Endocrine system Flashcards
What does the endocrine system consist of?
- Specialised ductless glands (or neurones) scattered throughout the body
What do the glands of the endocrine system secrete and how do they travel in the body and what is the response?
- They secrete biologically active chemical messengers
(hormones) into the blood stream. - The hormones are carried in the blood stream to interact with distant target cells.
- Interaction leads to specific target cell response in terms of metabolism, growth or reproduction.
What are the anatomical divisions of the endocrine system and what does each one consist of?
THE CENTRAL ENDOCRINE GLANDS: Hypothalamus, Pituitary gland, Pineal gland
THE PERIPHERAL ENDOCRINE GLANDS: Thyroid glands, Adrenal glands, Endocrine pancreas, Parathyroid glands
State the functions of the endocrine system.
- Regulate & Control Important Cellular & Body Functions.
- Cellular Metabolism and water & Electrolyte balance.
- Cell Growth & Development and Reproduction.
- Adaptive changes to help the body cope with stressful
situations. - Control & Integration of circulatory and digestive
systems.
Describe the synthesis of hormones.
Vesicle-mediated pathway
* Synthesised in rER & packaged in vesicle
* Amine/AA/Peptide/Protein hormones
Non-vesicle-mediated pathway
* Synthesised in sER & directly released
* Steroid hormones
Describe the transport of hormones.
Free & unbound
* Amine/AA/peptide hormones
Protein career-bound
* Steroid & thyroid hormones
How do hormones produce their effects on target cells?
- By interacting with specific receptors
What are the two broad types of hormonal receptors?
- Cell surface receptors:
Receptor-ion channels
G-protein coupled receptors
Tyrosine kinase-linked receptors - Intracellular or nuclear receptors
What may endocrine disorders result from?
- Hyposecretion
– Endocrine secretes too little of its hormone
– Primary, Secondary or Tertiary - Hypersecretion
– Endocrine secretes too much of its hormone
– Primary, Secondary or Tertiary - Abnormal Target Cell Responsiveness
– Receptor down regulation (hypo responsiveness)
– Receptor up regulation (hyper responsiveness)
Where are the hypothalamus and pituitary glands located?
In diencephalon: the pituitary gland lies in a pocket of bone at the base of the brain
State the function of the hypothalamus & pituitary gland.
Function cooperatively as ‘master regulators’ of the endocrine system - control of critical homeostatic & metabolic functions
State the two lobes the pituitary gland consists of and their functions?
- Anterior pituitary: secretes and releases 6 major hormones
- Posterior pituitary: stores and releases 2 hormones
What is the hypothalamus?
Brain’s coordinating centre for endocrine, behavioural & autonomic nervous system function
What does the hypothalamus act as?
A neuroendocrine transducer or bridge:
– receives & integrates multiple brain signals
– converts signals into chemical messages
– releases chemical messengers (hormones) to control secretion of pituitary hormones
– pituitary hormones control activity of peripheral endocrine glands
Describe the transport of hypothalamic releasing hormones.
- Hypothalamus makes releasing hormones
- Action potentials cause release of hormones into portal vessels which are carried to anterior pituitary
- The anterior pituitary releases its stored tropic hormones into systemic circulation
Describe the role of the hormones GH (ANTERIOR PITUITARY HORMONE)
– Important role in intermediary metabolism
* Exerts largely anti-insulin effects
* Increases lipolysis - increases free fatty acid (FFA)
mobilization & use as fuel
* Inhibits peripheral cellular glucose uptake - increases blood glucose levels & decreases use of
glucose as fuel
What is the secretion of the growth hormone modulated by?
- GHRH & somatostatin from hypothalamus
- Ghrelin from gastric fundus
What does GH output increase with?
Size - to maintain the concentration of GH pulses needed to sustain growth during childhood
Describe the pathology of GH.
*undersecretion BEFORE puberty will cause dwarfism
*overproduction BEFORE puberty will cause
gigantism
*AFTER puberty over-production causes acromegaly
State the role of the follicle-stimulating hormone FSH (ANTERIOR PITUITARY HORMONE)
– stimulates growth & development of ovarian follicles (F)
– promotes ovarian secretion of oestrogen (F)
– Required for sperm production (M)
How is FSH stimulated?
– Secretion stimulated by GnRH from the hypothalamus
Describe the role of the luteinising hormone (LH) (ANTERIOR PITUITARY HORMONE)
– Responsible for ovulation & development of the corpus luteum (F)
– Regulates ovarian secretion of sex hormones (F)
– Stimulates testes to secrete testosterone (M)
What is the secretion of LH stimulated by?
GnRH from hypothalamus
Describe the role of prolactin (PRL) (ANTERIOR PITUITARY HORMONE)
– Enhances breast development & milk production in females;
elevated in pregnancy and lactation
– Overproduction leads to infertility
What is the secretion of PRL inhibited by?
DA from hypothalamus (drugs – dopamine antagonist)
Describe he role of thyroid-stimulating hormone (TSH) (ANTERIOR PITUITARY HORMONES)
– Stimulates secretion of thyroid hormones
– Promotes vascularisation & growth of the thyroid gland
What is the secretion of TSH stimulated by?
TRH from hypothalamus
Describe the role of adrenocorticotropic hormone (ACTH)
– Stimulates secretion of cortisol by adrenal cortex
– Controls growth of the adrenal cortex
What is the secretion of ACTH stimulated by?
CRH from hypothalamus
- Inhibiting pain/stress signal
Describe the role of vasopressin (posterior pituitary hormone)
– Antidiuretic hormone (ADH)
– Controls water balance in the body
– Promotes renal water re-absorption - regulation of plasma volume & osmotic pressure
State the role of oxytocin. (posterior pituitary hormones)
- Stimulates uterine contraction during childbirth & milk ejection during breast-feeding
What is the secretion of oxytocin inhibited by?
DA from hypothalamus
What is the pineal gland?
- Tiny, pine cone-shaped gland – located in diencephalon
- Secretes melatonin – ‘hormone of darkness’
- Production stimulated by suprachiasmatic nucleus (SCN) – body’s master ‘biological clock’
What are the main functions of the pineal gland?
– synchronizes body’s circadian rhythms
with light-dark cycle
– Promotes sleep
– Influences reproductive activity – onset of puberty
Describe the structure of MSH?
Similar to that of ACTH
What is the role of MSH in animals?
It plays a role in skin pigmentation through
stimulation of melanocytes in the epidermis & in control of
sodium excretion.
Describe the binding of MSH and its effect
a-MSH binds to receptor (MC-1) on melanocyte membrane activating tyrosinase, an enzyme required for melanin synthesis
Where is the thyroid gland?
- Located in the neck, just below larynx
- Two lobes of endocrine tissue joined in middle by narrow strip of gland
What 2 cell types make up the thyroid gland?
– Follicular cells
– Secrete two iodine-containing hormones
* Tetra-iodothyronine (T4 or thyroxine)
* Tri-iodothyronine (T3)
– Parafollicular or C cells
* Secrete calcitonin (peptide hormone)
Describe the effect of the thyroid hormone on normal growth and CNS development.
– Effects on normal growth mediated via GH & IGF-1
* Stimulates GH secretion & hepatic production of IGF-1
* Promotes GH & IGF-1 effects on protein synthesis &
skeletal growth
– Required for normal development of nervous system in infants & children
– Promotes normal CNS activity in adults
Describe the effect of the thyroid hormone on metabolic rate and heat production.
– Increases the overall basal metabolic rate & heat
production (‘calorigenic effect’)
– main regulator of resting O2 consumption & energy
expenditure
Describe the effect of the thyroid hormone on intermediary metabolism.
– Biphasic effects on carbohydrate, fat & protein metabolism
Describe the effect of the thyroid hormone on sympathetic activity.
- Increase cellular responsiveness to catecholamines via β-
receptor upregulation
What are the adrenal glands?
Paired organs that cap the kidneys
What do the adrenal glands consist of?
– an outer adrenal cortex
Secretes 3 types of steroid hormones:
*Mineralcorticoids (aldosterone)
*Glucocorticoids (cortisol)
*Sex hormones (DHEA)
– an inner adrenal medulla
*Secretes catecholamines – AD & NA
Describe the role of mineralcorticoids (aldosterone) - adrenocortical hormone
– essential for life
– maintain Na + & K+ balance and ECF (extracellular fluid) volume
Describe the role of glucocorticoids - adrenocortical hormone
– involved in the regulation of carbohydrate, protein & fat
metabolism
– play a key role in adaptation to stress
– exert anti-inflammatory & immunosuppressive effects
Describe the role of sex hormones - adrenocortical hormone.
– supplement sex hormones secreted by gonads
– exert minor effects on reproductive function
– promote protein anabolism & growth
What does the adrenal medulla secrete?
- Adrenaline and Noradrenaline
What are the main functions of the adrenal medulla?
– Reinforce “fight-or-flight” responses
* Maintenance of arterial blood pressure
* ↑ respiratory rate, HR & CO
* ↑ glycogenolysis -↑ glucose mobilisation
* ↑ lipolysis -↑ mobilisation of free fatty acids
Describe the cells of the pancreas.
- Consists of clusters or ‘islands’ of secretory cells, called Islets of Langerhans
- Comprise 3 types of secretory cells:
– α (alpha) cells - Secrete glucagon
– β (beta) cells - Secrete insulin
– δ (delta) cells - Secrete somatostatin
What are secretion of the endocrine pancreas regulated by?
Changes in blood glucose concentration.
