The urinary tract is the body's drainage system for removing urine, which is made up of waste and fluid.

Micturition

The bladder is a muscular sac, located in the pelvis. The bladder is connected to the kidneys by two tubes called ureters. Each day the kidneys filter about 170 litres of blood, from which they produce about 2 litres of urine, which flows down the ureters to the bladder.

The flow of urine in both men and women is controlled by the internal and external urethral sphincter. Control of the internal sphincter is involuntary, control of the external sphincter is voluntary.

Urine flows down the ureters and collects in the bladder. As the bladder dills it expands, and as the surface starts to stretch. Receptors in the surface send a signal to the brain to indicate that the bladder is filling, and as it approaches its maximum capacity this generates a feeling of discomfort.

Eventually the need to urinate becomes urgent and the brain sends a signal to the sphincter muscles to relax and urine is released from the bladder. The bladder empties and process is repeated.

Kidneys 

The kidneys are two bean-shaped organs that filter waste products, chemicals and unneeded fluid from the blood and produce urine. Located just below the ribcage on either side of the spine, they filter about 170 litres of blood a day, which produces 1.5 to 2 litres of urine. 

Ureters

Ureters are thin tubes of muscle that carry urine from each of the kidneys to the bladder. 

Bladder 

Located in the pelvis between the pelvic bones, the bladder is a hollow, muscular, balloon-shaped organ that expands as it fills with urine. Sitting in the bladder, the trigone is a triangle shaped smooth muscle that contains the ureteric and internal urethral orifices.

A bladder can hold around 400-600mL of urine.

The bladder empties five to eight times a day.

How often an individual needs to urinate depends on how quickly the kidneys produce the urine that fills the bladder. 

As the bladder fills it expands, and as the surface starts to stretch, receptors in the surface send a signal to the brain to indicate that the bladder is filling. As it approaches its maximum capacity this generates a feeling of discomfort. The bladder is emptied through the urethra, which is located at the bottom of the bladder.

The digestive system

Food moves down the oesophagus from the mouth and into the stomach, which it mixes with the digestive juices and enzymes. After a period of time the food passes into the duodenum where most of the chemical digestion takes places. Muscles push the semi digested food into the small intestine for further mixing.

Food is moved through the different sections of the digestive tract by a process called peristalsis, which is a series of wave-like muscle contractions. It usually takes between 24 and 72 hours for food to move through the digestive system. The sections are separated by bands of muscles, known as sphincters, which are valves that control the movement of food from one area of the digestive tract to another. It's important that the food stays in each of the sections long enough for the gut to absorb fluid and nutrients before expelling it as waste.

The small intestine (small bowel) 

The small bowel is about six to eight meters long and two centimetres wide and is comprised of three parts: 

• duodenum 
• jejunum 
• ileum. 

Food passes from the stomach through each of these three parts. The purpose of the small intestine is to absorb nutrients and much of the fluid from foods. As food moves from the small intestine to the colon it has a porridge-like consistency. 

The colon (large intestine) 

The colon, or large intestine (also known as the large bowel), starts at the final portion of the small intestine and ends at the rectum. The colon is about two meters long and six to seven centimetres wide. It is made up of the caecum, ascending, transverse, descending and sigmoid colon. 

The colon is host to a countless number of micro-organisms that support the processing and elimination of waste. It can take between 12 and 48 hours for food to make its way through the colon. 

The rectum and anus 

Once food has passed through the bowel the waste moves to the rectum which stretches, triggering a message to the brain to say that the rectum is full and needs to be emptied. The pelvic floor muscles ensure that the anus remains closed until the person is ready to open their bowels. The nerves can usually tell the brain whether it’s wind or stool that is filling the rectum. 

Bowel and bladder movements

For the bowel to function properly it needs: 

• the nerves of the rectum and anus to be sending the correct messages to the brain so that it can sense when stool or wind arrives in the rectum and can transmit messages to the muscles to hold it in 
• the internal and external anal sphincters to be working 
• stools which are not too soft or too hard.

Normal bowel function

The frequency and consistency of bowel movements will vary from person to person. Frequency averages between three times a day to three times a week, with the stool being soft and easy to pass.

Stool consistency is usually measured using the Bristol Stool Chart and ideally should be between three and four.

Lewis SJ, Heaton KW (1997) Stool form scale as a useful guide to intestinal transit time. Scandinavian Journal of Gastroenterology 32: 920–4

A good position on the toilet is when knees are higher than hips (unless recent hip surgery), leaning slightly forward and with the elbows on knees, relax and breath easily and do not strain.