Download The kidney (Renal function tests)

The kidneys
(Renal function)
Role of the kidneys
Nephron and its blood supply
Formation of Urine
Some of the common renal disease
The Kidneys
There are two kidneys. The working unit of the kidney is
Nephron, each kidney contain one million of nephron . The
structure of nephron is shown below
Role of the kidneys
Eliminate soluble waste products of metabolism
Preserve the internal environment of the cells
(maintain water balance, pH, ionic equilibrium,
and fluid osmotic pressure)
Synthesis of erythropoietin (hormone stimulating
red blood cell production)
Synthesis of 1-hydroxylation of 25-hydroxyvitaminD3 to form the biological active vitamin
D –hormone
Representation of nephron and its
blood supply
Formation of Urine
• A large volume of arterial blood flows through the glomerulus, which
consider to be a very specialized blood filter.
• The red and white blood cells, platelet, and molecules with molecular
weight > 50,000 Dalton are retained in the capillaries, while ions and
small molecules like water and glucose pass through the capillary
membrane into the surrounding capsule.
• About 20% of the plasma is filtered in one single pass of the blood flowing
through the kidney. This the first step in the formation of urine.
• The filtration process is passive does not require energy input for it occur,
water and small molecules pass easily through the pores to form an
ultrafiltration of plasma.
• The ultrafiltration is large in volume (about 200L/day for average adult). A
bout 99% of ultrafiltrate water and a large percentage of its constituent
must be reabsorbed before the urine leaves the collecting tubules on its
way to the bladder.
• The second step in the formation of urine is the passage of the
ultrafiltrate down to the proximal tubule where the various selective
processes of absorption begin.
 The filtrate starts with the same specific gravity as plasma 1.010
and same pH 7.4
 About 70% of water, Na+ , and Cl- and all of glucose , amino acids
and K+ are reabsorbed in proximal tubules . Some substances
such as urea, phosphate, and Ca++ are incompletely reabsorbed.
H+ is exchange for Na+
throughout the tubule, while K+ is
exchanged for Na+ only in distal tubule.
 Na+ - K+ the exchange is regulated hormone aldosterone. The
filtrate is reduced to about 1/3 of its original volume in the
proximal tubule.
 Water is always reabsorbed passively when the osmotic pressure
outside of semipermeable membrane is higher than inside, it
follows an osmotic gradient toward restoration of equilibrium .
The osmotic gradient is usually produced by active Na+ transport
(the sodium pump).
 From the following table it can be seen that the kidney perform a
tremendous amount of work in forming normal urine.
Average filtration, Reabsorption and exchange of
certain substances of plasma
Renal hydrogen ion
excretion.
Reabsorption of bicarbonate in
the renal tubule
ADH and aldosterone in the control of the reabsorption of water and Na+ ,
respectively, by kidney. ADH secreted by the posterior pituitary is
stimulated by increased plasma osmolality, aldosterone secreted by the
adrenal cortex is triggered by a decreased blood volume.
Some of the common renal disease
 Glomerulonephritis
- Inflammatory disease
(caused by a group A, βhemolytic streptococcus ).
- Hematuria
- Proteinuria
- Varying degree of
hypertension
- Renal insufficiency and
edema
 Nephrotic syndrome
- Heavy proteinuria
- Hypoalbuminemia
- Edema
- Hyperlipidemia
- The syndrome is
associated other disease
like syphilis
- May caused by the
treatment with
adrenocortical steroids
 Pyelonephritis
- Inflammatory disease
(caused by infectious
organisms that have
ascended the urinary
tract and invaded kidney
tissues).
- Some loss in renal
function.
 Arteriolar nephrosclerosis
- A thickening of the inner
lining of the renal
arterioles, resulting in a
decrease lumen and
increase blood pressure.
- The blood vessels become
necrotic, the kidney
becomes contracted.
- Uncontrolled hypertension
- Fetal impairment of renal
function.