How the Bowel Works

肠道是我们消化系统的一部分,它的作用是消化我们吃下的食物,把有益的和营养物质吸收到我们的血液中,然后处理和排出身体不能利用的废物。

The digestive system works by pushing food through the intestines which usually takes between 24 to 72 hours. Muscular contractions squeeze (peristalsis) the food through the different sections of the intestine. These different sections are separated by bands of muscles, or sphincters, which act as valves.

The passage of food from one area of the intestines to another is coordinated so that food stays in a specific area for long enough for the gut to do a particular job – absorb fluids and nutrients, or process and expel waste.

Digestive System Diagram
How the Bowel Works: Diagram of the Digestive System

The small bowel (small intestine)

The Bowels And Digestive System Small Bowel

The small bowel (or small intestine) is around 6 – 8 m long and roughly 2cm wide.

There are 3 parts of the small bowel (small intestine): the duodenum, the jejunum and the ileum.

Food passes from the stomach into the duodenum, which is the tube that leads from the stomach into the intestines. The food then passes through the jejunum and ileum before going to the large bowel (colon). The small bowel (small intestine) absorbs nutrients and much of the liquid from foods. At the point where food is passed from the small bowel into the large bowel (colon) it is of a ‘porridge like’ consistency.

The Large Bowel (Colon – large intestine)

The Bowels And Digestive System Large Bowel

大肠(也被称为结肠,或大肠),从小肠的最后一部分(小肠)开始,一直到直肠。大肠(结肠)长约2米,宽6-7厘米。

这个肌肉管由升结肠、横结肠和降结肠组成,降结肠止于直肠和肛门。结肠最重要的工作是储存、处理和处理废物。结肠也会吸收一些营养和水分。这一过程的关键是结肠中成百上千的细菌——有“好”的也有“坏”的——它们共同构成了肠道菌群。直肠可以储存废物,但大多数时候它是空的。废物从肛门排出。

The rectum and muscles

一旦肠道完成了它的工作并从食物中吸收营养,废物就会到达直肠,直肠会伸展,触发大脑的信息,告诉它肠道已经满了,需要清空。如果盆底肌肉强健,可以确保肛门一直闭合,直到上厕所的时候。

The rectum and anus

After food has travelled along the gut, it has become digested and the nutrients and fluids absorbed; the waste is then expelled through the rectum and anus.

直肠和肛管上部有丰富的神经供应。当直肠充盈时,神经会感觉到充盈,然后通知大脑这是由于气体还是粪便。

When we need to go to the toilet, the brain tells the anal sphincter muscles, via the nerves, to relax. As the muscles relax, the anus opens and the rectum empties. In some neurological and spinal conditions the brain cannot tell whether the bowel is full of waste (faeces) or just wind. This can lead to accidental leakage.

Anal sphincters

女性的肛管约3 - 4厘米长,男性有时稍长。内括约肌和外括约肌形成两个同心环,沿肛管的长度排列。

The internal anal sphincter (IAS) is made of smooth muscle and we do not have voluntary control of this muscle. It works automatically to keep the anus closed until we are ready to have a bowel movement.

The external anal sphincter (EAS) is made of striated muscle (the same as the pelvic floor muscles); we do have voluntary control over the EAS – allowing us to hold on if we are aware of wind or diarrhoea.

The pelvic floor muscle

The pelvic floor muscles are layers of muscle stretched like a sheet from the pubic bone in the front, to the bottom of the backbone (coccyx). There are 3 openings through the pelvic floor in women and 2 in men -the anus (back passage), the vagina in women (birth canal) and the urethra (bladder outlet). The muscles support these 3 openings, but if they are weakened or not in good condition they cannot support the openings effectively.

An important part of the pelvic floor muscle regarding bowel control is the deepest layer called Levator Ani – which directly translated from Latin means ‘lift the anus’. One of the muscle groups within levator ani is the puborectalis. This muscle forms a supportive strap around the junction between the rectum and the anal canal and helps to keep us in control of our bowels by forming a flap like valve, which prevents stool passing too easily into the anal canal.

The sacral nerves

大脑通过向盆底肌肉、括约肌和尿道发送电信号来告诉肠道该做什么。

The commands from the brain to the bowel (colon) are sent as electrical impulses and are carried by a system of special fibres called nerves.

These signals start in the brain and go to the spinal cord and continue to the nerves located in the sacral area of the back.

Some of these sacral nerves go to the rectum, levator ani muscle, and external sphincter muscles, controlling their activities.

两根对肠道功能至关重要的骶神经是阴部神经和盆腔内脏神经。

Through a series of reflexes and signals the nerves in the bowel is coordinated with the pelvic floor muscles and anal sphincters in order to store bowel contents until there is an appropriate place to go to the toilet and then to allow complete bowel emptying once on the toilet.

This coordination ensures that the sphincters remain closed, opening only during defecation. So, when the rectum fills, and the pressure inside it increases, the nerves sense the pressure and tell the brain about it. The brain then sends signals via the nerves to keep the external sphincter closed. Normally, this prevents leakage and is called the guarding reflex.

When you need to go to the toilet, the brain tells the nerves to signal the rectum to empty, and relax the muscles surrounding the anus. The rectum empties and stool is expelled.

Sensory signals

神经通路还与传递感觉信号的纤维共享,比如疼痛或饱腹感。源自盆腔的疼痛沿着这些通道传递到骶区,沿着脊髓再回到大脑。

The same happens as the rectum fills. This sensation of filling is registered by the nerves, which transmit the information to the brain.

The nerves can also tell the brain whether it’s gas or stool that’s filling the rectum.

For thebowel to function and work properly, and torelieve constipation, you need:

  • 直肠和肛门的神经会向你的大脑发送正确的信息,这样当粪便或气体到达直肠时,你就能感觉到,并将信息传递给你想要坚持的肌肉。在某些神经系统和脊柱疾病中,这些细胞可能不能正常工作,有时在分娩时受损。
  • The internal and external anal sphincters need to be working properly.
  • 大便不能太软或太松,使括约肌能够承受,但也不能太硬,使括约肌难以通过。
  • You need to be able to get to and onto a toilet and to be able to hold on until the correct place is reached.