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Human and Social Biology

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Introduction

Human and Social Biology 1. The term endocrine comes from the Greek word 'endo', (meaning within), and the Greek word 'krinein', (meaning secrete). The endocrine system consists of a number of ductless glands situated around the body, which have the ability to secrete hormones directly into the blood stream. A hormone is a chemical messenger that travels through the blood to another target organ or tissue where it may influence activity, nutrition and growth. Hormones do not initiate reactions they modify the rate of those already taking place. The major endocrine glands present in every typical human are; one pituitary gland, one thyroid gland, four parathyroid glands, two adrenal glands, (suprarenal), the pancreatic islets, (islets of Langerhans), one pineal gland, one thymus gland, and either two testes in the male or two ovaries in the female. A diagram showing the location of the major endocrine organs within the human body Pituitary gland The pituitary gland and the hypothalamus are found within the brain and act together as a unit to regulate the activity of most of the other endocrine glands. The hypothalamus is sometimes referred to as the control centre as it controls pituitary function and plays a vital role co-ordinating between tissue and organ activity via the secretion of hormones. The pituitary gland, or master gland, is attached to the hypothalamus by a stalk and is positioned below it in the hypophyseal fossa of the sphenoid bone. A pituitary gland is a pea size object consisting of three distinct parts, the adenohypophysis or anterior lobe, the nerohypophysis or posterior lobe and an intermediate lobe, (Ross and Wilson.1999). Functions of the intermediate lobe are poorly understood and hormones can only be detected in this section during fetal life and in pregnancy. Some of the six hormones secreted by the adenohypophysis, (anterior pituitary lobe), stimulate or inhibit secretion by other target endocrine glands while others have a direct effect on specific tissues. ...read more.

Middle

The two ovaries are attached to the upper part of the uterus by the ovarian ligaments. The function of an ovary is to produce ova and secrete the hormones estrogen and progesterone, which affect many aspects of the female body including menstrual cycles and pregnancy. Oestrogen facilitates growth of the tissues of the sex organs and is responsible for the appearance of secondary female characteristics. Oestrogen also acts to strengthen bones and has a protective effect on the heart. Progesterone promotes the changes in the uterus that occur in preparation for the implantation of a fertilised ovum and prepares the mammary glands for milk production. Gonadotropic hormones produced by the pituitary gland control the levels of hormone secreted. Testicles, (testes), are the male reproductive glands or gonads. Testes are egg shaped organs that are attached by spermatic cords and hang suspended in a pouch of skin named a scrotum outside the male body. The scrotum serves as a protective covering and serves to maintain the testicular temperature about 2 degrees below abdominal temperature. Two testes are found in the scrotum where they produce the male gametes, the spermatozoa, and the male hormone, testosterone. It is the anterior pituitary gland that releases LH, which stimulates the leydig cells of the testis to produce and secrete testosterone. Testosterone is responsible for the characteristics of the masculine body, including hair growth on the face and body and muscle development. Testosterone is essential for the production or sperm, spermatogenesis, and also acts to strengthen bones. 2. The digestive system is the collective name used to describe the alimentary canal, some accessory organs and a variety of digestive processes, which take place to prepare food eaten for absorption. The accessory digestive organs are the teeth, tongue, salivary glands, lingual glands, liver, gall bladder and pancreas. The process begins when food enters the digestive system through voluntary action via the mouth or oral cavity and the lips, (labia). ...read more.

Conclusion

The tibiofemoral, or knee joint is an example of a hinge joint. Hinge joints are monoaxial and allow simple motion around a single axis. Pivot joining allows freedom of movement some where between ball and socket and hinge joining. An example of a pivot joint is the atlanto-axial joint, which allows an individual to turn their head from side to side, when wanting to produce the gesture 'no'. Other joints of the skull are extremely strong and mostly immovable. It is important to remember that a joint cannot function without a pair of opposing muscles to assist it. When one of the pair of muscles contracts, the other relaxes. The muscle performing the prime movement is the agonist, while the opposite acting muscle is the antagonist. An antagonist is never totally relaxed. Its function is to provide control and damping of movement by maintaining tone against the agonist, the whole process is termed eccentric movement. The skeletal system also provides mineral homeostasis. Bone tissue stores several minerals, predominantly calcium and phosphorus, which contribute to the strength of bone, etc. Bone has the ability to release these minerals into the blood stream in order to maintain critical mineral balances. Bones also contain red bone marrow that is the production site for red and white blood cells, (hemopoiesis); both are vital for body function. As an individual matures some of the red bone marrow converts into yellow bone marrow. Yellow marrow consists primarily of adipocytes, and is used to store triglycerides. Although human bones appear to be quite strong they can experience fractures and dislocations. A dislocation occurs when a bone is pushed out of its socket by a sudden unexpected pressure such as a fall. Dislocated bones often require a quick reverse pressure to realign them in the socket. Fractures are actual breaks in the bone and can be quite serious, taking anywhere from a month to six months to heal depending on the age and health of the individual and which bone is involved. ...read more.

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