Functions of the Kidneys  Regulation of extracellular fluid volume and blood pressure  Regulation of osmolarity--close to 300 mOsm  Maintenance of ion balance: Na + --regulates ECF volume  Homeostatic regulation of pH--kept in a narrow range  Excretion of nitrogenous and other water-soluble wastes  Urea & uric acid  Creatinine from muscle metabolism  Urobilinogen (breakdown of hemoglubin)  Production of hormones  Renin (sodium balance and blood pressure homeostasis

Anatomy: The Urinary System Figure 19-1a

Figure 19-1b Anatomy: The Urinary System

Figure 19-1c Anatomy: The Urinary System

Figure 19-1i Anatomy: The Urinary System

Figure 19-1g–h Anatomy: The Urinary System

Figure 19-1d–e Anatomy: The Urinary System

Figure 19-1f Anatomy: The Urinary System

Figure 19-1j Anatomy: The Urinary System

Renal Summary

Figure 19-2 Kidney Function Filtration, reabsorption, secretion, and excretion Efferent arteriole Afferent arteriole Glomerulus Peritubular capillaries Proximal tubule Bowman’s capsule Collecting duct To renal vein F R S E F R S RR R S R S E Loop of Henle To bladder and external environment = Filtration: blood to lumen = Reabsorption: lumen to blood = Secretion: blood to lumen = Excretion: lumen to external environment KEY Distal tubule

Figure 19-2 (1 of 4) Kidney Function: Filtration Efferent arteriole Afferent arteriole Glomerulus Peritubular capillaries Proximal tubule Bowman’s capsule Collecting duct To renal vein F F Loop of Henle = Filtration: blood to lumen KEY Distal tubule

Figure 19-2 (2 of 4) Kidney Function: Reabsorption Efferent arteriole Afferent arteriole Glomerulus Peritubular capillaries Proximal tubule Bowman’s capsule Collecting duct To renal vein F R F R RR R R Loop of Henle = Filtration: blood to lumen = Reabsorption: lumen to blood KEY Distal tubule

Figure 19-2 (3 of 4) Kidney Function: Secretion Efferent arteriole Afferent arteriole Glomerulus Peritubular capillaries Proximal tubule Bowman’s capsule Collecting duct To renal vein F R S F R S RR R S R S Loop of Henle = Filtration: blood to lumen = Reabsorption: lumen to blood = Secretion: blood to lumen KEY Distal tubule

Figure 19-2 (4 of 4) Kidney Function: Excretion Efferent arteriole Afferent arteriole Glomerulus Peritubular capillaries Proximal tubule Bowman’s capsule Collecting duct To renal vein F R S E F R S RR R S R S E Loop of Henle To bladder and external environment = Filtration: blood to lumen = Reabsorption: lumen to blood = Secretion: blood to lumen = Excretion: lumen to external environment KEY Distal tubule

Figure 19-3 Kidney Function The urinary excretion of substance depends on its filtration, reabsorption, and secretion

Figure 19-4a The Renal Corpuscle

Figure 19-4d The Renal Corpuscle

Figure 19-4c The Renal Corpuscle

Where does a drink of water go?

Figure 19-5 Filtration Fraction

Kidney Function

Measuring glomerular filtration rate  A. Compare the amount of material filtered at the glomerulus with the amount of material excreted in the urine:  1. You can measure the amount of material excreted per unit of time in the urine by measuring the volume of urine produced over a period of time and measuring the concentration of the material in the urine:  concentration X volume/min = amount/minute  2. It is much harder to measure directly the amount of material that was filtered, but it can be calculated.  3. The most common way to accomplish this calculation is to measure the renal clearance of inulin, which allows you to calculate the glomerular filtration rate (GFR).  a. Inulin (not INSULIN) is a fructopolysaccharide with a molecular weight of approximately A common source of this molecule is Jerusalem artichokes.  b. It is freely filtered. In other words, the concentration of inulin in the fluid within Bowman's capsule is identical to the concentration of inulin in plasma.  c. It is neither reabsorbed nor secreted in any portion of the nephron. All of the inulin that enters the nephron will be excreted in the urine. Any inulin that is not filtered into the tubule remains in the circulation.  e. Because of these properties, all of the inulin that is filtered into the nephron appears in the urine, and only the inulin that is filtered into the nephron appears in the urine. In other words,  or where V = volume/time.  f. This measurement is called a "clearance," because it tells you the amount of plasma that was "cleared" of inulin. (You can't measure that volume directly because a lot of it - but you don't know how much - was reabsorbed while the fluid was moving along the nephrons.)

Measuring renal plasma flow  It is difficult to measure total renal blood flow, but it can be calculated by measuring the renal clearance of PAH, or any other substance that is entirely removed from the blood in the renal vasculature in a single pass through the kidney.  1. All molecules of PAH that enter the afferent arterioles are either filtered or secreted into the tubular fluid, so all PAH has been transferred into the tubular fluid before the blood leaves the kidney.  2. I.e.,  and  C. The ratio of the inulin clearance to the PAH clearance, then, tells you the fraction of the plasma entering the kidney that got filtered into the nephrons; this value is called the filtration fraction.  D. Normal values for humans are (from Guyton and Hall's Textbook of Medical Physiology):  1. Renal blood flow = 1200 ml/minute.  2. The normal hematocrit is about 45%, so renal plasma flow = 650 ml/minute. REMEMBER TO CORRECT FOR HEMATOCRIT if a question asks for plasma flow, rather than blood flow!  3. Normal GFR = 125 ml/minute. This value remains remarkably constant even when the renal blood flow varies.

Forces that Influence Filtration  Hydrostatic pressure (blood pressure)  Colloid osmotic pressure  Fluid pressure created by fluid in Bowman’s capsule

Figure 19-6 Filtration Filtration pressure in the renal corpuscle depends on hydrostatic pressure, colloid osmotic pressure, and fluid pressure

Figure 19-7 Filtration Autoregulation of glomerular filtration rate takes place over a wide range of blood pressure

Figure 19-8a Filtration Resistance changes in renal arterioles after GFR and renal blood flow

Figure 19-8b Filtration

Figure 19-8c Filtration

GFR Regulation  Myogenic response  Similar to autoregulation in other systemic arterioles  Tubuloglomerular feedback  Hormones and autonomic neurons  By changing resistance in arterioles  By altering the filtration coefficient

Figure 19-9 Juxtaglomerular Apparatus

Figure 19-10, step 1 Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. 1 1

Figure 19-10, steps 1–2 Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases

Figure 19-10, steps 1–3 Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases. Flow past macula densa increases

Figure 19-10, steps 1–4 Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases. Flow past macula densa increases. Paracrine diffuses from macula densa to afferent arteriole

Figure 19-10, steps 1–5 (1 of 4) Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases. Flow past macula densa increases. Paracrine diffuses from macula densa to afferent arteriole. Afferent arteriole constricts

Figure 19-10, steps 1–5 (2 of 4) Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases. Flow past macula densa increases. Paracrine diffuses from macula densa to afferent arteriole. Afferent arteriole constricts. Resistance in afferent arteriole increases

Figure 19-10, steps 1–5 (3 of 4) Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases. Flow past macula densa increases. Paracrine diffuses from macula densa to afferent arteriole. Afferent arteriole constricts. Resistance in afferent arteriole increases. Hydrostatic pressure in glomerulus decreases

Figure 19-10, steps 1–5 (4 of 4) Tubuloglomerular Feedback Afferent arteriole Macula densa Efferent arteriole Bowman’s capsule GlomerulusDistal tubule Proximal tubule Collecting duct Loop of Henle Granular cells GFR increases. Flow through tubule increases. Flow past macula densa increases. Paracrine diffuses from macula densa to afferent arteriole. Afferent arteriole constricts. Resistance in afferent arteriole increases. Hydrostatic pressure in glomerulus decreases. GFR decreases