Endocrinology is the study of endocrine system,its organs, hormones and diseases associated to it. Endocrine system is an intricate system that forms messages and chemical signals which controls the body functions and responses. It consists of glands that secrete hormones into the circulation.
Functions of Endocrine System:
The above figure shows the different major glands of the endocrine system which are the: hypothalamus, pituitary gland, parathyroid, thymus, pineal, adrenal gland, pancreas, ovary and testes. These glands are located in the different parts of the body. Lets locate them one by one. Pituitary gland is located in the cranial cavity. Thyroid is in the neck. Thymus is in the thoracic cavity. The adrenal glands and pancreas are in the abdominal cavity. And the ovaries and testes are in the pelvic region. These glands secrete different hormones for a specific response to the body. The hormones they release regulate basic drives and emotions such as sexual urges, violence, anger, fear,sorrow and joy. Here is a summary of the glands and their functions on their target tissues.
Table 1: Endocrine Glands, Hormones and their Target Tissues and Responses
Hormone is a substance secreted by endocrine tissues that acts on a target tissue to produce a specific response.They possess a high degree of structural specificity. They regulate any alteration in their molecular composition results a drastic change in their physiological activity. Hormones transmit messages to a distant target organ to create a specific action. These are divided into three chemical classes, and these are aromatic amines,steroid hormones and protein hormones. These hormones differ from one another based on their structure, chemical composition, mechanism of action and metabolism.
Homeostasis depends on the precise regulation of organs and organ system. Endocrine and nervous system are the two major systems responsible for regulation and maintenance of homeostasis.They coordinate and regulate together almost all other body structures. They coordinate harmoniously to promote growth and development, respond with the stimuli,and body's internal state of balance. They have somewhat synonymous functions and mode of action in terms of their regulatory functions but they differ in other important ways.They differ in a way they transmit information throughout the tissues. Endocrine system releases chemical signal in the bloodstream to carry them to all parts of the body,thereby controlling the activity of the body tissues. It usually respond more slowly and has a longer-lasting effects.Whereas, nervous system sends action potentials along axons which release chemical signals at their ends near the cell they control. The cells which can detect the chemical signals produce responses and it acts more quickly and has short-term effects.
Functions of Endocrine System:
- Reproduction
- Growth and Development
- Mobilizing body defense against stressors
- Maintaining electrolytes, water, and nutrient balance of the blood
- Regulating cellular metabolism and energy balance
 | |||
| Figure 1: The Major Endocrine Glands and Their Locations in the Human Body |
The above figure shows the different major glands of the endocrine system which are the: hypothalamus, pituitary gland, parathyroid, thymus, pineal, adrenal gland, pancreas, ovary and testes. These glands are located in the different parts of the body. Lets locate them one by one. Pituitary gland is located in the cranial cavity. Thyroid is in the neck. Thymus is in the thoracic cavity. The adrenal glands and pancreas are in the abdominal cavity. And the ovaries and testes are in the pelvic region. These glands secrete different hormones for a specific response to the body. The hormones they release regulate basic drives and emotions such as sexual urges, violence, anger, fear,sorrow and joy. Here is a summary of the glands and their functions on their target tissues.
Table 1: Endocrine Glands, Hormones and their Target Tissues and Responses
|
GLAND
|
HORMONE
|
TARGET
TISSUE
|
RESPONSES
|
|
Pituitary Gland
Anterior
Pituitary Gland
Posterior
|
Growth Hormone
|
Most tissues
|
Increases protein synthesis,
breakdown of lipids and release of fatty acids from cells; Increase blood
sugar levels
|
|
Thyroid Stimulating Hormone
(TSH)
|
Thyroid Gland
|
Increases thyroid hormone
secretion (thyroxine and triiodothyronine)
|
|
|
Adrenocorticotropic Hormone (ACTH)
|
Adrenal Cortex
|
Increases secretion of
glucocorticoid hormones such as cortisol; Increases skin pigmentation at high
concentration
|
|
|
Melanocyte-Stimulating Hormone
(MSH)
|
Melanocyte in skin
|
Increases melanin production in
melanocytes to make the skin darker in color
|
|
|
Luteinizing Hormone (LH) or
Interstitial Cell-Stimulating Hormone (ICSH)
|
Ovary in females; Testes in
males
|
Promotes ovulation and
progesterone production in the ovary; Testosterone synthesis and support for
sperm cell production in testes
|
|
|
Follicle-Stimulating Hormone
(FSH)
|
Follicle in ovary in females;
Seminiferous tubules in males
|
Promotes follicle maturation
and estrogen secretion in ovary; Sperm cell production in testes
|
|
|
Prolactin
|
Ovary and mammary gland in females, testes in males
|
Stimulates milk production and
prolongs progesterone secretion following ovulation and during pregnancy in
woman; Increases sensitivity to LH in males
|
|
|
Antidiuretic Hormone (ADH)
|
Kidney
|
Increases water reabsorption
(less water is lost as urine
|
|
|
Oxytocin
|
Uterus
Mammary Gland
|
Increases uterine contractions
Increases milk “let down” from
mammary gland
|
|
|
Thyroid Gland
|
Thyroid Hormone (Throxine and
Triiodothyronine)
|
Most cells of the body
|
Increases metabolic rats,
essential for normal process of growth and maturation
|
|
Calcitonin
|
Primarily Bone
|
Decreases rate of bone
breakdown; Prevents large increase in blood Calcium levels following a meal
|
|
|
Parathyroid Gland
|
Parathyroid Hormone
|
Bone, Kidney
|
Increases rate of bone breakdown
by osteoclasts; Increases Vit.D synthesis, essential for maintenance of
normal blood calcium levels
|
|
Adrenal Medulla
|
Epinephrine mostly, some
Norepinephrine
|
Heart, Blood vessels, Liver,
Fat cells
|
Increases cardiac output;
Increases blood flow to skeletal muscles and heart; Increases release of
glucose and fatty acids into blood; In general, prepares the body for
physical activity
|
|
Adrenal Cortex
|
Mineralocorticoids
(Aldosterone)
|
Kidneys; to lesser degree,
Intestine and Sweat Gland
|
Increases rate of sodium
transport into body; Increases rate of Potassium excretion; Secondarily favor
water retention
|
|
Glucocorticoids (Cortisol)
|
Most tissues (e.g. Liver, Fat,
Skeletal Muscles, Immune Tissues)
|
Increases fat and protein
breakdown; Increases glucose synthesis from amino acids; Increases blood
nutrient levels; Inhibits inflammation and immune response
|
|
|
Adrenal Androgen
|
Mot tissues
|
Insignificant in males;
Increase female sexual drive, pubic hair and axillary hair growth
|
|
|
Pancreas
|
Insulin
|
Especially liver, skeletal
muscle, Adipose tissue
|
Increase uptake and use of
glucose and amino acids
|
|
Glucagon
|
Primarily Liver
|
Increase breakdown of glycogen
and release of glucose into the circulatory system
|
|
|
Reproductive Organs
Testes
Ovaries
Uteus, Ovaries, Inflammed
Tissues
|
Testosterone
|
Most tissues
|
Aid in sperm cell production,
maintenance of functional reproductive organs, secondary sexual characteristics, and sexual
behavior
|
|
Estrogen and Progesterone
|
Most tissues
|
Aid in uterine and mammary gland
development and function, external genitalia structure, secondary sexual
characteristics, sexual behavior and menstrual cycle
|
|
|
Prostaglandins
|
Most tissues
|
Mediate inflammatory responses;
Increases uterine contractions and ovulation
|
|
|
Thymus Gland
|
Thymosin
|
Immune tissues
|
Promote immune system development and function
|
|
Pineal Body
|
Melatonin
|
At least the hypothalamus
|
Inhibits secretion of gonadotropin-releasing hormone,
thereby inhibiting reproduction
|
Hormone is a substance secreted by endocrine tissues that acts on a target tissue to produce a specific response.They possess a high degree of structural specificity. They regulate any alteration in their molecular composition results a drastic change in their physiological activity. Hormones transmit messages to a distant target organ to create a specific action. These are divided into three chemical classes, and these are aromatic amines,steroid hormones and protein hormones. These hormones differ from one another based on their structure, chemical composition, mechanism of action and metabolism.
Homeostasis depends on the precise regulation of organs and organ system. Endocrine and nervous system are the two major systems responsible for regulation and maintenance of homeostasis.They coordinate and regulate together almost all other body structures. They coordinate harmoniously to promote growth and development, respond with the stimuli,and body's internal state of balance. They have somewhat synonymous functions and mode of action in terms of their regulatory functions but they differ in other important ways.They differ in a way they transmit information throughout the tissues. Endocrine system releases chemical signal in the bloodstream to carry them to all parts of the body,thereby controlling the activity of the body tissues. It usually respond more slowly and has a longer-lasting effects.Whereas, nervous system sends action potentials along axons which release chemical signals at their ends near the cell they control. The cells which can detect the chemical signals produce responses and it acts more quickly and has short-term effects.
Table 2: Differentiation of Nervous System and Endocrine System
|
|
Nervous
System
|
Endocrine
System
|
|
Mediators
|
Neurotransmitter
|
Hormones
|
|
Site of Action
|
Close to the site of release
|
Far from the site of release
|
|
Type of Target Cell
|
Muscles, cells, glands
|
Cells throughout the body
|
|
Time of onset of action
|
Milliseconds
|
Hours to days
|
|
Duration of action
|
Brief
|
Longer
|
The release of hormones should be regulated and maintained. if not, the hypo or hyper secretion of any of the said hormones have a counterpart diseases or disorders such as:
1) Goiter
- enlargement of the thyroid gland due to deficient iodine
 |
| Figure 2: A woman with Goiter |
2)Myxedema
- hypothyroidism in adults
 |
| Figure 3: A man with myxedema |
- hyposecretion of all adrenal cortex hormones
 |
| Figure 4: Patient with Addison's Disease |
- lack of stimulation of thyroid galnd during childhood
 |
| Figure 5: A child with cretinism |
5) Gigantism
- hypersecretion of Growth ormone during childhood
 |
| Figure 6: A man with gigantism, together with ladies with a normal height |
Thank you for reading! hope you enjoy and gain more knowledge about the topic. Its more fun to learn. Watch out for the next topic we will be talking about. have a great day ahead!
Photo Credit:
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http://www.google.com.ph/imgres?num=10&um=1&hl=fil&biw=1024&bih=636&tbm=isch&tbnid=KWd6YucyhqEzlM:&imgrefurl=http://www.liveliketim.com/html/iodine/iodinehealth.html&docid=LwA7XeALG23uOM&imgurl=http://www.liveliketim.com/images/Cretinism.jpg&w=210&h=260&ei=jY_LT6XILebFmQWJrbz0Dg&zoom=1&iact=hc&vpx=508&vpy=144&dur=985&hovh=208&hovw=168&tx=107&ty=145&sig=106199015242413653353&sqi=2&page=1&tbnh=138&tbnw=139&start=0&ndsp=18&ved=1t:429,r:3,s:0,i:70
http://www.google.com.ph/imgres?num=10&um=1&hl=fil&biw=1024&bih=636&tbm=isch&tbnid=7onleQFbrC2nhM:&imgrefurl=http://misskay03.edu.glogster.com/gigantism/&docid=SQcihpGguu9BzM&imgurl=http://edu.glogster.com/media/5/17/28/95/17289582.jpg&w=440&h=553&ei=mo_LT_qaKbCWmQWk0bCCDw&zoom=1&iact=rc&dur=366&sig=106199015242413653353&sqi=2&page=1&tbnh=153&tbnw=122&start=0&ndsp=20&ved=1t:429,r:1,s:0,i:66&tx=79&ty=98
http://www.google.com.ph/imgres?num=10&um=1&hl=fil&biw=1024&bih=636&tbm=isch&tbnid=KWd6YucyhqEzlM:&imgrefurl=http://www.liveliketim.com/html/iodine/iodinehealth.html&docid=LwA7XeALG23uOM&imgurl=http://www.liveliketim.com/images/Cretinism.jpg&w=210&h=260&ei=jY_LT6XILebFmQWJrbz0Dg&zoom=1&iact=hc&vpx=508&vpy=144&dur=985&hovh=208&hovw=168&tx=107&ty=145&sig=106199015242413653353&sqi=2&page=1&tbnh=138&tbnw=139&start=0&ndsp=18&ved=1t:429,r:3,s:0,i:70
http://www.google.com.ph/imgres?num=10&um=1&hl=fil&biw=1024&bih=636&tbm=isch&tbnid=7onleQFbrC2nhM:&imgrefurl=http://misskay03.edu.glogster.com/gigantism/&docid=SQcihpGguu9BzM&imgurl=http://edu.glogster.com/media/5/17/28/95/17289582.jpg&w=440&h=553&ei=mo_LT_qaKbCWmQWk0bCCDw&zoom=1&iact=rc&dur=366&sig=106199015242413653353&sqi=2&page=1&tbnh=153&tbnw=122&start=0&ndsp=20&ved=1t:429,r:1,s:0,i:66&tx=79&ty=98
Reference:
Kaplan, L., Pesce, A., Clinical Chemistry Theory 2nd Edition, Analysis and Correlation, Chapter 40, pg 608Seeley R. et al, Essential of Anatomy and Physiology 6h Edition, Chapter 10, pg 269-295
