2i Excretion Flashcards
What is excretion?
Removal of waste (often toxic) substances that have been produced from chemical reactions inside the body, such as carbon dioxide and urea in animals - metabolic reactions
What is egestion?
The removal of undigested material from the body (faeces) through the anus
What is metabolic reactions?
Getting rid of the waste products produced by the body’s metabolic reactions
What do animals excrete?
Carbon Dioxide - Product in respiration removed by the lungs
Urea - produced from excess amino acids broken down in the liver. It is removed by the kidneys
Sweat - removed through the skin
What do plants excrete?
Plants need to excrete excess carbon dioxide and oxygen
What are the two stages of creating urine?
Stage 1 - Ultrafiltration - filtering all small molecules out of the blood
Stage 2 - Selective Reabsorption - many substances that the body needs to keep are put back into the blood. Only the urea, excess water and mineral ions remain to form urine
What is ultrafiltration?
Ultrafiltration is filtration using pressure. The walls of the Bowman’s capsule and glomerulus are only one cell thick. Blood enters the glomerulus from the renal artery. The blood vessel will narrow which increases blood pressure. The pressure of blood inside the glomerulus squeezes many small molecules out from the blood and into the capsule. These molecules are water, glucose, mineral ions (eg. sodium and chloride), hormones, vitamins, urea and amino acids, which form the glomerular filtrate. Large molecules eg. blood proteins and blood cells (platelets) are too big to be filtered so they stay inside the blood.
What is selective Reabsorption?
Selective Reabsorption takes place in the proximal convoluted tubule. Some of the substances are reabsorbed from the filtrate back into the blood in the capillary that runs close by. Some substances are reabsorbed more than others, so it is called selective reabsorption. All glucose and amino acids and most of the sodium ions are reabsorbed back into the blood by active transport. These substances are very important in the body, so it is essential that they are not lost in the urine. A lot of water is also reabsorbed here by osmosis, because the concentration of water molecules is higher in the filtrate than the blood.
What is homeostasis?
Controlling your internal environment:
- Regulating your body temperature
- Controlling water potential
What is osmoregulation?
Regulating water potential in your body. Happens in the kidneys. Control of water potential in the blood
What is thermoregulation?
Controlling the temperature of the body
What is osmoregulation controlled by?
Osmoregulation is controlled by a specific hormone - ADH
What are hormones?
- Can help you grow
- Chemical messengers
- Change how the second part of the body works
- Some hormones can affect dopamine
- Mostly made from proteins
- Affect different parts of the body from the place they are releases
- Released from glands eg. pancreas
Describe the process of osmoregulation
The loss of water from the body means that the concentration of the blood increases. This is detected by the special cells in the hypothalamus located in the brain. This causes the pituitary gland to release more ADH. ADH travels to the kidney in the bloodstream. ADH causes the collecting ducts to become more permeable to water. More water is reabsorbed into the blood, making the urine more concentrated.
What are the consequences of kidney damage or disease?
The kidney is responsible for the removal of waste products from the blood. Damage from accidents or disease can lead to a build-up of poisonous wastes in the body. Humans can survive with one kidney, but for people who suffer from total kidney failure this would be fatal if not treated. Treatment is available for kidney failure and can be by organ transplant or by using kidney dialysis.
How does dialysis work?
Unfiltered blood that is high in urea is taken from a blood vessel in the arm, mixed with blood thinners or an anticoagulant to prevent clotting, and pumped into the dialysis machine. Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane the blood flows in the opposite direction to dialysis fluid, allowing exchange to occur between the two where a concentration gradient exists.
What does dialysis fluid contain?
- Glucose concentration that is similar to that of a normal level of blood
- A concentration of ions similar to that found in normal blood plasma
- No urea
What are the advantages of Dialysis?
Kidney dialysis allows a person with kidney failure to maintain their health.
The overall effect of this is that the blood leaving the machine and returning into the patient’s arm will have:
- greatly reduced levels of urea – it is ‘cleaned blood’
- no overall change in blood glucose levels
- the correct water and ion balance maintained or restored (with only excess ions removed)
What are the disadvantages of Dialysis?
Kidney dialysis requires highly specialised and expensive machinery. The patient must be connected to this machinery 2-3 times a week for periods (on average) of between 4-6 hours at a time. This is time consuming and restrictive, as this mainly happens in hospitals.
As the filtration only works when they are connected, kidney patients must monitor their diet carefully in between dialysis sessions. They need to avoid eating foods with a high salt content or a high protein content as excess amino acids are broken down into urea. This again can be difficult to control and monitor, but will help maintain the health of the patient.
Finally, dialysis will only work for a limited amount of time before a transplant is needed, and sadly many patients will die before a suitable one is found.
What is a kidney transplant?
Kidney transplantation is an alternative method for treating kidney failure and can save a patient’s life. This procedure involves implanting a kidney from an organ donor into the patient’s body to replace the damaged kidney. This is better than using a restrictive dialysis machine, as the recipient can lead a normal life afterwards.
What are the disadvantages of kidney transplant?
Differences in the antigens of the donor kidney cells and those of the patient receiving the transplant would mean that the patient’s immune system would quickly form antibodies against the kidney cell antigens, and would ultimately destroy the kidney. This is known as organ rejection. This is potentially very harmful for the patient.
What are the two precautions that can be taken to reduce organ rejection?
1) Tissue typing - a kidney is given to patients who have antigens that are very similar to the antigens of the donor kidney. This can lead to long waits for transplants while compatible donors become available - during which time patients must undergo dialysis, and in some cases they will die before a match is found.
2) Immuno-suppressant drugs – these drugs must be taken by transplant patients for the rest of their lives. They suppress the immune system, greatly reducing the immune response against the donor kidney. The negative effect of this is that it also suppresses the immune response against pathogens which enter the body, increasing the risk of infections.
Even with these two precautions most people will only survive for an extra 8-9 years with that kidney so they might need a further transplant or return to dialysis.
