Chapter 7 - Chapter 7 Regulation of Potassium Balance...

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Chapter 7 Regulation of Potassium Balance Potassium Homeostasis Why is it essential to maintain K + balance in the body? It is critical for normal function of excitable tissue: nerve, skeletal and cardiac muscle and smooth muscle Recall: K + concentration gradient across excitable membrane sets the resting membrane potential Changes in resting membrane potential alter excitability by opening or closing gates on the Na + channels … responsible for the upstroke of A.P. Changes in intracellular or extracellular K + concentration will alter the resting membrane potential … alter the excitability of these tissues In a 70 Kg individual, total body K + is 50 mEq/Kg of body weight, or 3500 mEq - 98% of total K + content is in cells (ICF) (150 mEq/L) - 2% in the ECF (4.5 mEq/L) - This large K + concentration gradient is maintained by which pump? Na + -K + ATPase - K + concentration > 5 mEq/L … hyperkalemia - K + concentration < 3.5 mEq/L … hypokalemia - Cardia arrythmias are produced by both hypokalemia and hyperkalemia It is a challenge to maintain low extracellular K + conentration 1. Large amount of intracellular K + … a shift can produce a change The distribution of K + across cell membranes is called internal K + balance - Hormones, drugs, and pathologic states alter this distribution … alter the extracellular K + concentration 2. Variation in dietary K + intake Varies between 50 mEq/day and 150 mEq/ day To maintain balance, urinary excretion of K + must be equal to K + intake - - In other words, K + excretion must be capable of varying from 50 – 150 mEq/day The renal mechanisms that allow for this variability are called external K + balance Internal K + Balance Ingested K + is absorbed by GI tract and enters ECF within minutes after a meal All of the absorbed K + must be excreted by the kidneys. - Done slowly (6 hours)
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- In this time period, buffering K + by cells is important to prevent life-threatening hyperkalemia The amount of K + remains constant. Several hormones, drugs and pathologic states affect internal K + balance. [Table 6.6 in C and fig 6-25 in C] Hormones Hormones such as insulin, epinephrine, and aldosterone increase K + uptake into skeletal muscle, liver, bone and RBC. How? -By stimulating the Na + -K + pump Insulin Stimulates K + uptake into cells after ingestion of K + in a meal A rise in plasma K + concentration after a K + -rich meal occurs in diabetic patients. Hyperkalemia Acute therapy for hyperkalemia is infusion of insulin. Epinephrine Catecholamines affect K + distribution across cell membranes - Done by activating α - and β 2 -adrenergic receptors Propanalol – Stimulation of α -receptors - K + released from cells … may produce hyperkalemia Albuterol – Stimulation of β 2 -receptors - K + enters cells (uptake) … may produce hypokalemia Aldosterone Promotes K + uptake into cells and urinary K + excretion Primary aldosteronism
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This note was uploaded on 01/07/2012 for the course PHCH 6234 taught by Professor Farqui during the Winter '11 term at Palmer Chiropractic.

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Chapter 7 - Chapter 7 Regulation of Potassium Balance...

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