1. Blood pressure

2. Factors maintaing blood pressure
Central factors
Cardiac out put
Heart Rate
Peripheral factors
Peripheral resistance
Blood volume venous return
Elasticity of blood vessels
Diameter of blood vessel
Viscosity of blood

3. Cardiac out put
To Systolic blood pressure depend upon CO&stroke volume –directly proportional
Dystolic BP is directly Peripheral resistance when PR decreased dystolic pressure is decreased
BP is directly proportion to blood volume
BP is directly pro to venous return
BP is inversly proport to elasticity of vessels& diameter of vessels

4. Control of blood pressure
Outline
Short term control (baroreceptors)
Location
Types of baroreceptor
Baroreceptor reflex
Other stretch receptors
Long-term control
Renin/ angiotensin/ aldosterone system
Vasopressin
Atrial natiuretic peptide
Response to blood loss (shock)

5. Regulation of blood pressure
Short term
Baroreceptors
Long term
Kidney via renin angiotensin system

6. . Baro-receptors Nerve endings in all large thoracic and neck arteries
2 major populations: Carotid sinus and Arch of the aorta
Activation on stretch
Carotid: Hering’s nerve to Glossopharyngeal nerve to tractus solitarius in brainstem
Aortic: Vagus nerve to tractus solitarius
If baro-receptors sense increased BP Secondary signals from tractus solitarius: Inhibition of vasoconstrictor centre and excitation of vagal parasympathetic centre

7. Baro-receptors
Important in maintaining postural blood pressure
(When standing from lying down  strong sympathetic discharge)
Long term changes in blood pressure result in resetting of baroreflexes (i.e. not influential)

8. Location of baroreceptors
Baroreceptors sense stretch and rate of stretch by generating action potentials (voltage spikes)
Located in highly distensible regions of the circulation to maximise sensitivity

9. Overview of short-term control mechanisms

10. . Anatomy of the autonomic nervous control of blood pressure:
Sympathetic vasomotor nerve fibres leave cord through (T+L) spinal nerves
Sympathetic chain 
1)Sympathetic nerves (viscera)
2)Spinal nerves (vasculature)
Vagus nerve (PNS) .

11. . Vasomotor centre: Vasoconstrictor area
origin of excitatory pre-ganglionic vasoconstrictor neurones
Vasodilator area
internal inhibition of vasoconstrictor area
Sensory area
input from vagus and glossopharyngeal nerves modulate vasoconstrictor/dilator area activity

12. . To raise the arterial pressure: SNS release NA from nerve terminals
NA acts on the α adrenergic receptors of the VSMC
All arterioles constricted
Veins strongly constricted
Heart directly stimulated

13. ….It’s all about intracellular calcium
VSMC
Stimulates formation of IP3
IP3 causes release of calcium from sarcoplasmic reticulum in the heart and increasing inotropy
Cardiovascular Physiology Concepts, Richard E Klabunde. 13

14. Beta-adrenoceptors Heart: Increased contractility
Blood vessel: reduced contractility
Usually sympathetic stimulation of VSMC leads to vasoconstriction. The alpha vasoconstrictor effects are far dominant over the beta vasodilator effects, BUT if given an alpha blocker then the beta function will dominate
G-proteins are linked to an enzyme, adenylyl cyclase, that dephosphorylates ATP to form cyclic AMP (cAMP). Gs-protein (stimulatory G-protein) activation (e.g., via β-adrenoceptors) increases cAMP. This activates PK-A (cAMP stimulated protein kinase) and causes increased influx of Ca++ by phosphorylation and activation of L-type calcium channels, and enhanced release of Ca++ by the sarcoplasmic reticulum in the heart. These and other intracellular events increase inotropy, chronotropy, dromotropy and lusitropy.
Cardiovascular Physiology Concepts, Richard E Klabunde. 14

15. Long term control of blood pressure
Involves control of blood volume/sodium balance by the kidneys
Hormonal control
Renin-angiotensin-aldosterone system
Antidiuretic hormone (vasopressin)
Atrial natiuretic peptide
Pressure natriuresis

16. Macula densa is the collective name for a specialised group of epithelial cells in the initial portion of the distal tubules
Juxtaglomerular cells (granular cells) produce Renin
Mesangial cell: provide anchor, may be involved in response to hypotension as contain actin + myosin and may act under sympathetic stimulation 16

18. Afferent arteriole Resistance
Glomerular Hydrostatic pressure
GFR
Arterial Pressure
Renin
Macula Densa NaCL
Na Cl resorption
Flow rate in loop of Henle
Angiotensin II
Efferent Arteriole Resistance
Glomerular Filtration Pressure
Afferent arteriole Resistance

19. Vasopressin

20. Atrial natiuretic peptide
Increases salt excretion via kidneys
By reducing water reabsorption in the collecting ducts
relaxes renal arterioles
inhibits sodium reabsorption in the distal tubule
Released in response to stimulation of atrial receptors

21. Atrial volume reflex
Reduced secretion of anti-diuretic hormone from hypothalamus
Atrial stretch due to pressure
Reflex dilation of renal afferent arteriole
Reduction in water resorbtion from renal tubule
Fluid loss by kidneys
Increased glomerular capillary pressure
Increased filtration of fluid into renal tubule 21

22. Summary of long term BP control
Cardiac output and BP depend on renal control of extra- cellular fluid volume via:
Pressure natriuresis, (increased renal filtration)
Changes in:
Vasopressin
Aldosterone
Atrial natiuretic peptide