11.4.1 Identify Different Organs of Urinary System
The urinary system includes:
- Kidneys: Two bean-shaped organs that filter blood and produce urine.
- Ureters: Tubes that transport urine from kidneys to the bladder.
- Urinary Bladder: Muscular sac that stores urine until excretion.
- Urethra: Tube that carries urine from the bladder to the outside.
11.4.2 Relate Structure of Kidney to Its Function
Structure:
- Renal Cortex: Outer layer containing glomeruli and proximal/distal tubules.
- Renal Medulla: Inner region with loops of Henle and collecting ducts, organized into pyramids.
- Renal Pelvis: Funnel-shaped structure collecting urine for ureter transport.
- Nephrons: Functional units (about 1 million per kidney) with glomerulus, Bowman’s capsule, and tubules.
Function:
- Filtration: Glomerulus filters blood in the cortex, forming filtrate in Bowman’s capsule.
- Reabsorption/Secretion: Tubules in cortex and medulla reabsorb water, nutrients, and ions and secrete wastes.
- Concentration: Medulla’s loop of Henle creates a concentration gradient to produce concentrated urine, conserving water.
- Urine Collection: Renal pelvis channels urine to ureters.
11.4.3 State That Nephron Is the Excretory Unit of Kidney
The nephron is the functional unit of the kidney responsible for filtering blood, reabsorbing essential substances, secreting wastes, and forming urine. Each kidney contains approximately 1 million nephrons.
11.4.4 Relate Structure of Different Parts of Nephron with Their Function
Glomerulus:
Structure: Network of capillaries with fenestrated walls.
Function: Filters blood to form a filtrate of water, ions, and small molecules, excluding large proteins and cells.
Bowman’s Capsule:
Structure: Cup-like structure surrounding the glomerulus.
Function: Collects filtrate from the glomerulus and directs it to the proximal tubule.
Proximal Convoluted Tubule (PCT):
Structure: Highly coiled tubule with microvilli for increased surface area.
Function: Reabsorbs ~65% of filtrate (water, glucose, amino acids, sodium) and secretes some wastes (e.g., drugs).
Loop of Henle:
Structure: U-shaped structure with descending and ascending limbs in the medulla.
Function: Creates a concentration gradient in the medulla, enabling water reabsorption (descending limb) and ion reabsorption (ascending limb) to concentrate urine.
Distal Convoluted Tubule (DCT):
Structure: Coiled tubule with fewer microvilli than PCT.
Function: Fine-tunes reabsorption of water, sodium, and calcium; secretes potassium and H⁺ ions; regulated by hormones (e.g., aldosterone).
Collecting Duct:
Structure: Tube that collects filtrate from multiple nephrons.
Function: Further concentrates urine by reabsorbing water (regulated by ADH) and excretes final urine to the renal pelvis.
11.4.5 Describe the Process of Urine Formation (Filtration, Selective Reabsorption, Secretion)
Filtration:
- Occurs in the glomerulus and Bowman’s capsule.
- Blood pressure forces water, ions, glucose, and small molecules through glomerular capillaries into Bowman’s capsule, forming filtrate (~180 liters/day).
- Large molecules (e.g., proteins, blood cells) are retained in the blood.
Selective Reabsorption:
- Occurs mainly in the proximal convoluted tubule, loop of Henle, distal tubule, and collecting duct.
- Essential substances (e.g., ~99% of water, glucose, amino acids, sodium) are reabsorbed into the blood via active transport (e.g., sodium pumps) or passive diffusion.
- Hormones (e.g., ADH, aldosterone) regulate water and ion reabsorption to maintain blood composition.
Secretion:
- Occurs in the proximal and distal convoluted tubules.
- Transports waste products (e.g., urea, creatinine), excess ions (e.g., K⁺, H⁺), and drugs from the blood into the tubule for excretion.
- Helps regulate blood pH and ion balance.
Outcome:
- Produces ~1–2 liters of concentrated urine daily, containing wastes and excess substances.