Transcript 10. Laboratory diagnostics of urine (1)

Laboratory
diagnostics of
urine
The kidneys are bean shaped organs that serve
several essential regulatory roles in vertebrate
animals. They are essential in the urinary system
and also serve homeostatic functions such as the
regulation of electrolytes, maintenance of acid–base
balance, and regulation of blood pressure (via
maintaining salt and water balance). They serve the
body as a natural filter of the blood, and remove
wastes, which are diverted to the urinary bladder. In
producing urine, the kidneys excrete wastes such as
urea and ammonium, and they are also responsible
for the reabsorption of water, glucose, and amino
acids. The kidneys also produce hormones including
calcitriol, erythropoietin, and the enzyme renin.
Urine formation
Structures responsible
for the urine formation:
 glomeruli,
 proximal canaliculi,
 distal canaliculi.
Mechanism of urine
formation:
 filtration
 reabsorption
 secretion
The urinary system, also known as the renal system, consists
of the two kidneys, ureters, the bladder, and the urethra.
Each kidney consists of millions of functional units called
nephrons. The purpose of the renal system is to eliminate
wastes from the body, regulate blood volume and pressure,
control levels of electrolytes and metabolites, and regulate
blood pH. The kidneys have extensive blood supply via the
renal arteries which leave the kidneys via the renal vein.
Following filtration of blood and further processing, wastes
(in the form of urine) exit the kidney via the ureters, tubes
made of smooth muscle fibers that propel urine towards the
urinary bladder, where it is stored and subsequently expelled
from the body by urination. The female and male urinary
system are very similar, differing only in the length of the
urethra.
Mechanisms of elimination:
 filtration
 reabsorption
 excretion
The kidneys cleanse the blood plasma of metabolic
products. In addition, through the kidneys excreted
substances necessary for the life of the body - water,
sodium ions, calcium phosphates - in the case where
the concentration in the blood than normal. Thus,
the function of the kidneys is to remove a sample of
various substances in order to maintain the relative
constancy of the chemical composition of blood
plasma and extracellular fluid.
Filtration
Takes place in glomeruli.
Substances with molecular mass below 40,000 Da pass
through the membrane of glomerulus into capsula.
About 120 mL/min
or 180 L/day of
blood is filtrated.
Filtration – passive
process.
After filtration –
primary urine (180
L/day)
Filtering. In renal glomeruli all low-molecular
substances such as glucose, water and urea,
go into the filtrate, filling boumenova capsule
and then has to renal tubule of the
nephron. Ultrafiltration rate is fairly constant
- 1 min produced about 125 ml of the filtrate.
If all the filtrate was removed in the form of
urine, its volume per day would amount to
about 180 liters. However, 124 ml of the
filtrate is sucked back.
Filtration is caused by:
-hydrostatic pressure of blood in
capillaries of glomeruli (70 mm
Hg)
-oncotic pressure of blood plasma
proteins (30 mm Hg)
-hydrostatic pressure of
ultrafiltrate in capsule (20 mm
Hg)
70 mm Hg-(30 mm Hg+20 mm
Hg)=20 mm Hg
Hydrostatic pressure in glomeruli
is determined by the ratio
between diameter of ascendant
and descendant arteriole
Reabsorption
Takes place in proximal and distal canaliculi.
What is reabsorbed? Glucose (100%), amino acids (93%),
water (98%), NaCl (70%) etc.
The urine is concentrated (toxins damages the
proximal canaliculi)
Reabsorption:
active
passive.
Lipophilic substances
- passive.
Na/K АТP-аse is very
active
Reabsorption. All substances that
may be used by the body or the
need to maintain water and
electrolyte composition of body
fluids are absorbed from the
filtrate into the blood capillaries
in the proximal convoluted renal
tubule.
Secretion
Transport of substances from blood into filtrate.
Takes place in proximal and
distal canaliculi.
Secretion:
active
passive.
Passive secretion depends on
the pH.
What is secreted?
•Ions of K, аmmonia, H+
•drugs
•xenobiotics
CLEARANCE
Clearance of any substance is expressed in ml of blood
plasma that is purified from this substance for 1 min while
passing through the kidneys.
About 180 L of primary urine is formed for 1 day, about
125 mL of primary urine for 1 min.
Glucose is reabsorbed completely; clearance = 0
Inulin is not reabsorbed absolutely; clearance = 125 mL/min
If clearance is more than 125 mL/min the substance is
secreted actively.
Clearance = (C urine/C plasma) * V
Clearance (born clearance purification) or purification
factor - speed indicator
purification of biological fluids or
tissues of the body from the
substance during its
biotransformation redistribution
in the body, and excretion.
MAINTAINING OF ACIDIC-BASE
BALANCE BY KIDNEYS
Three mechanisms:
-Conversion of two substituted
phosphates into one substituted in the
cavity of canaliculi
- Formation of carbonic acid in the cells
with the following dissociation to Н+ and
НСО3- ammonia excretion
MAINTAINING OF ACIDIC-BASE BALANCE BY
KIDNEYS
Blood
Cells of
canaliculus
Cavity of canaliculus
Na2HPO4
Na+
Na+
Na+
Na+
HPO42-
H+
H+
NaH2PO4
MAINTAINING OF ACIDIC-BASE BALANCE BY
KIDNEYS
Blood
Cells of
canaliculus
Cavity of canaliculus
NaHCO3
Na+
Na+
HCO3
-
H+
Na+
H+ HCO3-
H2CO3
H2CO3
H2O + CO2
H2O
CO2
MAINTAINING OF ACIDIC-BASE BALANCE BY
KIDNEYS
Blood
Cells of
canaliculus
Cavity of canaliculus
Glutamine
NH3
NH3+H+
Glutamic acid
NH4+
• Urine (from Latin Urina, ae, f.) is a typically sterile
liquid by-product of the body secreted by the kidneys
through a process called urination and excreted
through the urethra. Cellular metabolism generates
numerous by-products, many rich in nitrogen, that
require elimination from the bloodstream. These byproducts are eventually expelled from the body
during urination, the primary method for excreting
water-soluble chemicals from the body. These
chemicals can be detected and analyzed by urinalysis.
Certain disease conditions can result in pathogencontaminated urine
COLLECTION OF URINE:
• For biochemical investigations, urine can be
collected as a single specimen or for 24 hours.
Single specimens of urine, normally collected in
the morning, are useful for qualitative tests e.g.,
sugar, proteins.
• Urine specimens tend to deteriorate.
• The changes include:
• 1. destruction of glucose by bacteria;
• 2. conversion of urea to ammonia, by bacteria,
with fall in [H+] and precipitation of
phosphates;
• 3. oxidation of urobilinogen to urobilin and
porphobilinogen to porphyrins.
• Preservatives for urine : The preservatives are
used (1) to reduce bacterial action; (2) to
minimise chemical decomposition, and (3) to
decrease atmospheric oxidation of unstable
compounds.
• Formalin, thymol, chloroform, toluene,
concentrated HCI and glacial acetic acid are
the commonly used urine preservatives.
PROPERTIES OF URINE
Amount – 1500-2000 mL/day
Poliuria – diabetes mellitus and insipidus
Oliguria – heart failure, nephritis, vomiting, fever
Anuria – kidney failure, acute intoxication by heavy
metals
Color – straw-yellow
Pale – poliuria (diabetes insipidud)
Dark – jaundice, concentrated urine
Red – blood available
Green-blue – decay of proteins in the intestine
Transparency – transparent
Cloudy – pus or mucin available
Density – 1,003-1,035 g/mL
Increased density – organic or inorganic
substances available (diabetes mellitus)
Decreased density – diabetes insipidus
Isostenuria – continuously low density in
oliguria (kidney failure)
pH – 5.5-6.8
Acidic – meat food, diabetes mellitus,
starvation, fever
Alkaline – plant food, cystitis, pyelitis