Oedema and heart failure

Question 1

Why is the total cross section area high in capillary beds

Answer 1

Large surface area means functions can take place like gaseous exchange

Question 2

What is the function of a precapillary sphincter

Answer 2

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

Question 3

What important functions take place between capillaries and cells

Answer 3

• Removal of CO2 and waste products from cells

- Delivery of nutrients and oxygen to metabolising tissues

Question 4

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

Answer 4

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

Question 5

What does hydrostatic pressure exerted against the inner capillary wall cause

Answer 5

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

Question 6

What is colloid osmotic pressure

Answer 6

osmotic pressure exerted by plasma proteins

Promotes fluid re absorption into circulatory system

Question 7

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

Answer 7

It decreases

Question 8

What is Starling force

Answer 8

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

Question 9

What is the net pressure at arterial end of a capillary

Answer 9

Net pressure filtration (pushing fluid out)

Question 10

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

Answer 10

Net pressure absorption (fluid in)

Question 11

What is an oedema

Answer 11

An excessive accumulation of interstitial fluid

Question 12

What can cause oedema in relation to starling’s forces

Answer 12

• increased outward filtration
• decreased absorption
• leaky vessels

Question 13

What could cause increased venous pressure

Answer 13

• Obstruction of vessels

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

Question 14

What could cause a decrease in absorption pressure

Answer 14

• Fall in plasma colloid osmotic pressure

- this could lead to protein loss and reduced protein synthesis

Question 15

What could cause leaky vessels

Answer 15

• Local inflammation

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

Question 16

What are some signs of oedema

Answer 16

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

Question 17

Where does fluid collect in right/left sided heart failure

Answer 17

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

Question 18

What are the primary causes of heart disease

Answer 18

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

Question 19

Describe degenerative valve disease

Answer 19

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

Question 20

Describe heart muscle disease

Answer 20

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

Question 21

How can cardiomyopathy differ in cats

Answer 21

Heart rarely dilates, usually stiff/ restrictive

Or can be hypertrophic and heart wall becomes thicker

Question 22

What is myocardial hypertrophy

Answer 22

thickening of the heart muscle

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

Question 23

What is heart failure

Answer 23

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

Question 24

How does:
1. Degenerative valve disease
2. Dilated cardiomyopathy
3. Restrictive/ hypertrophic cardiomyopathy 
contribute to heart failure

Answer 24

1. Regurgitation means less forward flow in aorta
2. Forward flow falls due to poor contractility
3. Forward flow falls because heart cannot fill

Question 25

What mechanisms are activated to restore BP during heart failure

Answer 25

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

Question 26

Describe the renin-angiotensin-aldosterone system

Answer 26

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

Question 27

Why are these compensatory mechanisms not so good in long term

Answer 27

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

Question 28

What is detrimental about salt and water being retained

Answer 28

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