Course Content
Cardiovascular System
We'll explore the heart, blood vessels, and blood circulation. You'll learn about the heart’s structure, functions, and how blood travels through the body, delivering nutrients and removing wastes.
0/4
Heart Structure and Function
07:57
Blood Vessels and Circulation
13:50
Blood Pressure Regulation
11:09
End of Topic Quiz
00:20:00
Nervous System
We'll study the brain, spinal cord, and nerves that coordinate body functions. Understand how neurons communicate, and how our senses process information.
0/4
Central and Peripheral Nervous Systems
03:02
Anatomy of the Brain and Spinal Cord
12:15
Autonomic Nervous System
11:54
End of Topic Quiz
00:20:00
Endocrine System
Learn about major glands like the thyroid and pancreas, and see how hormones influence metabolism, growth, and mood.
0/3
Major Glands and Hormone Regulation
17:00
Hypothalamus-Pituitary Axis
05:00
End of Topic Quiz
00:20:00
Respiratory System
Examine lung structure, airway anatomy, gas exchange processes, and respiratory regulation.
0/3
Structure of the Lungs and Airways
07:30
Gas Exchange and Respiratory Regulation
10:15
End of Topic Quiz
00:20:00
Gastrointestinal System
Discover the anatomy of the GI tract, and explore the mechanisms of digestion and nutrient absorption.
0/3
Anatomy of the Gastro-Intestinal Tract
05:20
Digestion and Absorption
25:00
End of Topic Quiz
00:20:00
Renal System
Study the structure and function of the kidneys, focusing on fluid and electrolyte balance in the body.
0/3
Kidney Structure and Function
08:00
Fluid and Electrolyte Balance
08:05
End of Topic Quiz
00:20:00
Musculoskeletal System
Explore bone structure and function, and learn about the biochemical processes of muscle contraction and movement.
0/3
Bone Structure and Function
12:00
Muscle Contraction and Movement
19:00
End of Topic Quiz
00:20:00
Physiology of Major Body Systems
About Lesson

Introduction

Blood pressure (BP) is the force exerted by blood against the walls of blood vessels, and it provides insight into the heart and vessels. Maintaining BP within a normal range is essential because high or low BP can cause pathological conditions.

  • Blood pressure is controlled by complex physiological mechanisms that allow for short-term and long-term BP maintenance.

How is Blood Pressure Measured?

  • Systolic blood pressure (SBP): The highest pressure in the arteries when the heart contracts.

  • Diastolic blood pressure (DBP): The lowest pressure in the arteries when the heart relaxes between beats.

  • Mean arterial blood pressure (MABP): Calculated using SBP, DBP, and pulse pressure (SBP – DBP).

    MABP = DBP + (Pulse Pressure/3)

Mechanisms of Blood Pressure Regulation

Rapid Control of Blood Pressure: Baroreceptor Reflex

The baroreceptor reflex is the primary mechanism for rapid BP regulation. It relies on specialized mechanoreceptors called baroreceptors, which detect changes in blood vessel stretch. Information from the baroreceptors is relayed to the central nervous system, which adjusts the heart rate and vascular tone to maintain BP stability.

  • High-pressure baroreceptors: Located in the carotid sinus and aortic arch. These baroreceptors are activated by blood vessel distension during increased blood pressure, leading to a decrease in heart rate and vasodilation. Conversely, decreased blood pressure reduces baroreceptor firing, increasing heart rate and promoting vasoconstriction.

  • Low-pressure baroreceptors: Located in the venous system, atria, and pulmonary arteries. These baroreceptors are more sensitive to changes in blood volume than pressure, and they regulate BP by influencing hormone secretion. For instance, decreased blood volume activates low-pressure baroreceptors, stimulating the release of hormones that promote fluid retention and increase blood volume.

Intermediate and Long-Term Control of Blood Pressure

Renin-Angiotensin-Aldosterone System (RAAS)

The renin-angiotensin-aldosterone system (RAAS) is a hormonal system that plays a crucial role in BP regulation over a longer duration than the baroreceptor reflex. RAAS activation leads to the production of angiotensin II, a potent vasoconstrictor that increases BP. Angiotensin II also stimulates the release of aldosterone, a hormone that promotes sodium and water reabsorption in the kidneys, further increasing blood volume and BP. The steps of the RAAS pathway are:

  1. Renin Release: Renin is released by the kidneys in response to:

    • Decreased blood pressure
    • Sympathetic nervous system activation
    • Reduced sodium levels in the kidneys

  2. Angiotensinogen Conversion: Renin converts angiotensinogen (produced by the liver) into angiotensin I.

  3. Angiotensin II Formation: Angiotensin-converting enzyme (ACE) converts angiotensin I into angiotensin II.

  4. Angiotensin II Effects: Angiotensin II causes:

    • Vasoconstriction
    • Aldosterone release from the adrenal glands

  5. Aldosterone Effects: Aldosterone increases sodium and water reabsorption in the kidneys, leading to increased blood volume.

Antidiuretic Hormone (ADH)

Antidiuretic hormone (ADH), also known as vasopressin, regulates BP by conserving water. When released from the pituitary gland, ADH acts on the kidneys to increase water reabsorption, raising blood volume and consequently BP. Conversely, when ADH is suppressed, the kidneys excrete more water, reducing blood volume and lowering BP.

Atrial Natriuretic Peptide (ANP)

Atrial natriuretic peptide (ANP) is a hormone released from the atria of the heart in response to increased atrial pressure, often caused by increased blood volume. ANP counteracts the RAAS system, leading to a decrease in BP through:

  • Vasodilation
  • Inhibition of Sodium Reabsorption: ANP inhibits sodium reabsorption in the kidneys, increasing sodium excretion and water loss, reducing blood volume and BP.
  • Inhibition of Renin and Aldosterone Release

Other Blood Pressure Regulators

Low-Pressure Baroreceptors

Located in the venous system, atria, and pulmonary arteries, low-pressure baroreceptors respond to changes in plasma volume and regulate BP through various mechanisms, including the release of hormones.

Summary of Key Blood Pressure Regulators

Compound Site of Production Effects on Vasculature Effects on Extracellular Fluid Levels
Angiotensin II Primarily the lungs Vasoconstriction Increases
Aldosterone Adrenal glands – Increases
ADH Pituitary gland Vasoconstriction Increases
ANP Atria of the heart Vasodilation Decreases

Key Points

  • Blood Pressure Regulation is complex and involves several mechanisms working together to maintain homeostasis.
  • Rapid BP Adjustments are mediated by the baroreceptor reflex.
  • Intermediate and Long-Term BP Regulation is primarily controlled by vasoactive compounds.

References

  1. Thrift, A.G., Howard, G., Howard, V.J., et al. “Blood Pressure and Stroke: An Overview of Published Reviews.” Biomedicines, vol. 9, no. 5, 2021, p. 469. https://www.mdpi.com/2227-9059/9/5/469

  2. Lodish, H., Berk, A., Zipursky, S.L., et al. “Overview of Blood Pressure Regulation.” Molecular Cell Biology. 4th edition, National Center for Biotechnology Information, 2024. https://www.ncbi.nlm.nih.gov/books/NBK538509/

  3. Guyton, A.C., Hall, J.E. “Textbook of Medical Physiology.” 12th edition, National Center for Biotechnology Information, 2024.  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3230096/

  4. “Regulation of Blood Pressure.” Geeky Medics.  https://geekymedics.com/regulation-of-blood-pressure/

     

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