Lecture 12 – Properties of special circulation

Question 1

Special circulations (4)

Answer 1

E.g. cerebral, pulmonary,skeletal muscle, renal gastrointestinal.

Have 3 characteristics to consider:

1) special requirements met by the circulation
2) special structural or functional features of the circulation
3) specific problems relating to that circulation

Question 2

Coronary circulation (6)

Answer 2

Sheet

Question 3

Coronary circulation - problems (5)

Answer 3

Sheet

Question 4

Coronary circulation - Oxygen to myocardium (7)

Answer 4

Sheet

Question 5

Cutaneous circulation

Answer 5

Skin ulcer due to impaired micro vascular flow.

Question 6

Cutaneous circulation - special properties (3)

Answer 6

Defence against the environment
Lewis triple response to trauma (increase BF)
Temperature regulation

Question 7

Cutaneous circulation - special structural features (3,1,2)

Answer 7

Aterio-venous anastomoses (AVAs)
Direct connection of arterioles and venules which expose blood to regions of high SA
Convection/Conduction/Radiation/Evaporation
BF constricted in arterioles and stop BF through the skin and bypass it through the anastomoses.

Sympathetic VC fibres
Release NA, act on a1 receptors

Sudomotor VD fibres
Release ACh acts in endothelium to produce NO.
Driven by T regulation nerves in hypothalamus

Question 8

Cutaneous circulation - special functional features (5)

Answer 8

Responsive to ambient/core temperatures
Help heat loss IN ambient T causes VD
Help to conserve heat DE ambient T causes VC
Core T receptors in hypothalamus control sympathetic activity to skin and heave skin blood flow,
Severe cold causes paradoxical cold VD.

Question 9

Cutaneous perfusion and core temperature (4)

Answer 9

IN both e.g. exercise
IN core T stimulate warmth receptors in anterior hypothalamus causing during exercise.
IN cutaneous perfusion to IN heat loss via closing of the anastomoses and VD of arterioles
Sweating - increased S activity to sweat glands mediated by ACh produces NO which dilates arterioles in extremities.

Question 10

Other functional specialisations (4,2,3)

Answer 10

Baroreflex/RAAS/ADH stimulated VC of skin blood vessels
If there is low BP or bleeding then blood can be dir ted to more important organs/tissues during loss of BP following haemorrhage/sepsis/acute cardiac failure.
Mediated by sympathetic VC fibres and hormones (A/A2/V)= pale cold skin of patient in shock.
During a haemorrhage warming up the body too quickly may reduce cutaneous VC and be dangerous so BF to skin is NOT vital.

Emotional communication
Blushing, sympathetic sudomotor nerves connected to emotional centred resulting in an emotional response.

Response to skin injury
Lewis triple response, nociceptive afferent fibres to spinal cord and up to the brain which identifies it as pain. Collateral axons (which branch of) release substance P which will granulate mast cells, releasing histamine causing VD and recruits more cell to area and des, with more pathogens.
Local redness and inflammatory oedema and VD.

Question 11

Lewis triple response to skin trauma (3)

Answer 11

Lewis triple response, nociceptive afferent fibres (C fibres) to spinal cord and up to the brain (dorsal root ganglion) which identifies it as pain. Collateral axons (which branch of) release substance P which will granulate mast cells, releasing histamine causing VD and recruits more cell to area and des, with more pathogens.
Local redness and inflammatory oedema and VD.
Increased delivery of immune cells and antibodies to site of damage to deal with invading pathogens.

Question 12

What happens when BF is restricted to the skin? (1,1,3)

Answer 12

Result in pressure in certain areas so there is reduced circulation to that area - prolonged obstruction flow by compression.

Results in severe tissue necrosis which can cause:
- bed sores e.g. heels/buttocks/weight bearing areas

Avoided by:

• shifting positions = cause reactive metabolic hyperaemia on removal of compression
• reactive hyperaemia
• high skin tolerance to ischaemia - only during prolonged periods not sleep

Question 13

Postural hypotension/oedema due to gravity (2)

Answer 13

Standing for long periods in hot weather will DE CVP (hypotension) and increase capillary permeability (oedema) in the skin of hands/feet.
Feel faint.

Question 14

Pressure sore (2)

Answer 14

Damage to tissues due to prolonged obstruction of flow due to compression resulting in tissue necrosis.
O2/nutrients so close but diffusion is too slow.