HL Human Physiology: 11.3 Kidneys Flashcards
Outline the key function of the excretory system in removing nitrogenous waste from the body (why must it be removed, how it is produced in different organisms)
Nitrogenous wastes are produced from the breakdown of nitrogen-containing compounds like amino acids and nucleotides
Nitrogenous wastes are toxic to the organism and hence excess levels must be eliminated from the body
The type of nitrogenous waste in animals is correlated with the evolutionary history of the animal and the habitat
What kind of nitrogenous waste is eliminated by aquatic animals?
Most aquatic animals eliminate their nitrogenous wastes as ammonia (NH3)
Ammonia is highly toxic but also very water soluble and hence can be effectively flushed by animals in aquatic habitats
Explain types of nitrogenous wastes produced by terrestrial animals
Terrestrial animals have less access to water and hence must package nitrogenous waste in less toxic forms
Mammals eliminate their nitrogenous wastes as urea, which is less toxic and hence can be stored at higher concentrations
Reptiles and birds eliminate wastes as uric acid, which requires more energy to make but is relatively non-toxic and requires even less water to flush (it is eliminated as a semi-solid paste)
Outline the need for the excretory system to removes excess water to maintain a suitable osmolarity within the tissues and cells as its function?
Water levels within an organism are constantly changing as a result of metabolic activity
Water is produced via condensation reactions (anabolism) and is consumed during hydrolysis reactions (catabolism)
The concentration of water within cells (osmolarity) will impact tissue viability (i.e. governs osmotic pressure within cells)
Animals may be either osmoconformers or osmoregulators: Define them
Animals may be either osmoconformers or osmoregulators according to how they manage their internal osmotic conditions:
Osmoconformers maintain internal conditions that are equal to the osmolarity of their environment
Osmoregulators keep their body’s osmolarity constant, regardless of environmental conditions
Outline how osmoconformers work
By matching internal osmotic conditions to the environment, osmoconformers minimise water movement in and out of cells
Less energy is used to maintain internal osmotic conditions within an osmoconformer
Outline how osmoregulators work (the kind of process, benefit)
While osmoregulation is a more energy-intensive process, it ensures internal osmotic conditions are always tightly controlled
Osmoregulators can maintain optimal internal conditions whereas osmoconformers are affected by environmental conditions
Discuss the type of excretory system animals and insects have
All animals possess a specialised excretory system for osmoregulation and the removal of nitrogenous wastes
In mammals, the excretory system (kidneys) is separate from the digestive system of the animal
In insects, the excretory system (Malpighian tubules) connects to the digestive system of the animal
Describe the excretory system of an insect (9 marks)
Insects have a circulating fluid system called haemolymph that is analogous to the blood system in mammals
Malpighian tubules are a series of small tubes that extend from the body cavity and drain into the insect’s digestive system
The tubules are lined with cells that actively transport ions such as sodium (Na+) and potassium (K+) from the haemolymph into the tubule lumen, raising the osmolarity and altering the charge of the lumen contents
Water moves into the lumen from the haemolymph by osmosis
Nitrogenous waste enters the tubules from the haemolymph along an electrical gradient
The ions, water, and nitrogenous waste drain from the malpighian tubules into the digestive system
Nitrogenous waste is converted into uric acid
Useful salts and water are reabsorbed from the hindgut into the haemolymph
Uric acid remains in the digestive system, from which it later leaves the body along with faeces through the anus
List the structures of the human excretory system with their functions
Humans have two kidneys covered by a fibrous capsule, which remove waste products from the blood and maintain the blood’s balance of water and solutes
The renal artery supplies oxygenated blood to the kidneys, while the renal vein carries deoxygenated blood away
The filtrate produced by the kidneys forms urine which is transferred to the bladder via a tube called the ureter
Define nephron
Nephrons are the functional unit of the kidney and are responsible for the formation of urine
Different parts of the nephron are found in different regions of the kidney
The cortex
Location of the glomerulus, Bowman’s capsule, proximal convoluted tubule, and distal convoluted tubule
The medulla
Location of the loop of Henle and collecting duct
The renal pelvis
All kidney nephrons drain into this structure, which connects to the ureter
Why blood composition differs between renal artery and renal vein?
The kidney contains specialised structures called nephrons which function to filter the blood and eliminate wastes
Consequently, the composition of blood entering the kidney (via renal artery) differs to that exiting the kidney (via renal vein)
Outline how blood in the renal vein (i.e. after the kidney) will have a different composition
Blood in the renal vein (i.e. after the kidney) will have:
Less urea (large amounts of urea is removed via the nephrons to form urine)
Less water and solutes / ions (amount removed will depend on the hydration status of the individual)
Less glucose and oxygen (not eliminated, but used by the kidney to generate energy and fuel metabolic reactions)
More carbon dioxide (produced by the kidneys as a by-product of metabolic reactions)
Define each of the component structures in a nephron
Bowman’s capsule – first part of the nephron where blood is initially filtered (to form filtrate)
Proximal convoluted tubule – folded structure connected to the Bowman’s capsule where selective reabsorption occurs
Loop of Henle – a selectively permeable loop that descends into the medulla and establishes a salt gradient
Distal convoluted tubule – a folded structure connected to the loop of Henle where further selective reabsorption occurs