Chapter 44: Osmoregulation and Excretion

Overview

• Focuses on how kidneys work to maintain fluid balance, solute concentration, and waste removal.
• Osmoregulation: regulating solute concentrations and water balance.
• Excretion: removal of waste products and excess water.

Osmoregulation

• Fluid Environment:

  • Open circulatory system: lymph surrounds cells.
  • Closed circulatory system: interstitial fluid and blood.
  • Homeostasis: maintaining constant concentration of water and solutes.

• Solute and Water Balance:

  • Osmosis: movement of water based on osmolarity (solute concentration).
  • Isoosmotic solutions: no net water movement.
  • Hyperosmotic solutions: water moves towards higher solute concentration.

• Types of Organisms:

  • Osmoconformers: maintain internal conditions matching environmental osmolarity; mainly marine animals.
  • Osmoregulators: adjust internal osmolarity; expend energy to maintain balance.

Adaptations to Environments

• Marine Animals:

  • Marine invertebrates: osmoconformers.
  • Marine vertebrates: osmoregulators, drink seawater, excrete salts.
  • Freshwater fish: expel large amounts of urine, take in salts through gills and food.

• Land Animals:

  • Minimize water loss through body coverings, behavioral adaptations, and metabolic water.

Nitrogenous Wastes

• Types of Wastes:

  • Ammonia: toxic, used by aquatic animals.
  • Urea: less toxic, used by mammals, sharks.
  • Uric Acid: used by birds, reptiles, insects.

• Factors Influencing Waste Type:

  • Toxicity, energy cost, water availability.

Excretory Systems

• Functions:

  • Filtration, reabsorption, secretion, excretion.

• Structures:

  • Protonephridia: in flatworms, dead-end tubules.
  • Metanephridia: in earthworms, tubules collect coelomic fluid.
  • Malpighian Tubules: in insects, removes waste from hemolymph.
  • Kidneys: in vertebrates, regulate solute and water balance.

Kidney Functionality

• Nephron Structure:

  • Functional unit: renal corpuscle and renal tubule.
  • Types: cortical and juxtamedullary.
  • Pathway: filtrate moves through Bowman's capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct.

• Processes:

  • Filtration: blood pressure forces fluid into Bowman's capsule.
  • Reabsorption: solutes and water reabsorbed into blood.
  • Secretion: waste substances added to filtrate.

Hormonal Regulation

• ADH (Antidiuretic Hormone):

  • Regulates water reabsorption in collecting ducts.
  • Increases aquaporin channels for water movement.

• RAAS (Renin-Angiotensin-Aldosterone System):

  • Responds to blood pressure changes.
  • Angiotensin II constricts arterioles, increases aldosterone for ion and water reabsorption.

• ANP (Atrial Natriuretic Peptide):

  • Counteracts RAAS; reduces blood volume.

Key Points

• Osmoregulation and excretion are crucial for maintaining homeostasis.
• Different organisms have adapted various mechanisms to manage osmolarity and waste.
• The kidneys play a significant role in filtering blood, reabsorbing essential materials, and excreting waste.
• Hormonal systems like ADH and RAAS control kidney function and blood pressure.