Urinary System Physiology Quiz

Urine Formation and Excretion

• The glomeruli produce approximately 200 liters of filtrate per day, but only 1-2 liters are excreted as urine.
• Dehydration is indicated by darker urine, a slight scent of ammonia, and less frequent urination.
• Normal urine excretion is a minimum of 500ml per day to remove waste.

Urine Volume and Concentration

• Polyuria: more than 2.5 liters/day, indicating diabetes mellitus, diabetes insipidus, excess water, caffeine, or alcohol consumption, kidney disease, or sickle cell anemia.
• Oliguria: 300-500 mL/day, indicating dehydration, blood loss, diarrhea, cardiogenic shock, kidney disease, or enlarged prostate.
• Anuria: less than 50 mL/day, indicating kidney failure, obstruction, or enlarged prostate.

Urinalysis

• The presence of leukocytes indicates a urinary tract infection.
• The presence of trace protein indicates damage to the glomerulus.
• The presence of ketones indicates diabetes or a high-fat diet.

Urinary System Anatomy

• The urethra transports urine from the bladder to the outside of the body, with internal and external sphincters.
• The female urethra is 4 cm long, while the male urethra is 20 cm long and passes through the prostate gland.
• The bladder collects urine from both ureters and can hold 500-600 ml.
• The micturition reflex occurs with about 150 mL of fluid and is easily controlled.

Ureters

• The ureters propel urine by peristalsis from the kidney to the bladder, with a one-way valve to prevent reflux.
• They are about 30 cm long and coated with protective mucous from goblet cells.

Kidney Anatomy

• The kidneys lie on either side of the spine, are about the size of a fist, and receive 25% of cardiac output.
• The adrenal gland sits atop each kidney.
• The renal hilum is the entry and exit point for vessels, nerves, lymphatics, and ureters.
• The renal pelvis funnels urine into the ureters by peristalsis.

Nephron Function

• The nephron is the functional unit of the kidney, responsible for cleansing blood, balancing constituents, and forming urine.
• The afferent arteriole becomes the glomerulus, which sits next to Bowman's capsule to form the renal corpuscle.
• The efferent arteriole forms a network around the nephron before returning to the venous system.

Renal Hilum Function

• The renal hilum recovers water and solutes that need to be reabsorbed into circulation.
• The main purpose of the kidney is to maintain homeostatic balance of plasma and excrete potential toxins.

Filtration

• The glomerulus pushes solutes through filtration slits and into Bowman's capsule.
• The filtration slits match up with fenestrations along the capillary.
• Proteins associated with pores are slightly negative, allowing more positive substances to pass through easier.

Macula Densa

• The macula densa measures sodium and flow rate.
• It releases ATP and adenosine in response to changes in flow rate and sodium.
• The juxtaglomerular cell contracts or relaxes based on osmolarity of plasma fluid.

Proximal Convoluted Tubule (PCT)

• The PCT is between Bowman's capsule and the loop of Henle.
• Simple cuboidal cells with prominent microvilli for efficient absorption and secretion of solutes.
• Lots of mitochondria for active transport.

Loop of Henle

• The loop of Henle has descending and ascending portions.
• Thick cuboidal cells and thin simple squamous cells are closest to the peak of the loop.

Distal Convoluted Tubule (DCT)

• The DCT is similar to the PCT, but shorter and with fewer microvilli.
• Aldosterone increases sodium reabsorption.
• Parathyroid hormone causes a calcium channel to open in the luminal surface.

Collecting Duct

• The collecting duct regulates water reabsorption controlled by ADH.
• The amount of aquaporin channels is related to the osmolarity of the blood.
• Also, receptors for aldosterone to control Na+ reabsorption.

Regulation of Renal Blood Flow

• Reducing sympathetic stimulation increases blood flow, and vice versa.
• The kidneys auto-regulate filtration rate very well despite changes in BP.

Renin-Angiotensin-Aldosterone System

• Increases BP by vasoconstriction and reabsorption of Na+.
• Released due to changes in flow rate and sodium.

Diuretics

• Caffeine promotes vasodilation in the nephron.
• Alcohol inhibits ADH release.
• Sodium is controlled by aldosterone, natriuretic hormone, and ADH indirectly.

Electrolyte Balance

• Potassium moves opposite of sodium most of the time.
• Calcium is controlled by PTH.
• Phosphate is opposite of calcium.
• Hydrogen is regulated due to acid-base homeostasis.

Nitrogen Waste

• Produced by the breakdown of proteins.
• Converted into ammonia, ammonia ion, urea, and uric acid.

Vitamin D Synthesis

• Hydroxylation (-OH) must be added to make calcitriol.
• Receptors are present in almost all cells of the body.

Erythropoiesis

• EPO increases RBC production.

Blood Pressure Regulation

• ADH, renin, and ANH regulate BP.
• Loss of renal function leads to loss of effective vascular volume control and can lead to hypertension or hypotension.

Osmolarity

• Solutes must be balanced with water in the blood vessels and interstitial spaces to prevent lysis or widespread edema.

pH Regulation

• The kidney is essential for proper pH regulation and balance of hydrogen ions.