Physiology

(1) 27/3/2018

Hala Nsour

This lecture topic is about kidney function, nephron, renal blood flow

(RBF), glomerular filtration (Ma fe da3e trj3/e ll slides)

The doctor started with anatomy of renal system, which we were

supposed to know from anatomy lectures.

You can briefly see the renal system in the picture below which is

composed of two kidneys, renal arteries & veins, ureter and urinary

bladder which collects and stores the urine.

The picture below is a section in the kidney, you can see the cortex

(outer layer) ,medulla (inner layer),major and minor calyces ,and renal

pelvis which will end with ureter.

In this picture u can see the urinary

bladder, the two ureter, and urethra down from bladder and prostate.

There are many functions of the urinary system, some of them we

already took in CVS

1. Get rid of waste (ingested or metabolized)

2. Control the volume and composition of B.F

3. Regulation of water and electrolytes balances

4. Regulation of fluid osmolality

5. Regulation of Acid - Base balance

6. Regulation of Arterial pressure

7.Secretion of hormones like the angiotensin hemopoietin (also

called hematopoietin and erythropoietin )

8.Gluconeogenesis :formation of glucose particularly happen

during starvation

9. Producing erythropoietin & renin. Converting vit. D

The doctor explained some of these functions:

Water and electrolyte balance

Eating and drinking habits salts and other electrolytes might

increase 10 fold daily or decrease 1/10 fold daily slight or

modest changes in ECF volume or (Plasma Na)

Part of what we usually excrete from our body fluid volume done by

the kidney, other part is excreted by respiration, skin, vapor ….

*Anything we get during the day must be execrated at the end of the

day

*What's not completed today will be completed the next day

So there must be a balance between the input and the output, any

disturbance, this mean there is pathogenesis, there is some sort of

problem (disease)

The imbalance occurs if 1) we take too much water 2) too much

electrolytes (salts). 3) Shortage of water (starvation) and so on

Despite all this, the kidney still keep the change very minimum

(including the blood volume, extracellular volume, osmolality and

electrolytes)

Excretion of metabolic waste and foreign chemicals

1. Urea is the product from amino acids

2. Creatinine from muscles

3. Uric acid from nucleic acid

4. Bilirubin from Hb breakdown

5. Pesticides, drugs, food additives(toxic material excreted by kidney )

- Regulation of arterial pressure:

As u supposed to remember from the cardiovascular

system we have two mechanisms for regulation blood

pressure by the kidney:

1_ long term:

Excreting Na and water, and if u remember the anti-

diuretic hormones which depends on increase and

decrease of BP

*It takes hour or days

2_short term:

Renin and angiotensin, again if u remember from CVS

angiotensin take about 30 min to be fully active, that's

considered to be short term, the doctor mentioned also

with short term baroreceptors but without

explainnation so to make it easier remember

Short term…..>> regulation blood vessel diameter,

heart rate and contractility.

Long term…>> regulation of blood volume.

Short term regulation mediated by

*nervous system… (by baroreceptor) *chemicals

Regulation of acid-base balance: excreting acid or base urine

(Sulfuric & phosphoric acids)

(Hydrogen and bicarbonate)

Regulation of erythrocyte production: Secrete erythropoietin

Any patient with any renal problem (disease) mostly complain from

anemia (anemia is considered the main sign to renal diseases)

,because the kidney can't secrete erythropoietin so formation of

RBCs will be reduced and this will lead to anemia.

Regulation of 1,25 dihydroxy vitamin D3 production:

Kidneys produce active form of vit. D, by hydroxylating this vitamin

vit D is absorbed in non-active form, and the activation will be in the

kidney.

Glucose synthesis:

From amino acids and other precursors during prolonged fasting

this occur in starvation (prolonged).

**Physiological anatomy as we already mentioned:

150 2 kidneys posterior, outside peritoneal cavity. We have

, size clenched fist. gm

Outer cortex

Inner medulla: renal pyramids papilla renal pelvis major

and minor calyces ureter which ends in the urinary bladder.

(If u want go and see slides 11/12/13, it’s just a pic to kidney

and nephron u can google it)

*The function unit of the kidney is the nephron, structure of the

nephron is composed of different parts, one is the glomerulus,

as u can see in picture we have inside a network of capillary

(arterial capillary), this glomerulus has blood supply from the

renal artery which enters as afferent arteriole then a network of

capillary then leave as efferent arteriole.

Glomerulus surrounded by epithelial cells which are forming

bowman’s capsule which is the first part of renal tubule then

we have proximal tubule, loop of Henle (descending limb then

ascending one) then distal tubule which ends with collecting

tubules which later will be collecting duct & will go to pelvis

then ureter ….

We can see in the pic (slide 12/13) peritubular capillary which is

capillary surrounding the renal tubule, these capillary play a

role in the absorption or secretion.

Renal blood supply:

Renal blood flow is about 22% of C.O (cardiac output) ___ 1200

ml/min and again from anatomy :

Renal artery interlobar arteries arcuate arteries __

interlobular arteries afferent arterioles glomerular

capillaries efferent arteriolesperitubular

capillariesVenous systemInterlobular

arcuateInterlobarRenal vein

This is an actual diagram to the renal blood flow to the kidney, u can

see the cortex (red part) and medulla (pink part)

, its for nutritionis not s blood flow to the kidney purpose of the The

mainly for the regulation of the functions we mentioned before

(filtration, secretion, absorption and also controlling of osmolarity

and blood volume), but there is a very little amount for nutrition.

So regulation is the actual function of the kidney.

Nephron:

Human body have one million nephron in each kidney,

these nephrons will be decreased in function gradually

after the age of 40 years so any disease or damage

affecting the nephron is permanent, it’s not capable to

regenerate, so any problem or disease in kidneys will

make a permanent damage (not curable) and ends up

with renal failure, that’s why people with kidney

disease or diabetes end up with renal failure.

Tubular system

1.Proximal

2.loop of Henle:

a. Descending

b. Ascending (last part thick segment)

3.Distal tubule __ collecting tubule __ cortical collecting tubule

4.cortical collecting duct __ (8 to 10) ducts join to

form single large collecting duct__Medullary

collecting duct__ Renal papillae__Renal

pelvis__Ureter__Bladder (250 large coll.

Ducts/kidney

There are two sets of capillaries in the kidney:

1_ Glomerulus:

Beginning with afferent arteriole then a network of

capillary end with efferent arteriole, this type of

capillary is arterial capillary, as we know all capillaries in

the body consists of artery and vein networks but in

glomerulus of the kidney it is just arterioles.

*Pressure in this capillary is very high it’s about 60

mmhg, normal capillary pressure is about 37mmhg.

Arteriolar capillary is not involved in exchanging

process (reabsorption and secretion) they are mainly

for filtration (filtrate plasma to nephron)

2_ peritubular capillary:

This type of capillary is like other type of capillary in the

rest of the body, this type is involved in the exchange

process (reabsorption and secretion).

We have two type of nephrons (see the pic below)

1_ cortical nephron:

Which originates in the upper cortex, the end of loop of

Henle in the upper part of medulla near to the cortex so

most of it in the cortex and that’s the reason of its

name

2_ medullary nephron: (juxtamedullary)

Starts in the lower end of the cortex, go deep in

medulla even reach near the pelvic inlet, so it’s going

deeper in medulla than cortical type.

80%)-Cortical Nephrons: (70

Glomerulus in outer cortex, short

(medullary) Juxtamedulary Nephrons

Gl. In deep cortex

Long L - H

20 - 30% total

Vasa recta

70_80% of the nephron that present in our kidneys are

cortical the rest 20% are medullary,,,, why??

Kidney produces urine which is not pure water it

contains some waste products and electrolytes,

normally the kidney uses only cortical nephron, so

regulates normal day input and output

When there is a shortage of water, the osmolarity of

body fluids will be changed in this case other type of

nephrons will be involved.

So when there is a shortage of water, we need water so

anything that is filtrated, most of it must be reabsorbed

Increased absorption of water …..Increasing will get rid

of electrolytes so the kidney will form concentrated

urine.

The principle of forming concentrated urine of diluted

one is related to what we call counter balance and we

will take about it next time in details.

Kidney chooses the type of nephron according to body

needs, the principle function of medullary type is

mainly to produce concentrated urine when there is a

shortage of water.

Body needs is the actual stimulus for the regulation of

the body fluids.

Main function of the kidney is urine formation

(regulation is the upper but that's because of the end

product of kidney main function process urine)

We have four step in urine formation ..1.filtration

2.reabsorbtion 3.secretion 4. Excretion (Final step of

urine formation)

First step of formation the urine is filtration, 20% of CO

coming to kidney in the glomerulus arteriole, the

plasma will filtrate then go to Bowman’s capsule then

to renal tubule

So first thing is filtration, there must be a mechanism to

regulate this huge amount of filtration increase it or

decrease it according to body need

Filtrated fluid is same as the plasma component but

without protein (so no plasma protein present in

filtrated fluid

So what will happen to this filtration?

Normally the plasma(blood ) is re circulate to kidney

the filtrated fluid per day is about 180 liters( passing

through the kidney per day ) so you can imagine how

big it is (the doctor mean that the person cant loose

this big amount of fluid per day , we will die )so part of

this 180L which is 176.5 reabsorbed , all of them

absorbed except of 1.5 L which is the urine

So most of filtrated fluid (mainly all of it ) is reabsorbed

so if there is any imbalance between the output and

input any different of even 1 or 2 milliliter per day this

will make either edema or dehydration so this is prissy

regulated or control each day

So infiltrated fluid through the glomerulus per day

about 180 L

Other possibility that some of the waste product not

filtrated and the body don’t need them so they are

secreted from peritubular capillaries

As we mentioned above four functions (steps) in urine

formation filtration ,absorption, secretion , excretion

…but the major one is the reabsorption because most

of 180L per day is absorbed ,so the bulk is the

absorption so the mechanism of absorption is the main

function part of kidney

Urinary excretion rate (urine output)=

(filter. Rate )- (reabs. Rate )+ secr. Rate

So as we see in the picture below we have four type of

substance which run through the nephron and filtrated

(A,B,C,D)

Type (A) substance :

this represent substances that filtrated and excreted ,they are not

absorbed nor secreted , and these are mainly creatinine and

inulin(examples)

B) substance : )Type

They are filtrated but some of them are absorbed from the tubule to

the peritubuler capillaries because the body need it , so not all of the

filtrated excreted some of it absorbed , most the electrolytes belong to

this type ( Na & k for example or any useful material )

Type (C) substance :

Here what is filtrated all of it absorbed , simple example of this is

glucose

Acc to student question It is clear from the doctor answer to her that

these schemes illustrate the normal situation, but what happens in

patients is different Where we can find glucose in the urine in patients

with diabetes, which is not normal

In other word ….All of amino acids and glucose absorbed again to blood

after filtration so normally we don’t find them in urine

Type (D) substance :

here what filtrated not absorbed but secreted again ,so all of it

excreted in urine , example of this substance is hydrogen

here there is secretion from peritubular capillary add to filtrated

that’s what is called renal handling

A.Freely filtered, not reabs. , no secretion excretion rate = filtration

rate creatinine, inulin

B. Freely filtered, partialy reabs, most electrolytes

C. Freely filtered, not excreted completely reabs., a.a, glucose

D.Freely filtered, not reabs. , but secreted, H

The doctor repeated how kidney handle with substances thousands

times so I guess its very important ( for exam purposes )

Filtration, Reabs. And secretion

Reabs. > secretion : So as we say the major function is for the

reabsorption

Secretion determines K+ and H+ Concentration

But the secretion depend on the body need, if the body need sodium

for example keep it, not need it so secrete it and so on

IF the …Volume of plasma is only 3 L, and the filtration rate is 180, so

the doctor ask how many times this 3 L filtrate in the kidney??

60 time per day the plasma perfuse or filtrate in the kidney

So you can imagine why there is huge GFR

1_Most waste product removed rapidly (effective)

2_Allow all body fluids to be filtered and processed by kidneys

many times each day (precise & rapid control of volume &

composition

So again as we said the main blood supply to the kidney not for

nutrient, less than 1% for nutrition, main (all) blood supply is for

regulation of actual function……..

This is everything for today,,,,,,

I hope it’s clear, and sorry in advance of any mistakes ……..

Best wishes