#97 Structure of the kidney, the nephron

 Excretion is the removal  from organisms of toxic materials, the waste products of metabolism and substances in excess of requirements (carbon  dioxide, urea, salts…).

Common misconceptions

Remember that faeces is not an example of excretion – it is mainly undigested material that has passed through the gut, but which has not been made in the body. The only excretory materials in it are bile pigments.

The relative position of the ureters, bladder and urethra in the body

Examiner’s tip

Make sure you can label the diagram showing the relative positions of the kidneys, ureters, bladder and urethra. The spellings of the ureter and urethra are really important.

  

Structure of a kidney

The kidney has 3 main parts: the cortex, medulla, and pelvis. Leading form the pelvis is a tube, called the ureter. The ureter carries urine that the kidney has made to the bladder. 

Kidneys are made up of thousands of tiny tubules, or nephrons.  Each nephron begins in the cortex, loops down into the medulla, back into the cortex, and then goes down again through the medulla to the pelvis. In the pelvis, the nephrons join up with the ureter.

Sample question and answer

Figure above shows the human urinary system

a) Name parts X,Y and Z.                                                                 [3 marks]

b) Name the blood vessel that carries blood from the aorta to the kidneys. [1 mark]

c) Suggest two differences between the composition of the blood flowing to the kidneys and the blood flowing away from the kidneys.                       [2 marks]

Student’s answer

a) X ureta û   Y Bladder ü   Z vagina û

b) renal artery

c)1. Blood going to the kidneys contains more urea.

   2. Blood going to the kidney contains oxygen.

Examiner’s comments

The spelling of X (ureter) must be accurate because this name is so similar to urethra. 

Part Z is the urethra, not the vagina (the vagina is attached to the uterus, not the bladder).

In part (c) the second answer given does not make a comparison. If the candidate had stated ‘blood going to the kidney contains more oxygen’, this would have gained the mark.

Video: Urinary system The nephron