Urinary System 9-15

Nephron types (8) Cortical nephrons – 85% of nephrons located in the renal cortex Juxtamedullary nephrons – located at the cortex-medulla junction Loops of Henle deeply invade the medulla Extensive thin segments produce highly concentrated urine

Nephron functional unit of the kidney

The 2 Capillary beds of the nephron (9) Glomerular capillaries – inside glomerulus, fed by afferent arterioles, then exits glomerulus via efferent arterioles; efferent arteriole divides again into another capillary network: Peritubular capillaries – network that surrounds the PCT & DCT & ultimately the loop of Henle as vasa recta

Vasa recta (10) After the efferent arterioles descend into the medulla they divide into long thin STRAIGHT capillaries called the vasa recta (Latin for straight vessels)

Urine formation (11) The 3 big-picture processes Glomerular filtration – Tubular absorption + Tubular secretion = Excretion

3 levels of filtration – makeup of filters & filtrate (what is filtered) (12) & (9) Pressure differences of vessels Glomerular filtration Tubular reabsorption Tubular secretion

Glomerular filtration (13) Separates plasma fluid and small solutes from larger proteins and blood cells High blood pressure in glomerular capillaries forces fluid through capillary walls into Bowman’s capsule

Tubular reabsorption (14) Returns filtered water and nearly all major nutrients to the blood Primary active transport of Na+ across cell membrane drives diffusion of Cl- and water; provides energy for reabsorption by secondary active transport or passive diffusion of other substances

Tubular secretion (15) Removes harmful or excess substances from blood Substances move by active transport or passive diffusion from capillaries into the tubule

Filtrate contents (13) glomerular filtrate Contains all plasma components except protein Loses water, nutrients, and essential ions to become urine The urine contains metabolic wastes and unneeded substances

Countercurrent mechanism (14)Tubes that interact to make the excretory process work. Involves sodium pumps that create an area of high sodium concentration deep in the medulla, near the collecting duct This allows the kidneys to produce dilute or concentrated urine depending on your body’s needs Interaction between the flow of filtrate through the loop of Henle (countercurrent multiplier) and the flow of blood through the vasa recta blood vessels (countercurrent exchanger) allow this process to work