Category Zoology

The small intestine is the longest part of the digestive system. It’s where most of the digestive process takes place, releasing the nutrients in food so that they can be used to fuel the body’s cells.

By the time food reaches the small intestine, the stomach has turned it into a liquid called chyme. This chyme is squirted into the duodenum, the first part of the small intestine, along with bile from the gallbladder and enzymes from the pancreas, which break the chyme down even more. Finally, when most of the food has been broken down into simple nutrients, these pass through the walls of the small intestine and into the bloodstream. The remaining food progresses to the next stage – the large intestine.

As a person grows the small intestine increases 20 times in length from about 200 cm in a newborn to almost 6 m in an adult. The length of the small intestine is approximated by three times the length of the infant, or height of the child or adult.

The duodenum is about 25 cm (10 inches) long; the jejunum is about 2.5 m (8 feet) long and the ileum is about 3.6 m (12 feet) long.

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Ligaments are made out of connective tissue that has a lot of strong collagen fibers in it. They are found in different shapes and sizes in the body. Some look like pieces of string, others look like narrow or wide bands. There are arch-shaped ligaments, too.

Ligaments often connect two bones together, particularly in the joints: Like strong, firmly attached straps or ropes, they stabilize the joint or hold the ends of two bones together. This ensures that the bones in the joint don’t twist too much or move too far apart and become dislocated.

But there are also some ligaments that aren’t connected to bones. For instance, some make sure that internal organs are kept in place. A typical example is the womb, which is kept in the right position in the pelvis by ligaments. Ligaments may also connect two or more organs to each other. For instance, the liver, intestine and stomach are held in place by ligaments in the abdominal cavity. These ligaments often have sensitive structures like blood vessels or gland ducts running through them. The strong connective tissue in the ligaments protects these structures and prevents them from bending, twisting or tearing.

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The ossicles are situated in the middle ear and suspended by ligaments. They articulate with each other through synovial joints to form a chain across the length of the middle ear from the tympanic membrane (laterally) to the oval window (medially). The ossicles transmit mechanical vibrations of the tympanic membrane across this chain to the oval window where fluids of the inner ear will move and excite receptors. This process allows sound to be transformed into electrical signals which are then sent to the brain.  This article will explore the function of the auditory ossicles, their bony features, articulations, associated muscles, and some clinical aspects.

Their role is to mechanically amplify the vibrations of the tympanic membrane and transmit them to the cochlea where they can be interpreted as sound. They are located in the middle ear cavity and articulate with each other via two tiny synovial joints. The stapes also articulates with the oval window via the stapediovestibular joint, which is a syndesmosis 3; this joint transmits the ossicular vibrations to the endolymph in the vestibule.

Interestingly, they are the only bones in the body that do not grow after birth, and are also the smallest bones in the body (variant tiny sesamoids aside).

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Bone marrow is the spongy tissue inside some of the bones in the body, including the hip and thigh bones. Bone marrow contains immature cells, called stem cells.

Most red blood cells, platelets, and most of the white blood cells are formed in the red marrow. Yellow bone marrow produces fat, cartilage, and bone.

White blood cells survive from a few hours to a few days, platelets for about 10 days, and red blood cells for about 120 days. These cells must be constantly replaced by the bone marrow, as each blood cell has a set life expectancy.

Certain conditions may trigger additional production of blood cells. This may happen when the oxygen content of body tissues is low, if there is loss of blood or anemia, or if the number of red blood cells decreases. If these happen, the kidneys produce and release erythropoietin, a hormone that stimulates the bone marrow to produce more red blood cells.

The bone marrow also produces and releases more white blood cells in response to infections, and more platelets in response to bleeding. If a person experiences serious blood loss, yellow bone marrow can be activated and transformed into red bone marrow.

Healthy bone marrow is important for a range of systems and activities.

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The femur bone is the strongest and longest bone in the body, occupying the space of the lower limb, between the hip and knee joints.

The femur is an integral component of ambulation. A lot of the large thigh muscles arise from and insert on the various parts of the femur. Muscles that originate from the pelvis and insert on the anterior or posterior surface of the femur to facilitate flexion and extension around the hips. Muscles which arise from the femur will cross the knee joint to insert on the proximal tibia promote flexion and extension around the knee. The tables below summarize the thigh muscles and their points of origin or insertion with respect to the femur.

Important features of this bone include the head, medial and lateral condyles, patellar surface, medial and lateral epicondyles, and greater and lesser trochanters. The head is where the bone forms the hip joint with the innominate bone. The condyles are the points of articulation (connection) with the tibia, which is a lower leg bone. The patellar surface is the groove where the bone adjoins with the patella, or kneecap. The epicondyles and trochanters are all important attachment sites for various muscles.

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The hyoid bone is a ‘U’ shaped structure located in the anterior neck. It lies at the base of the mandible (approximately C3), where it acts as a site of attachment for the anterior neck muscles.

The hyoid consists of a body, two greater horns, and two lesser horns. The body forms the central quadrilateral-shaped broad segment of the hyoid. The greater horns are larger and longer than the lesser horns of the hyoid. The greater horns and lesser horns are also known as cornu majus and cornu minus, respectively. The body and the greater horns appear to give the hyoid its U-shape with the greater horns forming the limbs of the “U” on either side of the body. The greater and lesser horns normally unite to the body of the hyoid via fibrous tissue or a true joint. As age progresses, there is a physiological progression of ankylosis of the joints connecting the greater and lesser horns with the body of the hyoid.  

The hyoid takes part in all possible functional actions of the orofacial complex. It preserves the patency of the airway between the oropharynx above and tracheal rings below. It also connects to the larynx and hence plays a role in phonation. Other functions include tongue movement, mastication, swallowing, prevention of regurgitation, and even respiration. Furthermore, the hyoid maintains the posture of the head, due to the complex connection it presumes between the mandible and the cervical spine.

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