blood pressure

IX. Blood Pressure Maintenance

  • Cardiac Output 

    • Stroke Volume (mL/beat) x Heart Rate (beats/minute) 

    • Normal CO = 5.25 L/min

  • Peripheral Resistance 

    • Blood Viscosity, Blood Vessel Length, Blood Vessel Diameter  

  • Blood Volume: Kidneys 

    • More blood = high BP 

    • Less Blood = low BP

  • ΔP=CO x R 

  • ΔP= Change in Blood Pressure (MAP) 

  • CO= Cardiac Output (blood flow) 

  • R= Peripheral Resistance 

a. Variables Affecting BP

  1. Cardiac Output (CO): ↑ CO → ↑ BP

  2. Peripheral Resistance (PR): ↑ resistance → ↑ BP

  3. Blood Volume: ↑ volume → ↑ BP

b. Neural Control

  • Vasomotor center (medulla): Adjusts vessel diameter.

  • Sympathetic stimulation → vasoconstriction, ↑ BP.

c. Baroreceptors

  • Pressure sensors in carotid sinus/aortic arch.

  • Detect stretch → send signals to medulla.

  • If BP high: Inhibit sympathetic → vasodilation → ↓ BP.

  • If BP low: Stimulate sympathetic → vasoconstriction → ↑ BP.

d. Chemoreceptors

  • Sense O₂, CO₂, and pH (in carotid/aortic bodies).

  • Low O₂ or high CO₂ → ↑ cardiac output + vasoconstriction.

  • Located in the aortic arch (aortic bodies) and large arteries of the neck (carotid bodies)

  • Monitor for ↑CO2, ↓blood O2 levels, and ↑blood pH which results in ↑ cardiac output (cardioacceleratory centers) and vasoconstriction (vasomotor center)

e. Hormonal Regulation

Hormone

Source

Effect

Epinephrine & Norepinephrine

Adrenal medulla

Stress causes release of Epinephrine & Norepinephrine ↑ HR, ↑ CO, vasoconstriction

Angiotensin II

Kidneys (renin pathway)

↓ in BP or blood volume causes release of renin which results in angiotensin II release triggering vasoconstriction. Also stimulates aldosterone and ADH mechanism

Atrial Natriuretic Peptide (ANP)

Heart atria

The result is blood volume reduction leading to ↓BP

Antidiuretic Hormone (ADH)

Hypothalamus/posterior pituitary

Causes water retention → ↑ BP, increases blood volume by retaining sodium

f. Renal Mechanisms

  • Direct Mechanism: Kidneys remove water to lower BP or conserve water to raise BP.

  • Indirect Mechanism (Renin–Angiotensin–Aldosterone System):

    • Low BP → kidney releases renin → forms angiotensin II → vasoconstriction + aldosterone → ↑ blood volume → ↑ BP.