Blood Pressure Regulation

Slide 1 · Blood pressure regulation

Mechanisms linking the heart, vascular tone and renal sodium balance

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Relate systemic arterial pressure to cardiac output and resistance.

Explain neural, humoral, local, and renal control of pressure.

Trace renin–angiotensin–aldosterone and natriuretic responses.

Apply normal physiology to selected forms of secondary hypertension.

Slide 3 · Why arterial pressure requires regulation

Adequate pressure sustains organ perfusion despite unequal tissue demands.

Insufficient pressure can cause dysfunction or tissue death.

Excess pressure contributes to cumulative end-organ injury.

Pressure too low

Reduced organ perfusion

Ischemic dysfunction

Pressure too high

Vascular load and injury

Target-organ damage

Slide 4 · Two determinants of systemic pressure

Cardiac output determines the volume delivered per unit time.

Peripheral resistance opposes flow through the systemic circulation.

Either determinant can change measured arterial pressure.

Cardiac output

×

Peripheral resistance

Arterial pressure

Functional relationship

Slide 5 · Integrated control: Multiple linked effectors

Cardiac factors, blood volume, and arteriolar tone act together.

Renal, neural, hormonal, and local signals continually interact.

A single measured pressure may reflect different physiologic mechanisms.

Heart rate

Stroke volume

Cardiac output

Neural effectors

Hormonal mediators

Arteriolar resistance

Systemic blood pressure

Slide 6 · Cardiac output has two components

Heart rate is the number of ventricular beats per unit time.

Stroke volume is the blood ejected with each beat.

A change in either component may alter total cardiac output.

Heart rate

×

Stroke volume

Cardiac output

Functional relationship

Slide 7 · Heart rate: Autonomic control

Adrenergic neural signaling affects cardiac pacing.

An increase in rate can increase cardiac output if other determinants are maintained.

Rate changes need interpretation alongside stroke volume.

Adrenergic input

Heart rate

Cardiac output

Slide 8 · Ventricular filling drives stroke volume

Ventricular filling pressure is a major determinant of stroke volume.

Filling depends strongly on the circulating blood volume.

Renal sodium balance therefore influences cardiac output indirectly.

Blood volume

Filling pressure

Stroke volume

Cardiac output

Slide 9 · How sodium balance affects ventricular filling

Retained sodium favors retention of body water.

An increase in blood volume can increase filling pressure.

Enhanced filling can increase stroke volume and cardiac output.

Sodium retention

Blood volume ↑

Ventricular filling ↑

Stroke volume ↑

Slide 10 · Contractility is a second stroke-volume determinant

Myocardial contractility modulates stroke volume beyond filling effects.

Adrenergic signaling influences contractile force.

Blood pressure can therefore vary even when blood volume is unchanged.

Filling pressure

Myocardial contractility

Stroke volume

Convergent regulatory inputs

Slide 11 · Adrenergic systems act on heart and vessels

α- and β-adrenergic pathways regulate cardiac performance.

Adrenergic signaling also alters vascular tone.

The same systemic stimulus may affect cardiac output and resistance.

Adrenergic signaling

Heart rate

Contractility

Vascular tone

Slide 12 · Cardiac output: Distinguish two mechanisms

Volume-mediated change: Sodium balance alters filling and stroke volume.

Neural-mediated change: Adrenergic input influences rate and contraction.

Both routes converge on cardiac output but begin at different effectors.

Volume route

Renal Na⁺ retention

↑ filling → ↑ stroke volume

Adrenergic route

Autonomic signal

Heart rate / contractility

Slide 13 · Arterioles are the major resistance vessels

Peripheral resistance is regulated predominantly at the arteriolar level.

Changes in arteriolar smooth-muscle tone change vascular caliber.

Resistance can change independently of blood volume.

Contracted wall

Narrower lumen

Relaxed wall

Wider lumen

Slide 14 · Vascular smooth-muscle contraction changes resistance

Contraction narrows the arteriolar lumen and raises resistance.

Relaxation enlarges the lumen and reduces resistance.

The relevant final effector is the arteriolar smooth-muscle cell.

Contracted wall

Narrower lumen

Relaxed wall

Wider lumen

Slide 15 · Neural and humoral input to arteriolar tone

Neural signals provide coordinated changes in vascular resistance.

Circulating hormones provide additional vasomotor control.

Local tissue signals adjust tone to regional requirements.

Neural inputs

Hormonal effectors

Local metabolism

Arteriolar tone

Convergent regulatory inputs

Slide 16 · Principal vasoconstrictor mediators

Angiotensin II promotes vascular smooth-muscle contraction.

Catecholamines participate in vasomotor regulation.

Endothelin contributes to the constrictor side of vascular tone.

Angiotensin II

Catecholamines

Endothelin

Vasoconstriction → resistance ↑

Slide 17 · Angiotensin II: A direct pressor action

Angiotensin II acts on vascular smooth muscle to increase tone.

The resulting rise in peripheral resistance increases blood pressure.

This is distinct from its sodium-retaining actions in the kidney.

Angiotensin II

Smooth-muscle contraction

Arteriolar resistance ↑

Blood pressure ↑

Slide 18 · Principal vasodilator mediators

Kinins and prostaglandins can promote vascular relaxation.

Nitric oxide (NO) is an important vasodilator.

Their effects counterbalance vasoconstrictor influences.

Kinins

Prostaglandins

Nitric oxide (NO)

Vasodilation → resistance ↓

Slide 19 · Nitric oxide and vascular homeostasis

Nitric oxide contributes to the relaxing side of vasomotor balance.

Renal NO is one of the factors that offset pressor mechanisms.

Vascular tone reflects the net effect—not one mediator in isolation.

Angiotensin II

Catecholamines

Endothelin

Nitric oxide

Prostaglandins

Kinins

↔

Net vascular tone

Slide 20 · Vascular tone is a balance of opposing signals

Constrictors and dilators act simultaneously on resistance vessels.

Relative predominance of either side changes peripheral resistance.

Systemic pressure follows the integrated net vascular response.

Constriction

↑ resistance

Relaxation

↓ resistance

↔

Blood pressure response

Slide 21 · Autoregulation protects against hyperperfusion

Resistance vessels respond to changes in delivered blood flow.

Increased flow can induce local vasoconstriction.

The local response restrains excess tissue perfusion.

Regional flow ↑

Local arteriolar response

Vasoconstriction

Hyperperfusion limited

Slide 22 · Local pH and hypoxia fine-tune perfusion

Changes in tissue pH contribute to local regulation of vascular tone.

Hypoxia signals altered local metabolic conditions.

These mechanisms help match perfusion to regional demand.

Local tissue demands

Tissue pH

Oxygen availability

Regional vascular tone

Slide 23 · Local autoregulation is not the whole systemic response

Local vascular feedback protects individual tissue beds.

Neural and hormonal responses also alter systemic resistance.

Systemic pressure represents the combined behavior of many beds.

LOCAL

Flow / metabolism

Regional resistance adjustment

SYSTEMIC

Neural / humoral inputs

Overall vascular resistance

Slide 24 · Kidney: Long-term control of circulating volume

The kidneys regulate net sodium excretion and reabsorption.

Sodium balance governs the blood-volume component of pressure.

Renal signals also modify arteriolar vascular tone.

Renal Na⁺ handling

Blood volume

Cardiac output

Renin release

Angiotensin II

Vascular resistance

Blood pressure

Slide 25 · Filtered sodium: A large daily physiologic load

Roughly 170 L of plasma filtration per day.

The filtered salt load is approximately 23 moles daily.

Maintaining balance requires reabsorption of nearly all filtered sodium.

170 L

Plasma filtered / day

23 mol

Salt in filtered plasma / day

~99.5%

Reabsorbed at cited intake

Slide 26 · Most filtered sodium is reclaimed routinely

About 98% of filtered sodium is reabsorbed by constitutively active transporters.

This bulk transport precedes the regulated fine-adjustment step.

A small residual fraction can still determine net excretion.

Filtered sodium handling

~98% constitutive reabsorption

Small remaining fraction

Subject to regulated uptake

Slide 27 · Small distal adjustments determine net sodium balance

Most filtered sodium is already reabsorbed before final control.

Regulation of the remaining fraction can alter net daily retention.

A small fractional change matters because the filtered load is enormous.

Very large filtered load

Bulk Na⁺ reclamation

Regulated residual Na⁺

Net sodium balance

Slide 28 · ENaC is a regulated sodium-reabsorptive pathway

The epithelial sodium channel (ENaC) participates in distal sodium reabsorption.

Its activity is tightly connected to the renin–angiotensin–aldosterone system.

Distal channel regulation couples hormonal signals to volume homeostasis.

RAAS signaling

ENaC-mediated Na⁺ uptake

Water retention

Blood volume

Slide 29 · Sodium balance connects the kidney to the heart

Greater net sodium retention promotes water retention.

Expanded circulating volume influences filling pressure.

Stroke volume and cardiac output then transmit this change to pressure.

Renal Na⁺ balance

Blood volume

Ventricular filling

Cardiac output

Slide 30 · Three organ systems generate circulating regulators

Kidney releases renin in response to hemodynamic or tubular signals.

Adrenal cortex releases aldosterone downstream of angiotensin II.

Myocardium releases natriuretic peptides during volume-related signaling.

Kidney → renin

Adrenal → aldosterone

Heart → ANP / BNP

Regulation of vascular tone and Na⁺ balance

Slide 31 · The juxtaglomerular apparatus senses pressure

Renin is made by juxtaglomerular cells near afferent glomerular arterioles.

These specialized cells detect changes in renal perfusion pressure.

Reduced afferent pressure is a potent stimulus for renin secretion.

Afferent arteriole

Juxtaglomerular cells

Renin release

Slide 32 · Three signals promote renin secretion

Reduced afferent arteriolar blood pressure.

Elevated circulating catecholamine stimulation.

Low sodium delivery detected in the distal nephron.

Low renal perfusion

Catecholamine input

Low distal Na⁺ signal

Renin release

Convergent regulatory inputs

Slide 33 · Reduced renal perfusion activates renin

The kidney can experience low perfusion despite systemic pressure elsewhere.

Low afferent arteriolar pressure triggers juxtaglomerular renin secretion.

RAAS activation then promotes both vasoconstriction and volume retention.

Afferent pressure ↓

Renin ↑

Angiotensin II ↑

Pressure-support responses

Slide 34 · Catecholamines provide a renin-release signal

Elevated catecholaminergic input stimulates renin release.

Neural effects therefore intersect with endocrine regulation.

The downstream renin pathway amplifies control beyond direct vascular tone.

Catecholamines

Juxtaglomerular renin

Angiotensin II

Integrated BP response

Slide 35 · Low distal sodium delivery stimulates renin

Reduced filtration can change sodium reaching the distal nephron.

Increased proximal reabsorption also lowers distal delivery.

The low distal sodium signal promotes renin secretion.

Renal filtration ↓

Distal Na⁺ delivery ↓

Renin secretion ↑

RAAS activation

Slide 36 · Renin initiates the angiotensin cascade

Renin cleaves circulating angiotensinogen to angiotensin I.

Angiotensin-converting enzyme converts angiotensin I to angiotensin II.

Vascular endothelium is a major source of ACE.

Angiotensinogen

Renin → Angiotensin I

ACE → Angiotensin II

Slide 37 · Angiotensin II coordinates three pressor responses

It directly contracts vascular smooth muscle.

It stimulates adrenal secretion of aldosterone.

It also increases renal tubular sodium reabsorption.

Angiotensin II

Vasoconstriction

Aldosterone release

Tubular Na⁺ uptake

Slide 38 · The vascular branch raises resistance

Angiotensin II induces vascular contraction.

Arteriolar narrowing increases peripheral resistance.

Pressure rises through the resistance arm of the BP equation.

Angiotensin II

VSMC contraction

Resistance ↑

BP ↑

Slide 39 · The adrenal branch releases aldosterone

Angiotensin II stimulates aldosterone secretion from the adrenal gland.

Aldosterone enhances sodium reabsorption in the distal nephron.

Water retention follows sodium, expanding blood volume.

Angiotensin II

Adrenal aldosterone

Renal Na⁺ retention

Volume expansion

Slide 40 · Aldosterone acts through blood-volume regulation

The major pressure effect described is increased sodium and water resorption.

Blood-volume expansion raises cardiac filling pressure.

Changes in stroke volume and cardiac output contribute to higher pressure.

Aldosterone

Na⁺ + water retention

Filling pressure ↑

Cardiac output ↑

Slide 41 · Angiotensin II also acts directly on renal tubules

The source identifies increased tubular sodium reabsorption as a direct action.

This complements the indirect, aldosterone-mediated pathway.

Both mechanisms favor water retention and support circulating volume.

DIRECT

Angiotensin II

Tubular Na⁺ reabsorption

INDIRECT

Angiotensin II → aldosterone

Distal Na⁺ reabsorption

Slide 42 · One hormonal cascade influences both BP determinants

Direct vasoconstriction raises peripheral resistance.

Renal sodium retention expands blood volume and cardiac output.

This dual action explains the strong pressor potential of RAAS.

Angiotensin II

VSMC contraction

Resistance ↑

Angiotensin II / aldosterone

Renal Na⁺ retention

Cardiac output ↑

Arterial pressure ↑

Slide 43 · The kidney also releases vasodilating mediators

Renal prostaglandins are vascular relaxing factors.

Renal nitric oxide also counters pressor activity.

These actions provide local opposition to angiotensin-mediated vasoconstriction.

Angiotensin II

Pressor effect

Renal prostaglandins

Nitric oxide

↔

Balanced renal vascular responses

Slide 44 · Natriuretic peptides counter volume expansion

The heart participates in pressure and volume regulation as an endocrine organ.

Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) lower pressure.

Their actions include vasodilation and enhanced sodium elimination.

ANP / BNP

Systemic vasodilation

Renal Na⁺ excretion

Diuresis

Slide 45 · ANP and BNP arise from distinct cardiac sources

ANP is released from atrial myocardium, including constitutive secretion.

BNP is released from ventricular myocardium in volume-overload states.

Both peptides participate in volume-sensitive pressure homeostasis.

ANP

Atrial myocardium

Constitutive release

BNP

Ventricular myocardium

Volume-overload release

Slide 46 · Natriuretic peptides reduce vascular resistance

ANP and BNP promote systemic vasodilation.

Relaxation of resistance vessels decreases the resistance component of pressure.

This complements their independent renal effects.

ANP / BNP

Systemic vasodilation

Resistance ↓

BP ↓

Slide 47 · Natriuretic peptides increase renal salt excretion

ANP and BNP inhibit sodium reabsorption in the distal renal tubules.

More sodium is excreted, and urinary water loss increases.

Reduced volume lowers the filling-related component of cardiac output.

ANP / BNP

Distal Na⁺ uptake ↓

Natriuresis + diuresis

Volume ↓

Slide 48 · Elevated natriuretic peptides indicate volume stress

Robbins relates raised circulating ANP or BNP to a hypervolemic state.

Congestive heart failure is a typical associated setting.

Interpret the observation as a physiologic signal, not a stand-alone diagnosis.

Blood-volume overload

Myocardial peptide release

ANP / BNP in circulation

Slide 49 · RAAS and natriuretic peptides oppose one another

RAAS favors sodium retention and increases vascular tone.

ANP and BNP favor sodium excretion and systemic relaxation.

Blood pressure reflects their net effects alongside other inputs.

RAAS

Na⁺ retention

Vasoconstriction

Blood pressure ↑

ANP / BNP

Natriuresis

Vasodilation

Blood pressure ↓

Slide 50 · Pressure control integrates volume and tone

Volume regulation primarily modifies filling and cardiac output.

Vasomotor regulation modifies peripheral vascular resistance.

Angiotensin II and natriuretic peptides can influence both components.

Sodium and water balance

Ventricular filling

Cardiac output

Constriction / dilation

Arteriolar caliber

Vascular resistance

Blood pressure

Slide 51 · Hypertension: Essential versus secondary causes

The source attributes about 90–95% of cases to essential hypertension.

Secondary hypertension is linked to identifiable underlying mechanisms.

Understanding normal physiology clarifies the mechanism of secondary forms.

ESSENTIAL

Multifactorial contributions

Genetic and environmental inputs

SECONDARY

Identifiable disease or exposure

Renal, endocrine, vascular, other

Slide 52 · Renal causes of secondary hypertension

Parenchymal examples include acute glomerulonephritis and chronic renal disease.

Other examples include polycystic disease, renal vasculitis, and renin-producing tumors.

Renal artery stenosis is a major perfusion-mediated example.

Parenchymal renal disease

Renal artery stenosis

Renin-associated disease

Disturbed renal control of Na⁺ or RAAS

Slide 53 · Renal artery stenosis activates the RAAS

A narrowed renal artery reduces downstream glomerular perfusion pressure.

Reduced afferent pressure stimulates renin secretion.

Angiotensin II and aldosterone increase resistance and blood volume.

Renal artery stenosis

Afferent pressure ↓

Renin / RAAS ↑

Volume + resistance ↑

Slide 54 · Endocrine causes alter humoral regulation

The source lists primary aldosteronism and Cushing syndrome.

It also includes pheochromocytoma, acromegaly, and hyperthyroidism.

Hormonal exposures and pregnancy-related hypertension are additional categories.

Adrenal hormone excess

Catecholamine excess

Other endocrine states

Hormonal disruption of vascular or volume control

Slide 55 · Primary aldosteronism favors sodium retention

Primary aldosteronism is identified as a frequent secondary cause.

Idiopathic cases and aldosterone-secreting adenomas.

Excess aldosterone produces volume expansion through renal sodium uptake.

Adrenal aldosterone excess

Distal Na⁺ uptake ↑

Water retention

BP ↑

Slide 56 · Inherited defects in adrenal steroid metabolism

Monogenic disorders involving steroidogenic enzymes.

These disorders can produce excess mineralocorticoid effects.

The final common pathway is renal salt retention and volume-dependent pressure rise.

Steroid pathway gene defect

Mineralocorticoid effect ↑

Na⁺ + water retention

Hypertension

Slide 57 · Liddle syndrome: Abnormal distal sodium uptake

The source describes mutations affecting epithelial sodium channels (ENaC).

Abnormally increased distal sodium reabsorption favors volume expansion.

This illustrates hypertension from renal transport dysregulation.

ENaC channel abnormality

Distal Na⁺ uptake ↑

Volume expansion

BP ↑

Slide 58 · Additional secondary causes span several systems

Cardiovascular examples include coarctation of the aorta and aortic rigidity.

Neurologic/related contributors listed include intracranial pressure, sleep apnea, and stress.

Medication or hormonal exposures can alter vascular or sodium regulation.

Cardiovascular

Neurologic / stress-related

Drug or hormone exposure

Multiple pathways → elevated pressure

Slide 59 · Distinguish mechanisms, not merely diagnoses

Renal artery stenosis: Inappropriate renin drive from low renal perfusion.

Primary aldosteronism: Adrenal mineralocorticoid excess.

ENaC-related disease: Increased distal sodium transport.

Mechanism

Primary disturbance

Pressure effect

Renovascular

Low renal perfusion

RAAS / volume + tone

Aldosterone excess

Adrenal steroid signal

Renal Na⁺ retention

ENaC-related

Distal tubular transport

Renal Na⁺ retention

Slide 60 · Clinical reasoning: A poorly perfused kidney

Scenario: A kidney receives reduced arterial pressure distal to a stenosis.

Prediction: Renin rises despite pressure elevation elsewhere.

Consequence: Angiotensin II and aldosterone sustain systemic hypertension.

Why can renal hypoperfusion cause systemic hypertension?

Low kidney perfusion

Renin released

Volume and resistance rise

Slide 61 · Clinical reasoning: Sodium retention without RAAS drive

Scenario: A distal tubular sodium channel is abnormally active.

Prediction: Sodium and water retention increase circulating volume.

Mechanistic lesson: Hypertension can originate at the renal transporter.

Which pressure determinant changes first?

Distal Na⁺ retention

Blood volume rises

Cardiac filling increases

Slide 62 · High-yield physiologic synthesis

Cardiac output links heart rate, contractility, filling, and blood volume.

Arteriolar smooth muscle integrates constrictor and dilator signals.

Renal sodium handling anchors blood-volume control.

RAAS and natriuretic peptides connect organ-level sensors to both BP arms.

Heart + volume

Stroke volume / rate

Cardiac output

Arterioles

Constriction / dilation

Peripheral resistance

Integrated blood pressure

Slide 63 · Pressure regulation: three diagnostic questions

Is cardiac output changing through heart rate, contractility, or ventricular filling?

Are arteriolar resistance vessels responding mainly to constrictor or dilator signals?

Does the kidney favor sodium retention, or do natriuretic responses promote elimination?

Cardiac output?

Arteriolar resistance?

Renal Na⁺ balance?

Mechanistic interpretation

Convergent regulatory inputs