Lecture 8: Endocrine System Flashcards
Endocrinology
Concerned with chemical integration of the body
Integration with…
The nervous system, and it is very important for normal function that they work together
Hormone
- Greek for stimulate
- a chemical substance produced in one part of body (endocrine gland) that diffuses or is transported to another area where it influences activity and integrates component parts of the organism
- regulates rate of existing reactions that have enzymes or initiates metabolic reactions
How could an excess of hormones be as detrimental as a deficiency?
They influence reaction rate through interaction with enzymes, which can reduce the response of enzymes if overused
Local/Para Hormones
- Prostaglandins: reproduction
- Erythropoietins
- Histamines
- Gastro-intestinal hormones
- Kidney hormones: Renin, for Na/K balance
Erythropoietin
produced by anoxic kidney and stimulates bone marrow production of RBC
Histamine
produced by injured tissues and action locally on the surrounding tissue
Gastro-Intestinal Hormones
Gastrin, secretin, Pancreozymin, Cholecystokinin
Kidney Hormone:
Renin, for Na/K balance
History: how did Aristotle show possibility of internal control of functions of the body?
-through observing the effects of castrating birds
Endocrine organs
hypothalamus, pituitary, pineal, thyroid, parathyroid, pancreas (islets of langerhans, adrenal, ovary, testis, placenta, and many tissues (prostaglandins)
TRH, thyrotropin-releasing hormone activates,
originates from the hypothalamus
TSH, thyroid stimulating hormone, which stimulates the thyroid and parathyroid; originates from the anterior pituitary
PRH, prolactin releasing hormone
hypothalamus
PRL, prolactin, which stims the mammary glands
from anterior pituitary
PIH, prolactin release-inhibiting hormone; from the hypothalamus
inhibits PRL, prolactin
CRH, corticotropin-releasing hormone;
from the hypotalamus
ACTH, adrenocorticotropic hormone stims the adrenal glands;
from the anterior pituitary
GnRH, gonadotropin releasing hormone
from the hypothalamus
stimulates 1. LH, Luteinizing hormone for the testis, or 2. FSH, follicle-stimulating hormone for the ovaries;
from the anterior pituitary
GHRH, growth hormone releasing hormone;
from hypothalamus
stimulates GH, growth hormone, which stims growth of bone, muscle, and adipose tissue
SS, somatostatin;
from hypothalamus
inhibits GH, growth hormone
adrenal gland
sits atop the kidney and consists of the Cortex and Medulla
Adrenal cortex
produces glucocorticoids (cortisol, cortisone, and corticosterone), and aldosterone
Adrenal Medulla
produces epinephrine and norepinephrine
Glucocorticoids
- cortisol, cortisone, and corticosterone
- aid in gluconegenesis, decrease of peripheral glucose utilizatoin, anti-flammatory effect, anti-allergic effect, and euphoric effect
Aldosterone
-electrolyte and water metabolism
Epinephrine
glycogenolysis to raise blood glucose
Norepinephrine
Cardiovascular function; Mainly Pressor Effect
Ovaries produce
Progesterone, Estrogesn (estradiol, estrone, and others), and Relaxin
Progesterone
w/ estrogen it develops uterus for implantation and pregnancy maintenance
Estrogens
- estradiols, estrone, and others
- development, maintenance, and cyclic changes of female tubular genital tract
- glandular duct development of mammae and uterus
- secondary sex characteristics and behavior
- accessory sex organs
- calcium and fat metabolism in birds
Relaxin
-dissolution of symphysis pubis and relaxes pelvic tissues
Testis
produce testosterone
Testosterone
development of accessory sex organs and secondary sex characteristics
- behaviour
- spermatogenesis
- anabolism
Pancreas/Islets of Langerhans
Alpha cells that secrete glucagon and Beta cells that secrete insulin
Glucagon
Increases blood glucose level by favoring liver glycogenolysis
Insulin
Decreases blood glucose level by storage or utilization
-also aids fat and protein metabolism
Placenta
hCG-chorionic gonadotropin (primates) PMSG-Pregnant Mare Gonadotropin Estrogens Progesterone Relaxin
hCG-Chorionic Gonadotropin
Mainly LH-like, although some FSH-like properties
PMSG-Pregnant Mare Gonadotropin
Mainly FSH-like, but also some LH-like properties
Interrelation of Endocrine and Nervous system
hormones of hypothalamus, pituitary, and other endocrine glands interact with nervous system
- nervous system serves as an afferent branch bringing impulse to the hypothalamus, and then the endocrine system (pituitary) releases hormonal substances, which act peripherally to complete the reflex
- endocrine=wireless; nervous=wire system
- both important for maintenance of homeostasis
examples of interrelation of endocrine and nervous system
- physical stim of vagina/cervix during copulation causes impulse to travel to spinal cord
- impulse reaches hypothalamus and here GnRH is released
- GnRH is carried by hypophyseal portal vessels to the anterior pituitary
- anterior pituitary releases luteinizing hormone (LH) and LH is carried in the circulatory system
- LH will act on the mature follicles and cause ovulation
- another example is let-down of milk
genetic make up of individual affects…
phenotypic characteristics are manifestations of..
- growth and development and reproduction
- biochemical coding in DNA of the gene
relationship of genetics and endocrinology
- amount and kind of hormone produced are coded in the DNA
- thus errors could result in malfunction of the endocrine organ or a hereditary disease
- any malfunctions could result in over or underproduction or production of an abnormal hormone
- selection for growth, number of eggs laid/egg size, milk production, etc are all possible
Chemical classes of hormones
- polypeptide hormones
- steroid hormones
- catecholamines and iodothyronines
Polypeptide hormones
produced in hypothalamus, pituitary, parathyroid, and islets of langerhans
- building blocks are amino acids
- production depends on substrate, energy supply, biological stimulation
Polypeptide hormone administration
parenternal: outside digestive system
- oral administration thus leads to destruction of their structure by digestive enzymes
Steroid hormones
- produced by gonads, adrenal cortex, and placenta
- building blocks: acetate-cholesterol
- alterations can determine which steroid is released
- steroid structures are similar but have very different physiological/pharmacological effects
Catecholamines and Iodothyronines
- tyrosine derivatives, of which represent 5% of mammalian hormones
- catecholamines=epinephrine/nor-epinephrine
- iodothyronines=thyroxin, tri iodothyronine
Catecholamines
=epinephrine/nor-epinephrine
-share similar mechanism of action with polypeptide hormones
Iodothyronines
=thyroxin, tri iodothyronines
-more closely resemble the characteristics of steroid hormones
prostaglandins are made of …
fatty acids
Hormone Transport
- Polypeptide hormones are produced and stored in a gland until needed, then they are released into capillaries
- steroid hormones are not stored, but released when produced; they also do not circulate freely in the blood, but are bound to carrier proteins
- thyroxin and tri-iodothyronine are stored in thyroid follicles until needed
steroid and thyroxin hormone carrier proteins
TBG: thyroxin binding globulin
CBG: corticosteroid binding globulin; binds to corticosteroids and progesterone
SHBG: Sex-hormone binding globulin, binds to estradiol and testosterone
Significance of binding
- restricts diffusion through tissues/cells
- prolongs their action: binding protects against degradation/elimination
- bound form cannot enter the cell
steroid and thyroids are smaller or larger than peptide hormones?
smaller, and can diffuse freely into most cells, membrane does not act as a barrier
-polypeptide hormones are much larger, and therefore must exert action on surface of the target cell since they cannot pass through the plasma membrane
Target cells and receptor sites
though all cells are exposed to hormones produced by endocrine glands, only a few respond (target cells) because they have highly specific receptor sites
-receptor sites are on the surface of the cell for peptide hormones, in the nucleus chromatin for thyroid hormones, and in the cytoplasm and nucleus for steroid hormones
events of hormone-binding: polypeptide hormone LH
- specific receptor site in target organ binds a hormone, LH (first messenger), to the membrane of cell
- the binding stimulates an enzyme, Adenyl Cyclase in membrane to convert ATP to cyclic 3, 5 adenosine monophosphate (cyclic AMP), the second messenger
polypeptide hormone LH binding part two: cAMP second messenger
- cAMP conveys message of hormone to intracellular sites initiating a chain of reactions that result in physiological effects
- ACTH, LH, FSH, TSH, and HCG produce their effects by cAMP second messenger
- depending on its structure, cAMP will either modifiy the enzyme, affect membrane permeability, or stimulate hormone release
- cAMP is common amongst all peptide hormone action
Steroid/Thyroid hormone action
- stimulate targets by intracellular action on the control and synthesis of specific proteins
1. only target cells have specific receptor protein to bind the steroid in question
2. once bound, the hormone can move from the cytoplasm into the nucleus where there is an acceptor site on the chormosome
3. next the gene responds by forming a specific messenger RNA, which leaves the nucleus and directs synthesis of a particular protein necessary for the function of the particular steroid
Steroid/thyroid special points
- although most hormones have target organ that responds to a greater extent than any other tissue, other tissues may have some receptors
ie. estradiol exerts most profound action on uterus, vagina, and mammary glands, but also affects other tissues that have receptors to estrogen like skin, hair, and bone
can target organs function in absence of a hormone?
yes: at minimal levels they can continue to function
some physiological events require more than one hormone, name those for lactation and parturition
lactation: estrogen, progesteron, oxytocin, prolactin, somatotrophin, thyroxin, and cortisone
parturition: oxytocin, estrogen, relaxin, corticosteroids, prostaglandin
regulation of hormone secretions
endocrine glands are important regulators of many processes in the body, therefore careful regulation of their output is critical and depends on many mechanisms
types of control of hormone secretions
humoral and nervous
humoral regulation
- concentration of a blood constituent
ie. change in level of blood glucose; low blood glucose=insulin needed to facilitate glucose movement through the cell membrane (metabolized or stored), lowering blood glucose - concentration of another hormone
if blood glucose drops below normal levels…
glucagon, the blood glucose rising hormone is released, stimulating the release of glucose from the liver
Anterior pituitary’s role in regulation of hormone secretion
- inhibited directly or indirectly via hypothalamic releasing factors by hormones produced by endocrine organs
- therefore balance is maintained between stimulating effects of the anterior pituitary and the resultant inhibitory effects on anterior pituitary output; aka positive and negative feedback
Regulation of hormone output by concentration of another hormone
ie. anterior pituitary, which secretes hormones that regulate other gland, which is called a feedback mechanism
