Chapter 13 - Excretion in humans Flashcards
What gas do the lungs excrete and why?
The lungs excrete carbon dioxide which is the waste product of aerobic respiration during exhalation. Carbon dioxide must be excreted as it dissolves in water easily to form an acidic solution which can lower the pH of cells and cause the denaturation of enzymes necessary for controlling the rate of metabolic reactions. Too much carbon dioxide in the body is toxic.
What do the kidneys excrete and why?
The kidneys excrete urea, excess water and ions which are produced in the liver from excess amino acids through the formation of urine. Urea is a toxic substance to the body in high concentrations.
What is excretion?
Excretion is the removal of waste substances of metabolic reactions, toxic materials and substances in excess of requirements.
Diagram of the excretory system
What is the kidney?
Kidney is two bean-shaped organs that filter the blood. They regulate the water content of the blood which is vital for maintaining blood pressure as well as they excrete toxic waste products of metabolism, such as urea, and substances in excess of requirements, such as salts.
What is the ureter?
Ureter is the tube connecting the kidney to the bladder.
What is the bladder?
Bladder is the organ that stores urine (excess water, salts and urea) as it is produced by the kidney.
What is the urethra?
Urethra is the tuber that connects the bladder to the exterior and where urine is released.
What is the nephron?
The nephron is a tiny structure that start in the cortex of the kidney, loop down into the medulla and back up to the cortex. The contents of the nephrons drain into the innermost part of the of the kidney and the urine collects there before it flows into the ureter to be carried to the bladded for storage.
How do the kidneys remove waste?
Through ultrafiltration and then the reabsorption of glucose
What is the process of ultrafiltration?
Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the cup shaped bowman’s capsule. The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them, which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta. This eventually causes the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate. This process is known as ultrafiltration. The substances forced out of the capillaries are glucose, water, urea and salts. Some of these are useful and will be reabsorbed back into the blood further down the nephron. Water is reabsorbed at the loop of Henle and collecting duct, salts are reabsorbed at the loop of Henle and glucose is reabsorbed at the proximal (first) convoluted.
What is the process of reabsorption of glucose?
After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule. This takes place by active transport. The nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules. Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule. In a person with a normal blood glucose level, there are enough gates present to remove all of the glucose from the filtrate back into the blood. People with diabetes cannot control their blood glucose levels, and they are often very high, meaning that not all of the glucose filtered out can be reabsorbed into the blood in the proximal convoluted tubule. As there is nowhere else for the glucose to be reabsorbed, it continues in the filtrate and ends up in the urine. This is why one of the first tests a doctor may do to check if someone is diabetic is to test their urine for the presence of glucose. As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion and active transport. As salts are reabsorbed back into the blood, water follows by osmosis. Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time. This is called selective reabsorption.
Why are digested food molecules absorbed into the blood?
Digested food molecules absorbed into the blood in the small intestine are carried to the liver for assimilation which is when food molecules are converted to other molecules that the body needs. This is done by converting amino acids into proteins.
Where is urea formed?
Urea is formed in the liver from excess amino acids.
What is deamination?
Deamination is the removal of the nitrogen containing part of amino acids to form urea.
