Osmoregulation and Excretion (Campbell Biology Chapter 44)

Vocabulary-style flashcards covering key terms and definitions from the lecture notes on osmoregulation and excretion.

Osmoregulation

Maintenance of balance between water gain/loss and solute concentrations in body fluids by regulating movement of water and solutes across membranes.

Osmolarity

Solute concentration of a solution; determines the direction of water movement across a selectively permeable membrane.

Isoosmotic

Two solutions with equal osmolarity; no net water movement between them.

Hypoosmotic

A solution with lower osmolarity than another solution.

Hyperosmotic

A solution with higher osmolarity than another solution.

Osmoconformer

An animal that is isoosmotic with its surroundings and does not regulate its osmolarity.

Osmoregulator

An animal that uses energy to control water uptake and loss in an environment that differs from its internal osmolarity.

Stenohaline

Cannot tolerate substantial changes in external osmolarity.

Euryhaline

Can survive large fluctuations in external osmolarity.

Osmoreceptor

Sensory cells (often in the hypothalamus) that detect blood osmolarity and regulate hormone release (e.g., ADH).

TMAO

Trimethylamine oxide; protects sharks from urea’s denaturing effects in high-urea bodies.

Ammonia

Toxic nitrogenous waste excreted by many aquatic animals; requires lots of water for excretion.

Urea

Less toxic, highly water-soluble nitrogenous waste produced in the liver; energetically costly to synthesize but saves water.

Uric acid

Nontoxic nitrogenous waste excreted as a paste with very little water loss; energetically expensive to produce.

Anhydrobiosis

Desiccation-tolerance state allowing organisms (e.g., tardigrades) to survive extreme water loss.

Protonephridium

Network of dead-end tubules with flame bulbs; used for osmoregulation in some invertebrates.

Flame bulb

Cell at the end of a protonephridium that drives filtration through cilia.

Metanephridium

Segmentally arranged tubules in annelids that collect coelomic fluid and excrete dilute urine.

Malpighian tubules

Insects’ excretory system that removes nitrogenous wastes (primarily uric acid) from hemolymph and conserves water.

Kidney

Vertebrate excretory organ for excretion and osmoregulation; organized tubules and ducts that produce urine.

Nephron

Functional unit of the kidney; consists of a tubule and a glomerulus; processes filtrate into urine.

Bowman’s capsule

Cup-shaped container surrounding the glomerulus where filtration of blood begins.

Glomerulus

Tangled network of capillaries where filtration of blood into the nephron begins.

Proximal tubule

Segment where most reabsorption of ions, water, and nutrients occurs; some toxins secreted into filtrate.

Loop of Henle

U-shaped section of tubule with a descending limb (water reabsorption) and ascending limb (salt reabsorption); creates medullary osmotic gradient.

Descending limb

Part of the Loop of Henle where water exits filtrate via aquaporins, concentrating the filtrate.

Ascending limb

Part of the Loop of Henle where salt is reabsorbed but water cannot follow, diluting the filtrate.

Distal tubule

Tubule where K+ and NaCl concentrations are regulated; contributes to pH balance via H+ and HCO3− transport.

Collecting duct

Receives filtrate from nephrons; major site of water reabsorption; urine becomes hyperosmotic to body fluids.

Juxtamedullary nephron

Nephron with long loop of Henle penetrating deep into the medulla; essential for producing hyperosmotic urine.

Cortical nephron

Majority of nephrons with shorter loops of Henle that stay mostly in the cortex.

Vasa recta

Capillary network surrounding the loop of Henle; helps maintain the medullary osmotic gradient.

Filtration

Initial process in which water and solutes pass from blood into Bowman's capsule to form filtrate.

Reabsorption

Return of essential solutes and water from filtrate back into the bloodstream.

Secretion

Addition of nonessential or toxic solutes from blood into the filtrate.

Excretion

Elimination of processed filtrate as urine from the body.

Countercurrent multiplier

Mechanism by which a gradient of osmolarity is created in the medulla via active NaCl transport in the ascending limb and water movement in the descending limb.

Aquaporin

Water channel proteins that facilitate water movement across cell membranes; AQP2 is regulated by ADH.

ADH (vasopressin)

Antidiuretic hormone; increases water reabsorption by promoting aquaporin-2 insertion in collecting ducts.

Osmoreceptors

Hypothalamic neurons that sense blood osmolarity and regulate ADH release.

RAAS (renin-angiotensin-aldosterone system)

Hormonal system that regulates blood pressure and volume; renin release leads to angiotensin II and aldosterone effects.

Angiotensin II

Potent vasoconstrictor that raises blood pressure and stimulates aldosterone release.

Aldosterone

Steroid hormone that increases Na+ reabsorption and water retention, raising blood volume and pressure.

Atrial natriuretic peptide (ANP)

Hormone that opposes RAAS; relaxes Na+ reabsorption and reduces blood volume/pressure.

Thirst

Behavioral drive to drink water, coordinated with osmoregulatory signals to maintain balance.

Diuretic

Substance that increases urine production; alcohol inhibits ADH release, increasing urine output.

Diabetes insipidus

Condition from impairment of ADH signaling or aquaporin function, causing excessive dilute urination.

Renal cortex

Outer region of the kidney where many nephrons reside.

Renal medulla

Inner region of the kidney where high osmolarity concentrates urine.

Renal pelvis

Central collecting space in the kidney where urine collects before quiting via the ureter.

Ureter

Tube that transports urine from the kidney to the urinary bladder.

Urinary bladder

Sac that stores urine before it is excreted through the urethra.

Urethra

Tube that conveys urine from the bladder to the outside of the body.