IGCSE Biology - Excretion in humans (13.1)

Summary

This video provides a comprehensive lesson on human excretion, covering key topics from the Cambridge IGCSE Biology syllabus. It explains the roles of the lungs, kidneys, and liver in excretion. The lungs expel carbon dioxide, while the kidneys filter blood to remove urea, excess water, and ions. The structure and function of the kidneys are explored, detailing the nephron's role in filtration and reabsorption. The liver's role in assimilating amino acids and deaminating excess amino acids into urea is also highlighted. This lesson ensures viewers understand the critical processes of excretion in the human body.

Takeaways

• 😀 The lungs excrete carbon dioxide, a byproduct of respiration, by transporting it from the bloodstream to the alveoli, where it is exhaled.
• 😀 The kidneys are responsible for excreting urea, excess water, and ions, filtering blood and removing waste before transporting it to the bladder as urine.
• 😀 The urinary system consists of the kidneys, ureters, bladder, and urethra, each playing a key role in excreting waste and regulating bodily functions.
• 😀 A nephron is the functional unit of the kidney, consisting of a glomerulus, renal capsule, renal tubule, and collecting duct, responsible for filtration and reabsorption.
• 😀 Filtration occurs when blood flows into the glomerulus, forcing out substances like water, glucose, urea, and ions, forming filtrate.
• 😀 Reabsorption takes place in the renal tubule, where necessary substances like glucose, water, and ions are returned to the bloodstream.
• 😀 The remaining filtrate, after reabsorption, forms urine, which is excreted through the ureters, stored in the bladder, and expelled via the urethra.
• 😀 The liver plays a critical role in the assimilation of amino acids, removing them from the bloodstream and using them to synthesize proteins.
• 😀 Excess amino acids are either converted to glucose or undergo deamination in the liver, forming urea as a byproduct.
• 😀 Urea is toxic and must be excreted; the liver's conversion of excess amino acids into urea ensures its safe removal through the kidneys.

Q & A

What is excretion in humans?

Excretion in humans is the removal of waste products of metabolism and substances in excess of requirements, including toxic byproducts from chemical reactions in cells.

What are the main organs involved in excretion?

The main organs involved in excretion are the lungs, kidneys, and liver.

How do the lungs contribute to excretion?

The lungs excrete carbon dioxide, a byproduct of respiration, by transporting it from the blood to the alveoli, where it is then exhaled.

What is the role of the kidneys in excretion?

The kidneys are responsible for excreting urea, excess water, and ions. They filter the blood, removing these substances and sending them to the bladder as urine.

Describe the structure of a kidney.

The kidney consists of the cortex (outer region) and the medulla (inner zone), with many tiny structures called nephrons, which are responsible for filtering blood.

What is the function of a nephron?

A nephron filters blood, removes waste products, and reabsorbs substances like glucose, water, and ions back into the blood. What remains is urine, which is excreted through the urethra.

What happens in the glomerulus of a nephron?

In the glomerulus, blood pressure forces substances out of the capillaries and into the renal capsule, forming a solution called filtrate, which contains water, glucose, urea, and ions.

What is the process of reabsorption in the nephron?

Reabsorption occurs as the filtrate moves through the renal tubule, where substances like glucose, water, and ions are returned to the blood to maintain balance.

What role does the liver play in assimilation and deamination of amino acids?

The liver removes amino acids from the bloodstream for protein synthesis. Excess amino acids are either converted to glucose or undergo deamination, where their nitrogen part is removed to form urea, which is excreted by the kidneys.

Why is it important that urea is excreted from the body?

Urea is toxic and can be harmful if allowed to accumulate in the body. The kidneys filter it out from the blood and excrete it as part of urine to prevent poisoning.