Renal system
Learning objectives
To outline the renal system;
To describe the structure and function of
nephron,processes of urine formation;
To describe briefly the processes of urine
formation;
To describe the renin-angiotensin system;
To describe the regulationofpotassium,
calcium and pH.
RENAL SYSTEM
EXCRETION
~ removal of toxic waste
productions of
metabolism from the
body
WASTE
~ nitrogenous waste (urea
& ammonia), CO2, bile
pigment
RENAL SYSTEM
OSMOREGULATION
~ the process maintaining
constant osmotic
equilibrium between the
internal & external
environment of an
organism
Mammalian renal system I
KIDNEY
 paired organs in abdominal cavity
 held firmly by peritoneum
 embedded in fat
 solid, dark red & bean shape
 below stomach
 renal artery vs renal vein
Structure of kidney
Mammalian renal system II
URETERS
 narrow tubes
 passing urine from kidneys to bladder
 valves  prevent back flow of urine
 stop bacteria from going into kidney
Diaphragm
Kidney
Ureter
Bladder
Urethra
Mammalian renal system III
URINARY BLADDER
 muscular bag
 stores urine temporarily
 300 cm3 of urine  sensation of urination
 contraction of bladder + relaxation of
sphincter muscle forces urine out
Ureter
Ureteral
opening
Urethra
Urethral
orifice
Mammalian renal system IV
URETHRA
 muscular tube
 carries ONLY URINE in female
 carries URINE & SEMEN in male
A nephron unit
FLOW OF GLOMERULAR FILTRATE
Glomerulus
Bowman’s space in Bowman’s capsule
Descending limb of Henle’s loop
Ascending limb of Henle’s loop
Renal pelvis
Proximal convoluted tubule
Distal convoluted tubule
Collecting duct
NEPHRON
 1,000,000 nephrons / kidney
 structural & functional units
Cortical nephron
~ in cortex, short Loop of Henle,
osmoregulation under NORMAL condition
 Juxtamedullary nephron
~ at junction of cortex & medulla, long Loop
of Henle, osmoregulation when SHORT OF
WATER
Nephron
Renal corouscle
 Glomerulus: knot of blood capillaries
 Bowman’s capsule
 Proximal convoluted tubule
Descending limb of loop of Henle
Ascending limb of loop of Henle
Distal convoluted tubule
Collecting duct
Functions of kidney
Excretion
~ remove nitrogenous
waste i.e. urea, salts,
water, heat, toxic
substance
Osmoregulation
~ controlling amount of
water in body
~ maintain osmotic
potential
Urine Formation
Pressure filtration
(ultrafiltration)
Reabsorption
Tubular secretion
Ultrafiltration
Occur at Malpighian body
Glomerular filtrate: all substances in blood
except RBCs & plasma protein
 Blood pressure:
Diameter of afferent arteriole > Diameter of efferent arteriole
 Glomerular filtrate rate
180l/ day
 Adaptation
large area, great pressure, thin ,membrane
Reabsorption
99% of the glomerular filtrate are reabsorbed
matter reabsorbed:
 all glucose, amino acid
 mineral salts
 other useful substances
 SELECTIVE REABSORPTION
Method of reabsorption
diffusion  active transport
Sites of reabsorption
 Proximal convoluted tubule
~ major site of reabsorption (80%)
~ microvilli  surface area
~ numerous mitochondria
~ surrounded by pertubular capillaries
Sites of reabsorption
 Loop of Henle
~ conserve water in terrestrial mammal
~ creates & maintain an increasing osmotic
gradient in the medulla
~ Na+ in medulla vigorous osmotic
extraction of water from collecting ducts 
hypertonic urine
Formation of hypertonic urine
Sites of reabsorption
 Vasa recta
~ narrow capillaries situated close to loop of
Henle
~ freely permeable to ions, urea & water
~ Counter current exchanger system
Counter current exchange system
Sites of reabsorption
 Distal convoluted tubule
~ fine control of salt, water & pH balance of the
blood
 Collecting duct
~ water is extracted by osmosis   conc. 
hypertonic urine
Tubular secretion
Takes place in distal convoluted tubule
absorption of unnecessary: ammonia,
potassium & drug from capillary network &
secrete them into lumen of tubule
Regulation of urine composition
Anti-diuretic hormone(ADH)
Aldosterone
Renin-angiotensin system
ADH
ADH
ADH
Aldosterone
Renin angiotensin system
Potassium content
most abundant intracellular ion
reabsorbed by proximal convoluted tubule &
loop of Henle, secreted by collecting ducts
 K  secretion
aldosterone  secretion of K
Calcium content
 Ca   excitability of nerve & muscle cell
membranes  hypocalcemic tetany
 Ca  cardiac arrthythmias
most reabsorbed, no secretion
pH level
Metabolic reactions are highly sensitive to H+
Sources of H+ gain or loss
Gain ~ from CO2, metabolism of protein etc,
loss of CO3 2- in diarrhea & urine
Loss ~ in vomitus & urine