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D- Cardiovascular Physiology

D- Cardiovascular Physiology. Arterial Blood Pressure. Arterial Blood Pressure (BP). = The lateral pressure force generated by the pumping action of the heart on the wall of aorta & arterial blood vessels per unit area. OR = Pressure inside big arteries (aorta & big vessels).

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D- Cardiovascular Physiology

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  1. D- Cardiovascular Physiology Arterial Blood Pressure

  2. Arterial Blood Pressure (BP) =The lateral pressure force generated by the pumping action of the heart on the wall of aorta & arterial blood vessels per unit area. OR =Pressure inside big arteries (aorta & big vessels). ■Measured in (mmHg), & sometimes in (cmH2O), where 1 mmHg = 1.36 cmH2O. ■Of 2 components: • systolic … (= max press reached) = 110-130 mmHg. • diastolic … (= min press reached) = 70-90 mmHg. In normal adult ≈ 120/80 mmHg.

  3. Arterial Blood Pressure(continued) In normal adult ≈ 120/80 mmHg. ■Diastolic pressure is more important, because diastolic period is longer than the systolic period in the cardiac cycle. ■Pulse pressure= Systolic BP – Diastolic BP. ■Mean arterial pressure= Diastolic BP + 1/3 Pulse press.

  4. Factors affecting ABP: ■Sex… M > F …due to hormones/ equal at menopause. ■Age… Elderly > children …due to atherosclerosis. ■Emotions…↑ due to secretion of adrenaline & noradrenaline. ■Exercise…↑ due to ↑ venous return. ■Hormones …↑ (e.g. Adrenaline, noradrenaline, thyroid H). ■Gravity… ↑ Lower limbs > upper limbs. ■Race … Orientals > Westerns … ? dietry factors, or weather. ■Sleep … ↓ due to ↓ venous return. ■Pregnancy …↑ due to ↑ metabolism.

  5. Factors determining ABP: Blood Pressure = Cardiac Output X Peripheral Resistance • ■BP depends on: • 1. Cardiac output ⇒ CO = SV X HR. • 2. Peripheral resistance. • 3. Blood volume.

  6. Regulation of Arterial Blood Pressure

  7. Regulation of ABP: ■Maintaining B.P. is important to ensure a steady blood flow (perfusion) to tissues. ■B.P. is regulated neurally through centers in medulla oblongata: 1. Vasomotor Center (V.M.C.), or (pressor area): ⇒Sympathetic fibers. 2. Cardiac Inhibitory Center (C.I.C.), or (depressor area): ⇒Parasympathetic fibers (vagus).

  8. Regulation of ABP(continued) cardiac control centers in medulla oblongata 1. Cardiacaccelerator center (V.M.C) 2. Cardiacinhibitory center (C.I.C) Sympathetic n. fibers Parasympathetic n. fibers • Regulatory mechanisms depend on: • a.Fast acting reflexes: • Concerned by controlling CO (SV, HR), & PR. • b.Long-term mechanism: • Concerned mainly by regulating the blood volume.

  9. Regulation of Arterial Blood Pressure A. Regulation of Cardiac Output

  10. Regulation of CO: ■A fast acting mechanism. ■CO regulation depends on the regulation of: a. Stroke volume, & b. Heart rate

  11. Regulation of the CO: Mean arterial pressure Cardiac output = Stroke volume X Heart rate End Contraction diastolic strength volume (EDV) Stretch Sympathetic n Parasympathetic n Frank - Starling

  12. Regulation of Arterial Blood Pressure B. Regulation of Peripheral Resistance

  13. Regulation of Peripheral Resistance (PR): ■A fast acting mechanism. ■Controlled by 3 mechanisms: 1. Intrinsic. 2. Extrinsic. 3. Paracrine. ■Extrinsic mechanism is controlled through several reflex mechanisms, most important: 1. Baroreceptors reflex. 2. Chemoreceptors reflex.

  14. 1. Baroreceptors reflex: ■ Baroreceptors are receptors found in carotid sinus & aortic arch. ■ Are stimulated by changes in BP. ↑ BP + Baroreceptors = V.M.C ++ C.I.C = Sympathetic + Parasympathetic Slowing of SA node (↓ HR) & ↓ CO Vasodilatation & ↓ TPR

  15. 2. Chemoreceptors reflex: ■Chemoreceptors are receptors found in carotid & aortic bodies. ■Are stimulated by chemical changes in blood mainly hypoxia (↓ O2), hypercapnia (↑ CO2), & pH changes. ↓ BP Haemorrhage Hypoxia + Chemoreceptors = C.I.C ++ V.M.C + Sympathetic = Parasympathetic + Adrenal medulla Vasoconstriction & ↑ TPR ↑ HR

  16. 3. Other Vasomotor Reflexes: 1.Atrial stretch receptor reflex: ↑ Venous Return ⇒ ++ atrial stretch receptors ⇒ reflex vasodilatation & ↓ BP. 2.Thermoreceptors: (in skin/or hypothalamus) • Exposure to heat ⇒ vasodilatation. • Exposure to cold ⇒ vasoconstriction. 3. Pulmonary receptors: Lung inflation ⇒ vasoconstriction.

  17. 4. Hormonal Agents: ■NA ⇒ vasoconstriction. ■A ⇒ vasoconstriction (except in sk. ms.). ■ Angiotensin II ⇒ vasoconstriction. ■ Vasopressin ⇒ vasoconstriction.

  18. Regulation of Arterial Blood Pressure B. Regulation of Blood Volume

  19. Regulation of Blood Volume: ■A long-term regulatory mechanism. ■Mainly renal: 1. Renin-Angiotensin System. 2. Anti-diuretic hormone (ADH), or vasopressin. 3. Low-pressure volume receptors.

  20. 1. Renin-Angiotensin System: ■Most important mechanism for Na+ retention in order to maintain the blood volume. ■Any drop of renal blood flow &/or ↓ Na+, will stimulate volume receptors found in juxtaglomerular apparatus of the kidneys to secrete Renin which will act on the Angiotensin System leading to production of aldosterone.

  21. Renin-Angiotensin System: ↓ renal blood flow &/or ↓ Na+ ++ Juxtaglomerular apparatus of kidneys (considered volume receptors) Renin Angiotensinogen Angiotensin I Converting enzymes (Lungs) Angiotensin II (powerful vasoconstrictor) Angiotensin III (powerful vasoconstrictor) Adrenal cortex Corticosterone Aldosterone • N.B. Aldosterone is the main regulator of Na+ retention.

  22. 2. Anti-diuretic hormone (ADH), or vasopressin: ■Hypovolemia & dehydration will stimulate the osmoreceptors in the hypothalamus, which will lead to release of ADH from posterior pituitary gland. ■ADH will cause water reabsorption at kidney tubules.

  23. 3. Low-pressure volume receptors: ■Atrial natriuritic peptide (ANP) hormone, is secreted from the wall of right atrium to regulate Na+ excretion in order to maintain blood volume.

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