Introduction to the Endocrine System Flashcards
What is endocrinology
The study of the endocrine system
What is neuroendocrinology
The study of the control of the endocrine system by the nervous system
What is neuroendocrine integration
How the two systems interact in order to maintain homeostasis in the body
What is the endocrine system
Communication within the body using hormones
What is a hormone
A chemical produced by a ductless endocrine gland which is secreted into the blood. It is transported to a target elsewhere in the body where it causes an effect
How do hormones communicate with their target cells
They bind to receptors on their target cells
What happens if the appropriate receptor is not present on a cell
The hormone cannot affect it
Describe cell membrane receptors
A hormone binds to a receptor in the cell membrane which triggers a response in the target cell
Describe receptors in the nucleus
Once the hormone has crossed the cell membrane it bind to receptors in the nucleus. Forms a hormone-receptor complex which causes gene expression
What are the two types of receptors on target cells
Receptors on cell membranes and receptors in the nucleus
What types of chemical substances are hormones
- Steroids 2. Proteins/ peptides 3. Amines
Where are steroids synthesised
In the adrenal cortex, ovaries, testes and placenta
How are steroids transported
They are not very soluble in blood so are transported bound to proteins
How do steroids enter cells
They are fat soluble so cross membranes easily and diffuse out of cells
What type of receptors do steroids have
Intracellular receptors
Steroids are easily absorbed in the GI tract- True/ False
True
Why can steriods be administered orally
Because they are easily absorbed in the GI tract
In what form are proteins/ peptides synthesised
They are synthesised as ‘prehormones’/ ‘prepeptides’
Where are proteins/ peptides stored
They are stored in membrane-bound vesicles/ granules
How are proteins/ peptides transported
They circulate unbound in the blood
What type of receptors do proteins/ peptides have
Cell membrane receptors
Why can’t proteins/ peptides be administered orally
They are too easily digested
What are the two varieties of amines
- Thyroid hormones 2. Catecholamines
What are thyroid hormones derived from
Tyrosine
Do thyroid hormones cross cell membranes
Yes
What type of receptors do thyroid hormones have
Intracellular receptors
How are thyroid hormones transported
They are protein-bound
Where are thyroid hormones stored
In thyroid follicles
Can thyroid hormones be administered orally
Yes
What are catecholamines derived from
Tyrosine
DO catecholamines cross the cell membrane
Yes
What type of receptors do catecholamines have
Cell membrane receptors
How are catecholamines transported
Unbound in the blood
How how catecholamines stored
In membrane-bound vesicles/ granules
Can catecholamines be administered orally
Yes but their half life is too short
What 5 things does binding hormones to proteins do
- Prolongs their circulating half-life 2. Prevents them from entering the wrong type of cell 3. Prevents them from being lost through the kidneys 4. Maintains the right concentration of the hormone 5. Acts as a ‘buffer’ against a drop in the secretion of a hormone
How do hormones act on their target cells
- Receptor binding 2. Initiates intracellular cell-signalling events (2nd messenger hypothesis).
Describe second messenger hypothesis
A hormone binds to a receptor which initiates the production of cAMP which are called ‘second messengers’
Which are the male endocrine glands
- Pituitary gland 2. Thyroid gland 3. Adrenal gland 4. Testis
What are the female endocrine glands
- Pineal gland 2. Thymus 3. Pancreas 4. Ovary
What is a very important trace element in thyroid hormones
They contain iodine (iodothyronines)
What are the 3 thyroid hormones
- Thyroxine (T4) 2. Triiodothyronine (T3) 3. Reverse T
Describe the 3 components of a thyroid gland
- Colloid
- Follicular epithelium
- Follice
What are the 4 functions of thyroid hormones
- Maturation, development and growth. 2. Metabolism (Control basic metabolic rate). 3. Skeletal muscle (calcium availability). 4. Cardiovascular system
Describe the stages of thyroid hormone production
- Thyroglobulin (TG) couples to a follicular cell membrane by thyroid peroxidase.
- TG enclosed by lysosome containing proteolytic enzymes.
- Iodinated tyrosines (MIT and DIT) are then deiodinated.
- Tyrosine and iodine are recycled.
What two endocrine tissues are located within the adrenal gland
- Adrenal cortex 2. Adrenal medulla
Which two catecholamines are secreted by the adrenal medulla
- Noradrenaline 2. Adrenaline
What controls the adrenal medulla
The sympathetic nervous system
Which do receptors do adrenaline and noradrenaline act on
Alphareceptors and betareceptors
What effects to adrenaline and noradrenaline have on betareceptors
- Metabolic 2. Cardiovascular 3. Bronchodilation
What effects to adrenaline and noradrenaline have on alphareceptors
- Metabolic 2. Cardiovascular 3. Sweating 4. Dilation of pupils 3. Sphincter contractor
What 3 groups of hormones does the adrenal cortex produce
- Mineralocorticoids 2. Glucocorticoids 3. Sex hormones
Give an example of a mineralocorticoids and explain what they do
Aldosterone. Regulate mineral metabolsim- retention of Na+ and water resorption by the kidney. Secretion of H+ and K+
Give an example of a glucocorticoid and explain what they do
Cortisol. Regulates blood glucose levels
Give an example of a sex hormone and explain what they do
Weak androgens that can be converted into more potent sex hormones (androgens) such as testosterone and oestrogens, especially in women
Describe the pancreas
The pancreas is both an exocrine and endocrine gland
What is the endocrine part of the pancreas called
Islets of Langerhans
What are the 3 types of cells of the Islets of Langerhans
- Alpha cells 2. Beta cells 3. Delta cells
What do alpha cells produce and what is the function of this hormone
Glucagon- a catabolic hormone which can mobilise stores of glycogen, fat and protein to act as energy sources during food deprivation
What do beta cells produce and what is the function of this hormone
Insulin- an anabolic hormone which causes the uptake and use of glucose from the blood during times of excess nutrient availability
What do delta cells produce and what is the function of this hormone
Somatostain- inhibits growth hormone and gastrin
Describe what happens when there are low blood glucose levels
Detected by the pancreas -> glucagon is released by alpha cells > liver releases glucose into blood -> achieve normal blood glucose levels
Describe what happens when there are high blood glucose levels
Detected by the pancreas -> beta cells release insulin -> fat cells take in glucose from the blood -> achieve normal blood glucose levels
Why must the levels of Ca2+ be tightly regulated
Because it can become very toxic to cells
What percentage of Ca2+ is found in the bones and teeth
99%
What percentage of Ca2+ is found intracellulary
0.9%
What percentage of calcium is found in the ECM
0.1%
What is half of free Ca2+ bound to
Proteins or PO4(3+)
How much calcium is freely diffusible
About half is freely diffusible and can take part in chemical reactions- this must be tightly regulated
What happens in terms of neuromuscular excitability when Ca2+ levels decrease
Over excitability of nerves and muscles
What happens in terms of neuromuscular excitability when Ca2+ levels increase
Depressed the excitability of nerves and muscles
What is the function of Ca2+ in cardiac and smooth muscle
Excitation-contraction coupling. Ca2+ entry into these tissues initiated the contractile mechanism
What happens when Ca2+ enters nerves and cells that secrete peptide hormones
It triggers the secretory process
What increases Ca2+ levels
Parathormone (PTH)
What is parathormone produced by
The parathyroid gland
What does parathormone do
Increase levels of Ca2+ and so prevents hypocalcaemia
Apart from parathormone what else is involved in the regulation of Ca2+
Calcitonin and vitamin D
Which parts of the body does parathromone regulate the exchange of Ca2+
In the bone, kidneys and intestine
Which are the two main cells involved in reproductive endocrinology
Leydig cells Sertoli cells
Label the leydig and sertoli cells
Diagram
What are sertoli cells involved in
Maturation of sperm by producing peptodes that act as hormones
What do leydig cells produce
Testosterone which is a steroid hormone and an androgen
What are the effects of testosterone before birth
Regulates differentiation and development of internal and external genitalia
What are the effects of testosterone at puberty
- Regulates growth and maturation of the internal and external genitalia. 2. Development of secondary sexual characteristics (hair, deep voice, muscle growth). 3. Initiates and maintains spermatogenesis. 4. Develops sex drive.
What are the other effects of testosterone
- Aggression 2. Bone growth and fusion of epiphyses
Label the parts of the female reproductive endocrinology system
Diagram
What do the ovaries do
- Produce eggs (oogenesis). 2. Secrete the female sex hormones oestrogen and progesterone
What do oestrogen and progesterone help to promote
They help to promote fertilisation and get the reproductive system ready for pregnancy
What are the functions of oestrogen
Similar to those of progesterone (secondary sexual characteristics etc.)
What is the menstrual cycle controlled by
A very complex series of interactions between hormones
What are the components of the menstrual cycle synthesised by
The ovary, anterior part of the pituitary gland that the hypothalamus of the brain
What are the 3 aspects of the endocrinology of pregnancy
- Development of the placenta 2. Implantation of the fertilised ovum. 3. Birth (parturition).
What is the posterior lobe of the pituitary gland attached to
The hypothalamus at the base of the brain
What does the anterior pituitary gland regulate
Several physiological processes: stress, growth, reproduction, lactation
How many hormones does the pitutitary gland secrete and what do these hormones do
Secretes 9 hormones that regulate homeostasis
