CAIE Biology IGCSE Excretion in Humans Notes PDF

CAIE Biology IGCSE 13: Excretion in Humans Notes (Content in bold is for Extended students only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND...

CAIE Biology IGCSE 13: Excretion in Humans Notes (Content in bold is for Extended students only) This work by PMT Education is licensed under https://bit.ly/pmt-cc https://bit.ly/pmt-edu-cc CC BY-NC-ND 4.0 https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  Excretion in Humans Waste products: Urea - urea is formed in the liver as a result of an excess of amino acids. Amino acids cannot be stored in the body, unlike glucose and other nutrients, thus excess amino acids that cannot be converted to proteins and used in the body are removed from the body in a process called de-amination. De-amination takes place in the liver and involves the removal of the nitrogen-containing section of the amino acids. This forms urea, which is then filtered from the blood by the kidney and excreted from the body as urine. Carbon dioxide - Carbon dioxide is a waste product produced in cells during respiration; carbon dioxide exits cells and is dissolved in the blood, where it is carried to the lungs to be excreted. Excess water and ions - Filtered from the blood by the kidney and excreted as urine. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc  The Kidney The kidney’s role is to filter waste and excess substances from the blood to be excreted from the body as urine. It is important for these substances to be filtered out of the blood, as a build-up of toxins could cause harm to the organism. The renal system: Blood enters the kidney through the renal artery and exits through the renal vein. Cortex - the outer region of the kidney; the cortex contains nephrons. Nephron - the nephron is the functional unit of the kidney. It contains the glomerulus, which is where the blood is filtered and glucose, urea, water and salts are removed. Medulla - the inner region of the kidney. Ureter - tubes that transport urine from the kidneys to the bladder, where it is stored before being excreted from the body. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc Structure and function of a nephron: The kidney contains millions of functional units called nephrons. The cortex is the outermost area of the kidney. The medulla is the inner area of the kidney. Blood is transported to the kidney through the renal artery. The glomerulus is located at the beginning of the nephron and is surrounded by many capillaries branching from the renal artery. Blood enters the glomerulus, where substances such as glucose, water, urea and ions are filtered out. Along the nephron, useful substances are reabsorbed back into the blood. All of the glucose and some of the ions are reabsorbed. The tubule also reabsorbs most of the water back into the capillaries filled with blood. This blood returns to the heart via the renal vein. The remaining fluid in the nephron mostly consists of excess water which was not filtered out or reabsorbed into the blood. It also consists of urea and excess ions. This forms urine. Urea is toxic to the body at higher concentrations. Through excretion, urea is removed which prevents it from reaching toxic levels in the body. https://bit.ly/pmt-cc https://bit.ly/pmt-edu https://bit.ly/pmt-cc