Chapter 27 - Fluid, Electrolytes, and Acid-Base Homeostasis Flashcards
What is Body Fluids?
Between 55-65% of total body mass
2/3 inside cells
1/3 outside cells
1- Intracellular Fluid (ICF):
Cytosol
2- Extracellular Fluid (ECF):
Interstitial Fluid 80%
Blood Plasma 20%
What divides Body Fluids and how do they Interact?
Plasma Membrane:
Separates ICF from Interstitial Fluid
Blood Vessel Walls:
Divide the Interstitial Fluid from Blood Plasma
Capillary Walls:
Thin enough to allow exchange of water and solutes between Blood Plasma and Interstitial Fluid
What allows Continuous Exchange of Water and Solutes among Body Fluid Compartments?
Filtration, Reabsorption, Diffusion, and Osmosis:
Allow continuous exchange of water and solutes among body fluid compartments:
1- Balance of inorganic compounds that dissociate into ions (Electrolytes) is closely related to fluid balance
2- Body gains water by ingestion and metabolic synthesis
3- Body loses water via urination, perspiration, exhalation, and in feces
What determines Volume of Metabolic Water Formed?
Level of Aerobic Respiration determines volume of metabolic water formed:
Amount of water formed is directly proportional to the amount of ATP produced
When water loss is greater than water gain, dehydration occurs, leading to increased thirst
What is the Thirst Response?
1- Increased blood osmolarity:
Stimulates osmoreceptors in Hypothalamus
2- Decrease blood volume:
Decreased activity of Atrial Volume Receptors
3- Decrease BP:
Decreased activity of Baroreceptors in blood vessels
Increase release of Renin from Kidneys -> increased Angiotensin II formed
4- Dry Mouth
5- All of that stimulates Thirst Center in Hypothalamus
6- Increase Thirst
7- Increase water intake
8- Increased water intake:
Decrease blood osmolarity
Increase BP and Blood Volume
Relieves mouth dryness
What is Excess Body Water Elimination?
Elimination of excess body water occurs through urine production
Amount of Urinary salt loss is main factor determining body fluid volume
The 2 Main Solutes in urine:
1- Na+
2- Cl-
Wherever solutes go, water follows
What are the 3 Major Hormones that Control Renal Na+ and Cl-?
1- Angiotensin II
2- Aldosterone
3- Atrial Natriuretic Peptide (ANP)
The major hormone that regulates water loss is ADH
What is Regulation of Water and Solute Loss by ADH?
1- Increased blood osmolarity:
Stimulates osmoreceptors in Hypothalamus
2- Decrease blood volume:
Decreased activity of Atrial Volume Receptors
3- Decrease BP:
Decreased activity of Baroreceptors in blood vessels
4- Other factors such as pain, nausea, and stress
5- All of these increase synthesis of ADH by Neurosecretory Cells in Hypothalamus
6- Increased release of ADH from Posterior Pituitary Gland
7- Late DCT and CD of Kidneys become more permeable to water, which increases water reabsorption
8- The increase of water reabsorption in turn:
Decrease blood osmolarity
Increase BP and Blood Volume
What is Regulation of Water and Solute Loss by Aldosterone?
1- Decrease BP and Na+ deficiency in Plasma
2- Increased release of Renin by Kidneys
3- Increased Aldosterone formation
4- Aldosterone:
Increase Na+ reabsorption in late DCT and CD of Kidneys
Water reabsorption accompanies Na+ reabsorption via Osmosis because ADH is also released when there is decrease in BP
5- Increased Na+ reabsorption relives the Na+ deficiency in Plasma
The accompanying water reabsorption increase BP and Blood Volume
What is Regulation of Water and Solute Loss by ANP?
1- Increased Blood Volume
2- Increased stretch of Atria
3- Release of ANP
4- Increase excretion of Na+ into urine (Natriuresis)
Water excretion into urine also increases due to Osmosis
5- Increase water in excretion causes a decrease in BP and Blood Volume
What is Mechanism and Effect of Thirst Center in Hypothalamus?
1- Mechanism:
Stimulate desire to drink fluids
2- Effect:
Water gained if thirst is quenched
What is Mechanism and Effect of ADH?
1- Mechanism:
Promotes insertion of Aquaporin-2 into Apical membranes of Principal Cells in CD of Kidneys
As a result, water permeability of these cells increase and more water is reabsorbed
2- Effect:
Reduce water loss in urine
What is Mechanism and Effect of Aldosterone?
1- Mechanism:
By promoting urinary reabsorption of Na+ increases water reabsorption via Osmosis
2- Effect:
Reduce water loss in urine
What is Mechanism and Effect of ANP?
1- Mechanism:
Promotes Natriuresis
Elevated urinary excretion of Na+
Accompanied by water
2- Effect:
Increase water loss in urine
What is Water Movement Between Body Fluid Compartments?
When the ECF is Isotonic to the cells of body, they do not shrink or swell
However, changes in osmolarity of ECF (as with dehydration or over-hydration) can cause the cells of body to shrink or swell
What is Water Intoxication?
Water Intoxication:
Occurs when excess body water causes cells to swell dangerously
This may occur when a person consumes water faster than the Kidneys can excrete it
1- Excessive blood loss, sweating, vomiting, or diarrhea coupled with intake of plain water
2- Decrease Na+ concentration (Hyponatremia) of ECF
3- Decreased osmolarity of ECF
4- Osmosis of water from ECF into ICF
5- Water Intoxication (Cells swell)
6- Mental confusion, seizures, coma, and possible death
What is Electrolytes in Body Fluids?
Ions formed when Electrolytes dissociate and dissolve:
1- Control osmosis of water between fluid compartments
2- Help maintain the acid-base balance
3- Carry electrical current
4- Serve as Cofactors
Blood Plasma, Interstitial Fluids, and ICF have different concentrations of Electrolytes and protein ions
Blood Plasma contains more protein ions
Interstitial Fluid contains only a few
What is Na+?
Most abundant Cation (+) in ECF
Used for:
Impulse transmission
Muscle contraction
Fluid and Electrolyte balance
Its level controlled by:
Aldosterone
ADH
ANP
What is Cl-?
Major ECF Anion (-)
Helps regulate osmotic pressure between compartments
Forms HCL in Stomach
Regulated by:
Aldosterone
What is K+?
Most abundant Cation (+) in ICF
Involved in:
Fluid volume
Impulse conduction
Muscle contraction
Regulating pH
Regulated by:
Mineralocorticoids (mainly Aldosterone)
