Flashcards in 13. EXCRETION Deck (16)
What are the two excretory organs?
LUNGS- carbon dioxide
KIDNEYS- excess water, salts and urea
Excretion is the removal of the waste products of metabolic reactions , toxic materials and substances in excess of requirements
Why should carbon-dioxide and urea be excreted?
Carbon dioxide must be excreted as it dissolves in water easily to form an acidic solution which can lower the pH of cells. This can reduce the activity of enzymes in the body which are essential for controlling the rate of metabolic reactions
Urea is also toxic to the body in higher concentrations and so must be excreted
the removal of the nitrogen-containing part of amino acids to form urea.
What is the role of the liver in excretion?
Many digested food molecules absorbed into the blood in the small intestine are carried to the liver for assimilation- when food molecules are converted to other molecules that the body needs
These include amino acids, which are used to build proteins such as fibrinogen, a protein found in blood plasma that is important in blood clotting
Excess amino acids absorbed in the blood that are not needed to make proteins cannot be stored, so they are broken down in a process called deamination
Enzymes in the liver split up the amino acid molecules
The part of the molecule which contains carbon is turned into glycogen and stored
The other part, which contains nitrogen, is turned into ammonia, which is highly toxic, and so is immediately converted into urea, which is less toxic
The urea dissolves in the blood and is taken to the kidney to be excreted
A small amount is also excreted in sweat
What are the factors that affect the concentration and the volume of urine and how?
1. Water intake – the more fluids drunk, the more water will be removed from the body and so a large quantity of pale yellow, dilute urine will be produced
2. Temperature – the higher the temperature the more water is lost in sweat and so less will appear in urine, meaning a smaller quantity of dark yellow, concentrated urine will be produced
3. Exercise – the more exercise done, the more water is lost in sweat and so less will appear in urine, meaning a smaller quantity of dark yellow, concentrated urine will be produced
What are the two important functions of the kidney?
1. They regulate the water content of the blood (vital for maintaining blood pressure)
2. They excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts)
Brief the process ULTAFILTRATION.
1. The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them
2. This eventually causes the smaller molecules being carried in the blood to be forced out of the capillaries and into the Bowman’s capsule, where they form what is known as the filtrate
3. This process is known as ultrafiltration
4. The substances forced out of the capillaries are: glucose, water, urea, salts
What are the components of filtrate and where are they reabsorbed at ?
water- loop of Henle and collecting duct
salts- loop of Henle
glucose- proximal convoluted
urea- not absorbed
Brief the process of selective REABSORPTION.
1. glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule- BY ACTIVE TRANSPORT
2. Reabsorption of glucose cannot take place anywhere else in the nephron as the gates that facilitate the active transport of glucose are only found in the proximal convoluted tubule
3.As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion
4.As salts are reabsorbed back into the blood, water follows by osmosis
5. Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time
What is kidney dialysis?
This is an artificial method of filtering the blood to remove toxins and excess substances
Brief how dialysis works?
1. As the dialysis fluid has no urea in it, there is a large concentration gradient – meaning that urea diffuses across the partially permeable membrane, from the blood to the dialysis fluid
2. As the dialysis fluid contains a glucose and salts concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists
4. The fluid in the machine is continually refreshed so that concentration gradients are maintained between the dialysis fluids and the blood
5. Dialysis may take 3-4 hours to complete and needs to be done several times a week
What does dialysis fluid contain?
a glucose concentration similar to a normal level in blood
a concentration of salts similar to a normal level in blood
What are the advantages of kidney transplants over dialysis ?
- the patient has much more freedom as they are not - - tied to having dialysis several times a week in one --place
- their diets can be much less restrictive than they are when on dialysis
- use of dialysis machines is very expensive and so this cost is removed
- a kidney transplant is a long-term solution whereas dialysis will only work for a limited time
What are the disadvantages of kidney transplants?
1. Donors won’t have the same antigens on cell surfaces so there will be some immune response to the new kidney.
2. his has to be suppressed by taking immunosupressant drugs for the rest of their lives – these can have long term side effects and leave the patient vulnerable to infections
3. There are not enough donors to cope with demand