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GFR is influenced by the hydrostatic pressure and colloid osmotic pressure on either side of the capillary membrane of the glomerulus. Recall that filtration occurs as pressure forces fluid and solutes through a semipermeable barrier with the solute movement constrained by particle size. Hydrostatic pressure is the pressure produced by a fluid against a surface. If you have a fluid on both sides of a barrier, both fluids exert a pressure in opposing directions. Net fluid movement will be in the direction of the lower pressure. Osmosis is the movement of solvent (water) across a membrane that is impermeable to a solute in the solution. This creates a pressure, osmotic pressure, which will exist until the solute concentration is the same on both sides of a semipermeable membrane. As long as the concentration differs, water will move. Glomerular filtration occurs when glomerular hydrostatic pressure exceeds the luminal hydrostatic pressure of Bowman’s capsule. There is also an opposing force, the osmotic pressure, which is typically higher in the glomerular capillary.

To understand why this is so, look more closely at the microenvironment on either side of the filtration membrane. You will find osmotic pressure exerted by the solutes inside the lumen of the capillary as well as inside of Bowman’s capsule. Since the filtration membrane limits the size of particles crossing the membrane, the osmotic pressure inside the glomerular capillary is higher than the osmotic pressure in Bowman’s capsule. Recall that cells and the medium-to-large proteins cannot pass between the podocyte processes or through the fenestrations of the capillary endothelial cells. This means that red and white blood cells, platelets, albumins, and other proteins too large to pass through the filter remain in the capillary, creating an average colloid osmotic pressure of 30 mm Hg within the capillary. The absence of proteins in Bowman’s space (the lumen within Bowman’s capsule) results in an osmotic pressure near zero. Thus, the only pressure moving fluid across the capillary wall into the lumen of Bowman’s space is hydrostatic pressure. Hydrostatic (fluid) pressure is sufficient to push water through the membrane despite the osmotic pressure working against it. The sum of all of the influences, both osmotic and hydrostatic, results in a net filtration pressure (NFP)    of about 10 mm Hg ( [link] ).

Net filtration pressure

This figure shows the different pressures acting across the glomerulus.
The NFP is the sum of osmotic and hydrostatic pressures.

A proper concentration of solutes in the blood is important in maintaining osmotic pressure both in the glomerulus and systemically. There are disorders in which too much protein passes through the filtration slits into the kidney filtrate. This excess protein in the filtrate leads to a deficiency of circulating plasma proteins. In turn, the presence of protein in the urine increases its osmolarity; this holds more water in the filtrate and results in an increase in urine volume. Because there is less circulating protein, principally albumin, the osmotic pressure of the blood falls. Less osmotic pressure pulling water into the capillaries tips the balance towards hydrostatic pressure, which tends to push it out of the capillaries. The net effect is that water is lost from the circulation to interstitial tissues and cells. This “plumps up” the tissues and cells, a condition termed systemic edema    .

Questions & Answers

what is a positive and negative feedback and give examples of both positive and negative feedback
esther Reply
what then is Pathological anatomy
acquosuah Reply
anatomy study about normal human organ... pathological anatomy study of diseased organ
Aswin
thanks
acquosuah
wow
Morshed
that's are good
Morshed
why oral glucose make insulin response in 1 phase but IV glucose make insulin response in 2 phase?
qwe Reply
what is anatomical position?
Kakande Reply
it's de description of any region or part of the body in specific strance
Andy
how many cell do we have in our body
Sawmtei Reply
around 37.2 trillion
Jeremiah
how do you know when a women is lying
Hernandez
go with your gut
Stephanie
tell right answer plz
SAJJAD
what is a positive and negative feedback and give examples of negative and positive feedback
esther Reply
messa I didn't understand this too
Shammy
and would love to know as well
Shammy
what are the various types of white blood cells
Andy Reply
what is cpr in first aid
Andy
various whiteblood cells includes Granulocytes (neutrophils,basophils ana eosinophils) and Agranulocytes (monocytes and lymphocytes)
Waziri
Cardiopulmonary resuscitation (cpr) is an emergency procedure. Uses chest compressions with artificial ventilation in an effort to preserve brain function until further measures are taken to restore blood circulation and breathing in a person who is in cardiac arrest.
Jeremiah
wow thanks alot
Andy
respiration is not just taking in of oxygen and bringing out Co2. that is called INHALATION AND EXHALATION. BUT RESPIRATION IS THE BREAKDOWN OF LARGE MOLECULES OF GLUCOSE OR OTHER SUBSTRATES IN THE PRESENCE OF OXYGEN AND SUBSEQUENT REMOVAL OF WASTE PRODUCT
Osuji Reply
why study anatomy?
esther Reply
to know the detailed functioning of the internay body organs
Jam
we study anatomy to know about the structure of the organs which in turn help to study physiology which is the knowledge related to function of the vital organ,and when we know the normal functionality we can understand the abnormalities in that organ,and the study of disease is called pathology
Lubabah
why is it so hard to know the spelling and words
Sawmtei
they were made so that only the best and thr brightest would understand.
Senen
thank you
esther
to know the internal structure of the human body and how it function
Jaafar
whats antonmy
Jaan Reply
the study of structure and function of internal body parts
Jam
is a branch of biology which describes the structures of the body and relationship from one part to another
esther
I believe it is the scientific study of body structures that are both macro and micro.
acquosuah
wat the question is tis ! without knowing tis simple thing.. y didn't install tis app ..
Aswin
what is anatomy and physiology
mwitwa Reply
Anatomy is the study of structures of the body
Zunehri
Physiology the study functions of the body
Zunehri
anatomy is study of structure of body nd physiology is study of function of body.
PRIYANKA
anatomy is the study of internal body structures and physiology is the functioning of these structures in the body
Jam
what is lungs
Shipon Reply
it an organ found in our thoracic cavity
Richard
lungs are spongy organs where our respiration takesplace
Maryama
Lungs is a spongy organs located in the chest , is an a primary organs of respiration in human body and other Animals
Zunehri
lungs thorex me present hote hai ye organ hai and gas exchange (o2,co2 exchange)inka inka function hai.
PRIYANKA
lungs ka function hai
OM
pls am a student I don't know
Mavis
main function is respiration
faheem
respiration is the taking ing of oxygen by the body tissues and the removal of carbondioxide from the body tissues
Jam
what is heart beat,?
Naqeeb Reply
heart beat is the process briting
Mavis
what functions of heart
Muthu Reply
To circulate the blood
Arshad
it pump blood to the lungs
Laura
very twiest
Shipon
what should be the nature of cell
Kashish Reply
Cells die and reproduce
Nejat

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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