Download hey every body, this is the 1st lec. Of the renal system by dr. Saleem

hey every body, this is the 1st lec. Of the renal system by dr. Saleem
5reesha...
20/3/2011
Lec# 24 physiology
By Omar Fodeh
Ok in this lec. We'll talk about the renal system...
Not only the real system excretes excess water and substances, also there
are:
Skin, lungs, and intestines.
So we have 4 excreting organs: 1-kidneys 2-skin 3-lungs 4-intestines.
The renal system consists of; two kidneys, two ureters, one bladder, and
urethra.
Normally one kidney is sufficient, many people has only one kidney.
1-kidneys The general functions of kidneys: (arranged in sequence
maintain normal conc. Of electrolytes.
(these electrolytes are mainly Na+, k+, cl- , they maintain normal
osmolality of the body fluids.)
2- consequently normal osmolality of the blood.
Q: what is the range of osmolality of plazma?
A: 300 ml osm/kg water 4 simlification….normally 290 ml osm/kg.
3-maintaning normal body fluid volume.
4-maintaining normal blood volume.
5-maintaining normal blob pressure (the main purpose for previous
functions)
7-excrete foreign chemical such as drugs.
8-secrete erythropoietin which maintains normal erythropoieses
.
9-secrete rennin hormone.
10-kidneys produce the active form of vitamin D, 1,25Dihydroxyvitamin D3.
These are the general functions of the kidneys.
- the unit of structure and function in kidneys is the nephron.
- the nephron is composed of 2 parts :renal corpuscle, renal tubule.
-the renal corpuscle is also composed of 2 subparts:
1-glomerulus which is : network of branching and anastomosing
glomerular capillaries , and these glomeruli are encased in boemans
capsule.
-the glomeruli receive blood through afferent arteriole, and the blood
leaves the glomeruli through efferent arteriole.
2-the renal tubule: first part that rises from renal corpuscle is the
proximal tubule.
-so fluid filtered from the glomerular capillaries flows into bowmans
capsule then into the proximal tubule then it flows into the loop of henle.
-loop of henle dips into the renal medulla.
-loop of henle consists of: descending limb and ascending limb.
(fe 9ora bel slides 3anhom).
-Then the loop of henle ends in distal tubule...then the distal tubule ends
in connecting tubule... then to the collecting tubules which collects fluids
from other nephrons.
-in each kidney there are about 1 million nephrons. So in a human being
there are 2 million nephron.
-one sixth of these 2 million functioning normal are sufficient for a
human being.
- in a section of a kidney we see:1- cortex 2- medulla 3-inner medulla.
-notice the border between cortex and medulla.
-when most of the nephron (renal corpuscle + proximal tubule + distal
tubule + most of the loop of henle lies in the cortex... these nephrons are
called cortical nephrons.)
(these nephrons are the majority) 85%...(70%-80%) in the book.
-and when the proximal and distal tubules of nehrons ars just beside the
medulla (adjacent to the border) and most of the loop of henle descend
deep down in the medulla... this nephron is called juxtamedullary
nephron. 15%...(20%-30%) in the book.
- juxtamedullary nephrons is responsible for urine concentrating.
-the blood comes into the glomerulus through afferent arteriole...
Lsn carefully :P...usually 1 afferent arteriole for 1 glomerulus...very rare
1 afferent for 2 glomeruli, 3 glomeruli, 4 glomeruli...(no more than 4).
-But the blood leaves through one efferent arteriole, what ever the no. of
glomeruli supplied.
-when the blood leaves the glomerulus through the efferent arteriole the
efferent arteriole forms capillary network around many nephrons (not 1
nephron)
-this capillary network is called (peritubular capillary network).
This is also applied on the juxtamedullary nephrons, there is asecond
capillary net work... it's called the vasa recta.
-when the percentage of juxtamedullary nephrons increases, the conc. Of
excreted urine also increases)
-the percentage of these nephrons in the desert animals reaches
sometimes to 30%-40% because these animals (like rabbits) need to keep
water in their bodies.
-the kidneys receive directly blood from aorta (almost all the vital organs
of the body receives directly blood from aorta) .
And that's important for the kidneys to insure constant blood
supply...constant blood pressure...to give constant filtration rate (main
function of kidneys).
And to get rid of extra substances and waste products.
-when the kidney is exposed to abnormality we usually do dialysis.
-so the renal artery has a high blood pressure and supply.
-this hydrostatic pressure of the blood causes filtration... for example this
pressure is 45%, it'll be opposed by two forces :- 1st:colloidal osmotic
pressure = 25%............2nd:the pressure inside the powmans capsule =
10% .
So 10% + 25% = 35% (the total resistance pressure )
45% - 35% = 10% (the net filtration pressure).
-about 25% of the left ventricular output of blood in each cardiac cycle is
distributed to the kidneys for filtration.
-the least blood flow in kidneys is in the medulla because of the present
of the second capillary net work the vasa recta which has high resistance.
-the medullary flow is least when a concentrated urine being prodused
and rises during (diuresis)...
-the kidneys have a high blood flow relating with its weight ... because
the liver 4 example is heavier and has less blood pressure.
-also has a high oxygen consumption (ml/min).
Done by: Omar Fodeh
TIC