Endocrine System W3 Flashcards
What is the endocrine system
Collection of glands that produce and secrete hormones
It regulates…
Growth and development, metabolism, maintenance and repair of tissues, reproduction nand sexual function, tissue function and sleep
Major glands
Hypothalamus, pituitary, thyroid, parathyroid, adrenals, pineal, pancreas, ovaries and testes
What cells that secrete aren’t part of the e.system
E.cells in the gastrointestinal tract which secrete gastrin, histamine, somatostatin and some in the kidneys that secrete renin, calcitrol and erythropoietin
What are hormones
Chemical messenger that travel in blood stream and sometimes bound to proteins to help transport them to their target cells
Three classes of hormone
Steroid - lipophyllic ie cortisol
Peptide - hydrophylllic ie insulin
Amino acid derivded - hydrophilic ie thyroid
Why is the pituitary gland called the master gland
Secretes hormones that control the actions of other endocrine glands nad tissues
What is the pituitary gland physically
Pea sized and oval struure that is suspended under the brain by the pituitary stalk annd sits with a crevice of the sphenoid bone
What does th pineal gland secrete
Melatonin which plays part in the role of sleep and circadian rythums
The posterior consists of…
Nervous tissue
Anterior consists of…
Glandular epithelial tissue
Posterior connects by…
Glandular neural pathway
Anterior connects by …
Unique vascular link
Unique vascular link
Posterior releases
Oxytocin and vasoprssin(nit-diuretic)
Anterior releases…
ACTH, TRH, GH, prolactin, FSh, LH and MSH
Oxytocin
Produced by the posterior pituitary and has several functions in women:
• Contraction of the uterine muscle to help expel infant during childbirth
- Secretion increased by reflexes originating within birth canal during birth
• Promotes ejection of milk from mammary glands during breast feeding
- Secretion increased by suckling
• Influences social behaviours
- Mating/bonding with infant/relationships
• Injection (Syntocinon) used to induce labour and prevent postpartum haemorrhage
Vasopressin
Produced by the posterior pituitary and has two main functions:
• Enhances retention of water by nephrons during urine formation (anti-diuretic)
- Primary regulator of water balance
- Binds to V2 receptor causing an increase in water permeability in distal tubule
and collecting ducts leading to increased water reabsorption
• Contraction of arteriolar smooth muscle (vessel pressor effect)
- Minor role in regulating blood pressure
- Binds to V1 receptor causing an increase in vasoconstriction
Diabetes insipidus
This is caused by a lack of vasopressin (ADH)
The main symptoms are polyuria (excessive dilute urine >2L/day) and polydipsia
Left untreated, it leads to shock-like symptoms – hypotension, tachycardia, tachypnea etc
and can lead to hypernatremia
Treatment
- Vasopressin injection
- Desmopressin injection/tablet/nasal spray (this is longer acting and has no
effects on V2 receptors so no vasoconstriction)
Anterior pituitary Synthesises …
hormones and releases them into blood stream
Five cell types in the anterior pituitary secrete six major hormones:
- Somatotropes – GH (growth hormone (somatotropin))
- Thyrotropes – TSH (thyroid stimulating hormone)
- Corticotropes – ACTH (adrenocorticotrophic hormone) - Gonadotropes – FSH (follicle stimulating hormone) and LH (luteinizing
hormone) - Lactotropes – PRL (prolactin)
three-hormone sequence
Hormones from the hypothalamus cause the release of these hormones and in response
they travel in the blood and cause the release of hormones from other tissues and organs or
directly affect those tissues. . When sufficient
hormone has been released, the increase in blood concentrations has a negative feedback
on the hypothalamus and pituitary to decrease further secretion.
Control of anterior pituitary hormones
They are not secreted at a constant rate
Secretion of each is independent of each other
Major factors controlling secretion of anterior pituitary hormones
- Hypothalamic hormones (releasing and inhibitory hormones)
◦ Neural or hormonal inputs to stimulate or inhibit secretion
◦ Somatostatin (GHIH) inhibits GH and TSH
◦ Dopamine (PIH) inhibits PRL - Feedback by target-gland hormones
The hypothalamic pituitary (hypophyseal) portal system
This is a unique vascular link between hypothalamus and anterior pituitary
There is a direct capillary to capillary bed so the hypothalamic hormones just travel locally
within this
Upon arrival to the pituitary, the hypothalamic hormones bind to specific receptors on
specific cells in the anterior pituitary
GHRH from the hypothalamus binds …
receptors on somatotroph cells in the anterior
pituitary, triggering the release of GH
GH stimulates..
growth and development resulting in:
- Net synthesis of proteins
- Lengthening of long bones
- Increase in size and number of cells in soft tissues
GH works by…
stimulating IGF (insulin-like growth
factor)
Doesn’t directly affect tissues
What else is growth influenced by
genetics, adequate diet,
chronic disease, stressful environment, other growth influencing hormones eg
thyroid hormone, insulin estrogens, androgens etc
What s GH deficiency due to
Primary dficineccy : A pituitary defect
Secondary deficiency : A hypothalamic or target dysfunction - lack of GHRH or IGF or lack of tissue response
GH in adulthood result in…
Muscle effects eg at risk off heart failure
Treatment of GH deficiency
There are ethical considerations around treatment with growth hormone - balancing normal short stature with a potential risk of cancer
Treatment is somatotropin (recombinant GH) treatment (monitored)
Recombinant somatotrophin is given for…
Short stature eg pituitary dwarfism, Turner’s
syndrome, chronic renal insufficiency in children. It is also used illicitly by athletes to
increase muscle mass
Somatorelin
is a 44 amino acid residue peptide, which is
sometimes given if relevant.
Mecasermin
is given when there is growth failure in children
lacking adequate IGF-1
GH excess
Most often this is due to a benign tumour of somatotrophs. In childhood, this results in gigantism, where there is no distortion of body proportions but the person is taller. If not treated, may reach > 8 ft
In adulthood, results in acromegaly. Patients present with thicker bones and soft tissue proliferation, bone thickening in the face and extremities and sometimes peripheral nerve disorders as nerves can become trapped
Treatment for excess GH
Surgery - trans-sphenoidal and/or debulking
Medicines - Somatostatin analogues given as an adjunct to surgery
Somatostatin acts on all of the somatostatin receptors (sst1-5)
Different forms of analogues
octreotide, lanreotide, pasireotide, which act on
specific sst receptors
Other drugs that may be given depending on the cause include
Dopamine agonist , bromocriptine or the GHRH antagonist Pegvisomant
Somatostatin
Is a 14 amino acid residue peptide produced by hypothalamus which inhibits the release of GH, TSH, insulin and glucagon
Octroeotide
It’s a long lasting analogue or somatostatin used for treatment of carconoid and other hormone secreting tumours
It is given subcutaneously and has side effects of GI disturbances and pain at site of injection
Lanreotide
Has similar effects and is also used in treatment of thyroid tumors
Pasireotide
Has similar effects and is also used in Cushing’s syndrome when surgery is inappropriate or ineffective
Where are the adrenal glands located?
Above the left and right kidneys and they have a cortex and a Medalla
The outer cortex and the inner medulla are divided into three zones:
Zona glomerulosa – outermost; ; Zona fasciculata – middle ; Zona reticularis - inner zone
Where is aldosterone produced in the adrenal gland?
Zona glomerulosa
Where is cortisol and corticosteroids produced in the Adrena gland
Zona fasciculata
Where are androgens produced in the adrenal gland?
Zona reticularis
Where are Epinephrine and norepinephrine produced in the adrenal glands?
Medalla
Three categories of steroid produced in the district zones
◦ Mineralocorticoids – aldosterone, influences electrolyte balance
◦ Glucocorticoids – cortisol, major role in glucose, protein and lipid
metabolism and response to stress
◦ Sex hormones - for example, dihydroepiandrosterone (DHEA) is
involved in male sexual development
How many steroids are produced from cholesterol?
More than 30
How do steroid hormones act on the cell to increase protein synthesis?
Steroid hormones act by crossing the cell membrane and binding to intracellular receptors. the hormone receptor complex then enters the nucleus, binds to specific DNA sequences, and activates gene transcription. This leads to increased mRNA production, which is translated into proteins, enhancing protein synthesis.
Aldosterone
Is the major mineralocorticoid and is essential for life and it acts on the distal and collecting tubes of the kidney
Functions of aldosterone
Promotes sodium absorption in the kidney
Increases potassium and hydrogen excretion in urine
The sodium retention reduces water retention expanding ECF volume
This increased blood pressure in the long-term
Cortisol
The major glucocorticoid
Functions of cortisol
Role in metabolism to increase blood glucose concentration at the expense of proteins and fat stores
Stimulates hepatic gluconeogenesis
Inhibits glucose uptake by several tissues
Control of cortisol secretion
Released in response to ACTH from the pituitary which intern is released in response to CRF from the hypothalamus
Cortisol rhythm
Has a diurnal rhythm as cortisol levels are highest in the morning and lowest at night
Cortisol and stress
Is increased by both physical stress and psychological stress
Aldosterone hypersecretion
Can primarily be due to a hyper secreting adrenal tumour made of aldosterone secreting cells (cons syndrome) or due to high activity of rennin angiotensin aldosterone system causing narrowing a blood vessels
What does hyper secretion result in?
hypernatraemia, hypokalaemia and high blood pressure (due to
sodium & water retention)
Cortisol and aldosterone deficiency
Results in Addison’s disease due to a deficiency in glucocorticoids and deficiency in mineralocorticoids which is due to atrophy of the adrenal cortex
Where is the thyroid gland?
Located below the larynx and wrapping around the tracker and looks like a bowtie
What hormones does the thyroid secrete?
Thyroid hormone which contains iodine and calcitonin
Actions of thyroid hormone in the body
It is not essential for life, but imbalances in thyroid hormone can cause severe problems and acts on nearly every cell in the body where it:
– Increases basil metabolic rate
– Increases heat production
– Stimulates GH and IGF – I secretion
