Excretion 🌱💧

Excretion is the process of removing toxic metabolic waste products from the bodies of living organisms. These waste products are called excretory products, and the organs that remove them are known as excretory organs. 🚽✨

Excretion in Mammals (e.g., Humans) 🐾👩‍⚕️

The primary excretory organs in mammals and their corresponding waste products are summarized below:

Sources of Major Excretory Products in Humans 🧬🔍

The Kidneys 🥤🏥

The kidneys are two bean-shaped organs located in the lower abdomen. They are part of the excretory (or renal) system. 🏥💖

Structure and Functions of the Renal System 🛠️🔧

• Aorta ❤️: Carries oxygenated blood from the heart to other parts of the body. 🩸
• Vena cava 💙: Carries deoxygenated blood from body organs back to the heart. ❤️
• Renal vein 🩸: Carries deoxygenated blood away from the kidneys to the vena cava. 🚶‍♂️
• Renal artery 🩸: Supplies oxygenated blood to the kidneys from the aorta. 🏃‍♀️
• Ureter 🚽: Transports urine from the kidneys to the urinary bladder. 💧
• Urinary bladder 🛁: Temporarily stores urine. ⏳
• Urethral sphincter 🔒: A ring of muscle controlling the release of urine from the bladder. 🔄
• Urethra 🚪: Passage through which urine leaves the body; in males, it also carries semen. 🍆
• Kidney 🥤: Filters blood to remove urea, excess salts, and water, forming urine. 💧

Structure and Function of a Kidney Nephron 🧪🔬

The nephron is the functional unit of the kidney and is involved in the following processes:

1. Ultrafiltration 💧🔍

Small molecules (water, salts, glucose, and urea) are filtered from the blood in the glomerulus into the Bowman’s capsule. High pressure in the glomerulus (due to the afferent end being wider than the efferent end) drives this filtration. Larger molecules like red blood cells and plasma proteins remain in the blood. The filtered liquid, called the glomerular filtrate, enters the renal tubule. 🧪

2. Selective Reabsorption 🔄💧

Useful substances (such as glucose, some water, and some salts) are reabsorbed from the filtrate back into the bloodstream in the convoluted sections of the renal tubule. Glucose is absorbed by diffusion, salts by active transport, and water by osmosis. 🌊

3. Osmoregulation 🌊⚖️

Water levels in the body are regulated in the loop of Henle. When the body is low on water, the pituitary gland secretes antidiuretic hormone (ADH), which increases water reabsorption and produces concentrated urine. When sufficient water is present, ADH secretion stops, resulting in more dilute urine. 💧

4. Secretion 🚽🗑️

Waste substances (urea, salts, and excess water) form urine, which is passed through the collecting duct and ureter to the urinary bladder for temporary storage. 🛁

Kidney Failure and Treatment ⚠️🩺

Kidney failure can occur due to poisoning, injuries, infections, or drug abuse. Treatments include:

• Kidney Transplant 🏥💖: A donor kidney is surgically implanted into the recipient. The donor kidney must be compatible to avoid tissue rejection. 🤝
• Dialysis Machine (Kidney Machine) 🩺🔄:
  • A dialysis machine uses a coiled dialysis tubule to filter the patient’s blood. The tubule’s selective permeability allows small molecules (urea, salts, and water) to diffuse into the dialysis fluid. 💧
  • Blood is drawn from the patient's arm, filtered, and then returned. Dialysis fluid flows in the opposite direction to blood (counter-current flow) to maintain a diffusion gradient and enhance the removal of waste. 🔄
  • A patient typically requires dialysis twice weekly, with each session lasting about 8 hours. ⏳🕒

Excretion in Plants 🌿🌼

Plants also produce and remove metabolic waste, which varies in form and disposal method:

• Alkaloids 🌼: Nitrogen-based compounds (e.g., morphine, quinine, and cocaine) produced by plants like opium and cinchona. 🌱
• Tannins 🌳: Red-brown compounds deposited in bark, e.g., in Acacia trees. 🌲
• Anthocyanins 🌸: Color pigments (red, blue) in petals, released when petals shed. 🌺
• Oils and Sugars 🍏: Deposited in fruits and seeds, discarded when these fall or are dispersed. 🍇
• Latex 🌱: A milky liquid excreted by plants such as Euphorbia and Ficus. 🌿
• Resins, gums, and mucilages 🌲: Sticky substances produced by some trees. 🌳
• Carbon dioxide 🌬️: Released from respiration through leaf stomata. 🌬️
• Oxygen 🌞: Released during photosynthesis. 🌼
• Water 💧: Excreted through leaf pores by a process called guttation. 💦