E2 Take 2 Flashcards
What is the big idea of urine formation?
Each nephron filters blood, reabsorbs essential substances (e.g., sodium, glucose), and secretes excess or toxic substances (e.g., urea) to produce urine.
Like cleaning a fridge: take everything out, put back only what you need.
What are the four crucial processes of urine formation?
Glomerular filtration, Tubule reabsorption, Tubular secretion, Water reabsorption.
What happens during Glomerular Filtration?
Water and small solutes move from blood plasma to nephron.
What happens during Tubule Reabsorption?
Useful solutes (e.g., sodium) are reabsorbed into the bloodstream.
What happens during Tubular Secretion?
Additional wastes move from capillaries into the nephron.
What happens during Water Reabsorption?
Water is removed from filtrate and returned to blood.
What are glomerular capillaries like?
Extra permeable due to pores (fenestrae) in cells. Small particles (water, ions, glucose, amino acids, ammonia, urea, uric acid) pass easily. Larger particles (blood cells, platelets, proteins) are retained.
What drives glomerular filtration?
High blood pressure forces fluid and solutes into Bowman’s capsule.
What is the fluid in Bowman’s capsule called?
Filtrate.
Is glomerular filtration active or passive?
Passive (no energy required). Driven by pressure and concentration gradients.
Is glomerular filtration selective?
No, it’s non-selective: anything small enough passes through the pores.
What happens in the Proximal Tubule?
Hydrogen ions (H+) are actively secreted; ammonia diffuses in. Nutrients (glucose, amino acids) and positive ions (Na+, K+) are actively reabsorbed. Negative ions (Cl-, HCO3-) are passively reabsorbed by diffusion. Water reabsorbed by osmosis. Cells here have many mitochondria for ATP production.
What happens in the Loop of Henle?
Continues reabsorbing water and ions.
What is special about the Descending Loop of Henle?
Permeable to water; water reabsorbed by osmosis. Filtrate becomes saltier (higher salt concentration).
What is special about the Ascending Loop of Henle?
Impermeable to water. Salt diffuses and is actively transported back into capillaries.
What happens in the Distal Tubule?
Active transport of wastes (ammonia, urea, uric acid, excess H+ and K+ ions, medications like penicillin) from blood to nephron. Continued reabsorption regulated by hormones. Water reabsorbed by osmosis; Na+, Cl-, HCO3- actively reabsorbed.
What happens in the Collecting Duct?
Further concentration of filtrate by reabsorption of water via osmosis. Salt gradient in medulla (created by Na+ ions) pulls water out of filtrate. Permeability adjusted by hormones based on blood plasma concentration. Filtrate is now highly concentrated urine (~1% of original volume).
What happens in the Bladder and during Urination?
Urine (super-concentrated filtrate) collects in renal pelvis. Travels down ureters into the bladder. Stored in bladder until stretch receptors signal need to urinate. Relaxation of sphincters allows urine to flow out via urethra. We have some conscious control over this process.
