Comprehensive Study Notes on Blood Pressure Control and Its Physiology


What is Blood Pressure?

  • Blood pressure (BP) is defined as the ratio between the pressure in the arteries during two specific physiological states:

    • Systolic pressure: The pressure in the arteries when the heart is actively pumping (during contraction).

    • Diastolic pressure: The pressure in the arteries when the heart is at rest (during filling).

  • BP serves as a measure of how effectively the heart is functioning and reflects the pressure in the arteries overall.

Blood Vessels: Need for Balance

  • Maintaining blood pressure involves a balance between vessel constriction and dilation.

    • Vasoconstriction: The narrowing of blood vessels, leading to increased blood pressure.

    • Vasodilation: The widening of blood vessels, resulting in decreased blood pressure.

Anatomy of a Blood Vessel

  • Blood vessel structure: Includes two primary types:

    • Arteries: Carry oxygen-rich blood away from the heart.

    • Veins: Carry oxygen-poor blood back to the heart.

Understanding Receptors and Channels

  • What are Receptors?

    • Receptors are proteins found on cell surfaces that, when activated, trigger cellular responses. Antagonist( stops something from happening) vs. Agonist (causes something to happen).

  • Effects of Blocking a Receptor:

    • Blocking a receptor prevents the usual response from occurring, acting as an antagonist.

  • What is a Channel? - Proteins pass through a channel

    • Channels are proteins that facilitate the passage of substances in and out of cells. They allow specific molecules, such as ions or water, to cross the cellular membrane.

  • Effects of Blocking/ Causing A reaction in a channel:

    • Blocking a channel prevents the flow of the substance between cellular compartments, acting as an antagonist.

    • Causing a reaction in a channel is agonist.

Examples of Receptors and Channels

  • Receptor Types:

    • Beta 1 receptors (1 heart = Beta 1): Located in the heart, activated by epinephrine and norepinephrine, increase heart rate.

    • Beta 2 receptors ( 2 lungs= Beta 2) : Found in the lungs, also activated by epinephrine and norepinephrine, facilitate bronchodilation and vasodilation.

    • Alpha receptors: Associated with peripheral arteries (arms, legs), activated by norepinephrine and epinephrine, cause vasoconstriction.

    • Angiotensin II receptors: Activated by angiotensin II, play a significant role in blood pressure regulation.

    • Vasopressin receptors: Respond to vasopressin, impacting blood pressure through various mechanisms.

  • Channels:

    • Calcium channels: Facilitate the entry of calcium ions into cells which is crucial for various cellular functions (e.g., muscle contractions).

Pathophysiology of Blood Pressure Control

1. Renin-Angiotensin/Aldosterone System (RAAS)

  • A critical hormone system for blood pressure regulation.

    • Function: Helps maintain blood pressure and fluid balance.

2. Vasopressin System of BP Control

  • Regulates blood pressure through water retention and vasodilation or vasoconstriction.

3. Sympathetic Nervous System Activation

  • Low blood volume or blood pressure is detected by baroreceptors located in the aorta and carotid arteries.

    • Baroreceptors send signals to the brain, which then prompt the brain to signal adrenal medulla to produce:

    • Epinephrine (more stronger, greater effect in Beta 1) : Increases heart rate.

    • Norepinephrine: Causes vasoconstriction, increasing blood pressure.

    • Where is epinephrine and Norepinephrine made? Adrenal medulla

    • Both Epinephrine and Norepinephrine causes constriction

Adrenal Glands and Their Functions

  • Anatomy Overview:

    • Comprised of three sections: capsule, medulla, and cortex.

Actions of the Sympathetic Nervous System

  • Upon stimulation:

    • Beta-1 receptors increase heart rate.

    • Beta-2 receptors cause bronchodilation and vasodilation. Help you breathe easier. Gas exchange better due to adequate blood flow.

    • Alpha receptors are stimulated (agonist) to facilitate vasoconstriction and increase venous return.

Renin-Angiotensin-Aldosterone System (RAAS) Explained

  • Pathway:

    • Low blood volume blood vessels dilate due to blood loss or infection, sensed by kidneys leads to renin production.

    • Renin converts angiotensinogen to angiotensin I.

    • Angiotensin I is converted into angiotensin II by angiotensin-converting enzyme (ACE). You need ACE to convert angiotensin I to angiotensin II.

  • Activation of Angiotensin II:

    • Angiotensin II activates specific receptors on blood vessels, resulting in:

    • Vasoconstriction.

    • Increased blood pressure.

    • Increased venous return (increased blood flow) to the heart.

Aldosterone's Role in BP Control

  • Secretion: Aldosterone is released from the adrenal cortex in response to high levels of angiotensin II and norepinephrine.

    • Function: Tells kidney tubules to retain water and sodium, resulting in increased blood volume and, consequently, increased blood pressure.

Neurohormonal Activation and Vasopressin

  • Vasopressin (ADH):

    • Synthesized in the hypothalamus and stored in posterior pituitary gland.

    • Released in response to low circulatory volume and elevated levels of epinephrine, norepinephrine, and angiotensin II.

    • Function of Vasopressin:

    • Activates V1, V2, V3 receptors, leading to vasoconstriction and increased blood pressure.

    • Activates V2 receptors in the kidneys to increase water reabsorption, further raising blood pressure.

    • If the BP is high, then Vasopressin continue to operate, causing BP to continue to rise. An antagonist(blocker) is needed to stop BP rise.

Calcium Channels in the Cardiovascular System

  • Heart:

    • Calcium channels, when activated, cause the heart to beat faster and increase the strength of contractions.

    • Effects of Blocking Calcium Channels:

    • Slows heart rate and decreases contraction strength.

  • Blood Vessels:

    • Calcium channels, when stimulated, lead to contraction of vascular smooth muscle, raising blood pressure.

    • Effects of Blocking Calcium Channels:

    • Causes dilation of blood vessels, reducing blood pressure.

Reasoning and Clinical Implications

  • Key Questions to Consider:

    • What happens when beta 1 receptors are activated or blocked?

    • What happens when beta 2 receptors are activated or blocked?

    • What happens when alpha receptors are activated or blocked?

    • What happens when calcium channels are activated or blocked?

    • Pathophisiology and how to treat hypertension with this info?