Steroid Hormones Flashcards
What is the precursor for steroid hormones?
Cholesterol
What happens to cholesterol during steroid hormone synthesis?
C atoms undergo redox reactions
To what are cytochrome P450 enzymes bound within the cell?
Mitochondrial/endoplasmic reticulum membranes
What do cytochrome P450 enzymes contain?
Haeme group
What type of reaction are cytochrome P450 enzymes involved in during the synthesis of steroid hormones?
Reduction using NADPH
Hydroxylation of C-H bond to C-OH
- For some, coupled with cleavage of C-C bond
What happens in the first step of steroid hormone biosynthesis?
Cholesterol side chain cleavage enzyme (cholestero SCC) converts cholesterol > pregnenolone
What is the first intermediate of steroid hormone synthesis?
Pregnenolone
What do hydroxysteroid dehydrogenases (HSD) do?
Catalyse interconversion of C-OH to C=O
Reduction reaction using NADH
What are the major pituitary hormones regulating steroid hormone synthesis?
ACTH
LH
FSH
What hormone has a negative feedback effect on ACTH?
Cortisol
What hormones have a negative feedback effection LH and FSH?
Testosterone
Oestrogens
What regulates cholesterol import into the mitochondria?
LH in gonads
ACTH in adrenal cortex
What imports cholesterol into cells?
LDL receptor
What imports cholesterol into mitochondria?
Steroidogenic acute regulatory protein (StAR)
What is the acute effect of LH on cholesterol transport?
Formation of cAMP and PKA
PKA phosphorylates and activates StAR
What is the chronic effect of LH on cholesterol transport?
Gene transcription of steroidogenic enzymes; eg: StAR
What are the two endocrine glands of the adrenal glands?
Cortex
Medulla
What are the three regions of the adrenal cortex?
Zona glomerulosa
Zona fasciculata
Zona reticularis
What regulates the zona glomerulosa?
Renin-angiotension
What does the zona glomerulosa secrete?
Minerolcorticoids: aldosterone
What regulates the zona fasciculata?
ACTH