MLT GlobePhysiology: Renal physiology & acid-base
29 Physiology MCQs on Renal physiology & acid-base with answers and explanations.
At rest, roughly what fraction of cardiac output goes to the two kidneys?
Renal blood flow is about 1.1-1.2 L/min, around a fifth of cardiac output, although the kidneys are under 1% of body weight.
A healthy adult with normal fluid intake passes roughly how much urine per day?
Typical adult output is about 1-2 L/day. Less than about 0.4 L/day is oliguria, and more than about 3 L/day is polyuria.
Serum creatinine is used to estimate GFR. Creatinine comes from the breakdown of creatine phosphate in:
Creatinine is made at a fairly steady rate from muscle creatine phosphate, so its level reflects both GFR and muscle mass. Creatine itself is synthesised mainly in the liver.
Which finding is within the normal range for urine?
Urine is about 95% water, usually slightly acidic (pH around 6), and contains little protein. Its specific gravity varies with hydration from about 1.001 to 1.035.
Which statement about the afferent arteriole of a nephron is correct?
Blood enters the glomerulus by the wider afferent arteriole and leaves by the narrower efferent arteriole, which then forms peritubular capillaries; this keeps glomerular pressure high.
In a healthy person, which substance should be almost absent from glomerular filtrate?
The glomerular barrier holds back large, negatively charged proteins such as albumin. Glucose, creatinine and electrolytes filter freely. Protein in urine suggests glomerular damage.
Which body fluid is normally slightly alkaline, with a pH of 7.35-7.45?
Arterial blood is held at pH 7.35-7.45. Gastric juice is strongly acidic (about 1.5-3.5), vaginal fluid is acidic (about 4-4.5), and urine is usually around 6.
In urine formation, the glomerulus itself performs:
The glomerulus is a filter driven by capillary pressure, producing a protein-free ultrafiltrate. Reabsorption and secretion happen in the tubules, and final concentration in the collecting ducts.
The structural and functional unit of the kidney is the:
Each kidney has about a million nephrons, each consisting of a glomerulus and tubule that filter blood and form urine. Cortex and pyramids are regions, not units.
In a healthy young adult, the normal glomerular filtration rate is about:
Normal GFR is about 120-125 mL/min (around 180 L/day). A sustained eGFR below 60 mL/min/1.73 m2 for 3 months indicates chronic kidney disease.
On routine urinalysis of a healthy adult on a mixed diet, which result is typical?
Normal urine is usually slightly acidic (pH around 6, range 4.5-8). Specific gravity varies 1.005-1.030, daily output is about 1-2 L, and glucose should be negative.
The substrate of renin, angiotensinogen, is a plasma protein synthesised mainly by the:
Hepatocytes produce angiotensinogen; renin from the kidney cleaves it to angiotensin I, and ACE, mostly in lung capillaries, converts that to angiotensin II.
Colicky pain radiating from the loin to the groin most likely originates from the:
Renal and ureteric pain (e.g., a ureteric stone) is referred along T10-L1 dermatomes from loin to groin. Cardiac pain refers to the chest, arm and jaw.
Blood leaves the glomerular capillaries through which vessel?
The afferent arteriole brings blood into the glomerulus and the efferent arteriole carries it away to the peritubular capillaries and vasa recta.
Renin-secreting granular cells and the macula densa together form the:
The juxtaglomerular apparatus lies where the distal tubule touches the afferent and efferent arterioles; granular cells release renin in response to reduced perfusion or NaCl delivery.
What is the main function of the urinary bladder?
The bladder is a muscular reservoir that stores urine until micturition. Urine is formed and concentrated by the nephrons of the kidney.
Granular cells of the juxtaglomerular apparatus release which substance when renal perfusion falls?
JG cells in the afferent arteriole secrete renin, starting the renin–angiotensin–aldosterone cascade. Vasopressin comes from the posterior pituitary; erythropoietin from peritubular interstitial cells.
The act of emptying the urinary bladder is called:
Micturition is the reflex, voluntarily controlled emptying of the bladder. Filtration occurs at the glomerulus; fibrillation is disorganised muscle contraction.
Shortly after a person drinks two litres of water, plasma ADH concentration will:
Water loading lowers plasma osmolality, so hypothalamic osmoreceptors reduce ADH release, producing dilute urine and excreting the excess water.
A renal failure patient passes less than 100 mL of urine per day. This is termed:
Anuria is near-absent urine production. Inability to empty a full bladder is retention, haematuria is blood in urine and nocturia is night-time urination.