Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

sem 2 CVS > Properties of special circulations > Flashcards

Properties of special circulations Flashcards

1
Q

name some special circulations - why are they “special”?

A

cerebral, pulmonary, skeletal muscle, renal, GI

-they all have unique requirements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what 3 characteristics do special circulations have to consider?

A

1) Special requirements are met by circulation
2) Special structural or functional features of the circulation
3) Specific problems relating to that circulation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

where do the coronary arteries originate from?

A

the left side of the heart at the beginning (root) of the aorta, just after it exits the left ventricle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

cardiac veins

A

carry blood with a poor level of oxygen, from the myocardium to the right atrium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

most of the blood of the coronary veins runs through where?

A

the coronary sinus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

name some special requirements of coronary circulation

A
  • Needs a high basal supply of O2 – even at rest it’s using 20x more than skeletal muscle
  • Increase O2 supply in proportion to increased demand/cardiac work
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what are some special structural features of cardiac muscle:

A
  • High capillary density
  • Large surface area for O2 transfer
    o Together these reduce diffusion distance to myocytes – diffusion
  • Time is proportional to distance squared, so O2 transport is fast
  • Cardiac muscle contains high numbers of fibres and capillaries giving rise to shorter diffusion distances
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what are some special functional features of cardiac muscle:

A

During normal activity

  • High blood flow – 10x the flow per weight of rest of the body
  • Relatively sparse sympathetic innervation
  • High NO released leading to vasodilation
  • High O2 extraction (75%) – average in body is 25%

During increased demand

  • Coronary blood flow increases in proportion to demands
  • Production of vasodilators (adenosine, K+, acidosis) out-compete relatively low sympathetic vasoconstriction
  • Circulating adrenaline dilates coronary vessels due to abundance of β2-adrenoreceptors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

explain the Bohr Shift

A
  • Coronary sinus blood returning to the right atrium from myocardial tissue has a greater CO2 content
    o Due to high capillary density, surface area and small diffusion distance
  • The high CO2 and low pH has shifted the saturation curve to the right meaning that haemoglobin has less affinity for oxygen and more O2 is given up to the myocardial tissues
  • The myocardium is able to extract 75% of the oxygen as opposed to typically 25% in other tissues
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

explain how increased O2 requirement produces increased blood flow?

A
  • Extraction is near maximum during normal activity
  • Therefore, to provide more O2 during demand, we must increase blood flow
  • Myocardium metabolism generates metabolites to produce vasodilation which increases blood flow (metabolic hyperaemia)
  • E.g. adenosine is produced by ATP metabolism and is released form cardiac myocytes
  • There is also an increase in pCO2, H+, K+ levels
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what type of arteries are human coronary arteries?

A

Functional End-Arteries

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what does functional end mean?

A

not a lot of cross links between the arteries, so if it gets blocked anything downstream of it will get starved of blood

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what produces major problems in the coronary arteries?

A

decreased perfusion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what types of obstruction is the heart susceptible to?

A

sudden and slow obstruction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what occurs in sudden obstruction?

A

o Acute thrombosis, produces myocardial infarction, when blood supply to a small part of the heart is blocked

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what occurs in slow obstruction?

A 
o	Atheroma (sub-endothelium lipid plaques, on the inside of blood vessels)
o	Chronic narrowing of lumen, produces angina
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

does systole or diastole obstruct coronary blood flow?

A

systole

18
Q

how will thrombosis cause ischaemic heart disease?

A

(thrombosis in left coronary artery)

  • total occlusion of the left anterior descending coronary artery
  • leads to obstruction of blood flow to anterior (front) left ventricle
o	Myocardial infarction:
	Ischemic tissue
	Acidosis
	Pain (stimulation of C-fibres)
	Impaired contractility
	Sympathetic activation 
	Arrhythmias
	Cell death (necrosis)
19
Q

how can you “fix” partial occlusion of left coronary arteries?
(surgery)

A
  • inject an x-ray opaque dye into the vessels around the heart, track it with a live x-ray
  • see there is a partially occluded LCA
  • go into artery and exert a stent to keep it open
20
Q

normal heart: arterioles normally and during exercise

A
  • Resistances in series – add together, artery goes into lots of smaller arterioles
  • In exercise, metabolic vasodilation of arterioles reduces total resistance
    o Increased blood flow to meet increased O2 demands, perfuse the heart.
    • Total R (resistance) reduced
21
Q

heart with angina: arterioles normally and during exercise

A
  • Stenosis in large coronary artery
    o Increases resistance
  • Metabolic hyperaemia occurs at rest, so blood flow meets needs of the heart- no symptoms shown
  • During exercise, arterioles further dilate to reduce resistance
    o However, total resistance is still too high due to dominance of stenosis
    o O2 demand cannot be met, so angina develops
22
Q

when you have angina when is there a problem?

A

during increased activity

23
Q

what is metabolic hyperaemia?

A

increase in BF to tissues

24
Q

name some mechanical factors reducing coronary flow:

A

1) Shortening diastole
E.g. high heart rate

2) Increased ventricular end-diastolic pressure
E.g. heart failure (aortic stenosis, stiffening of ventricle meaning it doesn’t fully relax)

3) Reduced diastolic arterial pressure
E.g. hypotension, aortic regurgitation

25
Q

importance of diastole:

A

window for coronary flow

aortic pressure > ventricular pressure

26
Q

Special Properties of Cutaneous Circulation

A
  • Defence against the environment
  • Lewis triple response to trauma increased blood flow, due to histamine release, firm stroking of the skin, initial red line, flare around the line and then a wheal
  • Temperature regulation
27
Q

importance of temperature regulation:

A

o Blood flow delivers heat from body core
o Radiation (proportional to skin temperature)
o Conduction to skin – convection from skin (skin temperature)
o Sweating (latent heat of evaporation)
o Skin is an organ
o Skin temperature can rage from 0 degrees to 40 degrees (briefly) without damage
e.g. Poikilothermic (internal temperature varies considerably) rather than homeothermic

28
Q

what does skin temperature depends on:

A

o Skin blood flow

o Ambient temperature

29
Q

Special Structural Features of Cutaneous Circulation:

A

Arterio-Venous Anastomoses (AVAs)- adaptation of the skin (the joining of tubes)

  • Direct connections of arterioles and venules which expose blood to regions of high surface area
  • Convection, conduction, radiation, evaporation

Sympathetic vasoconstrictor fibres
- Release NA acting on α1 receptors

Sudomotor vasodilator fibres
- Acetylcholine acting on endothelium to produce NO

30
Q

what are the fibres driven by?

A

temperature regulation nerves in the hypothalamus

31
Q

Special Functional Features of Cutaneous Circulation:

A
  • Responsive to ambient and core temperatures
  • Help heat loss
    o Increased ambient temperature causes vaso- and venodilation
  • Help to conserve heat
    o Decreased ambient temperature causes vaso- and venoconstriction
  • Severe cold causes “paradoxical cold vasodilation”- acute increase in peripheral blood flow observed during cold exposures
  • Core temperature receptors in the hypothalamus control sympathetic activity to skin and hence skin blood flow
32
Q

what do temp receptors in the hypothalamus control?

A

sympathetic activity to skin and hence skin blood flow

33
Q

explain the importance of cold-induced vasoconstriction and how it works:

A
  • Conserves heat
  • Sympathetic nerves react to local cold by releasing noradrenaline which binds to α2 receptors on vascular smooth muscle in the skin
    o α2 receptors bind to noradrenaline at lower temperatures than α1 receptors
34
Q

explain the importance of paradoxical cold vasodilation, what its caused by and how it works:

A
  • Protects against skin damage
  • Caused by paralysis of sympathetic transmission
  • Long-term exposure leads to oscillations of contraction/relaxation
  • When you first get into freezing cold water, you first get vasoconstriction, blood flow shuts down, you want to conserve heat. But, if that continues you’ll get damage to the skin as skin doesn’t get oxygen. When the skin reaches a certain low temperature, the sympathetic nerves stop working which causes vasodilation to occur again
35
Q

how does exercise affect cutaneous perfusion and core temperature?

A

increase in both

36
Q

what does an increase in cutaneous perfusion and core temperature lead to?

A

warmth receptors in anterior hypothalamus are stimulated, causing:

• Sweating
o Increased sympathetic activity to sweat glands mediated by Ach

• Vasodilation
o Increased sympathetic sudomotor activity so Ach acts on endothelium to produce NO. NO dilates arterioles in extremities

37
Q

name some other functional specialisations of cutaneous circulation:

A
  • Baroreflex/RAAS/ADH-Stimulated-Vasoconstriction of Skin Blood Vessels
  • Emotional communication, e.g. blushing (sympathetic sudomotor nerves)

Response to skin injury, the lewis triple response

38
Q

explain the role of: Baroreflex/RAAS/ADH-Stimulated Vasoconstriction of Skin Blood Vessels

A
  • Blood directed to more important organs/tissues during loss of BP following haemorrhage, sepsis, acute cardiac failure
  • Mediated by sympathetic vasoconstrictor fibres + adrenaline + vasopressin + angiotensin II
    o Responsible for the pale cold skin of a patient in shock
  • During a haemorrhage, warming up the body too quickly may reduce cutaneous vasoconstriction and be potentially dangerous
    o Blood flows to the skin and not to the vital organs
39
Q

what is the Lewis Triple Response of Skin To Trauma

A
  • Local redness
    o Site of trauma
  • Local swelling
    o Inflammatory oedema (wheal)
  • Spreading flare
    o Vasodilation spreading out from the site of trauma
  • The C-fibre axon reflex mediates the flare to trauma
  • Increased delivery of immune cells & antibodies to the site of damage to deal with invading pathogens
40
Q

Special Problems:

A
  • Prolonged obstruction of flow by compression

- Postural hypotension/oedema due to gravity

41
Q

explain the problem of prolonged obstruction of flow by compression

A
  • Severe tissue necrosis
  • Bed sores
    o Heels, buttocks, weight bearing areas

Avoided by:
• Shifting position/turning which causes reactive hyperaemia (on removal of compression
• High skin tolerance to ischemia

42
Q

explain the problem of postural hypotension/oedema due to gravity

A
  • Often standing for long periods in hot weather will decrease central venous pressure (hypotension)
    o As well as increased capillary permeability (oedema)
  • You feel faint, rings of fingers can be tighter

sem 2 CVS (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions