Week 10 - Endocrine System and Disorders Flashcards
Differentiate an endocrine gland from an exocrine gland
- Endocrine glands are ductless and produce hormones (e.g. oestrogen) that travel to target cells via the bloodstream
- Exocrine glands produce substances (e.g. enzymes, bile) and release them via ducts
Define the term “hormone”
- Chemical messengers that travel via the blood to act on specific receptors of target cells
List the differences between hormonal and nervous communication. In what ways are they similar?
Differences:
- Transmission Speed
- Hormone - slow
- Nerves - fast
- Length of Effect
- Hormone - long
- Nerves - short
- Mechanism of Action
- Hormone - travel via bloodstream, to act at specific receptors at target cells
- Nerves - changes in membrane potential push transmission from one neuron to another, where neurotransmitters act on target receptors
Similarities
- Both act on specific receptors in target cells
- Both can cause a change in the activity of a cell
Explain how hormones may be classified based on chemical structure.
- The chemical structure of a hormone determines its mechism of action on a target cell
- For example, hormones derived from amino acids generally act via secondary messenger systems, whilst hormones that are lipid/steroid-based generally act via direct gene activation
- This is why they are classified differently
List the hormones that are referred to as steroid hormones. What nutrient are steroid hormones synthesised from?
- Steroid hormones are synthesised from lipids
- Examples:
- Aldosterone
- Oestrogen
- Testosterone
- Cortisol
- Progesterone
Describe how amino acid based hormones differ to steroid hormones in terms of their (i) solubility in water and (i) ability to cross target cell membranes
- Amino acid based hormones
- soluble in water
- therefore, cannot diffuse across cell membrane
- must use secondary messenger systems
- Steroid based hormones
- not soluble in water
- therefore, can diffuse directly across cell membrane
- can use direct gene activation
Provide some examples of eicosanoids. What nutrient are eicosanoids synthesised from?
- derived from fatty acids (arachidonic acid)
- e.g. prostaglandins and leukotrienes (involved in allergic response of respiratory tract)
- generally act as paracrines
List four general actions of hormones. Can you provide an example for each?
- stimulate synthesis or secretion (e.g. leutenising hormone -> testosterone production)
- increase permeability or exciteability of cell (antidiuretic hormone -> increase water uptake)
- activation/deactivation of enzymes (e.g. trypsin -> activates pancreatic zymogens to pancreatic enzymes)
- stimulation of mitosis (e.g. growth hormone -> stimulate somatic growth)
Explain the difference (at the cellular level) between a second messenger system and direct gene activation – you may wish to use diagrams to illustrate your point
- second messenger system
- hormone is water-soluble and unable to diffuse across membrane
- binds to a receptor within cell membrane
- causes a cascade of events involving second messengers within the cell
- this results in changed cellular activity
- direct gene activation
- hormone is lipid-soluble and able to diffuse across membrane
- binds to receptor within a cytosol, creating a receptor-hormone complex
- this complex enters the nucleus, and causes a change in cellular activity (e.g. transcription of mRNA)
Which class of hormones relies on second messenger systems? Can you explain why these hormones need to work in this way?
- amino-acid based hormones rely on second messenger systems
- they are water-soluble / lipid-phobic, meaning they are unable to diffuse across the cell membrane
- in cyclic amp second messenger system, this leads to the reliance on the activation of G protein to activate a cascade of events to execute the change in cell activity (ATP is involved)
Provide some examples of molecules that are used as second messengers
- cyclic AMP (e.g. in FSH, LH and glucagon mechnanisms)
- tyrosine kinase (e.g. in insulin activity)
- PIP2 and calcium (e.g. oxytocin, ADH)
Which hormones are capable of direct gene activation? Can you explain why these hormones are capable of achieving this?
- steroid hormones and T3, T4 are capable of direct gene activation
- steroid hormones are lipid soluble, therefore, they are able to easily diffuse through the cell membrane
- T3 and T4 are transported into target cells by membrane-bound transporter proteins, and therefore, are also capable of direct gene activation
How do the receptors for thyroid hormone differ to the receptors targeted by other hormones?
- receptors for thyroid hormones are located within the nucleus of the target cell
- whilst, in steroid hormones, these receptors are located within the cytosol
- also, other amino-acid based hormones bind to receptors located on the cell membrane
Describe the three main types of stimuli that can trigger an endocrine gland to synthesise and release hormones. Provide examples for each type of stimuli.
- humoral stimulus (altered blood levels of ions or nutrients)
- e.g. insulin released in response to high blood glucose levels
- nervous stimulus
- e.g. stimulation of SNS leads to release of adrenaline (from adrenal medulla)
- hormonal stimulus
- e.g. hypothalamis-pituitary axis - gonadotrophin-releasing hormone (hypothalamus) stimulates secretion of FSH and LH (anterior pituitary gland)
What is meant by the term negative feedback control? Provide an example to illustrate your point.
- when hormone levels rise sufficiently to cuse target organ effects
- target organ sends feedback to reduce the initial stimulus for hormone release
- results in inhibition of further hormone release
- example:
- testosterone released in response to low levels
- testosterone produced by interstitial (Leydig) cells provides feedback to anterior pituitary gland to stop releasing FSH and LH
- sustentacular cells, which are producing androgen-binding protein, produce inhibin to act on hypothalamus to stop releasing gonadotrophin-releasing hormone
Differentiate the terms adenohypophysis and neurohypophysis
- adenohypophysis refers to the action of the anterior pituitary gland, via vessels connected to the hypothalamus
- whilst, neurohypophysis refers to neurological regulation between hypothalamus and the posterior pituitary gland
What is the vascular supply of the adrenal glands? Can you explain why these glands have such an abundant vascular supply?
- adrenal glands have an abundant vascular supply, due to their significant endocrine output
- they are supplied by:
- superior adrenal arteries
- middle adrenal arteries
- inferior adrenal arteries
Conceptually map the hormonal secretions of the adrenal cortex. Your concept map should make reference to (i) the regions of cortex where these hormones are produced (ii) the types of stimuli that cause the release of these hormones and (iii) the functions of these hormones
Zona glomerulus
- mineralocorticoids e.g. aldosterone
- stimuli: low blood pressure; high plasma levels of K+, stress response, atrial natriuretic peptide
- effect: Na+ reabsorption and K+ secretion
Zona fasciculus
- glucocorticoids e.g. cortisol
- stimuli: prolonged stress
- effect:
- gluconeogenesis
- SNS response on smooth muscles of blood vessel walls
- regulation of immune response
Zona reticularis
- androgens supplementing gonads e.g. oestrogen after menopause or during puberty
- stimuli: puberty; menopause
Medulla
- Chromaffin cells
- stimulus: short term stress
- effect: produce adrenaline and noradrenaline - increased HR and heart contractility; peripheral vessel constriction; increased BP; increased blood glucose
Describe the cells of the adrenal medulla. Why are these cells referred to as modified postganglionic sympathetic neurons?
- preganglionic sympathetic fibres, leaving the cord at T10-L1, do not synapse at the prevertebral ganglia
- instead, they terminate at the adrenal medulla, where they synapse directly with chromaffin cells
- as a result, chromaffin cells are considered to be modified postganglionic sympathetic neurons
Discuss the role that adrenal glands play in the short-term and long-term stress response.
- short term response:
- nerve impulse travel via preganglionic sympathetic fibres to adrenal medulla
- synapse with chromaffin cells results in production and release of adrenaline and noradrenaline
- these catecholamines:
- increase HR
- increase BP
- dilate bronchioles
- convert glycogen to glucose in liver (increase blood glucose level)
- reduce blood flow to peripheral blood vessels (vasoconstriction)
- increase metabolic rate
- long term response:
-
zona glomerulus releases mineralocorticoids (aldosterone)
- kidneys retain sodium and water
- blood volume and blood pressure rises
-
zona fasciulus release glucocorticoids (cortisol)
- proteins and fats converted into glucose or broken down for energy
- blood glucose levels increase
- immune system is suppressed
-
zona glomerulus releases mineralocorticoids (aldosterone)
Summarise the clinical features of hypercortisolism. Can you explain the pathological basis of each feature?
- effects on metabolism
- truncal obesity
- lemon on toothpicks appearance
- moon face with flushed red cheeks, buffalo hump
- muscle weakness/wasting, myalgia, arthralgia
- osteoporosis, pathological fracture
- hyperglycaemia -> insulin resistance
- effects on blood pressure
- hypertension
- effects on immunity
- poor wound healing, skin infections
- involvement of zona reticularis may produce features of hyperandrogenism
- hirsutism
- menstrual irregularity
Define the term phaeochromocytoma
- malignancy/tumour arising from chromaffin cells of adrenal medulla
Summarise the clinical features of phaeochromocytoma. How might an osteopath be able to detect this disorder?
- related to hypertension or complication of hypertension
- AMI
- stroke
- heart failure
- AAA
- intermittent catecholamine secretion causing episodes of:
- pallor, palpitations, sweating, severe headaches, anxiety, tremours
- abdominal pain, vomiting, constipation, weight loss, hyperglycaemia
