Endocrinology I Flashcards by Charlotte King

What are the functions of endocrine glands?

Regulate concentration of blood fluid (haemostasis)
Regulate body temperature
Regulation of reproduction, development and metabolism

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What are the three major classes of hormones?

Polypeptide - proteins and peptides (water soluble)
Amine - derived from amino acids (water soluble)
Steroid hormones (lipid soluble)

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What is the HPA pathway for stress and circadian rhythm?

Stressful stimulus causes the hypothalamus to release CRH
CRH stimulates the pituitary gland to release ACTH
ACTH stimulates the adrenal cortex which releases cortisol and androgens > stress metabolism. Positive and negative feedback

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How is hormone secretion regulated?

Positive feedback and negative feedback loops
Positive feedback loop: hormones act on anterior pituitary
Negative feedback long loops: hormones act on anterior pituitary and hypothalamus. Short loops from anterior pituitary to hypothalamus

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What is the embryological origin of the pituitary gland?

Anterior lobe (adenohypophysis) - protrusion of the ectoderm from roof of mouth
Posterior lobe (neurohypophysis) - neuroectoderm

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What is the difference between the anterior and posterior pituitary gland?

Anterior pituitary: synthesise and stores hormones
Posterior hormones: only stores and releases them

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What are examples of hormones released by anterior lobe of pituitary gland? what cells release them?

GH by somatotrophs
TSH by thyrotrophs
ACTH by corticotrophs
FSH and LH by gonadotrophs
Prolactin by lactotrophs

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What hormones are released by the posterior pituitary gland? what cells release them?

ADH and oxytocinby cell bodies of hypothalamic neurons, secreted by nerve terminals

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Where do the problems lie in primary, secondary and tertiary endocrine disorders?

Primary - Thyroid gland, parathyroid gland
Secondary - Anterior pituitary
Tertiary - Hypothalamus

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What may cause hypersecretion?

Hormone secreting tumours
Hyperplasia
Autoimmune stimulation
Ectopically produced peptide hormone - ACTH, ADH

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What may cause hyposecretion?

Autoimmune disease
Tumours
Infection
Haemorrhage

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What regulates GH release from the anterior pituitary?

GNRH from hypothalamus has positive feedback, stimulates GH release
Somatostatin from hypothalamus has negative feedback, inhibits GH release

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What are the two functions of GH? How does it exert these functions?

Growth of skeletal and soft tissue
Metabolic on carbohydrate, lipid and protein metabolism
- Indirect - through hormone - IGF1/somatomedins
- Direct - through GH receptors in target tissue

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When may GH secretion increase/decrease?

Increase: sleep, stress, young age
Decrease: old age, obesity

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What are the direct actions of GH?

Increased cartilage formation, bone growth
Increaesd protein synthesis, cell growth and proliferation

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What are the indirect actions of GH?

Increased lipolysis
Increased blood sugar

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What can GH deficiency cause in children?

Pituitary dwarfism:
- Impaired pituitary GH secretion
- Decreased rate of growth and short stature
- Normal brain development
- Decreased plasma GH and IGF1
Laron dwarfism:
- Defective GH receptors in target tissue and defective IGF1 production
- Decreased plasma IGF1 but elevated plasma GH

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What can GH deficiency cause in adults?

If GH deficiency occurs after epiphyseal fusion of long bones, height unaffected
- Increased body fat
- Reduced muscle mass
- Fatigue
- Decreased physical fitness

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What does excess GH in children cause - before epiphyseal plates have fused?

Gigantism
Rapid increase in growth and weight
Can be due to tumour in pituitary that hypersecretes GH
- Large hands and feet
- Coarse facial features, frontal bossing, prognathism
- Headaches
- Excessive sweating

What can excess GH cause in adults - once epiphyseal plates have fused?

Acromegaly
Excessive skeletal, soft tissue and internal organ growth
Acral bony overgrowth ->
- Frontal bossing
- Increased hand and foot size
- Mandibular enlargement with prognathism
- Frontal bossing
- Headaches, sweating, increased BP, increased blood glucose

How may acromegaly be treated?

Somatostatin analogues - lanreotide, octreotide, pasireotide

What does prolactin do? 4

Breast development
Milk production
Suppresses sex drive in both sexes
Anovulation in ovary

What releases prolactin, and what causes increase in levels?

Secreted by lactotrophs
Inhibited mainly by hypothalamic dopamine in male and female
Level very low in male and female
Increases inly during pregnancy and breast feeding

What are prolactinomas?

Tumour in pituitary gland that causes excess secretion of prolactin

What are the symptoms of prolactinomas in men? 4

Men: - Low sperm count - Erectile dysfunction - Low testosterone - Gynaecomastia

What are the symptoms of prolactinomas in women? 3

Women: - Loss of menstruation - Anovulation - Galactorrhoea

What are the symptoms found in both men and women with prolactinomas? 5

- Loss of libido - Headache - Infertility - Secondary hypogonadism - Osteoporosis

What synthesises and releases oxytocin?

Synthesised by paraventricular nucleus in hypothalamus Stored and released by posterior pituitary

What is the action of oxytocin?

- Stimulates Myoepithelial cells of the mammary gland -> milk ejection - Stimulates Myometrium -> expulsion of foetus and placenta Both positive feedback mechanism

What synthesises and releases ADH?

Synthesised by supraoptic nuclei of the hypothalamus Stored and released by posterior pituitary

What are the actions of ADH?

- Increases water permeability of principal cells in late DCT and CT in kidney - Acts via V1 receptors in vascular smooth muscles to cause contractions

What stimulates ADH secretion?

- Increased body fluid osmolality - Decreased blood volume - Decreased blood pressure - Angiotensin II - Pain/stress - Nausea and vomiting

What inhibits ADH secretion?

- Decreased body fluid osmolality - Increased blood volume - Increased blood pressure - Atrial natriuretic peptide - Ethanol - Diuretic

What can decreased ADH cause?

Decreased ADH action > diabetes insipidus (DI) - Neurogenic DI - Nephrogenic DI

What causes neurogenic (central) DI?

(Decreased ADH secretion) - Hypothalamus, pituitary tumour

What causes nephrogenic DI?

(Failure to respond to circulating ADH) - Polycystic kidneys - Chronic pyelorephritis - Lithium in drugs - Mutation in V2 receptor gene

What are the symptoms of DI?

- Polyuria - Nocturia - Polydipsia - Passage of large volumes of dilute urine - Marked dehydration - Anorexia and epigastric fullness - Hypernatremia - Fatigue

What investigatory tests are used to diagnose DI?

- Serum osmolality - Serum electrolyte level - Urine osmolarity - Water deprivation test followed by vasopressin test

What are the treatments for the different types of DI?

Central: synthetic AVP analogue desmopressin (DDAVP) Nephrogenic: adequate fluid intake; salt restriction

What disorders can occur with increased ADH?

- Small cell lung cancer - Severe brain trauma - Sepsis or infection of the brain (meningitis)

What are the signs and symptoms of increased ADH?

- Plasma ADH abnormally high - Physiologic ADH regulation not working - Highly concentrated (hypertonic) urine - Hyponatremia and osmolality - Normal or high BP

What is the treatment for increased ADH?

Stop fluid and Treatment of underlying cause

Where are gonadotrophins released from and what is there function?

FSH and LH released from gonadotropic cells of anterior pituitary FSH: - stimulate production of gametes LH: - female: matures follicles, trigger ovulation, stimulate release of estrogen and progesterone - male: stimulate production of testosterone Sex hormones have key role in bone metabolism

What is the release of GnRH like? What is the HPG affected by? What eventually happens to HPG axis over time in males vs females?

GnRH secretion is pulsatile HPG axis affected by: stress, weight loss, excercise In time: Deregulation of HPG leads to menopause in females HPA activity in males decreases over time

What is hypopituitarism and panhypopituitarism?

Hypopituitarism: deficiency of one or more hormones of the pituitary gland Panhypopituitarism: absent production of all anterior pituitary hormones

What may cause hypopituitarism?

Congenital or acquired defects Compression (tumour), gene mutation, tumours, ischaemia, iatrogenic or chronic inflammation