Urinary System

Functions of the excretory system 

Filter waste (nitrogenous waste, excess water, and salts) 

Path of urine out of the body 

Collecting Duct: Urine from the distal convoluted tubules of nephrons drains into the collecting ducts. 

Renal Papilla: The collecting ducts merge and release urine at the tips of the renal pyramids, known as the renal papillae. 

Minor Calyx: Urine flows from the renal papillae into small chambers called the minor calyces. 

Major Calyx: Several minor calyces merge to form major calyces. 

Renal Pelvis: The major calyces empty into a central area called the renal pelvis. 

Ureter: From the renal pelvis, urine flows into the ureter, which carries it down to the bladder for storage. 

Structure and function of the bladder 

Can hold up to 1 L and is lined by transitional epithelium 

Muscle surrounding bladder is detrusor. It contracts to force urine out and into urethra 

Urethra in males vs females 

Males in penis (not separate from repro system) while females it empties in front of the vaginal orifice (separate from repro system) 

Path through the nephron and components 

Glomerulus: Blood is filtered in the glomerulus within the renal cortex, producing filtrate. 

Bowman's Capsule: Filtrate enters Bowman's capsule, beginning the journey through the nephron. 

Proximal Convoluted Tubule: Filtrate flows through the proximal tubule, where reabsorption of nutrients, ions, and water begins. 

Loop of Henle: The filtrate descends and then ascends through the loop of Henle in the medulla, concentrating the urine by reabsorbing water and salts. 

Distal Convoluted Tubule: Further adjustment of ion levels and water occurs in the distal tubule. 

Collecting Duct: The filtrate (now urine) travels down the collecting ducts, where additional water reabsorption can occur based on the body's needs. 

Glomerulus structure and function 

Glomerulus + capsule = renal corpuscle 

Kinking of capillaries in glomerulus causes hydrostatic pressure to force fluid into capsule (slows flow but inc pressure) 

Major processes in PCT 

65% of Na is re-absorbed here via active transport (glucose, proteins, Cl, and bicarb are symported with Na) 

Water re-absorbed via osmosis through aquaporins 

Re-absorbed via diffusion: Ca, Mg, PO4-, HCO3-, K+, and urea 

Secreted by diffusion and facilitated diffusion: H, NH4+, drugs, and creatine 

Take aways 

Re-absorbs Na, glucose, ions, and proteins 

Water follows biosmosis 

Ions move out and toxins move in 

Descending limb of the nephron loop 

Simple squamous epithelium 

Re-absorption of water via aquaporins 

Urea is secreted simultaneously via diffusion 

Take aways  

Re-absorbs lots of water 

Ascending limb of the nephron loop 

No aquaporins so impermeable to water 

Simple cuboidal epithelium 

Na+ is actively re-absorbed and symported with K, Cl, and bicarb 

HCO3-, Ca2+, and Mg2+ are passively re-absorbed via diffusion 

Take aways 

Re-absorbs lots of ions 

No aquaporins, ions pulled out to maintain concentration gradient 

What happens in the DCT? 

Wastes are dumped out 

Na, water, and ions are re-absorbed based on hormone levels 

What happens in the collecting duct? 

Summary: Ca, Na, and water are re-absorbed based on what hormones are telling it to do 

Wastes are actively secreted 

Absorption depends on hormones 

Ca if PTH is present 

Na if aldosterone is present 

Water if ADH (vasopressin) is present 

K secreted if aldosterone is present 

Regions under hormonal control 

DCT and collecting duct 

Path of urine through the kidney  

Glomerulus: Blood is filtered in the glomerulus within the renal cortex, producing filtrate. 

Bowman's Capsule: Filtrate enters Bowman's capsule, beginning the journey through the nephron. 

Proximal Convoluted Tubule: Filtrate flows through the proximal tubule, where reabsorption of nutrients, ions, and water begins. 

Loop of Henle: The filtrate descends and then ascends through the loop of Henle in the medulla, concentrating the urine by reabsorbing water and salts. Urea enters 

Distal Convoluted Tubule: Further adjustment of ion levels and water occurs in the distal tubule. 

Collecting Duct: The filtrate (now urine) travels down the collecting ducts, where additional water reabsorption can occur based on the body's needs. 

Renal Sinus/Pelvis: Urine is collected in the renal pelvis. 

Ureter: Urine exits the kidney via the ureter, which transports it to the bladder for storage.