Urinary System Overview and Kidney Anatomy

Urinary System Overview

• The urinary system is the main excretory system, made up of kidneys, ureters, urinary bladder, and urethra.
• Two kidneys secrete urine.
• Two ureters transport urine from the kidneys to the bladder.
• The urinary bladder stores urine.
• The urethra carries urine out of the body.

Kidney Anatomy

• Bean-shaped organs, approximately 11cm long, 6cm wide, and 3cm thick, weighing 150 grams.
• Held in place by fat.
• Surrounded by a fibrous capsule.
• Consists of three main areas: cortex, medulla, and renal pelvis.
• The cortex is a reddish-brown layer of tissue immediately below the capsule, and outside the renal pyramids.
• The medulla is the innermost layer, consisting of conical-shaped renal pyramids.

Renal Pelvis

• Funnel-shaped tube that connects to the ureter at the hilum.
• Branches emerging from the pelvis form major and minor calyces.
• Urine is collected by the calyces and drained into the renal pelvis and then the ureter.
• Smooth muscles in the walls of the calyces, pelvis and ureter contract rhythmically to propel urine.

Kidney Location

• Lie on the posterior abdominal wall, one on each side of the vertebral column, behind the peritoneum, and below the diaphragm.
• The right kidney is usually slightly lower than the left kidney due to the liver.

Kidney Functions

• Form urine.
• Maintain water, electrolyte, and acid-base balance.
• Excrete waste products.
• Produce and secrete erythropoietin, a hormone that stimulates red blood cell production.

Nephron Structure

• Functional units of the kidneys.
• Consist of a glomerulus (cluster of capillaries surrounded by Bowman's capsule), proximal convoluted tubule, loop of Henle, and distal convoluted tubule.
• Bowman's capsule surrounds the glomerulus.
• Collects material filtered from the blood.
• Afferent arteriole leads blood into the glomerulus, and efferent arteriole leads blood out of the glomerulus.

Glomerular Filtration

• The glomerulus and Bowman's capsule act as a filter.
• Allows water and small molecules to pass through, but not blood cells or large proteins.
• Difference in blood pressure between the glomerulus and Bowman's capsule drives filtration.

Glomerular Filtration Rate (GFR)

• Amount of filtrate formed by both kidneys per minute (approximately 125 mL/min in healthy adults).
• 180 liters of filtrate are formed each day.
• Most filtrate is reabsorbed but about 1-1.5 liters are excreted as urine.
• Renal blood flow and glomerular filtration are autoregulated.

Selective Reabsorption

• Process of reclaiming essential substances from the filtrate.
• Most reabsorption happens in the proximal convoluted tubule.
• Reabsorption of nutrients like glucose, water, and electrolytes.

Tubular Secretion

• Process of actively transporting substances from the blood into the filtrate.
• Cleanses the filtrate from excess substances like drugs, and foreign materials.

Urine Composition

• Clear, amber color due to urobilin.
• Specific gravity between 1020 and 1030.
• pH around 6 (normal range 4.5-8).
• Water (95-96%).
• Urea, uric acid, creatinine, ammonia, sodium, and potassium (all remaining amounts are small percentages).
• Amount varies from 1000-1500ml per day for an adult

Hormones Affecting Urine Formation

• Hormonal influence on selective reabsorption.
  • Parathyroid hormone (PTH): Regulates calcium and phosphate reabsorption.
  • Antidiuretic hormone (ADH): Influences water reabsorption.
  • Aldosterone: Regulates sodium and potassium reabsorption.
  • Atrial Natriuretic Peptide (ANP): Decreases sodium reabsorption.

Ureter Overview

• Transports urine from kidneys to the bladder.
• About 25-30 cm long and 3 mm in diameter.
• Continues as a funnel-shaped renal pelvis.
• Peristaltic waves propel urine.
• Three layers of tissues.

Urinary Bladder

• Reservoir for urine.
• Located in the pelvis.
• Three layers: outer connective tissue, middle smooth muscle, and inner mucosa.
• Lined with transitional epithelium which allows for significant expansion.
• Rugae: folds in the bladder that allow expansion when the bladder fills.
• Internal and External urethral sphincter.
  • Internal is involuntary
  • External is voluntary.
• Capacity roughly 600ml.

Urethra

• Canal extending from the bladder neck to the exterior.
• Longer in males (approximately 20cm) than in females (approximately 4cm).
• In males, the urethra is part of both the reproductive and urinary systems.
• Two layers: outer muscle and inner mucosa.
• External urethral sphincter is under voluntary control.

Micturition (Urination) Reflex

• Process of emptying the bladder.
• Initiated when the bladder fills and stretches to a certain point.
• Involves an autonomic spinal cord reflex and impulses from the brain.
• Relies on the relaxation and contraction of muscles, and on the relaxation of the external urethral sphincter.

Role of Renin-Angiotensin-Aldosterone System(RAAS)

• Regulation of cardiac output, and blood pressure by the kidneys.
• Renin, a proteolytic enzyme is released in response to drops in blood pressure

Explore the fascinating details of the urinary system, including its main components such as the kidneys, ureters, bladder, and urethra. Learn about the structure and function of the kidneys and the renal pelvis. This quiz covers key anatomical features and their roles in excretion.