The Endocrine System Flashcards
What do exocrine glands do?
Secrete their products into ducts
What do endocrine glands do?
Release their hormones directly into the blood (without a duct)
What are hormones?
Chemical messengers carried by the blood to target cells
What are the functions of hormones?
• Help regulate chemical composition and volume of internal environment, metabolism and energy balance, contraction of smooth and cardiac muscle fibres, glandular secretions, and some immune system activities
• Control growth and development
• Regulate operation of reproductive system
• Help establish circadian rhythm
What are the three major structural classes of hormones?
• Amines (derivatives of the amino acid ‘tyrosine’)
• Peptides and proteins
• Steroids (produced from cholesterol by the adrenal cortex and the gonads)
Give examples of amines
• Thyroid hormones
• Dopamine
• Catecholamines (epinephrine and norepinephrine)
Give an example of a peptide hormone
Insulin
Give examples of steroid hormones
• Aldosterone
• Cortisol
• Androgens (e.g. testosterone)
• Estrogens
How do peptide and catecholamine hormones circulate the body?
Mainly dissolved in plasma as they are water soluble (some bind to plasma proteins)
How do steroid and thyroid hormones circulate the body?
Mainly bound to plasma proteins (as they’re not water soluble)
What is the liver’s role in removing hormones from the plasma?
It is responsible for metabolic inactivation (metabolism/biotransformation)
What is the kidneys’ role in removing hormones from the plasma?
Filtering the blood, removing waste products (including hormones and their metabolites)
Which hormones are rapidly removed from the blood?
Peptide hormones and catecholamines (as they aren’t bound to plasma proteins)
Where are the majority of receptors for lipid-soluble steroid and thyroid hormones?
Inside target cells
Where are the receptors for water-soluble peptide hormones and catecholamines?
On the plasma membrane
What does the responsiveness of a target cell depend on?
• The hormone’s concentration in the blood
• The abundance of the target cell’s receptors
• Influences exerted by other hormones
What are the three types of hormonal interactions?
• Permissive
• Synergistic
• Antagonistic
Describe a permissive interaction and give an example of one
• An action of one hormone that enhances the responsiveness or activity of another hormone (one needs the other to work to its full extent)
• E.g. epinephrine and thyroid hormones (T3 and T4) stimulation of lipolysis
Describe a synergistic interaction and give an example of one
• The effect of two hormones acting together is greater or more extensive than one hormone acting on its own
• E.g. follicle-stimulating hormone and estrogens
Describe an antagonistic interaction and give an example of one
• One hormone opposes the actions of another hormone
• E.g. insulin and glucagon
What are the inputs that control hormone secretion?
• Plasma concentration of an ion or nutrient that the hormone regulates
• Neural input to the endocrine cells
• Other hormones
What are the inputs that control hormone secretion?
• Plasma concentration of an ion or nutrient that the hormone regulates
• Neural input to the endocrine cells
• Other hormones
What is a tropic hormone?
A hormone that stimulates the secretion of another hormone
What is hyposecretion?
Too little hormones
What is hypersecretion?
Too much hormone
What is hyporesponsiveness?
Decreased responsiveness of the target cells to hormones
What is hyperresponiveness?
Increased responsiveness of the target cells to hormones
Which part of the pituitary gland is connected via nerves?
Posterior
Why is the posterior pituitary a neural extension of the hypothalamus?
• Hormones are synthesised in the hypothalamus
• Axons pass down the infundibulum, terminate in the posterior pituitary and release the hormones
Which hormones does the anterior pituitary gland secrete?
- Growth hormone (GH)
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Prolactin
- Follicle-stimulating hormone (FSH)
- Luteinising hormone (LH)
What controls the secretion of anterior pituitary gland hormones?
Hypophysiotropic (hormones that act on other hormones) hormones via the portal vessels connecting the hypothalamus and anterior pituitary gland (hypothalamo-hypophyseal portal vessels)
What does GnRH stand for?
Gonadotropin-releasing hormone
What does GnRH do?
Stimulates release of FSH and LH
What does GHRH stand for?
Growth hormone-releasing hormone
What does SST stand for?
Somatostatin
What does GHRH do?
Stimulates release of growth hormone
What does SST do?
Inhibit release of GH
What does TRH stand for?
Thyrotropin-releasing hormone
What does TSH stand for?
Thyroid stimulating hormone
What does TRH do?
Stimulates release of TSH
What does DA stand for?
Dopamine
What does CRH stand for?
Corticotropin-releasing hormone
What does DA do?
Inhibits release of prolactin
What does CRH do?
Stimulates release of ACTH
What does ACTH stand for?
Adrenocorticotropic hormone
What is TSH production controlled by?
Negative feedback action of T3 and T4 on the anterior pituitary gland and (to a lesser extent) the hypothalamus
What condition does TSH cause?
Goiter (hypertrophy of thyroid tissue)
What does TSH do?
Stimulate the release of thyroxine (T4 - four iodines) and triiodothyronine (T3 - three iodines)
What are the actions of thyroid hormones (T4 and T3)?
• Oxidative substrate metabolism
• Mitochondrial enzyme activity
• Carbohydrate and lipid metabolism
• Metabolic rate
What does ACTH do?
Secretes cortisol (from adrenal glands)
What are the physiological functions of cortisol in non-stressful situations?
• Affects responsiveness of smooth muscle to epinephrine and norepinephrine (permissive action) - thus helps maintaining normal blood pressure
• Required to maintain the certain enzyme concentrations involved in metabolic homeostasis - prevents plasma glucose concentration dropping too far below normal
• Has anti-inflammatory and anti-immune functions
What are the physiological functions of cortisol in stressful situations?
• Stimulation of protein catabolism in bone, lymph, muscle, and elsewhere
• Stimulation of liver uptake of amino acids and their conversion to glucose (gluconeogenesis)
• Maintenance of plasma glucose concentrations
• Stimulation of triglyceride catabolism in adipose tissue, with release of glycerol and fatty acids into the blood
• Enhanced vascular reactivity (improving cardiovascular performance)
• Unidentified protective effects against the damaging influences of stress
• Inhibition of inflammation and specific immune responses
• Inhibition of nonessential functions (e.g. reproduction and growth)
Why does massaging to reduce circulating cortisol levels improve recovery?
• Cortisol at rest inhibits immune system
• Cortisol at rest inhibits inflammatory response
• Cortisol decreases capillary permeability in injured areas
What are the most important hormones to human growth?
• GH
• IGF 1 and 2
• T3 (essential during childhood and adolescence)
• Insulin (mainly during foetal life)
• Testosterone and estradiol
What does GH do?
• Stimulates the release of IGF-1 from the liver and many other cells
• IGF-1 then acts locally (and as a circulating hormone) to stimulate cell division
• GH also acts directly on cells to stimulate protein synthesis
Where is testosterone produced in males and females?
• Males: testes (and others mentioned later)
• Females: smaller quantities produced in ovaries and adrenal cortex, and peripheral conversion of androgens
What does testosterone do?
Promotes muscle growth and development of male sex characteristics
Where is oestrogen and progestogen produced in females, post-menopausal females and in males?
• Females: ovaries
• Post-menopausal females: some produced in smaller amounts by other tissues (e.g. liver, pancreas, bone, adrenal glands, skin, brain, adipose tissue and breasts)
• Males: oestrogen produced when FSH binds to FSH receptors
What do oestrogen and progestogen do?
• Promotes development of female sex characteristics, regulates menstrual cycle and adipose tissue growth
• Oestrogen also promotes endothelia function (leading to reduced risk of CVD)
What does DHEA stand for?
Dehydroepiandrosterone
What does DHEAS stand for?
Dehydroepiandrosterone sulfate
What do DHEA and DHEAS do?
• Produced by adrenal cortex
• Precursors for sex hormones (e.g. testosterone and estradiol)
• Purported to be anti-ageing
What hormones does the posterior pituitary gland secrete?
• Oxytocin
• Vasopressin
What hormones does the anterior pituitary gland secrete?
• GH
• TSH
• SCTH
• Prolactin
• FSH
• LH
