renal (kidneys) physiology

kidney function

main H2O balance, maintain proper osmolarity of body fluids, primarily through regulating H20 balance, maintain proper plasma volume, help maintain proper acid-base balance, removal of metabolic waste products from blood and their excretion in urine

kidney production of hormones/enzymes

• erythropoietin- controls erythrocyte production (red cells)

• renin

renal pyramids

6 to 18 triangular structures

• base of each pyramid in next to cortex

minor calyx

receives urine from renal papilla

major calyx

formed by union of 4-5 minor calyces

renal pelvis

large, funnel-shaped chamber

• formed by union of 2-3 major calyces

juxtaglomerular complex (JGC)

helps regulate blood pressure and filtrate formation

macula densa

specialized epithelial cells in wall the distal convolutes tubule

• detect changes NaCl concentration of the fluid in the DCT

juxtaglomerular cells (JG)

smooth muscle cells in the wall of the afferent arteriole near the entrance to the renal corpuscle

• helps communication between macula densa and JG cells

extraglomerular mesangial cells

located between afferent and efferent arterioles

tubular secretion

transports substances from the peritubular capillaries into the renal tubules

tubular reabsorption

moves substances from renal tubules into the peritubular capillaries

basic renal processes and urine excretion

glomerular filtration → tubular secretion → tubular reabsorption

glomerular filtration

filtration is driven by glomerular capillary hydrostatic (blood) pressure

• blood cells in urine (hematuria) or proteins in urine (proteinuria) indicates a potential problem with the glomerular filtration barrier

glomerular hydrostatic pressure (GHP)

• blood pressure within the glomerulus

• pushes water and solutes out of the blood (glomerulus) into the filtrate

• blood leaving the glomerulus flows into the efferent arteriole

capsular hydrostatic pressure (CsHP)

• pressure within Bowman’s capsule

• opposes glomerular hydrostatic pressure

• favors reabsorption by resisting filtration

glomerular filtration rate (GFR)

the volume of fluid filtered from the glomeruli into bowman’s space per unit time

autoregulation of glomerular filtration rate (GFR)

involves changing the luminal diameters of:

• afferent arterioles

• efferent arterioles

Autoregulation of Glomerular Filtration Rate (GFR) example

(Decreased Blood Pressure):

• ↓ BP → ↓ GFR → ↓ stretch of arteriole smooth muscle

• Smooth muscle cells relax

• Vasodilation of the afferent arteriole

• Constriction of the efferent arteriole

• More blood enters and is retained in the glomerulus

• GFR increases back to normal

This keeps GFR relatively constant despite changes in blood pressure.

effects of angiotensin II

aldosterone increases Na+ reabsorption and K+ secretion in the distal convoluted tubule (DCT) and collecting duct (CD)

increases production of ADH- increase in systemic BP and blood volume

tubular reabsorption

movement of a substance from tubular fluid into the peritubular capillaries

involves

• transepithelial transport

• paracellular transport- through tight junctions

• uses passive and active transport

tubular reabsorption of Na+

an active process occurring in all tubular segments except the descending limb of the nephron loop

• the basolateral Na+-K+ pump actively transports Na+ OUT of the tubular epithelial cell into the interstitial fluid within the lateral space

tubular maximum

actively reabsorbed substances exhibit a tubular maximum

• bind with plasma membrane carriers

• a maximum reabsorption rate is reached when all carriers are fully occupied (saturated)

tubular secretion

transfer of substances from the peritubular capillaries into the tubular lumen

• H+ secretion and K+ secretion

• controlled by: aldosterone

ascending limb of loop of henle

permeable of NaCl

descending limb of loop of henle

responds by diffusion of H2O (water)

• impermeable to NaCl

vasopressin/ antidiuretic hormone (ADH)

promotes water H2O reabsorption for it to occur:

• the tubular segment must be permeable to H20

• DVT and CD are impermeable to H2O except presence of vasopressin

concentrated urine (dilute)

• H2O deficient + increased blood osmolarity

• increased vasopressin (ADH) secretion

• increases H2O permeability in the DCT and collecting duct

• results in small volume of concentrated urine and reduced urine output

micturition (urination)

urine is stored in the bladder and intermittently ejected during urination

aging and urinary system

• Decrease in the number of functional nephrons

• Reduction in glomerular filtration rate (GFR)

• Reduced sensitivity to ADH

• Problems with urinary reflexes

• External urethral sphincter loses muscle tone

• Voluntary control of urination may be reduced or lost