The Fluid, Electrolyte and Acid-Base Balance (Pt. 1) Flashcards
What are the two main barriers that separate body fluids?
- Plasma membrane of cells
- Blood vessel walls
What does the plasma membrane separate?
The plasma membrane separates intracellular fluid (inside cells) from interstitial fluid (between cells)
What do blood vessel walls separate?
Blood vessel walls separate interstitial fluid from blood plasma
What makes capillaries special compared to other blood vessels?
Capillaries have thin walls that allow water and solutes to pass between blood plasma and interstitial fluid
What does ‘fluid balance’ mean?
Fluid balance occurs when water and solutes are present in the correct amounts and proportions across all fluid compartments in the body
Name the three main fluid compartments in the body.
- Intracellular fluid (inside cells)
- Interstitial fluid (between cells)
- Blood plasma (in blood vessels)
What is intracellular fluid (ICF)?
Intracellular fluid (ICF) is the cytosol found within cells.
What is extracellular fluid (ECF)?
Extracellular fluid (ECF) includes interstitial fluid (80%) and blood plasma (20%).
What other fluids are grouped with interstitial fluid as part of ECF?
Lymph, cerebrospinal fluid, synovial fluid, aqueous humor, vitreous humor, and fluids between serous membranes (pleural, pericardial, and peritoneal).
What percentage of ECF is interstitial fluid?
Interstitial fluid makes up about 80% of extracellular fluid (ECF).
What percentage of ECF is blood plasma?
Blood plasma makes up about 20% of extracellular fluid (ECF).
What does the plasma membrane separate?
The plasma membrane separates intracellular fluid (inside cells) from interstitial fluid (around cells).
How does the plasma membrane function?
It acts like a ‘gatekeeper,’ allowing some substances (like water and nutrients) to cross while blocking others.
What do the ‘pumps’ in the plasma membrane do?
They maintain balance by keeping specific amounts of ions inside and outside the cell.
What do blood vessel walls separate?
Blood vessel walls separate interstitial fluid from blood plasma.
What role do capillaries play in fluid exchange?
Capillaries have thin walls that allow water and small substances to pass between blood plasma and interstitial fluid.
Why is fluid balance important for the body?
Fluid balance is essential for health, as it ensures water and dissolved substances are correctly shared between compartments, allowing proper function.
What is fluid balance?
When water and solutes are at the right levels and evenly distributed across different body compartments (cells, tissues, blood plasma).
What percentage of body weight is water?
45-75% of body weight, varying by age, gender, and body fat content.
How much water is in fat tissue (adipose)?
Less than 20% of fat tissue is water.
How much water is in muscle tissue?
About 65% of muscle tissue is water.
Why do leaner people have higher water content?
Because muscle contains more water (65%) than fat tissue (20%), and leaner people have more muscle mass.
Which age group has the highest percentage of body water?
Infants, with up to 75% of their body mass being water.
Between which compartments does water exchange occur?
- Between blood plasma and interstitial fluid (in capillaries) 2. Between interstitial fluid and intracellular fluid (inside cells)
Why do people with more body fat have less total body water?
Because fat tissue contains very little water (less than 20%) compared to other tissues.
What are the four main processes of fluid and solute exchange?
- Filtration - moves substances from blood to interstitial fluid
- Reabsorption - returns substances to blood
- Diffusion - moves solutes from high to low concentration
- Osmosis - moves water based on solute concentration
How does osmosis work?
Water moves toward areas with higher solute concentration to balance concentrations.
What are electrolytes and what is their role?
Electrolytes are ions (like Na+, K+, Cl-) that dissolve in water. They control water movement because water follows electrolytes through osmosis.
What are the two ways the body gains water?
- Drinking fluids and eating foods
- Metabolic synthesis (chemical processes in cells)
What are the four ways the body loses water?
- Urination (primary way)
- Sweating
- Breathing (water vapor)
- Feces
How do kidneys handle excess water?
They produce dilute urine to get rid of extra water.
How do kidneys handle excess electrolytes?
They produce concentrated urine to excrete excess electrolytes.
What is the main purpose of kidney regulation of water and electrolytes?
To maintain homeostasis (stable internal conditions) in the body.
What are three examples of electrolytes?
Sodium (Na+), Potassium (K+), and Chloride (Cl-)
What are Starling Forces?
Forces (hydrostatic and osmotic) that control fluid movement in and out of capillaries at both arterial and venous ends.
What are the two types of Starling Forces?
- Hydrostatic pressure 2. Osmotic pressure
What is hydrostatic pressure in capillaries?
The pressure exerted by blood pushing against capillary walls, which pushes fluid and solutes out into interstitial fluid.
What is osmotic pressure in capillaries?
Pressure created by solutes (like blood proteins) inside capillaries that pulls water back into the blood vessels.
What is filtration in capillaries?
The movement of fluid through capillary walls into the interstitial fluid (occurs at arterial end).
What is reabsorption in capillaries?
The movement of fluid from interstitial fluid back into the capillary (occurs at venous end).
Where does filtration occur in capillaries?
At the arterial end of the capillary.
Where does reabsorption occur in capillaries?
At the venous end of the capillary.
Why are Starling Forces important?
They maintain proper fluid balance between blood and tissues, ensuring nutrient delivery and preventing swelling (edema).
What is Blood Hydrostatic Pressure (BHP)?
The pressure exerted by blood against the capillary walls, generated by the pumping action of the heart.
What is the BHP at the arterial end of the capillary?
35 mmHg
What is the BHP at the venous end of the capillary?
16 mmHg
What is the role of Blood Hydrostatic Pressure in filtration?
It pushes fluid and nutrients out of the blood and into the interstitial fluid.
What is Interstitial Fluid Osmotic Pressure (IFOP)?
A pressure created by solutes in the interstitial fluid that ‘pulls’ water out of the capillaries.
What is the constant value of IFOP?
About 1 mmHg
How does IFOP contribute to filtration?
It adds a minor pulling effect, helping to draw water and solutes into the tissues.
What is the main effect of BHP and IFOP working together?
BHP pushes fluid out while IFOP pulls some fluid in, ensuring tissues receive necessary nutrients and oxygen.
What is Blood Colloid Osmotic Pressure (BCOP)?
The pulling pressure created by plasma proteins in the blood that are too large to pass through capillary walls.
What is the constant value of BCOP at both ends of the capillary?
26 mmHg
Why do plasma proteins stay within the capillaries?
They are too large to pass through the capillary walls.
What is Interstitial Fluid Hydrostatic Pressure (IFHP)?
The pressure exerted by interstitial fluid on capillary walls.
What is the normal IFHP value?
Close to 0 mmHg
When does IFHP become significant?
During edema (fluid accumulation in tissues)
What are the two pressures that promote reabsorption?
- Blood Colloid Osmotic Pressure (BCOP) 2. Interstitial Fluid Hydrostatic Pressure (IFHP)
Which pressure is the dominant force in reabsorption?
Blood Colloid Osmotic Pressure (BCOP)
What is the main purpose of reabsorption?
To move fluid back into the capillaries from the surrounding interstitial fluid to maintain fluid balance.
What pressure pushes fluid out of the capillaries at the arterial end?
Blood Hydrostatic Pressure (BHP) at 35 mmHg.
What is the Blood Colloid Osmotic Pressure (BCOP) at both ends of the capillary?
26 mmHg.
What is the Net Filtration Pressure (NFP) at the arterial end?
10 mmHg, favoring filtration.
What happens to fluid at the arterial end of the capillary?
Fluid moves out into the interstitial fluid (net filtration).
What pressure at the venous end pulls fluid back into the capillaries?
Blood Colloid Osmotic Pressure (BCOP).
What is the Blood Hydrostatic Pressure (BHP) at the venous end?
16 mmHg.
What is the Net Filtration Pressure (NFP) at the venous end?
-9 mmHg, favoring reabsorption.
What system collects excess fluid not reabsorbed into the capillaries?
The lymphatic system.
Why is fluid balance important?
To ensure tissues receive nutrients and oxygen while preventing fluid accumulation (swelling).
What happens in the descending limb of the Loop of Henle?
Water is reabsorbed by osmosis, concentrating the filtrate.
What does increasing osmolarity in the renal medulla cause?
It leads to more water being reabsorbed from the descending limb.
What is the role of symporters in the thick ascending limb?
They actively reabsorb sodium (Na⁺), potassium (K⁺), and chloride (Cl⁻) ions.
Why does water not leave the thick ascending limb?
This segment has low water permeability, so water remains in the tubule.
What is the effect of solute reabsorption in the thick ascending limb?
It makes the remaining fluid in the nephron more dilute.
What happens in the late distal convoluted tubule (DCT) and collecting duct?
They have low water permeability in the absence of ADH.
What effect does ADH (antidiuretic hormone) have on the collecting duct?
It increases water reabsorption, concentrating the urine.
What type of urine is produced when there is no ADH present?
Dilute urine, due to low water reabsorption.
What happens in the descending limb of the nephron?
Water is reabsorbed, which increases osmolarity.
What happens in the ascending limb of the nephron?
Solutes are reabsorbed without water, which decreases osmolarity.
What is the effect of no ADH (antidiuretic hormone) on urine?
It results in the formation of dilute urine.
What makes concentrated urine formation possible?
The action of ADH (antidiuretic hormone) and the osmotic gradient of solutes in the interstitial fluid of the renal medulla.
What are juxtamedullary nephrons?
Special nephrons with long loops of Henle that extend deep into the renal medulla.
What is the countercurrent multiplier?
A mechanism that creates and maintains the osmotic gradient in the kidney by pumping solutes out of the ascending limb.
What happens in the ascending limb during urine concentration?
Solutes are pumped out, but water stays in the tubule because it’s impermeable to water.
How does urea contribute to urine concentration?
Movement of water carries urea into the medulla, contributing to its osmolarity.
What is the role of ADH in concentrated urine formation?
It increases water permeability in the distal tubules and collecting ducts, allowing more water reabsorption.
Why are long loops of Henle important?
They help create and maintain the osmotic gradient necessary for concentrating urine.
What is the main purpose of concentrating urine?
To conserve water in the body, especially when fluid intake is low.
What is necessary for the formation of concentrated urine?
The action of ADH (antidiuretic hormone) and the osmotic gradient of solutes in the renal medulla.
How is the osmotic gradient in the kidney created?
By the countercurrent multiplier mechanism.
What happens in the ascending limb of the loop of Henle?
Solutes are actively pumped out, but water stays in the tubule because it is impermeable to water.
What happens to the osmolarity of the medulla during urine concentration?
Medulla osmolarity is increased.
How does the movement of water affect urea in the renal medulla?
It carries urea into the medulla, contributing to its osmolarity.
What is the primary role of ADH in the formation of concentrated urine?
To increase water reabsorption in the collecting ducts.
Why are long loops of Henle important in urine concentration?
They help create and maintain the osmotic gradient necessary for water reabsorption.
How does the body gain water?
Through ingestion (liquids and moist foods) and metabolic synthesis.
How much water is gained from ingested liquids daily?
About 1600 mL.
How much water is gained from moist foods daily?
About 700 mL.
What is the total water gain from ingestion per day?
Approximately 2300 mL (1600 mL + 700 mL).
What is metabolic water, and how much is produced daily?
Water produced during aerobic respiration and dehydration synthesis, totaling about 200 mL/day.
What is the total daily water gain in the body?
About 2500 mL (2300 mL from ingestion + 200 mL from metabolic synthesis).
What is the primary source of water loss in the body?
Kidneys, excreting about 1500 mL/day as urine.
How much water is lost through the skin daily?
About 600 mL (400 mL from insensible perspiration + 200 mL from sweat).
How much water do the lungs exhale daily?
About 300 mL as water vapor.
What is the daily water loss through the digestive canal?
About 100 mL in feces.
How does water loss vary in women of reproductive age?
They may lose additional water during menstrual flow.
What is the total daily water loss in the body?
Approximately 2500 mL (1500 mL from kidneys + 600 mL from skin + 300 mL from lungs + 100 mL from digestive canal).
What is fluid homeostasis?
The balance between water gain and loss to maintain stable internal conditions.
What can affect the amount of water lost by the body?
Increased sweating during physical activity or heat and fluid loss during diarrhea or illness.
What determines the volume of metabolic water formed in the body?
The level of aerobic respiration (ATP demand in body cells).
Where is the thirst center located and what does it do?
Located in the hypothalamus; regulates water intake by controlling the urge to drink.
What is dehydration?
A condition when water loss is greater than water gain, leading to decreased blood volume and increased osmolarity.
What are the 5 main triggers that stimulate the thirst center?
- Osmoreceptors detecting high blood osmolarity 2. Volume receptors detecting low blood volume 3. Baroreceptors detecting low blood pressure 4. Angiotensin II production 5. Mouth dryness from decreased saliva.
What happens when blood volume decreases?
Blood pressure falls and blood osmolarity increases, stimulating the thirst center.
Who is most at risk for delayed thirst response?
Elderly people, infants, and those in confused mental states.
When should you drink fluids during excessive fluid loss?
Before feeling thirsty, especially during heavy sweating, diarrhea, or vomiting.
What is the relationship between ATP production and metabolic water?
More ATP production leads to more metabolic water formation.
How is normal fluid volume restored?
Through increased fluid intake triggered by thirst sensation, which balances fluid loss.
How does the body primarily eliminate excess water?
Through urine production.
What is the main factor determining body fluid volume?
The amount of urinary salt (NaCl) loss.
What are the two main solutes in urine?
Sodium ions (Na⁺) and chloride ions (Cl⁻).
What happens to water in relation to solutes during osmosis?
Water follows solutes.
What determines body fluid osmolarity?
The extent of urinary water loss.
What hormone regulates water loss?
ADH (Antidiuretic Hormone).
What are the four main triggers for ADH release?
- Increased blood osmolarity 2. Decreased blood volume 3. Decreased blood pressure 4. Other factors (pain, nausea, stress)
What detects increased blood osmolarity?
Osmoreceptors in the hypothalamus.
What detects decreased blood volume?
Atrial volume receptors.
What detects decreased blood pressure?
Baroreceptors in blood vessels.
Where is ADH synthesized?
In neurosecretory cells of the hypothalamus.
Where is ADH released from?
The posterior pituitary gland.
What effect does ADH have on the kidneys?
Makes late distal tubules and collecting ducts more permeable to water, increasing water reabsorption.
What are the three main effects of increased water reabsorption?
- Decreases blood osmolarity 2. Increases blood volume 3. Increases blood pressure
What are the three main stimulants of ADH release?
- Decreased blood volume 2. Decreased blood pressure 3. Pain, nausea, and stress
What detects decreased blood volume?
Atrial volume receptors in the heart
What detects decreased blood pressure?
Baroreceptors in blood vessels
How does alcohol affect ADH?
Alcohol inhibits ADH secretion, leading to increased urine production (diuresis)
What are the two major hormones that control renal Na⁺ and Cl⁻?
- Aldosterone 2. Atrial Natriuretic Peptide (ANP)
Why do Cl⁻ ions typically follow Na⁺ ions?
Due to electrical attraction or transport via symporters
What triggers Aldosterone release?
- Decreased blood pressure 2. Decreased blood volume 3. Deficiency of Na⁺ in plasma
What is the main effect of Aldosterone?
Increases Na⁺ reabsorption in late distal tubules and collecting ducts of kidneys
What triggers ANP release?
Increased blood volume stretching the atria of the heart
What is natriuresis?
Elevated excretion of Na⁺ into urine
What are the main effects of ANP?
- Promotes Na⁺ excretion in urine 2. Increases water loss through osmosis 3. Decreases blood volume and pressure 4. Slows renin release
How does ANP affect the renin-angiotensin-aldosterone pathway?
It slows renin release, leading to less aldosterone production and decreased Na⁺ reabsorption
What does it mean when extracellular fluid (ECF) is isotonic to body cells?
The osmolarity of intracellular fluid (ICF) and extracellular fluid (ECF) is the same, so cells do not shrink or swell.
What happens to cells when extracellular fluid becomes hypertonic?
Water moves from cells into the ECF, causing cells to shrink.
What is hypertonic ECF?
ECF with a higher concentration of solutes than ICF, leading to increased osmolarity.
What causes increased osmolarity in extracellular fluid?
Increased levels of Na⁺ and Cl⁻, often from consuming a salty meal.
What can happen if brain cells shrink due to prolonged hypertonic conditions?
Mental confusion, convulsions, coma, or even death.
How does the body correct hypertonicity?
Through the thirst mechanism and secretion of antidiuretic hormone (ADH) to increase water intake and retention.
What happens to cells when extracellular fluid becomes hypotonic?
Water moves into cells from the ECF, causing cells to swell.
What is hypotonic ECF?
ECF with a lower concentration of solutes than ICF, leading to decreased osmolarity.
What role do Na⁺ and Cl⁻ play in fluid movement?
They are major contributors to the osmolarity of ECF, affecting how water moves between compartments.
What is the consequence of drinking large amounts of water on ECF osmolarity?
It decreases osmolarity in ECF, leading to water moving into cells, which causes them to swell.
What is water intoxication?
Water intoxication occurs when excess body water causes cells to swell dangerously.
When does water intoxication usually happen?
It may occur when a person consumes water faster than the kidneys can excrete it.
What problems can swelling of cells cause?
Swelling of cells causes similar types of problems as shrinking of cells does.
What are the symptoms of swelling neurons in the brain due to water intoxication?
Symptoms include mental confusion, seizures, coma, and possibly death.
What are electrolytes?
Substances that dissociate into ions when dissolved in water.
What is one role of ions in body fluids?
To control osmosis of water between fluid compartments.
How do ions help maintain the acid-base balance?
By regulating pH levels in the body.
How do ions carry electrical currents?
They generate signals for processes like nerve impulses and muscle contractions.
What role do electrolytes play as cofactors?
They assist in enzymatic activities in the body.
In what unit is the concentration of ions in body fluids expressed?
Milliequivalents per liter (mEq/L).
What does mEq/L indicate about ions?
It gives the concentration of cations or anions in a given volume of solution.
