Endocrine System detailed information, Study notes of Human Biology

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ENDOCRINE

SYSTEM

DIFFERENCE BETWEEN ENDOCRINE AND EXOCRINE

SYSTEM

ENDOCRINE SYSTEM EXOCRINE SYSTEM Endocrine glands are a type of glands that secrete subs (hormones) into the blood stream Exocrine glands are a type of glands which release its secretion external to or at the surface of an organ with the help of a canal or duct Are a type of ductless glands May or may not have ducts Secrete into the blood Pour their secretions directly at the site of action Secrete hormones Secrete enzymes Target of the glands is located away from the gland Target of the glands is very close to the gland Response is delayed since the secretion should be transported through the blood to the target organ Show a rapid response since the substances are secreted directly to the target organ There are two types-Primary and Secondary There are different types such as uni and multicellular exocrine glands, merocrine glands, serous glands, mucous glands and mixed glands Ex:- Thyroid gland, pituitary gland, and adrenal glands, etc Ex:- Gastric glands, Salivary glands, and sweat glands, etc

CONT….

 (^) Several mediators act as both neurotransmitters and hormones.  (^) One familiar example is norepinephrine, which is released as a neurotransmitter by sympathetic postganglionic neurons and as a hormone by chromaffin cells of the adrenal medullae.  (^) Difference between NS and ES Nervous System Endocrine System Works by nerve impulses (has chemicals in synapse) Works by hormones transmitted in blood stream Travel fast and usually have ‘instant’ effect Travel slowly and may take some time Affects only the particular muscle or the gland Affects any organ (widespread in body) Coordinates rapid & precise responses Control activities of long duration e.g. Growth, Reproduction, Metabolism, etc.

ENDOCRINE GLANDS

CIRCULATING AND LOCAL

HORMONES

 (^) Circulating hormone :- They pass from the secretory cells that make them into interstitial fluid and then into the blood.  (^) Local hormones :- They act locally on neighboring cells or on the same cell that secreted them without first entering the blood stream.  (^) Local hormones that act on neighboring cells are called paracrines ( para=beside or near).  (^) Local hormones that act o the same cell that secreted them are called autocrines ( auto=self).  (^) For ex:- Interlukin-2,NO

CHEMICAL CLASSES OF HORMONES  (^) Chemically, hormones can be divided into two broad classes: those that are soluble in lipids , and those that are soluble in water.  (^) Lipid-soluble hormones : The lipid-soluble hormones include steroid hormones, thyroid hormones, and nitric oxide.  (^) Steroid hormones:- They are derived from cholesterol. For example, cholesterol is the precursor for the steroid hormones, which include cortisol and aldosterone from the adrenal cortex, estrogen and progesterone from the ovaries, and testosterone from the testes.  (^) Two thyroid hormones (T3 and T4) are synthesized by attaching iodine to the amino acid tyrosine. The benzene ring of tyrosine plus the attached iodines make T3 and T4 very lipid soluble.  (^) The gas nitric oxide (NO) is both a hormone and a neurotransmitter. Its synthesis is catalyzed by the enzyme nitric oxide synthase.

STEROID HORMONES

 Pass through the cell

membrane

 Binds to specific receptors

 Then enters the nucleus to

bind with the cells DNA

which then activates certain

genes (Direct gene activation).

 mRNA is synthesized in the

nucleus and enters the

cytoplasm and promotes

protein synthesis for:

 (^) Enzymes as catalysts  (^) Tissue growth and repair  (^) Regulate enzyme function

NON-STEROID HORMONES

 (^) React with specific receptors outside the cell  (^) This triggers an enzyme reaction with lead to the formation of a second messenger (cAMP).  (^) cAMP can produce specific intracellular functions:  (^) Activates cell enzymes  (^) Change in membrane permeability  (^) Promote protein synthesis  (^) Change in cell metabolism  (^) Stimulation of cell secretions

PITUITARY GLANDS

 (^) The pituitary gland is no smaller than a pea in size but carries out very important functions.  (^) It consists of two glands – each of a different type.  (^) Anterior pituitary gland – adenohypophysis  (^) Posterior pituitary gland – neurohypophysis  (^) The anterior pituitary gland has the structure of an endocrine gland.  (^) The posterior pituitary gland has the structure of nervous tissue

CONT…

 (^) Hormones released from the adenohypophysis serve different functions from those released from the neurohypophysis.  (^) The pituitary gland is located in the sella turcica of the sphenoid bone.  (^) The pituitary stalk attaches the pituitary gland to the hypothalamus.

CONT…

 (^) Follicle Stimulating Hormone – FSH stimulates the growth and estrogen secretion of primary ovarian follicles in the ovary. - In the male FSH aids in sperm production.  (^) Luteinizing Hormone – LH acts with FSH to perform various functions.  (^) Causes estrogen production increase and ovulation.  (^) Stimulates the formation of the corpus luteum and its production of progesterone.  (^) Stimulates the interstitial cells of the testes to secrete testosterone.  (^) Growth Hormone – GH Speeds up the movement of amino acids out of the blood and into cells to promote anabolism(synthesis) of amino acids into tissue proteins.

CONT…

 (^) GH also promotes fat catabolism(breakdown) and slows down glucose catabolism.  (^) Less glucose leaves the blood to enter cells. GH therefore increases blood glucose concentrations.  (^) Hypersecretion of insulin produces hypoglycemia.  (^) Hypersecretion of GH produces hyperglycemia.  (^) Prolactin –PRL or lactogenic hormone. Stimulates the development of the breasts for producing milk during pregnancy.

CONT…

 (^) OT is secreted by the posterior pituitary of a female before and after she has a baby.  (^) OT stimulates uterine contractions to initiate and maintain labor.  (^) It stimulates glandular cells of the breast to release milk into ducts from which the baby can obtain nutrients.  (^) Production of ADH and OT occurs in the hypothalamus.  (^) Two groups of neurons make the posterior gland hormones and pass them along axons to the neurohypophysis.  (^) Release is controlled by nervous stimulation.

HYPOTHALAMUS

 (^) The hypothalamus produces Releasing hormones (RHs) and Inhibiting Hormones (IHs).  (^) They travel to the adenohypophysis via a specialized capillary system.  (^) They can cause the release of anterior pituitary hormones or inhibit their production and release into the general circulation.  (^) The hypothalamus plays a dominant role in regulating many body functions including:  (^) • Body temperature  (^) • Appetite  (^) • Thirst