Cardiovascular Physiology

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Cardiovascular Physiology

• Arterial Blood Pressure

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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.
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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.

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Factors affecting ABP

• Sex M gt F due to hormones/ equal at
  menopause.
• Age Elderly gt 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 gt upper limbs.
• Race Orientals gt Westerns ? dietry
  factors, or weather.
• Sleep ? due to ? venous return.
• Pregnancy ? due to ? metabolism.

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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.
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Regulation of Arterial Blood Pressure
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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).

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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.

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Regulation of Arterial Blood Pressure

• A. Regulation of Cardiac Output

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Regulation of CO

• A fast acting mechanism.
• CO regulation depends on the regulation of
• a. Stroke volume,
• b. Heart rate

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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
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Regulation of Arterial Blood Pressure

• B. Regulation of Peripheral Resistance

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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.

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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
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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.

Haemorrhage
? BP
Hypoxia
Chemoreceptors
C.I.C
V.M.C
Sympathetic
Parasympathetic
Adrenal medulla
? HR
Vasoconstriction ? TPR
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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.

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4. Hormonal Agents

• NA ? vasoconstriction.
• A ? vasoconstriction (except in sk. ms.).
• Angiotensin II ? vasoconstriction.
• Vasopressin ? vasoconstriction.

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Regulation of Arterial Blood Pressure

• B. Regulation of Blood Volume

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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.

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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.

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• 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.

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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.

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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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