Overview of endocrinology Flashcards
What are major endocrine organs
hypothalamus: found in the base of the forebrain; converts the neural signals recieved from brain into chemical signals (hormones)
-pituitary gland: found at the base of the brain inferior to the hypothalamus. It releases hormones into the blood
-peripheral endocrine tissues:
*thyroid, adrenal cortex, gonads, pancreas, parathyroid glands
Explain the major endocrine organs and their secretion
1) Hypothalamus- releasing and inhibiting hormones
2) pituitary glands:
-anterior lobe- trophic hormones
-posterior lobe- oxytocin and vasopressin (ADH)
3) Thyroid glands- thyroxine, tri-iodothyronine
4) Adrenal gland:
-cortex: cortisol, aldosterone
-medulla: adrenaline/noradrenaline
5) Gonads- oestrogens, androgens, progesterones
6) Pancreas: Insulin, glucagon
7) Parathyroid glands- parathyroid hormone
Name other major endocrine organs their secretion
Kidney: Vit. D, EPO
CVS: atrial natruitic peptides (ANP), endothelia’s
Pineal gland: melatonin
Thymus: thymic hormones
Adipose tissue: leptin; controls appetite
How are different ways that cells communicate via hormones
Endocrine- Hormones released by an endocrine cell into the general circulation and acting on distant target sites; such as renin released by the kidney
Paracrine- Hormones released by an endocrine cell which act locally on adjacent cells, an example clotting factors
Autocrine- Hormones released by a cell which act back on the same cell, e.g. cytokines such as IL-1, also can be seen in cancers
Intracrine- Conversion of an inactive hormone to an active hormone that acts within that cell. E.g. steroid hormones; androgen that act through nuclear receptors
what are general functions of hormones
1) reproduction, growth and development:
-sex steroids, thyroid hormones, prolactin, growth hormone
2) maintenance of internal environment: aldosterone, parathyroid hormones, vitamin D
3) energy production, utilisation and storage: insulin, glucagon, thyroid hormones, cortisol, growth hormone
Explain the chemical nature of protein and peptide hormones
Protein and Peptide Hormones:
Made of chains of amino acids (small molecules that build proteins).
Example: Insulin — has two chains (A and B) connected together.
Example: Endothelin — comes from a longer inactive form called a “prohormone.”
These hormones are large, water-soluble molecules.
Explain The chemical nature of steroid hormones
Steroid Hormones
Made from cholesterol, which has a four-ring carbon structure (called a steroid nucleus).
Examples: Cortisol, testosterone, estrogen (not shown here, but all follow this basic shape).
These hormones are small, lipid-soluble and can pass through cell membranes.
Explain the chemical nature of tyrosine derivatives
Tyrosine Derivatives
Made from the amino acid tyrosine.
Example: Thyroxine (T4) — a thyroid hormone with iodine atoms.
Example: Epinephrine (adrenaline) — a hormone involved in the fight-or-flight response.
These hormones can be either water- or lipid-soluble, depending on their structure.
Discuss parvocellular neurones and magnocellular neurones
Parvocellular neurones:
-neurosecretory cells release hormones to capillaries of median eminence (supplied by superior hypophysial artery)
- conveyed by portal veins to anterior pituitary where they regulate endocrine secretion
Magnocellular neurones:
-project to posterior pituitary and release to capillaries supplied by inferior hypophysial artery
Explain what the posterior and anterior pituitary gland do simply
Posterior pituitary = releases brain-made hormones.
Anterior pituitary = makes its own hormones, controlled by the hypothalamus.
What are glands controlled by the hypothalamic-pituitary axis
Hypothalamus releases/inhibits neurohormones to the anterior pituitary gland
the trophic hormones of the anterior pituitary gland:
-TSH (thyroid)
-ACTH (adrenal cortex)
-LH/FSH (Gonads)
How does the hypothalamus and pituitary gland control different glands and bodily functions through hormones
✅ Hypothalamus (top row) → releases signals (hormones) to tell the pituitary what to do.
✅ Pituitary (middle row) → releases hormones that act on other glands or tissues.
✅ Target glands/tissues (next row) → these organs respond and produce their own hormones.
✅ Final effect (bottom row) → the body functions controlled.
Explain hypothalamic control of anterior pituitary secretions
If the hypothalamus wants the anterior pituitary to release Adrenocorticotropic hormone (ACTH), it sends Corticotropin releasing hormone (CRH).
To get the anterior pituitary to release Thyroid stimulating hormone (TSH), the hypothalamus sends Thyroid releasing hormone (TRH).
To control Luteinizing hormone (LH) and Follicle stimulating hormone (FSH) release, the hypothalamus sends Gonadotropin releasing hormone (GnRH).
The hypothalamus mostly stops the anterior pituitary from releasing Prolactin (PRL) by sending Dopamine.
To tell the anterior pituitary to release Growth hormone (GH), the hypothalamus sends Growth hormone releasing hormone (GHRH).
It can also stop the release of growth hormone using Growth hormone inhibiting hormone (GHIH) (also called somatostatin).
What are disorders of the endocrine system
-excess or deficiency
-impaired synthesis
-transport and metabolism of hormones
-resistance to hormone action
explain what happens in acromegaly (excess growth hormone)
-most commonly due to pituitary adenoma: increase in GH-secreting somatotrophs
-less commonly secondary: tumour elsewhere secretes GHRH
Explain hypothyroidism (thyroid hormone imbalance)
Hypothyroidism is because of:
-decrease in thyroid hormone production
-impaired action of thyroid hormones on target tissues
Explain the stages of cortisol secretion
1) Your hypothalamus (a part of your brain) senses a need for cortisol and releases CRH (Corticotropin-releasing hormone). This is like the boss sending a
message.
2) CRH travels to the anterior pituitary (another gland in your brain). The anterior pituitary receives the CRH message.
3) In response, the anterior pituitary releases ACTH (Adrenocorticotropic hormone). This is like the worker getting the message and taking action.
4) ACTH travels in the blood to the adrenal cortex (part of your adrenal glands, which sit on top of your kidneys).
The adrenal cortex then releases cortisol.
What are the effects of cortisol in the body
Now, cortisol has several effects in the body, shown on the right side:
Gluconeogenesis: Helps make glucose (sugar) for energy.
Protein mobilisation: Breaks down proteins.
Fat mobilisation: Breaks down fats for energy.
Anti-inflammatory effects: Reduces inflammation.
Explain the feedback loop
There’s also a feedback loop: high levels of cortisol can signal back to the hypothalamus and anterior pituitary to reduce the release of CRH and ACTH. This is like a thermostat, preventing cortisol levels from getting too high.
What happens if theres a lack or excess of cortisol
Lack of cortisol: addisons disease (Deficiency of adrenocortisol hormones)
Excess of cortisol: Cushing’s disease (excess of glucocorticoids)
Explain vitamin D resistant Rickets
-Vitamin D supplementation has no effect
-it can cause bone deformity including short stature
-due to defective renal tubular 25-hydroxyvitamin D-1 a hydroxylase or is due to end-organ resistance to active metabolite of vitamin D
Explain androgen insensitivity syndrome (AIS)
-the inability to respond to androgens, typically due to androgen receptor syndrome dysfunction
-this unresponsiveness can impair or prevent the development of male genitalia
