University of Jordan
Faculty of Medicine
Physiology || for Pharmacy
L05 –Dr. Yanal
Renal System
Note:
1) Make sure you understand everything, exams questions will be based on
understanding NOT memorizing alone
2) Anything between *** was not mentioned during the lecture (only for your
knowledge)
----------------------------------------------------------------------------------------------------------3) Potassium
K+ intake is100 mEq/day  output must also be 100mEq/day for balance
insurance.
K+ balance  when intake = output
 Potassium is removed from our body through kidney
As we mentioned in the last lecture (L04):
4mEq/L in Plasma so in 180L/Day  4*180 = 720 mEq/day  Filtered
Load of K+
Let’s consider that urine should contain roughly 100mEq/day K+
Proximal Tubule 65%  Descending limb of Henle (the nephron) 0%
ascending limb of Henle 25% (impermeable to water)
100-65-0-25= 10% of Urine
10% of 720 is 72 mEq/day but the output is 100mEq/day so the extra
28mEq/day will be from Secretion
Sources of K+ in Urine:
1) Filtration-Reabsorption = 72mEqlday
2) Secretion= 28mEq/day
TOTAL =100 (in Urine (output))
Sources of Na+ in Urine:
1) Filtration-Reabsorption ONLY
So if your K+ Intake was 200mEq/day instead of 100 mEq/day
 The extra 100 will be in the secretion (secretion will be 128 instead of
28mEq/day)

Secretion is more important in K+
if your K+ intake increased  Aldosterone from Adrenal cortex(gland) 
Reabsorption for Na+ & Secretion for K+
As we said in the previous lecture (L04) loop diuretics and thiazides
(which are Aldosterone Antagonists) cause hypokalemia
Note: adrenaline is secreted from the medulla
4) Phosphate  in L04
5) Glucose



Mwt of Glucose = 180
Freely Filtered
Concentration of Glucose in GFR from 70-100 mg/dL
 Renal blood flow (RBF) is the volume of blood delivered to the kidneys per
unit time. In humans, the kidneys together receive roughly 25% of cardiac
Output which equals 1250 ml/min
RBF = Plasma + Cells
 650 of the RBF  Plasma (Renal Plasma Flow)
 20% of the Renal Plasma Flow will be filtered  125ml/min (GFR)
 80% of the Renal Plasma Flow will continue through the efferent 
535ml/min
The Na+_Glucose co-transporter:
Located in the apical membrane of
the proximal tubule (on brush
border), 2 Na+ and a molecule of
glucose attach to the co-transporter
Na+ goes from high  low
concentration
Glucose goes from low  high
concentration
Transporter (carrier) must be specific in kind and amount  it has a saturation
phenomenon (when it reaches plateau  can’t carry
any added molecules)
Secondary active transport  there is a saturation
limit
For glucose it has a filtered load that can be carried
out in the proximal tubule to be reabsorbed in the
blood  NO glucose in the Urine (Normally all
Glucose molecules are reabsorbed) NO glycosuria
Glycosuria: the condition where Glucose appears in
the Urine.
Note: If Glucose escaped the proximal tubule, it
cannot be reabsorbed anymore; because there is no
Glucose transporter in the rest of the nephron
Glucose will appear in the Urine  Glycosuria
 After max saturation of Glucose in it’s transporters  Glucose will start to
appear in the Urine
 Glucose Normal concentration is 70-100 mg/dl (NO Glycosuria) when it
reaches 180mg/dl (threshold for Glycosuria) it will start appearing in the
urine.
 After threshold: Glucose in Plasma  Glucose in Urine
+1
+1
+2
+2
 Q: How to distinguish Diabetes?
When the fasting blood sugar is equal or more than 126mgldl
So as a conclusion:
1) 70-100 mg/dl  Normal
2) 100-125 mg/dl  Pre-diabetic
3) Equal or more than 126  Diabetes
Note: When post-prandial (after eating) blood sugar is 150mg/dl 
this is normal.
 Q: a patient have a fasting blood sugar = 140mg/dl, does he have Glucose
in Urine?
NOOOOO!! ONLY DIABETES

In other cases, there might be a problem in the Glucose carrier itself
For example the post-prandial blood sugar is 150mg/dl BUT there is
Glucose in Urine!!
This happens due to up normality in carriers  Nephrogenic Glycosuria
Nephrogenic Glycosuria: is a form of diabetes insipidus primarily due to
pathology of the kidney
Diabetogenic Glycosuria: due to lack of insulin
5) Amino Acids



Average Mwt of Amino Acids = 110
we have large amino acids  Phenylalanine
Small amino acids  Glycine
So if we had a protein that it made of 400 amino acids then it’s Mwt =
110*400 = 44000
Which means it’s freely filtered  44000<70000
 Q: where are amino acids reabsorbed?
It is totally reabsorbed In the Proximal Tubule 100% (with Na+ via
secondary active transport)
Na+ goes from high  low concentration
Amino acids go from low  high concentration
There are many kinds of carriers for amino acids:
1) Neutral carriers
2) Acidic carries
3) Basic carriers
4) Cysteine carriers (if no carrier  cystinuria: high concentration of the
amino acid cysteine in the urine)
And this will start stone formation (Cysteine stones) in the kidney ‫حصى الكلى‬
Note: there are many types of Kidney stones like:
1) Calcium stones
2) Struvite stones
3) Uric acid stones
4) Cysteine stones
Q: what does the proximal tubular cell look like?
Since the proximal tubule has many functions in the kidney  it has brush
border (to increase surface area) on the other side there is the Basolateral
side
Note: when we talked about
sodium reabsorption we mentions
that it occurs by secondary active
transport (which does not require
ATP) at the luminal side
At the basolateral side any Na+
that enters the proximal tubule
epithelial cell will leave it by the NaK pump (from low concentration to
high concentration) which
consumes ATP produced by the
mitochondria at the basolateral side
Remember when we mentioned that our body during normal metabolism
makes acids not bases which means it has tendency for acidosis
Some acids that are produced by metabolism: Sulfuric acid, phosphoric
acid, lactic acid and CO2.
When our body produces acids  this will lead to too much H+
But our body will not tolerate acidosis because it will affect our enzymes
activity
 Q: how my body will take care of the extra acids?
By Bicarbonates
H+ + HCO3-  H2CO3 (carbonic acid)  CO2 + H2O
And then CO2 is removed by the lungs
 Q: How much Bicarbonate do I have in my body?
Bicarbonate concentration in plasma = 24 mmol or mEq /L (both units
work)
 Q: How much is the filtered load of Bicarbonate by day?
180L * 24 =4320 mEq/day
That will be 100% reabsorbed
Bicarbonate is very important in our body because the kidneys excrete a
variable amount of H+ into the urine and conserve Bicarbonate ions
HCO3- , which are an important buffer of H+ in the blood.
Buffer  ‫الدارئة‬
Our body produces around 1mmol/kg (of our bodyweight) acids per day
 Example: If your body weight is 70  70 mmol acids are produced per
day
Then your body will need 70mmol of bicarbonate
By the end of the day the body will lose 70mmol of bicarbonate
So I will expect the kidney not to reabsorb all the filtered bicarbonate only,
actually I will produce new bicarbonates
So concentration of Bicarbonate will be higher in the Renal Vein
When a renal failure occurs the kidney might not be able to reabsorb the
original bicarbonates or maybe will not be able to produce new ones 
this will lead to acidosis
Henderson- Hasselbalch equation 
H+ + HCO3pH = pKa + log (HCO3-/CO2)
HCO3- =24 mmol/day
CO2 = 1.2 mmol/day
So 24/1.2 = 20
pH = 6.1 + log(20)
7.4 = 6.1 + 1.3
When acidosis happen  low pH (less than 7.35)  the reason is either
bicarbonates
or CO2
If bicarbonates  Metabolic acidosis
If CO2
 Respiratory acidosis
When alkalosis happen  high pH (higher than 7.45)  the reason is
either bicarbonates
or CO2
If bicarbonates  Metabolic alkalosis
If CO2
 Respiratory alkalosis
Renal Failure will lead to Metabolic Acidosis
The function of the kidney in Acid-base balance  to reabsorb the filtered
Bicarbonates and to produce new ones.
This is the end of the Renal System for this course. (L01-L05)
Good Luck