Excretion in Humans: Kidneys & Nephron

Flashcards about the renal system and excretion in humans.

Kidney Function

Excretes waste, maintains homeostasis of body fluid volume & solute composition, and regulates blood pressure

Macula Densa

Monitors filtrate pressure in kidney tubules

Low Blood Pressure Response

Signals adrenal cortex to synthesize aldosterone when blood pressure is low, leading to more water reabsorption and increased blood pressure

Urine Formation & Flow

Filtration in renal corpuscle, reabsorption/secretion in PCT, descending loop of Henle concentrates solutes, ascending loop dilutes filtrate, reabsorption/secretion in DCT, filtrate descends collecting duct and becomes more concentrated, emptying into renal calyces, then renal pelvis, ureter, urinary bladder, & urethra

Glomerulus

Capillary network that interacts with Bowman's capsule

Bowman's Capsule

Structure that surrounds glomerulus; materials are forced out of blood and into the tubule

Podocytes

Cells in Bowman's capsule that filter blood

Filtration

Large particles (blood cells & albumin) remain in circulatory system; only small particles go through and form the filtrate

Reabsorption

Glucose is completely reabsorbed; molecules & ions are pulled back into blood from kidney

Secretion

Substances are removed and secreted from the blood through peritubular capillaries into the nephron

Excretion

Urine physically leaves the body

Proximal Convoluted Tubule (PCT)

Portion between Bowman's capsule and the loop of Henle where most reabsorption occurs

Descending loop of Henle

Permeable only to water; water leaves the kidney tubules, which increases the solute concentration

Ascending loop of Henle

Impermeable to water; NaCl gets removed, which decreases the solute concentration

Distal Convoluted Tubule (DCT)

More reabsorption of glucose, ions, and water occurs here

Collecting Duct

Collects remaining filtrate; hormones can act on it to affect secretion & reabsorption

Aldosterone

Increases Na+ reabsorption from the kidney tubules into the bloodstream, leading to increased water retention in blood

ADH

Increases collecting duct permeability to water, leading to more concentrated urine and increased blood pressure

NH3 & NH4

Aquatic animals excrete these directly into water.

Urea

Mammals, sharks, and amphibians convert NH3 to this.

Uric Acid

Birds, insects, and reptiles secrete this.

Marine Fish

Body cells are hypotonic to environment, leading to water loss; constantly drink water and rarely urinate

Freshwater Fish

Body cells are hypertonic to environment, leading to water enters; rarely drink water and constantly urinate