The urinary system removes urine
Definition
Urinary system
The organ system formed by the kidneys, ureters, bladder and urethra that makes, stores and removes urine.
- The urinary system consists of two kidneys, two ureters, the bladder and the urethra.
- Its route can be written as kidneys→ureters→bladder→urethra→outside the body\text{kidneys} \rightarrow \text{ureters} \rightarrow \text{bladder} \rightarrow \text{urethra} \rightarrow \text{outside the body}kidneys→ureters→bladder→urethra→outside the body.
- Each structure has a distinct position so a labelled diagram should show the kidneys above the bladder and one ureter joining each kidney to the bladder.
Kidneys receive and filter blood
Definition
Kidney
An organ that filters the blood, removes urea and regulates the water and ion content of the blood by forming urine.
- Each kidney is a bean-shaped organ supplied by a renal artery and drained by a renal vein.
- The renal artery carries blood containing urea, water, ions, glucose and other dissolved substances into the kidney.
- The renal vein carries blood away after the kidney has removed urea and adjusted water and ion contents.
- Urine leaves separately through the ureter rather than through a blood vessel.
Ureters carry urine to the bladder
Definition
Ureter
A tube that carries urine from a kidney to the bladder.
- A ureter is a tube that carries urine from one kidney to the bladder.
- There are two ureters because each kidney has its own connection to the bladder.
- The ureters do not carry blood and they do not carry urine directly out of the body.
The bladder stores urine
Definition
Bladder
A muscular organ that stores urine before it leaves the body.
- The bladder is a muscular sac that stores urine until urination.
- Storage separates continuous urine production by the kidneys from periodic removal from the body.
- The bladder is not a filter because filtration and urine formation occur in the kidneys.
The urethra leads outside
Definition
Urethra
The tube that carries urine from the bladder to the outside of the body.
- The urethra is the single tube that carries urine from the bladder to the outside of the body.
- Ureter and urethra have similar names but different connections and functions.
Common Mistake
A ureter connects a kidney to the bladder, while the urethra connects the bladder to the outside.
Blood and urine follow different routes
Definition
Renal artery
The blood vessel that carries blood containing urea and other dissolved substances to a kidney.
- Blood enters through the renal artery and leaves through the renal vein.
- Urine leaves through a ureter and then passes through the bladder and urethra.
- The two routes meet inside the kidney because substances are removed from blood to form urine without blood itself entering the ureter.
Example
Tracing a urea molecule
- Arrival: a urea molecule reaches a kidney in the blood carried by the renal artery.
- Removal: the kidney transfers the urea from the blood into the forming urine.
- Urine route: the molecule passes through a ureter, is stored in the bladder and leaves through the urethra.
- Filtered blood: blood with less urea leaves the kidney through the renal vein.
Diagram labels need exact connections
Definition
Urine
The liquid formed by the kidneys that contains urea, excess water and excess mineral ions.
- Urine is the liquid formed by the kidneys that contains urea, excess water and excess mineral ions.
- A correct diagram distinguishes the two ureters from the one urethra and keeps the blood vessels separate from the urine pathway.
- A label line should end on the named structure rather than the space beside it.
Exam technique
Describing the urinary system
- Name every main structure: kidneys, ureters, bladder and urethra.
- Use carries and stores accurately: ureters carry urine, the bladder stores it and the urethra carries it outside.
- Separate the blood supply: the renal artery enters a kidney and the renal vein leaves it.
- Check the common swap: ureter is kidney to bladder, while urethra is bladder to outside.
Self review
- Which structures form the urinary system?
- What is the route taken by urine?
- How do the ureter and urethra differ?
- Which vessels carry blood into and away from a kidney?
- Which organ stores urine?
