Category Human Body

Pelvic girdle

The pelvis is made up of two hip bones, one on each side. Each hip bone has three parts – the ilium, ischium, and pubis. They connect to the sacrum – the lower  part of the spine – to form a ring like shape, called the pelvic girdle.

Spine

The spine, or backbone is a column of bones that runs from the pelvis to the neck. The spine is classified into 4 distinct areas.

The cervical area consists of 7 bony parts in the neck. The thoracic spine consists of 12 bony parts in the back area. The lumbar spine consists of 5 bony segments in the lower back area; 5 sacral* bones; and 4 coccygeal* bones (the number of coccygeal bones can vary from 3 to 5). (* By adulthood, the 5 sacral vertebrae fuse to form 1 bone, and the 4 coccygeal vertebrae fuse to form 1 bone.)

Sacrum

At the base of the spine, this triangular-shaped bone connects the two hip bones. It consists of the last four or five vertebrae that by adulthood, fuse together to form a single bone. Located just above the coccyx and wedged between the right and left iliac bones (hip bones), the sacrum forms the back wall of the pelvis. The coccyx, commonly referred to as the tailbone, is the very bottom segment of the vertebral column. The right and left iliac bones are joined together in the front by the symphysis pubis.

Ilium

The largest bone in the pelvis is the ilium, or hip bone. One on each side connects the muscles used to stand and walk. The body of the ilium forms the superior part of the acetabulum (acetabular roof). Immediately above the acetabulum, the ilium expands to form the wing (or ala).

Fixed joint

These bones are held firmly together by strong ligaments. The relatively fixed joint between the sacrum and the lumbar spine is ideal for bearing the load of the upper body. At the most ventral area of the pelvis, there is a fibrocartilaginous joint in the pubic symphysis.

Pelvic cavity

The pelvic cavity is formed by three bilateral pairs of bones (pubis, ilium and ischium) and two posteriorly located bones (sacrum and coccyx). The intestines and bladder are contained here, surrounded by the protective pelvis.

Pubis

The pubis is one of the two smallest bones in the pelvis. In vertebrates, the pubic bone is the most forward-facing (ventral and anterior) of the three main bones making up the pelvis. The left and right pubic bones are each made up of three sections, a superior ramus, inferior ramus, and a body.

Pubic symphysis

This strong cartilage joint connects the two pubis bones together. It is located in front of and below the urinary bladder. In males, the suspensory ligament of the penis attaches to the pubic symphysis.

Coccyx

Below the sacrum is the Coccyx, or tailbone all that remains of the tail of our distant ancestors. Although the tailbone is considered vestigial (or no longer necessary) in the human body, it does have some function in the pelvis. For instance, the coccyx is one part of a three-part support for a person in the seated position. Weight is distributed between the bottom portions of the two hip bones (or ischium) and the tailbone, providing balance and stability when a person is seated.

Hip joint

The ball shaped top of the thighbone sits in this hollow creating the ball and socket hip joint. The adult os coxae, or hip bone, is formed by the fusion of the ilium, the ischium, and the pubis, which occurs by the end of the teenage years. The 2 hip bones form the bony pelvis, along with the sacrum and the coccyx, and are united anteriorly by the pubic symphysis.

Ischium

The lowest bone in the pelvis the ischium carries all the weight when the body is sitting down. Situated below the ilium and behind the pubis, it is one of these three bones whose fusion creates the hip. The superior portion of this bone forms approximately one third of the acetabulum.

Holes

Small holes in the bones are for nerves and blood vessels.

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The pelvis is a large bowl-shaped group of bones at the base of the abdomen. This section of the skeleton is made up of several bones fused and linked together. It surrounds and protects the soft organs inside the lower abdomen. The pelvis has many functions. It supports the intestines and bladder and the space in the middle allows waste from the intestines and bladder to leave the body In women, the pelvis supports the uterus as it expands to hold a growing baby and also provides the baby’s route out of the body during childbirth. Many muscles in the back, abdomen, and legs are anchored to the pelvis, helping to keep the body upright. The pelvis allows us to stand walk, and run without falling over.

The muscles of the pelvic floor wrap around and control the opening of your bladder and rectum. When there is an increase in abdominal pressure (for example when you cough, sneeze, laugh or jump), these muscles contract around your urethra and anus to prevent leakage. Equally as important, these muscles have to relax and lengthen to allow us to urinate or have bowel movements easily.  

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After hours of mechanical and chemical digestion, food has been reduced into chyme. As particles of food become small enough, they are passed out of the stomach at regular intervals into the small intestine, which stimulates the pancreas to release fluid containing a high concentration of bicarbonate. This fluid neutralizes the gastric juices, which can damage the lining of the intestine and result in duodenal ulcer. Other secretions from the pancreas, gallbladder, liver, and glands in the intestinal wall help in digestion.

When food particles are sufficiently reduced in size and composition, they are absorbed by the intestinal wall and transported to the bloodstream. Some food material is passed from the small intestine to the large intestine. In the large intestine, bacteria break down any proteins and starches in chyme that were not digested fully in the small intestine.

When all of the nutrients have been absorbed from chyme, the remaining waste material changes into semisolids that are called feces. The feces pass to the rectum, to be stored until ready to be discharged from the body during defecation.

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At every stage of digestion, food is pushed through the system by a powerful muscle action called peristalsis. The muscles lining the intestine contract then relax in a rhythmic, wave-like action. As the intestine walls are squeezed together, the food is forced further along the tube.

The job of your large intestine is to absorb water, minerals, and some of the remaining nutrients from your food. It will change the leftover waste into a bowel movement. This is also called stool. Your rectum stores the stool until you feel the need to have a bowel movement. Muscles of your rectum then push the stool through your anus and out of your body.

 It takes about 36 hours for food to move through the entire colon. All in all, the whole process — from the time you swallow food to the time it leaves your body as feces — takes about two to five days, depending on the individual.

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Up, across, and down

The large intestine is a wide tube that goes around the small intestine. The tube goes up. across the abdomen, then down again. It has a lumpy appearance because of the way the muscles in its wall contract.

Transverse colon

Passing just below the stomach, this is the middle part of the large intestine.  It extends between the right and left colic (splenic) flexures, spanning the right hypochondriac, epigastric and left hypochondriac regions of the abdomen. 

Ascending colon

On the right side of the abdomen, this section of the intestine rises from the caecum. The ascending colon is retroperitoneal and it is connected to the posterior abdominal wall by the Toldt’s fascia. 

Descending colon

The descending colon extends between the left colic flexure and sigmoid colon. It travels through the left hypochondriac region, left flank and left iliac fossa. This section passes down the left side of the abdomen.

lleocaecal valve

A valve stops waste flowing back into the small intestine. An ileocecal valve regulates the passage of intestinal contents from the small into the large intestine. 

Caecum

The caecum receives chyme from the small intestine. The cecum is intraperitoneal with various folds and pockets (retrocecal peritoneal recesses) surrounding it.

Appendix

The vermiform appendix is a blind lymphoid pouch located in the right iliac fossa which arises from the cecum. These two parts of the large intestine are connected by the meso-appendix. This small tube may help digestion by storing “friendly” gut bacteria.

Sigmoid colon

The S-shaped sigmoid colon travels from the left iliac fossa until the third sacral vertebra (rectosigmoid junction). The sigmoid colon contracts forcefully pushing the faeces (waste) into the rectum

Rectum

The rectum is the last section of the large intestine. The typical characteristics of the large intestine (taenia coli, haustra, epiploic appendages) change or even terminate at the rectum. The roles of the rectum include temporary storage of fecal matter and defecation.

Anus

This is where waste leaves the body as faeces. The anal canal forms the terminal part of the gastrointestinal tract. It extends from the anorectal junction to the anus.

Gut bacteria

Trillions of bacteria live in the large intestine. Most are either harmless or actively help to complete digestion by processing the remaining nutrients that could not be digested by enzymes. However, some microorganisms that enter the digestive system can cause illness.

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The large intestine is the final stage of the digestive system. It’s where most of the water, and the last few nutrients, are taken from the chyme that enters from the small intestine.

It then moves unusable waste out of the body. Most nutrients have been taken from the food before it gets to the large intestine – but there is still vital work for it to do Here, trillions of bacteria help to break the remaining food down into valuable nutrients. The large intestine is wider than the small intestine but it’s not nearly as long.

The large intestine has 3 primary functions: absorbing water and electrolytes, producing and absorbing vitamins, and forming and propelling feces toward the rectum for elimination. By the time indigestible materials have reached the colon, most nutrients and up to 90% of the water has been absorbed by the small intestine. The role of the ascending colon is to absorb the remaining water and other key nutrients from the indigestible material, solidifying it to form stool. The descending colon stores feces that will eventually be emptied into the rectum. The sigmoid colon contracts to increase the pressure inside the colon, causing the stool to move into the rectum. The rectum holds the feces awaiting elimination by defecation.

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