Intro to Endocrinology Flashcards
What is a hormone?
A chemical substance
What secretes hormones?
A gland or group of glands, or a tissue into body fluid
What do hormones do?
They have a physiological control effect on other cells of the body
Define endocrine and exocrine.
Endocrine: secretes within the body
Exocrine: secretes outside of the body
What are the various time frames in which hormonal control can take place?
Seconds (epinephrine/ norepinephrine)
several days/weeks
Months ( thyroxine/ growth hormone)
True or False. The nervous system can interact with hormonal system.
True
The sympathetic nervous system can stimulate which glands?
the adrenal glands
The central nervous system can control which gland?
the pituitary gland
True or False. The nervous system can control all hormones
False. It can control some but not all
What metabolic functions of the body does the endocrine system control?
Chemical reaction rate of cells
Transport of substances through cell membrane
Growth of body
Secretion of other hormones
Name the 9 endocrine glands and tissues.
- Pituitary
- Adrenal
- thyroid
- Parathyroid
- Islets of Langerhans
- ovaries
- Testes
- Placenta
- duodenum
What is the anterior pituitary primarily controlled by?
Controlled by other hormones
What hormones does the anterior pituitary gland secrete? (6)
Growth hormone
Adrenocorticotropin
thyroid-stimulating hormone
Follicle-stimulating hormone
Luteinizing hormone
Prolactin
The posterior pituitary is primarily under what control?
Neuronal control
What hormones does the posterior pituitary secrete?
Oxytocin
antidiuretic hormone
The adrenal glands can be separated into two parts. What two parts are these?
The adrenal cortex and the adrenal medulla
The adrenal cortex is primarily under what control?
Hormonal control
What hormones does the adrenal cortex secrete?
Cortisol
Aldosterone
The adrenal medulla is under what control?
Neural control
What hormones does the adrenal medulla secrete?
Secretes two catecholamine hormones:
adrenaline (epinephrine) (major secretion)
Noradrenaline (norepinephrine) (minor secretion)
Where is the thyroid gland located?
Located up in the sternal and mediastinal area of the thorax. Situated above the thymus which sits above the heart.
What hormones does the thyroid secrete?
Thyroxine
Triiodothyronine
Calcitonin
Why is the parathyroid gland considered separate from the thyroid gland even though it is located within it?
Due to its function
What hormone does the parathyroid gland secrete?
Parathyroid hormone
The parathyroid gland consists of what?
Four small blobs located within the thyroid gland
Where are the Islets of Langerhans found?
In the pancreas
Are the Islets of Langerhans considered glands or endocrine tissue
Endocrine tissue
What hormones do the Islets secrete?
Insulin
Glucagon
True or False. The ovaries are considered to be an endocrine gland.
True
What hormones do the ovaries produce?
Estrogen
Progesterone
True or False. The testes are an endocrine tissue.
False. They’re a gland
What hormone does the testes produce?
Testosterone
The placenta is considered to be an endocrine tissue during certain times. What are those times?
During menstruation, conception, gestation
What hormones does the placenta secrete?
Human chorionic gonadotropin
estrogen
Progesterone
Somatomammotropin
What glands does the duodenum contain?
Brunner’s Glands
What do the Brunner’s glands do?
Secretin hormone signals to the pancreas
Coordinates digestion
What is the purpose of brown adipose tissue?
Receives hormonal input to help regulate body temperature
Is brown adipose tissue an endocrine tissue?
No, because it does not secrete hormones.
What categories can hormones be classified into according to their range of effect?
Local hormone or general hormone
What are local hormones?
Hormones that have specific local effects on specific tissues. (not based on where it comes from but where it has effect)
What are three examples of local hormones?
Secretin (Released from duodenal (intestinal) wall, transported in blood to pancreas, cause pancreas secretions for digestion)
Cholecystokinin (Released in small intestine, transported to (1) gallbladder cause gallbladder contraction,(2) pancreas cause secretion of digestive enzyme.)
Adrenocorticotropin (Released from anterior pituitary gland, stimulates adrenal cortex to secrete adrenocortical hormones)
What are general hormones?
Hormones that have effects on many parts of the body and cause many different reactions
Describe Epinephrine and Norepinephrine
Secreted by the adrenal medulla under sympathetic stimulation
Secreted by sympathetic nerves
Cause constriction of blood vessels and increase in arterial pressure
Has effects on most organs and tissues of the body (general hormones)
Give 4 examples of general hormones.
Epinephrine
Norepinephrine
Growth hormone: secreted from anterior pituitary, cause growth in all body parts
Thyroid hormone (T3 & T4): secreted from thyroid gland, increases reaction rates in almost all cells of the body
Hormones can also be classified by their chemical structures. What are the three different classifications?
Steroid, protein and tyrosine
Steroid-based hormones are based from what?
Cholesterol
Why are steroid hormones called as such?
Because testosterone is built from cholesterol and many anabolic steroids are made from testosterone
The adrenal cortex can turn cholesterol into what?
many hormones including aldosterone and cortisol
What can the placenta and ovaries turn cholesterol into?
Estrogen
What can the testes turn cholesterol into?
testosterone
Where are the receptors for steroid hormones found and why?
Usually found within the cell cytoplasm or nucleus. This is due to the fact that steroid hormones are hydrophobic and lipophilic
What is the mechanism of steroid hormone action?
Steroid hormones enter cytoplasm of cell ==> bind with receptors* ==> diffuse or transported into nucleus ==> bind to and activate DNA strands ==> initiate transcription process of genes to form RNA messenger ==> RNA goes into cytoplasm through nuclear pore complex ==>promote functions inside the cells.
What can the thyroid gland turn tyrosine into?
Thyroxine (T4) and triiodothyronine (T3)
What can the adrenal medullae turn tyrosine into?
epinephrine and norepinephrine
How does the thyroid gland make T3 and T4 from tyrosine?
It adds iodine molecules to tyrosine which in turn makes T3 and T4 lipophilic.
How does the adrenal medulla turn tyrosine into epinephrine and norepinephrine?
It hydroxylates tyrosine which makes the molecules lipophobic.
What is the chain of action for thyroid hormones?
Thyroid hormones ==> bind with receptor in cell nucleus* ==> bind and activate DNA ==> initiate transcriptions of specific genes to form RNA messenger ==> RNA goes into cytoplasm through nuclear pore complex ==> new proteins (enzymes) are formed and become the controller to promote metabolic activities in all cells of body
*In some cases the receptors are found within the nucleus not the cytoplasm.
What is the chain of action for epinephrine, norepinephrine and acetylcholine
E or NE ==> bind with receptors on the cell membrane ==> cause conformational change of proteins structure of the receptor ==> open or close channels for ions (Na or K) (change of membrane permeability) ==> change of cell membrane potential ==> cause cell excitation or inhibition
What is the chain of action for protein and peptide-based hormones?
Protein or peptide-based hormones bind receptors on membrane (protrudes to exterior of cell) ==> structure change in receptor ==> receptor becomes activated enzyme “adenyl cyclase” ==> activate the formation of “cyclic adenosine monophosphate” (cAMP) ==> second messenger activates a cascade of enzymes ==> cause powerful effects on cells
Why do peptide-based and protein hormones bind to receptors on the cell membrane?
Because they are lipophobic (hydrophilic)
What are second messengers?
they are cell-signaling pathways that communicate with the receptors on the cell surface and the inside of the cell.
What is the pathway of cyclic adenosine monophosphate (cAMP) as a second messenger
Hormones ==> receptor ==> activate enzyme “adenyl cyclase” ==> activates the formation of cAMP ==> activate a cascade of enzymes ==> cause different effects on cells.
what is the pathway of Ca2+-Calmodulin as second messenger
Hormones ==> receptor ==> open channels for Ca2+ ions ==> Ca2+ diffused into cell and bind with calmodulin ==> calmodulin is activated by conformational change ==> activated calmodulin can cause multiple effects inside the cell in the same way that cAMP does
what is the pathway of IP3 and diacylglycerol as second messenger
Hormones ==> receptor ==> activates enzyme phospholipase C attached to the inside projection of the receptor ==> cause phospholipids in the cell membrane to split into small substances such as inositol trisphosphate (IP3) and diacylglycerol that serve as “second messenger”
What factors make it hard to measure hormones?
Blood hormone concentration is very low. The rate of secretion of hormones is extremely small. Hormones are very small chemical molecules that defy conventional measuring techniques
How can hormones be measured?
By method of radioimmunoassay or mass spectrometry
What is the advantage of controlling the secretion rate of hormones?
The body can control how much effect the hormone is having and can shut it off if the secretion becomes too much
What are two types of ways to control hormones and which one is the more common?
Negative and Positive feedback. Negative feedback is the most common way.
What is direct negative feedback?
when the hormone inhibits its own secretion when it reaches a high enough level.
Gland secretes hormone ==> hormone accumulates in blood ==> hormone gets back to gland ==> hormone inhibits its own secretion.
What is indirect negative feedback?
When the effect of the hormone inhibits the secretion of the hormone
Gland secretes hormone ==> hormone accumulates in blood ==> hormone stimulates a tissue ==> the tissue produces some effects, for example, heat is produced ==> the effects, in this example heat, will go back to the gland and inhibit the secretion of the hormone.
Why is positive feedback less common?
It’s hard for the body to control
What is direct positive feedback?
Gland secretes hormone ==> hormone accumulates in blood ==> the hormone goes back to the gland and promotes the secretion of the hormone.
What is indirect positive feedback?
Gland secretes hormone ==> hormone accumulates in blood ==> the hormone stimulates a tissue ==> the gland and produces some effect which then promotes the secretion of the hormone.
How are hormone receptors regulated?
The number of receptors in the target cell varies depending on time
Receptors can be activated or deactivated by altering their second messenger cell signaling pathway, or by altering their location in the cell.
Receptors can be destroyed by enzymes
Receptors can be created by synthesis
What does chronic over stimulation of a receptor lead to?
Leads to a deactivated or destroyed receptor. so the hormone will not have an effect until the receptor is reproduced.
