1. Biology 2672a: Comparative Animal Physiology Circulation II: Regulation of Circulation

2. What happens in the ‘systemic circuit’?

3. The ‘Systemic circuit’  Blood is delivering oxygen and nutrients and picking up waste products (and delivering them to the kidneys)  Organs & muscles  Linear flow rate is reduced Cross-sectional area increases

4. Major Arteries  Muscular, elastic thick walls (smooth muscle and elastin)  Pressure of 10- 20 kPa  Elastic Dampen pressure differences Store some elastic energy  e.g. Aorta, carotid artery, femoral artery  16/10 kPa

5. Terminal arteries  12/8 kPa

6. Arteriole: 8/3.5 kPa Capillaries: c. 2.5-3 kPa Venules: c. 1.3-2 kPa Fig. 24.11 Right ventricle then increases pressure to c. 1.9 kPa for passage through lungs

7. Precapillary sphincter Can close off flow to capillary bed Arteriolar-venular anasomosis Allows blood to bypass the capillary bed Fig. 23.11

8. Veins  Low pressure  Have a system of one-way valves  Much thinner-walled than arteries

9. Pressure drop across vascular system Fig. 24.12b

10. What about birds?  Broadly similar Heart pumps more and faster to meet greater oxygen demands Higher pressures

11. What about birds?  Jugular Anastamosis

12. Gravity also affects pressure ΔP = ρgΔh Fluid density (mercury>seawater>water>oil) Acceleration due to gravity Height difference across the system See Fig 24.7

13. The problem of being a giraffe  The brain of a standing giraffe is 2m above its heart  To maintain a pressure of c. 13 kPa in brain arteries, needs an aortic pressure of c. 29 kPa (!)

14.  Tight skin on legs  Muscular arteries  High interstitial fluid pressure, efficient return of venous blood

15. Giraffes have a drinking problem  Very high pressure blood into brain  Blood can pool in brain ΔP = ρgΔh

16. Solving the giraffe drinking problem  Vasodilation in lower body reduces blood pressure  Elastic arteries near brain absorb some increased pressure  One-way valves in jugular vein prevent backflow of blood into head

17. Brain Heart Kidneys – Require a regulated blood pressure to function Need blood flow to be maintained

18. Animals with a closed circulatory system are able to regulate  Where blood goes  How much of it goes there  Need to respond to central requirements e.g. fight-or-flight  Also need to respond to local conditions O 2 demand, localised damage

19. How to regulate blood flow? Change Energy input Q = ΔPπr 4 8Lη8Lη Change tube diameter

20. Energy input: Cardiac Output stroke volume = heart rate × Cardiac Output Can be modulated by both endocrine and nervous systems Modulated by nervous activity (via norepinephrine) and circulating epinephrine (=adrenaline) Equation 24.1

21. Myogenic autoregulation (stretch response) Increased blood flow Increased pressure on arteriole wall Smooth muscle stretched Smooth muscle contracts Increased resistance Decreased blood flow

22. Neural control of vasoconstriction  Sympathetic nervous system can be activated to induce vasoconstriction Thermoregulation Fight or flight  Mediated by Norepinephrine released by sympathetic neurons

23. Neural Regulation of vasomotor tone  sympathetic nerves  noradrenaline : smooth muscle   receptors : constriction  : dilation  Relative receptor population density

24. Smooth Muscle Cell NO Produced Viagra inhibits cGMP breakdown

25. Endocrine control of vasomotor tone  Epinephrine (Adrenaline) from Adrenal medulla induces vasodilation Fight or flight  Vasopressin (ADH) & Angiotensin II – vasoconstriction  Activate Adrenergic receptors on smooth muscle Not necessarily mediated by nerves

26. Paracrine control of vasomotor tone  NO Produced by endothelial cells to maintain vasomotor tone in response to hormonal cues Same mechanism as for parasympathetic activation Nitroglycerine  Also responses to local factors indicating hypoxia and damage

27.  Hormonal Adrenaline (Epinephrine)  receptors  Local Control low O 2, pH, ATP high CO 2, K + dilates vessels locally override neural & hormonal control Fig. 23.11 Local regulation

28. Reading for Tuesday  Intro to Gas Exchange + breathing in water  pp 533-560