Introduction to systems of the body

Systems in the body

1. The cardiovascular system

2. The lymphatic system

3. The nervous system

4. The endocrine system

5. The respiratory system

6. The digestive system

7. The urinary system

8. The musculoskeletal system

9. The reproductive system

10. The special senses

• Eye
• Ear
• Nose
• Skin
• Tongue

The cardiovascular system:

            The cardiovascular system in humans consists of a four-chambered heart to pump blood and a series of vessels needed to transport blood in the body. Blood is a connective tissue used to deliver oxygen, nutrients, water, hormones, and ions to all the cells of the body. It is also used to pick up the carbon dioxide and wastes produced by cells and to move these to the appropriate areas for elimination. Further, it assists in thermoregulation in the body as well as fighting infectious agents.

The critical functions of the cardiovascular system are achieved by blood transported through the system. For this reason, the composition of blood needs to be examined more closely.

The lymphatic system:

The lymphatic system consists of a series of vessels running throughout the body, lymph, and lymphoid tissue. The system serves to return fluids that were unclaimed at the capillary beds to the circulatory system, picks up chylomicrons from the digestive tract and returns them to circulation, and fights infection via leukocytes.

The nervous system:

          The nervous system has the daunting task of coordinating all of the body’s activities. The central nervous system is composed of the brain and spinal cord. The peripheral nervous system (PNS) is composed of any nervous tissue located outside of the brain and spinal cord. Nerves are the primary structures within the PNS. In order to understand the functioning of the CNS and PNS, it is necessary to look at the detailed function of neurons.

The endocrine system:

          This system is composed of endocrine glands located throughout the body. Hormones are generally secreted from an endocrine gland into the bloodstream. In order to maintain homeostasis in the body, it is necessary to regulate the functioning of specific targets within the body. Hormones achieve this regulation. Hormones are chemical messengers secreted into the bloodstream that travel to a specific target in the body and change the functioning of that target. The target can be individual cells, tissues, or entire organs.

The respiratory system:

The respiratory system has the primary jobs of providing the body with oxygen and eliminating carbon dioxide. The Pulmonary arteries, coming from the right side of the heart, carries deoxygenated blood, which is low in oxygen and high in carbon dioxide, to the lungs. Oxygen that enters the lungs will be distributed to hemoglobin in the erythrocytes within the capillaries that branch off the pulmonary arteries that surround the alveoli. Carbon dioxide will diffuse into the alveoli from the pulmonary arteries to be exhaled. Now blood is oxygenated and will travel back to the left side of the heart via pulmonary veins. In addition to oxygenating blood, the respiratory structures are responsible for pH regulation, vocal communication, the sense of smell, and protection from infectious agents and particles.

The digestive system:

The digestive system is designed to extract nutrients from food and eliminate wastes. The system is set up as a series of modified tubes to keep food and digestive enzymes sequestered from the body. It is also known as the gastrointestinal (GI) tract. In addition to the GI tract, there are several accessory structures (the liver, gallbladder, and pancreas) which perform functions vital to the digestive system. The three primary components of the diet that require digestion are carbohydrates, proteins, and fats. The digestive system has the following functions: mechanical digestion of food achieved by chewing, chemical digestion of food achieved by assorted digestive enzymes, absorption of nutrients into the bloodstream, and elimination of waste products.

The urinary system:

This urinary system mainly composed of the kidneys, which are produces urine, and supporting tubing to store and eliminate urine from the body. The kidneys are the main excretory organ of the body: however, the skin can also act as an excretory organ. In addition to producing urine as a means of eliminating nitrogenous cellular waste products, the urinary system adjusts blood pH, also regulates blood pressure by means of blood volume, and regulates the osmotic concentrations of the blood.

The musculoskeletal system:

Muscles provide structural support, help maintain body posture, regulate openings into the body, assist in thermoregulation via contractions (shivering) that generate heat, and contract to help move blood in veins towards the heart, assisting in peripheral circulation. Skeletal and cardiac muscle is striated, while smooth muscle is not. Cardiac and smooth muscles are involuntary, while skeletal muscle is under voluntary control.

The reproductive system:

The female and male reproductive systems have the common function of producing gametes for sexual reproduction. Egg cells in females and sperm cells in males are produced by the gonads. In addition, the female reproductive system has to be structured to accept sperm from the male system and to allow for embryonic and fetal development.

Special senses:

            The senses have specialized sensory receptors that is present outside the brain. The special senses are meant for smell, sight, hearing, and taste: these are found in eye, nose, ear and tongue and one of the special senses is skin that is useful as protecting and for survival to the body.

Eye: It is the organ of sight. This is situated in the orbital cavity and it is supplied by the optic nerve. The optic nerve is located at the second cranial nerve. It is spherical in shape with the diameter of 2.5 cm. The space between the orbital cavity and eye is occupied by adipose tissue.

            The eye consists of 3 layers of tissue in the wall.

• The outer layer( fibrous) layer: sclera and cornea
• The middle layer(vascular layer):choroid, ciliary body and iris
• The inner layer(nervous): retina

Ear: It is the organ of hearing and it is supplied by the cochlear part of the vestibulocochlear nerve that is present in the 8^th cranial nerve. The ear is divided into 3 parts.

• The outer ear: auricle(pinna), external acoustic meatus(auditory canal)
• The middle ear (tympanic cavity): auditory ossicles(malleus, incus, stapes)
• The inner ear: bony labyrinth and membranous labyrinth.

Nose: It is the sense of smell, or olfaction, which is also act as passageway for respiration. It is originated in the nasal cavity. The olfactory nerves present in the first cranial nerves. Inflammation of the nasal mucosa prevents odorous substances from reaching the olfactory area of nose causes loss of the sense of smell.

Skin: The skin is the largest organ of the body and it covers the whole body with the surface area of about 1.5-2 m² in adults and it contains hair, nails and glands.

            The skin is made up of two layers i.e., epidermis and dermis. The functions of skin are

• Regulation of body temperature
• Sensation of pain, touch and temperature due to the presence of somatic nerve endings
• Protection of underlying organs from microbes and injury

Tongue: The sense of gestation or taste, it is closely linked to the sense of smell and it also involved in the stimulation of chemo-receptors by dissolved chemicals.

            The fundamental sensations of taste are salt, sweet (at the tip), sour (at the sides) and bitter (at the back). The trigger of the sense of taste is salivation and the secretion of gastric juice.

Systems, cardiovascular, central nervous, endocrine, digestive