Oedema and heart failure Flashcards

1
Q

Why is the total cross section area high in capillary beds

A

Large surface area means functions can take place like gaseous exchange

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2
Q

What is the function of a precapillary sphincter

A

Cuff of smooth muscle fibres that surround the roof of each true capillary at the metaarteriole that act as a valve to regulate blood flow into the capillary

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3
Q

What important functions take place between capillaries and cells

A
  • Removal of CO2 and waste products from cells

- Delivery of nutrients and oxygen to metabolising tissues

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4
Q

How is water distributed throughout the body with regards to extra / intracellular components

A
2/3= intracellular fluid 
1/3= extracellular fluid (80% interstitial fluid and 20% blood plasma)
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5
Q

What does hydrostatic pressure exerted against the inner capillary wall cause

A

Promotes the formation of tissue fluid- net filtration pressure, out of the vessel

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6
Q

What is colloid osmotic pressure

A

osmotic pressure exerted by plasma proteins

Promotes fluid re absorption into circulatory system

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7
Q

What happens to the hydrostatic pressure difference as the length of the capillary increases

A

It decreases

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8
Q

What is Starling force

A

(Capillary hydrostatic pressure + Colloid osmotic pressure of interstitial fluid) - (Interstitial fluid hydrostatic pressure + Colloid osmotic pressure of blood plasma)

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9
Q

What is the net pressure at arterial end of a capillary

A

Net pressure filtration (pushing fluid out)

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10
Q

What is the net pressure at the venous end of a capillary

A

Net pressure absorption (fluid in)

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11
Q

What is an oedema

A

An excessive accumulation of interstitial fluid

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12
Q

What can cause oedema in relation to starling’s forces

A
  • increased outward filtration
  • decreased absorption
  • leaky vessels
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13
Q

What could cause increased venous pressure

A
  • Obstruction of vessels

- generalized increase in venous pressure i.e. heart failure

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14
Q

What could cause a decrease in absorption pressure

A
  • Fall in plasma colloid osmotic pressure

- this could lead to protein loss and reduced protein synthesis

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15
Q

What could cause leaky vessels

A
  • Local inflammation

- Vasculitis, inflammation of the blood vessels (usually a secondary disease)

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16
Q

What are some signs of oedema

A
  • pitting
  • unexplained weight gain (early sign)
  • functional impairment
  • localised swelling, pale or red in colour
  • fluid within tissues/ around body system
17
Q

Where does fluid collect in right/left sided heart failure

A
Left= lungs 
Right= body cavities, plueral fluid in cat, ascites (abdomen) in dog
18
Q

What are the primary causes of heart disease

A
  • Degenerative valve disease
  • Heart muscle disease (cardiomyopathy)
  • Valve/endocardial infection
  • pericardial disease
  • rhythm abnormalities
19
Q

Describe degenerative valve disease

A
  • Develops later in life
  • cause unknown
  • may or may not develop heart failure
  • regurgitation into atrium during systole
20
Q

Describe heart muscle disease

A
  • Cardiomyopathy
  • Develops later in life
  • usually develops heart failure
  • in dogs, heart is usually dilated (heart gets bigger so cannot pump as effectivley)
21
Q

How can cardiomyopathy differ in cats

A

Heart rarely dilates, usually stiff/ restrictive

Or can be hypertrophic and heart wall becomes thicker

22
Q

What is myocardial hypertrophy

A

thickening of the heart muscle

- occurs with pressure load (hypertension or aortic/ pulmonic stenosis)

23
Q

What is heart failure

A

The inability of the heart to pump sufficient blood to meet the needs of the tissues for oxygen and nutrients

24
Q
How does:
1. Degenerative valve disease
2. Dilated cardiomyopathy
3. Restrictive/ hypertrophic cardiomyopathy 
contribute to heart failure
A
  1. Regurgitation means less forward flow in aorta
  2. Forward flow falls due to poor contractility
  3. Forward flow falls because heart cannot fill
25
Q

What mechanisms are activated to restore BP during heart failure

A
  • sympathetic nervous system activation
  • R.A.A.S
  • cardiac enlargement
26
Q

Describe the renin-angiotensin-aldosterone system

A

decreased blood pressure causes the juxtaglomerular cells of kidney to secrete renin

renin cleaves angiotensinogen, a plasma protein, to its active form angiotensin I

angiotensin I converted to angiotensin II by angiotensin convertin enzyme (ACE) in lungs

angiotensin II stimulates the adrenal cortex to secrete aldosterone

From here, systemic vasoconstriction, Increase blood volume, renal sodium and fluid retention

27
Q

Why are these compensatory mechanisms not so good in long term

A
  • a sick heart works faster
  • oxygen need goes up
  • contractility increases
  • vasoconstriction= increased afterload, therefore cardiac output will fall
  • Increased afterload= valves leak more
28
Q

What is detrimental about salt and water being retained

A
  • Volume returned to heart goes up
  • Volume of fluid in vessels goes up
  • pressure in capillaries goes up
  • oedema develops