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.

Learn about the components of the urinary system, the process of urine formation, and factors affecting urine composition. Explore the significance of urinalysis and how external factors can impact urine characteristics.