The kidney has four main functions: excretory, homeostatic, endocrine, and metabolic. As part of its excretory function, the kidney removes waste from the bloodstream such as urea, uric acid, and creatinine. Its homeostatic functions include regulating blood volume and pressure, stabilizing ion concentrations and pH levels. The kidney also produces important hormones like erythropoietin and renin. Urine is formed through a process of filtration, reabsorption, and secretion as fluid passes through the nephron. Key components like water and electrolytes are reabsorbed while others like urea and drugs are excreted in the urine.

1. By
Dr KHALED ALGARIRI
CAMS- QASSIM UNIVERSITY
March 2023

2. KIDNEY FUNCTIONS
Kidney has main functions
 excretory function
 homeostatic function
 endocrine function
 metabolic function

3. EXCRETORY FUNCTION
The kidney is involved in the excretion of wastes such as:
1. Urea ( from protein metabolism)
2. Uric acid ( from nucleic acid metabolism)
3. Creatinine (from metabolic breakdown of creatine phosphate)
4. End-products of Hb metabolism
5. Metabolites of hormones
6. Foreign substances: drugs, pesticides, other chemicals
ingested in food

4. HOMEOSTATIC FUNCTIONS
1. Regulate blood volume and blood
pressure:
– by adjusting volume of water lost in urine
– releasing erythropoietin and renin
2. Regulate plasma ion concentrations:
– sodium, potassium, and chloride ions (by
controlling quantities lost in urine)
– calcium ion levels

5. HOMEOSTATIC FUNCTIONS
3. Help stabilize blood pH:
– by controlling loss of hydrogen ions and bicarbonate ions
in urine
4. Conserve valuable nutrients:
– by preventing excretion while excreting organic waste
products
5. Assist liver to detoxify poisons

6. ENDOCRINE FUNCTIONS
 Kidneys have primary endocrine function since they produce
hormones
 The kidneys are site of degradation for hormones such as
insulin and aldosterone.
 In their primary endocrine function, the kidneys produce
erythropoietin, renin and prostaglandin.
Erythropoietin is secreted in response to a lowered oxygen
content in the blood. It acts on bone marrow, stimulating the
production of red blood cells.

7. Renin -the primary stimuli for renin release include
reduction of renal perfusion pressure and hyponatremia.
Renin release is also influenced by angiotension II and
ADH.
It is a key stimulus of aldosterone release. The effect of
aldosterone is predominantly on the distal tubular
network, effecting an increase in sodium reabsorption in
exchange for potassium.
The kidneys are primarily responsible for producing
vitamin D3 from dihydroxy cholecalciferol

8. METABOLIC FUNCTION
Kidney perform gluconeogenesis during periods of
starvation.

9. URINE
 Urine is a liquid product of the body secreted by kidney
through the process is called urination ( micturition) excreted
through urethra.
 Cellular metabolism generates numerous by product ,(rich in
nitrogen) that require clearance from the blood stream as
urination.
 Urination is the primary method for excreting water soluble
chemicals from the body.

10. COMPOSITION OF URINE
 ● 95% of volume of normal urine is due
to water
 Organic components:
 ● urea
 ● urobilinogen
 ● uric acid
 ● creatinine
 ● amino acids
 ● metabolites of hormones
 -
 Inorganic components:
 ● cations: Na+, K+, Ca2+,
NH4+
 anions: Cl-, SO4, HCO3
HPO4

11. Processes in Urine Formation

13. The pressure of the blood within the glomerulus forces water and
dissolved solutes through the semipermeable capillary membrane and
into the Bowman′s space.
-Approximately 120 ml/min ( 7.2L/ hr, 172L/day) of the renal plasma is
filtered through the glomeruli forming ultrafiltrate which is further
processed as it travels through the nephron.
-The ultrafiltrate has the same composition as blood plasma but it is
normally free of proteins and also cellular-free.
-Some of the filtered products include water, glucose, electrolytes,
amino acids, urea, uric acid, creatinine, and ammonia.
-[The rate of filtration (the glomerular filtration rate) is an important
indicator of renal function] How?
1. Glomerular Filtration

14. -blood pressure forces small
molecules from the glomerulus
to the capsule
Filtrates:
glucose, amino acids
uric acid, urea
1. Glomerular Filtration

15. -As the ultrafiltrate (glomerular filtrate) passes through the proximal tubules,
a large portion of the water, sodium chloride, bicarbonate, potassium,
calcium, amino acids, glucose and other substances needed by the body are
reabsorbed and pass back into the bloodstream.
-Like the proximal tubule, the descending limb of the loop of Henle is very
permeable to water, but the reabsorption of solutes does not occur in this
part of the loop. The ascending limb, however, is nearly impermeable to
water, but there is active reabsorption of sodium chloride. In this section of
the tubule and in the remaining tubule, hydrogen ion and ammonia are
secreted
2. TUBULAR REABSORPTION

17. The glomerular filtrate enters the proximal tubules in an isotonic state.
-In the proximal tubules, the reabsorption process begins. Water and salt
( Nacl) is reabsorbed.
-At the descending limp of Henle, the water reabsorption continues
(75% of water reabsorption occurs here ) and the water becomes more
and more concentrated as it descends.
-At the hairpin of Henles loop the fluid reaches the maximum
concentration (becomes hypertonic) and the epithelium becomes water
impermable, so water reabsorption Ceases
2. TUBULAR REABSORPTION

18. 2. TUBULAR REABSORPTION
-the fluid continues ascending entering the
ascending limb , which is impermeable to
water ,and becomes progressively less
concentrated due to Nacl reabsorption and will
become isotonic then hypotonic at the end of
the thick ascending limp of Henles loop .
-In the distal tubules, active reabsorption of
Nacl continues to a less extent .

19. Loop of Henle
i). Permeability of water
Water can leave the descending limb but not the ascending limb
ii). Permeability of Na+
Na+ cannot leave the descending limb but can the ascending limb
This difference in permeability results in concentrating the urine.

20. Water reabsorption here is dependent on hormones.
Aldosterone: promotes the excretion of potassium (K+) and the reabsorption of
sodium ions (Na+).
Aldosterone mediated active transport of Na+, which cotransports H+, K+, HCO3-,
and Cl-
Atrial Natriuretic Hormone (ANH): promotes the excretion of Na+ and so is water
which decreases blood volume and blood pressure.

21. It involves sending molecules from the blood capillaries into the tubular filtrate
for excretion. (out of the body)
-The tubular secretion process:
● removes unneeded foreign waste substances that are not filtered by the
glomerulus including various medications and toxins.
● promotes secretion of hydrogen ions and other ions to help regulate acid –
base and electrolytes balance.
-Various ions are also secreted including hydrogen ions, ammonium ions,
sodium ions, potassium ions, bicarbonate ions, uric acid and some weak acids
and bases.
- Hydrogen ions is secreted in the proximal and distal tubules.
- Tubular secretion is caused mainly by active transport.
3. TUBULAR SECRETION

23. 3. TUBULAR SECRETION
-movement of molecules from blood
into the distal convoluted tubule
-Molecules:
drugs and toxins

24. Filtration, Reabsorption, and Secretion of
Different Substances
Nutritional substances, such as amino acids and glucose, are
completely reabsorbed from the tubules and do not appear in the
urine even though large amounts are filtered by the glomerular
capillaries. Each of the processes -glomerular filtration, tubular
reabsorption, and tubular secretion - is regulated according to the
needs of the body.

25. Urination (micturition)
A). As the bladder fills with urine, sensory
impulses go to the spinal cord and then the brain.
B). The brain can override the urge to urinate.
C). When urination occurs motor nerve impulses
cause the bladder to contract and the internal and
external sphincters to open. until 200 additional
ml are collected. After 200 ml of urine have
collected afferent impulses send impulses to the
brain.
D). The decision to empty the bladder is made in
the inferofrontal region of the brain.

26. THANK YOU