The Urinary System

The Urinary System

• The urinary system consists of the kidneys, ureters, bladder, and urethra
• The kidneys filter waste and excess fluids from the blood and regulate electrolyte levels
• The ureters carry urine from the kidneys to the bladder
• The bladder stores urine until it is eliminated from the body through the urethra

The Kidney

• The kidney has three main parts: the renal cortex, renal medulla, and renal pelvis
• The renal cortex is the outer layer of the kidney and contains the glomeruli
• The renal medulla is the inner layer of the kidney and contains the nephrons
• The renal pelvis is the funnel-shaped structure that collects urine from the nephrons

The Nephron

• The nephron is the functional unit of the kidney and consists of the renal corpuscle, proximal convoluted tubule, loop of Henle, and distal convoluted tubule
• The renal corpuscle, also known as Bowman's capsule, is the site of glomerular filtration
• The proximal convoluted tubule reabsorbs water and solutes from the filtrate
• The loop of Henle is responsible for concentrating the urine
• The distal convoluted tubule and collecting duct refine the concentration of the urine

Urine Formation

• Urine formation involves three processes: glomerular filtration, tubular reabsorption, and tubular secretion
• Glomerular filtration occurs when the blood pressure forces water and solutes out of the capillaries and into the glomerular capsule
• Tubular reabsorption occurs when the proximal convoluted tubule reabsorbs water and solutes from the filtrate
• Tubular secretion occurs when the distal convoluted tubule and collecting duct secrete waste products and excess ions into the urine

Hormonal Influences

• Aldosterone stimulates the kidneys to reabsorb sodium and water, increasing blood volume and blood pressure
• Antidiuretic hormone (ADH) stimulates the kidneys to reabsorb water, reducing urine production and increasing blood volume
• Atrial natriuretic peptide (ANP) inhibits the reabsorption of sodium, increasing urine production and reducing blood volume
• Parathyroid hormone (PTH) increases calcium reabsorption in the kidneys, regulating blood calcium levels

Other Functions of the Kidney

• The kidney produces erythropoietin, which stimulates the production of red blood cells in response to low oxygen levels
• The kidney activates vitamin D, which is essential for calcium absorption and bone health
• The kidney helps regulate blood pH by secreting hydrogen ions and reabsorbing bicarbonate ions

The Bladder and Urethra

• The bladder is a muscular sac that stores urine until it is eliminated from the body
• The urethra is the tube that carries urine from the bladder to the outside of the body
• The internal urethral sphincter is an involuntary muscle that relaxes to allow urine to flow
• The external urethral sphincter is a voluntary muscle that can be controlled to delay urination

Micturition

• Micturition is the process of urination, which involves the relaxation of the internal and external urethral sphincters and the contraction of the bladder wall

Developmental Changes Across the Lifespan

• Newborns have incomplete bladder control and may urinate frequently
• Toddlerhood is a time of toilet training, during which the child learns to control the external urethral sphincter
• In older adults, the kidneys shrink, and the bladder loses tone, leading to incontinence and increased frequency of urination
• During pregnancy, the kidneys enlarge, and the ureters become dilated, leading to increased urine retention and risk of UTIs

The Urinary System

• The urinary system consists of the kidneys, ureters, bladder, and urethra
• The kidneys filter waste and excess fluids from the blood and regulate electrolyte levels
• The ureters carry urine from the kidneys to the bladder
• The bladder stores urine until it is eliminated from the body through the urethra

The Kidney

• The kidney has three main parts: the renal cortex, renal medulla, and renal pelvis
• The renal cortex is the outer layer of the kidney and contains the glomeruli
• The renal medulla is the inner layer of the kidney and contains the nephrons
• The renal pelvis is the funnel-shaped structure that collects urine from the nephrons

The Nephron

• The nephron is the functional unit of the kidney and consists of the renal corpuscle, proximal convoluted tubule, loop of Henle, and distal convoluted tubule
• The renal corpuscle, also known as Bowman's capsule, is the site of glomerular filtration
• The proximal convoluted tubule reabsorbs water and solutes from the filtrate
• The loop of Henle is responsible for concentrating the urine
• The distal convoluted tubule and collecting duct refine the concentration of the urine

Urine Formation

• Urine formation involves three processes: glomerular filtration, tubular reabsorption, and tubular secretion
• Glomerular filtration occurs when the blood pressure forces water and solutes out of the capillaries and into the glomerular capsule
• Tubular reabsorption occurs when the proximal convoluted tubule reabsorbs water and solutes from the filtrate
• Tubular secretion occurs when the distal convoluted tubule and collecting duct secrete waste products and excess ions into the urine

Hormonal Influences

• Aldosterone stimulates the kidneys to reabsorb sodium and water, increasing blood volume and blood pressure
• Antidiuretic hormone (ADH) stimulates the kidneys to reabsorb water, reducing urine production and increasing blood volume
• Atrial natriuretic peptide (ANP) inhibits the reabsorption of sodium, increasing urine production and reducing blood volume
• Parathyroid hormone (PTH) increases calcium reabsorption in the kidneys, regulating blood calcium levels

Other Functions of the Kidney

• The kidney produces erythropoietin, which stimulates the production of red blood cells in response to low oxygen levels
• The kidney activates vitamin D, which is essential for calcium absorption and bone health
• The kidney helps regulate blood pH by secreting hydrogen ions and reabsorbing bicarbonate ions

The Bladder and Urethra

• The bladder is a muscular sac that stores urine until it is eliminated from the body
• The urethra is the tube that carries urine from the bladder to the outside of the body
• The internal urethral sphincter is an involuntary muscle that relaxes to allow urine to flow
• The external urethral sphincter is a voluntary muscle that can be controlled to delay urination

Micturition

• Micturition is the process of urination, which involves the relaxation of the internal and external urethral sphincters and the contraction of the bladder wall

Developmental Changes Across the Lifespan

• Newborns have incomplete bladder control and may urinate frequently
• Toddlerhood is a time of toilet training, during which the child learns to control the external urethral sphincter
• In older adults, the kidneys shrink, and the bladder loses tone, leading to incontinence and increased frequency of urination
• During pregnancy, the kidneys enlarge, and the ureters become dilated, leading to increased urine retention and risk of UTIs