L27 & 28: Endocrine System Flashcards
What is the difference between the mediator molecules in the nervous system and the mediator molecules in the endocrine system?
Nervous system uses neurotransmitters that are released locally in response to impulses.
Endocrine system uses hormones delivered to tissues throughout the body by blood.
What is the difference between the site of mediator action in the nervous system and endocrine system?
Nervous system: Close to site of release at the synapse. Binds to the receptors on the post synaptic membrane.
Endocrine system: Far from the site of release. Binds to receptors on or in target cells.
What is the difference between the types of target cells in the nervous and endocrine systems?
Nervous: Targets muscle cells (all 3 types), gland cells, and neurones.
Endocrine: Targets all cells in the body.
What is the difference between the time to onset of action in nervous and endocrine systems?
Nervous: Milliseconds
Endocrine: Hours or days
What is the difference between duration of action in nervous and endocrine systems?
Nervous: Milliseconds
Endocrine: Seconds to days
Define “hormone”
A mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body.
Roughly how may hormones do we produce?
30
True or false: Some mediators can act as a neurotransmitter and a hormone
True. e.g. Noradrenaline
Complete the sentence:
“Homones work by ____?____.”
Hormones work by…binding to specific receptors on target cells.
Which type of gland produces hormones?
Endocrine
Fill in the gaps:
Most hormones enter __1__ and then the __2__.
1) interstitial fluid
2) blood stream
What does interstitial mean?
Refers to something being between two structures.
Which of the following is not exclusively an endocrine gland?
A) Thyroid
B) Pituitary
C) Pineal
D) Thymus
D) Thymus
It contains cells that secrete hormones, but is not exclusively an endocrine gland.
What are the 5 major endocrine glands?
1) Pineal
2) Pituitary
3) Thyroid
4) Parathyroid
5) Adrenal
Hormones travelling in the blood will pass all cells, but they will only affect certain cell types. Why is this?
Hormones bind to specific receptors, not all cell will have these receptors
What are the 2 chemical classes of hormones?
1) Lipid soluble
2) Water soluble
What are the 3 types of lipid-soluble hormones?
1) Steroid hormones
2) Thyroid hormones (T3 & T4)
3) Gas (Nitric Oxide, NO)
Name the steroid hormones (7 total) and where they are secreted (4 sites).
Adrenal cortex: Aldosterone, cortisol, and androgens.
Kidneys: Calcitriol
Testes: Testosterone
Ovaries: Oestrogens and progesterone
What are the 2 thyroid hormones?
T3 (triiodothyronine) and T4 (thyroxine)
What hormone is secreted by the endothelial cells lining the blood vessels?
Nitric Oxide (NO)
What are the three types of water-soluble hormones?
1) Amines
2) Peptides and proteins
3) Eicosanoid hormones
Which type of hormone is derived by decarboxylation of amino acids?
Amine hormones (these are water-soluble)
E.g. histamine & serotonin
Protaglandins and leukotrienes are examples of what type of hormone?
Eicosanoid hormones (these are water-soluble)
ADH & oxytocin are examples of what type of hormone?
Peptide/protein hormones
True or false: Water soluble hormones tend to bind to a transporter in the blood?
False. They tend to pass through in a free form
Which type(s) of hormone tend to bind to a transport protein in the plasma?
Steroid and thyroid hormones tend to bind to a transport protein to circulate in the plasma.
Why do steroid and thyroid hormones tend to bind to a transport protein?
1) Soluble
2) Stop/slow filtration by kidneys
3) Act as a hormone reserve
How does a hormone reserve work?
0.1-10% of the hormone molecules are free, as they leave the bound hormones take their place.
Which are typically longer lasting, circulating or local hormones?
Circulating
Do lipid-soluble hormones bind inside or outside the cell?
Inside the cell
What can cells do about the number of receptors when hormone levels are high?
Receptor numbers can be down-regulated.
What can cells do about the number of receptors when hormone levels are low?
Receptor numbers can be up-regulated.
How are cell-hormone receptors up-regulated?
Ribosomes make more of the protein receptors, Golgi apparatus sends to the membrane.
How are cell-hormone receptors down-regulated?
Receptor-mediated endocytosis. The receptors are pulled back into the cell.
How are hormones T3 & T4 made?
By attaching iodine to tyrosine
Do white blood cells and T-cells work by circulating or local hormones?
Local - including autocrine action
Why can the same hormone and receptor produce different effects in different cell types?
The receptors may be the same, but the signalling molecules inside the cells are different. Therefore the action is different.
Which of the following is NOT a lipid-soluble hormone?
A) Aldosterone
B) T4
C) Insulin
D) NO
C) Insulin
T helper cells release the hormone interleukin 2, causing the t-helper cells to proliferate. What is this an example of?
A) Autocrine action
B) Paracrine action
C) Endocrine action
D) Exocrine action
A) Autocrine action
Which of the following is NOT part of the endocrine system?
A) Thalamus
B) Heart
C) Small Intestine
D) Pineal Gland
A) Thalamus
Regarding hormones mechanism of action, which of the following is correct?
A) cAMP is a second messenger for lipid soluble hormones
B) Peptide hormones directly regulate mRNA synthesis
C) Cholesterol based hormones work through phosphorylation amplification cascades
D) Phosphodiesterases inactive peptide hormone signalling
D) Phosphodiesterases inactive peptide hormone signalling
Which is not a feature of hormone signalling?
A) Slow onset
B) Only regulates muscles and glands
C) Diffuse, systemic effect
D) Prolonged effect
B) Only regulates muscles and glands
Transport proteins do not help lipid hormones to:
A) Circulate in the plasma for longer
B) Avoid filtration by kidney
C) Be stored as a reserve
D) Bind to their receptors
D) Bind to their receptors
True or false:
After binding to their receptors, hormones trigger mechanisms of synthesis, degradation, motility changes, secretion, electrical impulses etc.
True.
What does insulin stimulate in liver cells? What does it stimulate in adipose cells?
Liver cells: glycogen synthesis
Adipose cells: triglyceride synthesis
The same hormone can trigger a different mechanism, depending on the responding molecules in the cell.
What are the four steps of lipid-soluble hormone action?
1) Lipid-soluble hormone diffuses into target cell cell
2) Activated receptor-hormone complex alters gene expression
3) Newly formed mRNA directs synthesis of specific proteins on ribosomes
4) New proteins alter cell’s activity
Are lipid-soluble hormones slower or quicker than water soluble?
Lipid-soluble hormones are slower, because they require the formation of new mRNA and then a protein. The process can take 24 hours.
What are the 5 stages of water-soluble hormone action?
1) Water-soluble hormone (first messenger) binds to it’s receptor, activating G protein, which activates adenylate cyclase.
2) Activated adenylate cyclase converts ATP to cAMP (second messenger)
3) cAMP serves as a second messenger to activate protein kinases
4) Activated protein kinases phosphorylate cellular proteins
5) Millions of phosphorylated proteins cause reactions that produce physiological responses
True or false: Water soluble hormones act quicker than lipid-soluble hormones.
True. Water-soluble hormones trigger a quick cascade of action to phosphorylate existing proteins; whereas lipid-soluble hormones trigger the production of new proteins.
How can hormone responses be controlled?
Drugs can inhibit key steps.
e.g. Viagra (phosphodiesterase) inactivates cAMP, preventing the activation of protein kinases.
Fill in the gap:
FSH and oestrogen are an example of __?__ hormones.
Synergistic
Fill in the gap:
Insulin and glucagon are an example of __?__ hormones.
Antagonistic
What is a permissive hormone?
A hormone that works to enhance the response to another hormone. May increase receptor density or promote enzyme activation required for signalling.
Describe the relationship between adrenaline and T3/T4.
Adrenaline is a weak stimulator of lipolysis, but is greatly elevated by T3 and T4.
True or false:
Hormones are released in short bursts.
True
Fill in the gaps:
Endocrine tissue can be __1__/__2__ to control the rate of hormone __3__ (regulated by __4__ and __5__ systems and __6__ of the blood)
1) stimulated
2) inhibited
3) release
4) nervous
5) endocrine
6) chemical composition
What happens to inactive breakdown products?
They are excreted in the urine
What is the major link between the nervous and endocrine systems?
The hypothalamus
Which gland is controlled directly by the hypothalamus?
Pituitary gland
True or false:
Together, the hypothalamus and pituitary play a role in the regulation of almost all aspects of growth, development, metabolism, and homeostasis.
True
Name the hormone(s) secreted by the hypothalamus
1) Thryotropin-releasing hormone
2) Dopamine
3) Growth hormone-releasing hormone
4) Somatostatin
5) Gonadotropin-releasing hormone
6) Corticotropin-releasing hormone
7) Oxytocin
8) Vasopressin
Name the hormone(s) secreted by the pineal gland
Melatonin
Name the hormone(s) secreted by the anterior pituitary
1) Growth hormone
2) Thyroid-stimulating hormone
3) Adrenocorticotropic hormone
4) Follicle-stimulating hormone
5) Luteinizing hormone
6) Prolactin
Name the hormone(s) secreted by the intermediate pituitary
Melanocyte-stimulating hormone
Name the hormone(s) secreted by the posterior pituitary
1) Oxytocin
2) Vasopressin
3) Oxytocin (stored)
4) Anti-diuretic hormone (stored)
Name the hormone(s) secreted by the thyroid gland
1) Triiodothyronine
2) Thyroxine
True or false: Many hormones are produced in both the anterior and posterior pituitary.
False. The anterior pituitary contains endocrine tissue that can produce hormones; posterior cannot produce hormones. Posterior can store and release hormones.
The pituitary portal system is a network of capillaries that directly links the hypothalamus to the pituitary gland. Why is it useful to have their own private circulatory network?
Master hormones can quickly get from the hypothalamus to the pituitary gland, without having to circulate through the whole body. Speeds up response time.
What is the infundibulum?
A connecting stalk between the hypothalamus and pituitary
What are the 5 types of anterior pituitary cell?
1) Somatotrophs
2) Thryotrophs
3) Gonadotrophs
4) Lactotrophs
5) Corticotrophs
Which pituitary cells secrete human growth hormone (hGH)?
Somatotrophs.
Human growth hormone is also known as somatotropin
Which pituitary cells secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH)?
Gonadotrophs
Which pituitary cells cause the secretion of oestrogen & progesterone?
Gonadotrophs. Also stimulate sperm and testosterone production.
Which hormone regulates the thyroid gland? Where is it secreted?
Thyroid stimulating hormone (TSH). Secreted by thyrotrophs in the anterior pituitary.
What is secreted by corticotrophs?
Adrenocorticotropic hormone (ACTH). Some also secrete melanocyte stimulating hormone.
What does ACTH do?
ACTH = adrenocorticotropic hormone
Stimulates adrenal cortex to produce glucocorticoids.
What is the term used to describe anterior pituitary hormones that act on other endocrine glands?
They are known as tropic hormones
Which inhibitory hormones are released by neurosecretory cells in the hypothalamus?
1) Growth hormone inhibitory hormone (GHIH)
2) Prolactin inhibitory hormone (PIH)
Which stimulatory hormones are released by neurosecretory cells in the hypothalamus?
1) Growth hormone-releasing hormone (GHRH)
2) Thyrotropin-releasing hormone (TRH)
3) Gonadotropin-releasing hormone (GnRH)
4) Prolactin-releasing hormone (PRH)
5) Corticotropin-releasing hormone (CRH)
Describe the stimulation pathway activated by GHRH.
GHRH stimulates hGH, which stimulates insulin-like growth factors (IGFs)
Describe the stimulation pathway activated by TRH
TRH stimulates thyroid-stimulating hormone (TSH), which stimulates T3 & T4
Describe the stimulation pathway activated by GnRH
GnRH stimulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which stimulate oestrogen and progesterone or testosterone
Describe the stimulation pathway activated by PRH
PRH stimulates prolactin
Describe the stimulation pathway activated by corticotropin-releasing hormone (CRH)
CRH stimulates adrenocorticotropic hormone (ACTH), which stimulates glucocortocoids
How does negative feedback relate to the regulation of hypothalamus and pituitary gland?
Negative feedback by hormones from target glands decreases activity in hypothalamus/pituitary
Which 3 secretory cells in the pituitary are affected by negative feedback from their target gland hormones?
Thyrotrophs, gonadotrophs, and corticotrophs
Why are somatotrophs the most numerous cell-type in the anterior pituitary?
To ensure lots of growth hormone (hGH) can be released as needed by the body.
What effect does hGH have?
hGH promotes the release of IGFs, which stimulate amino acid uptake by target cells - promoting protein synthesis.
hGH and IGFs also speed up release of glucose by liver
In a state of hypoglycaemia, which hormone would be released by the hypothalamus?
Growth hormone-releasing hormone.
This leads to increased hGH and IGFs, which promote glucose release by the liver
In a state of hyperglycaemia, which hormone would be released by the hypothalamus?
Growth hormone-inhibiting hormone.
This leads to decreased hGH and IGFs, which lowers how much glucose is released by liver
Some people take supplements containing hGH to build more muscle mass. What are the dangers of long-term use of hGH supplements?
hGH stimulates glucose release by liver, resulting in hyperglycaemia. This constantly stimulates insulin secretion by the pancreas and burns out beta cells, resulting in diabetes.
Vasopressin is more commonly known as what?
Anti-diuretic hormone (ADH)
What is the main role of the posterior pituitary?
Storage and release of 2 hormones:
1) Oxytocin
2) ADH
What structures make up the posterior pituitary?
Axons and axon terminals of hypothalamic neurosecretory cells
If they are only stored and released in the posterior pituitary, where are oxytocin and ADH produced?
Hypothalamus. They are then packaged in vesicles and stored in the axon terminals in the posterior pituitary
What is a permissive and synergistic effect? How do they differ?
Hormones that work in conjunction with one another are described as synergistic. Permissive effects occur when one hormone causes an increased sensitivity or greater activity in another hormone.
What is the name given to the microscopic spherical sacs that make up most of the thyroid?
Thyroid follicles
What is a colloid?
A cavity in the follicle that is used to store hormones
What is BMR?
Basal metabolic rate (BMR) is the amount of energy expended while at rest in a neutrally temperate environment
What effect do T3 & T4 have on BMR?
Increases by stimulating respirating
How do thyroid hormones help you to keep warm?
Stimulate synthesis of Na+/K+ ATPase. Causes rapid turnaround of ATP, generating heat (calorigenic effect).
How do thyroid hormones increase the effect of catecholamines (adrenaline and noradrenaline)?
Thyroid hormones increase the number of beta receptors for catecholamines
What are the effects of thyroid hormones?
1) Increase BMR by stimulating respiration
2) Stimulate synthesis of Na+/K+ ATPase, causing rapid turnaround of ATP, generating heat
3) Stimulates protein synthesis, cause glucose and FAs to be used for ATP production
4) Increase beta receptors, enhancing effect of catecholamines
5) Accelerate body growth
Which cells can thyroid hormones affect?
Most cells have thyroid hormone receptors
How are thyroid hormone levels regulated?
Negative feedback - elevated T3 inhibits release of thyrotropin-releasing hormone (TRH) and thyroid stimulating hormone (TSH)
True or false: Conditions that decrease ATP demand also induce secretion of thyroid hormones?
False. Conditions that INCREASE ATP demand also induce secretion of thyroid hormones.
What types of cell make up the parathyroid glands? What is their function?
1) Chief cells: produce parathyroid hormone (PTH)
2) Oxyphilic cells: function unknown
Hypo- or hyper-thyroidism?
Dry, coarse hair Loss of eyebrow hair Puffy face Goiter Bradycardia Arthritis Cold intolerance Depression Dry skin Fatigue Forgetfulness Heavy menstruation Infertility Muscle aches Weight gain Constipation Brittle nails
HYPOthyroidism
Hypo- or hyper-thyroidism?
Hair loss Bulging eyes Sweating Goiter Tachycardia Difficulty sleeping Heat intolerance Infertility Irritability Muscle weakness Nervousness Scant menstruation Weight loss Frequent bowel movements Warm, moist palms Finger tremors Soft nails
HYPERthyroidism
What are the symptoms associated with congenital hypothyroidism?
Severe mental retardation
Stunted bone growth
What is hypothyroidism known as in adults?
Myxoedema
Why doesn’t myxoedema cause mental retardation?
Because the brain has already reached maturity. Physical symptoms such as puffy face.
What is graves disease?
Autoimmune disease that causes hyperthyroidism by mimicking TSH. Water retention causes bulging eyes. Goiter.
Where are the adrenal glands located?
On top of each kidney
What do adrenal glands consist of?
1) Adrenal cortex
2) Adrenal medulla
What is the role of the adrenal cortex?
Adrenal cortex produces steroid hormones essential for life
What is the role of the adrenal medulla?
Adrenal medulla produces 3 catecholamines (adrenaline, noradrenaline, and dopamine)
Within the adrenal cortex are 3 zones, what are they and what hormones do they regulate?
1) Glomerulosa: Mineral corticoids
2) Fasciculata: Glucocorticoids (mainly cortisol)
3) Reticularis: Androgen synthesis
What is the role of glucocorticoids?
Regulate metabolism and resistance to stress
How is secretion of glucocorticoids regulated?
Negative feedback: low levels cause corticotropin-releasing hormone (CRH) release from hypothalamus, stimulating release of ACTH from pituitary.
What effects do glucocorticoids have on the body?
1) Protein breakdown (mainly from muscles)
2) Gluconeogenesis from AAs & lactic acid
3) Lipolysis
4) Resistance to stress (ATP burst & increase vessel sensitivity to other hormones, increasing vasoconstriction)
5) Anti-inflammatory effects (also slow wound healing)
6) Depression of immune system (useful for organ transplants)
What do androgens do?
In men: no effect after puberty
In women: promote libido, can be converted to oestrogen
Why are androgens important to postmenopausal women?
After menopause, androgens are their only source of oestrogens
Which part of the adrenal gland is a modified sympathetic ganglion of ANS?
Adrenal medulla
What are the cells in the adrenal medulla known as? What are their characteristics?
Chromaffin cells: they lack axons and cluster around large blood vessels. They secret noradrenaline and adrenaline to strengthen the fight or flight response
What condition is a result of hypersecretion of cortisol?
Cushing’s syndrome
What are some of the classic symptoms of Cushing’s?
Moon face Dorsal fat pad Central obesity Thin skin, easy bruising Ulcers Muscle weakness
What condition results from hyposecretion of glucocorticoids and aldosterone?
Addison’s disease
What are the symptoms of Addison’s disease?
Bronze skin Changes in body hair distribution Weight loss Hypoglycaemia Postural hypotension
What are gonads?
Men: Testes
Women: Ovaries
What hormones are secreted by the male gonads?
Testes secret testosterone and inhibin.
Inhibin inhibits production of FSH
What are the side effects of too much testosterone?
Gynecomastia
Increased BP
Polycythemia
Acne
Benign prostatic hypertrophy
What hormones are produced by the female gonads?
Ovaries secrete oestrogens, progesterone, inhibin, and relaxin
What cells make up the pineal gland?
Neuroglia and secretory cells (pinealocytes)
What is the role of melatonin?
Promotes sleep, protects from free radicals
What condition may arise from too much melatonin?
Seasonal affective disorder (SAD)
What are the 2 types of stress?
1) Eustress: prepares us to meet certain challenges & is useful
2) Distress: harmful
How is the body’s response to stress controlled by the hypothalamus?
1) Fight or flight (ANS)
2) Slower resistance reaction (CRH, GHRH, TRH)
3) Exhaustion (mainly cortisol) causes muscle wasting, suppressed immunity, ulceration, failure of pancreatic beta cells
How does the hypothalamus signal the adrenal medulla?
Neural impulses, via spinal cord
Once signalled by the hypothalamus, how does the adrenal medulla send signals to the visceral effectors?
Hormones: adrenaline and noradrenaline
Interleukin-1, released by macrophages, stimulates ACTH release. What will this stimulate in turn?
Cortisol release
Why are glucocorticoids used as immunosuppressant’s for organ transplants?
Cortisol stops IL-1 production, so the immune system turns on the stress reponse, which turns off the immune system.
