26. Urinary System Flashcards
Urinary Systems Function
- Excretion: waste (nitrogenous urea, ammonia, creatinine)
- Regulates: water [ ], blood pH, plasma ions (Na+, K+, Ca+2, P)
- Produces: erythropoietin (endocrine: stimulates RBC production)
- Releases: renin (activates hormonal mechanisms that control BP)
kidneys
- layers
- regions
- functional unit
- Bean-shaped retroperitoneal organs
- Covered by 3 layers of tissue: Renal fascia + Adipose capsule + Renal capsule
- Have 2 main regions: cortex + medulla
- Functional unit is the nephron: cortical (85%) + juxta-medullary (15%)
Nephron
- cortical (85%) + juxta-medullary (15%)
- renal corpuscle = glomerulus + Bowman’s capsule
- renal tubule
- Many distal convoluted tubules open into a single collecting duct which open into papillary ducts at the tip of a pyramid which drain into the minor calyx
Blood Flow in Kidney
• Renal artery supplies blood to kidney
> divides into afferent arterioles (supplies blood to 1 nephron) –> glomerulus –> efferent arteriole–> peritubular capillaries (found in cortex) OR vasa recta (found in medulla)
• Renal vein drains venous blood from the kidneys
Ureter-how does blood move through them?
- Transport urine from the renal pelvis of the kidney to the posterior wall of the bladder
- peristaltic waves of the smooth muscle move urine through the ureters (assisted by hydrostatic pressure and gravity)
Urinary Bladder
- Distensible sac that functions in the temporary storage of urine
- average capacity = 500 ml-800 ml
- Lined with transitional epithelium
- Muscularis layer is called the detrusor muscle
Urethra
- from the floor of the bladder to the exterior
* In males: prostatic urethra + intermediate urethra + spongy urethra
Micturition
- Process of voiding urine (urination)
- When bladder contains about 200-400 ml of urine, stretch receptors in the wall are stimulated
- nerve impulses –> sacral region of the spinal cord –>pons and cerebrum
- When a conscious effort is made to urinate, impulses from pons cause contraction of detrusor muscle and relaxation of the internal and external sphincters
Pathway of Urine
glomerulus → Bowman’s capsule → PCT → loop of Henle → DCT → collecting duct → papillary duct → minor calyx → major calyx → renal pelvis → ureter → urinary bladder → urethra
Glomerular Filtration
- Location: Glomerulus
- Filter substances according to SIZE!
- process by which water and solute molecules in the blood plasma pass from the glomerulus into Bowman’s capsule forming the filtrate that enters the capsular space
- filter water, glucose, amino acids, Na+, Cl- (and other ions), nitrogenous wastes (ammonia, urea, creatinine), fatty acids, electrolytes and vitamins
- most large anions, protein-bound minerals, hormones, cells and large proteins are retained in the blood due to their large size
Tubular Secretion
- Location: proximal and distal convoluted tubules
- selective process removes substances from the blood and adds them to the filtrate
- dispose of unwanted substances such as urea, uric acid, bile salts, ammonia and creatinine
- secretion of H+ (if blood pH ↓) and HCO3- (if blood pH ↑)serves to regulate pH of the blood
Filtration process is efficient because the:
- glomerulus is coiled and has a large SA
- filtration membrane between glomerulus/Bowman’s capsule is thin and porous
- blood pressure in glomerulus is very high because the efferent arteriole is smaller in diameter than afferent arteriole ↑ blood pressure to 55 mmHg (only 18 mmHg in other capillary beds)
Tubular Reabsorption
- Location: Renal Tubule + Collecting Duct
- a selective process that removes substances from the filtrate and returns them to the blood
- majority of water and solute reabsorption (Na+, K+, Ca+2, HCO3-, HPO4-, Cl-) from the filtrate occurs in the proximal CT
- all glucose & amino acids: reabsorbed by facilitated diffusion and co-transport
- urea: reabsorbed by diffusion
- small proteins: reabsorbed by pinocytosis
Tubular Reabsorption: Na+ Reabsorption
Two Routes of Na+ Reabsorption
transcellular route – ACTIVE PROCESS
-pass through cytoplasm of tubule cell and then use Na+/K+ pump
paracellular route – PASSIVE PROCESS
-pass between tubule cells Na+ reabsorption creates an osmotic and electrical gradient that drives reabsorption of other solutes and water
Tubular Reabsorption: Water Reabsorption
obligatory water reabsorption – reabsorb 90% of water along with solutes to maintain equilibrium (in proximal convoluted tubules)
facultative water reabsorption – reabsorb final 10% of water as regulated by anti diuretic hormone (ADH) (after proximal convoluted tubules)
