Chapter 25 The Urinary System Overview

The Urinary System

• The glomerulus is the first part of the nephron, creating about 200 liters of filtrate each day.
• Urine production is affected by water intake, exercise, environmental temperature, nutrient intake, and other factors.

Urine Analysis (Urinalysis)

• Urine analysis is used to determine urine content.
• Normally, there are few proteins in urine.
• Color can be affected by certain foods, bile obstruction, dehydration, or bleeding.
• Specific gravity measures the amount of solutes in the urine, with pure water having a specific gravity of 1.0.

Urine Abnormalities

• Leukocytes in the urine indicate a urinary tract infection.
• Ketones in the urine indicate the body is using fat for energy instead of glucose or that the diet is low in carbs and proteins.
• Nitrates are normally found in the urine.
• 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.

Regulation of Urine pH

• Meats lower urine pH, while citrus fruits, vegetables, and dairy raise pH.
• Chronic levels can lead to kidney stones or osteomalacia.

The Urethra and Bladder

• The urethra transports urine from the bladder to outside the body.
• The bladder collects urine from both ureters and can hold about 600 mL of urine.
• Micturition is the medical term for urination.

Vitamin D and Hematopoiesis

• Vitamin D must undergo hydroxylation in the kidney to become active.
• Active vitamin D (calcitriol) regulates calcium in the blood.
• Vitamin D receptors are present in almost all cells, and some scientists consider it a hormone.
• Inadequate vitamin D can lead to osteoporosis.
• Hematopoiesis is the production of red blood cells, and erythropoietin (EPO) is produced primarily in the kidneys.

Kidney Function

• The kidneys regulate blood pressure, osmolarity, and electrolyte balance.
• They help recover electrolytes like sodium, potassium, and calcium.
• The kidneys regulate blood pH levels.

Nephron Structure and Function

• Nephrons in the kidney make urine, which flows through ducts to the ureters.
• The nephron works through filtration, reabsorption, and secretion.
• Filtration occurs in the glomerulus, and most solutes are reabsorbed in the PCT.
• The DCT and collecting ducts also reabsorb solutes and water.

Glomerular Filtration Rate and Urine Production

• Glomerular filtration rate is the amount of filtrate produced per minute.
• The rate is important to know if renal failure is an issue and if toxicity of drug doses may occur.

Blood Pressure Regulation

• Smooth muscle contracts if BP increases and relaxes if BP decreases.
• BP below a mean arterial pressure of 60 mm Hg will impair renal function and can cause shock.

Hormonal Regulation of Kidney Function

• ADH causes aquaporin channel proteins to reabsorb water in the collecting ducts.
• Aldosterone increases the number of sodium pumps in the DCT.
• Parathyroid hormone (PTH) increases calcium channels in the DCT.
• Calcitriol produces calcium-binding proteins to enhance calcium recovery.