Chapter 26 fluid, electrolyte, acid base
Name three receptors stimulated by low blood volume.
(or other stimuli) Baroreceptor Angiotensin II
Explain the importance of obligatory water losses.
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Describe factors that determine fluid shifts in the body.
Increasing the ECF solute content can be expected to cause osmotic & volume changes in the ICF - a shift of water out of the cells. Conversely, decreasing ECF osmolality causes water to move into the cells, Thus the ICF volume is determined by the ECF solute concentration.
List and compare the water content of males, females, and infants
Infants = 73% Elderly =45% Healthy young man = 60% Healthy young woman = 45%
Describe the osmotic effects of the electrolytes and nonelectrolytes in each compartment.
Substances must pass through both the plasma & IF in order to reach the ICF. Water moves freely between the compartments along osmotic gradients, solutes are unequally distributed because of their size/electrical charge/or dependence on transport proteins.
ADH acts on the ____________ to ___________ water excretion.
kidneys; decrease
Explain how potassium, calcium, and anion balance of plasma is regulated.
~90% of filtered potassium is reabsorbed by the more proximal regions of the nephrons. Potassium ion secretion via aldosterone. Calcium balance is regulated by PTH, which enhances blood Ca2+ levels by targeting the bones, intestine & kidneys. PTH reabsorption occurs in the DCT. Chloride is the major anion accompanying sodium resborption.
The kidneys reabsorb most of the filtered K+ in the proximal parts of the kidney's tubules and then secrete just the right amount in the distal parts.
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Water in the body occupies two main fluid compartments. Most fluid is in the intracellular fluid (ICF) compartment. ICF is fluid found inside of cells. The rest of our body water is in the extracellular fluid (ECF) compartment. The ECF consists of plasma and interstitial fluid (IF), the fluid in the spaces between tissue cells.
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Indicate the typical volume of water intake per day.
2500ml a day in adults
Indicate the typical volume of water output per day.
2500ml a day in adults
Describe the effect of ADH on arterioles and blood pressure.
ADH also acts to constrict arterioles, directly increasing blood pressure
ADH by itself cannot reduce an increase in osmolality in body fluids. Why not? What other mechanism is required?
ADH cannot add water. It can only conserve what is there. In order to reduce an increase in osmolality of body fluids, the thirst mechanism is required.
What change in plasma is most important for triggering thirst? Where is that change sensed?
An increase in osmolality of the plasma is most important for triggering thirst; hypothalamus
Aldosterone
Atrial natriuretic peptide (ANP) and progesterone increase Na+ excretion. Aldosterone is the key regulator of sodium reabsorption in the kidney. It encourages Na+ reabsorption. Estrogens, like aldosterone, also encourage Na+ reabsorption.
Describe mechanisms involved in regulating sodium balance, blood volume, and blood pressure.
Declining blood pressure stimulate granular cells to release renin. Cardiovascular system baroreceptors sense changing blood pressure; falling arterial pressure promotes vasoconstriction and conserves Na+ and water.
Describe possible causes and consequences of dehydration, hypotonic hydration, hyponatremia, and edema.
Dehydration occurs when water loss exceeds water intake over time, can lead to hypovolemic shock; Hypotonic hydration occurs when body fluids are excessively diluted & cells become swollen by water entry, cerebral edema; Edema is abnormal accumulation of fluid in the IF which may impair blood circulation
Name the forces that determine fluid movement from plasma to interstitial fluid.
Exchanges between plasma and IF occur across capillary membranes
Hypotonic hydration
Hypotonic hydration causes hyponatremia (low concentration of Na+ in the extracellular fluid), leading to cell swelling. ,br>Edema (tissue swelling) is an atypical accumulation of fluid in the interstitial space, leading to tissue (not cell) swelling. Edema can be caused by any event that increases fluid loss from the blood to the tissues, or that prevents effective return of fluid from the interstitial space to the bloodstream
Name the two main fluid compartments of the body and indicate their relative fluid volumes.
Intracellular fluid compartment & Extracellular fluid compartment: IFC accounts for 25 L of the 40 L of water EFC accounts for the remaining 1/3 or 15L
Which do you have more of: extracellular or intracellular fluid? Plasma or interstitial fluid?
Intracellular; and more interstitial fluid then plasma
Indicate the routes of electrolyte entry and loss from the body.
Most electrolytes (salts) are obtained from ingested foods and fluids. Electrolytes are lost in perspiration, feces & urine. The kidneys are MOST important in regulating electrolyte balance
List the sources of the water intake; indicate their volumes and percentage of the total intake.
Most water enters the body through ingested liquids & solid foods. Beverages = 60%, Foods = 30%, Metabolism = 10%
Glucose
NOT an electrolyte
Name and indicate the chemical symbols of the predominant extracellular and intracellular electrolytes of each compartment
Na+ = sodium; K+ = potassium, Ca2+ = calcium, Mg2+ = magnesium, HCO-3 = Bicarbonate, Cl- = Chloride, HPO42- = Hydrogen phosphate, SO42- = sulfate
What is the major cation in the ECF? in the ICF? What are the intracellular anion counterparts of ECF's chloride ions?
Na+ is the major cation in the ECF & K+ is the major cation in the ICF. The intracellular counterparts to extracellular Cl- are HPO and protein anions.
List the factors that determine body water content and describe the effect of each factor.
Not all bodies contain the same amount of water. Total body water is a function not only of age and body mass but also of sex and the amount of body fat.
What hormone is the mjr regulator of Ca2+ in the blood? What are the effects of hypercalcemia? Hypocalcemia?
PTH; Hypercalcemia decreases excitability of neurons & muscle cells and may cause life threatening cardiac arrhythmias. Hypocalcemia increases excitability & causes muscle tetany.
Jacob has Addison's disease (insufficient aldosterone release) How does this affect his plasma Na+ and K+ levels? Blood pressure?
Plasma Na+ would decrease and his plasma K+ elevated. The decrease in plasma Na+ would cause a decrease in blood pressure, because plasma Na+ is directly related to blood volume, which is a mjr determinant of blood pressure.
Name the predominant nonelectrolytes of each compartment.
Plasma contains more proteins than does interstitial fluid; otherwise, extracellular fluids are similar. the most abundant ECF electrolytes are sodium/chloride/bicarbonate ions. ICF contain lrg amounts of protein anions/potassium/phosphate/magnesium ions
Compare the relative concentration of the solutes in Extracellular (ECF) and Intracellular fluids (ICF).
Proteins & some of the nonelectrolytes found in the EFC are lrg molecules. They account for ~90% of the mass of dissolved solutes in plasma, 60% in the IF, and 97 in the ICF.
Progesterone
Reabsorption of sodium does not exhibit a transport maximum. In healthy individuals, nearly all sodium in the renal filtrate is reabsorbed in the proximal convoluted tubules of the kidneys.
Most of the hydrogen ions in the body DOES NOT come from acidic substances in the foods we ingest.
Small amounts of acids enter the body via ingested foods. However, most H+ ions originate as metabolic by-products or end products. For example, the breakdown of phosphorus-containing proteins, the anaerobic breakdown of glucose, fat metabolism, and the loading and transport of CO2 in the blood all serve as sources of hydrogen ions in the body.
Describe the importance of ionic sodium in fluid and electrolyte balance of the body, and indicate its relationship to normal cardiovascular system functioning.
Sodium ion balance is linked to ECF volume & blood pressure regulation & involves both neural & hormonal controls.
Name the two stimuli that excite the hypothalamic thirst center and identify which one is more potent.
The hypothalamic thirst center neurons are stimulated when their osmoreceptors lose water by osmosis to the hypertonic ECF, or are activated by angiotensin II, by baroreceptor inputs or other stimuli
Describe the hormonal controls of water output in urine.
The kidney must normally flush 600 mmol per day of urine solutes out of the body in water. The maximum concentration of urine is about 1200 mOsm, so a minimum of 500ml of water must be excreted.
Most abundant cation in ECF
The most abundant cation (or positively charged ion) in the extracellular fluid (ECF) is sodium (Na+). The most abundant anion (or negatively charged ion) in the ECF is chloride (Cl-).
Most abundant cation in ICF
The most abundant cation in the intracellular fluid (ICF) is potassium (K+). The most abundant anion in the ICF is hydrogen phosphate (HPO4-).
Which of the following has the least influence over the pH of blood plasma?
The phosphate buffer system
Describe feedback mechanisms that regulate water intake.
Thirst Mechanism is the driving force for water intake. An increase in plasma osmolality of only 2-3% excites the hypothalamic thirst center.
List the routes of water output per day and indicate their volumes and percentage of the total output.
Urine = 60%, skin/lungs = 28%, Sweat = 8%, Feces = 4%
If you eat salty pretzels, what happens to the volume of your extracellular fluid?
Your extracellular fluid will expand even if you don't ingest fluids, because water will flow by osmosis from the intracellular fluid to the extracellular fluid.
Describe the degree of reabsorption of water by the collecting ducts and indicate the type of urine produced when ADH levels are high.
aquaporins are inserted in the pricipal cell luminal membranes, nearly all of the filtered water is reabsorbed and a small volume of concentrated urine is excreted.
Copious sweating
dehydration
Loss of plasma proteins due to liver failure
edema
One way the kidneys maintain HCO3- balance is by:
generating new HCO3-. The most important renal mechanism for regulating acid-base balance of the blood involves controlling blood bicarbonate (HCO3-) levels. This is achieved by conserving or generating HCO3- and excreting HCO3-.
Using ecstasy (MDMA) which promotes ADH secretion
hypotonic hydration (interferes with the body's ability to get rid of extra water)
Describe the degree of reabsorption of water by the collecting ducts and indicate the type of urine produced when ADH levels are low.
most of the water reaching the collecting ducts is NOT reabsorbed but simply allowed to pass through because the lack of aquaporins in the luminal membranes of the principal cells prevents the movement of water. The result is dilute urine & a reduced volume of body fluids
Describe the factors that promote or inhibit the secretion of ADH
prolonged fever, excessive sweating, vomiting or diarrhea, severe blood loss, traumatic burns
Someone who is suffocating would develop:
respiratory acidosis:The most common cause of acid-base imbalance is respiratory acidosis, a result of elevated blood levels of CO2 due to shallow breathing, suffocation, or lung diseases that impede O2 and CO2 exchange.
Hyperventilation can lead to:
respiratory alkalosis:Decreased CO2 levels will increase blood pH. If one hyperventilates, the levels of CO2 drop to below normal levels and can cause respiratory alkalosis.
Define osmolality
the # of solute particles dissolved in 1 kilogram of water; reflects the solution's ability to cause osmosis.
Describe the relationship between the volume of water reabsorbed by the renal collecting ducts and the release of ADH.
the amount of water reabsorbed in the renal collecting ducts is proportional to ADH release
The most important factor that influences K+ secretion is:
the concentration of K+ in blood plasma
Indicate another name for the antidiuretic hormone (ADH) and indicate its source.
vasopressin - ADH release by stimulating the hypothalamic osmoreceptors.
