Miyerkules, Mayo 16, 2012

Endocrinology:Overview

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:
  • 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
3)Addison's Disease
  • hyposecretion of all adrenal cortex hormones 
Figure 4: Patient with Addison's Disease
 4)Cretinism
  • 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
These disease are only few of the diseases associated with the hyper or hyposecretion of hormones.

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:
http://www.google.com.ph/imgres?start=36&num=10&um=1&hl=fil&biw=1024&bih=636&tbm=isch&tbnid=rb1xYseyyH7SEM:&imgrefurl=http://www.as.miami.edu/chemistry/2086/adrenal%2520glands%2520-%2520end.htm&docid=UO0SHnGt_HnOJM&imgurl=http://www.as.miami.edu/chemistry/2086/Adrenal%252520glands%252520-%252520end_files/image002.jpg&w=600&h=459&ei=1Y3LT8mYLYrumAXBqbTlDg&zoom=1&iact=hc&vpx=407&vpy=222&dur=3954&hovh=196&hovw=257&tx=221&ty=133&sig=106199015242413653353&page=3&tbnh=149&tbnw=196&ndsp=20&ved=1t:429,r:17,s:36,i:89
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 608
Seeley R. et al, Essential of Anatomy and Physiology 6h Edition, Chapter 10, pg 269-295 



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