Endocrine System Flashcards
What are the actions of the endocrine system mediated by?
Hormones
What regulatory systems does the endocrine system control?
- Regulation of cellular metabolism
- Maintenance of homeostasis
- Sexual development and reproduction
- Growth and development from childhood to adult
- Modulating long term behaviour (mood, sleep)
What are the three classes of hormones, based on their structure?
Proteins - chains of amino acids (usually injected)
Steroids - modified cholesterol fat structure (oral administration)
Amino acid derivatives - start with amino acids which have turned into signals; thyroid hormone, catecholamines
What do glands develop from?
Epithelial cells
What are the three (+1) types of glands/secretion?
Describe them both
Exocrine
- when you are secreting something to the outside of your body
- the epithelial cells are arranged as ducts/tubes
- the ducts lead to the lumen of the organ (e.g.: sweat gland open onto the skin, pancreatic duct opens into the duodenum)
Endocrine
- the epithelial cells are arranges as clumps of cells
- these release their hormones between the cell
- the hormones then diffuse into the bloodstream
Paracrine
- similar to endocrine, but when hormone released, it does not diffuse away; instead, it act locally
- e.g.: neurocells diffuse from synapse and bind to the dendrites of another cell
Autocrine
- hormone released comes back to join the receptor on the cell, stopping it from producing more of the same hormone
List all the main glands of the endocrine system
Pineal gland
- sleep patterns
- releases melatonin and seratonin
Hypothalamus
- neuroendocrine junction
- regulates endocrine systems
Pituitary gland
- regulates hormones
Thymus
- matures T-cells and lymphocytes
Pancreas
- both endocrine and exocrine
Thyroid gland
- controls metabolic pathways
Adrenal gland
- secretes adrenaline and steroids
Parathyroid glands
Ovary and Testis
Describe how the hormones in the blood work
Low concentration;
Steroid and thyroid hormones are transported by specific carrier/binding proteins because they are hydrophobic and insoluble in blood
- this improves their solubility
- increases half life since you don’t filter out the proteins
- provides a reserve in the blood
When are hormones biologically active?
When they are free
Protein-bound hormones are inactive
Where are the protein receptors for hormones found?
Cell-membrane receptors: peptides, glycoproteins, catecholamines (adrenalin, dopamine, noradrenalin)
Intracellular receptors in the nucleus: steroid and thryoid hormones
The hormones can diffuse through the nuclear membrane because they like lipids - they will bind onto the receptor of the nucleus and alter the transcription of genes
Where does the anterior pituitary develops from?
The epithelium of the mouth
Where does the posterior pituitary develops from?
Downgrowth of the hypothalamus; consist of nerve fibres
Function of the neuronal-endocrine junction
Controls neurosecretory cells in the hypothalamus, controlling the secretions from the anterior and posterior pituitary
Ultimately, it combines the nervous system and endocrine system
What is the Endocrine Axes/Cascade?
The hormones of one endocrine gland targets another endocrine gland - therefore, production of one type of hormone influences the production of another type of hormone
e.g.: the hypothalamus secretes hormones that control the secretion and releas of pituitary hormones;
pituitary hormones then control the production of thyroid hormones, gonads etc
What is the function of the Hypothalamus?
- Sends neural hormones to the anterior pituitary and controls the release of its hormones via releasing hormones
- Secretes hormone that are stored and released by the posterior pituitary gland (eg oxytocin and ADH - neuralsecretory hormones - made in Hypothalamus, transferred to p.p.g.)
Structure and function of the anterior pituitary gland
Also called ADENOHYPOPHYSIS
It consists of clumps of epithelial cells, secreting 6 hormones
What are the 6 hormones the anterior pituitary gland secretes?
- Growth Hormone (GH)
- Thyroid stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle stimulating hormons (FSH)
- Luteinising hormone (LH)
- Prolactin (milk production)
Which of the anterior pituitary gland’s 6 hormones regulate other endocrine hormones?
TSH, ACTH, FSH, LH
What hormones are controlled by hypothalamic secretory factors, and which are inhibited by them?
Controlled: GH, TSH, ACTH, FSH, LH
Inhibited: Prolactin
Structure and function of the posterior pituitary gland
Also called NEUROHYPOPHYSIS
Consists of neural tissue - extensions of axons from the hypothalamus
Stores hormones which are secreted by the neurosecretory cells in the hypothalamus, and transported by the neuronal axons
Two hormones released are:
- ADH (vasopressin) - prevents you losing water from the kidneys; causes constriction of smooth muscle around arteries, increasing BP
- Oxytocin - constriction of uterus, helps during birth giving; constricts alveoli of lungs
What is the concept of negative feedback?
The final product of a cascade acts to inhibit a hormone higher up in the cascade (e.g.: negative feedback inhibition of GnRH by gonadal steroid)
What is the name of the tumour found in the pituitary gland, and what does it result in?
Pituitary Adenoma - causes over-secretion of hormones, compressing on and killing the pituitary gland
What is the condition of having excess growth hormone referred to as?
Acromegaly
What is the position of the thyroid gland?
Anterior to the trachea
What did the thyroid gland develop from?
It is a downgrowth of the epithelium of the tongue
What is the foramen caecum?
Pit left behind by the thyroid gland, at the back of the tongue
Describe the microscopic structure of thyroid
The thyroid epithelial/follicular cells are arranged as thyroid follicles - these are filled with colloid/thyroglobulin
What hormones do follicular cells secrete?
Where are they stored?
Tri-iodothyronine (T3) and Thyroxine (T4) - requires iodine
These are stored in colloid/thyroglobulin
What is the function of Thyroxine?
Regulates:
- energy use - rate of metabolism
- protein production - growth and development
- regulates sensitivity of cells to other hormones
Function of Parafollicular (aka C) cells
They produce Calcitonin which regulates Calcium homeostasis - stimulates osteoblasts
How many parathyroid glands do we have?
What is their location?
Two pairs, aka 4
Posterior aspect of the thyroid
What hormones do parathyroid glands secrete and what is their function?
Parathyroid hormones - regulates calcium homeostasis - stimulates osteoclasts to breakdown bone matrix and increase blood calcium levels
Describe the structure of the adrenal glands?
Cortex - produces steroid hormones; has three layers of epithelial cells:
- Zona glomerulosa - mineralocorticoids e.g.: aldosterone (- conserve sodium, increase water retention)
- Zona fasciculata - glucocorticoids e.g.: cortisol (- increase blood sugar)
- Zona reticularis - sex steroids e.g.: androgens (- activity of sex organs)
Medulla - forms from neural crest cells/NEUROECTODERM
Contains chromaffin cells that produce cathecolamines:
- Epinephrine
- Norepinephrine
- Dopamine
Has a direct connection with the SNS (controlling the fight or flight response)
What is Cushing’s syndrome?
A collection of symptoms that develop as the result of very high levels of a hormone called CORTISOL in the body
Describe the endocrine and exocrine nature of the pancreas
Exocrine
- pancreatic acini cell - synthesises, stores and secrete digestive enzymes; e.g.: amylase, lipase
Disorder: pancreatitis
Endocrine - islets of Langerhans - produce hormones like: - Alpha cells - glucagon - Beta cells - insulin Disorder: diabetes mellitus
What hormone does the GI tract produce?
Gastrin
What hormone do the kidneys produce?
Renin
What hormones do the gonads produce?
Testosterone or Oestrogen
