What distinguishes excretion from secretion in organisms?
Excretion removes metabolic waste, secretion releases useful substances.
What are the main human excretory waste products?
Carbon dioxide, water, bile pigments, urea, and mineral salts.
Which substances do the lungs excrete in exhaled air?
Carbon dioxide and water vapour.
What waste does the kidney excrete in urine?
Urea, excess mineral salts, and water.
From where is urea in urine produced?
From deamination of excess amino acids in the liver.
What does the skin excrete in sweat?
Mineral salts, traces of urea, and water.
What does the colon excrete in faeces?
Bile pigments and excess mineral salts.
What organs make up the urinary system?
Two kidneys, two ureters, the bladder, and the urethra.
What is one main function of the urinary system?
Osmoregulation.
Which artery carries oxygenated, unfiltered blood to the kidney?
The renal artery.
What protects each kidney from damage and infection?
Adipose tissue and a renal capsule.
What waste does the urinary system excrete?
Nitrogenous waste such as urea.
What does the renal vein carry away from the kidney?
Deoxygenated, filtered blood.
What body-fluid aspect does the urinary system regulate besides pH?
Salt concentration.
What is a nephron in the kidney?
The microscopic functional unit that filters blood and regulates substances.
How many nephrons does each human kidney contain?
About 1 million nephrons.
What components make up each nephron?
Tubes, arterioles, capillaries, and ducts.
What does the Malpighian body consist of?
Bowman's capsule and the glomerulus.
Where is the Malpighian body located?
In the kidney cortex.
What parts make up the renal tubule?
Proximal convoluted tubule, loop of Henle, distal convoluted tubule, and collecting ducts.
What surrounds the renal tubule?
Peritubular capillaries.
What features do renal-tubule epithelial cells have for transport?
Microvilli and many mitochondria.
How does blood enter and leave the glomerulus during ultrafiltration?
Blood enters via the afferent arteriole and leaves via the efferent arteriole.
What causes high pressure in the glomerulus during ultrafiltration?
The narrower efferent arteriole creates high pressure.
What forces plasma into Bowman's capsule during ultrafiltration?
High pressure in the glomerulus forces plasma into Bowman's capsule.
What limits passage of substances through the glomerulus into Bowman's capsule?
Thin capillary walls and podocyte filtration slits limit passage.
Which substances pass into Bowman's capsule during filtration?
Only small dissolved substances pass into Bowman's capsule.
Why is glomerular filtration considered non-selective?
Because useful substances and wastes are filtered together.
What substances are actively reabsorbed in the proximal convoluted tubule?
Glucose, amino acids, vitamins, and other important substances.
How much water is reabsorbed by osmosis in the proximal convoluted tubule?
About 65% of the water returns to the blood by osmosis.
What is the water permeability of cells in the ascending loop of Henle?
Cells are impermeable to water in the ascending loop of Henle.
What do cells in the ascending loop of Henle actively pump into the medulla?
They actively pump salt into the medulla.
What effect does salt pumping in the ascending loop of Henle have on the medulla?
It makes the medulla hypertonic and establishes a steep water-potential gradient.
What substances are secreted from peritubular capillaries into the distal convoluted tubule?
Creatinine, hydrogen ions, ammonia, sodium ions, potassium ions, bicarbonate ions, and drugs like penicillin.
Where does urine collect before emptying into the renal pelvis?
In the collecting ducts.
Through which structure does urine pass from the renal pelvis to the bladder?
Through a ureter.
Which tube releases urine from the bladder during urination?
The urethra.
What are the main components of urine?
Urea, excess water, and excess salts.
Should useful substances be excreted in urine?
No, useful substances should not be excreted in urine.
What happens when blood pH is low due to high hydrogen-ion concentration?
Hydrogen ions move from peritubular capillaries into the distal convoluted tubule.
Where do hydrogen ions move during renal pH regulation when blood pH is low?
Into the distal convoluted tubule from peritubular capillaries.
What is the blood pH target after hydrogen ions move into the distal convoluted tubule?
Blood pH returns toward 7.4.
What is osmoregulation?
The homeostatic control of water levels in blood and tissue fluid.
Where is ADH produced and secreted?
Produced by the hypothalamus and secreted by the pituitary gland.
What effect does ADH have on kidney tubules?
It increases water permeability of distal tubules and collecting ducts.
How does increased ADH affect urine during dehydration?
More water is reabsorbed, producing smaller volume of concentrated urine.
How does reduced ADH affect urine during overhydration?
Less water is reabsorbed, producing more dilute urine.
What triggers aldosterone release?
Low blood sodium levels.
What does aldosterone do in the kidneys?
Stimulates sodium reabsorption and reduces sodium excretion.
What effect do alcohol and caffeine have on urination?
They act as diuretics that increase urination and water loss.
Test your knowledge with 22 questions on Human Excretion and Homeostasis.
1. Regarding excretion and waste products, which statements are correct?
2. Concerning the distinction between excretion and secretion, select the correct statements:
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