneys?

Excrete more Na+ and water when blood pressure rises Signup and view all the answers

Which electrolyte is primarily regulated through the process of natriuresis?

Na+ Signup and view all the answers

How does the kidney maintain water and sodium balance?

Through integrated regulation of water and Na+ balance Signup and view all the answers

Which mechanism helps minimize changes in sodium and water excretion related to glomerular filtration rate (GFR)?

Glomerulotubular balance Signup and view all the answers

Which disorder is characterized by the kidneys being unresponsive to ADH?

Nephrogenic Diabetes Insipidus Signup and view all the answers

What is a major stimulus to thirst regulated by the body?

Hypertonicity (osmolality) Signup and view all the answers

What is the primary compensatory mechanism for dehydration?

Secretion of Aldosterone Signup and view all the answers

Which hormone is primarily responsible for increasing sodium reabsorption?

Aldosterone Signup and view all the answers

How does ANP contribute to the regulation of body fluid?

Reduces blood volume Signup and view all the answers

Which mineral is regulated by parathyroid hormone (PTH)?

Calcium Signup and view all the answers

What effect does high potassium (K+) levels in extracellular fluid have on the adrenal cortex?

Increased aldosterone secretion Signup and view all the answers

Which condition is associated with excessive loss of body water?

Dehydration Signup and view all the answers

What is the primary function of glucocorticoids in renal physiology?

Enhance Na+ reabsorption Signup and view all the answers

What compensatory response occurs in overhydration?

Inhibition of thirst Signup and view all the answers

Study Notes

Electrolyte and Body Fluid Regulation

Body water content varies by sex and age
- Females have ~55% body water
- Males have ~60% body water
- Children have ~65% body water
- Infants have ~75% body water
Total body water (TBW) is ~40 liters in healthy males
TBW in healthy females is ~35-40 liters
Intracellular fluid (ICF) is ~25 liters (~40% of TBW)
Extracellular fluid (ECF) is ~15 liters (~20% of TBW)

Body Fluid Compartments

ICF: Holds ~2/3 of TBW
Interstitial fluid: ~80% of ECF (~12 liters)
Plasma: 20% of ECF (~3 liters)
Transcellular fluid
- Cerebrospinal fluid (CSF)
- Aqueous humor of the eye
- Synovial fluid
- GI secretions

Distribution of Electrolytes

ECF:
- Major cation: Na+
- Major anion: Cl-
ICF:
- Major cation: K+
- Major anion: PO4-

Water Balance

Water gain = Water loss
Water gain percentages:
- Beverages: ~60%
- Foods: ~30%
- Metabolism: ~10%
Water loss percentages:
- Urine: ~60%
- Insensible losses (skin, lungs): ~28%
- Feces: ~4%
- Sweat: ~8%

Kidney Regulation of Water Loss

ECF sodium (Na+) concentration ([Na+]) determines TBW distribution
Water and Na+ balance are intertwined
Kidneys regulate water through diuresis (increased urine volume)
Kidneys regulate water through natriuresis (increased Na+ secretion)

Kidney Regulation of Water Loss Mechanisms

Vasopressin (ADH)
Autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR)
Glomerulotubular Balance
Intrinsic pressure-volume control system
Tubular concentrating ability
Renin-angiotensin-aldosterone system
Natriuretic peptides

Intrinsic Pressure-Volume Control System

A local renal mechanism
Minimizes the effects of GFR changes on sodium and water excretion.
Maintains a constant blood volume through pressure diuresis and pressure natriuresis
Kidneys excrete more water and sodium when blood pressure is elevated, to maintain blood pressure and volume

Disorders of Kidney Affecting Water Balance: Diabetes Insipidus

Central Diabetes Insipidus: Due to ADH deficiency
Nephrogenic Diabetes Insipidus: DCT, CD unresponsive to ADH, usually due to genetic mutations affecting receptor or aquaporin 2 channel protein.

Water Gain Sensors

Osmoreceptors (hypothalamus)
Thirst center (hypothalamus)
Volume receptors (atria)
High pressure baroreceptors (carotid sinus & aortic arch)

Factors Affecting Thirst

Plasma volume
Plasma osmolarity
Dry mouth/throat
Metering of water intake by the GI tract
Baroreceptors
Osmoreceptors
Angiotensin II

Disorders of Water Balance

Dehydration
Over-hydration

Dehydration

Excessive loss of body water
Mild Symptoms:
- Thirst
- Dry skin
- Headache
- Blurred vision
- Mouth sores
- Exhaustion
- Irritability
- Dizziness
- Dark yellow urine
Serious Symptoms:
- Shortness of breath
- Increased heart rate
- Low blood pressure
Fatal Symptoms:
- Seizures
- Muscle cramps
- Kidney damage
- Pain in joints

Dehydration Compensatory Mechanisms:

Stimulation of thirst - ↑ Water intake
Secretion of ADH - ↓ urine volume
Inhibition of high pressure baroreceptors - ↑ Sympathetic tone - ↓ GFR & RBF - ↓ Urine output
Stimulation of renin-angiotensin → ↑ Na+ reabsorption, thirst, vasoconstriction
Secretion of aldosterone - ↑ Na+ reabsorption

Overhydration

Too much fluid entering the body, with inadequate removal
Neurologic: changes in level of consciousness (LOC), confusion, headache, seizures
Respiratory: pulmonary congestion
Cardiovascular: bounding pulse, ↑ Blood Pressure (BP), ↑ Jugular Venous Distention (JVD), presence of S3 heart sound, tachycardia
Gastrointestinal: anorexia, nausea
Edema: generalized swelling (dependent pitting edema)

Overhydration Compensatory Mechanisms

Inhibition of thirst - ↓ Water intake
Stimulation of high pressure baroreceptors - ↓ sympathetic tone - ↑ RBF & GFR - ↑ Urine output
Inhibition of ADH, renin-angiotensin, aldosterone secretion - ↑ Urine output
Stimulation of ANP - Natriuresis (↑ Na+ excretion in urine)

Regulating Na⁺ Balance

Normal Na⁺ level: 135-145 mmol/L
Hypernatremia (excess Na⁺) / Hyponatremia (low Na⁺)
Aldosterone
Stimulated → ↑ Na⁺ reabsorption
Inhibited → ↓ Na⁺ reabsorption
Renin-angiotensin mechanism
- JG apparatus releases renin → stimulates aldosterone release.
Atrial natriuretic peptide (ANP)
Atrial stretch stimulates ANP release → Reduces BP and blood volume.
Inhibits Na⁺ H₂O retention, and vasoconstriction.
Other hormones:
- Estrogens and Progesterone: affect Na⁺ and water balance
Glucocorticoids: affect Na⁺ reabsorption, GFR, and edema

Regulating K⁺ Balance

High ECF K⁺ (hyperkalemia) → increased secretion
Stimulates aldosterone release from the adrenal cortex
- High ECF K⁺ stimulates adrenal cortex to release aldosterone
Aldosterone enhances K⁺ secretion.
Renin-angiotensin mechanism is also part of K⁺ regulation

Regulating Ca²⁺ and PO₄²⁻ Balance

Parathyroid hormone (PTH) – ↑ blood calcium level, ↑ phosphate excretion
Calcitonin – ↓ blood calcium level

Learning Resources

Vander's Human Physiology, 13th Edition
Guyton and Hall: Textbook of Medical Physiology
Moodle power-point presentations

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Description

This quiz covers essential concepts related to body water content, fluid compartments, and electrolyte distribution. You will learn the differences in body water percentage by age and sex, as well as the major ions in intracellular and extracellular fluids. Test your understanding of water balance in the human body.