Anatomy of the Nephron and Urinalysis Quiz

Urinary System Structure

• The female urethra is approximately 4cm long, making it more prone to infections and UTIs.
• The male urethra is approximately 20cm long and passes through the prostate gland.
• The bladder collects urine from both ureters and can hold around 600mL of urine.
• The ureters are approximately 30cm long and transport urine from the kidneys to the bladder.

Urination and Micturition

• Micturition is the medical term for urination.
• The urge to urinate is first felt when the bladder contains around 150mL of fluid.
• Urine is formed in the kidneys and propelled into the bladder through the ureters.

Kidney Function

• The kidneys are approximately the size of a fist and receive around 25% of cardiac output while at rest.
• Blood flow to the kidneys comes from the descending aorta and exits to the inferior vena cava.
• The right kidney sits slightly lower than the left kidney due to the liver's placement.
• Nephrons in the kidney make urine, which flows through ducts and empties into the ureters.
• Capillaries recover most of the solutes and water from the nephron and return them to circulation.

Nephron Function

• Nephrons work through filtration, reabsorption, and secretion.
• Filtrate goes from the capillary to Bowman's capsule easily due to filtration slits and fenestrated capillaries.
• Fenestrations prevent large objects like cells and proteins from passing into the nephrons.
• Positively charged filtrate passes through more easily.
• The basement membrane prevents medium-sized objects from passing through.
• The macula densa regulates renin release to influence blood volume.
• Nephrons also have many microvilli to absorb and secrete solutes.
• They have many mitochondria to produce enough ATP.

Urine Formation and Regulation

• The glomerular filtration rate is the amount of filtrate produced per minute.
• Fluid is absorbed into Bowman's capsule due to hydrostatic and osmotic pressure.
• Osmotic pressure in the blood is important to prevent excessive water loss or retention.
• ADH regulates water reabsorption in the collecting ducts.
• Without ADH, aquaporin channels are not inserted into the membrane.
• Most cells have aquaporin molecules for water transport.
• The kidneys regulate blood pressure, osmolarity, and electrolyte balance.
• They also regulate pH levels and recover electrolytes like sodium, potassium, and calcium.

Urine Characteristics

• Urine is affected by water intake, exercise, environmental temperature, nutrient intake, and other factors.
• Urinalysis is done to determine urine content.
• Color is affected by some foods, bile obstruction, dehydration, or bleeding.
• Specific gravity is the amount of solutes in the urine.
• Leukocytes in the urine indicate a urinary tract infection.
• Ketones in the urine mean that the body is using fat for energy in preference of glucose or that the diet is low in carbs and proteins.
• Nitrates are normally found in the urine.
• We must produce at least 500mL of urine each day to get rid of wastes.
• Anuria is the absence of urine production, polyuria is the overproduction of urine, and oliguria is the term for renal disease causing little urine production.

Hormonal Regulation

• The renin-angiotensin-aldosterone system is important for kidney function.
• Aldosterone is released due to angiotensin 2 or increased potassium levels.
• Progesterone binds to receptors like aldosterone, but it is much weaker.
• Anti-diuretic hormone (ADH) is also called vasopressin and it works to reabsorb water.
• Endothelins are powerful vasoconstrictors found in the kidneys.
• Natriuretic hormones work to inhibit aldosterone and let sodium leave, resulting in water excretion.
• Parathyroid hormone influences calcitriol and will result in higher calcium levels in the blood.

Blood Pressure Regulation

• Blood pressure reflects blood volume and is measured in the aorta and carotid sinuses.
• Baroreceptors send signals to the central nervous system for a sympathetic or parasympathetic response.
• Diuretics increase urine volume.
• Caffeine promotes vasodilation in the nephron and inhibits ADH.
• Glucose in the urine will increase water in the urine, as in the case of a person with uncontrolled diabetes.