1. Describe the structures of the skin.
2. Describe the structures of the endocrine system.

 

1) The structures of the skin include the 3 main layers and its 3 accessory structures.

• Epidermis - This structure is mainly composed of keratinocytes. This structure is avascular and is dependent on the underlying dermis for the its nutrients and waste disposal. It is further subdivided into 5 more layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale (arranged from outermost to innermost layers)
• Dermis - This is the inner layer of the skin and is much thicker than the epidermis. This is composed of connective tissue, particularly collagen, and is further divided into two layers: the superficial papillary dermis and the deeper reticular dermis. This layer contains blood vessels arranged into the superficial and deep plexus for nutrient delivery and waste disposal.
• Hypodermis - This is the skin's subcutaneous layer which is mainly composed of fat. The fat cells contribute to insulating the body from any temperature changes, and also for shock absorption.
• Sweat glands - Sweat glands also function for thermoregulation, as the sweat produced is used to cool the body when it is warm. Sweat glands also come from the dermis and are classified into eccrine and apocrine sweat glands.
• Hair - This is found in most areas of the skin for protection and thermoregulation. The strands originate from the hair follicle found in the dermis. The rest of the hair strand then penetrates through the epidermis out to the external surface of the body.
• Nails - These structures are made up of packed and hardened keratin. They function to protect the fingertips and toes from mechanical damage.

2) The endocrine system includes several organs in different areas of the body. This includes:

• Hypothalamus - This links the endocrine system with the nervous system. This organ produces hormones which stimulate other organs to produce their respective hormones.
• Pituitary gland - This gland is located in the sella turcica, and is divided into both the anterior and pituitary gland. This gland mainly receives signals in the form of hormones released by the hypothalamus. The anterior pituitary gland produces hormones like the growth hormone, prolactin, follicle-stimulating hormone, luteinizing hormone, thyroid-stimlating hormone, and adrenocorticotrophic hormone. On the other hand, the pituitary gland produces the anti-diuretic hormone and oxytocin.
• Thyroid gland - This gland is located in the neck area. Hormones produced by this gland include T4 and T3 which function for the body's metabolism. This gland also produces calcitonin which functions for calcium metabolism.
• Parathyroid gland - These are 4 small glands located on the back of the thyroid gland. It produces parathyroid hormone which also functions for calcium metabolism.
• Adrenal glands - These are a pair of triangular glands located on the top of either kidneys. It is divided into the cortex and medulla. The cortex produces aldosterone, cortisol, and weak androgens, while the medulla produces both norepinephrine and epinephrine.
• Pancreas - The pancreas has both exocrine and endocrine functions. Its exocrine components are mainly involved in glucose metabolism with the hormones insulin and glucagon.
• Ovaries - These are a pair of organs located on the ends of either fallopian tubes in females. These are responsible for sexual development and reproduction. Hormones produced by these organs include estrogen and progesterone.
• Testicles - These are also a pair of organs located in the testes of males. These organs produce testosterone, which also function for sexual development and reproduction.

Step-by-step explanation

The skin is the largest organ of the body. It has 3 main layers and 3 accessory structures. From outermost to innermost, the layers are the epidermis, dermis, and hypodermis.

The epidermis is the body's barrier from allergens and irritants, and at the same time, is responsible for protecting the body from water loss and the maintenance of homeostasis. The melanocytes, which are the cells responsible for one's skin color and protection from ultraviolet rays, are also found in the epidermis. Other cells found in the epidermis include Langerhans cells, which functions for the body's immune response, and the Merkel cells, which are involved in sensation and nervous stimulation.

The dermis functions to cushion the deeper structures of the body from mechanical injury, to provide nourishment to the avascular epidermis, and to help in wound healing. It also contains nerve fibers to provide sensation and mast cells for immune and inflammatory responses.

The hypodermis mainly functions to provide structural support to the skin.

The endocrine system functions to produce hormones for the body to help regulate several functions. This includes controlling the amount of fluids in the body, the metabolic rate, the body's biological clock or circadian rhythm, contraction of muscles in the body, secretion of glands, and immune functions. It is also responsible for growth and development, and reproduction.

Despite the distance of the different organs of the endocrine system, they are still able to communicate with each other through the hormones they produce, and are able to coordinate their functions. An example would be the hypothalamus producing the thyrotropin-releasing hormone. This hormone stimulates the anterior pituitary gland to produce thyrotropin or the thyroid-stimulating hormone. This then stimulates the thyroid gland to produce the hormones T3 and T4. These hormones are able to influence several functions of the body including growth and metabolism. It can stimulate the endocrine pancreas to release insulin to allow the body to utilize glucose for its growth and other activities.