BIOS1170 & BIOS2170: Urinary System Anatomy

The Urinary System

• The urinary system has three main functions:
• Homeostatic balance: regulating blood ionic composition, blood volume, blood pressure, blood osmolarity, and blood pH.
• Endocrine production: producing hormones that regulate various physiological processes.
• Excretion and elimination: removing metabolic wastes and foreign chemicals from the blood.

Homeostatic Balance

• Blood ionic composition and volume are regulated by the kidneys.
• For a 70 kg person, total body water is approximately 42 L, with 2/3 being intracellular fluid (ICF) and 1/3 being extracellular fluid (ECF).
• Blood plasma makes up approximately 25% of ECF.
• Dehydration leads to a decrease in blood volume, resulting in reduced cardiac output, increased blood pressure, and increased solute concentration.
• The kidneys regulate blood volume by regulating urine volume.

Endocrine Production

• The kidneys produce hormones, including vitamin D and erythropoietin.
• Vitamin D helps control calcium absorption from the gut and is produced in the skin, liver, and kidney.
• Erythropoietin stimulates the production of mature red blood cells from precursor cells in the bone marrow in response to hypoxia.
• Severe kidney disease can lead to anemia due to inadequate erythropoietin production.

Excretion and Elimination

• The urinary system eliminates organic wastes and foreign chemicals from the blood through filtration, processing, and additional secretion.
• The most toxic endogenous wastes are nitrogenous compounds, including urea, uric acid, and creatinine.
• Urea is produced in the liver and is a by-product of protein breakdown, with a daily production of approximately 21 g.
• Uric acid is generated from the breakdown of purine nucleic acids, with a daily production of approximately 480 mg.
• Creatinine is derived from creatine phosphate in muscle tissue, with a daily production of approximately 1.8 g.

Anatomy of the Urinary System

• The urinary system consists of the kidneys, ureters, bladder, and urethra.
• The kidneys are located in a retroperitoneal position, behind the peritoneum, and are protected by the 11th and 12th ribs.
• The kidneys receive approximately 20-25% of cardiac output at rest and are responsible for producing urine.
• The ureters transport urine from the kidneys to the urinary bladder.
• The urinary bladder temporarily stores urine prior to elimination.
• The urethra transports urine to the exterior, and in males, also transports semen.

The Kidney

• The kidney is comprised of a fibrous capsule, renal fascia, and perinephric fat.
• The fibrous capsule is a tough layer that surrounds the kidney.
• The renal fascia is a tough, fibrous outer layer that anchors the kidney to surrounding tissue.
• The perinephric fat is located between the fibrous capsule and renal fascia.
• The kidney is divided into two layers: the renal cortex and the renal medulla.
• The renal cortex is the outer layer, and the renal medulla is the inner layer.
• The renal medulla is composed of 6-18 triangular structures called renal pyramids.
• The renal papilla is the tip of the pyramid that projects into the renal sinus.
• The renal columns are cortical tissue that separates the pyramids.

External Structures of the Kidney

• The kidney is ensheathed by a shiny, tough fibrous capsule.
• The renal vein exits the kidney via the hilum on the medial border.
• The renal artery enters the kidney at the hilum, usually posterior to the vein.
• The renal pelvis exits at the hilum, usually posterior to the artery and vein, and droops down to become the ureter.

Urinary System in Exercise and Sports Science

• The urinary system plays a crucial role in water and electrolyte balance during exercise.

• Dehydration can lead to decreased cardiac output, reducing oxygen delivery to tissues and impairing heat dissipation.

• The widely accepted belief that a ≥2% decrease in body weight due to dehydration adversely affects athletic performance is being challenged by recent studies.

• Drinking to thirst boosts performance, while drinking more offers no extra benefit.

• Over-hydration can lead to severe health risks, including exercise-associated hyponatremia (water poisoning).### Renal Lobe Structure

• Urine production occurs in a renal lobe, which drains into a minor calyx.

• A renal lobe consists of renal cortex, renal medulla, and a renal pyramid.

Urine Drainage

• 4-5 minor calyces merge to form a major calyx.
• 2-3 major calyces form the renal pelvis, a large funnel-shaped chamber.
• The renal pelvis is located in the renal sinus and fills most of the space.
• The renal pelvis drains into the ureter, which then drains the kidney into the bladder.

Renal Anatomy

• The renal columns are located between the renal pyramids.
• The fibrous capsule surrounds the kidney and provides protection.

Diagram Reference

• Figure 26-4 from Martini et al.'s Fundamentals of Anatomy and Physiology, 11th Ed.

Urinary System

• The urinary system is responsible for eliminating organic wastes and foreign chemicals from the blood through filtration, processing, and secretion.
• The system eliminates nitrogenous compounds, such as urea, uric acid, and creatinine, which are produced in the liver and muscle tissue.
• Urea production is approximately 21g per day, while uric acid production averages around 480mg per day, and creatinine production is around 1.8g per day.
• Exogenous wastes, such as pharmaceuticals like penicillin, can also be eliminated through the urinary system.

Importance of Urinary System

• The urinary system plays a crucial role in homeostatic regulation, not just waste elimination.
• It helps regulate water balance, with the importance of hydration being emphasized.

Hydration and Performance

• Over-hydration can lead to severe health risks, including exercise-associated hyponatremia (water poisoning), which can cause deadly cerebral and pulmonary edema.
• Drinking to thirst boosts performance, while drinking more offers no extra benefit.
• Losing up to 4% of body weight from exercise-induced dehydration does not significantly affect endurance performance.
• Aiming for 'euhydration' may actually impair performance.

Anatomy of the Kidney

• The kidney is located in a retroperitoneal position, behind the peritoneum, and is protected by the 11th and 12th ribs.
• The kidney is about 10 cm long, 5.5 cm wide, and 4 cm thick, and represents around 0.5% of body weight.
• The kidney receives around 20-25% of cardiac output at rest.
• The kidney's position and stability are maintained by two layers of connective tissue and fat.

Structure of the Kidney

• The kidney has a fibrous capsule, renal fascia, and perinephric fat that surround and anchor it to the surrounding tissue.
• The renal pelvis is a large funnel-shaped chamber that drains into the ureter.
• The ureter transports urine from the kidney to the urinary bladder.
• The kidney has a renal cortex, renal medulla, and renal pyramid, which produce urine that drains into a minor calyx.