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Physiology 31 Lecture
Chapter 20 – Fluid & Electrolyte Balance
I. Overview
A. Cellular function requires a fluid medium with a homeostatic balance of the following
1. ______, in which daily water intake and loss are equal
2. ______, in which the amount of electrolytes absorbed by the small intestine balance the amount lost from the body, mainly through the urine
3. ______-_____, in which the body rids itself of acid (H+ ions) at a rate that balances its metabolic production, maintaining a stable pH
B. These balances are maintained by the all of the bodily systems, except for the reproductive system
II. ______Balance & the regulation of ECF Volume
A. The average person’s body is about ___-__% water
B. ______in which water is found include
1. 65%in intracellular fluid (___) within cells
2. 35% in extracellular fluid (___), which includes
a. 25% ______fluid around cells
b. 8% blood ______and lymph
c. 2% ______fluid, such as cerebrospinal, synovial, serous, vitreous & aqueous humors, bile, and fluids in the GI, urinary, and respiratory tracts
C. Water moves by ______ from one compartment to another, so the ECF and ICF osmolarities rarely differ
D. A person is in a state of water ______when daily water intake and losses are equal
1. Water gains come mainly from ______water, in addition to a small amount of water from cellular respiration
2. Water is lost mainly in ______, as well as from feces, expired breath, and sweat through the skin
3. ______can cause a significant water loss
4. Intravenous (___) fluids may be needed to replace water loss
E. Fluid intake is regulated by the thirst center in the ______
1. The hypothalamus responds to signs of ______, such as
a. ______II, produced in response to falling blood pressure
b. Decreased ______stretch, due to low blood volume
c. Signals from ______ neurons in the hypothalamus that monitor blood osmolarity
d. _____ (vassopressin), is synthesized and released in response to rising blood osmolarity
e. ADH stimulates water ______from kidney tubules
2. ______is stimulated and satiated by
a. The thirst center sends sympathetic signals to the salivary glands to inhibit ______
b. Short-term satiation of thirst is accomplished by cooling and ______the mouth and inflating the stomach
b. Long-term satiation of thirst depends on ______ water from the small intestine and lowering blood osmolarity
F. Fluid output and retention is regulated by factors that control ______output
1. ADH is secreted by the posterior pituitary gland in response to ______, which causes the kidneys to reabsorb water. ADH release is ______if
a. Blood ______or pressure are too high, or
b. Blood ______is too low
2. Aldosterone, released by the adrenal cortex, causes ______(and water)to be reabsorbed from the kidneys. Adosterone secretion is influenced by
a. Increased plasma ___ concentration causes aldosterone release; results in K+ ______from the blood to the kidney tubules (prevents hyper______)
b. Angiotensin II, formed in response to ______ release when BP is low, causes secretion of ______
c. Increased ECF osmolarity inhibits aldosterone secretion, thus more ____ is excreted in the urine
3. Atrial Naturetic Peptide (_____), released during high BP,promotes Na+ and water ______, and inhibits the release of _____, renin, and aldosterone
G. ______of Water Balance occur if there is an abnormality of total fluid volume, concentration, or distribution among the compartments
1. Fluid deficiency arises when output exceeds intake over a period of time. Two kinds of fluid ______are
a. Volume depletion (hypo______), in which proportionate amounts of water and ______are lost; may be due to hemorrhage, burns, vomiting, diarrhea, or hyposecretion of ______
b. Dehydration (negative water balance), in which volume is reduced and osmolarity is elevated because the body has lost more ______than sodium; caused by lack of drinking water, diabetes mellitus, _____ hyposecretion, profuse sweating
c. Severe fluid deficiency can result in circulatory _____ and death
2. Fluid ______can occur in two forms
a. Volume excess - the retention of excess fluid with normal ______; can result from aldosterone hypersecretion or ______failure
b. ______hydration (water intoxication) – the retention of more water than sodium, reducing osmolarity, as when one loses water and sodium in ______and drinks plain water; can cause pulmonary and cerebral edema
3. Fluid sequestration – total body water may be normal, but fluid may accumulate in a particular location; occurs in ______, hemorrhage, and pleural effusion where fluids accumulate in the pleural cavity
III. Electrolyte Balance
A. Electrolyte (_____) functions include
1. Provide enzyme ______(e.g., Zn2+, Mg2+)
2. Allow action potentials in neurons and muscles (____, K+, Cl-)
3. Stimulate the secretion and action of hormones and neurotransmitters (e.g., _____)
4. Allow muscle contraction (____)
5. Maintain acid-_____ balance (H+, HCO3-, and phosphates)
6. Allow secondary active ______across membranes (Na+, K+)
7. Stimulate ______across cell membranes
B. Major ______ include Na+, K+, Ca2+, and H+
C. Major ______ are Cl-, HCO3- , phosphates (HPO42- and H2PO4-), and proteins
D. Sodium (____)is the main cation in the _____
1. Na+ ______include
a. ______and fluid balance
b. ______and muscle activity
c. ______of molecules (e.g., glucose, amino acids) across cell membranes
d. Acid-base ______(NaHCO3)
e. ______generation via the Na+/K+ pump
2. Sodium homeostasis is maintained by
a. ______ promotes Na+ reabsorption
b. ______reduces Na+ concentration by promoting water reabsorption independently of Na+
c. Atrial naturietic ______ inhibits Na+ and water reabsorption, lowering blood pressure
3. Imbalances of sodium include
a. Hyper______ is an excess of Na+, which causes water retention, hyper______, and edema
b. ______natremia is a deficiency of Na+, often a result of hypotonic ______; salt appetite is stimulated in the hypothalamus
E. Potassium (___) is the major cation in the _____. It has similar functions as Na+, and is a cofactor for some enzymes
1.Potassium homeostasis is maintained mainly by ______, which promotes excess K+ excretion by the kidneys
2. Imbalances of potassium include
a. Hyper______ causes serious nerve and muscle dysfunction, and can cause cardiac arrest!
1) If plasma and ECF K+ increases, the concentration ______decreases, and more K+ remains inside cells, ______them initially
2) Cells are unable to ______fully, causing cells to become less excitable
b. ______kalemia inhibits nerve and muscle function
1) Increase in K+ gradient causes more K+ to ______cells, ______polarizing them
2) Hyperpolarized cells are more difficult to depolarize to ______for action potentials
F. Chloride (___) is the major anion of the _____
1. Chloride ______include
a. Regulation of osmotic balance (with ____)
b. Formation of stomach acid (____)
c. The chloride shift mechanism in respiratory and renal function
2. Chloride homeostasis follows Na+ and other cations, and is regulated as a side effect of ____ homeostasis
3. The primary effect of chloride imbalances is a ___ imbalance
G. Calcium (_____) has low intracellular concentrations, but is often sequestered in smooth ___. __., then released when needed
1. Calcium is necessary for
a. ______contraction
b. ______transmission and exocytosis of neurotransmitters
c. Blood ______
d. A second ______for some hormone actions
e. ______and tooth formation
2. Calcium homeostasis is ______by
a. Parathyroid hormone (____) – ______serum Ca2+ levels by ______reabsorption and intestinal uptake
b. Calcitriol (vit. ___) is required for intestinal uptake of Ca2+
c. Calcitonin – ______serum Ca2+ levels and increases bone deposition
3. Hyper______can result from alkalosis, hyperparathyroidism, or hypo______; causes muscle weakness, depressed reflexes, and cardiac ______
4. ______calcemia can result from acidosis, vit. ___ deficiency, diarrhea, pregnancy, lactation, hypoparathyroidism, or hyperthyroidism; causes potentially fatal muscle ______
H. Phosphates (PO43-, HPO42-, H2PO4-) are relatively concentrated in the ____, where they are generated by _____ hydrolysis
1. Phosphate ______include
a. Phosphates are a component of nucleic acids, phospholipids, ______, GTP, cAMP, and related compounds
b. Phosphates activate many metabolic pathways by ______substances such as glucose and enzymes
c. Phosphates are important acid-base ______
2. Phosphate levels are regulated by parathyroid hormone, which increases phosphate ______and minimizes the formation of CaPO4
3.Phosphate imbalances are not as ______as other electrolyte imbalances
IV. Acid-Base Balance
A. The pH of the ECF is normally maintained between ____-____, despite constant production of ______products (e.g., lactic acid, phosphoric acids, fatty acids, carbonic acid)
B. Acids, Bases, & Buffers
1. An ______ is any chemical that releases H+ ions in solution
a. ______acids (HCl) give up most of their ____ ions and can lower pH significantly
b. ______acids (H2CO3) do not give up many ___ ions, thus affect pH only slightly
2. A ______is any chemical that takes up ____ ions in solution
a. ______bases (-OH) have a strong tendency to bind H+ ions and ______pH
b. ______bases (HCO3-) bind less H+, thus have less of an effect on pH
3. A ______is any mechanism that resists changes in pH by converting strong acids or bases to ______ones. The body has both physiological and chemical buffers
a. Physiological buffers, such as the respiratory and ______systems, stabilize pH by controlling the body’s output of acids, bases, or _____
b. Chemical buffers bind ____ and remove it from solution as its concentration begins to rise, or releases H+ into solution as its concentration falls.
4. Three chemical ______systems in the body are the
a. ______buffer system, represented by the eqn.:
CO2 + H2O H2CO3 HCO3- + H+
(has an optimal pH of 7.4)
1) The lungs and kidneys remove ____, which keeps the rxn. moving to the ______, reducing H+ ions
2) If there is a need to lower pH, the kidneys excrete ______, which moves the rxn. to the ______, increasing the H+ concentration
b. ______buffer system has an optimal pH of 6.8, and is important for buffering the renal tubules & ICF. The rxn. is
H2PO4- HPO42- + H+
c. ______buffer system accounts for ¾ of all chemical buffering in body fluids, due to side groups of amino acids
1) Carboxylic ______groups (-COOH) release H+ when ph begins to rise
2) ______groups (-NH2) bind H+ when pH falls too low
C. Respiratory control of pH - the respiratory system buffers pH by adjusting pulmonary ______
1. Reduced ventilation allows _____ to accumulate in the blood and ______its pH by the rxn.
CO2 + H2O H2CO3 HCO3- + H+
2. Increased ventilation expels ____, reversing the above rxn, lowering H+, and ______the pH
D. Renal control of pH – the ______neutralize more acid or base than any other buffer system in the body
1. They secrete H+ into the tubular fluid, where it binds to chemical buffers and is ______in the urine
2. The above H+ normally ______all the HCO3- in the tubular fluid, making urine bicarbonate free
3. Excess H+ in the tubular fluid can be ______by phosphate and ammonia (NH3+)
E. Disorders of acid-base balance
1. ______is a pH of 7.35
a. ______acidosis occurs when pulmonary gas exchange is insufficient to expel ____ as fast as the body produces it
b. ______acidosis is the result of lactic acid or ______accumulation, ingestion of acidic drugs, such as aspirin, or loss of base, as in diarrhea
2. ______is a pH of 7.45
a. Respiratory alkalosis results from ______ventilation
b. Metabolic alkalosis is rare, but can be caused by overuse of antacids or loss of stomach acid through ______
3. ______acidosis or alkalosis is a pH imbalance that the body cannot correct on its own; it requires clinical intervention (i.e., fluid replacement therapy)
4. ______acidosis or alkalosis is an imbalance that the body’s homeostatic mechanisms can correct
a. Respiratory compensation is correction of the pH through changes in pulmonary ______
b. Renal compensation is correction of pH by changes in ___ excretion by the kidneys
5. ______, electrolyte, and acid-base imbalances are intimately entwined; an imbalance in one area can cause or result from an imbalance in another