Urinary System

Kidney Functions

• Regulation of blood ionic composition• Regulation of blood pH• Regulation of blood volume• Regulation of blood pressure• Maintenance of blood osmolarity• Production of hormones• Regulation of blood glucose levels• Excretion of waste and foreign

substances

Kidneys AnatomicallySupportive

tissue• Fibrous

capsule• Perirenal

fat capsule• Renal

fascia

Renal blood supply

Kidney Anatomy

• Renal cortex• Renal

medulla– Renal

pyramids– Renal

columns• Renal pelvis– Minor

calyces– Major

calyces

The nephron and ducts• Renal corpuscle is

where the blood plasma is filtered.– Glomerulus is the

capillary network– Glomerular capsule

(Bowman’s)• Renal tubule– Proximal convoluted

tubule– Loop of Henle– Distal convoluted tubule

• Collecting ducts• Papillary ducts

Nephron Anatomy

Overview• Glomerular

filtration• Tubular

reabsorption• Tubular secretion

– Rate of excretion = filtration rate + secretion rate - reabsorption rate

Filtration

Regulation of GFR

1. Adjust blood flow 2. Alter capillary surface

area3. Control arteriole

diameter

• Renal autoregulation• Neural regulation• Hormonal regulation

Tubular reabsorption and secretion

• Reabsorption leads to the return of 99% of the filtered water.

• Reabsorption of solutes by both active and passive processes (glucose, AAs, urea, Na+, Ca2+, K+, Cl-, HCO3-, HPO4-)

• Tubular secretion of K+, H+, NH4+, creatine and certain drugs– Secretion of H+ controls

blood pH– Secretion of other

substances removes them from the body.

Proximal convoluted tubules

Reabsorption of other solutes

Movement of solutes leads to osmotic flow of water.

Proximal convoluted

tubules

• Reaborbs most of the water and solutes—Na+

• Apical membrane—Na+ symport

• Basolateral membrane-Na+ /K+ ATPase

• Na+/ H+ antiporters moves H + from cytosol to tubular lumen

• Na+ is pumped (Na/K ATPase) from cytosol into IF

• H+ is produced from CO2

• ADH Regulation

Loop of Henle

• Reabsorption of water and solutes is independently regulated.

Loop of Henle

• Na+/K+/2Cl- symporters

Distal convoluted tubule

• Apical Na+/Cl- symporters

• Basolateral Na+/K+ ATPase and Cl- leak channels permit reabsorption into peritubular capillaries.

• Site of action for PTH and reabsorption of Ca2+

Collecting duct

• Na+/K+ ATPase• Na+ leak channels• K+ leak channels

Hormonal regulation: RAA

Hormonal regulation: ADH

• Antidiuretic hormone (ADH or vasopressin)– Increases water

reabsorption via the principal cells

– Stimulates insertion of aquaporin 2

• Atrial natriuretic peptide (ANP)

Tubular secretion• Disposing of drugs and

metabolites bound to plasma proteins.

• Eliminate undesirable products that have been passively reabsorbed (i.e., urea)

• Eliminate excess K+ • Control blood pH

Urine concentration

• Keep body fluids at a constant 300 mOsm/kg

• Countercurrent mechanism– Countercurrent

multiplier– Countercurrent

exchanger

Counter Current Medullary Gradient

Urine formation:Dilute

• H2O leaves from descending LH

• Thick ascending limb reabsorbs Na+, K+ and Cl- but not water

• When ADH levels are low water remains in tubule

Urine formation:Concentrated

• When water loss is high/during heavy sweating kidneys conserve water by concentrating urine and preventing loss of excess ions

• ADH concentrates the urine up to 4x the osmolarity of blood (1200 mOsm).

Summary

Renal plasma clearance

• Renal plasma clearance is the volume of blood that is cleared of a substance per unit time.– High renal clearance—efficient excretion– Low renal clearance—inefficient excretion

• Drug clearance determines dosage• S = (U X V)/P

– S = substance– U = concentration of substance in urine– V = volume of urine (mL/min)– P = concentration of substance in plasma

• Clearance depends on glomerular filtration, tubular reabsorption, and tubular secretion.

Kidney function: Normal Urine• Normal urine is 95% water

with 5% electrolytes, solutes, drugs.

• Typically is protein free• Volume excreted is

typically 1-2 liters per 24 hrs.

• Color is yellow or amber—concentrated urine is more intensely colored.

• Transparent when freshly voided

• Mildly aromatic turning ammonia-like after standing

• pH Ranges between 4.6-8.0, average is 6.0

Kidney function: Abnormal constituents• Albumin—problems with

filtration membranes or excessive blood pressure

• Glucose—glucosuria is an indication of diabetes mellitus or occasionally stress

• RBCs—hematuria indicates inflammation in urinary system, kidney stone, tumors, kidney disease

• Ketone bodies—diabetes mellitis, anorexia, high protein diet, starvation

• Microbes—common infections include those caused by E. coli, common yeast is Candidas albicans, and most frequent protozoan is Trichimonas vaginalis

Kidney function: Blood tests

• Blood urea nitrogen (BUN) measures the nitrogen associated with urea.– High levels indicate kidney disease

• Plasma creatinine– Levels above 1.5mg/dL indicate poor

renal function

Urine transportation

• Papillary ducts minor calyces major calyces renal pelvis ureters urinary bladder urethra

• Peristaltic contractions (1-5 per min.) push urine through the ureters from renal pelvis.

• Physiological valve (pressure) at the opening to the bladder prevents backflow of urine into the ureters.

Ureters

• Extend from kidneys to bladder • Carries urine to bladder by waves of

smooth muscle.

Bladder• Bladder capacity is 700-

800mL• Hollow distensible organ that

is collapsed when empty and spherical when full.

• Discharge of urine is micturition.– When volume reaches 200-400

mL stretch receptors send a signal to the micturition center in sacral spinal cord.

– Micturition reflex is triggered – Learned control of external

urethral sphincter muscle and other muscles of the pelvic floor allow for voluntary control

Urethra

• Tube leading from bladder to outside of body

• Female- 2.5 cm long

• Males- 15 cm long

Micturition reflexes• Stretch receptors in

bladder wall parasympathetic nerves relax band of smooth muscle forming internal urethral sphincter urethra opens urine is voided

• A 2nd, external urethral sphincter is skeletal muscle consciously controlled by motor neurons

• Urinary Incontinence

Dialysis• the process of removing excess urea,

fluid, electrolytes, minerals, and other wastes when the kidneys can't.

• In dialysis (hemodialysis or peritoneal), a machine, or the body’s peritoneal membane is used to filter waste products from the body. Blood passes through the machine's special filteror membrane, where water, waste products, minerals, and electrolytes diffuse from the blood into the dialysis solution and are removed from the body.

Resources• Urinary System Anatomy• The Mammalian Kidney: concentration of urine• Urinary System• Renal Blood Supply Flash • Kidneys Notes • Kidney Tutorial