Phy-Sino-Logy : the kidney 肾 Inspired by Hello Kitty!

Kidney carry out many functions, and is not merely an excretory organ of metabolic waste such as urea (you'll get uremia when your kidney damaged), and metabolic acid load (you'll get metabolic acidosis when your kidney damaged, please differentiate this with the function of lung in excreting the volatile acid CO2). Kidney is also a major conservation centre of CATion (Meow~ such as sodium and potassium). Kidney also serve endocrine function in activating Vitamin D and secreting Erythropoietin in hypoxic state.

the 2 vertical stroke(blue color hormone and yellow color nerve) on the left upper 肾 can be thought as Neuro-Hormonal control of kidney function. Kidney receives only sympathetic innervation of autonomic nervous system, that's the renal sympathetic nerve that mediate renal arteriolar vasocontriction during hypovelemia via baroceptor reflex, as a mean to increase "total" peripheral resistance (and hence blood pressure) and to decrease sodium filtered load (as a mean of sodium conservation in negative sodium balance, hence blood volume and blood pressure homeostasis). Various hormones release by and act on kidney such as the Renin release from Juxta-Glomerular cell, Angiotensin ll that act on kidney, Atrial/Brain Natri-uretic peptide, aldosterone, ADH and so on.

The 又 in right upper 肾 can be thought of being a glomerulus which is important for kidney to generate glomerular filtrate. (Remember that urine formation occur by filtration but not secretion! so remember the glomerulus) Glomerular filtration rate (GFR) is an indicator of kidney function.GRF is about 180L/day OR 120ml/min.When we compared with our plasma volume which is 3L in adult male of 70kg, the kidney GFR is 60 X greater than plama volume, this underlies the important function of kidney in conserving ECF& Plasma volume and Blood Pressure.(BP OR B.Pee)

In vivo/clinically, we can use endogenous Creatinine clearance/Cystitin C clearance to estimate GFR. In vitro, we can infuse exogenous inulin and calculate inulin clearance to estimate GFR. there is also 2 arterioles supplying the glomerulus known as afferent arteriole and efferent arteriole that involve in regulation of the Starling Forces - Glomerular Hydrostatic Pressure, thus GFR. The 2 arterioles can be thought of being the "tail" of the word 又 in right upper 肾.

There is a phenomenon called autoregulation, which is the INTRINSIC ability of DENERVATED kidney in local regulation/maintenence of renal perfusion/blood flow and hence glomerular filtration rate, despite fluctuating perfussion pressure (the physiologic range of kidney autoregulation is mean arterial blood pressure of 80-160 mmHg). In vivo, during hypovolemia, symphathetic innervation override the autoregulation of kidney, but the autoregulation has it's protective function to prevent serious ischemic damage of kidney from intense vasoconstrictive effect of renal symphathetic nerve leading to what we called acute kidney injury (AKI). Prostaglandin(PG) is one of the mediator of the kidney autoregulation and NSAID that block PG synthesis can precipitate AKI.

Speaking of clearance, it is a concept rather than a real life phenomenon. it is the VOLUME of PLASMA(NOT WHOLE BLOOD!) cleared of a solute per unit TIME (Unit: ml/min). Clearance of Inulin is used to estimate GFR because inulin is freely filtered and not modify (secretion and reabsorption) any further along the nephron. Clearance of Para-AminoHippuric acid (PAH) is used to estimate EFFECTIVE renal PLASMA flow. PAH is freely filtered and complete secretion occur at low plasma PAH concentration. the word "effective" is used because not all blood (90%) that reach kidney supply the glomerulus where filtration occur. Estimation of renal plasma flow involve the application of the Fick's Principle/principle of mass conservation.(You can see from the 3 different colors tube emerging from the Kitty-Kidney that anatomically represent the renal vein, artery and pelvis that involves in the working Fick's Principle)

Hello Kitty is not a Kitty Cat, but Hello Kidney involve in regulation of important CAT-ion, meow! they are Sodium. Potassium, Calcium, Hydrogen and so on. Detail discussion of each regulation is beyond the scope of this picture. Kidney handling of sodium happen nearly at all segment of nephron and the mechanism of action of different diuretic agents are targeting on the physiologic basis of kidney handling of sodium. However, i wish to point out that, Potassium NET reabsorption never/rarely occur in adult with normal diet, only with low potasium diet will the body start to conserve potassium. It is because potassium imbalance has drastic effect on extracellular potassium concentration that will affect the function of excitable tissue especially cardiac tissue (arrhythmia)

the 2 green drops of Urine that excreted by Kitty Kidney is the urine. Here i wish to bring out the concept of Free Water Clearance, which give in an equation, Free Water Clearance = Urine Flow rate - Osmotic Clearance (Unit: ml/min). Negative free water clearance occurs when body try to conserve water. Positive water clearance occurs when body try to excrete water. This function of kidney is important in Osmoregulation/regulation of ECF Osmolality/Sodium CONCENTRATION/water balace. Osmoregulation is mediate by ADH secreted from neuroendocrine cell in posterior pituitary originate from supraoptic nucles of hypothalamus.

Phiew~ after the long passage.
Remember
Hello Kidney is not a Kitty, but it definitely important in CAT-ion regulation! Meow~