Hypothalamic pituitary gland Flashcards
1
Q
T H E E N D O C R I N E S Y S T E M
A
- It is a collection of glands that release hormones into the blood
- It regulates growth and development
- It is responsible for homeostatic control and metabolism
- It has a role in reproduction, pregnancy, parturition (birth), lactation and urine production
2
Q
H O R M O N E S
A
- Chemical messenger produced by cells, carried by blood and detected by non-adjacent target cells
- Distal hormones travel in blood stream to reach the target cells i.e. histamine
- Specialised cells of the nervous system also synthesise and secrete hormones i.e. serotonin
- Local hormones are when nerve cell release neurotransmitter molecules into a narrow space (synapse) between it and its target cell i.e. acetylcholine
- Paracrine signalling is where secreting cells discharge hormones into the interstitial fluid surrounding the target cells
3
Q
S T E R O I D H O R M O N E S
A
- Chemically derived from cholesterol by adrenal cortex, testes and ovary
- They enter the cell and bind with cytosolic receptor which then interacts with DNA
- Affect DNA gene transcription
- Examples include cortisol, estradiol
4
Q
P E P T I D E / P R O T E I N H O R M O N E S
A
- Interact with membrane bound receptors
- Adrenaline and noradrenaline are amines
- Oxytocin and ADH are peptides
- Growth hormone and insulin are proteins
- FSH and TSH are glycoproteins
- Each hormone has a specific shape
5
Q
A C T I V A T I O N O F T A R G E T C E L L
A
- Peptide hormones bind to membrane receptor which produces a second messenger
- This causes phosphorylation and enzyme regulation
- The second messenger may also enter the nucleus and increase/decrease DNA gene transcription
- Steroid hormones can passively diffuse across the membrane
- It then attaches to nuclear receptor and affects DNA gene transcription
- T3 has a cholesterol backbone so it can also passively diffuse across the membrane and attaches to T3 nuclear receptor
- Affects DNA gene transcription
6
Q
S T E R O I D R E C E P T O R S
A
- Steroid binds to the receptor in the cytosol
- It is associated with a heat shock protein and forms a complex
- This then enters the nucleus and binds with DNA elements (SRE within DNA)
- This initiates transcription
- Resulting in mRNA and protein synthesis
7
Q
H Y P O T H A L A M U S P I T U I T A R Y G L A N D
A
- Hypothalamus is responsible for temperature regulation, osmolarity of the blood, feeding, stress response
- It controls the secretions of the pituitary gland
- Pituitary gland (hypophysis) consists of posterior (neurohypophysis) and anterior (adrenohypophysis)
8
Q
T H Y R O I D G L A N D A X I S
A
- Hypothalamic release of thyroid releasing hormone (TRH) into hypothalamic hypophyseal portal system
- TRH stimulates thyrotrophs of the anterior pituitary gland to synthesise and secrete thyroid stimulating hormone (TSH)
- TSH binds to its receptor which is Gs linked, activating AC and increasing cAMP
- This increases iodide uptake by thyroid gland to synthesis and release thyroid hormone
- There are two forms of thyroid hormone – T4 (thyroxin) and T3 (tri-iodothyronine)
- Their main functions are to control metabolic rate
9
Q
A D R E N A L G L A N D A X I S
A
- Hypothalamus releases corticotropin releasing factor/hormone into hypothalamic hypophyseal portal system
- CRH acts on corticotrophs stimulating anterior pituitary to stimulate ACTH production
- ACTH is released in the systemic circulation and stimulate receptors found on the adrenal cortex
- They are Gs linked, activating AC and increase cAMP
- This results in the production and stimulation of cortisol, aldosterone and dehydroepiandrosterone
- Cortisol regulate metabolism and adaptation to stress
- Aldosterone function in the kidney in the maintenance of plasma sodium levels and blood volume
- DHEA has androgenic properties
10
Q
H Y P O T H A L A M I C P I T U I T A R Y G O N D A L A X I S
A
- Production of male sperm gametes – spermatogenesis
- Hypothalamus produces a gonadotropin releasing hormone (GnRH)
- GnRH binds to receptors on anterior pituitary gland which is G αq and increases PLC
- Stimulate gandotrophs in anterior pituitary to release gonadotrophs – LH and FSH
- Act on testicular Leydig cells causing androgen (testosterone) synthesis
- Act on testicular Sertoli cells
- Luteinising hormone binds to receptor on Leydig cells increasing transcription of genes responsible for testosterone synethesis
- FSH bind to receptors on Sertoli cells and stimulates gene transcription of aromatase, growth factors, inhibin and androgen binding protein
- For LH and FSH the α 92 amino acid chain is identical however the β 115 amino acid chain are different
- Leydig and Sertoli cells are PKA controlled
- Leydig cells make testosterone which can act on Sertoli cells to get converted to Estradiol
- Estradiol can act on Leydig cells
11
Q
F O L L I C L E S T I M U L A T I N G H O R M O N E
A
- FSH act on Sertoli cells activating PKA and up regulating gene transcription
- Angdrogen binding protein bind to testosterone and maintain high local levels
- Aromatase convert testosterone to estradiol which diffuses to the Leydig cells
- Growth factors support spermatogenesis, increase fertility potential of sperm and stimulates motility
- Inhibins inhibit FSH secretion by anterior pituitary
12
Q
G R O W T H H O R M O N E A X I S
A
- Growth hormone releasing factor acts on somatotrophs in the anterior pituitary
- This stimulates the release of growth hormone which binds to its receptors
- They utilise cAMP as a second messenger
- Stomatostatin may induce a decrease in cAMP levels to inhibit the release of growth hormone
- GH targets the liver, bone, cartilage, muscle and kidneys via the PKA pathway to produce igf-1 (somatomedins)
- This acts on adipose tissue via the JAK/STAT pathway increasing lipolysis and decreasing glucose uptake
- It acts on muscle tissue via JAK/STAT pathway increasing protein synthesis and decreasing glucose uptake
- It acts on hepatocytes to form gluconeogenic enzymes
13
Q
P R O L A C T I N A X I S
A
- Prolactin releasing factors act on lactotrophs in anterior pituitary gland to stimulate the secretion of prolactin – this can be inhibited by dopamine
- The releasing factors are thyrotropin releasing hormone, vasoactive intestinal peptide and peptide histidine methionine
- Prolactin secretion increases during pregnancy to assist in breast tissue development to stimulate lactation during the post partum period
14
Q
P O S T E R I O R P I T U I T A R Y
A
- Axons from hypothalamus extend and terminate on capillaries located in the posterior pituitary lobe
- Does not require releasing factors
- Neuronal depolarisation and Ca2+ influx induce exocytotic release
- They are released into the systemic circulation
15
Q
A N T I D I U R E T I C H O R M O N E
A
- They cause contraction of arteriolar smooth muscle resulting in vasoconstriction – to treat hypotension
- Enhance water absorption by the kidney to decrease urine volume
- Stimulate synthesis of aquaporin water channel proteins and their transport to the apical surface of collecting duct
- V1 – arterioles and GIT smooth muscle
- V2 – Anti-diuretic effect on kidney
- V3 – Control in secretion of ACTH
- V2 is AC coupled via Gs and V1/V3 is coupled to PLC/IP3 pathway
