Excretory kidney

1. 1
Excretory System

2. 2
Outline
•The Mammalian Kidney
•Transport Processes in Mammalian Nephron
•Ammonia, Urea, and Uric Acid
•Hormones Control Homeostatic Functions

3. 3
Vertebrate Kidney
•Kidney is made up of thousands of repeating
units (nephrons), each with the structure of a
bent tube.
–Blood pressure forces the fluid in blood
past a filter, glomerulus, at the top of each
nephron.
Water and small molecules pass
through filter and into the nephron tube.
Sugars and ions are removed by
active transport.

4. 4
Vertebrate Nephron Organization

5. 5
The Mammalian Kidney
•Each kidney receives blood from a renal
artery, and produces urine.
–Urine drains from each kidney through a
ureter which carries urine to urinary
bladder.
–Within the kidney, mouth of ureter flares to
form renal pelvis.
Divided into renal cortex and renal
medulla.

6. 6
Urinary System of a Human Female

7. 7
The Mammalian Kidney
•Nephron structure and function
–Blood is carried by an afferent arteriole to
the glomerulus.
Blood is filtered as it is forced through
porous capillary walls.
Glomerular filtrate enters Bowman’s
capsule.
Moves to the proximal convoluted
tubule.

8. 8
The Mammalian Kidney
•Fluid then moves down the medulla and
back into the cortex in a loop of Henle.
–After leaving the loop, the fluid is delivered
to a distal convoluted tubule in the cortex
that drains to a collecting duct.
merges with other collecting ducts to
empty its contents into the renal pelvis

9. 9
Mammalian Kidney Nephron

10. 10
The Mammalian Kidney
•Reabsorption and secretion
–Most of the water and dissolved solutes
that enter the glomerular filtrate must be
returned to the blood.
–Reabsorption of glucose and amino acids,
is driven by active transport carriers.
–Secretion of waste products involves
transport across capillary membranes and
kidney tubules.
•Excretion

11. 11
Fig. 49.18(TE Art)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Renal tubule
Excretion
Filtration
Reabsorption to blood
Secretion from
blood
Glomerulus
Bowman's
capsule

12. 12
Transport Processes in the Mammalian Nephron
•Some mechanism is needed to create an
osmotic gradient between the glomerular
filtrate and the blood, allowing reabsorption.
•Proximal convoluted tubule
–Approximately two-thirds of NaCl and
water filtered in Bowman’s capsule is
immediately reabsorbed across the walls
of the proximal convoluted tube.

13. 13
Transport Processes in the Mammalian Nephron
•Loop of Henle
–Descending limb is permeable to water,
thus water leaves via osmosis.
–Water loss in the descending limb multiples
concentration achieved at each loop.
–Ascending limb actively extrudes N
+
and Cl
follows.
–NaCl pumped out of ascending limb is
trapped within surrounding interstitial fluid.
–countercurrent multiplier system

14. 14
Transport Processes in the Mammalian Nephron
•Distal tubule and collecting duct
–Permeability of the collecting duct to water
is adjusted by antidiuretic hormone (ADH -
vasopressin).
Kidneys also regulate the balance of
electrolytes in the blood by reabsorption
and secretion.

15. 15
Reabsorption of Salt and Water

16. 16
Hormones Control Homeostatic Functions
•Antidiuretic hormone
–Stimulates reabsorption of water by the
kidneys.

17. 17
Hormones Control Homeostatic Functions
•Aldosterone
–Promotes reabsorption of NaCl and water
across the distal convoluted tubule and
the secretion of K
+
into the tubule.
•Atrial natriuretic hormone
–decreases NaCl reabsorption

18. 18
Fig. 49.22(TE Art)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Low blood
pressure
Bowman's
capsule
Distal
convoluted
tubule
Glomerulus
Afferent
arteriole
Efferent
arteriole
Loop
of Henle
Increased NaCl
and H
2
O
reabsorption
Increased
blood
volume
Negative
feedback
1
2
8
9
Low blood
flow
Proximal
convoluted
tubule
Renin
Adrenal
cortex
Angiotensinogen
Angiotensin II
3Juxtaglomerular
apparatus
Kidney
Aldosterone
4
5
6
7