Physiology of Blood Pressure Regulation
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Questions and Answers

What does the renin-angiotensin-aldosterone system (RAAS) primarily regulate?

  • Blood pressure and volume (correct)
  • Oxygen levels in the blood
  • Respiratory rate
  • Metabolic rate

    • Which factor does NOT contribute to the calculation of blood pressure?

  • Systemic vascular resistance
  • Body temperature (correct)
  • Cardiac output
  • Arteriolar cross-sectional area

    • What role do baroreceptors play in blood pressure regulation?

  • Secrete hormones that increase heart rate
  • Increase blood viscosity to raise blood pressure
  • Sense blood pressure and initiate feedback mechanisms (correct)
  • Dilate blood vessels to lower blood pressure

    • How does the vagus nerve influence blood pressure?

    <p>It promotes relaxation of the heart muscle</p> Signup and view all the answers

    According to Poiseuille's law, how does a change in the radius of a blood vessel affect resistance?

    <p>Resistance increases by the fourth power of the decrease in radius</p> Signup and view all the answers

    What is the primary function of the sympathetic nervous system in blood pressure control?

    <p>To constrict blood vessels and raise blood pressure</p> Signup and view all the answers

    Which of the following statements about arterial baroreceptors is incorrect?

    <p>They send information directly to the heart for adjustments.</p> Signup and view all the answers

    What happens to blood pressure when blood viscosity increases?

    <p>Blood pressure increases due to more resistance.</p> Signup and view all the answers

    What primary function does the control centre serve in regulating blood pressure?

    <p>It compares actual variable values with normal reference values.</p> Signup and view all the answers

    Which systems are responsible for regulating blood pressure?

    <p>Fast-acting neural system and slower acting hormonal system.</p> Signup and view all the answers

    What is the primary role of the neural system in blood pressure regulation?

    <p>To provide moment-to-moment regulation.</p> Signup and view all the answers

    What effect does the neural control system have during a change from lying down to standing up?

    <p>It increases blood flow to the legs and heart rate.</p> Signup and view all the answers

    What is orthostatic hypotension?

    <p>A temporary drop in blood pressure upon standing.</p> Signup and view all the answers

    What role do baroreceptors play in neural control of blood pressure?

    <p>They provide feedback for moment-to-moment regulation.</p> Signup and view all the answers

    Which of the following is a key characteristic of the neural control of blood pressure?

    <p>It is a fast homeostatic process controlled by negative feedback.</p> Signup and view all the answers

    What happens in the body without the regulation provided by the neural control system?

    <p>It can lead to dizziness or fainting due to insufficient blood flow.</p> Signup and view all the answers

    What is the primary location of baroreceptors involved in blood pressure neural homeostasis?

    <p>In the carotid sinus</p> Signup and view all the answers

    Which cranial nerve provides sensory innervation to the baroreceptors in the carotid sinus?

    <p>Cranial nerve IX</p> Signup and view all the answers

    During systole, the frequency of action potentials in the carotid sinus nerve tends to:

    <p>Increase</p> Signup and view all the answers

    Where do the sensory signals regarding blood pressure from carotid sinus baroreceptors primarily transmit to?

    <p>Nucleus of solitary tract</p> Signup and view all the answers

    How does the aortic arch baroreceptors receive sensory innervation?

    <p>Through the vagus nerve</p> Signup and view all the answers

    Which of the following accurately describes the physiological response of baroreceptors during a decrease in blood pressure?

    <p>Sensory firing decreases</p> Signup and view all the answers

    What is the role of the nucleus of solitary tract in blood pressure regulation?

    <p>Processing sensory information</p> Signup and view all the answers

    Which of the following best describes the action of baroreceptors in line with blood pressure changes?

    <p>They increase firing rate with lower pressure and decrease with higher pressure</p> Signup and view all the answers

    What is the expected effect on cardiac output (CO) in a patient experiencing hypovolemic shock due to extensive blood loss?

    <p>Cardiac output will decrease.</p> Signup and view all the answers

    In the context of the described patient with hypotension, what role does renin play?

    <p>It is released to increase blood pressure.</p> Signup and view all the answers

    What happens to the levels of sodium in the distal convoluted tubules (DTNa) during hypovolemic shock?

    <p>DTNa levels will decrease due to reduced renal perfusion.</p> Signup and view all the answers

    What is the most likely change in systemic vascular resistance (SVR) in a patient with severe blood loss and low blood pressure?

    <p>SVR will increase due to compensatory mechanisms.</p> Signup and view all the answers

    In a patient experiencing marked pallor and unconsciousness from blood loss, what is the physiological reason for pallor?

    <p>Decreased blood flow to the skin.</p> Signup and view all the answers

    What signal does decreased blood pressure provide to the kidneys?

    <p>To increase renin production.</p> Signup and view all the answers

    What is the net filtration pressure in the capillaries of the patient described?

    <p>Below 10 mm Hg.</p> Signup and view all the answers

    What compensatory mechanism is indicated by the body's response to low blood pressure in the capillary beds?

    <p>Initiation of reabsorption processes.</p> Signup and view all the answers

    Which compensatory mechanism is likely insufficient in a patient experiencing orthostatic hypotension?

    <p>Enhanced parasympathetic outflow leading to reduced heart rate.</p> Signup and view all the answers

    What is the primary function of the vagus nerve in regards to the parasympathetic nervous system?

    <p>Facilitating digestive processes by increasing peristalsis.</p> Signup and view all the answers

    What occurs during orthostatic hypotension when a person moves from lying to standing?

    <p>Significant drop in blood pressure due to reduced blood volume.</p> Signup and view all the answers

    How does enhanced sympathetic outflow typically affect arterioles?

    <p>It induces constriction of arterioles, increasing peripheral resistance.</p> Signup and view all the answers

    What role do carotid sinus baroreceptors play during changes in blood pressure?

    <p>They detect changes in blood pressure and signal for heart rate reduction.</p> Signup and view all the answers

    What is the effect of enhanced sympathetic outflow leading to arteriolar dilation?

    <p>It decreases blood pressure significantly.</p> Signup and view all the answers

    Which structure is primarily responsible for parasympathetic output to the heart?

    <p>The nucleus ambiguus.</p> Signup and view all the answers

    Which physiological response is not directly influenced by the dorsolateral region of the spinal cord?

    <p>Parasympathetic vagal output.</p> Signup and view all the answers

    What is the primary neurotransmitter released by postganglionic sympathetic neurons in the lateral reticulospinal tract?

    <p>Noradrenaline</p> Signup and view all the answers

    What role does the lateral reticulospinal tract play in the autonomic nervous system?

    <p>Modulating blood pressure through smooth muscle contraction</p> Signup and view all the answers

    Which component of the renin-angiotensin-aldosterone system is NOT a direct hormone?

    <p>Angiotensin converting enzyme (ACE)</p> Signup and view all the answers

    During hypotension, which hormone is primarily involved in maintaining blood pressure?

    <p>Antidiuretic hormone (ADH)</p> Signup and view all the answers

    What percentage of blood plasma is filtered through the glomerulus of the nephron?

    <p>20%</p> Signup and view all the answers

    Which receptor type does noradrenaline act on to induce contraction of arterial smooth muscle?

    <p>Alpha 1 adrenoreceptors</p> Signup and view all the answers

    What is the main physiological outcome when the blood pressure decreases?

    <p>Increased renin secretion</p> Signup and view all the answers

    Which part of the kidney is primarily involved in filtering blood plasma?

    <p>Glomerulus</p> Signup and view all the answers

    Study Notes

    Neural & Hormonal Control of Blood Pressure

    • The lecture is about the neural and hormonal control of blood pressure.
    • The presenter is Dr. Tatiana Christides, MD, PhD from Queen Mary University of London.
    • The focus is on the physiological mechanisms.
    • Blood pressure regulation is primarily automatic and unconscious.
    • Homeostasis is based on sensors, processing, and effectors.

    Intended Learning Outcomes

    • Understand the renin-angiotensin-aldosterone system (RAAS) and its role in blood pressure and volume regulation.
    • Learn about drugs used to control hypertension that work on the RAAS.
    • Describe physiological sensors and effectors in arterial blood pressure control.
    • Know the position and innervation of aortic and carotid sinus baroreceptors, their central nervous system connections, and the brainstem's role.
    • Understand the role of the vagus and sympathetic nervous systems in blood pressure control.

    Control Blood Pressure

    • Blood pressure control is primarily an unconscious, automatic process.
    • Key elements of homeostasis include sensors, information processing, and effectors.

    What is Blood Pressure?

    • Blood pressure is force per unit area exerted by blood on arterial walls.
    • It's calculated as cardiac output multiplied by systemic vascular resistance.
    • Factors that influence blood pressure include stroke volume (preload, afterload), heart rate, cardiac contractility, blood vessel length, arteriolar smooth muscle tone, arteriolar cross-sectional area, and blood viscosity.

    General Principles of Blood Pressure Homeostasis

    • Baroreceptor blood pressure (BP) system is a negative feedback system.
    • A receptor (sensor) detects a variable—for example, blood pressure.
    • A control centre compares it to a normal reference value (set point).
    • If a difference exists, effectors adjust the variable until it returns to the set point.

    Two Systems Regulate Blood Pressure

    • Fast-acting neural system
    • Slower-acting hormonal system

    Neural Control Blood Pressure

    • The lecture details neural control of blood pressure.
    • It includes the role of the medullary cardiovascular center, carotid baroreceptors, carotid sinus nerve, aortic depressor nerve, and aortic baroreceptors.
    • It also discusses the role of the cardiac parasympathetic (vagal) and sympathetic systems and sympathetic vasomotor activity in relation to heart rate, stroke volume, and peripheral vessels.

    Neural control blood pressure - fast

    • The neural system regulates blood pressure moment to moment.
    • Lying down to standing automatically regulates blood flow and heart rate.
    • Without this regulation, blood flow to the brain would be reduced leading to dizziness.

    Neural Control of Blood Pressure Sensors: Baroceptor system

    • Neural control of blood pressure is a fast homeostatic process controlled by negative feedback mechanisms.
    • Baroreceptors, primarily located in the carotid sinus and aortic arch sense changes in blood pressure.

    Innervation of Carotid Sinus and Aortic Arch Baroreceptors

    • The walls of carotid sinus and aortic arch contain sensory endings of the carotid sinus nerve and vagus nerve respectively.
    • These receptors, which are sensitive to stretch, constantly monitor changes in blood pressure, which in turn leads to changes in the frequency of action potentials in the nerve fibres.

    Where do the messages about blood pressure go?

    • The glossopharyngeal nerve carries messages from the carotid sinus baroreceptors.
    • The vagus nerve (cranial nerve X) relays signals from aortic arch baroreceptors.
    • The nucleus of the solitary tract processes the messages in the brainstem.

    Brainstem – Nucleus of solitary tract

    • The nucleus of the solitary tract is a crucial portion in the brainstem, processing information received from the sensory afferents (e.g., baroreceptors).
    • This structure assesses whether blood pressure values diverge from the established reference values.

    Neural control blood pressure – actions of brainstem centres

    • This section describes the functions of various brainstem centres in controlling cardiovascular function.
    • The role of the Nucleus Tractus Solitarius (NTS) in processing sensory input from various sensors, as well as the actions of sympathetic and parasympathetic systems is detailed.

    Neural blood pressure control after the brainstem

    • The postganglionic neurons deliver signals to the heart, smooth muscles in blood vessels from the medulla oblongata.

    How are sympathetic nervous system (SNS) signals relayed?

    • The lateral reticulospinal tract relays SNS signals.
    • It originates from the reticular formation.
    • Presynaptic SNS neurons innervate the arterioles to control smooth muscle, which is crucial in regulating blood pressure.
    • The postganglionic SNS neurons release noradrenaline to affect the arterioles.

    Putting it all together - neural control blood pressure when blood pressure DECREASES

    • The sympathetic nervous system increases heart rate and contractility to increase cardiac output when blood pressure decreases.
    • The sympathetic neurons cause vasoconstriction of arterioles to increase resistance to flow.

    Putting it all together - neural control blood pressure when blood pressure INCREASES

    • The parasympathetic system via the vagus nerve decreases heart rate, thereby decreasing cardiac output.
    • The autonomic centers also inhibit the sympathetic neurons, resulting in vasodilation of arterioles and decreasing resistance to flow, when blood pressure increases.

    Hormonal control Blood pressure

    • Kidneys (Renin-angiotensin-aldosterone system),
    • Autonomic Nervous System,
    • and CNS (Anti-Diuretic Hormone (ADH)) are the principal components.

    Hormones and blood pressure

    • The adrenal cortex regulates blood pressure (aldosterone).
    • Sympathetic activation regulates BP.
    • Na+ & H2O retention is important.
    • Blood vessel length and blood viscosity affect BP.

    Hormones and blood pressure – Renin-Angiotensin-Aldosterone System – in hypotension

    • The body reduces blood flow when blood pressure falls.
    • This section describes how RAAS system responds to reductions in blood pressure during hypotension.

    Functional unit of the kidney: the nephron

    • Nephrons—the functional units of the kidneys—are responsible for filtering blood.
    • The glomerulus, Bowman's capsule, proximal convoluted tubule, Loop of Henle, and distal convoluted tubule are key parts.

    How is glomerular filtration rate (GFR) maintained constant as BP fluctuates?

    • Processes involved include myogenic mechanism and tubuloglomerular feedback.

    How is glomerular filtration rate (GFR) maintained constant as BP fluctuates? – myogenic mechanism

    • Afferent arterioles respond intrinsically to changes in blood pressure.
    • Blood pressure increases, arterioles constrict to prevent excessive filtration.
    • Blood pressure decreases, arterioles dilate, maintaining GFR.

    How is glomerular filtration rate (GFR) maintained constant as BP fluctuates? – juxtaglomerular cells acting as baroreceptors

    • Juxtaglomerular cells detect low renal perfusion and secrete renin.
    • Renin increases angiotensin 2 leading to increased GFR and BP systemically.

    How is glomerular filtration rate (GFR) maintained constant as BP fluctuates? Tubuloglomerular Feedback

    • To understand this mechanism, need to understand the juxtaglomerular apparatus.
    • Low sodium concentration in the distal tubule triggers renin release.
    • This, in turn, leads to increased GFR and systemic blood pressure.

    Juxtaglomerular apparatus

    • Juxta-glomerular cells and macula densa are involved.
    • This structure controls GFR in response to sodium levels in the distal convoluted tubule.

    How is glomerular filtration rate (GFR) maintained constant as BP fluctuates? Tubuloglomerular Feedback

    • In the presence of low sodium in the distal convoluted tubule, the macula densa signals to the juxtaglomerular cells to release renin.
    • This leads to increased GFR and systemic blood pressure.

    SNS mechanism: juxtaglomerular cells

    • Juxtaglomerular cells are directly innervated by sympathetic nerve fibers.
    • Increased SNS activity leads to increased renin release.
    • Reduced SNS activity leads to decreased renin release.

    Importance of SNS-Renin in hypertension

    • The studies mentioned relate to the efficacy and safety of renal denervation in patients with uncontrolled hypertension.
    • These studies suggest beneficial use of renal denervation for patients with hypertension.

    Summary: Factors that affect renin release

    • Factors affecting renin release include intrarenal baroreceptors, sympathetic nerves, and alterations in sodium chloride delivery to macula densa cells.

    ANGIOTENSIN 2 – Vascular effects

    • Angiotensin II acts on G-protein-coupled receptor AT1r, activating phospholipase C and increasing cytosolic Ca2+, triggering smooth muscle constriction of systemic arterioles.
    • This raises peripheral vascular resistance (PVR or SVR), thus increasing blood pressure.
    • Angiotensin II reduces hydrostatic pressure in capillaries by constricting arterioles, causing water to flow back into the blood stream.

    ANGIOTENSIN 2 – Renal effects

    • Angiotensin II directly acts on the nephron’s proximal tubule cells to increase sodium reabsorption via increased Na+/H+ antiporter activity.
    • Subsequently, Na+/K+ ATPase and Na/HCO3 symporter activity are involved.

    ANGIOTENSIN 2 – INDIRECT renal effects

    • Aldosterone: Increases sodium reabsorption in distal nephron tubules by stimulating synthesis and insertion of ENAC into principal cells apical membrane.
    • This action increases sodium-potassium ATPase activity on the basolateral membrane and promotes increased excretion of potassium into the tubules.

    ANGIOTENSIN 2 – Neural effects

    • The hypothalamus and posterior pituitary are involved in ADH release.
    • In turn, ADH acts on the DCT and collecting ducts (CD). The insertion of aquaporin 2 channels in the apical membrane increases permeability to water in the distal convoluted tubules and collecting ducts, enhancing reabsorption of water.
    • Angiotensin II stimulates thirst, resulting in increased fluid intake, enhancing blood volume which in turn enhances blood pressure. The sympathetic system is also stimulated.

    The importance of sodium

    • Angiotensin II, aldosterone, and SNS increase renal sodium reabsorption when blood pressure is low.
    • Blood volume depends partly on sodium. Sodium dynamics partly determine blood pressure.

    Main ion contributing to plasma osmotic pressure?

    • Sodium is the main ion contributing to plasma osmotic pressure.
    • Low blood sodium (hyponatremia) decreases osmotic pressure and leads to fluid shifting from blood to tissues.
    • Symptoms like fatigue, confusion, muscle weakness and cramps can occur.

    Can the RAAS system malfunction?

    • RAAS malfunction can occur due to renal artery narrowing (atheroma), reducing blood flow.
    • Less sodium is filtered, leading to abnormally reduced sodium concentration in the distal tubule.
    • Juxtaglomerular cells increase renin release causing a chronically raised blood pressure and circulating blood volume.

    Pharmacological treatment elevated blood pressure (Hypertension) – targeting the RAAS System

    • ACE inhibitors block the angiotensin-converting enzyme, preventing Angiotensin II formation.
    • Angiotensin receptor antagonists block angiotensin receptors.
    • Thiazide derivatives block sodium-chloride symporters in the distal convoluted tubule.
    • Aldosterone antagonists block aldosterone.
    • Loop diuretics are another class of diuretic drugs used to lower blood pressure that can remove excess fluid.

    Bradykinin and Angioedema

    • ACE inhibitors increase bradykinin levels, potentially causing dry cough or angioedema.
    • This may contribute to stopping ACE inhibitors.
    • This is a side effect of some medications affecting the blood pressure cascade.
    • People of African descent may have a higher risk of ACE inhibitor induced angioedema.

    Overview Hormones and blood pressure – Renin-Angiotensin-Aldosterone System

    • The renin-angiotensin-aldosterone system controls blood pressure by regulating systemic vascular resistance and blood volume.
    • Renin release is increased due to reduced renal perfusion, low sodium in the distal tubular fluid, or sympathetic nervous system (SNS) activity.
    • The system increases reabsorption of sodium and water, eventually raising blood pressure.

    Practice questions

    • Practical questions covering the topics of the presentations.

    Answer to practice Question One

    • Patient arrives with low blood pressure,
    • Blood colloid osmotic pressure normal.

    Answer to practice Question Two

    • 26-year-old male patient.
    • Presented to A&E after suffering extensive blood loss; unconscious and pale.

    Answer to practice Question Three

    • 26-year-old female patient.
    • Presents with flu-like symptoms accompanied by vomiting.

    Answer to practice Question Four

    • Patient with hypertension.
    • Prescribed a calcium channel blocker, but their blood pressure remains elevated.

    Answer to practice Question Five

    • Patient with a car accident, impaired swallowing and sensation in the back of the tongue.
    • The MRI reveals damage to the glossopharyngeal nerve.

    Answer to practice Question Six

    • 45-year-old male with a previous spinal injury
    • Presented to the clinic.
    • The dorsolateral region of the spinal cord is damaged.

    Answer to practice Question Seven

    • 72-year-old female with a history of hypertension and recently increased diuretic dose.
    • Dizziness upon standing.
    • Diagnosed with orthostatic hypotension.

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    Description

    Test your knowledge on the mechanisms involved in blood pressure regulation, including the renin-angiotensin-aldosterone system, baroreceptors, and the effects of the sympathetic nervous system. This quiz covers essential concepts that are crucial for understanding cardiovascular physiology.

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