Archive for category Anatomy
Anatomy of the Human Heart
Posted by in Anatomy on June 30, 2011
Human heart is a muscular pump, which is located between the lungs, but slightly to the left side. The heart of an adult weighs between 250 to 300 grams in females, and 300 to 350 grams in males. The length of a human heart is around six inches, and the width is roughly four inches. An average human heart beats approximately 72 times per minute, and pumps 4-5 liters of blood (per minute) at rest.
Human Heart – Location
The human heart is located in the middle of the chest – anterior to the spine and posterior to the sternum or breastbone (long flat bone in the center of the chest). The heart lies slightly to the left, from the center of the thorax (region between head and abdomen). Hence, the left lung is smaller compared to the right lung.
Parts of the Human Heart
The heart is divided into two cavities (left cavity and right cavity) by a wall of muscle called septum. The two cavities consist of two chambers each. Upper chambers are called atrium and the lower ones are called ventricles. The right cavity receives de-oxygenated blood from various parts of the body (except the lungs) and pumps it to the lungs, whereas the left cavity receives oxygenated blood from the lungs, which is pumped throughout the body. Let us discuss the anatomy of this amazing organ in detail.
* Outer Covering – Pericardium: The heart and the roots of its major blood vessels are surrounded and enclosed by a sac-like structure called pericardium. It comprises of two parts – the outer fibrous pericardium, made of dense fibrous connective tissue and an inner double-layered membrane (parietal and visceral pericardium). The fibrous pericardium is attached to the spinal column, diaphragm and other parts of the body, by ligaments. The double-layered membrane consists of an inner layer called visceral pericardium, outer layer called parietal pericardium (fused to fibrous pericardium) and a pericardial cavity (between the two layers), which contains serous fluid – pericardial fluid. This fluid helps in reducing the friction caused by the contractions of the heart.
* Heart Wall: The wall of the heart is made up of three layers of tissues – outer epicardium, middle myocardium and the inner endocardium. The outer epicardium functions as a protective outer layer, which includes blood capillaries, lymph capillaries and nerve fibers. It is similar to the visceral pericardium, and consists of connective tissues covered by epithelium (membranous tissue covering internal organs and other internal surfaces of the body). The inner layer called myocardium, which forms the major part of the heart wall, consists of cardiac muscle tissues. These tissues are responsible for the contractions of the heart, which facilitates the pumping of blood. Here, the muscle fibers are separated with connective tissues that are richly supplied with blood capillaries and nerve fibers. The inner layer called endocardium, is formed of epithelial and connective tissue that contains many elastic and collagenous fibers (collagen is the main protein of connective tissues). These connective tissues contain blood vessels and specialized cardiac muscle fibers called Purkinje fibers. This layer lines the chambers of the heart and covers heart valves. It is similar to the inner lining of blood vessels called endothelium. Read the rest of this entry »
Small Intestine Anatomy
Posted by in Anatomy on June 30, 2011
The small intestine is a part of the digestive system. The digestive system consists of the stomach, small intestine and large intestine. The small intestine is the part that connects the stomach and the large intestine. This is the main region where maximum amount of absorption of food takes place. The small intestine is so named not because it is small, it measures on an average five meters (sixteen feet), when uncoiled. This part of the gastrointestinal tract is called the small intestine because it is only 2.5 – 3 cm in diameter. The small intestine is divided into three parts – the duodenum, jejunum and ileum. Given below are details regarding the small intestine anatomy.
Small Intestine Anatomy and Physiology
Duodenum
The duodenum is the first section of the region of the small intestine that precedes the jejunum and the ileum. This is the shortest part of the intestine where most of the initial biochemical reactions take place. The duodenum is around 25 – 30 cm in length and it connects the stomach to the jejunum. It begins with a structure called the duodenal bulb and ends at the ligament of Treitz. The duodenum has the primary function of aiding in breakdown of food in the small intestine with the help of enzymes. Brunner’s glands, which are a part of the glandular epithelium, are present in the duodenum and are responsible for secreting mucus. The duodenum also has the function of regulating the rate of emptying the stomach with the help of hormones, thus, preventing the occurrence of dumping syndrome. The duodenum is also responsible for secreting hormones like secretin and cholcystekinin. The duodenal lining consists of a very thin layer of cells which form the muscularis mucosae.
Jejenum
The jejunum is the middle section of the small intestine that is present between the duodenum and the ileum. The transition from the duodenum and the jejunum is called the ligament of Treitz. The jejunum is around 2.5m in length. The jejunum has a pH of around 7 to 8, that is, it is either neutral or slightly alkaline in nature. This kind of pH is brought about with the help of the bile, which is carried by the bile duct coming from the gallbladder. The pH in this region is maintained at 7 to 8 because, 7 to 8 is the optimum pH for the functioning of the enzymes in this region. The jejunum and the ileum are suspended in the abdomen by the mesentery, which gives them space for bowel movement. It is wrapped by smooth muscle that helps to move food forward, which is known as peristalsis. Read the rest of this entry »