A previously healthy 61-year-old man comes to the physician because of a 6-month history of morning headaches. He also has fatigue and trouble concentrating on his daily tasks at work. He sleeps for 8 hours every night; his wife reports that he sometimes stops breathing for a few seconds while sleeping. His pulse is 71/min and blood pressure is 158/96 mm Hg. He is 178 cm (5 ft 10 in) tall and weighs 100 kg (220 lb); BMI is 31.6 kg/m2 . Which of the following is the most likely cause of this patient's hypertension?

Nocturnal upper airway obstruction

Proliferation of adrenal chromaffin cells

A 33-year-old woman presents to her primary care physician for a wellness check-up. She states that recently she has been feeling well other than headaches that occur occasionally, which improve with ibuprofen and rest. She has a past medical history of hypertension and headaches and is currently taking hydrochlorothiazide. Her temperature is 99.2°F (37.3°C), blood pressure is 157/108 mmHg, pulse is 90/min, respirations are 14/min, and oxygen saturation is 98% on room air. Physical exam reveals a young woman who appears healthy. A normal S1 and S2 are auscultated on cardiac exam, and her lungs are clear with good air movement bilaterally. From her previous visit, it was determined that she has an elevated aldosterone and low renin level. Laboratory values are ordered as seen below. Serum: Na+: 139 mEq/L Cl-: 100 mEq/L K+: 3.7 mEq/L HCO3-: 29 mEq/L BUN: 20 mg/dL Creatinine: 1.1 mg/dL Which of the following is the most likely diagnosis?

Narrowing of the renal arteries

A 42-year-old man is brought to the emergency room because of confusion. His wife says he has been urinating more frequently than usual for the past 3 days. He has not had fever or dysuria. He has bipolar disorder, for which he takes lithium. His pulse is 105/min, and respirations are 14/min. He is lethargic and oriented only to person. Physical examination shows dry mucous membranes and increased capillary refill time. Laboratory studies show a serum sodium concentration of 158 mEq/L and an antidiuretic hormone (ADH) concentration of 8 pg/mL (N = 1–5). Which of the following is the most likely site of dysfunction in this patient?

Hypothalamic supraoptic nucleus

A physician is choosing whether to prescribe losartan or lisinopril to treat hypertension in a 56-year-old male. Relative to losartan, one would expect treatment with lisinopril to produce which of the following changes in the circulating levels of these peptides?

Bradykinin increase; angiotensin II decrease

Aldosterone increase; bradykinin decrease

Angiotensin II increase; bradykinin decrease

Renin decrease; angiotensin I increase

Renin decrease; angiotensin II increase

Which change in CSF production most directly affects intracranial pressure?

Decreased carbonic anhydrase activity

Decreased arachnoid granulation function

Increased choroid plexus blood flow

A 35-year-old man presents to the physician’s clinic due to episodic chest pain over the last couple of months. He is currently pain-free. His chest pain occurs soon after he starts to exercise, and it is rapidly relieved by rest. He recently started training for a marathon after a decade of a fairly sedentary lifestyle. He was a competitive runner during his college years, but he has only had occasional exercise since then. He is concerned that he might be developing some heart disease. He has no prior medical issues and takes no medications. The family history is significant for hypertension and myocardial infarction in his father. His vital signs include: pulse 74/min, respirations 10/min, and blood pressure 120/74 mm Hg. The ECG test is normal. The physician orders an exercise tolerance test that has to be stopped after 5 minutes due to the onset of chest pain. Which of the following contributes most to the decreasing cardiac perfusion in this patient's heart?

Force of myocardial contraction

Regulation of blood pressure for USMLE Step 1: High-Yield Physiology Lessons

Baroreceptors & Chemoreceptors - The Body's BP Spies

Baroreceptors (Stretch): Rapid, moment-to-moment BP control.
- Locations: Carotid Sinus (glossopharyngeal n. - CN IX), Aortic Arch (vagus n. - CN X).
- Mechanism: ↑ Arterial stretch → ↑ firing → inhibits sympathetic & stimulates parasympathetic output → ↓ HR, ↓ contractility, vasodilation → ↓ BP.
Chemoreceptors (Chemical): Respond primarily to hypoxia.
- Locations: Carotid & Aortic bodies.
- Mechanism: Sense ↓ PaO₂, ↑ PaCO₂, or ↓ pH → ↑ sympathetic firing → vasoconstriction & ↑ HR → ↑ BP.

Baroreceptor locations and nerve pathways to the brain

⭐ Cushing Reflex: Increased intracranial pressure compresses cerebral arterioles, causing ischemia. The CNS triggers a powerful sympathetic response (hypertension) to restore perfusion, which in turn stretches peripheral baroreceptors, causing a reflex bradycardia.

RAAS - The Salt & Squeeze System

Renin-Angiotensin-Aldosterone System (RAAS) Cascade

Activated by ↓ renal perfusion to increase blood pressure.

Angiotensin II (The “Squeeze”):
- Potent vasoconstrictor → ↑ SVR.
- Stimulates aldosterone & ADH release.
Aldosterone (The “Salt”):
- Acts on collecting tubule.
- ↑ Na+ reabsorption (water follows).
- ↑ K+ & H+ excretion.

⭐ ACE is abundant in the lungs; ACE inhibitors can cause a dry cough due to ↑ bradykinin.

ADH & ANP - The Fluid Balance Crew

Antidiuretic Hormone (ADH): Secreted from posterior pituitary.
- Trigger: ↑ Plasma osmolality, ↓ blood volume.
- Action: Inserts aquaporin-2 in collecting ducts → ↑ H₂O reabsorption.
- Result: ↑ Blood volume, ↑ blood pressure; concentrated urine.
Atrial Natriuretic Peptide (ANP): Released from atria.
- Trigger: Atrial stretch due to ↑ blood volume.
- Action: Vasodilation & inhibits renin-angiotensin-aldosterone system.
- Result: ↑ Na⁺ and water excretion → ↓ blood volume & pressure.

⭐ B-type Natriuretic Peptide (BNP) is released from ventricles due to stretch and is a key diagnostic marker for heart failure.

Local Vaso-Regulators - The Micro-Managers

Metabolic (Active Hyperemia): Blood flow matched to local metabolic demand.
- Vasodilators: ↓$O_2$, ↑$CO_2$, ↑H⁺, ↑K⁺, Adenosine, Nitric Oxide (NO).
- Vasoconstrictors: Endothelin-1 (potent).
Myogenic (Autoregulation): Intrinsic smooth muscle response to pressure changes.
- ↑Pressure → Stretch → Vasoconstriction.
- ↓Pressure → ↓Stretch → Vasodilation.

⭐ Local metabolic control is the primary mechanism in vital organs like the heart and brain, overriding systemic sympathetic input to ensure constant perfusion.

Integrated Control - The BP Grand Finale

Overall Goal: Maintain tissue perfusion without damaging vessels.
Key Equation: Mean Arterial Pressure (MAP) is the product of Cardiac Output (CO) and Total Peripheral Resistance (TPR), expressed as $MAP = CO \times TPR$.

⭐ The Cushing reflex-hypertension, bradycardia, and irregular respirations-is a critical sign of increased intracranial pressure, representing a last-ditch effort to maintain cerebral perfusion.

High‑Yield Points - ⚡ Biggest Takeaways

Baroreceptors (carotid/aortic) are the fastest mechanism, responding to stretch to modulate autonomic tone.

RAAS is the key long-term regulator; Angiotensin II is a potent vasoconstrictor, and aldosterone increases volume.

ANP/BNP are released from stretched cardiac chambers, causing vasodilation and natriuresis to lower BP.

ADH (vasopressin) increases free water reabsorption and causes vasoconstriction at high concentrations.

The Cushing reflex-hypertension and bradycardia-is a response to increased intracranial pressure.

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