Excretion in humans

The lungs excrete carbon dioxide (CO2), a waste product of aerobic respiration. This is achieved through gas exchange in the alveoli during exhalation, where CO2 diffuses from the blood into the lungs and is expelled.

The kidneys are responsible for excreting urea, excess water, and excess ions from the body. They filter blood and produce urine containing these waste products.

The urinary system consists of the kidneys, ureters, bladder, and urethra. The kidneys filter blood to produce urine, which travels through the ureters to the bladder for storage, and is then expelled through the urethra.

The two main regions of the kidney are the cortex (outer region) and the medulla (inner region). These regions contain different structures and perform different functions in filtering blood and producing urine.

The nephron is the functional unit of the kidney, responsible for filtering blood and forming urine. Each kidney contains millions of nephrons that work together to maintain homeostasis in the body.

The glomerulus filters blood, allowing water, glucose, urea, and ions to pass into the nephron. This process is called ultrafiltration, and it separates small molecules from larger proteins and blood cells that remain in the blood.

The nephron tubule reabsorbs useful substances like glucose, some ions, and most of the water back into the blood. This process ensures that essential substances are not lost in the urine.

The nephron forms urine, which contains urea (a waste product of protein metabolism), excess water, and excess ions. Urine is then transported to the bladder for storage before excretion.

The liver assimilates amino acids by converting them into proteins, which are essential for building and repairing tissues. It also plays a role in synthesizing enzymes and hormones.

Urea is formed in the liver from excess amino acids. This process is a part of the urea cycle, which detoxifies ammonia produced during amino acid breakdown.

Deamination is the removal of the nitrogen-containing part (amino group) of amino acids. This process forms ammonia, which is then converted to urea in the liver, thus reducing its toxicity.

Excretion is important because urea is toxic and can damage cells if it accumulates in the body. Removing urea through urine helps maintain a stable internal environment and prevents harmful effects.