4. Regulation of Blood pressure

Question 1

Blood pressure

Answer 1

Hydrostatic pressure in arterial system pushing blood through the capillary beds to organs / tissues.

results from: Co x TPR

• > Systolic pressure (maximum 90 - 240 mmHg)
• > Diastolyc pressure (minimum 60 - 140 mmHg)
• > Pulse pressure (SP - DP)
• > major cardiovascular variable regulated by body -> arterioles major resistance vessel
• > closely regulated as too low (brain / other tissues not receive adequate flow) and too high (extra work for heart + risk of vascular damage)

-> blood vessels don’t burst but tend to leak

Question 2

Haemodynamics

Answer 2

Study of how blood flows

• > variety of factors influence haemodynamics
  - Vessel length (L)
  - vessel radius (R)
  - viscosity of blood (V)

Flow (Q) = Pressure differece (delta p) / Resistance (R)

CO = (mean arterial p (beginning of tube) - central venule p (end of tube)) / TPR

Question 3

Factor affecting Blood pressure

Answer 3

BP = CO xTPR

Regulation of blood pressure is achieved by controlling the determinants of BP:

1.)

Question 4

Cardiac Output

Answer 4

Heart Rate:
-> determined by sino-atrial node, “pacemaker” -> regulated by nervous activity

• > Parasympathetic stimulation (low temperature)
• > Sympathetic nerve stimulation (adrenalin - high temperature)

Control:

• > Stroke volume
• > amount of blood ejected by ventricle during single beat
• > difference between end diastolyc + end systolic volumes (EDV (preload, contractility, afterload) - ESV(filling time, venous term))

Question 5

Systolic pressure

Answer 5

• > influenced by stroke volume which is th eamount of blood ejected from heart per heart beat
• > Increase in SV increases pressure, therefore increasing pulse pressure
• > left ventricular ejection velocity
• > loss of arterial compliance, e.g. increase stiffness, increases pressure ->

Question 6

Diastolic pressure

Answer 6

-> increase in HR and decrease in pulse pressure

Question 7

Total peripheral resistance

Answer 7

Primary resistance in arterioles -> important in regulating blood pressure

Affected by:

• > radius of arterioles
• > vasolidation increase radius - resistance falls
• > vasoconstriction reduces radius - resistance increases

Question 8

A - Vascular Tone

Answer 8

constriction or tone of blood vessels alter resistance + pressure (hypertension)

Modulated by the action of vasoconstrictors and vasodilators

Question 9

Vasodilators

Answer 9

-> endothelial cells determine dilation + constriction

• > Sheer stress : Ca 2+ ions released due to the stress -> enzyme Nitric oxide centase released (nitric oxide - very small enzyme and can go from one cell to another very quickly - doesn’t care about obstacles but not very stable hence it can’t affect much in the body, just the neighbouring cells)
• > nitric oxide activates + releases G cyclase -> G cyclase a signalling molecules, activating GTP -> cGMP, activating PHG -> cannot contract and hence relaxation occurs
• > G protein has a receptor but activates ATP -> cAMP -> RKA -> Relaxation
• > Vasodilators such as Bradykinins or ADP can have a bigger impact by releasing Ca 2+
• > EDF recognise hypertension (high BP) -> relaxation

=> Nitric oxide synthesised by nitric oxide syntahse (NOS) from L-arganine + oxygen

  - > eNOS in endothelium (constitutive)
  - > iNOS induced in monocytes in response to inflammation
  - > nNOS in neurons

=> Peptide hormones: reduce BP

Question 10

Vasoconstrictos

Answer 10

e.g. angiotensin II, thrombin -> all have own receptors (Endothelin, TX A2, PG H2 -> molecules released) -> picked up y smooth muscle cells -> Ca 2+ influx -> constriction

Superoxide another molecule -> present in free radicals -> 1.) gets rid of nitric oxide produced by endothalial cells

=> Endothelin 1 is 21 amino acid peptide released by EC
=> Prostaglanding A2 + H2 released from platelets + EC
=> Superoxide radicals react with NO

Question 11

Blood flow, pressure + Viscosity

Answer 11

• > blood flow related to pressure
• > blood viscosity -> dependent on amount of colloidal (non-soluble) material in blood, e.g. lipoproteins, RBC alter viscosity
• > volume fraction of colloidal material increases viscosity

=> colloidal partical such as lipoproteins are in suspension due to attractive + repulsive van der waals + electrostatic forces -> there is a balance - come together and don’t go further away from each other
=> alteration in electrolytes can neutralise these charges allowing the
=> Oxidation neutralises the charge of the surface of these particles -> e.g. smoking oxidises lipoproteins -> allows them to come together easier -> remember: Lana

Question 12

Aggragation of lipoproteins

Answer 12

• > separated -> 4 times the volume (vol. fraction)
• > aggregation: stuck together -> volume fraction 4 + all the dead volume between them -> increased volume fraction hugely

Question 13

Blood Volume

Answer 13

• > decrease in blood volume -> loss of blood, e.g. haemorrhage / chronic bleeding
  - > dehydration + fall in CO
• > Increase in Blood volume

Question 14

Neuronal regulation of BP

Answer 14

• > major cardiovascular control centre in in medulla of brain
• > VASOMETER CENTRE one of the subgroups within control centre -> consists of group of

Question 15

Baroreceptors

Answer 15

• > pressure sensors
• > located in walls of large arteries in neck and thoracic regions
• > rapid response system for dealing with change in BP
• > Stimulated by stretch of arterial walls caused by rise in BP
• >

Question 16

Chemoreceptors

Answer 16

• > Located in carotid + aortic bodies

- > respond to increased H+, increased CO2 + most strongly to hypoxia (low O2 tension)

Question 17

SUMMARY

Answer 17

• > regulation of BP depends on control of CO + TPR
  • control of CO depends on regulation of HR + SV
  • TPR determined by degree of arteriolar vasoconstriction