S1: Overview to Endocrinology Flashcards
List some major endocrine glands/organs in the body
Hypothalamus Pituitary Gland Thyroid Adrenal Pancreas Parathyroid
What forms the hypothalamic-pituitary axis?
Hypothalamus
Pituitary Gland
What major endocrine structures are regulated by the hypothalamic-pituitary gland?
Thyroid
Adrenal cortex/medulla gonads
What regulates the pancreas and parathyroid glands?
They are regulated by other controlled variables e.g. insulin in pancreas and glucagon, which are dependent on glucose levels, parathyroid regulate calcium levels
What structure is responsible for releasing and inhibiting hormones?
Hypothalamus
What hormones does the thyroid gland release?
Thyroxine
Triidothyronine
What hormones does the adrenal glands release?
Adrenal Cortex: Cortisol and Aldosterone
Adrenal Medulla: Adrenaline and Noradrenaline
What hormones does the gonads release?
Oestrogens
Androgens
Progestagens
What hormones does the pancreas release?
Insulin
Glucagon
What hormone does the parathyroid gland release?
Parathyroid hormone
GIve examples of other tissue releasing hormones
kidneys (vitamin D, EPO), CVS (ANP, endothelins), pineal gland (melatonin), thymus gland (thymic hormones), bone (phosphate) and adipose tissue (leptin).
What are the 4 types of signalling mechanisms?
- Endocrine
- Paracrine
- Autocrine
- Intracrine
What does endocrine mean?
Hormones are released by an endocrine cell into the general circulation and act on distant target sites
What does paracrine mean?
Hormones released by endocrine cell which act on locally adjacent cells
What does autocrine mean?
Hormones released by a cell which act back on the same cell
What does intracrine mean?
Conversion of an inactive hormone to an active hormone that acts within the cell
What are the general functions of hormones?
- Reproduction, growth and development: sex steroids, thyroid hormones, prolactin, growth hormones
- Homeostasis (maintenance of internal enviroment) : Aldosterone, parathyroid hormone, vitamin D
- Energy production, utilisation and storage: Insulin, glucagon, thyroid hormones, cortisol, growth hormones
How are hormones chemically classified?
- Protein/peptide hormones (long chain amino acids)
- Steroid hormones (derivatives of cholesterol)
- Amino acid derivatives (one or two amino acids, mostly deriving from tyrosine and is very small)
- Fatty acid derivatives
Give examples of protein/peptide hormones
Hypothalamic hormones Pituitary hormones Insulin PTH Calcitonin
These tend to act in classical endocrine signalling
Give examples of steroid hormones
Cortisol Aldosterone Oestrogen Androgens Progestagens Vitamin D
Give examples of amino acid derivatives
Adrenaline
Noradrenaline
Thyroid hormones (all from tyrosine)
Melatonin (from tryptophan)
Give examples of fatty acid derivatives
Prostaglandins
Thromboxanes
Prostacyclin
What type of hormone starts out as a prohormone?
Protein and Peptide Hormones
What is the precursor of all steroid hormones?
Cholesterol
What is a steroid nucleus?
It is made from the cleaving of certain groups of cholesterol which eventually forms a steroid hormone.
Explain how hormones have different natures of transport in the body
They will spend different lengths of time in circulation and the mode of transport will vary
Compare the natures of transport of protein and peptide hormone, Tyrosine dervative hormones , thyroid hormones and steroids
Protein and Peptides
- Half life of minutes
- Mostly circulating freely (unbound) because it is soluble and can easily be transported dissolved in water
Tyrosine Derivatives
- Half life of seconds
Thyroid hormones
- Hours
- They are bound to plasma proteins in their transport in blood
Cholesterol derivatives (steroids)
- Hours to days
- Bound to plasma proteins
What is neuroendocrine integration?
The nervous system and endocrine system are linked and interact
Describe the structure of the posterior lobe of the pituitary gland
The magnocellular neuron projects to the posterior lobe of the pituitary gland and regulates this area.
It is supplied by the inferior hypophyseal artery which then becomes a capillary network and then becomes inferior hypophyseal vein.
What does the posterior lobe of the pituitary gland release?
Oxytocin
ADH
Describe the structure of the anterior lobe of the pituitary gland
The parvocellular neuron project down the the capillaries in the mediam eminence.
It is supplied by the superior hypophyseal artery and its capillaries become the hypophyseal portal vein which travels to the secondary capillary network and finally becomes the hypophyseal portal vein again.
What does the anterior lobe of the pituitary gland release?
GH Prolactin TSH ACTH LH FSH
Explain the three tier system of the hypothalamus pituitary axis
Hypothalamus —-> Releasing/Inhibiting neurohormones
This stimulates the
Pituitary Gland —————>stimulating trophic hormones
TSH ——> Thyroid
ACTH—-> Adrenal Cortex
LH/FSH —–> Gonads
Explain the role of the posterior pituitary hormones (Oxytocin and ADH)
Oxytoxin- Involved with cervix/uterus and are a type of positive feedback in uterine contractions. It is also involved with the nipples and cause milk ejection (neuroendocrine relax)
ADH acts as a vasoconstrictor (V1 receptors) as well as increasing permeability of collecting ducts (V2 receptors). ADH is stimulated to be released depending on the osmoreceptor/volume receptors
Does the posterior pituitary gland produce hormones?
No
It secreted hormones brought down from the hypothalamus
Which part of the pituitary gland releases trophic hormones and what are they?
The anterior pituitary gland
TSH
ACTH
LH/FSH
Explain how ACTH is released
The hypothalamus releases corticotrophin releasing hormone (CRH)
This increases the release of adrenocorticotrophic hormone (ACTH) from anterior pituitary gland
ACTH acts on the adrenal cortex
Explain how TSH is released
Hypothalamus releases thyroid releasing hormone (TRH)
This stimulates the anterior pituitary gland to release thyroid stimulating hormone (TSH)
TSH acts on the thyroid
Explain how TSH is inhibited
Growth hormone inhibiting hormone (GHIH=Somatostatin) is released from the hypothalamus
This decreases the amount of TSH released from anterior pituitary
Explain how LH and FSH is released
Gonadotrophin releasing hormone (GnRH) is released from the hypothalamus
This stimulates Luteinising hormone (LH) and Follicle stimulating hormone (FSH)
FSH/FSH act on the gonads
Explain how prolactin (PRL) is release is inhibited
Dopamine is released from the hypothalamus
This inhibits prolactin from the anterior pituitary
Explain how growth hormone is released and inhibited
The hypothalamus produces growth hormone releasing hormone (GHRH) or growth hormone inhibiting hormone (GHIH)
This either stimulates or inhibits growth hormone (GH) from anterior pituitary
Explain negative feedback on the hypothalamic-pituitary axis
Hypothalamus will interact with the pituitary (by releasing neurohormones) which will act on the effector of the organ causing release of hormone
This feedbacks to the hypothalamus and pituitary. If there is excess hormone, this will be detected and less stimulation occurs so less hormone is produced.
What keeps hormone concentration in the body constant?
There is negative/positive feedback regulation of hormones in the body, to try keep the levels constant.
Explain negative feedback control of thyroid hormone synthesis and secretion
The anterior pituitary gland is stimulated by TRH from the hypothalamus. The anterior pituitary gland then secretes TSH which stimulates the thyroid gland to release T4 and T3.
If there becomes too much T3 and T4 circulating, T3 and T4 will negatively feedback to the anterior pituitary and the hypothalamus which will produce less TSH and TRH respectively.
Conversely if there is too little thyroid hormone, the lack of negative feedback means more TRH and TSH will be produced leading to rise on thyroid hormones.
What releases TSH and what does it do?
The anterior pituitary releases TSH.
TSH which stimulates the thyroid gland to release T4 and T3.
How is cortisol androgen production stimulated?
Hypothalamus releases CRH and VP.
This stimulates the anterior pituitary to release ACTH. The adrenal cortex then releases cortisol androgens.
What regulates cortisol?
Our biological clock
What stimulates the hypothalamus to release CRH and VP?
Circadian rhythm
Stress
What pattern are hormones secreted in?
Pulsatile pattern
Name the 4 different type of rhythms
Daily rhythms include:
- Circadion (bio clock-24 hours)
- Diurnal (Day/night cycle)
Monthly cycles (e.g. female reproduction)
Annual cycles (mostly to do with animals)
Compare the pulsatile rhythm of LH and Prolactin
The pulsatile rhythm of LH shows it peaking every two hours, whereas prolactin is only released during sleep.
Explain how distrupted sleep can affect a childs’ growth
If the dinurnal pattern is broken up (distrupted sleep) there is not a big spike in growth hormone.
In other words, the sleep related rise in growth hormone secretion doesn’t occur when the normal light/dark cycle is disturbed.
Does the pulsatile pattern of hormones stay constant?
The pulsatile pattern of LH (and other hormones such as growth hormone) can vary throughout life
How can disorders of the endocrine system arise?
There may be an excess or deficiency of hormones due to:
- Impaired synthesis of hormones
- Problems with transport and metabolism of hormones
- Resistance to hormone action which can cause disorders
What happens if there is to little cortisol?
If your adrenal glands stop working (due to autoimmune or cancer) and you therefore produce little cortisol, then the levels of ACTH and CRH will increase, because there will not be that negative feedback. This would be detected as Addisons’s disease.
What happens when there is too much cortisol?
If there is too much cortisol (due to a tumour secreting cortisol or ACTH), this can be detected. If the tumour is in the anterior pituitary secreting lots of ACTH, it will mean lots of cortisol will be being produced but unable to carry out negative feedback properly as the tumour is producing lots of ACTH. This is the reason for Cushing’s disease where the patient has high levels of cortisol and ACTH.
What can resistance to circulating androgens result in?
Testicular feminisation
What can vitamin D resistance result in?
Rickets
What does exocrine again?
Glands that produce substances directly onto epithelial surface
