Excretory Systems Flashcards
(18 cards)
What is the main function of the excretory system in animals?
The excretory system removes metabolic waste products from the body, maintains water and salt balance (osmoregulation), and regulates blood pH. Key organs include the kidneys, liver, ureters, bladder, and urethra.
Which organs are involved in excretion and urine production in mammals?
Kidneys: Filter blood and produce urine.
Ureters: Carry urine from kidneys to bladder.
Bladder: Stores urine.
Urethra: Excretes urine.
Liver: Converts ammonia to urea.
Skin and lungs: Minor excretory roles (sweat, CO₂).
Describe the structure of a kidney
Cortex: Outer layer, contains glomeruli and Bowman’s capsules.
Medulla: Inner region with nephron loops and collecting ducts.
Renal pyramids: Triangular structures in the medulla.
Renal pelvis: Collects urine and channels it to ureter.
Capsule: Tough outer covering.
Adrenal gland: Sits atop each kidney.
What is a nephron and what is its function?
A nephron is the functional unit of the kidney responsible for filtering blood, reabsorbing needed substances, and forming urine. Each kidney contains about 1 million nephrons
List the main parts of a nephron
Glomerulus
Bowman’s capsule
Proximal convoluted tubule
Loop of Henle (descending and ascending limbs)
Distal convoluted tubule
Collecting duct
Explain the process of ultrafiltration.
Blood enters the glomerulus under high pressure. Small molecules (water, glucose, ions, urea) are forced into the Bowman’s capsule. Larger molecules (proteins, blood cells) remain in the blood.
What is selective reabsorption in the nephron?
Occurs in the proximal tubule, where all glucose and some ions and water are reabsorbed into the blood via active transport and osmosis. Cells have many mitochondria and folded membranes to aid this
What happens in the Loop of Henle?
Descending limb: Water is reabsorbed via osmosis.
Ascending limb: Salt (Na⁺ and Cl⁻) is actively transported out.
This counter-current system concentrates urine in the medulla.
How is urine formed?
After filtration and reabsorption, remaining waste (mostly urea, excess ions, water) enters the collecting duct, then moves to the ureter, and finally to the bladder as urine.
What is osmoregulation?
The control of water and salt balance in the body. Regulated by ADH (antidiuretic hormone), which affects water reabsorption in the kidneys.
What is ADH and what is its role?
ADH (vasopressin):
Produced in the hypothalamus, released by the pituitary gland
Targets collecting ducts in the kidneys
Increases water reabsorption when the body is dehydrated
Results in concentrated urine and increased blood water content
What happens when the body is overhydrated?
Detected by osmoreceptors in the hypothalamus
Less ADH is released
Collecting ducts become less permeable to water
More dilute urine is produced, less water reabsorbed
How does nitrogenous waste form and how is it managed?
Proteins break down into amino acids. The amino group (NH₂) is removed by deamination, forming ammonia (toxic).
In land animals, ammonia is converted to urea in the liver via the ornithine cycle.
How is excretion different in birds?
Birds have no bladder; urine goes directly to the cloaca.
They excrete uric acid, a paste-like, water-insoluble substance.
This conserves water and reduces body weight for flight.
What is the role of the liver in excretion?
Converts ammonia to urea
Stores fat-soluble vitamins (A, D, E, K)
Breaks down hemoglobin and reuses iron
Produces bile and detoxifies harmful substances
Regulates glucose and clotting factors
Describe nephritis and its symptoms.
Nephritis is inflammation of the kidneys. Symptoms include:
Blood in urine
Swelling due to fluid retention
High blood pressure
Fatigue and nausea
Describe cirrhosis and its symptoms
Cirrhosis is chronic liver damage causing scarring. Symptoms include:
Jaundice
Fatigue
Swelling in legs/abdomen
Easy bruising
Confusion (due to toxin buildup)
How is kidney function adapted in desert animals?
Desert mammals have longer Loops of Henle, allowing more water reabsorption and production of highly concentrated urine, conserving water.
