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Questions and Answers
Which nitrogenous waste is primarily excreted by mammals?
Which nitrogenous waste is primarily excreted by mammals?
What is the primary advantage of excreting uric acid compared to urea?
What is the primary advantage of excreting uric acid compared to urea?
In which group of animals is uric acid primarily produced?
In which group of animals is uric acid primarily produced?
Which nitrogenous waste is most toxic and requires large amounts of water for excretion?
Which nitrogenous waste is most toxic and requires large amounts of water for excretion?
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What is a common characteristic of excretory systems across different species?
What is a common characteristic of excretory systems across different species?
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Which aquatic animals predominantly excrete ammonia?
Which aquatic animals predominantly excrete ammonia?
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What is the main disadvantage of converting ammonia to urea in mammals?
What is the main disadvantage of converting ammonia to urea in mammals?
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Which type of animal primarily excretes nitrogenous waste in the form of uric acid?
Which type of animal primarily excretes nitrogenous waste in the form of uric acid?
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What is the primary function of filtration in excretory systems?
What is the primary function of filtration in excretory systems?
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Which structure is responsible for excreting a dilute fluid in protonephridia?
Which structure is responsible for excreting a dilute fluid in protonephridia?
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How do Malpighian tubules in insects primarily function?
How do Malpighian tubules in insects primarily function?
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What is the role of renal arteries in the function of kidneys?
What is the role of renal arteries in the function of kidneys?
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What component of the nephron surrounds the glomerulus?
What component of the nephron surrounds the glomerulus?
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Which part of the excretory system helps produce urine in earthworms?
Which part of the excretory system helps produce urine in earthworms?
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What primarily drives the filtration process in the nephron?
What primarily drives the filtration process in the nephron?
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Which of the following statements correctly describes the function of nephrons in the kidneys?
Which of the following statements correctly describes the function of nephrons in the kidneys?
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What role does osmoregulation play in animals?
What role does osmoregulation play in animals?
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How do osmoconformers manage their osmolarity?
How do osmoconformers manage their osmolarity?
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What is the difference between hypoosmotic and hyperosmotic solutions?
What is the difference between hypoosmotic and hyperosmotic solutions?
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What adaptations do freshwater animals typically develop for osmoregulation?
What adaptations do freshwater animals typically develop for osmoregulation?
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What effect does seawater have on marine bony fishes regarding osmoregulation?
What effect does seawater have on marine bony fishes regarding osmoregulation?
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Which of the following statements about osmotic challenges is incorrect?
Which of the following statements about osmotic challenges is incorrect?
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In what way do desert animals cope with their environment regarding osmoregulation?
In what way do desert animals cope with their environment regarding osmoregulation?
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What mechanism describes the movement of water across a selectively permeable membrane?
What mechanism describes the movement of water across a selectively permeable membrane?
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What is the primary method by which freshwater animals maintain water balance?
What is the primary method by which freshwater animals maintain water balance?
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Which adaptation allows some aquatic invertebrates to survive in temporary ponds?
Which adaptation allows some aquatic invertebrates to survive in temporary ponds?
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How do desert animals mainly conserve water?
How do desert animals mainly conserve water?
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What is the average water loss through urine for a kangaroo rat?
What is the average water loss through urine for a kangaroo rat?
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What role do transport epithelia play in osmoregulation?
What role do transport epithelia play in osmoregulation?
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How do marine birds eliminate excess salt from their bodies?
How do marine birds eliminate excess salt from their bodies?
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Which of the following typically represents the nitrogenous waste product of land animals?
Which of the following typically represents the nitrogenous waste product of land animals?
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What is a characteristic of osmoregulators?
What is a characteristic of osmoregulators?
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What process primarily occurs in the proximal tubule of the nephron?
What process primarily occurs in the proximal tubule of the nephron?
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What characterizes the movement of filtrate in the descending limb of the loop of Henle?
What characterizes the movement of filtrate in the descending limb of the loop of Henle?
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What is the primary role of the ascending limb of the loop of Henle?
What is the primary role of the ascending limb of the loop of Henle?
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How do the vasa recta function in the nephron?
How do the vasa recta function in the nephron?
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What occurs in the distal tubule of the nephron?
What occurs in the distal tubule of the nephron?
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What percentage of water is typically reabsorbed during kidney filtration?
What percentage of water is typically reabsorbed during kidney filtration?
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What adaptation helps terrestrial animals conserve water through kidney function?
What adaptation helps terrestrial animals conserve water through kidney function?
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What happens to the filtrate as it moves through the collecting duct?
What happens to the filtrate as it moves through the collecting duct?
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Study Notes
Module BL1004: Animal Physiology
- This module focuses on animal physiology, specifically osmoregulation and excretion.
- The professor is Rob McAllen, in the School of Biological, Earth & Environmental Sciences, University College Cork, Ireland.
- Contact information is provided.
Osmoregulation and Excretion
- Animal excretory systems and Chapter 44 of Campbell's Biology (pg 1029) are the focus.
- Physiological systems in animals operate within a fluid environment.
- Maintaining the relative concentration of water and solutes is crucial for normal function..
- Osmoregulation is vital for balancing solute concentrations and managing water gain and loss.
- Freshwater animals have adaptations that limit water uptake and conserve solutes.
- Desert and marine animals face challenging environments that can quickly lead to dehydration.
- Excretion involves removing nitrogenous metabolic wastes and other waste products.
Overview: A Balancing Act
- Animal physiological systems operate in fluid environments which have narrow limits and balances of water and solutes.
- Osmoregulation is a process regulating solute concentrations and balancing water gain and loss.
- Freshwater animals reduce water uptake and preserve solutes.
- Desert and marine animals counteract water loss in dry and salty environments respectively.
- Excretion eliminates nitrogenous and other metabolic waste products.
Osmotic Challenges
- Osmoconformers are marine animals that have osmolarity similar to their surroundings and don't control it.
- Most marine invertebrates are osmoconformers.
- Stenohaline and euryhaline tolerances apply to osmoconformers and regulators.
- Osmoregulators control water uptake in hypotonic and loss in hypertonic environments.
- Marine bony fishes are hypoosmotic to seawater, losing water and gaining salt.
- Fishes balance water loss by drinking seawater and then excreting salts.
- Freshwater animals continuously absorb water and lose salts via osmosis.
- Salts lost are re-acquired from food and gill uptake.
Animals That Live in Temporary Waters
- Some aquatic invertebrates in temporary ponds lose nearly all their body water and survive a dormant state.
- This adaptation is called anhydrobiosis.
- Anhydrobiosis is a survival strategy where the animal becomes dehydrated, and can survive harsh environments.
Osmotic Challenges (Land Animals)
- Land animals manage water budgets by consuming moist food and drinking water.
- Desert animals conserve water through anatomical adaptations and behaviours such as nocturnal or underground lifestyles.
Water balance in two terrestrial mammals
- The comparison shows different water intake, metabolism, and water loss.
Conservation of Water
- Kidneys are adapted to minimize water loss.
- Concentrated urine, like in kangaroo rats, conserves water.
- Droppings from kangaroo rats are significantly drier than other mammals.
- Uric acid requires less water to excrete compared to urea.
Storage of Water
- Animals store water in fatty deposits and tissues (e.g., Gila monster's tail).
- Water is also obtained from the food consumed.
- Example mentioned is the Kangaroo rat's primarily seed-eating diet.
Energetics of Osmoregulation
- Osmoregulators need energy to maintain osmotic gradients.
- Precise control of body fluid composition is vital for cellular function.
- Transport epithelia are critical for solute movement and waste disposal.
- These specialized cells are arranged in complex networks to facilitate these functions.
How do seabirds eliminate excess salt?
- Seabirds, for example, have salt glands that remove excess sodium chloride from the blood.
- Salt glands use a countercurrent exchange mechanism for maximum efficiency in this function.
An animal's nitrogenous wastes
- Nitrogenous wastes reflect evolutionary history (phylogeny) and the environment (habitat) of the animal.
- The type and amount of waste products can greatly affect water balance.
- Examples include ammonia, urea, and uric acid.
Nitrogenous wastes (Ammonia, Urea, Uric Acid)
- Ammonia is toxic and requires lots of water for excretion.
- Urea is less toxic, requiring less water for excretion.
- Most mammals and adult amphibians use urea.
- Uric acid is largely insoluble in water, is excreted as a paste, and conserves water. This is typical in insects and reptiles (and birds).*
Diverse excretory systems
- Excretory systems regulate solute movement between internal fluids and the external environment.
- Most excretory systems create urine by processing filtrate.
- Some functions include filtration, reabsorption, secretion and excretion.
Excretory Systems
- Systems for waste removal vary across animal groups.
- The systems most often involve complex networks of tubules; examples include protonephridia, metanephridia, Malpighian tubules and nephrons.
Protonephridia
- Protonephridia form a network of dead-end tubules connected to external openings.
- Smallest branches are capped by cells (flame bulbs).
- The tubules excrete dilute fluid and are involved in osmoregulation.
Metanephridia
- Earthworms have a pair of open-ended tubules (metanephridia) per segment.
- These tubules collect coelomic fluid to produce dilute urine.
- Metanephridia function in both excretion and osmoregulation as well.
Malpighian Tubules
- In insects and other terrestrial arthropods, Malpighian tubules remove nitrogenous wastes from hemolymph.
- Malpighian tubules open into the digestive tract and create uric acid-based dry waste.
- This adaptation is highly efficient for water conservation in these animals.
Kidneys
- Kidneys are the primary excretory organs in vertebrates.
- Kidneys function in both excretion and osmoregulation.
- Mammalian kidneys are principally responsible for regulating water balance and salt.
- Each kidney has renal arteries for blood supply and renal veins for drainage.
- Urine exits the kidneys via the ureter, passing to a urinary bladder, and out through the urethra.
Kidneys: Nephrons (Functional Units)
- The nephron is a functional unit in vertebrate kidneys, consisting of a long tubule and a capillary network (glomerulus).
- Bowman's capsule surrounds glomerulus and collects filtrate.
Filtration: Glomerulus → Bowman's Capsule
- Filtration occurs due to blood pressure.
- Small molecules like water, salts, glucose, etc. are filtered from blood into Bowman's capsule; the process is not selective.
Pathway of the Filtrate
- Filtrate travels through the proximal tubule, loop of Henle, and distal tubule.
- Multiple nephrons drain into a collecting duct, entering the renal pelvis, and eventually the ureter.
Pathway of the Filtrate (Vasa Recta)
- Vasa recta are capillaries that surround the loop of Henle.
- Vasa recta and loop of Henle work as countercurrent systems for water conservation in the kidney.
- Urine becomes more concentrated than body fluids.
Proximal Tubule
- Reabsorption of ions, water and nutrients occurs in the proximal tubule.
- Active and passive transport processes move molecules into the interstitial fluid and then capillaries.
- Some toxins are also actively secreted into the filtrate.
- Filtrate volume decreases in the proximal tubule.
Descending Limb of the Loop of Henle
- Water reabsorption continues in this section via aquaporin channels.
- High interstitial fluid osmolarity drives water movement out of filtrate.
- Creates increasingly concentrated filtrate as it descends.
Ascending Limb of the Loop of Henle
- Salt reabsorption occurs here with little to no water movement.
- Filtrate gradually becomes more dilute.
Distal Tubule
- This segment regulates the precise K+ and NaCl concentration in body fluids.
Collecting Duct
- The collecting duct carries filtrate through the medulla to the renal pelvis.
- Water, some salts, and urea are reabsorbed.
- Urine becomes hyperosmotic to body fluids (increasingly concentrated).
The Nephron (Summary)
- Human kidneys filter about 180 litres of fluid daily.
- Reabsorption is highly efficient (approximately 99% of water, and nearly all sugars, amino acids, vitamins.)
Adaptations of the Vertebrate Kidney to Diverse Environments
- Nephron form and function are adapted to osmoregulatory needs based on the environment.
- Juxtamedullary nephron contributes to water conservation in terrestrial mammals by having longer loops of Henle (compared to those in freshwater environments).
- Birds and other reptiles conserve water because they excrete uric acid (instead of urea) with shorter loops of Henle.
Acknowledgements
- The majority of the text and power point slides came from Campbell's Biology.
- Dr Ramiro Crego contributed to the content of the slides.
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Description
Test your knowledge on the mechanisms and types of nitrogenous waste excretion in various animal groups. This quiz covers essential functions, advantages, and the anatomy of excretory systems in mammals, insects, and aquatic animals. Explore the differences in how different species manage waste products.
