Physiology Unit 4 RENAL PHYSIOLOGY

Transcription

1 Physiology Unit 4 RENAL PHYSIOLOGY

2 Func1ons Primary: regulate ECF through urine forma1on Kidneys Regulate volume of blood plasma Regulate concentra1on of waste products Regulate concentra1on of electrolytes Regulate acid- base balance Produce and secrete hormones

3 Renal Tubules Nephrons Cor1cal Juxtamedullary Afferent arteriole has a wider diameter than the efferent arteriole

4 Renal Corpuscle Renal corpuscle Bowmans capsule Glomerulus Filtrate: protein- free, acellular Restric1on based on size of pore and electrical charge Different pore sizes Podocytes Glomerulus Electrical charge Nega1vely charged surface prevents movement of proteins

5 Juxtaglomerular Apparatus Patch of cells in the DCT called the macula densa Monitor osmolarity Chemoreceptors Sensi1ve o a drop in [Na + ] Secretory cells called juxtaglomerular (JG) cells surround the afferent arteriole Monitor blood pressure Barroreceptors Sensi1ve to a drop in blood pressure

6 Juxtaglomerular Apparatus Mesangial cells Structural support of the glomerulus Proper1es of smooth muscle Filtra1on Phagocytosis in response to injury or disease

7 Renal Func1on

8 Glomerular Filtra1on Starling forces hydrosta1c pressure vs. osmo1c pressure Net filtra1on pressure 16mmHg Subject to physiological control Neural, hormonal input to afferent and efferent arterioles Cause changes in vessel diameter

9 Glomerular Filtra1on Rate Volume of filtrate produced by both kidneys per minute Factors Net filtra1on pressure Permeability of corpuscular membranes Surface area for filtra1on At any given filtra1on pressure, GFR will be directly propor1onal to the membrane permeability and surface area 115 ml/min in women (166 L/day) 125 ml/min in men (180 L/day) En1re plasma volume is filtered 60 1mes a day

10 Control of GFR

11 Glucose Reabsorp1on Glucose and amino acids are reabsorbed at proximal tubule Carrier mediated transport can become saturated 325 mg/min is transport maximum Normally only 125mg of glucose per 100ml of filtrate in tubules (1 mg/ml) When glucose is 180mg per 100ml of filtrate, glucose gets into urine Renal plasma threshold for glucose Diabetes mellitus is when there is not enough secre1on of insulin Lots of urine to help get glucose out

12 Regula1on of Ion and Water Balance 180 L of filtrate produced each day 99% reabsorbed Obligatory water loss 444 ml Primary ac1ve transport of Na + out of the cells and into inters11al fluid PCT Collec1ng duct Na + /K + /ATPase pumps As Na + and Cl - are reabsorbed, H 2 O follows passively by osmosis

13 Na + Reabsorp1on 65% H 2 O + NaCl reabsorbed in PCT Osmolarity remains unchanged due to equal transport of both substances

14 Coupling of H 2 O and Na + Reabsorp1on

15 Countercurrent Mul1plier System Defini1on Countercurrent: flow in opposite direc1ons Mul1plier = posi1ve feedback Descending limb No NaCl transport Permeable to water Ascending limb Ac1ve transport of NaCl Impermeable to water

16 Inters11al Fluid Osmolarity Gradient Collec1ng Ducts Permeable to water, mostly impermeable to NaCl ADH increases number of water channels

17 Vasa Recta The hairpin loop structure of the vasa recta minimizes excessive loss of solute from the inters11um by diffusion Urea trapping Effects of urea contributes to hypertonicity of 1ssues

18 Control of Na + Reabsorp1on Aldosterone Role of aldosterone in Na+/K+ balance Secreted by adrenal cortex DCT Na + reabsorp1on h aldosterone = h Na + reabsorbed =h H 2 0 = h blood pressure When Na + is reabsorbed, K + is excreted 90% reabsorbed before DCT Without aldosterone 8% reabsorbed 2% filtered Na + into urine With aldosterone all Na + reabsorbed

19 Control of Na + Reabsorp1on Angiotensin II A component of the renin- angiotensin system Renin produced by JG cells Renin splits angiotensinogen (produced by the liver) into angiotensin I Angiotensin I converted to angiotensin II Angiotensin II S1mulates secre1on of aldosterone Causes vasoconstric1on Increases BP Levels are high during salt deple1on (Na + levels are low) Retension of Na + and H 2 0 Increases BP

20 Control of Na + Reabsorp1on Renin Renin acts as an enzyme that catalyzes splikng off of angiotensin I from angiotensinogen in plasma Juxtaglomerular apparatus The macula densa Sensi1ve to a decrease in [Na + ] in tubular fluid Causes increased renin secre1on The juxtaglomerular (JG) cells Sensi1ve to drop in BP Secrete Renin

21 Control of Na + Reabsorp1on Atrial Natriure1c Pep1de (ANP) Atrial Natriure=c Pep=de (ANP) produced by cardiac muscle cells in the atria Responds to high BP Inhibits Na + reabsorp1on in the kidney tubules Can also act on renal blood vessels to increase GFR Further increases Na + excre1on Directly inhibits aldosterone secre1on Further increases Na + excre1on

22 Renal Regula1on of K + Cor1cal collec1ng ducts can secrete K + Normal ECF values range between mmol/l 90% reabsorbed in PCT Without aldosterone 100% K + reabsorbed in DCT With aldosterone K + secre1on into DCT & CD

23 Acid- Base Balance Adults produce about 100 mmol/day of H + Goal: maintain rela1vely constant plasma ph in spite of daily varia1ons in produc1on of acids from metabolism and food intake Role of the kidney Reabsorb all HCO 3 - filtered and excre1ng H + into urine 90-95% reabsorbed in PCT and DCT Excre1ng 1-2L of un- buffered urine only eliminates 1mmol/day of H + Generate new HCO 3 - Filterable phosphate is primary buffer anion in urine Nitrogen is excreted as ammonium rather than urea, sparing bicarbonate

24 Reabsorp1on of Bicarbonate Significant tubular reabsorp1on PCT, LOH, cor1cal CD Can be secreted in the CD Bicarbonate reabsorp1on depends on tubular secre1on of H +

25 Addi1on of New Bicarbonate Tubular secre1on of H + Renal metabolism of glutamine and excre1on of ammonium (NH 4+ )