Physiology of renal hormones

This chapter is related to Section U1(vi) from the 2023 CICM Primary Syllabus, which asks the exam candidate to  "describe the control, secretions and functions of renal and adrenal hormones". It is recognisably a duplication of other primary exam material, such as Section H1(iv) from the renal collection ("outline the endocrine functions of the kidney") and Section G5(iv) from the cardiovascular system ("explain the humoral regulation of blood volume and flow"). 

The reader is referred to the page on the endocrine functions of the kidney and the page dealing with the humoral regulation of blood volume (which involves a lot of renin and angiotensin). More detail is available over there. Here, only the barest summary is reproduced, to wreck some SEO and simplify revision:

  • Hormones which are secreted by the kidney
    • Erythropoietin
      • Secreted from modified cortical fibroblasts
      • Stimulated by hypoxia and angiotensin II
      • Inhibited by inflammatory cytokines
      • Effect is increase in the rate of red cell production and maturation
    • Renin
      • Secreted from juxtaglomerular cells
      • Stimulated by hypotension, sympathetic activation and decreased renal salt delivery
      • Inhibited by angiotension II and normalised blood pressure/volume
      • Effect is to activate RAAS, producing vasoconstriction and salt/water retention
    • Thrombopoietin
      • Secreted from the proximal convoluted tubule
      • Stimulated by thrombocytopenia and inflammatory cytokines
      • Inhibited by itself (negative feedback loop)
      • Effect is to stimulate megacaryocytes and increase platelet production
    • Urodilatin
      • Secreted from DCT cells, directly into the tubule
      • Stimulated (probably) by increased sodium deliery
      • Inhibited (presumably) by decreased sodium delivery
      • The effect to increase sodium reabsoprtion in the collecting duct
  • Hormones which are modified by the kidney
    • Calcitriol (active form of Vitamin D)
      • Modified in the proximal tubule
      • Increased  conversion is stimulated by hypocalcemia, PTH and low vitamin D levels
      • Conversion is inhibited by hypercalcemia, low PTH and high vitamin D levels
      • Physiological role is to increase calcium levels by increasing renal/GI absorption and enhancing osteoclast activity
  • Hormones which are cleared or metabolised by the kidney
    • Insulin
      • 90% cleared by the kidney (proximal tubule)
    • Gastrin
      • 30% cleared by the kidney (probably also proximal tubule)
    • Other hormones:
      • PTH
      • Vasopressin
      • Oxytocin
      • TSH
      • Growth hormone
      • Luteinising hormone

In terms of exam readiness, renal hormones only been specifically been asked about, once, as a part of Question 4 from the first paper of 2017. On the other hand, adrenal hormones are a huge favourite with SAQ writers, as the influence of this group covers half of the ICU drug cupboard (catecholamines, glucocorticoids and mineralocorticoids). Most of these questions understandably have a thoroughly pharmacological inclination, asking the candidate to compare one steroid to another. For this reason, adrenal hormone physiology has been banished to a series of chapters all on its own, where this exam-relevant material is dealt with more thoroughly, and from the viewpoint of a critical care prescriber.