Excretion

Biology - Homeostasis & Excretion - Excretion

‘Excretion is the process by which waste products of metabolism are removed from the body’

Excretion happens in both animals and plants. Plants also oxygen (a waste product of the photosynthesis reaction) and carbon dioxide (from the respiration reaction). However, most of the detail here is about excretion in animals.


Nitrogenous waste has to be excreted by all animals.This is because it cannot be stored in the body in the same way that carbohydrates and fats can. Excess proteins are the main source of nitrogenous waste, and are converted either into carbohydrates or into urine.


Humans have a special excretory system. Most of the body's waste products are removed in sweat and urine.

Urine contains:

• ·       Urea
• ·       Ammonia
• ·       Other nitrogenous waste
• ·       Potassium (not nitrogenous)
• ·       Phosphate (not nitrogenous)

Filtration happens in 3 stages:

1.     Blood from the aorta (the largest artery in the body) enters the renal artery (renal meaning to do with the kidneys). This blood is carried to the kidneys.

2.     The kidney filters out the waste products

3.     The ‘clean’ blood leaves via the renal vein and enters the vena cava (a larger vein).

The urine travels down the ureters (connecting tubes) into the bladder. At the top of the urethra, the two sets of sphincter muscles control whether the urine can flow out of the body.
The voluntary sphincter muscles can be relaxed consciously, but the upper sphincter muscles relax when the bladder is full.

The kidney has 3 important types of structure:

Ø  Cortex. The blood flows into the cortex from the renal artery. The cortex contains blood vessels that branch from there, as well as nephrons (also known as kidney tubules)

Ø  Nephrons/kidney tubules run from the cortex to the medulla. The urine is emptied from there into the pyramids.

Ø  Pyramids join to the medulla, and they take the urine from there that has been filtered by the nephrons. The urine collects in the pelvis, which leads to the ureter.

The First Anaestetics

History - Medicine through time - 18th/19th Century
In the 18th Century, surgery was very dangerous and often lethal. Patients very often died of trauma and pain or blood loss during the operation, or of infection shortly afterwards. Blood transfusions usually failed because it was not known that there were blood groups to be matched. There were no anaesthetics except for alcohol and  opium, and operations were carried out in unhygienic conditions. Many doctors in ordinary clothes would gather around an operating table while surgeons performed the operation with unclean instruments and no gloves or face-masks. Surgery in the Middle ages was grim indeed.

The discovery of Anaesthetics - a timeline

1. The first anaesthetic was the result of progress in the field of chemistry when chemist Humphrey David discovered pain could be relieved by inhaling nitrous oxide. He suggested this would be useful in the field of surgery but was ignored by the medical profession.
2. During the 1840s there were several attempts to find an effective anaesthetic and an American doctor, Crawford Long, found out ether was a useful anaesthetic. He did not announce this.
3. In 1845 an American dentist, Horace Wells, made the same connection between nitrous oxide and anaesthesia as Humphrey David. When he tried to demonstrate this he failed as he did not realise nitrous oxide did not have the same affect on everybody, including his volunteer. 
4. In 1846 William Thomas Green Morton convinced the head of surgeon of the Boston Hospital to carry out an operation using ether as an anaesthetic. The patient had a tumor removed from his neck painlessly. News of this spread quickly and use of ether as an anaesthetist soon became common and widely accepted.
5. In 1847, James Young Simpson, a professor of Midwifery at Edinburgh University, wanted to find something to relieve pain during childbirth. He found ether had a pungent smell and irritated the lungs. He discovered the effects of chloroform, which he found was easier to administer than ether. Within a month of his discovery he had used it 50 times with a 100% success rate.

Opposition to anaesthetics

Most people agreed with the use of anaesthetics, however there were certain groups who did oppose it. Some thought that the surgeons could not be trusted to give the correct dose or control the side effects, or that they didn't want to leave themselves unconscious and in the surgeon's power. Lots of Christians thought that women should have to bear pain during childbirth because it is written in the Bible, and the army considered it to be 'soft'.

There were problems that followed the use of anaesthetics which will be covered in another post. An example would be the extra confidence that painless operations gave to surgeons, which led them to delve far too deeply into the human body and expose their patients to disease and infection. As well as the problem of infection, blood loss had also yet to be conquered.