Hi everyone, welcome to IGCSE Study Buddy where you can revise biology topics from the Cambridge IGCSE syllabus. If you're enjoying this video so far, please don't forget to hit the like button and subscribe to my channel. This video summarizes topic 13, excretion in humans. Our body produces waste products during metabolic reactions or sometimes the body may have excess unnecessary substances.
Excretion is the process of removing toxic materials, the waste products of metabolism and substances in excess of requirements in the body. This is an important process. that balances all the body systems and prevents damage. Some of the organs involved in the removal of these waste substances are lungs and kidneys. The liver also plays an important role in excretion.
Let's talk about the lungs first. Carbon dioxide is excreted through the lungs. Carbon dioxide is a waste product produced in cells during respiration. The blood carries this waste product to the lungs from where it is excreted out of the body.
The kidneys excrete urea and excess water and ions from the body through urine. Urea is toxic to the body in higher concentrations and must be excreted. These are the parts of the urinary system in humans. These are the kidneys.
The blood is filtered here. These are the ureters, the tubes which connect the kidneys to the bladder. This is the bladder where urine is stored.
And this is the urethra, the tube from where urine flows out of the body. It is very easy to get confused between the names ureter and urethra. So make sure to learn these carefully.
You should also know the structure of a human kidney. This is the cortex and this is the medulla. Each kidney contains around a million tiny structures called nephrons. Nephrons are located between the cortex and medulla and this is where urine is produced. So this is a nephron.
This is the glomerulus. This is called the Bowman's capsule. This is the loop of Henle.
This is the proximal convoluted tubule. This is the distal convoluted tubule. And this is the collecting duct.
Arterials from the renal artery form a knot of capillaries called the glomerulus which sits inside the cup-shaped structure of the nephron called Bowman's capsule. The blood pressure inside the glomerulus is high and this forces out smaller molecules from the blood into the Bowman's capsule. The substances forced out of the capillaries are water, glucose, urea and ions. This process is known as ultrafiltration. Some of the filtrate or substances that were forced out of the glomerulus will be reabsorbed back into the blood further down the nephron since they are useful.
This is called selective reabsorption. As the filtrate moves along the nephron, some of the filtrate is reabsorbed back into the blood. The nephron reabsorbs all of the glucose, some of the ions and most of the water back into the blood.
None of the urea is reabsorbed. This process is known as selective reabsorption. Details of these processes are not required in the syllabus. What's left of the filtrate forms urine containing urea, excess water and excess ions. Next, let's learn how the liver plays an important role in excretion.
Assimilation is when digested food molecules are converted to other molecules that the body will use. For example, amino acids are used to build new proteins. Assimilation takes place in the liver. When the liver has excess amino acids that are not needed to make proteins, it cannot be stored.
Therefore, it is broken down in a process called deamination. Deamination is the removal of the nitrogen-containing part of amino acids to form urea. It forms ammonia first and then urea.
Therefore, urea is formed in the liver from excess amino acids. The urea dissolves in the blood and is taken to the kidney to be excreted. It is very important for urea to be excreted from the body since it is very toxic to the body in high levels.
A buildup of toxins could cause harm to the organism. So that concludes chapter 13, excretion in humans. Hope this video helped you. Thank you for watching and please don't forget to subscribe to IGCSE Study Buddy for more biology revision videos. Bye-bye.