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Chapter 15 - The Urinary System PowerPoint

Chapter 15: The Urinary System

Functions of the Urinary System

The urinary system plays a crucial role in maintaining homeostasis and overall health through the following functions:

Waste Removal:

It disposes of various waste products via urine, including:

  • Nitrogenous wastes: Such as urea, uric acid, and creatinine, which are byproducts of protein metabolism and cellular processes.

  • Toxins: Harmful substances that need to be eliminated to maintain body health.

  • Drugs: Pharmaceuticals and their metabolites that the body must expel after their functions are completed.

  • Excess ions: Includes ions such as sodium, potassium, and calcium that must be balanced to ensure proper cellular function.

Regulatory Functions:

The urinary system also performs key regulatory functions, including:

  • Production of renin: An enzyme important in regulating blood pressure by influencing vasoconstriction and sodium balance.

  • Production of erythropoietin: A hormone that stimulates the production of red blood cells in response to low oxygen levels, impacting oxygen transport throughout the body.

  • Conversion of vitamin D to its active form: Crucial for calcium absorption and bone health, thereby playing a key role in maintaining skeletal integrity.

Organs of the Urinary System:

The major organs involved in the urinary system include:

  1. Kidneys

  2. Ureters

  3. Urinary Bladder

  4. Urethra

Kidneys

Location and Structure:

  • Positioned retroperitoneally, which means they are located behind the parietal peritoneum in the abdominal cavity.

  • Extends from the level of the T12 to L3 vertebrae in adults.

  • The right kidney is typically positioned slightly lower than the left kidney due to the placement of the liver.

Structure:

  • Size: Approximately 12 cm long and 6 cm wide, with a bean-like shape.

  • Renal hilum: This is the entry and exit point for the ureters, blood vessels, and nerves.

  • Adrenal glands: Located atop each kidney, these glands produce hormones that regulate metabolism, immune response, and blood pressure.

Protective Layers:

  • Fibrous Capsule: A dense connective tissue that encloses and protects the kidneys from physical damage.

  • Perirenal Fat Capsule: Layers of fat that cushion the kidneys and help maintain their position.

  • Renal Fascia: A connective tissue layer that anchors the kidneys and adrenal glands to surrounding structures.

Kidney Regions:

  • Renal Cortex: The outer region of the kidney that contains the renal corpuscles and parts of the nephrons.

  • Renal Medulla: The inner region that contains renal pyramids, which are structures involved in urine formation.

  • Renal Pelvis: A funnel-shaped tube that collects urine from the calyces before it moves into the ureters.

Blood Supply to Kidneys

Arterial Supply:

  • The renal artery branches into segmental, interlobar, arcuate, and cortical radiate arteries to supply blood to the kidneys.

Venous Flow:

  • Blood is returned through cortical radiate veins, arcuate veins, interlobar veins, and finally to the renal vein, which carries deoxygenated blood back to the heart.

Nephrons

Structural and Functional Unit:

  • Each kidney contains approximately 1 million nephrons, the basic functioning units of the kidney engaged in urine production.

  • Composed of:

    • Renal Corpuscle: Contains the glomerulus and Bowman’s capsule where filtration occurs.

    • Renal Tubule: Comprises the proximal convoluted tubule (PCT), nephron loop, and distal convoluted tubule (DCT) where reabsorption and secretion processes take place.

Blood Supply:

  • Glomerulus: High pressure within this capillary tuft facilitates the initial filtration of blood to form urine.

  • Peritubular capillaries: Surround the nephron tubule and are specialized for reabsorption of filtered substances back into the bloodstream.

Urine Formation

Processes:

  1. Glomerular filtration: Water and solutes move from blood into the renal tubule through the glomerular capillaries.

  2. Tubular reabsorption: Essential substances such as glucose, ions, and water are reabsorbed back into the bloodstream from the tubular fluid.

  3. Tubular secretion: Additional wastes and excess ions are secreted into the tubular fluid to be excreted.

Characteristics:

  • Normal urine output ranges between 1.0 to 1.8 liters per day.

  • Urine composition includes nitrogenous wastes (urea, uric acid, creatinine), and its characteristics such as color, odor, and pH can vary depending on diet, hydration status, and metabolic health.

Ureters

Function:

  • Slender tubes (approximately 25-30 cm in length) that transport urine from the kidneys to the urinary bladder.

Structure:

  • Continuous with the renal pelvis, aided by peristaltic contractions to propel urine downward.

Urinary Bladder

Function:

  • Serves as a reservoir to store urine temporarily until it is expelled from the body. The trigone region indicates the openings for the ureters and urethra.

Structure:

  • Composed of smooth muscle walls, which allow for significant expansion as the bladder fills.

Capacity:

  • A moderately full bladder typically holds about 500 ml of urine.

Urethra

Function:

  • Conducts urine from the bladder to the outside of the body.

Differences:

  • In females, the urethra is typically 3-4 cm long and solely carries urine.

  • In males, it is approximately 20 cm long and serves a dual purpose of carrying both urine and sperm.

Control:

  • Two sphincters regulate urine release:

    • Internal sphincter: Involuntary control, relaxing as the bladder fills.

    • External sphincter: Voluntary control, allowing for conscious decision to urinate.

Micturition

Definition:

  • The process of voiding urine, which is controlled by the urethral sphincters and pelvic floor muscles.

Process:

  • Stretch receptors in the bladder wall trigger impulses that stimulate bladder contractions, leading to the expulsion of urine.

Balance Maintenance

Fluid and Electrolyte Balance:

  • Managed by factors such as dietary intake, metabolic processes, and urine output. Proper balance is crucial for normal cellular function and homeostasis.

Acid-Base Balance:

  • The kidneys help regulate acid-base balance through the reabsorption and secretion of bicarbonate ions and hydrogen ions, aiding in the maintenance of a stable pH in the blood.

Developmental Aspects

  • The development of kidneys begins early in fetal life, around the 5th week of gestation, demonstrating the importance of renal function from early stages of life.

  • Urinary issues may arise due to complications such as infections, congenital defects, or abnormalities in the structure and function of the urinary tract.

  • Aging can impact the urinary system by altering the concentration of urine, affecting bladder control, and