Podcast
Questions and Answers
What primarily causes cells to swell when the osmolarity of interstitial fluid decreases?
What primarily causes cells to swell when the osmolarity of interstitial fluid decreases?
Which of the following ions is primarily associated with the extracellular fluid (ECF)?
Which of the following ions is primarily associated with the extracellular fluid (ECF)?
What effect does aldosterone have on sodium levels in the blood?
What effect does aldosterone have on sodium levels in the blood?
What is the predominant cation found within intracellular fluid (ICF)?
What is the predominant cation found within intracellular fluid (ICF)?
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What is a potential consequence of drinking excessive water in relation to electrolytes?
What is a potential consequence of drinking excessive water in relation to electrolytes?
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Which of the following hormones decreases renal sodium excretion?
Which of the following hormones decreases renal sodium excretion?
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Which ion largely contributes to the resting membrane potential in neurons and muscle fibers?
Which ion largely contributes to the resting membrane potential in neurons and muscle fibers?
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What happens to the osmolarity of extracellular fluid when sodium concentration changes?
What happens to the osmolarity of extracellular fluid when sodium concentration changes?
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What is the primary role of Antidiuretic hormone (ADH) in water management?
What is the primary role of Antidiuretic hormone (ADH) in water management?
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What conditions might trigger an increase in ADH release?
What conditions might trigger an increase in ADH release?
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Which physiological process occurs when water is lost but electrolytes are retained?
Which physiological process occurs when water is lost but electrolytes are retained?
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What is oliguria, often associated with dehydration?
What is oliguria, often associated with dehydration?
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What is the minimum daily sensible water loss needed to excrete metabolic wastes?
What is the minimum daily sensible water loss needed to excrete metabolic wastes?
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What happens to ADH release when there is an increase in body water content without a corresponding increase in electrolytes?
What happens to ADH release when there is an increase in body water content without a corresponding increase in electrolytes?
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Which of the following is NOT a factor leading to water loss from the body?
Which of the following is NOT a factor leading to water loss from the body?
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Which effect does hypotonic extracellular fluid (ECF) have on intracellular fluid (ICF)?
Which effect does hypotonic extracellular fluid (ECF) have on intracellular fluid (ICF)?
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What triggers the thirst center in the hypothalamus?
What triggers the thirst center in the hypothalamus?
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Which part of the nephron is primarily responsible for filtering blood?
Which part of the nephron is primarily responsible for filtering blood?
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How is body fluid balance primarily maintained?
How is body fluid balance primarily maintained?
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What is the primary function of the Loop of Henle in the nephron?
What is the primary function of the Loop of Henle in the nephron?
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Which body fluid compartment does the plasma membrane separate from extracellular fluid?
Which body fluid compartment does the plasma membrane separate from extracellular fluid?
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What role does urination play in the body’s water regulation?
What role does urination play in the body’s water regulation?
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In fluid balance, what is indicated by dehydration?
In fluid balance, what is indicated by dehydration?
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How much filtrate does an average human kidney produce daily?
How much filtrate does an average human kidney produce daily?
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Study Notes
Homeostasis: Regulation of Body Water & Electrolyte Balance
- Homeostasis involves regulating body water and electrolyte balance
- Water makes up approximately 60% of the body, ranging from 45-75% depending on factors like age and sex
- Water is crucial for protecting sensitive tissues, removing waste, regulating temperature, lubricating joints, and enabling cell function and chemical reactions in the digestive system
Previously on Homeostasis Pt 1
- Introduction to homeostasis
- Negative feedback mechanisms
- Body temperature regulation
- Blood glucose regulation were discussed
Importance of Body Water
- Functions:
- Protects spinal cord and other sensitive tissues
- Removes waste through urination, sweating, and bowel movements
- Regulates body temperature
- Lubricates and cushions joints
- Provides optimal medium for cell function
- Facilitates chemical reactions
- Breaks down food particles in the digestive system
Body Fluid Compartments
- Total body fluids make up 55-60% of total body mass
- Intracellular Fluid (ICF) - about 2/3 of fluid
- Extracellular Fluid (ECF) - about 1/3 of fluid includes plasma (~20% of ECF) and interstitial fluid (~80% of ECF).
- Diagram illustrating distribution of water in body compartments
- Diagram illustrating exchange of water between compartments
Fluid Balance
- Two barriers separate intracellular fluid (ICF) and extracellular fluid (ECF):
- Plasma membrane separates ICF from ECF
- Capillary membranes separate interstitial fluid (IF) from plasma
- Body is in fluid balance when correct amounts of water and solutes are present and balanced in the body compartments
- Constant exchange of water and solutes among compartments takes place through filtration, reabsorption, diffusion, and osmosis
Daily Water Gain and Loss
- Water gain through metabolic water production, ingested fluids (including food)
- Water losses include those from the GI tract, lungs (respiration), skin (perspiration), and kidneys
- Quantities associated with different loss mechanisms
Regulation of Body Water Gain
- Primarily driven by water intake
- Dehydration occurs when water loss exceeds intake, leading to decreased blood volume, increased blood osmolarity, and reduced blood pressure.
- Reduced blood volume triggers mechanisms to increase thirst, stimulating the release of ADH to retain water, increasing renin release to increase in angiotensin II formation to cause vasoconstriction
Kidneys
- The kidneys act as the primary organs involved in regulating body water and electrolyte balance
- They are responsible for urine formation, and help regulate blood electrolyte levels
- Consist of Cortex, Medulla (pyramids), renal artery, renal vein, ureter, pelvis
Nephron
- Nephron acts as the functional unit of the kidney
- One human kidney contains ~one million nephrons
- Nephron manufactures urine
Nephron: Parts & Function
- Glomerulus filters blood
- Proximal convoluted tubule reabsorbs glucose, salt, and amino acids
- Loop of Henle reabsorbs water and salts from filtrate
- Distal convoluted tubule reabsorbs salt and some water
- Collecting duct reabsorbs water and salt, and makes urine more concentrated
Selective Reabsorption in the Nephron
- Tubules of nephron reabsorb all glucose, amino acids, and most mineral salts
- Majority of water is reabsorbed in loop of henle and parts of collecting ducts.
- Metabolic wastes are directed towards collecting ducts.
Large Volume of Filtrate
- Kidneys produce a large volume of filtrate (~180 liters/day).
- The excess amounts of water and wastes are removed from the blood to maintain homeostasis via urine
Hormone Regulating Water Balance
- Antidiuretic hormone (ADH) is the main hormone regulating water balance
- ADH is produced by the hypothalamus and released from the posterior pituitary
- ADH increases the permeability of the kidney tubules to water, leading to water reabsorption and more concentrated urine
- Increased or decreased ADH released results in changing urine output
Factors Regulating Body Water Balance
- Thirst centre in hypothalamus, stimulus for drinking water
- Angiotensin II triggers aldosterone release in kidneys
- Aldosterone promotes sodium and water reabsorption
- Atrial natriuretic peptide (ANP) promotes natriuresis
- Antidiuretic hormone (ADH) regulates water permeability to maintain water and sodium retention
Plasma Osmolality and Plasma Volume
- Hypothalamic thirst center receives signal based on water and osmolality levels
- This center causes sensation of thirst to prompt drinking water to re-establish homeostasis
- Water is carried to target regions in body, to replenish body and blood hydration levels
Regulation of Water Output
- Obligatory water loss involves insensible loss from lungs and skin, and water loss through feces
- Minimum daily sensible water loss is 500 ml of urine to excrete wastes
- Water and sodium levels are regulated together to maintain cardiovascular function and blood pressure
Influence of ADH on Water Output
- Water reabsorption in collecting ducts is proportional to ADH release
- Low ADH results in diluted urine and low body fluid volume
- Higher ADH results in concentrated urine
- Hypothalamic osmoreceptors trigger and inhibit ADH release
- Other factors like fever, sweating, vomiting, diarrhea, blood loss, or traumatic burns can trigger ADH release
Homeostasis: Water Level in the Blood
- Hypothalamus detects high solute concentration in blood. Posterior pituitary releases more ADH.
- The person drinks more water. Kidneys reabsorb more water.
- Water levels rise above the normal range. Hypothalamus detects low solute concentration. Pituitary releases less ADH. Kidneys reabsorb less water
Disorders of Water Balance: Dehydration
- Dehydration is due to excess fluid loss (ECF)
- Causes include haemorrhage, severe burns, vomiting, diarrhea, diuretic abuse, and excessive perspiration
- Signs and symptoms include thirst, dry skin, oliguria, weight loss, fever, mental confusion, and hypovolemic shock
- Electrolyte loss also occurs
Disorders of Water Balance: Mechanism (Hypotonic Hydration)
- Excessive water intake leads to lower osmotic pressure in ECF, causing water to move to ICF by osmosis
- Cells swell
If Water is Lost but Electrolytes Are Retained
- ECF osmotic concentration (osmolarity) rises
- Water moves from intracellular fluid (ICF) to ECF
- Both ECF and ICF become slightly concentrated relative to the initial state
- Net change in ECF is small
- Homeostatic responses (increasing ADH release) will replenish lost water
If Water is Gained but Electrolytes Are Not
- ECF osmotic concentration (osmolarity) decreases
- Fluid loss (urine) occurs: ICF looses water back to ECF
- Restore both volume and concentration balance
Electrolytes in Body Fluids
- Electrolytes become ions when they dissolve and dissociate in the body fluids
- Electrolytes in body regulate osmosis of water across the body compartments, maintain acid-base balance, carry electrical current, and serve as co-factors
Movement of Water Between Compartments
- Normally, cells neither shrink nor swell because intracellular and interstitial fluids have same osmolarity
- Increasing osmolarity of the interstitial fluid draws water out of the cells and causes them to shrink.
- Decreasing the osmolarity causes cells to swell
ICF Differs Considerably from ECF
- ECF's main cation is sodium (Na+) while ECF's anion is chloride (Cl⁻).
- ICF's main cation is potassium (K+), while the main anion is phosphate (HPO₄⁻²).
- The Na+/K+ ion pump maintains high K+ inside cells and high Na+ outside.
Sodium (Na+)
- Most abundant extracellular cation
- Important for fluid and electrolyte balance
- Contributes to osmolarity of ECF
- Sodium levels are controlled by aldosterone, ADH, and ANP (atrial natriuretic peptide)
Chloride (Cl-)
- Most prevalent anion in ECF
- Helps balance levels of anions in different body fluids
- Regulated by ADH and urine
Potassium (K+)
- Most abundant cation in ICF
- Key role in establishing resting membrane potential of muscle fibers and neurons
- Maintaining normal ICF fluid volume
- Controlled by aldosterone; stimulates principal cells in renal collecting ducts to secrete excess K+
Dangers of Too Much Water
- Drinking too much water can dilute electrolytes, leading to hyponatremia (sodium levels below 135 mmol/L)
- Kidneys have limits on water excretion rate
Series of Events in Water Intoxication
- Excessive water intake, reduced blood osmolarity (lowered Na+). Causes water into cells via osmosis
- Cellular swelling can lead to convulsions, coma, and death
Dialysis
- Technique used to remove wastes and excess fluids from the body when kidneys fail
- Hemodialysis uses a filtration process, while peritoneal dialysis uses the lining of the abdominal cavity
Principles of Homeostasis
- Stimuli cause changes in the internal environment. These changes are detected by receptors.
- The self-corrective mechanism responds and rectifies the changes, often through negative feedback mechanisms.
- Examples of homeostasis regulation include blood glucose, body temperature, and fluid balance.
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