Endocrine system Flashcards
How are hormones chemically classified?
peptides:
- small peptides
- proteins like insulin and GH
- glycoproteins: long carbohydrates
Amines
Steroids: hydrophobic hormones derived from cholesterol
How are the effects of hormones mediated?
by specific hormone receptors in the cell
- receptors for hydrophilic hormones are on CSM
- receptors for hydrophobic hormones are intracellular
How do membrane receptors work?
G-protein-linked: activate 2nd messenger pathway
ion-channel-linked: mostly for neuropeptide hormones
enzyme-linked: most are protein kinases
What are the types of endocrine disorders?
hyposecretion:
- due to heredity, dietary deficiency, immunologic factors
- causes can be primary or secondary
- most can be treated by hormone replacement therapy
hypersecretion:
- due to tumours of endocrine glands; autoimmune disease
- causes can be primary or secondary
can also arise from the unresponsiveness of target cells
What is the structure of the pituitary gland?
attached to hypothalamus by infundibulum
anterior lobe consists of glandular tissue
posterior lobe consists of neural tissues
How does the hypothalamus regulates the secretion of anterior pituitary gland?
hypothalamus neurones secret releasing and inhibiting hormones > regulate secretion of anterior pituitary
hypothalamic hormones transported to AP through hypothalamic-hypophyseal portal system
How does the hypothalamus regulates the secretion of anterior pituitary gland?
thyrotropin-releasing hormone(TRH): stimulates TSH release
CRH: stimulates ACTH release > to release cortisol
GnRH: stimulates LH and FSH
GHRH: stimulates GH release
GHIH: inhibits GH release
prolactin-releasing hormone (PRH)
prolactin-inhibiting hormone (PIH) = dopamine
What happens during stress?
increase in CRH > increase in ACTH > increase in corticosteroid
What is the structure of the bone?
bone cells:
- osteoblast: bone formation
- osteoclasts: bone remodelling
- osteocytes: bone maintenance
- chondrocytes: cartilage cells
matrix:
- collagen fibres
- calcium phosphate crystals
nerves and blood vessels
How do bones grow in width?
osteoblasts produce a metric of osteoid and deposit calcium phosphate
at the same time osteoclast carry out bone resorption on inner side of bone
IGF-1 stimulates activity of osteoblasts and osteoclasts
What are the types of cells in the thyroid gland?
follicular cells: secrete T3 and T4
parafollicular cells: secrete calcitonin
What is hypothyroidism?
insufficient secretion of TH
causes:
- inadequate supply of iodine
- autoimmune disease
- deficiency of TSH, TRH or both
loiter develops when thyroid gland is over stimulated by TSH
neonatal hypothyroidism can lead to cretinism: condition of severely impaired physical and mental growth in infant
What is hyperthyroidism?
over secretion of TH
most common cause: grave’s disease - body erroneously produces thyroid-stimulating immunoglobulin (TSI) > exerts TSH-like effects on thyroid but not subjected to negative feedback
What happens when ECF calcium level is not maintained at proper levels?
hypocalcemia:
- increases neuromuscular excitability > spasm
- may lead to muscle cramps
- severe hypocalcemia > spasm of respiratory muscles > suffocation
hypercalcemia:
- reduces excitability
- cardiac arrhythmia: irregular heartbeat
How does PTH increase blood calcium?
on bones:
- promote transfer of Ca2+ from bone fluid to plasma (fast effect)
- stimulate dissolution of calcium phosphate crystals to release Ca2+ and Po43- ( slow effect)
on kidneys:
- stimulate Ca2+ reabsorption
- promote PO43- elimination to prevent re-precipitation of Ca2+
on intestine:
- increase both Ca2+ and PO43- absorption via vitamin D activation in kidneys
