The document details the endocrine system, covering major glands like the pituitary, thyroid, and adrenal glands. It explains hormone production, regulation, and their roles in maintaining homeostasis. Emphasis is placed on understanding hormonal pathways, feedback mechanisms, and their impact on b...
ENDOCRINE SYSTEM
GLANDS, HORMONES AND THEIR FUNCTIO
,INTRODUCTION
• The multiple activities of the cells, tissues, and organs of the body are coordinated
interplay of several types of chemical messenger systems:
1. Neurotransmitters are released by axon terminals of neurons into the synaptic junctions and
to control nerve cell functions.
2. Endocrine hormones are released by glands or specialized cells into the circulating blood an
the function of cells at another location in the body.
3. Neuroendocrine hormones are secreted by neurons into the circulating blood and influence
function of cells at another location in the body.
4. Paracrines are secreted by cells into the extracellular fluid and affect neighbouring cells of a
type.
5. Autocrines are secreted by cells into the extracellular fluid and affect the function of the sam
that produced them by binding to cell surface receptors.
6. Cytokines are peptides secreted by cells into the extracellular fluid and can function as auto
paracrines, or endocrine hormones. Examples of cytokines include the interleukins and othe
lymphokines that are secreted by helper cells and act on other cells of the immune system. C
hormones (e.g., leptin) produced by adipocytes are sometimes called adipokines.
,• Many of the body’s chemical messenger systems interact with one another to mai
homeostasis.
• For example, the adrenal medullae and the pituitary gland secrete their hormones
primarily in response to neural stimuli.
• The neuroendocrine cells, located in the hypothalamus, have axons that terminate
posterior pituitary gland and median eminence and secrete several neurohormone
including antidiuretic hormone (ADH), oxytocin, and hypophysiotropic hormones,
control the secretion of anterior pituitary hormones.
• The endocrine hormones are carried by the circulatory system to cells throughout
body, including the nervous system in some cases, where they bind with receptors
initiate many reactions.
• Some endocrine hormones affect many different types of cells of the body; for exa
growth hormone (from the anterior pituitary gland) causes growth in most parts o
body, and thyroxine (from the thyroid gland) increases the rate of many chemical r
in almost all the body’s cells.
, • Other hormones affect only specific target tissues, because only these tissues have recep
the hormone.
• For example, adrenocorticotropic hormone (ACTH) from the anterior pituitary gland spec
stimulates the adrenal cortex, causing it to secrete adrenocortical hormones, and the ova
hormones have specific effects on the female sex organs as well as on the secondary sexu
characteristics of the female body.
• Figure 1 illustrates the locations of the various endocrine glands throughout the body.
• These glands take on the critical task of releasing hormones, and include:
• Adrenal Glands
• Hypothalamus
• Ovaries
• Pancreas
• Parathyroid
• Pineal Gland
• Pituitary Gland
• Testes
• Thymus
• Thyroid
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