Endrocrine System 2 Flashcards
Hypothalamus
- master endocrine gland and neuroendocrine control centre in the body
- composed of severe; sections called nuclei, each of which controls specific functions (some through the production of regulatory hormones)
How does the hypothalamus integrate activities of the nervous and endocrine systems?
- secretes regulatory hormones
- special hormones control endocrine cells in the pituitary gland
- acts as an endocrine organ
- contains autonomic centres:
- exert direct neural control over endocrine cells of adrenal medulla
Hypothalamix Hormones
2 classes of hypothalamic regulatory hormones
- releasing hormones
- inhibiting hormoens
- rate of secretion is controlled by negative feedback
Releasing and Inhibiting hormones
Releasing:
-stimulate synthesis and secretion of 1 or more hormones at anterior lobe of pituitary
Inhibiting:
-prevent synthesis and secretion of hormones from anterior lobe and pituitary
Pituitary Gland
-also called hypophysis
-lies within sella turcica
-hangs inferior to the hypothalamus
-connected by infundibulum
-divided into
anterior lobe: adenohypophysis
posterior lobe: neuropophysis
-releases 9 peptide hormones
-7 from anterior lobe
-2 from posterior lobe
Anterior Pituitary Gland
- secretion of anterior pituitary hormones controlled by:
- negative feedback
- releasing and inhibiting factors from hypothalamus
- synthesised by neurosecretory cells in the hypothalamus
- packaged in vesicles at axon terminals
- released in response to nerve impulses
- reach anterior pituitary via hypophyseal postal system
Anterior Pituitary - 7 Hormones
1. Growth Hormone
Growth Hormone GH (somatotrophs)
-secreted in bursts every few hours (especially during sleep)
-stimulates general body growth and regulates metabolism by stimulating production of IGFs (insulin-like growth factors)
-increases protein synthesis
-decreases protein catabolism
-increases uptake of amino acids
Major target organs: liver, adipose tissue
Major physiological effects:
promotes growth (indirectly), control of protein, lipid and carbohydrate metabolism
Anterior Pituitary - 7 Hormones
2. Thyroid Stimulating Hormone
Thyroid stimulating hormone TSH (thyrotrophs)
-controls secretions and activities of the thyroid gland
Anterior Pituitary - 7 Hormones
3 and 4 - Gonadotropins
Gonadotrophs regulate the function of the gonads
- Follicle stimulating hormone = FSH
- in males stimulates sperm production
- in females stimulates follicle, egg and strogen production - Leutenizing hormone = LH
- in males stimulates cells to synthesise testosterone
- in females stimulates ovulation and lutenisation and estrogen and progesterone production
Anterior Pituitary - 7 Hormones
5. Prolactin
Prolactin (lactotroph)
- initiates and maintains milk secretion by mammary glands
- other hormones exert permissive effects (e.g. oestrogen’s, progesterone)
Anterior Pituitary - 7 Hormones
6. Adrenocorticotrophic hormone
ACTH (corticotroph)
-stimulates adrenal cortex to release glucocorticoids
Anterior Pituitary - 7 Hormones
7. Malanocyte stimulating hormone
MSH (also a corticotroph)
- precise role unknown but causes darkening of skin by stimulating melanocytes
- MSH also produced locally within sun-exposed skin (skin tan)
Posterior Pituitary
- also called neuropophysis (under neural stimulation)
- contains unmyelinated axons of hypothalamic neurone
- does not synthesise hormones
- supraoptic and paraventricular nuclei manufacture:
- antidiuretyc hormone (ADH)
- oxytocin
Posterior Pituitary
ADH and Oxytocin
ADH
-decreases amount of water lost at kidneys (increases water retention at distal convoluted tubule)
-increases blood pressure (as more water in blood stream)
-release inhibited by alcohol (as you drink alcohol frequency of urination increases, absorption of water decreases)
Oxytocin
-stimulates contractile cells in mammary glands
-stimulates smooth muscles in uterus (prostate in male)
-secretion and milk ejection are part of neuroendocrine reflex
Clinical Note: Pituitary Adenoma
- tumour of pituitary gland
- benign or malignant
- usually involves increased hormone production e.g. gigantism or acromegaly due to increased secretion of GH
- treatment often involves removal of tumour
- transsphenoidal surgery
