Kidney of biochemistry

1. Biochemistry of kidney
BCH415 (Tissue Biochemistry)
BIOCHEMISTRY DEPT, FACULTY OF SCIENCE
FEDERAL UNIVERSITY DUTSE

3. Functions of the Kidney
• Regulation of the water and electrolyte content of the body.
• Retention of substances vital to the body
• Maintenance of acid/base balance.
• Excretion of waste products, water soluble toxic substances
and drugs.
• Endocrine functions

4. Urine is formed as a result of a three phase
process
• Glomerular filtration
• Selective (active) and passive reabsorption
• Secretion

5. Glomerular filtration
• Filtration takes place through the semipermeable walls of the
glomerular capillaries
• The driving hydrostatic pressure is provided by arterial pressure
• About 20% of renal plasma flow is filtered each minute (~ 125
ml/min) GFR
• Result is glomerular filtrate GF (primary urine)
(~ 150 l).

6. Reabsorption
• In the proximal and distal tubule, the GF becomes
highly concentrated as the result of the removal of
water.
• At the same time, many other low molecular
weight constituents are reabsorbed by active
transport – glucose, AA and organic and inorganic
ions

7. Proximal Tubule
• Reabsorbs 60% of all solute (100% of glucose and AA, 90% of
bicarbonate, 80-90% of inorganic phosphate and water.

8. Loop of Henle
• Next reabsorption of NaCl
• In descending loop of Henle
- resorption of water by osmosis
- increasing of osmolarity (hypertonic)
• In ascending loop of Henle
- active transport of NaCl out of the tubule
- decreasing of osmolarity (hypotonic)

9. Distal Tubule and Collecting Ducts
• Aldosterone promotes Na+ ions and water reabsorption
• Excretion of H+ ions
• The final concentration of urine depends upon antidiuretic hormone
(ADH).

11. Secretion
• Some of the substances that have to be excreted from the body are
released into urine in the kidney by active transport – H+ and K+ ions,
urea, creatinine and drugs.

12. Energy for the transport
• ATP is derived from the oxidative metabolism of glucose, lactate,
pyruvate, fatty acids, glycerol, citrate and AA absorbed from the
blood.

14. Maintenance of acid base balance
Proton secretion
• The tubule cells absorb CO2 from the blood and then hydrate it to
carbonic acid (carbonate dehydratase).
• Carbonic acid then dissociates to HCO3- and H+.
• H+ is exported to the urine by an ATP-driven membrane-localised
transport system, while HCO3- returns to the blood.

16. Maintenance of acid base balance

17. Endocrine function of kidney
Hormones of the kidney
• Erythropoietin
• Calcitriol
• Angiotensin

19. Erythropoietin
• Polypeptide hormone that is formed predominantly by the kidney
(also by the liver)
• It controls the differentiation of the bone marrow stem cells
• The release is stimulated by hypoxia (low pO2)
• The hormon ensures that the bone marrow cells are converted to
erythrocytes, so that their concentration in the blood increases

20. Calcitriol
• 1-alpha,25-dihydroxycholecalciferol is a steroid-related hormone
involved in calcium homeostasis.
• It is formed in the liver from calcidiol by hydroxylation at C-1
• The activity of hydroxylase (calcidiol-1-monooxygenase) is regulated
by the hormone parathyrin (parathormone).

21. Renin – angiotensin system
• Renin is an enzyme which converts the plasma protein
angiotensinogen to angiotensin I.
• Angiotensin converting enzyme (ACE) which is formed in the lungs
converts angiotensin I to angiotensin II which causes vasoconstriction
and an increase in blood pressure.
• Angiotensin II also stimulates the aldosterone production (water and
sodium retention which together increase blood volume).

22. Renin increases the production of angiotensin II which is
released when there is fall in intravascular volume and
dehydration. This leads to:
• Constriction of the efferent arteriole to maintain
GFR, by increasing the filtration pressure in the
glomerules.
• Release of aldosterone.
• Increased release of ADH.
• Thirst
• The opposite occurs when fluid overload occurs.

24. Other hormones present