Excretory Organs: Lungs, Skin and Kidney | Biology for JAMB PDF Download

Introduction

• The excretory system plays a vital role in eliminating waste products and maintaining homeostasis in the human body.
• The main organs involved in excretion are the kidneys, lungs, and skin.
• This set of notes will focus on the excretory products produced by these organs.

Kidneys

A. Structure and Function

• The kidneys are bean-shaped organs located in the abdominal cavity.
• They are responsible for the filtration of blood and the formation of urine.
• Each kidney is made up of millions of nephrons, which are the functional units.

B. Excretory Products

Urine Formation

• The primary excretory product of the kidneys is urine.
• The process of urine formation involves three main steps: filtration, reabsorption, and secretion.
• Filtration occurs in the glomerulus, where blood is filtered to remove waste products and excess water.
• Reabsorption takes place in the renal tubules, where essential substances are reabsorbed back into the bloodstream.
• Secretion involves the selective movement of substances from the blood into the urine.

• Urine consists of water, nitrogenous waste products, electrolytes, and other dissolved substances.
• The major nitrogenous waste product in urine is urea, which is produced from the breakdown of proteins.
• Other waste products present in urine include uric acid and creatinine.
• Electrolytes such as sodium, potassium, chloride, and bicarbonate are also excreted in urine.

Lungs

A. Structure and Function

• The lungs are paired organs located in the thoracic cavity.
• Their primary function is the exchange of gases, but they also contribute to the excretory process.
• The respiratory system brings oxygen into the body and eliminates carbon dioxide as a waste product.

B. Excretory Products

• Carbon Dioxide
• Carbon dioxide (CO₂) is produced as a waste product of cellular respiration in body tissues.
• It diffuses from the cells into the bloodstream and is transported to the lungs.
• In the lungs, carbon dioxide is eliminated from the body during exhalation.

Skin

A. Structure and Function

• The skin is the largest organ of the human body, covering its external surface.
• It serves as a protective barrier and regulates body temperature.

B. Excretory Products

• Sweat
• Sweat is produced by sweat glands located in the skin.
• It contains water, salts, urea, and other metabolic waste products.
• Sweat is excreted through sweat ducts and evaporates from the skin's surface, helping to cool the body.

Summary

• The kidneys, lungs, and skin are organs involved in the excretory system.
• The kidneys excrete urine, which contains waste products such as urea, uric acid, and creatinine.
• The lungs excrete carbon dioxide as a waste product of cellular respiration.
• The skin excretes sweat, which contains water, salts, and metabolic waste products.