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Oncotic (Osmotic Pressure) in the blood pressure

Oncotic (Osmotic Pressure) in the blood pressure


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I just wanted to ask, why is the oncotic pressure more negative in the blood plasma even though the hydrostatic pressure is higher since the blood comes from the pumping of the heart?


How does albumin maintain osmotic pressure?

Albumin is essential for maintaining the oncotic pressure in the vascular system. A decrease in oncotic pressure due to a low albumin level allows fluid to leak out from the interstitial spaces into the peritoneal cavity, producing ascites. A low serum albumin indicates poor liver function.

One may also ask, how does albumin help blood pressure? Albumin is also the main contributor to oncotic pressure, which means that it helps keep fluid in your blood vessel rather than allow it to leak into your tissues which causes swelling or edema. To prevent protein in the urine you need to have good control of your blood pressure and glucose levels.

Similarly one may ask, what is the role of albumin in the body?

Function. Serum albumin is the main protein of human blood plasma. It binds water, cations (such as Ca 2 + , Na + and K + ), fatty acids, hormones, bilirubin, thyroxine (T4) and pharmaceuticals (including barbiturates): its main function is to regulate the oncotic pressure of blood.

How is albumin made in the liver?

Albumin is synthesized in the liver as preproalbumin, which has an N-terminal peptide that is removed before the nascent protein is released from the rough endoplasmic reticulum. The product, proalbumin, is in turn cleaved in the Golgi vesicles to produce the secreted albumin.


Ch.10 Biology Homeostasis: Excretory System and Skin

As descending limb of loop of henle descends it enters inner medulla, then outer medulla where the osmolarity in the interstitium can be:
1. isotonic - if trying to excrete water, prevent reabsorption
2. hypertonic - much higher than plasma - if trying to conserve, reabsorb water

this prevents equilibrium from being reached quickly

-at beginning segment (OUTER MEDULLA - deep): salt ions diffuse passively
-at thicker "diluting segment" (INNER MEDULLA - closer to cortex): ions ACTIVELY pumped out of the filtrate, diluting filtrate and increasing plasma osmolarity

large amounts of mitochondria in cells = active transport reabsorption of Na+ and Cl-

Result:
-increases plasma volume and pressure while osmolarity remains unchanged
-increases concentration of urine and reduces volume

when the pH is too low - can excrete more H+ and reabsorb more HCO3-

layers of dead flattened keratinocytes

barrier to pathogen invasion, fluid and salt loss

most abundant epidermal cell

produce melanin and protect skin from DNA damage due to UV radiation

serve as antigen-presenting cells to T-cells

when body temp rises above set point

unique postganglionic sympathetic neurons that utilize AcH innervate sweat glands originating in dermis - promote secretion of water/ions to skin as "sweat"

*production of sweat isn't cooling mechanism itself:
body heat is then absorbed when water evaporates

skeletal muscle rapid contraction

this will prevent aldosterone from being secreted
-aldosterone normally increases Na+ reabsorption followed by water, increased BP, and secretion of K+/H+ in DCT

urination = PNS = all synapses contain AcH
sweating = unique post ganglia with cholinergic synapse as well


What is osmotic pressure of blood?

Secondly, what causes blood osmotic pressure? Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure induced by proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that displaces water molecules, thus creating a relative water molecule deficit with water molecules moving back into the circulatory system within the lower

Keeping this in view, what is osmotic pressure in the body?

Osmotic pressure can be described as the pressure of a water solution of salts exerted in either direction against a semipermeable membrane. This pressure is caused by differences between the concentrations of dissolved salts within the body and those outside, in the sea.&hellip

What is the difference between osmotic pressure and blood pressure?

Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in. Osmotic pressure is determined by osmotic concentration gradients, that is, the difference in the solute-to-water concentrations in the blood and tissue fluid.


Oncotic pressure

Oncotic pressure is the part of osmotic pressure which is contributed by the large molecules, the "colloid osmotic pressure".
This is 25-30mmHg, or about 0.5% of the total osmotic pressure. Its not much, but its enough to keep the water in the vascular compartment.

The calculated oncotic pressure is lower than the actual oncotic pressure, because of the Gibbs-Donnan Effect.

The calculated pressure is 20mmHg the measured is around 30mmHg. Because the anionic proteins in the blood attract sodium cations, there is a net increase in 0.4 mOsm/L, which contributes the additional 10mmHg difference.

Albumin contributes 75% to the oncotic pressure of the plasma. There are four albumin molecules for every globulin molecule, and it has more anionic charge.

All of this works only while there is not much protein in the interstitial fluid. If there was lots of protein there (or conversely if protein were lost from the intravascular space) the oncotic pressure would drop, and fluid would migrate easily between the intravascular space and interstitial space, causing oedema.

Oedema does not develop until plasma oncotic pressure has decreased below 11mmHg.
That equates to an albumin level around 20g/l.

The flow of lymph keeps the protein out of the interstitial space, and thus prevents oedema from developing. One of the roles of lymph is to de-proteinate the interstitial fluid.

Overall, this interaction of oncotic pressure and hydrostatic pressure is known as Starling's Principle, and is discussed in greater detail elsewhere.

Previous chapter: Difference between osmolarity, osmolality and tonicity

Next chapter: Movement of fluid between the intravascular and interstitial compartments

References

Additonally I have used Ganongs Review of Medical Physiology 23rd edition.


[Biology/G.Chem] Osmotic pressure vs. Hydrostatic Pressure

I am having trouble understanding the differences and relationship with osmotic and hydrostatic pressure.

So a solvent will move from an area of high osmotic pressure to an area of low osmotic. I am also reading online that osmotic pressure acts in the direction opposite of water movement. So why wouldn't a high osmotic pressure mean that that there would be no movement of water?

As a corollary, in the arteriole end of a blood vessel, the hydrostatic pressure is greater than osmotic pressure and fluid is pushed out of the capillary and into the interstitium. On the venule end, the osmotic pressure is greater than hydrostatic pressure and fluid flows into the capillary and out of intersititium. I don't understand why.

Things with high osmolarity have high osmotic pressure. The osmotic pressure is the pressure that must be applied to a solution to stop osmosis. The higher the solute concentration, the more water will want to cross the membrane into the solution, and the more pressure you have to apply to keep that from happening.

Hydrostatic pressure is just how hard water is pushing on whatever it's touching. As you fill a water balloon, it's hydrostatic pressure goes up until it bursts.

So, let's talk capillaries. The arteriolar end of the capillary has higher hydrostatic pressure because it's closer to the heart, the pump that generates your blood pressure. It's got the consistency of normal blood at this point, with "normal" osmotic pressure. Because hydrostatic pressure is high, water is squeezed through the leaky endothelial membrane and into the interstitium. Note that only some components of blood can leave the capillary, so some stuff gets left behind, increasing the osmolarity and thus osmotic pressure. Also, since you're losing water, the hydrostatic pressure in the capillary drops. As you continue along the capillary toward the venule end, the hydrostatic pressure falls below the osmotic pressure and no longer prevents osmosis of water into the capillary.


Is Oncotic pressure the same as osmotic pressure?

The net pressure that drives reabsorption&mdashthe movement of fluid from the interstitial fluid back into the capillaries&mdashis called osmotic pressure (sometimes referred to as oncotic pressure). Whereas hydrostatic pressure forces fluid out of the capillary, osmotic pressure draws fluid back in.

what is the difference between hydrostatic and osmotic pressure? Hydrostatic pressure is the pressure pushing the fluid out favoring filtration, which is higher at the arterial end of the capillary. Osmotic pressure is the pressure pushing the fluid in favoring absorption, which is higher at the venous end of the capillary.

Also to know is, what is the meaning of oncotic pressure?

Oncotic pressure, or colloid osmotic pressure, is a form of osmotic pressure induced by proteins, notably albumin, in a blood vessel's plasma (blood/liquid) that displaces water molecules, thus creating a relative water molecule deficit with water molecules moving back into the circulatory system within the lower

Why does Oncotic pressure stay the same?

Oncotic Pressure. The other force that contributes to fluid movement across the capillary wall is oncotic pressure. This means that in effect, these proteins pull water into that compartment, as the force of osmosis tries to equalize the amount of water in blood and in the interstitial fluid.


What is Colloid Osmotic Pressure? (with pictures)

Colloid osmotic pressure, also referred to as oncotic pressure, is a measurement of pressure exerted within the cardiovascular system by proteins found in blood plasma. The special nature of these protein cells helps ensure that fluids pass in and out of the capillaries at the proper rate. Maintaining the proper pressure ensures that the body tissues maintain the proper levels of liquid and that too much liquid does not escape from the capillaries. Under normal conditions, oncotic pressure tends to cause fluid to be drawn into the capillaries. Variations can lead to buildup of fluid in the tissues, a condition known as edema.

Osmotic pressure in general refers to the pressure that must be maintained on either side of a cell membrane to prevent a solution, or solids dissolved in a liquid, from passing through that cell membrane. Colloidal osmotic pressure refers specifically to the relevant pressure for a solution of plasma proteins. These proteins are relatively large molecules, meaning that they do not readily pass through the cell membrane. Their size also affects the tendency of liquids to move out of the capillaries, maintaining the proper amount of liquid and pressure inside these tiny blood vessels.

Another way in which colloid osmotic pressure affects the cardiovascular system is in intravenous (IV) therapy. Fluids used for IV treatment typically contain either colloid or crystalline solubles, depending on the substance required for the relevant treatment. A common example of an IV therapy using a crystalline solution is intravenous saline used to counter dehydration. This solution contains sodium chloride, or salt, which occurs naturally in a crystalline form. In order for the solutions to remain within the circulatory system, appropriate pressure must be maintained within the blood vessels.

Measuring an individual's colloid osmotic pressure is one way that medical professionals diagnose pulmonary edema, and it can be used to calculate a patient's likelihood of surviving a critical case. This condition, in which fluids escape from the circulatory system and fill the lungs, can be fatal if not treated promptly. It can occur as a result of cardiovascular disease or because of a rapid change in air pressure such as that experienced when climbing at high altitudes. Pulmonary edema also is closely associated with congestive heart failure. Treatment includes maintaining oxygenation of the body tissues as well as treating the underlying cause.


What Is Osmotic Pressure? (with pictures)

Osmotic pressure is a volumetric force that resists the natural process of osmosis. It is most often referenced in human biology, where a living cell contains a concentrated solution of water and certain other elements that it separates from outside solutions by a semipermeable membrane. The natural process of osmosis tends to equalize the concentrations of solute materials in a solution by passing the solution through such membranes, and osmotic pressure is the quantity of pressure that a living cell exerts to resist this force. Such pressure protects inner components of the cell from dilution and harmful solutions that might cross the membrane and disrupt normal cell activity or mitosis.

Like many natural forces, osmosis is a force that drives solutions towards a state of equilibrium. When a solution surrounded by a thin membrane contains a higher concentration of a chemical, such as salt or sugar, than the same solution outside of the membrane, equilibrium forces drive the entire solution towards a state of uniform concentration of chemicals. This natural process is especially important in regard to water in lifeforms on Earth, which has a level of potential energy that causes it to dilute concentrated solutions through various forces such as osmosis and gravity. This condition is referred to as water potential, and the ability of water to exert this force increases with water's volume and depth, which is a form of osmotic hydrostatic pressure.

While water potential is an equalizing force for different solutions, the opposite of this force is known as osmotic potential, which is the value of potential energy that osmotic pressure has to resist a state of equilibrium. Calculations for determining the actual value of osmotic pressure were first worked out by Jacobus Hoff, a Nobel Prize-winning Dutch chemist of the late 19 th to early 20 th century. His ideas were later refined by Harmon Morse, a US chemist of the same time period.

Since the process of osmotic pressure can also be considered for gasses separated by a semipermeable membrane, it obeys the same physical rules as ideal gas law. The osmotic pressure equation can, therefore, be stated as P = nRT/V, where “P” is the osmotic pressure and “n” is the amount of solute or number of moles of molecules present in the volume — “V” — of solution. The value of “T” represents the average temperature of the solution and “R” is the gas constant value of 8.314 joules per degree Kelvin.

Though osmotic pressure is important in cellular biology for animals in terms of protecting the cell from intrusion by unwanted chemical solutes or the external solution itself, it serves a more fundamental purpose in plants. By counteracting the force of water potential, plant cells utilize osmotic pressure to lend a degree of turgidity or stiffness to plant cell walls. In combining this force among multiple plant cells, it gives the plant the ability to produce stems that stand upright and can resist damage from climate forces like wind and rain. This is why plants tend to wither and droop when they lack water, as the cell walls have insufficient osmotic hydrostatic pressure to resist the forces of gravity and weather conditions.


Osmotic Pressure: Definition, Significance and Factors | Biophysics

In this article we will discuss about:- 1. Definition of Osmotic Pressure 2. Significance of Osmotic Pressure in the Absorption of Food 3. Factors Regulating 4. Pressure in Cells 5. Physiological Importance 6. Factors Regulating the Volume of the Extracellular Water 7. ADH 8. Vant Hoff’s Laws 9. Calculations Involving 10. Distribution of a Solute between Two Immiscible Solvents.

  1. Definition of Osmotic Pressure
  2. Significance of Osmotic Pressure in the Absorption of Food
  3. Factors Regulating Osmotic Pressure
  4. Osmotic Pressure in Cells
  5. Physiological Importance of Osmotic Pressure
  6. Factors Regulating the Osmotic Pressure and the Volume of the Extracellular Water
  7. ADH and Osmotic Pressure
  8. Vant Hoff’s Laws of Osmotic Pressure
  9. Calculations Involving Osmotic Pressure
  10. Distribution of a Solute between Two Immiscible Solvents

1. Definition of Osmotic Pressure:

Osmotic pressure can be defined as the excess pressure which must be applied to a solution to prevent the flow of solvent of low osmotic pressure when they are separated by a perfectly semi-permeable membrane.

2. Significance of Osmotic Pressure in the Absorption of Food:

i. Osmotic pressure is only permanent if the membrane is truly semipermeable, i.e. if it stops all solute molecules and only passes the solvent molecules.

ii. In case of dialysis, if the collodion or cel­lophane bag is filled with a solution of a dye with small molecules and placed in contact with water, water will pass into the dye, but, at the same time, water plus dye will pass out from the bag.

As water molecules are smaller than the dye mol­ecules, water will pass into the bag more quickly than water plus dye will leave it. Therefore, an osmotic pressure will be de­veloped, but it will only be small and tran­sient because the membrane is permeable to both water and dye.

But, if the bag is filled with a dye of large molecules, the dye cannot pass out into the water but water will pass into the dye—causing a permanent pressure difference.

If the bag is surrounded with a solution of NaCl of greater osmotic pressure than the dye, water will at first pass out of the bag faster but, at the same time, NaCl will pass into the bag. The final equilibrium will be at­tained when the osmotic pressure of the salt solution outside the bag equals the osmotic pressure of salt inside, so that the ultimate permanent osmotic pressure dif­ference will be that of the dye alone.

3. Factors Regulating Osmotic Pressure:

i. Osmotic pressure depends on the number of solute molecules but not on the size of the molecules.

Example: A solution of urea (Mol. wt. 60) of 60 g. per litre has the same osmotic pres­sure as a solution of cane sugar (mol. wt. 342) of 342 g. per litre because these two solutions contain the same number of mol­ecules per litre.

ii. In case of salts which ionize, it is the number of ions plus molecules which count, so that fully ionised NaCl has twice the osmotic pressure it would have as judged by the number of molecules.

iii. Other substances, such as soaps, form mo­lecular aggregates, so that their solutions have lower osmotic pressure.

iv. The osmotic pressure increases with the rise in temperature.

4. Osmotic Pressure in Cells:

i. If the cell is kept in a hypotonic solution, the cell wall and the vacuolar membrane both will allow water to pass into it and will set up an excess pressure in the inte­rior of the cell causing the cytoplasm to be forced tightly against the cell wall. In normal health, this condition is known as “turgor” and the cell is said to be turgid.

ii. If the cell is immersed in a concentrated solution (high osmotic pressure), water will pass out of the interior of the cell. The cytoplasm will then shrink and detach it­self from the cell wall. This phenomenon is said to be “plasmolysis”. Iso-osmotics: Solutions with the same pres­sure are termed iso-osmotics.

A pair of solutions which produce no flow through a semi­permeable membrane are said to be isot­onic solutions.

5. Physiological Importance of Osmotic Pressure:

i. Absorption from gastro-intestinal tract, as also fluid interchange in various compart­ments of the body follow the principles of osmosis.

ii. The osmotic pressure of plasma proteins regulates water to flow from the protein- free intestinal fluid into the blood vessels.

iii. Living red cells, if suspended in 0.92% NaCl solution, neither gain nor lose wa­ter. Briefly speaking, intracellular fluid of red cells is isotonic with the red cell mem­brane in 0.92% NaCl solution.

6. Factors Regulating the Osmotic Pressure and the Volume of the Extracellular Water:

In the maintenance of life, the body has homeostatic or regulatory mechanisms which help to maintain the osmotic pressure and the volume of the extra­cellular water within physiological limits. The os­motic pressure of the extracellular water is control­led by antidiuretic hormone ADH and the volume of the extracellular water is controlled by aldoster­one, the adrenocortical hormone.

7. ADH and Osmotic Pressure:

ADH, the antidiuretic hormone, is an octapeptide. It regulates the osmotic pressure of the extracellu­lar water and of the cells by regulating the reten­tion or excretion of water by the kidneys. The posterior pituitary gland is stimulated to secrete ADH, when the osmotic pressure of the ex­tracellular water becomes relatively greater than the osmotic pressure of the cells.

ADH liberation is stopped, when the osmotic pressure of the extracel­lular water is relatively less than that of the cells. The site of action of ADH is probably the distal tubules and collecting ducts of the kidneys. ADH increases the permeability of the structures to wa­ter.

When this happens an increased amount of water is reabsorbed resulting in the volume of urine decrease. ADH secretion is not affected when the total osmotic pressure of the body changes. If urea is infused, it does not cause an antidiuretic effect even though it increases the osmotic pressure of the ex­tracellular water.

Because, it is able to penetrate the cells freely. Hence it also raises the osmotic pressures of the cells to the same degree as the ex­tracellular water.

If, for any reason, the osmotic pres­sure of the cells in relation to the osmotic pressure of the extracellular water changes, ADH secretion either decreases or increases.

If a large amount of hypertonic glucose or sucrose is infused into the body, it raises the osmotic pressure of the extracel­lular water.

The glucose or sucrose is unable to pen­etrate cells freely. Therefore, the osmotic pressure of the extracellular water rises above that of the cells. As a result, ADH secretion occurs and water excretion by the kidneys decreases.

If a person drinks plain water, the immediate effect of the imbibed water is to dilute the extracel­lular water.

This causes the osmotic pressure of the extracellular water to become lower than that of the cells. Therefore, ADH secretion stops and water diuresis takes place.

ADH stimulation occurs in various ways, e.g., it occurs as the result of fear, pain or in acute infec­tions such as pneumonia. The mechanism by which ADH secretion occurs in these conditions is un­known.

Recently it has been found that the liver acts as an osmoreceptor to regulate the intake of water from the gastro-intestinal tract.

When water is im­bibed, it is absorbed into the splanchnic circula­tion and is brought to the liver by way of the portal vein.

This causes the osmolality of the portal vein to decrease very rapidly. The hypothalamus then stimulates the kidneys to excrete water.

8. Vant Hoff’s Laws of Osmotic Pressure:

1. The osmotic pressure of a solution varies directly with the concentration of the sol­ute in the solution and is equal to the pres­sure the solute would exert if it would be a gas in the volume occupied by the solu­tion, if the volume of the solute molecules relative to volume of solvent be negligi­ble.

2. The osmotic pressure of a solution varies directly with absolute temperature in the same way as the pressure of a gas varies when its volume is kept constant.

These laws of osmotic pressure have been thor­oughly verified by accurate observations. As with gases, the laws of osmotic pressure hold closely only for dilute solutions. Proper correction must be made for concentrated solution.

9. Calculations Involving Osmotic Pressure:

Osmotic pressure is due to the difference in activ­ity of pure solvent molecules and of solvent mol­ecules associated with solute molecules. It is pro­portional to the number of and independent of the kind of dissolved particles present.

The general equation for gases applies to os­motic pressure:

where π = the osmotic pressure in atmosphere, n = the number of moles of solutes, R = the molar gas constant (0.082 litre-atmosphere/mol/Å), T = the absolute temperature, V = the volume in litres.

Since n = g/M, where g = grams of solute and

M = the molecular weight of the solute, the equa­tion may be written

where C = the molal concentration of the solution and corrects for the volume occupied by the solute molecules.

10. Distribution of a Solute between Two Immiscible Solvents:

When a water solution of succinic acid is shaken with ether, the molecules of acid distribute them­selves in such a way that the ratio of acid mol­ecules dissolved in water to those dissolved in ether is constant, regardless of the total amount of acid dissolved. The ratio of concentration of acid in water C1 to concentration of acid in ether C2 is relatively constant

The principle of the distribution of solutes between immiscible solvents is of much importance in the body. In general, a substance that is more soluble in organic solvents than in water is also more soluble in lipids. Consequently, drugs and other molecules that are more soluble in organic solvents than in water will tend to concentrate in the tissues and fluids of the body that contain more lipid material.

On the other hand, molecules that are highly soluble in water and slightly soluble in lipids will be present in greater concentration in the body fluids and tissues that contain little lipid or fat-like material.

For example, when ether is used as an anaesthetic, the concentration in the brain and nervous tissue (rich in lipids) will be much greater than the concentration in the blood and tis­sues, which are much poorer in lipid material. Theo­retically, the ether will be distributed in the body according to its distribution coefficients for the various fluids and tissues that serve as solvents for it.



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