Excretory System Flashcards
(6 cards)
Introduction and Need for Excretion
Metabolism: Living organisms carry out metabolism, which consists of anabolism (building compounds) and catabolism (breaking down compounds for energy).
Metabolic Waste Products: The catabolism of carbohydrates, proteins, and lipids generates waste products like carbon dioxide (CO₂), water (H₂O), and ammonia (NH₃), which must be removed from the body to prevent toxicity.
Ammonia: Highly toxic, must be converted to less toxic forms for excretion.
Excess CO₂: Increases blood acidity, affecting pH balance.
Excess Water: Can lead to dropsy (water accumulation) or dehydration.
Excretory System Purpose: Essential for removing these waste products and maintaining homeostasis.
Excretion in Vertebrates
Major Waste Products:
CO₂
Mineral salts
Urea
Creatinine
Uric acid
Excess water
Excretion Across Different Organisms:
Unicellular organisms: Excrete waste through diffusion.
Small animals: Excrete waste through specialized cells or organs.
Large animals: Have complex excretory systems.
Adaptations: Excretion varies depending on habitat, such as marine, desert, or freshwater environments.
Excretory Organs
Skin: Acts as an excretory organ in some animals.
Salt Glands: Found in marine or brackish water organisms.
Intestine: Can serve as an excretory structure in some species.
Kidney: Primary excretory organ in vertebrates, also plays a role in osmoregulation.
Human Excretory System
Kidneys: Paired, bean-shaped structures located in the abdominal cavity.
Hilus: Depressed region where blood vessels and ureter enter/exit.
Kidney Structure: Consists of renal cortex (outer layer) and renal medulla (inner layer with pyramid-like structures).
Renal Pelvis: Funnel-shaped cavity that collects urine.
Nephron: Functional unit of the kidney, responsible for urine production.
Components include:
Glomerulus: Capillary network for filtration.
Bowman’s Capsule: Encases the glomerulus.
Convoluted Tubules: Filtered substances are reabsorbed here.
Loop of Henle: Further processing of filtrate.
Collecting Duct: Final passage for urine.
Kidney Function: Urine Formation
Pressure Filtration:
Filtration occurs due to blood pressure in the renal artery, filtering molecules like salts, glucose, and urea, leaving out red blood cells (RBCs).
The filtrate entering the Bowman’s capsule contains waste substances like urea and uric acid.
Reabsorption:
Useful compounds (glucose, water, and salts) are reabsorbed back into the bloodstream.
The remaining waste forms urine, which travels to the renal pelvis and enters the ureters.
Urination:
Urine is stored in the urinary bladder until full, triggering a reflex to release urine via the urethra.
In infants, urination is not under conscious control; in adults, it is controlled by a sphincter at the junction of the bladder and urethra.
Osmoregulation and Blood Pressure
Osmoregulation: Kidneys help maintain water balance in the body.
Increased blood pressure: Dilute urine is produced to expel excess water.
Decreased blood pressure: Concentrated urine is produced, and water is reabsorbed.
Thirst Reflex: Stimulated when water levels in the blood drop, prompting the body to seek hydration.
