Physiology 10 Flashcards
Total body water of 70 kg young man? What does total body water consist of? (2) What is extracellular fluid composed of? (2)
- 60% (~42 L)
- Intraceullular fluid (2/3) and extraceullular fluid (1/3)
- Interstitial fluid (75%) and plasma volume (25%)
What is interstitial fluid? What is its role? What does this have t diffuse from?
- Fluid bathing the body cells
- Acts as the go-between blood and body cells - delivers oxygen and nutrients to body cells
- Have to diffuse from intravascular compartment to reach body cells
What are capillaries composed of? What is their function? What does blood flow in capillaries depend on?
- Single layer of endothelial cells
- Allow rapid exchange of gases, water & solutes with INTERSTITIAL FLUID
- Blood flow in the capillaries depends on the contractile state of the arterioles
What is the function of terminal arterioles? What regulate flow only some tissues? Example?
- Regulate regional blood flow to the Capillary Bed (CB) in most tissues
- ‘Precapillary Sphincters’ regulate flow in few tissues
- e.g. mesentery
Is blood flow through capillary bed fast or slow? Why? What do capillaries unite to form?
- Slow
- To allow adequate time for exchange
- Post-capillary venules
Explain the transport of substances across capillary wall (5)
- Small water-soluble substances pass through water-filled capillary pores e.g. Na+, K+, glucose, amino acids
- Lipid soluble substances pass through the endothelial cells e.g. O2, CO2
- Exchangeable proteins moved across by vesicular transport
- Plasma proteins generally cannot cross capillary wall (usually stay within the blood)
What does fluid movement across capillary wall depend on? What does movement of gases and solutes follow?
- Pressure gradient (bulk flow)
* Fick’s Law of Diffusion (i.e. downhill)
What is transcapillary fluid flow driven by? What is transcapillary fluid flow?
- Passively driven by pressure gradients across the capillary wall
- Ultra-filtration i.e. exchange across the capillary wall of essentially protein-free plasma
What is Net Filtration Pressure? What also affects net fluid filtration?
- NFP = forces favouring filtration - forces opposing filtration
- A filtration coefficient (Kf)
What are forces involved in transcapillary flow known as? What are forces favouring filtration? (2) Forces opposing filtration? (2)
- Starling Forces
Favouring
- Pc - capillary hydrostatic pressure
- nI - interstitial fluid osmotic pressure
Opposing
- nC - capillary osmotic pressure
- Pi - Interstitial fluid hydrostatic pressure
NOTE: n = pi
Look at picture showing forces affecting arteriolar and venular end of capillary (pic)
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What is the most important force favouring filtration? What does it occur as a result of?
- Capillary hydrostatic pressure
* Results from blood pressure itself - BP falls from arterioles to capillaries - this forces fluid outside capillary
What is osmotic pressure inside the capillary? Why?
- ~25 mmHg
* Due to presence of plasma proteins
What is another way of writing NFP = forces favouring filtration - forces opposing filtration? What is NFP at arteriolar end? Venular end?
- NFP = (PC + ni) - (nC + Pi)
- NFP arteriolar = (35 + 1) - (25 +1) = +10 mmHg
- NFP venular = (17 + 1) - (25 +1) = -8 mmHg
What do Starling forces favour at each capillary end?
Starling forces favour filtration at arteriolar end, reabsorption at venular end
Value of NFP at arteriolar end? Venular end? What does this mean?
- Ateriolar - +10 favouring movement from capillary into interstitial fluid
- Venular - ~-8mmHg favouring filtration back into capillary
Describe Starling forces at arteriolar end? Venular end?
- Forces at arteriolar end higher in direction from capillary outwards so fluid travels out
- At venular end forces are greater in direction from IF into capillary so fluid travels in
How does filtration compare to reabsortion? How is excess fluid returned to circulation?
- In a day, filtration exceeds reabsorption by 2-4 litres
* Excess fluid returned to circulation via lymphatics as lymph
How do Starling forces in pulmonary capillaries differ from systemic circulation? How is accumulation of interstitial fluid prevented?
- Pulmonary resistance is only ~10% of that of the systemic circulation
- Pulmonary capillary hydrostatic pressure is low (~ 8-11 mmHg)
- Capillary osmotic pressure at 25 mmHg
- Efficient lymphatic drainage removes any filtered fluid
What is pulmonary oedema? What is the effect of pulmonary oedema?
- Accumulation of fluid in interstitial space
* Diffusion distance increases - gas exchange compromised in pulmonary oedema
What are causes of oedema?
- Raised capillary pressure
- Reduced plasma osmotic pressure
- Lymphatic insufficiency
- Changes in capillary permeability
Causes of raised capillary pressure? (2) Examples? (3)
- arteriolar dilatation
* raised venous pressure e.g. LVF (pulmonary oedema), RVF (peripheral oedema), prolonged standing (swollen ankles)
What effect does heart failure have on Frank-Starling curve? Treating heart failure?
- Shifts Frank-Starling curve to right
* HF treatment moves curve to left
Cause of reduced plasma osmotic pressure? When does oedema occur? What can cause this? (4)
- Lack of plasma protein
- Oedema if <30g/l
Causes
- Malnutrition
- Protein malabsorption
- Excessive renal excretion of protein
- Hepatic failure
What is lymphatic insufficiency? Causes? (2)
Is it pitting oedema?
- Lymphatic obstructing
- Lymph node damage
- Filariasis (elephantiasis)
- No, it is different from oedema caused by heart failure
Causes of changes in capillary permeabilty? (2)
- Inflammation
* Histamine increases leakage of protein
What oedema does left ventricular failure lead to? What is this?
- Pulmonary oedema
* Accumulation of fluid in the interstitial and intraalveolar lung spaces
Symptoms of pulmonary odema? Clinical signs? CXR?
- SOB
- crepitations in auscultation of lung bases
- CXR shows haziness in perihilar region
Where is pitting oedema due to right heart failure felt? (2)
- Ankles
* Sacrum
