EXCRETION Part 1

Dwayne

EXCRETION

Egestion is the passing out of undigested food through faeces.

Excretion is the passing out of metabolic waste. Metabolic waste is waste that was made in the body:

  • Carbon dioxide
  • Sweat
  • Urine

 

The EXCRETORY ORGANS are:

(1)   Lungs – CO2

(2)   Skin – Sweat

(3)   Kidneys – Urine

 

The EXCRETORY PRODUCTS are:

(1)   CO2 

(2)   Urea

 

Carbon dioxide is made in the mitochondria of all cells during respiration. Carbon dioxide leaves the body when we breathe out.

 

Urea is made in the liver from excess proteins. Urea is excreted mainly through the kidneys through urine. Some urea is also lost in sweat. Sweat and Urine both contain three substances: water, salt, urea.

 

Urine = water + urea + salt                             Sweat = water + urea + salt

 

The KIDNEYS

There are two kidneys located in the abdomen. The kidneys have two functions:

(1)   To remove toxic waste – urea

(2)   To control the amount of water in the blood (osmoregulation)

 

The kidney receives blood from the renal artery. The kidney contains thousands of nephrons that filter/ strain/ clean the blood to remove toxic substances. A long tube called the ureter carries urine (containing waste) from the kidney to the bladder.

 

HOW THE KIDNEY EXCRETES UREA

The renal artery brings blood to the kidney. The blood then passes through smaller arteries inside the kidney. Each smaller artery leads to a nephron/ tubule. Each nephron is approximately 12-14mm in length. Each kidney has approximately 1.5 million nephrons. The nephrons/ tubules are the exact place where the blood is cleaned.

 

The KIDNEY TUBULE/ NEPHRON has five main parts:

  • The Bowman’s Capsule
  • The 1st Convolution/ 1st Coiled Tubule
  • The Loop of Henle
  • The 2nd Convolution/ 2nd Coiled Tubule
  • The Collecting Duct

 

The BOWMAN’S CAPSULE

Very small molecules such as water, salt, glucose, urea, and amino acids pass out of the blood and enter the tubule/ nephron. These small molecules now form a filtrate as they pass through the nephron.

 

The GLOMERULUS

This is the cluster of blood vessels inside the Bowman’s Capsule. Ultra-filtration takes place here. Small particles leave the blood and enter the nephron.

 

The FIRST COILED (CONVOLUTED) TUBULE

There are a lot of microvilli which provide a large surface area for absorption. Here useful substances are reabsorbed. These include: Glucose, amino acids, some water, and some salt. These go back into the blood to be used by the body.

 

The LOOP OF HENLE

Here water is reabsorbed into the blood. The Loop of Henle is long so an adequate amount of water can be reabsorbed.

 

The SECOND COILED (CONVOLUTED) TUBULE

If the body still does not have enough water, water will be reabsorbed here. The body gets rid of ammonium ions and some drugs from the blood by releasing them into this tubule.

 

The COLLECTING DUCT

This is where the liquid (urine) is collected. Urine contains water, salt, and urea. It has no glucose (sugar). If the body needs more water, it will be reabsorbed here. From the collecting duct, the urine travels through the ureter to the bladder.

 

The BLADDER

The bladder is a muscular sac that holds between 600 and 800 cm3 of urine. A sphincter muscle at the opening of the urethra allows us to control the opening of the bladder . Urea (Urine) goes from:

 

 

Kidney → ureter→ bladder→ urethra

 

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