(BQ) Part 2 book “Physiology question - based learning” has contents: Renal hemodynamics and GFR, tubular function, potassium and calcium balance, water balance, sodium balance, cardiorespiratory physiology, cardiorenal physiology, respi-renal physiology. | Part III Renal Physiology 98 Part III Renal Physiology Introduction: Renal Physiology The kidneys produce urine. Pee Wee! The kidneys are not merely excreting urine and its contents as a waste product. The formation of urine is linked to a diverse range of physiological functions. The ability of the kidneys to vary the urine concentration is part and parcel of renal osmoregulation. The excretion of small or large urine volumes is associated with regulation of water balance in the body. Renal osmoregulation and control of water balance are both linked to the homeostasis of the common parameter of extracellular fluid (ECF) sodium concentration. The ECF volume and blood volume are also under the governance of the kidneys. ECF volume is determined by the total body sodium, the cation being the key extracellular osmoactive electrolyte. The plasma volume, a fourth part of ECF is thus under renal control. The kidneys also secrete an erythropoietic hormone that maintains the normal hematocrit. Maintaining normal total body sodium or sodium balance is a major role of the renal nephrons. The nephrons and its supply of blood vessels are the target of renal sympathetic nerve which acts during sodium conservation. It might seem odd, unrelated, and a surprise to think about a sympathetic neural activity being involved in sodium electrolyte balance. The kidneys are the primary source of the hormone/enzyme renin which is the initiator of a family of antinatriuretic hormones including angiotensin II and aldosterone. Blood volume control by the kidneys is part of what is also termed “long-term” blood pressure (BP) regulation. To remind students not to forget this, think of BP and BPee. The other important ECF cation that is under renal control is potassium. The renal handling of potassium includes tubular reabsorption and secretion. The adrenal steroid hormone aldosterone has a dual action in regulating the potassium balance besides sodium balance. The blood pH cannot remain .
