Endo Flashcards
What are the major endocrine systems?
Pituitary
Thyroid
Parathyroid
Adrenal
Pancreas
Ovary
Testes
What is a basic definition of hormone
To excite
What do we mean by Endocrine?
Within/separate - glands ‘pour’ secretions into blood stream (thyroid, adrenal, beta cells of pancreas)
What do we mean by Exocrine?
Outside - glands ‘pour’ secretions through a duct to site of action (pancreas - amylase, lipase)
What does hormone action depend on?
blood level of hormone
numbers of target cell receptors
affinity for receptors
What are the different types of hormone action?
Endocrine
Paracrine
Autocrine
What does Endocrine mean?
blood-borne, acting at distant sites
What does paracrine mean?
acting on adjacent cells
What does autocrine mean?
feedback on same cell that secreted hormone
What are the crucial mediators of body homeostasis?
reproduction, sexual differentiation development and growth
maintenance of the internal environment regulation of metabolism and nutrient supply
What are the features of water-soluble hormone?
Transport : Unbound - dont need to bind
Cell interaction: Bind to surface receptor of organ or whatever its working on
Half life : short
Clearance : fast
Eg : peptides, monoamines
What are the features of fat hormone?
Transport : Protein bound
Cell interaction: Diffuse into cell
Half life : long
Clearance : slow
Eg : Thyroid hormone, steroids
Where are peptides/ monoamines stored in?
Vesicles
Whats the difference between peptide and steroid hormone production?
Steroids are synthesised on demand
Features of Peptide hormones:
-Vary in length – TRH: 3 amino acids, Gonadotrophins: 180 amino acids
-Linear or ring structures
-Two chains and may bind to carbohydrates e.g LH,FSH
-Stored in secretory granules, hydrophilic, water soluble
-Released in pulses or bursts
-Cleared by tissue or circulating enzymes
-E.g insulin
How are peptides granularly stored?
Synthesis: Preprohormone> prohormone
Packaging: Prohormone>hormone
Storage: Hormone
Secretion: Hormone
How does the insulin receptor work?
- Insulin binds to insulin receptor
- Causes phosphorylation of insulin receptor > Tyrosine kinase now active
- Signal molecules becomes phosphorylated > cascade of effects > glucose uptake and anabolic reactions
Where is insulin released/ secreted from?
Pancreas - beta cell islets of langerhans
What are the features of Amine hormones?
Amines: water soluble, stored in secretory granules, release pulsatile, rapid clearance,
Bind to alpha and beta receptors or D1 and D2
E.g Adrenaline / Noradrenaline
What happens when amine hormones bind to alpha adrenoreceptors?
vasoconstriction, dilated pupil, alertness, contraction of stomach, bowel, anal sphincter
What happens when amine hormones bind to beta adrenoreceptors?
Beta adrenoceptors: vasodilatation, increased heart rate, bronchial and visceral smooth muscle relaxation
What are the features of phenylalanine derivatives?
Secreted by medulla
Neurotransmitters
Rate limiting step is the conversion to l-DOPA
Cortisol potentiates conversion of norepinephrine to epinephrine
Look back “the endocrine system and functional anatomy and physiology” lecture slide on amine ask if relevant
Where is adrenaline released from?
Adrenal medulla
What hormones are produced from adrenal cortex?
aldosterone (a mineralocorticoid)
cortisol (a glucocorticoid) androgens
estrogen (sex hormones)
What stimulates the secondary messenger system?
Hormone is primary messenger – stimulates secondary messenger system – could lead to inhibitory effect or stimulatory effect
What are the features of Iodothyronine hormones? (Thyroid hormones)
-Not water soluble; 99% is protein bound
-Only 20% of T3 in the circulation is secreted directly by thyroid
-Secretory cells release thyroglobulin into colloid – acts as base for thyroid hormone synthesis
-Incorporation of iodine on tyrosine molecules to form iodothyrosines
-Conjugation of iodothyrosines gives rise to T3 and T4 and stored in colloid bound to thyroglobulin
-TSH stimulates the movement of colloid into secretory cell, T4 and T3 cleaved from thyroglobulin
What makes up follicles?
Secretory cells + colloid
Thyrosine comes from…?
Thyroglobulin
Iodine comes from…?
Iodide
Thyroid hormones will bind to what protein?
thyroid binding globulin
Synthesis of Thyroxine T4 and T3
- Thyroglobulin synthesised and discharged in the follicle lumen - goes through RER and GA and forms Tyrosines
- Iodide (I-) actively transported into follicle lumen
- Iodide oxidised to iodine
- Iodine attached to tyrosine in colloid to forming DIT and MIT
- Iodinated tyrosines (DIT and MIT) linked together to form T3 and T4
- Thyroglobulin colloid is endocytosed and combined with a lysosome
- Lysosomal enzymes cleave T4 and T3 from thyroglobulin and hormones diffuse into bloodstream
3,4,5 - happens in colloid
What are 3 hormone receptor locations ?
Cell membrane
Cytoplasm
Nucleus
What hormones work on cell membranes?
Peptides
What hormones work on cytoplasm?
Steroids
What is the steroid receptor family?
Glucocorticoids - cortisol
Mineralocorticoids - aldosterone
Androgens - testosterone
Progesterone
What hormones work on the nucleus?
Thyroid hormones
What is the nuclear receptor family?
Oestrogen
Thyroid Hormone
Vitamin D
What are the features of cholesterol derivatives and steroid hormones (Vitamin D)
Fat soluble
Enters cells directly to nucleus to stimulate mRNA production
Transported by Vitamin D binding protein
What are the features of cholesterol derivatives and steroid hormones (Adrenocortical and gonadal steroids)
-95% protein bound
After entering cell:
-Pass to nucleus to induce response
-Altered to active metabolite
-Bind to a cytoplasmic receptor
Not too rapid inactivation
- In liver by reduction and oxidation, or conjugation to glucoronide and sulphate groups
How do we get the Vitamin D we need?
Sunlight > 7-dehydrocholesterol > Cholecalciferol (Vit D3) > Liver > Converted to 25-hydroxyvitamin D3> Kidney> converted to 1,25-dihydroxyvitamin D3 WHICH maintains calcium balance in the body
Where is progesterone secreted?
Corpus luteum of ovaries
Where is testosterone secreted from?
Leydig cells of testes
Where is estradiol secreted from?
Follicles of ovaries
What is the intracellular pathway for steroid action?
- Steroid hormone diffuses through plasma membrane and binds to receptor
- Receptor hormone complex enters nucleus
- Receptor hormone complex binds to GRE
- Binding initiates transcription of gene to mRNA
- mRNA directs protein synthesis
What are the different ways of controlling hormone secretion?
-Basal secretion – continuously or pulsatile
-Superadded rhythms e.g day-night cycle – ACTH, prolactin, GH and TSH
-Release inhibiting factors – dopamine inhibiting prolactin, sum of positive and negative effects (GHRH and somatostatin on GH)
-Releasing factors
Why should we know the time of day when we measure hormone levels?
range will vary depending on time of day
Cortisol level – at 4pm its 100 9am could be different
This is due to circadian rhythm of hormones
What is hormone metabolism?
increased metabolism to reduce function
What is hormone receptor induction?
Induction of LH receptors by FSH in follicle
What is Hormone receptor down regulation?
Hormone secreted in large quantities cause down regulation of its target receptors
What is synergism in hormones?
Combined effects of 2 hormones amplified ( glucagon with epinephrine-
What is antagonism in hormones?
One hormone opposes another hormone (glucagon antagonises insulin)
Negative feedback loop?
Initial stimulus > Response > Decrease in stimulus > Response loop shuts off
Positive feedback loop?
Initial stimulus > response > Increase in stimulus
Outside factor is required to shut off
If we saw an MRI of a pituitary gland what would we see?
Anterior and posterior pituitary gland
Optic chiasm
Hypothalamus
Pituitary stalk
What does the pituitary stalk do?
Carries hormones
What does the optic chiasm do?
carries optic nerves over pituitary gland
What does the hypothalamus do?
Stimulates production of hormones
What could happen if we have a pituitary gland tumour?
– press on optic chiasm – present with visual problems – bitemporal hemianopeia
Cavernus sinuses – get cranial nerve – CN 4 and CN6 are P and P2 of trigeminal nerve – patient will present with double vision
Features of posterior pituitary gland?
1.Hypothalamic neurons synthesis oxytocin or ADH in hypothalamus and paraventricular nucleus
2. Oxytocin and ADH are transported down the axons of the hypothalamic-hypophyseal tract to the posterior pituitary.
3. Oxytocin and ADH are stored in axon terminals in posterior pituitary.
4. When hypothalamic neurons activated, hormones released.
ADH
ant diuretic hormones – controls blood volume and sodium levels
Osmolality – conc of fluid in circulation – if increased ADH will reabsorb water from kidneys and prevent sodium levels get too high
Have conditions where you lose ADH – diabetes insipidus
What hormones does the anterior pituitary release?
Adrenocorticotrophic hormone (ACTH)
Thyroid-stimulating hormone (TSH)
Luteinising hormone (LH)
Follicle-stimulating hormone (FSH)
Prolactin (PRL)
Growth hormone (GH)
Melanocyte-stimulating hormone (MSH)
What hormones do PPG release?
Oxytocin and ADH
What happens if you have pituitary dysfunction?
Tumour mass effects
Hormone excess
Hormone deficiency
Headaches
Eye problems
Blindness – ignore initial problems
Acromegaly – young but very tall
Cushings syndrome - excess ATCH – excess cortisol
How do we get acromegaly?
Excess growth hormone
Growth hormone axis
Hypothalamus secretes growth hormone releasing hormone (GHRH) (as well as somatostatin which is GHIH)
GH released from anterior pituitary - inhibits GRHR release and stimulates GHIH release - inhibits GH synthesis and release
Hypothalamo-pituitary-thyroid axis
Hypothalamus releases thyroid releasing hormone > Ant pituitary releases TSH > Thyroid gland releases thyroid hormones
What important artery is next to thyroid artery?
Common carotid artery
Thyroid hormone functions
Accelerates food metabolism
Increases protein synthesis
Stimulation of carbohydrate metabolism
Enhances fat metabolism
Increase in ventilation rate
Increase in cardiac output and heart rate
Brain development during foetal life and postnatal development
Growth rate accelerated
Hypothalamo-pituitary-adrenal axis & Cortisol Actions
Hypothalamus secretes corticotropin releasing hormone (CRH) > AP releases Adrenocorticotropic hormone (ACTH) > Acts on Adrenal cortex causing cortisol release > causes negative feedback on ant pituitary and hypothalamus to not release ACTH and CRH
Adrenal gland zones
Capsule
Zona glomerulosa
Zona fasciculata
Zona reticularis
Adrenal medulla
Whats released from zona glomerulosa?
aldosterone
mineralcorticoids
Whats released from zona fasciculata?
cortisol
glucocrticoids
Whats released from zona reticularis?
sex hormones
Androgens
androstenedione
- dihydroepiandrosterone
(DHEA)
Cortex of adrenal gland?
Epinephrine
Norepinephrine
RAAS
relearn this
Short term stress response
Heart rate increases
BP increases
Bronchioles dilate
Liver converts glycogen to glucose and releases glucose into blood
Metabolic rate increases
Long term stress response
Kidneys retain sodium and water
Blood volume and blood pressure rise
Proteins and fats converted to glucose or broken down for energy
blood glucose increases
Immune system suppressed
Hypothalamo – pituitary - gonadal axis
Gonadotropin releasing hormone released from hypothalamus > Acts on FSH and LH to release testosterone and progesterone > negative feedback reduces FSH and LSH producion GnRH production
What does FSH do?
FSH – stimulates puberty to start and start producing sperm – supported by LH
Prolactin
Look it up and edit this
What is satiety?
feeling of fullness -
disappearance of appetite after a meal
BMI
- wt (kg)/ht (m2)
What are the scales of BMI?
<18.5 underweight
18.5 - 24.9 normal
25.0 - 29.9 overweight
30.0 - 39.9 obese
>40 morbidly obese
Risks of obesity?
Type II diabetes
Hypertension
Coronary artery disease
Stroke
Osteoarthritis
Obstructive sleep apnoea
Carcinoma - breast, prostate, colon
Obesity in the UK
In excess of 20% of population are obese and 40% overweight; uk economy costs exceed 3 billion per year; 40% of children are obese or overweight and are the first generation at risk to die before parents
Link between obesity and shift work?
HSE 2013 25% of population carry out shift work; outside 7am to 7pm; more likely to report ill health and be diabetic or obese
Affect your rhythyms
When sleeping in day and waking up at night – glucose levels and insulkin levels higher – cortisol level is high when it should be low – body is not made up to work in that sort of situation
What does weight regulation depend on?
Environment
Genes
Maintenance (homeostasis) systems
Normal fat mass
Which hormone makes you lose appetite and stop eating?
Leptin
What is the main organ that controls appetite?
Hypothalamus
Lateral hypothalamus - hunger centre
Ventromedial hypothalamic nucleus (satiety center)
Features of Leptin
Expressed in white fat
Binds to leptin receptor
- cytokine receptor family
- in hypothalamus
Switches off appetite and is
immunostimulatory
What happens if you are deficient in leptin?
hyperphagic
hyperinsulinaemic
very obese
Blood levels increase after meal
Blood levels decrease after fasting
Continue eating without stopping
What are the important peptides in appetite suppression?
NPY - Neuro peptide Y
AgRP - Agouti-related peptide
POMC - Pro-opiomelanocortin
CART - cocaine and amphetamine regulated
transcript
How does leptin work
Increase in fat cell mass > increase in leptin action expression and action on hypothalamus >
1. inhibits NPY/AgRP neuron > decreased expression and release of these peptides > decreased food intake
2. Activates POMC neuron > increased alpha-MSH expression and release > increased alpha MSH binding and activation of melanocortin receptors > decreased food intake
Where are the NPY/AgRP neurons found
Arcuate nucleus
What does decreased AgRP release do?
Decreased inhibition of melanocortin receptors
What is peptide YY
36 amino acids
Structurally similar to NPY
Binds NPY receptors
secreted by neuroendocrine cells in ileum, pancreas and colon
in response to food
inhibits gastric motility
reduces appetite
What can PYY do?
Infusion of PYY diminishes appetite
Likely action by pre-synaptic Inhibitory Y2 receptors on NPY Neurones
- so less NPY released and hence hunger diminished
What does cholecystokinin (CCK) do?
Receptors in pyloric sphincter
- delays gastric emptying
- gall bladder contraction
- insulin release
and via vagus - satiety
What is Ghrelin?
28 amino acid
Acyl side chain
Expressed in stomach
What is the action of Ghrelin?
Growth hormone release
appetite - orexigenic
Blood levels high when fasting, fall on re-feeding
Levels lower after gastric bypass surgery
What will happen if you have a Proopiomelanocortin (POMC) deficiency?
Pale skin
Adrenal insufficiency
Hyperphagia and obesity
What are the effects of leptin and insulin together?
- Stimulate- POMC/CART neurons > increase CART and alpha-MSH levels
- Inhibit NPY/AgRP neurons > decrease NPY and AgRP
Net effect : ↑ Satiety and decreased Appetite
What are the effects of ghrelin?
stimulates NPY/AgRP > increases NPY and AgRP secretion
↑ Appetite
What is PYY 3-36?
homolog of NPY
Binds to an inhibitory receptor on NPY/AgRP > decreased secretion of NPY and AgRP > decreased Appetite
What are incretins?
gut hormones that are secreted from enteroendocrine cells into the blood within minutes after eating.
Augment the secretion of insulin released from beta cells by a blood-glucose–dependent mechanism
What is the incretin effect on glucagon?
Blunting of GLUCAGON, in a glucose-dependent fashion.
means that glucagon is only blunted with normal or high glucose levels
What is the incretin effect on insulin?
Beta-cell stimulation of INSULIN production, in a glucose-dependent fashion.
Means that insulin is stimulated only when glucose levels are high.
What do sulfonylurea agents do?
stimulate beta cells to produce insulin, but continue to stimulate the beta cell even when hypoglycemia is present, hence worsening or prolonging the hypoglycvemia
What is the incretin effect on satiety?
Because weight control is an issue for the majority of T2DM patients, improved satiety enhances the ability to maintain diet and weight goals.
What is the incretin effect on gastric motility?
Decreased GASTRIC MOTILITY delivers smaller, less frequent amounts of calories to the small intesting per unit time.
Although not widely recognized, early diabetes is associated with an INCREASE in the rate of gastric motility.
Slowing the rate of delivery of gastric contents to the small intesting reduces the rate of rise of post-prandial glucose, hence the observed effects on postprandial glucose measurements.
Other effects of incretin?
Increased glucose uptake by muscles
Decreased glucose production
Increased glucose-dependent insulin release
Increased beta cell regeneration
Decreased glucose dependent glucagon release from alpha cell
What receptors in the stomach increase satiety?
Stretch
What are the actions of parathyroid hormone?
Increased calcium reabsorption because of increased 1,25 (OH) vit D
Decreased phosphate reabsorption
Decreased serum phosphate
Decreased FGF-23
Increased 1,25 (OH)2vit D
Increased bone remodelling + bone reabsorption > Bone formation
What is parathyroid hormone response to decreased serum calcium?
serum Ca2+ decreases > increased PTH > increased urinary phosphate excretion (increased bone resorption + increased Ca2+ reabsorption) > due to increased u-phos > decreased serum phosphate> increased 1,25-(OH)2 vit D>Increased Ca2+ absorption
Where do we find calcium detecting receptors?
Parathyroid glands
Calcium homeostasis is an example of what type of feedback?
Negative
Return serum ionised calcium back to the set point of about 1.1 mmol/l
What is the normal relationship between serum calcium and PTH?
Usually both at the same level
What happens if you have a low serum calcium?
Get very high PTH
What happens if you have a high serum calcium?
Get very low PTH
Why is calcium very important?
Functioning of nerves and muscles
Why would changes in PTH be appropriate?
To maintain calcium balance however could be inappropriate as it could cause calcium imbalance
What is hypocalcaemia?
Low total serum calcium + low albumin
(Not low ionised calcium)
Calcium bound to albumin
If albumin is outside normal range will effect calcium levels
What is the corrected calcium formula?
total serum calcium + 0.02 * (40 – serum albumin)
What are the consequences of hypocalcaemia ?
Parasthesia
Muscle spasm
-Hands and feet
-Larynx
-Premature labour
Seizures
Basal ganglia calcification
Cataracts
ECG abnormalities
o Long QT interval
Vitamin D is made from what?
the action of UVB on cholesterol on the skin
What are the uses of 1,25-dihydroxyvitamin D3 ?
Intestines - increases absorption of Ca2+
Bones - increases bone mineralisation
Immune cells - induces differentiation
Tumour microenvironment - Inhibits proliferation and angiogenesis, induces differentiation
How can hypoparathyroidism be caused?
Surgical radiation
Syndromes
Genetic
Surgical
Radiation
Autoimmune
Infiltration
Magnesium deficiency