Water is an essential nutrient which is needed by every part of the body and is taken in through the process of digestion to aid the metabolic process. The colon absorbs most of the water from the faeces in order to conserve mositure in the body.

Revision summary of the urinary system 305

Key words associated with the urinary system



collecting duct

renal artery

Bowman's capsule

renal pelvis

renal vein

proximal convoluted






loop of Henle

urinary bladder


distal convoluted tubule


Revision summary of the urinary system

• The organs that contribute to the elimination of wastes in the body are the kidneys, lungs, skin and the digestive system.

• The organs of the urinary system are the kidneys, ureters, urinary bladder and urethra.

• The kidneys are bean-shaped organs lying on the posterior wall of the abdomen.

• The kidney has two main parts - the outer cortex where fluid is filtered from blood and the inner medulla which is the area where some materials are selectively reabsorbed back into the bloodstream.

• The cortex and the medulla contain tiny blood filtration units called nephrons.

• Urine is produced by three processes — filtration, selective reabsorption and collection.

• Blood to be processed enters the kidneys via the renal artery.

• Filtration takes place inside a network of capillaries in the nephron called the glomerulus.

• The sac encasing the glomerulus is called the Bowman's capsule.

• The filtered liquid then continues through a series of twisted tubes called the convoluted tubules, to the loop of Henle and the distal convoluted tubule before passing to the collecting duct and to the renal pelvis.

• The composition of the filtered liquid alters as it flows through the convoluted tubules.

• Some substances in the filtrate like glucose, amino acids, mineral salts and vitamins are reabsorbed back into the bloodstream via the renal vein.

• From the distal convoluted tubule the filtrate then flows into the collecting duct (as urine) and passes to the pelvis of the kidney to be passed to the ureter and bladder.

• The composition of urine is 96 per cent water, 2 per cent urea and 2 per cent other substances (uric acid, creatinine, sodium, potassium, phosphates, chlorides, sulphates, excess vitamins and drug residues).

• Functions of the kidneys include filtration of impurities and metabolic waste from blood, regulation of water and salt balance, formation of urine and regulation of blood pressure and volume.

• The ureters are muscular tubes that transport urine from the pelvis of the kidney to the urinary bladder.

• The urinary bladder is a pear-shaped sac which lies in the pelvic cavity behind the symphysis pubis.

• It functions as a storage organ for urine.

• The urethra is a canal which extends from the neck of the bladder to the outside of the body.

• The urethra serves as a tube through which urine is discharged from the bladder to the exterior and as a conducting channel for semen in men.

The urinary system Multiple-choice questions

1 The function of the kidneys is the:

a filtering of impurities from the blood b regulation of water and salt balance c formation of urine d all of the above

2 Which of the following is not considered an excretory organ?

a muscular system b digestive system c respiratory system d skin

3 Blood is filtered inside what section of the kidney?

a Bowman's capsule b loop of Henle c glomerulus d proximal convoluted tubule

4 The blood filtration unit inside a kidney is known as the:

a hilus b medulla c nephron d renal pyramid

5 The hormone responsible for controlling water reabsorption in the kidneys is:

a insulin b oxytocin c anti-diuretic hormone (ADH) d adrenocorticotropic hormone (ACTH)

6 The function of the ureter is to: a store urine b filter impurities c propel urine from the bladder to the exterior d propel urine from the kidneys to the bladder

7 The bladder is situated:

a in the pelvic cavity behind the symphysis pubis b in the abdominal cavity behind the intestines c on the posterior of the abdominal cavity d behind the urethra

8 The condition cystitis commonly affects females as: a women tend to have a weaker bladder than men b women have a shorter urethra c women have smaller kidneys d all of the above

9 Which of the following factors does not affect fluid balance?

a diet b body temperature c time of day d blood pressure

10 Which of the following also serves as a conducting channel for semen in the male?

a ureter b urethra c bladder d penis

11 Inside the kidney, the renal artery splits into a network of capillaries called the:

a afferent arteriole b glomerulus c efferent arteriole d hilus

12 The part of the kidney where the fluid is filtered from blood is the:

a medulla b cortex c hilus d renal pyramid

13 The composition of the filtered liquid alters as it flows through the:

a convoluted tubules b glomerulus c renal pelvis d collecting duct

14 As well as being lost through the kidneys as urine, water is also lost from the body through:

a faeces b skin c lungs d all of the above

15 Which muscle contracts to allow micturition? a detrusor b external urethral sphincter c internal urethral sphincter d anal sphincter

16 You are feeling dehydrated due to failing to drink enough fluids. How do your kidneys respond?

a release aldosterone b increase urine output c release ADH d inhibit the release of ADH

17 Kidney stones may be deposited in: a renal pelvis b ureter c bladder d all of the above

18 Which of the following best describes the position of the kidneys on the posterior of the abdomen?

a between 12th thoracic and 3rd lumbar vertebrae b between 10th thoracic and 5th lumbar vertebrae c between 12th thoracic and 5th lumbar vertebrae d between 10th thoracic and 3rd lumbar vertebrae

19 Which vessels drain the filtered blood away from the kidneys?

a renal arteries b renal veins c hepatic arteries d hepatic veins

20 Nephrons are approximately: a 2 to 4 cm long b 12 to 14 cm long c 5 to 10 cm long d 15 to 20 cm long

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