13. The Excretory System Flashcards
What is a difference between plants and humans in terms of the removal of waste products?
Unlike plants, humans have organs which are specialised for the removal of certain excretory products
What are 3 examples of organs which are vital for excretion?
- lungs
- kidney
- liver
What do the lungs mainly excrete?
carbon dioxide
Why are lungs a part of the excretory system?
The lungs excrete CO2 (a waste product of aerobic respiration) during exhalation
What do the kidneys mainly excrete?
excess water, salts and urea
Why are kidneys a part of the excretory system?
The kidneys excrete excess water, excess salts and urea (formed in the liver from excess amino acids) by producing urine
Excretion definition
Excretion is the removal of the waste substances of metabolic reactions (the chemical reactions that take place inside cells), toxic materials and substances in excess of requirements
Why must carbon dioxide 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
What substances are toxic to the body?
For this reason, too much carbon dioxide in the body is toxic
Urea is also toxic to the body in higher concentrations and so must be excreted
What happens to many digested food molecules once absorbed?
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)
What is an example for the use of amino acids?
Amino acids, which are used to build proteins such as fibrinogen, a protein found in blood plasma that is important in blood clotting
- What happens to excess amino acids and why?
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
- What plays a key role in deamination?
ENZYMES in the liver split up the amino acid molecules
- During deamination, what happens to the carbon present in the amino acids?
The part of the molecule which contains carbon is turned into glycogen and stored
- During deamination, what happens to the nitrogen present in the amino acids?
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
- What happens to the urea after deamination?
The urea dissolves in the blood and is taken to the kidney to be excreted
A small amount is also excreted in sweat
- What is a brief summary of deamination?
In deamination, the nitrogen-containing amino group is removed and converted into ammonia and then urea to be excreted
What is the difference between excretion and egestion? Give definitions
Excretion is the removal from the body of waste products of metabolic reactions, toxic substances and substances in excess of requirements.
Egestion is the expulsion of undigested food waste from the anus.
What are the 4 main structures involved in the urinary system?
Kidney
Ureter
Bladder
Urethra
Kidney definition
two bean-shaped organs that filter the blood
ureter defintion
Tube connecting the kidney to the bladder
Bladder definition
Organ that stores urine (excess water, salts and urea) as it is produced by the kidney
urethra definition
Tube that connects the bladder to the exterior,; where urine is released
What are two different factors to examine when looking at changes in urine?
The colour and quantity of urine produced in the body can change quickly
What are large quantities of urine associated with?
Large quantities of urine are usually pale yellow in colour because it contains a lot of water and so the urea is less concentrated
What are small quantities of urine associated with?
Small quantities of urine are usually darker yellow / orange in colour because it contains little water and so the urea is more concentrated
What are three factors which affect the concentration of urine?
- water intake
- temperature
- exercise
How does water intake affect urine?
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
How does temperature affect urine?
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
How does exercise affect urine?
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
Where are the kidneys located?
The kidneys are located in the back of the abdomen
What are the two important functions of the kidney?
They regulate the water content of the blood (vital for maintaining blood pressure)
They excrete the toxic waste products of metabolism (such as urea) and substances in excess of requirements (such as salts)
What does each kidney contain?
Each kidney contains around a million tiny structures called nephrons, also known as kidney tubules or renal tubules
What are examples of waste substances that need to be removed from the blood?
- urea
- excess hormones
- excess water
- uric acid
- excess salt/ions e.g Na+ or Cl-
- ammonia
Where does the nephron start?
The nephrons start in the cortex of the kidney
Where does the nephron loop down into? (where is it’s main body located?)
loop down into the medulla and back up to the cortex
Where do the contents of the nephron drain into?
The contents of the nephrons drain into the innermost part of the kidney and the urine collects there
Where does the collected urine flow to?
it flows into the ureter to be carried to the bladder for storage
- What is the first process which takes place in the nephron?
Ultrafiltration
- What is the glomerulus and where is it located?
Ultrafiltration
Arterioles branch off the renal artery and lead to each nephron, where they form a knot of capillaries (the glomerulus) sitting inside the cup-shaped Bowman’s capsule
- What happens to the capillaries as they get further into the glomerulus and what does this do?
Ultrafiltration
The capillaries get narrower as they get further into the glomerulus which increases the pressure on the blood moving through them (which is already at high pressure because it is coming directly from the renal artery which is connected to the aorta)
- What does this high pressure do?
Ultrafiltration
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
This process is known as ultrafiltration
- What substances are forced out the capillaries?
Ultrafiltration
The substances forced out of the capillaries are: glucose, water, urea, salts
These compose the filtrate
- What happens to the useful substances forced out the capillaries?
Ultrafiltration
Some of these are useful and will be reabsorbed back into the blood further down the nephron
Where is water reabsorbed at? (in the nephron)
loop of henle and collecting duct
Where are salts reabsorbed at? (in the nephron)
loop of henle
Where is glucose reabsorbed at? (in the nephron)
proximal (first) convoluted tubule
Where is urea reabsorbed at? (in the nephron)
NOT REABSORBED
- What is the second process that takes place in the nephron?
Selective reabsorption
- What is the first substance to be reabsorbed and where is it reabsorbed?
Reabsorption of Glucose
After the glomerular filtrate enters the Bowman’s Capsule, glucose is the first substance to be reabsorbed at the proximal (first) convoluted tubule
- By what process is glucose reabsorbed?
Reabsorption of Glucose
This takes place by active transport
- How is the nephron adapted for reabsorption of glucose?
Reabsorption of Glucose
The nephron is adapted for this by having many mitochondria to provide energy for the active transport of glucose molecules
- Can reabsorption of glucose take place anywhere? Why?
Reabsorption of Glucose
NO
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
- What is the difference of the glucose reabsorption in a normal / diabetic person’s body?
Reabsorption of Glucose
In a person with a normal blood glucose level, there are enough gates present to remove all of the glucose from the filtrate back into the blood
People with diabetes cannot control their blood glucose levels and they are often very high, meaning that not all of the glucose filtered out can be reabsorbed into the blood in the proximal convoluted tubule
- In a diabetic person, where does this excess glucose end up?
Reabsorption of Glucose
As there is nowhere else for the glucose to be reabsorbed, it continues in the filtrate and ends up in urine
- What check might a doctor do to test if a person is diabetic?
Reabsorption of Glucose
one of the first tests a doctor may do to check if someone is diabetic is to test their urine for the presence of glucose
- By what process are salts and water reabsorbed and where?
Reabsorption of water and salts
As the filtrate drips through the Loop of Henle necessary salts are reabsorbed back into the blood by diffusion
As salts are reabsorbed back into the blood, water follows by osmosis
- Apart from the loop of Henle, where is the water reabsorbed?
Reabsorption of water and salts
Water is also reabsorbed from the collecting duct in different amounts depending on how much water the body needs at that time
Why may the kidney not function?
The kidneys might not work properly for several reasons, including accidents or disease
With how many kidneys can a person survive? Why?
Humans can survive with one functioning kidney, but if both are damaged then there will quickly be a build-up of toxic wastes in the body which will be fatal if not removed
What are two treatments for kidney failure?
dialysis or transplant
- What is the basic concept of dialysis?
This is an artificial method of filtering the blood to remove toxins and excess substances
- What are patients connected to and what does this do?
dialysis
Patients are connected to a dialysis machine which acts as an artificial kidney to remove most of the urea and restore/maintain the water and salt balance of the blood
- What is done once the patient is connected to a dialysis machine?
dialysis
Unfiltered blood is taken from an artery in the arm, pumped into the dialysis machine and then returned to a vein in the arm
- What is inside the machine and how are these things separated
dialysis
Inside the machine the blood and dialysis fluid are separated by a partially permeable membrane
- In what direction does the blood and dialysis fluid flow and why?
dialysis
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? (3)
dialysis
- a glucose concentration similar to a normal level in blood
- a concentration of salts similar to a normal level in blood
- no urea
- Why is it important that dialysis fluid doesn’t have any urea in it?
dialysis
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
- Why is it important that dialysis fluid has the same glucose concentration as in normal blood in it?
dialysis
As the dialysis fluid contains a glucose concentration equal to a normal blood sugar level, this prevents the net movement of glucose across the membrane as no concentration gradient exists
- Why is it important that dialysis fluid has the same salt concentration as in normal blood in it?
dialysis
As the dialysis fluid contains a salt concentration similar to the ideal blood concentration, movement of salts across the membrane only occurs where there is an imbalance (if the blood is too low in salts, they will diffuse into the blood; if the blood is too high in salts, they will diffuse out of the blood)
- What is done to the fluid in the dialysis machine?
dialysis
The fluid in the machine is continually refreshed so that concentration gradients are maintained between the dialysis fluids and the blood
- How often must dialysis be carried out?
dialysis
Dialysis may take 3-4 hours to complete and needs to be done several times a week to prevent damage to the body from the buildup of toxic substances in the blood
- What is added to the blood before dialysis is carried out?
dialysis
An anticoagulant is added to blood before it runs through the machine to prevent the blood from clotting and slowing the flow
What is an advantage of a kidney transplant?
Kidney transplants are a better long term solution to kidney failure than dialysis; however, there are several disadvantages to kidney transplants, including:
What are 3 disadvantages of kidney transplants?
- Donors won’t have the same antigens on cell surfaces so there will be some immune response to the new kidney (risk of rejection is reduced – but not removed – by ‘tissue typing’ the donor and the recipient first)
- This has to be suppressed by taking immunosuppressant drugs for the rest of their lives – these can have long term side effects and leave the patient vulnerable to infections
- There are not enough donors to cope with demand
What are 4 advantages of kidney transplants?
- 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
