Human Body Anatomy - Structure of the Human Body & Parts
Human body Anatomy is a branch of biology that deals with the study of the structure of the human body. Though humans have evolved separately from the animals, there are many similarities in their anatomy. This is mainly because the human and those animals share a common ancestor. One best example to explain this case is the similarity in the number of vertebrae in Giraffe’s neck with that of the human body. Both have 7 vertebrae in their necks.
The shape of the human body is due to the presence of skeletons which is made up of bones and cartilage. The structure of the human body comprises of head and neck, limbs that are connected to a torso. The basic building blocks of all our organs are cells which in turn combines to form tissues. The combination of tissues would result in organs. A set of the organs form the organ systems which in turn result in the making of the entire organism.
The human body mainly consists of water and other organic compounds like proteins, carbohydrates, lipids, and nucleic acids. Water is found in the blood plasma, the lymph which are the extracellular fluids of the body and within the cells themselves. Water serves as a solvent and it constitutes to about 60% of the body weight.
For a better understanding of the anatomy, it is explained in terms of organ systems.
1. Circulatory System:
It is also referred to as the cardiovascular system. The heart is an important part of the system. It also consists of blood vessels which include arteries, capillaries, and veins. This helps in the transfer of oxygen and nutrients to various parts of the body and the removal of waste products away from the body.
Themain and the primary function of the heart is to serve as a muscular pump propelling blood through and into the vessels to and from all the parts of the body and also carry oxygen and nutrients to tissues removing the carbon dioxide and other wastes from the body.
The arteries receive blood at high velocity and pressure and conduct it throughout the body which has thick walls that are composed of elastic fibrous tissues and muscle cells.
2. Digestive System:
The digestive system helps in the breakdown of food particles and assimilation of those nutrients in the different parts of the body. This helps in ensuring the overall growth and cell repair. The process of digestion starts in the mouth and here is where the chemical mechanical digestion occurs. Saliva is produced by the salivary glands which are located under the tongue and near to the lower jaw. The digestive enzymes called amylase that is present in the saliva begin to breakdown the carbohydrates. The main and important function of the mouth is chewing where it allows the food to get mashed into a soft mass that will be easier to swallow and digest. The movements made by the tongue and the mouth, push the food to the back of the throat for swallowing the food.
The teeth help in the grinding of foods. The easy passage of the food through the alimentary canal can be ensured by mixing the food particles with saliva which is secreted by the salivary glands. Then, the mixed food passes through the food pipe which is also known as the esophagus and reaches the stomach. As soon as the food is swallowed, it will enter the esophagus which is a muscular tube about 10 inches long. It is located between the throat and the stomach. In order to push the food from the esophagus to the stomach, muscular wave-like contractions called peristalsis push occurs. A muscular ring called cardiac sphincter which is present at the end of the esophagus allows the food to enter into the stomach and then it squeezes shut in order to prevent the food and the fluids from going back up to the esophagus again.
The stomach is a J-shaped organ that is located in between the esophagus and the small intestine in the upper abdomen. The three important functions of the stomach are to store the swallowed food and fluid, to mix the food, fluid and the digestive juices produced by the stomach and then to slowly empty the mixture into the small intestine. Few ingredients like water and alcohol will be directly absorbed by the stomach. The rest of the foods will undergo the digestive process of the stomach.
The stomach expands once the food enters it. Once the food enters the stomach, the gastric glands which are present in the wall of the stomach would release hydrochloric acid, pepsin, and mucus. This partially digested food reaches the small intestine which takes care of the process of complete digestion. This is facilitated by the secretions from various organs such as the liver and pancreas. The villi which are the finger-like projections in the body absorb the nutrients needed for the functioning of the body. The rest of the unabsorbed food passes through the large intestine where the excess water is absorbed, and waste material is thrown out of the body through the anus. This is regulated by anal sphincter.
3. Respiratory System: The process of respiration involves the inhalation and the exhalation of the air i.e. breathing. Through the process of inhalation, the oxygen enters into the human body and the carbon-di-oxide exits the system by means of exhalation. The two most important functions of the respiratory system are to bring the oxygen into our body through which the cells live and function properly and to get rid of the carbon dioxide, the waste products of the cellular function.
The air enters the body through the nostrils and passes through pharynx and larynx. Then, the air passes through the trachea which connects the larynx with the bronchi. These work as a system of pipes through which the air is funneled into the lungs. When breathing takes place, the air enters the body through the nose, and it travels down the throat through the larynx then passes through the trachea before entering the lungs.
The lungs are a pair of cone-shaped organs that takes up the maximum space in the chest of the human body along with the heart. The role of the lungs is to take the oxygen into the body that the cells need. The lungs are divided into left and right lungs and are divided into lobes. The left lung has two lobes where the right lung has three and the lungs can be divided into further smaller portions called bronchopulmonary segments which are pyramid shaped ones. Each lung has 10 segments and one receive its own blood and air supply.
The lungs receive a large amount of blood supply which is because the pulmonary arteries that supply the lungs come directly from the right side of the heart. It carries blood that is low in oxygen and high in carbon dioxide into the lungs so that the carbon dioxide can be blown off and more amount of oxygen can be absorbed into the blood. The new oxygen-rich blood travels into the left side of the heart through the pulmonary veins. Then it is pumped all around the body into the cells and organs for oxygen supply.
The bronchi are divided into right and left bronchi which end up in bronchioles. Through this, the air enters the lungs. The lungs consist of alveoli on its surface. Alveoli help in the exchange of gases. The important muscle in the respiratory system is the diaphragm. The lungs are housed inside the rib cage.
4. Nervous System:
Nervous system helps in the coordination of various movements of the body by means of transmission of signals. The nervous system consists of two major parts, they are the central nervous system and the peripheral nervous system. In the central nervous system, there are two mains parts namely the brain and the spinal cord. The brain is made up of forebrain, midbrain, and hindbrain. The peripheral nervous system consists of nerves that connect every part of the body with the central nervous system.
The nervous system is made up of some special type of cells called neurons that consist of various parts like axon, dendrite, and nucleus. The neurons play a major role is the transmission of signals by means of electrical impulse created by the chemical reaction. The neurons have a cell body called soma and also have extensions of the cell where each extension is referred to the process. The important process of every neuron is called axon, it is a fiber that connects the neuron with its target. The other process of the neuron is the dendrite which is responsible for receiving most of the input from other neurons.
There are two regions that contain cell bodies and regions composed of just axons. The two regions that are present in the nervous system are referred to as gray matter and white matter. The gray matter is the region that has many cell bodies and dendrites. The white matter is the region that has many axons.
5. Endocrine System:
The endocrine system consists of glands that help in the production of the hormones which are the chemical substances that help in the regulation of various activities of cells. Some of the important glands of the endocrine system include the hypothalamus, pituitary, thyroid, parathyroid, pineal body, adrenal, and the reproductive organs (ovaries and testis). Though the pancreas is the part of the digestive system, it also plays a role in the endocrine system.
The hypothalamus is situated in the lower central part of the brain which is important in the regulation of satiety, metabolism and the temperature of the body. The pituitary gland is situated beneath the hypothalamus at the base of the brain. It is one of the most important parts of the endocrine system as it produces some hormones that control many functions of the other endocrine glands. Next is the thyroid gland which is located in the front part of the neck and produces thyroid hormones which regulate the metabolism of the body. It also helps in maintaining normal blood pressure, digestion, reproductive functions, and muscle tone. The parathyroid glands are present in two pairs of small glands that are embedded in the surface of the thyroid gland.
The adrenal glands are two in number with triangular shaped glands that are situated on the top of each kidney. It has two parts namely the adrenal cortex that is the outer part and the adrenal cortex that is the inner part.
6. Excretory System:
The excretory system is responsible for removal of wastes which are produced by the process of homeostasis. The parts of the body which are involved in this process are the liver, the lungs, sweat glands, and the kidneys. The kidneys are made up of three parts: renal cortex(outer layer), renal medulla(inner layer) and renal pelvis. The blood enters the kidney through the renal artery which has arterioles at its ends. The arterioles pass the blood to Bowman’s capsules where the filtration of blood takes place. The waste product is taken by the renal pelvis to the urinary bladder through the ureter. Then, it is expelled through the urethra when the bladder is full.
7. Reproductive System:
Reproductive system consists of the internal and external parts that help in the reproduction of offspring. Unlike all other systems, it is different for the male and the female.
The female reproductive system consists of:
• Internal structure: Vagina which is connected to the external part of the body through cervix which lies in the lower part of the uterus. The uterus is the pear-shaped organ which houses the fetus. It comprises two parts: cervix and corpus. Ovaries are positioned on the two sides of the uterus. The eggs are produced in ovaries and are carried by the fallopian tube to the uterus.
• External structure: This consists of labia majora(protects the other external reproductive organs), labia minora, Bartholin’s glands(produces mucous secretions) and clitoris ( a smaller and sensitive protrusion).
The male reproductive system consists of
• Testicles which are involved in the function of producing and storing the sperms.
• Duct system which comprises the epididymis and the vas deferens which is involved in the production of the fluid called semen.
• Accessory glands which consist of the seminal vesicles and prostate gland. The main functions of these glands are to secrete the fluid that lubricates the duct system and nourish the sperms.
• Penis: It has two parts, they are the glans and the shaft.