Waste Disposal: The kidneys play a crucial role in filtering and eliminating waste products from the bloodstream. This includes nitrogenous wastes, such as urea and creatinine, which are byproducts of protein metabolism, as well as acting to detoxify drugs and excess ions.
Regulatory Functions:
Production of Renin: This enzyme is vital in regulating blood pressure through the renin-angiotensin-aldosterone system.
Production of Erythropoietin: This hormone stimulates the production of red blood cells in the bone marrow, which is critical under conditions of low oxygen.
Conversion of Vitamin D: The kidneys convert vitamin D into its active form, calcitriol, enabling the body to properly use calcium and phosphate for bone formation and maintenance.
Kidneys: Two bean-shaped organs that filter blood, remove wastes, and regulate fluid balance.
Ureters: Muscular tubes that transport urine from the kidneys to the urinary bladder, utilizing peristaltic movements.
Urinary Bladder: A hollow muscular sac that stores urine prior to excretion.
Urethra: A duct that conveys urine from the bladder to the exterior of the body.
Position: The kidneys are located retroperitoneally, behind the peritoneum, between the T12 and L3 vertebrae. The right kidney is typically lower than the left due to the anatomical positioning of the liver above it.
Structure:
Size: Each kidney is approximately 12 cm long and 6 cm wide.
Renal Hilum: A medial indentation where the renal vessels (arteries and veins) and ureters enter and exit the kidneys.
Adrenal Glands: Located on top of each kidney, they produce hormones such as adrenaline.
Fibrous Capsule: A tough exterior layer protecting the kidney.
Perirenal Fat Capsule: Provides cushioning and insulation.
Renal Fascia: Surrounds the kidneys, anchoring them to surrounding structures.
Regions Revealed in a Longitudinal Section of the Kidney
Renal Cortex: The outer region responsible for filtering blood and forming urine. It contains the renal corpuscles and the proximal convoluted tubules.
Renal Medulla: The inner region that contains renal pyramids and renal columns. It plays a significant role in the concentration of urine and has the loop of Henle and collecting ducts.
Renal Pelvis: This is the funnel-shaped section that collects urine before it flows into the ureters.
Approximately 1/4 of the body's total blood supply passes through the kidneys each minute.
The renal artery branches out into segmental, interlobar, arcuate, and cortical radiate arteries to deliver blood.
Cortical Radiate Veins drain into the renal vein, returning filtered blood to the inferior vena cava.
Definition: Nephrons are the functional units of the kidneys, with over a million per kidney.
Components:
Renal Corpuscle: Comprises the glomerulus (a tuft of capillaries) and Bowman's capsule (which encases the glomerulus).
Renal Tubule: Made up of the proximal convoluted tubule (PCT), loop of Henle (nephron loop), and distal convoluted tubule (DCT).
Cortical Nephrons: Primarily located in the cortex, accounting for about 85% of all nephrons, involved in the routine filtration process.
Juxtamedullary Nephrons: Extend deep into the medulla and play a vital role in the concentration of urine and maintaining water balance.
Fed and drained by arterioles:
Afferent arteriole: Arises from a cortical radiate artery and feeds the glomerulus.
Efferent arteriole: Receives blood that has passed through the glomerulus.
Specialized for filtration.
High pressure forces fluid and solutes out of blood and into the glomerular capsule
Arise from the efferent arteriole of the glomerulus.
Low-pressure, porous capillaries adapted for absorption instead of filtration.
Cling close to the renal tubule to receive solutes and water from tubule cells.
Drain into the cortical radiate veins → arcuate veins → interlobar veins.
Glomerular Filtration: A passive process where water, ions, and small molecules filter from the blood into the renal tubule through the glomerular membrane.
Tubular Reabsorption: Useful substances such as water, glucose, and ions are reabsorbed back into the bloodstream, primarily occurring in the PCT.
Tubular Secretion: Additional wastes are actively secreted from the blood into the renal tubule for elimination.
Volume: The typical daily urine output ranges from 1.0 to 1.8 liters.
Appearance: Urine is typically clear to deep yellow due to a pigment called urochrome.
Composition: Generally consists of nitrogenous wastes like urea, uric acid, and creatinine, but healthy urine should not contain glucose, proteins, or blood cells under normal conditions.
Description: Two smooth muscle tubes, about 25-30 cm long, that transport urine from the kidneys to the urinary bladder through muscular contractions known as peristalsis.
Structure: A muscular sac designed to store urine until excretion, with a triangular area at its base known as the trigone, which is critical for bladder stability.
Capacity: The bladder can hold approximately 400- 600 ml of urine and can expand significantly without a marked increase in pressure due to its distensible walls.
thick wall
Function: Conducts urine from the bladder to the outside of the body; it varies in length, approximately 20 cm in males and 3-4 cm in females, contributing to differences in urinary pathologies.
Control Mechanisms:
Internal Urethral Sphincter: Composed of smooth muscle and is involuntary, maintaining urinary continence.
External Urethral Sphincter: Composed of skeletal muscle and is under voluntary control, allowing the body to initiate or delay urination.
thin wall
Function
• Females—carries only urine
• Males—carries urine and sperm
Definition: Voiding, or emptying of the urinary bladder.
Sphincters: Two sphincters control the release of urine:
Internal urethral sphincter
External urethral sphincter
Bladder Capacity: The bladder collects urine up to approximately 200 milliliters.
Stretch Receptors: Transmit impulses to the sacral region of the spinal cord.
Nerve Impulses: Impulses travel back to the bladder via the pelvic splanchnic nerves, causing bladder contractions.
Blood Composition Factors:
Diet
Cellular metabolism
Urine output
The kidneys play a crucial role in maintaining fluid, electrolyte, and acid-base balance in the body.
Excretion: Helps in the removal of nitrogenous wastes from the body to maintain a healthy internal environment.
Water Balance: Regulates the body's fluid levels through the excretion or retention of water.
Electrolyte Balance: Adjusts the levels of critical ions such as sodium, potassium, and calcium in the bloodstream.
Regulation of Blood pH: Maintains acid-base homeostasis by excreting hydrogen ions and reabsorbing bicarbonate from urine.
ADH (Antidiuretic Hormone): Regulates water balance by increasing water reabsorption in the kidneys.
Aldosterone: Promotes sodium reabsorption, which is essential for fluid balance and blood pressure regulation.
The kidneys start developing early during fetal life and the control of voluntary sphincter function matures as children develop.
Aging impacts renal function, often resulting in decreased efficiency in concentrating urine and regulating fluid balance, which can lead to conditions such as urinary frequency and incontinence.
Substance | Name of Condition | Possible Causes |
---|---|---|
Glucose | Glycosuria (gli”ko-su’re-ah) | Nonpathological: Excessive intake of sugary foods |
Pathological: Diabetes mellitus | ||
Proteins | Proteinuria (pro”te- ̆ı-nu’re-ah) (also called albuminuria) | Nonpathological: Physical exertion, pregnancy |
Pathological: Glomerulonephritis, hypertension | ||
Pus (WBCs and bacteria) | Pyuria (pi-u’re-ah) | Urinary tract infection |
RBCs | Hematuria (he”mah-tu’re-ah) | Bleeding in the urinary tract (due to trauma, kidney stones, infection) |
Hemoglobin | Hemoglobinuria | Various: Transfusion reaction, hemolytic anemia |
Normal Amount of Water in the Human Body:
Young adult females: 50%
Young adult males: 60%
Babies: 75%
The elderly: 45%
Water is necessary for many body functions, and levels must be maintained.
Water occupies three main fluid compartments:
Intracellular fluid (ICF)
Fluid inside cells.
Accounts for two-thirds of body fluid.
Extracellular fluid (ECF)
Fluids outside cells; includes blood plasma, interstitial fluid (IF), lymph, and transcellular fluid.
Plasma (blood) is ECF, but accounts for 3L of total body water.
Links external and internal environments.
Regulation of Water Intake and Output: Water intake must equal water output if the body is to remain properly hydrated.
Sources for Water Intake:
Ingested foods and fluids.
Water produced from metabolic processes (approximately 10%).
Thirst Mechanism: The driving force for water intake.