How is edema caused Watch

Stormragexox
Badges: 9
Rep:
?
#1
Report Thread starter 5 months ago
#1
Hey guys I understand edema is caused due to something dealing with hydro static pressure but how and why
0
reply
macpatgh-Sheldon
Badges: 16
Rep:
?
#2
Report 5 months ago
#2
Hi,
Oedema i.e. the collection of fluid in the extracellular compartment OUTSIDE BLOOD VESSELS i.e. in the interstitial space, occurs, as we can work out, when the amount of water leaving the capillaries [arterial end] exceeds that re-entering the capillaries [venous end]. (these processes act in a dynamic fashion, so the net effect of the two determines the overall direction of fluid flow).

The main force that tends to push fluid out of the capillaries is the hydrostatic pressure, which is what remains of the blood pressure (generated by the heartbeat) by the time blood reaches the capillaries.

The main force that tends to retain blood in the vascular compartment is the osmotic pressure (determined by osmolality) of the blood. This is contributed to by all solutes in blood, but importantly by blood proteins, the most abundant of which is albumin.

So, any situation where either:

a) there is an increase in hydrostatic pressure [including back pressure due to reduction of blood pressure]
OR
b) there is a reduction in osmotic pressure [increase in water potential in recent terminology],

OEDEMA WILL OCCUR.

EXAMPLES:
a) hepatic failure leading to hypoalbuminaemia [causing reduced blood osmotic pressure] since the liver is the principal site of the synthesis of serum protein.
b) renal failure leading to the same as in a) due to proteinuria [mainly albuminuria]. [loss of protein in the urine causes reduced blood osmotic pressure].
c) cardiac failure due to back pressure [see bold print above] e.g, in left ventricular failure [LVF], pulmonary oedema occurs due back pressure into the lungs from the failing left ventricle via [backwards] the left atrium and the pulmonary veins.
OR
in RVF, systemic oedema due to back pressure from the failing right ventricle via the right atrium and inferior vena cava (in ambulant patients, ankle oedema occurs while in bedridden patients, pelvic oedema occurs [effects of gravity]).

Hope this explains clearly your enquiry.
Last edited by macpatgh-Sheldon; 5 months ago
1
reply
Jpw1097
Badges: 15
Rep:
?
#3
Report 5 months ago
#3
A fantastic answer by macpatgh-Sheldon, I'd just to like to add another example. Exchange across capillaries is determined by the balance between capillary hydrostatic pressure and oncotic pressure (that is, osmotic pressure due to proteins in the plasma). The classic example of oedema is during inflammation. When a tissue is damaged, mast cells (a type of white blood cell which reside in the tissues) are activated and release various vasoactive substances such as histamine, bradykinin, prostaglandins, leukotrienes, etc. Other inflammatory cells such as macrophages also become activated and release cytokines such as TNFα, IL-6 and IL-1 and other pro-inflammatory mediators. These mediators cause vasodilation, and also increase vascular permeability (that is, the permeability of blood vessels to solutes such as proteins) by causing the endothelial cells lining the vessels to contract, increasing the size of the gaps between the cells). Vasodilation increases the hydrostatic pressure in the capillary because more blood is flowing into the capillary bed - this tips the balance in the favour of filtration (i.e. movement of plasma out the of the capillaries into the interstitial space). Furthermore, the increased vascular permeability (essentially the size of the gaps between endothelial cells) allows proteins to leak out of the capillaries into the tissue/interstitial space - thereby reducing the oncotic pressure in the capillaries. Since the proteins in the blood act to hold onto water, the leak of proteins from the blood into the tissue causes water to move from the blood into the tissue - again, tipping the balance in the favour of filtration causing oedema.

Another similar example is during anaphylaxis; in anaphylaxis, there is a massive release of histamine and bradykinin from mast cells - this causes systemic vasodilation and increases vascular permeability. By the same mechanisms I've just described (increased hydrostatic pressure and plasma protein leak), this causes fluid to leave the blood and enter the tissues - causing oedema. In anaphylaxis however, this can cause the tissues of the face, tongue, eyes, lips, throat and lungs to become swollen (oedematous) - this can be life-threatening as it can block the airway. This pattern of oedema is known as angioedema.

Another example of oedema is lymphodema. As you may be aware, not all of the fluid filtered into the tissue/interstitial space returns to the blood at the venule end of the capillary - some of it remains and must re-enter the circulation via the lymphatic system. However, if for any reason there is a problem with the lymphatic system (a good example is if lymph nodes have been removed from the armpit due to breast cancer), fluid will accummulate in the tissues as it is not being returned to the circulation.
0
reply
Stormragexox
Badges: 9
Rep:
?
#4
Report Thread starter 5 months ago
#4
(Original post by macpatgh-Sheldon)
Hi,
Oedema i.e. the collection of fluid in the extracellular compartment OUTSIDE BLOOD VESSELS i.e. in the interstitial space, occurs, as we can work out, when the amount of water leaving the capillaries [arterial end] exceeds that re-entering the capillaries [venous end]. (these processes act in a dynamic fashion, so the net effect of the two determines the overall direction of fluid flow).

The main force that tends to push fluid out of the capillaries is the hydrostatic pressure, which is what remains of the blood pressure (generated by the heartbeat) by the time blood reaches the capillaries.

The main force that tends to retain blood in the vascular compartment is the osmotic pressure (determined by osmolality) of the blood. This is contributed to by all solutes in blood, but importantly by blood proteins, the most abundant of which is albumin.

So, any situation where either:

a) there is an increase in hydrostatic pressure [including back pressure due to reduction of blood pressure]
OR
b) there is a reduction in osmotic pressure [increase in water potential in recent terminology],

OEDEMA WILL OCCUR.

EXAMPLES:
a) hepatic failure leading to hypoalbuminaemia [causing reduced blood osmotic pressure] since the liver is the principal site of the synthesis of serum protein.
b) renal failure leading to the same as in a) due to proteinuria [mainly albuminuria]. [loss of protein in the urine causes reduced blood osmotic pressure].
c) cardiac failure due to back pressure [see bold print above] e.g, in left ventricular failure [LVF], pulmonary oedema occurs due back pressure into the lungs from the failing left ventricle via [backwards] the left atrium and the pulmonary veins.
OR
in RVF, systemic oedema due to back pressure from the failing right ventricle via the right atrium and inferior vena cava (in ambulant patients, ankle oedema occurs while in bedridden patients, pelvic oedema occurs [effects of gravity]).

Hope this explains clearly your enquiry.
(Original post by Jpw1097)
A fantastic answer by macpatgh-Sheldon, I'd just to like to add another example. Exchange across capillaries is determined by the balance between capillary hydrostatic pressure and oncotic pressure (that is, osmotic pressure due to proteins in the plasma). The classic example of oedema is during inflammation. When a tissue is damaged, mast cells (a type of white blood cell which reside in the tissues) are activated and release various vasoactive substances such as histamine, bradykinin, prostaglandins, leukotrienes, etc. Other inflammatory cells such as macrophages also become activated and release cytokines such as TNFα, IL-6 and IL-1 and other pro-inflammatory mediators. These mediators cause vasodilation, and also increase vascular permeability (that is, the permeability of blood vessels to solutes such as proteins) by causing the endothelial cells lining the vessels to contract, increasing the size of the gaps between the cells). Vasodilation increases the hydrostatic pressure in the capillary because more blood is flowing into the capillary bed - this tips the balance in the favour of filtration (i.e. movement of plasma out the of the capillaries into the interstitial space). Furthermore, the increased vascular permeability (essentially the size of the gaps between endothelial cells) allows proteins to leak out of the capillaries into the tissue/interstitial space - thereby reducing the oncotic pressure in the capillaries. Since the proteins in the blood act to hold onto water, the leak of proteins from the blood into the tissue causes water to move from the blood into the tissue - again, tipping the balance in the favour of filtration causing oedema.

Another similar example is during anaphylaxis; in anaphylaxis, there is a massive release of histamine and bradykinin from mast cells - this causes systemic vasodilation and increases vascular permeability. By the same mechanisms I've just described (increased hydrostatic pressure and plasma protein leak), this causes fluid to leave the blood and enter the tissues - causing oedema. In anaphylaxis however, this can cause the tissues of the face, tongue, eyes, lips, throat and lungs to become swollen (oedematous) - this can be life-threatening as it can block the airway. This pattern of oedema is known as angioedema.

Another example of oedema is lymphodema. As you may be aware, not all of the fluid filtered into the tissue/interstitial space returns to the blood at the venule end of the capillary - some of it remains and must re-enter the circulation via the lymphatic system. However, if for any reason there is a problem with the lymphatic system (a good example is if lymph nodes have been removed from the armpit due to breast cancer), fluid will accummulate in the tissues as it is not being returned to the circulation.
Thank you so much I understand it clearly now XD
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

University open days

  • University of Warwick
    Undergraduate Open Day Undergraduate
    Fri, 21 Jun '19
  • University of Bath
    Find out about life at the University and discover our diverse range of Undergraduate courses. Our course areas include the Sciences, Humanities & Social Sciences, Engineering & Design, and Management. Undergraduate
    Fri, 21 Jun '19
  • University of Liverpool
    Undergraduate Open Day Undergraduate
    Fri, 21 Jun '19

How did your AQA A-level Chemistry Paper 3 go?

Loved the paper - Feeling positive (297)
32%
The paper was reasonable (439)
47.31%
Not feeling great about that exam... (114)
12.28%
It was TERRIBLE (78)
8.41%

Watched Threads

View All