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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