Urine formation
Summary
TLDRThis script offers an in-depth look at urine formation, focusing on the nephron's role as the kidney's filtration unit. It explains the journey of blood through the nephron, detailing the filtration process in the glomerulus and the subsequent reabsorption along the tubules. The script also touches on the body's ability to regulate the reabsorption of substances like water and sodium through hormonal control, ultimately highlighting how only 1% of filtered substances become urine, with the rest being reabsorbed or secreted back into the bloodstream.
Takeaways
- 😀 The nephron is the functional unit of the kidney responsible for filtering blood and forming urine.
- 🌀 Blood enters the nephron through the afferent arteriole, which leads to the glomerulus where filtration occurs.
- 🔎 The glomerulus is a capillary bed that filters blood due to its high pressure, typically around 50 millimeters of mercury.
- 🚫 Large molecules like proteins and blood cells do not pass through the filtration membrane due to size and charge.
- 💧 Approximately 120 milliliters of filtrate are produced per minute in each kidney, totaling 240 milliliters for both kidneys.
- ⏳ The body reabsorbs 99% of the filtrate back into the bloodstream through various parts of the nephron.
- 🔄 The proximal convoluted tubule reabsorbs 65% of the filtrate, the loop of Henle 15%, the distal convoluted tubule 15%, and the collecting ducts 4-5%.
- 🌡 Hormones like antidiuretic hormone and aldosterone can regulate the amount of water and sodium reabsorbed, respectively.
- 📉 Urine formation is the result of glomerular filtration, tubular reabsorption, and tubular secretion, with only about 1% of the filtrate becoming urine.
- ➕ Tubular secretion is the process by which substances from the blood are secreted into the nephron for excretion in urine.
Q & A
What is the functional unit of the kidney?
-The functional unit of the kidney is the nephron, which is responsible for the filtration process.
What is the role of the glomerulus in the nephron?
-The glomerulus is a capillary bed within the nephron where the initial filtration of blood occurs, separating plasma from blood cells and larger proteins.
What is the purpose of the tubules in the nephron?
-The tubules in the nephron are responsible for further processing of the filtrate, including reabsorption of necessary substances back into the blood and secretion of waste products.
Why is the blood pressure higher in the glomerulus compared to other capillary beds?
-The blood pressure in the glomerulus is higher, at about 50 millimeters of mercury, to facilitate the filtration process and push substances from the blood plasma into the nephron.
How much of the blood plasma is filtered at the glomerulus per minute?
-Approximately 20% of the blood plasma, which is about 120 milliliters per minute, is filtered at the glomerulus in both kidneys combined.
What is the total amount of filtrate produced by the kidneys in a day?
-The kidneys produce approximately 172,800 milliliters or about 172.8 liters of filtrate per day.
How much of the filtrate actually becomes urine, and why?
-Only about 1% of the filtrate becomes urine, as 99% of it is reabsorbed back into the blood through the tubules of the nephron.
What is the role of the afferent and efferent arterioles in the nephron?
-The afferent arteriole brings blood into the glomerulus, and the efferent arteriole carries the blood away from the glomerulus, with the peritubular capillaries surrounding the tubules to facilitate reabsorption.
What is tubular reabsorption and where does it primarily occur?
-Tubular reabsorption is the process by which filtered substances are returned to the bloodstream. It primarily occurs in the proximal convoluted tubule, where 65% of the filtrate is reabsorbed.
What is tubular secretion, and how does it differ from reabsorption?
-Tubular secretion is the process where substances are actively transported from the blood into the tubules to be excreted in the urine. It differs from reabsorption as it adds substances to the filtrate rather than returning them to the blood.
How does the body regulate the balance between filtration, reabsorption, and secretion to control urine output?
-The body regulates urine output by adjusting the rates of filtration, reabsorption, and secretion through hormonal controls such as antidiuretic hormone and aldosterone, which can increase water and sodium reabsorption respectively.
Outlines
🔬 Understanding Nephrons and Urine Formation
This paragraph introduces the process of urine formation in the kidneys, focusing on the nephron as the functional unit responsible for filtration. It explains the blood supply to the nephron, particularly the role of the glomerulus as the site of filtration. The nephron's tubules are highlighted as the pathway for filtrate, which, if not reabsorbed, becomes urine. The paragraph also reviews the structure of the nephron, including the glomerular capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting duct. The importance of the peritubular capillaries, which facilitate the reabsorption of filtrate back into the blood, is emphasized.
💧 Glomerular Filtration and Cardiac Output
The second paragraph delves into the specifics of glomerular filtration, detailing how blood plasma is forced through the filtration membrane due to high pressure within the glomerulus. It clarifies that large molecules like proteins and blood cells are too big or repelled by the filtration membrane's charge to pass through. The paragraph then connects this process to cardiac output, explaining that the heart pumps approximately 70 ml of blood per beat, resulting in about 5 liters per minute. Of this, 20% reaches the kidneys, and 60% of that volume is plasma, which is subject to filtration. The calculation shows that 120 ml of filtrate is produced per minute by both kidneys, leading to a significant daily volume that is mostly reabsorbed, leaving only about 1.7 liters as urine.
🔁 Tubular Reabsorption and Its Regulation
This paragraph discusses the reabsorption process, where the majority of the filtrate is returned to the bloodstream through the nephron's tubules. It outlines the percentages of reabsorption at different segments of the nephron: 65% in the proximal convoluted tubule, 15% in the loop of Henle, another 15% in the distal convoluted tubule, and 4-5% in the collecting ducts, totaling nearly 99% reabsorption. The paragraph also touches on how the body can adjust these percentages through hormonal regulation, such as the release of antidiuretic hormone to increase water reabsorption or aldosterone to enhance sodium reabsorption.
➡️ Tubular Secretion and Urine Composition
The final paragraph introduces tubular secretion, a process where substances from the blood are actively secreted into the nephron's tubules, contributing to urine composition. It contrasts this with reabsorption and emphasizes that secretion involves moving substances from the blood into the tubules, which are on the path to excretion. The paragraph concludes by summarizing that urine formation is a complex process involving filtration, reabsorption, and secretion, with the latter two processes being adjustable to maintain the body's homeostasis.
Mindmap
Keywords
💡Nephron
💡Glomerulus
💡Filtrate
💡Afferent Arteriole
💡Efferent Arteriole
💡Proximal Convoluted Tubule
💡Loop of Henle
💡Distal Convoluted Tubule
💡Collecting Duct
💡Tubular Reabsorption
💡Tubular Secretion
Highlights
The nephron is the functional unit of the kidney responsible for filtration.
Blood supply to the nephron is crucial for oxygen delivery and filtration.
The glomerulus is a capillary bed where filtration begins.
Filtrate from the blood contains what has been filtered out and is destined to become urine if not reabsorbed.
The afferent arteriole brings blood into the glomerulus.
The efferent arteriole carries blood away from the glomerulus to the peritubular capillaries.
The glomerular capsule is the initial part of the nephron where filtration occurs.
The proximal convoluted tubule is the first section of the tubule where reabsorption begins.
The loop of Henle is responsible for concentration and dilution of the filtrate.
The distal convoluted tubule plays a role in fine-tuning the composition of the filtrate.
The collecting duct gathers filtrate from multiple nephrons and contributes to the final concentration of urine.
Glomerular filtration rate is approximately 120 ml per minute in both kidneys combined.
Cardiac output contributes to the volume of blood filtered by the kidneys.
Only 20% of cardiac output reaches the kidneys, equating to 1 liter of blood per minute.
Of the blood plasma filtered, 20% becomes filtrate, amounting to 120 ml per minute.
The kidneys filter approximately 175 liters of filtrate per day, yet produce only about 1.7 liters of urine.
Tubular reabsorption reclaims 99% of the filtrate back into the bloodstream.
Tubular secretion allows the nephron to secrete substances from the blood into the filtrate.
Hormones such as antidiuretic hormone and aldosterone regulate the reabsorption process.
Transcripts
so let's have a quick look at how the
blood in our body moving through into
the kidneys gets filtered and ultimately
forms urine so we're going to have a
look at urine formation so a couple of
things you need to go through the
previous videos and understand what a
nephron is and understand how the blood
supply gets to the nephron and how that
blood supply starts to become filtered
okay so just as a very quick recap we're
going to go through some functional
anatomy and we're going to name
different aspects of this nephron so
remember this is the functional unit of
the kidney this is the filtration unit
is the nephron and what you can see is a
blood supply coming through now this
blood supply is it here to give this
nephron oxygen this blood supply is
coming in because here is a capillary
bed now remember this capillary bed is
called the glomerulus remember
glomerulus means ball of yarn so you've
got a blood vessel coming in that
branches into this gun Miralles
capillary bed and this is where
filtration happens and remember the
tubules here of the nephron contain
what's just been filtered from this
blood and so this is called filtrate and
if this filtrate remains in the nephron
all the way through it comes out as
urine okay so urine formation has to do
with this filtration process here okay
and what's happening to this filtrate
all the way through the nephron that's
what we're going to discuss today but
before we begin let's label some things
so that you know exactly where we are so
first thing is that we have blood coming
into or towards this nephron remember
this is called the afferent arteriole
and afferent arteriole comes down into a
capillary bed which we call the
glomerulus
the glove mirrorless that continues down
into not a vein remember but an artery
another arterial which are called the
efferent arterial and you can see that
the efferent arteriole continues and it
basically hugs all the tubules of the
nephron and we call this peri tubular
capillaries okay why does this capillary
bed here hug the tubules of the nephron
because remember what gets filtered into
the nephron doesn't necessarily stay in
the nephron 99% of this filtrate that
gets into the nephron actually gets
thrown back into the blood and it gets
thrown back into this peritubular
Network okay so that's labeling the
blood supply let's label the nephron now
I'm not going to write the labels down
because I'll have to rub them out but
what you can see is the first part here
we call the glomerular capsule okay so
that's the glomerular capsule looks like
a little pac-man the first portion of
the tube you'll closest to the capsule
is called the proximal convoluted tubule
proximal because it's closest to
convoluted because usually you'll see it
as these squiggly wavy lines but I've
just drawn here straight for simplicity
sake
so proximal convoluted sugar you've got
the loop of Henle also known as the
nephron loop which is made up of the
thin descending loop of Henle and the
thick a sending loop of Henle then you
have the distal convoluted tubule and
then you have the collecting duct okay
now when it comes to your information
what you're going to find is couple
things that urine formation is actually
equal to a couple of things your
information is equal to glove Marilyn
filtration what that means is remember
our ultimate goal is your information
here so we're going to talk about how we
can get from here to here firstly we
need to start off with glomerular
filtration let's write that as number
one so you know from previous videos
that as the blood comes through that
there is a relatively high pressure here
the glomerulus that now remember that at
most capillary beds that pressures
around about thirty twenty to thirty
millimeters of mercury so what's that
mean there's a hydrostatic pressure are
pushed behind the blood pushing stuff
out of the capillaries at the tissues of
your body but once you get here to the
kidneys this capillary bed is different
and the push is greater it's fifty
millimeters of mercury okay so you have
this very strong push pushing substances
within the blood plasma throat okay now
remember proteins do not go through and
cells do not go through why while cells
are too big so white blood cells red
blood cells and platelets they're all
too big to move through this filtration
membrane or I should say filtration
membranes proteins
well the proteins are actually small
enough to get through but there is a
negative charge at this filtration
membrane and remember proteins are
negatively charged and like charges
repel each other so in a healthy
filtration membrane proteins are
repelled and stay in the blood okay
first thing so filtration now off the
blood that comes down through into here
what you'll find is so think about
cardiac output right so your heart will
contract and relax contraction will exit
as it does this it pushes out blood
right so every time it contracts it
pulls it pushes out around about 70 ml
of blood from one ventricle so left
ventricle squirt 70 mils of blood and it
does that about 72 times a minute
so if it squirts out 70 mils in one go
times 72 in a minute that gives you
around about five liters a minute so
your heart pushes out from one ventricle
five liters a minute that's the cardiac
output and that five liters a minute
goes to the whole body right so only a
fraction of that's going to get to the
kidneys 20% of that will get to a
kidneys what's 20% of 5 blenders 1 litre
so 1 litre of blood goes to the kidneys
every minute
now that 1 litre of blood is made up of
all these different components is made
up of cells
it's about proteins it's made up of
blood plasma and so forth what gets
filtered only plasma right because the
cells and proteins don't go through so
of that one liter what you'll find is 60
percent of it is plasma
so what's 60 percent of one liter six
hundred mils so you have six hundred
mils of blood plasma that's coming
through that can be filled in it now of
this how much of that six hundred mils
actually goes through twenty percent
okay so 20% of this six hundred mils
gets filtered through how what's twenty
percent of six hundred it's 120 mils so
every minute every minute in here you
have a hundred and twenty mils being
filtered through so that means you
create 120 mils of filtrate every minute
in both both your kidneys together so
not one nephron this is representing on
both your kidneys okay so 120 mils a
minute is what your kidney creates of
filtrate now think about that 120 miles
a minute now let's do some very quick
math how many minutes are there in an
hour 60 minutes so now okay how many
hours are there in a day 24 so 60 times
24 is
1440 minutes
okay 1440 minutes in a day but and you
have 120 mils per minute being mowed so
120 times 1440 and this is something
that I wrote down before
here's 172 800 mils per day your kidneys
create one hundred seventy two thousand
eight hundred mils of filtrate per day
that is nearly that's approximately 175
litres a day but you know that all this
100 that this is 175 litres you know PA
you know P at 175 litres a day you
actually pay out round about 1.7 liters
per day it's something 1% so of
everything that you filter through you
only pay 1% so let's just say here 175
litres per day or by the time it gets to
here it's only 1 point 7 litres a day so
what does that mean that means of
everything you've filtered 99% of it 99
percent of it goes back into your blood
back into your body okay so that means
that in order to create urine we need to
add something else to this equation we
said urine formation is equal to ik
lamella filtration which is 120 mils per
minute
-
tubular reabsorption right so this is
that's the tubules and it's going back
into the body so it's reabsorption not
absorption because you've already
absorbed this stuff before in the gr to
your reabsorbing it back into the body
okay so this is step two tubular
reabsorption so let's just leave this a
bit better here
step one filtration and this is step two
tubular reabsorption so tubular
reabsorption you've got all these to do
the proximal convoluted tubule you have
the loop of Henle and the distal
convoluted tubules are collecting that
in actual fact that happens all
throughout okay so if you'll have a look
here you'd find that and the proximal
convoluted tubule 65% of what's just
being filtered goes back into the body
and the proximal convoluted tubule 65%
okay at the loop of Henle that you'll
find is that 15% goes back into the body
okay so what's that so far certainly
only 80% okay here at the distal
convoluted tubule you'll find that
another 50% gets reabsorbed back into
the body that's 95% and here at the
collecting ducts four to five percent
that equals 99 percent to 100 percent
okay because remember 99 percent of what
just got filtered goes back into the
body 65 percent of it happens here at
the proximal convoluted tubule 15
percent happens at loop of Henle 15
percent happens at the distal convoluted
tubules and 45 percent happen at the
collecting ducts now the great thing is
your body can't alter this so it's not
always going to be 65 percent 1515 and 4
or 5 percent if you want to reabsorb
more this percentage can go up if you
want to reabsorb less it can go down and
vice versa with all these ok so for
example if you want to reabsorb all why
don't you can release 88 antidiuretic
hormone which makes you reabsorb more
water here at the collecting ducts if
you want to reabsorb more sodium into
your body you can release out dosterone
and this can tell the process of the
distal convoluted tubules to reabsorb
more sodium okay so your information is
equal to glomerular filtration
- tubular reabsorption so let me just do
some more room so does that make sense
why it's - because we remember 120 mils
per minute here but we need to - what's
going back 99 percent so now we have 1
point 2 mils coming through run 120 mils
take 1% of that is 1.2 mil because that
99% scrub back so now we only have by
the time we reach here where they have
one point two mils per minute which is
one point seven liters a day ok coming
through a one point two litres a day now
that's not the end of it because your
nephron can actually take some stuff
from the bodies not just give substances
to the blood it can receive substances
the blood and this is called this is
number three and this is called tubular
secretion now why is it called secretion
is because it's secreting substances
from the blood into the tube you'll
people get confused about reabsorption
or secretion and so forth whatever is in
the tube you need to remember is
essentially being outside the body this
is what's going to be pin out if it
stays in the tube so if it goes fund the
blood into into this tube you'll it's
secretion and this is number three
tubular secretion and again this can
happen at different stages or different
parts of the nephron okay
but usually it's not a huge amount okay
not a huge amount so what can we see we
can see when it comes to urine formation
it's made up of three different
components glomerular filtration which
is about 120 mils a minute chabela
reabsorption throwing back 99% of all
that stuff back into the body okay and
tubular secretion throwing out some
stuff this stuff is going to be for
example urea for example this is urea
can be thrown back into the tubules to
be excreted or to be paid out so this is
your information
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