Week 8 - Hormonal Control Flashcards
What are the three broad categories of hormones?
steroids, peptides, amino acid derivatives
What are the two lobes of the pituitary gland?
anterior and posterior pituitary
linked to the hypothalamus by the pituitary stalk
What is the adenohypophysis?
anterior pituitary
posterior pituitary - neurohypophysis
What hormones are secreted by the posterior pituitary gland?
oxytocin and vasopressin (ADH)
What two physiological signals generate the CNS stimulus for ADH secretion?
rise in osmolarity of the blood
decrease in blood volume
What is the main physiological action of ADH?
increase water reabsorption in the collecting ducts and distal tubule of the kidneys
results in decreased water secretion and osmotically concentrated urine
What are the two physiological signals that stimulate the secretion of oxytocin?
breast-feeding
neural input from the female reproductive tract during childbirth
What is the mechanism of action of oxytocin?
stimulates contraction of myoepithelial cells causing milk ejection
stimulates contraction of smooth muscle cells in the uterus during labour
What are the five different cell types located in the anterior pituitary?
somatotrophs
lactotrophs
gonadotrophs
corticotrophs
thyrotrophs
What hormone do the somatotrophs secrete?
Growth Hormone
What hormone inhibits GH secretion?
somatostatin
GHRH and ghrelin stimulate GH secretion and it is the net effect of these antagonistic hormones on somatotrophs that determines the rate of GH secretion
How does GHRH cause GH secretion?
GHRH binds to receptors on plasma membranes of somatotrophs
Sets off a cAMP G protein cascade (Gs)
PKA phosphorylates proteins that stimulate GH gene expression and secretion
What does GH do?
regulates growth during childhood and puberty
GH plays no role in foetal development, becomes important at about 2yrs
exerts important effects through adult life
How does somatostatin regulate the release of GH?
binds to g protein-coupled receptors on somatotrophs
these receptors are coupled to an inhibitary g-protein (Gi) which decreases adenylyl cyclase activity, reducing intracellular cAMP
Where does GH exert its effect?
almost every cell type except neurons
principle targets are bone and skeletal muscle
What is acromegaly?
a condition that occurs when the anterior pituitary produces excess growth hormone later in life after fusion of epiphyses
What is the difference between gigantism and acromegaly?
Gigantism occurs when GH is produced in excess prior to epiphyseal growth plate closure
What metabolic disorder may patients with acromegaly develop?
diabetes
GH stimulates glycolysis, inhibits glycogenesis and increases gluconeogenesis, antagonises insulin
What is the precursor molecule for all steroid hormones?
cholesterol
What is the first step in the conversion of cholesterol to a steroid hormone?
conversion to pregnenolone
What is the indirect effect of GH?
stimulates production of IGF - 1 by the liver
What are the effects of IGF -1/2 in the body?
skeletal growth - bone deposition, cartilage formation
soft tissue growth - protein synthesis, cell proliferation and hypertrophy
What hormone stimulates the breakdown of glycogen in the liver?
glucagon
- glucagon binds to a GPCR on the extracellular membrane
- activates G protein binding
- Gs subunit is released and activates adenylyl cyclate
- increase in concentration of cAMP
Describe how acetylcholine signalling induces nitric oxide production
ACTIVATION OF ENDOTHELIAL NITRIC OXIDE SYNTHASE
