Excretion in Humans
1.0 What is Excretion?
Definition: Excretion is the biological process by which metabolic waste products are removed from the body of an organism.
Inside our cells, various chemical reactions (metabolism) take place. These reactions produce useful substances along with some toxic byproducts. If these wastes accumulate, they can be harmful or even fatal.
2.0 Necessity of Excretion
- Removal of Toxins: Waste products like urea and uric acid are poisonous; excretion prevents their buildup.
- Osmoregulation: It helps in maintaining the correct balance of water and mineral salts (like sodium and potassium) in the body.
- pH Balance: It helps in maintaining the constant alkalinity/acidity of the blood.
3.0 Primary Excretory Organs
While the Kidneys are the main organs of the excretory system, several other organs also assist in removing waste:
4.0 The Human Urinary System
The urinary system (also known as the renal system) is the primary system responsible for filtering blood and removing nitrogenous wastes in the form of Urine.
Components of the Urinary System:
Definition: A pair of bean-shaped, reddish-brown organs located on either side of the backbone, just above the waist.
Function: They filter the blood to remove urea, excess water, and salts to form urine.
Definition: Two narrow, muscular tubes that emerge from the notch (hilum) of each kidney.
Function: They carry urine from the kidneys down to the urinary bladder.
Definition: A muscular, sac-like organ located in the lower abdomen.
Function: It stores urine temporarily until it is expelled from the body.
Definition: A short canal leading from the urinary bladder to the outside of the body.
Function: It serves as the passage through which urine is voided (released).
5.0 Internal Anatomy of the Kidney
A longitudinal section (L.S.) of the kidney shows three distinct regions:
- 🌑 Renal Cortex: The outermost, dark red region of the kidney.
- 🌑 Renal Medulla: The inner lighter region, containing several cone-shaped structures called Renal Pyramids.
- 🌑 Renal Pelvis: The funnel-shaped central cavity where urine collects before entering the ureter.
6.0 The Nephron
Definition: A nephron is the microscopic, structural, and functional unit of the kidney. Each kidney contains approximately one million nephrons that filter the blood.
Parts of a Nephron:
- Bowman's Capsule: A cup-shaped structure that encloses a cluster of capillaries.
- Glomerulus: A network of blood capillaries within the Bowman's capsule where filtration begins.
- Renal Tubule: A long, coiled tube that reabsorbs useful substances back into the blood.
7.0 How Urine is Formed
Urine formation is a complex process occurring in two main stages:
Blood flows into the Glomerulus under high pressure. Water, glucose, urea, and salts are forced out into the Bowman's capsule, forming the Glomerular Filtrate.
(Note: Large molecules like proteins and blood cells stay in the blood.)
As the filtrate passes through the Renal Tubule, useful substances like glucose, some salts, and most of the water are reabsorbed back into the surrounding blood capillaries. The remaining liquid, containing mainly urea and waste, is Urine.
8.0 Composition of Normal Human Urine
An average adult passes about 1 to 1.8 litres of urine per day. Its composition is generally:
9.0 Common Disorders
When the kidneys or the urinary tract do not function properly, it can lead to various medical conditions:
Definition: Hard, small deposits of mineral and acid salts that form inside the kidneys.
Cause: Often caused by dehydration or high intake of certain minerals (like calcium). They can block the flow of urine and cause severe pain.
Definition: An infection in any part of the urinary system (kidneys, ureters, bladder, or urethra).
Cause: Usually caused by bacteria entering the system. Symptoms include pain during urination and frequent urge to urinate.
10.0 Kidney Failure & Dialysis
Kidney Failure: When both kidneys stop working, toxic wastes like urea build up in the blood. This condition is life-threatening.
Dialysis (Artificial Kidney):
Definition: Dialysis is a medical procedure used to filter waste products and excess water from the blood using an artificial kidney machine.
- Blood is taken out from an artery in the arm.
- It passes through the dialysis machine where wastes are removed.
- Clean blood is pumped back into the body through a vein.
11.0 Kidney Transplantation
Definition: A surgical procedure where a healthy kidney from a living or deceased donor is placed into a person whose kidneys no longer function properly.
This is often a permanent solution for end-stage kidney failure, though the patient must take medications to prevent the body from rejecting the new organ.
12.0 Keeping Your Kidneys Healthy
- 💧 Drink plenty of water to help kidneys flush out toxins.
- 🧂 Reduce salt intake to maintain healthy blood pressure.
- 🥗 Eat a balanced diet and avoid excessive protein or fatty foods.
- 🚠Avoid smoking and alcohol, which can damage blood vessels in the kidneys.
CHAPTER COMPLETED: EXCRETION IN HUMANS
From Definitions to Disorders - Full syllabus covered.