Steroidgenesis Flashcards

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Questions and Answers

Steroid hormones are synthesized 'as needed'.

True

Steroid hormones are synthesized from _____

cholesterol

What are the sources of cholesterol for steroid hormone synthesis?

Dietary fat or can be synthesized de novo from acetyl CoA.

What are the steroid hormones?

Progesterone, cortisol, aldosterone, testosterone, and estradiol. Signup and view all the answers

What tissues are steroidogenic?

Adrenal gland, gonads, and placenta. Signup and view all the answers

Cholesterol can be synthesized in __ or be taken up via

tissues; dietary sources Signup and view all the answers

What are the 2 regulated steps in cholesterol uptake in steroid hormone synthesis?

StAR protein takes free cholesterol from the OMM into the IMM and P450SCC converts cholesterol to pregnenolone. Signup and view all the answers

What are 2 inherited disorders of cholesterol transport?

Wolman disease and congenital lipoid adrenal hyperplasia. Signup and view all the answers

What is the mutation in Wolman disease?

Mutation in lysosomal acid lipase (LAL). Signup and view all the answers

What is the mutation in congenital lipoid adrenal hyperplasia?

Mutations in StAR. Signup and view all the answers

What are the functions of P450SCC in steroid hormone synthesis?

It converts cholesterol to pregnenolone and is the rate limiting step in all steroid hormone synthesis. Signup and view all the answers

What is required to convert cholesterol to pregnenolone?

P450SCC (CYP11A1), 3 O2, and 3 NADPH. Signup and view all the answers

What are the locations and functions of StAR protein and CYP11A1?

StAR protein is on the OMM and brings cholesterol into the mitochondria; CYP11A1 converts cholesterol to pregnenolone in the IMM. Signup and view all the answers

What hormones are produced from the different locations in the adrenal glands?

Medulla produces catecholamines; adrenal cortex produces steroids (aldosterone, cortisol, DHEA). Signup and view all the answers

How are different products produced from the medulla and different zones in the cortex?

Through differential gene expression and enzymatic activity. Signup and view all the answers

How is ACTH produced and where is it produced from?

Stress triggers Ach and 5HT release from hypothalamus, leading to CRH secretion by the hypothalamus to the anterior pituitary, which secretes ACTH. Signup and view all the answers

What is the effect of ACTH activation?

PKA activation leads to acyl transferases activation, StAR activation, CYP11A1 activation, and increased fat uptake. Signup and view all the answers

How is gene expression of cortisol synthesis regulated?

ACTH regulates gene expression via cAMP response elements in PKA-sensitive transcription factor promoters. Signup and view all the answers

The conversion of pregnenolone to 11-deoxycortisol occurs in the . 11-deoxycortisol is converted to cortisol in the .

cytoplasm; mitochondria Signup and view all the answers

Glucocorticoid receptor (GR) is an (intra/extracellular) receptor.

intracellular Signup and view all the answers

Study Notes

Overview of Steroid Hormones

Steroid hormones are synthesized "as needed," unlike peptide hormones which are pre-synthesized.
They play critical roles in metabolism, osmotic balance, differentiation, and reproduction.

Synthesis of Steroid Hormones

Steroid hormones are synthesized from cholesterol.
Cholesterol sources include dietary fats or synthesis via acetyl CoA.
Key steroid hormones: progesterone, cortisol, aldosterone, testosterone, and estradiol.

Steroidogenic Tissues

Primary tissues involved in steroid hormone synthesis: adrenal glands, gonads, and placenta.
Initial steps in steroid synthesis are identical across different tissues.

Cholesterol Uptake and Regulation

Cholesterol can be synthesized in the body or obtained from food.
Key regulated steps involve:
- StAR protein transporting cholesterol into the mitochondria.
- P450SCC enzyme converting cholesterol to pregnenolone, the rate-limiting step.

Genetic Disorders Affecting Steroid Synthesis

Wolman disease: mutation in lysosomal acid lipase (LAL), leading to cholesterol accumulation and organ failure.
Congenital lipoid adrenal hyperplasia: mutation in StAR causing hormone deficiencies and impaired steroid synthesis.

P450SCC Function

Catalyzes hydroxylations and cleavage to convert cholesterol into pregnenolone.
Recognized as the rate-limiting step in steroid hormone synthesis, requiring oxygen and NADPH.

StAR Protein and CYP11A1 Locations

StAR protein is found in the outer mitochondrial membrane (OMM) facilitating cholesterol import.
CYP11A1 (P450SCC) is located in the inner mitochondrial membrane (IMM) for pregnenolone conversion.

Adrenal Gland Hormones

Adrenal medulla produces catecholamines (tyrosine derivatives).
Adrenal cortex divides into three zones:
- Glomerulosa: produces aldosterone
- Fasciculata: produces cortisol
- Reticularis: produces DHEA

Activation and Regulation of ACTH

ACTH is produced in response to stress; hypothalamus releases corticotropin-releasing hormone (CRH) into portal circulation.
ACTH stimulates steroidogenesis in the adrenal cortex, promoting cortisol release.

Effects of ACTH Activation

Activates protein kinase A (PKA), leading to:
- Stimulation of cholesterol transfer and increased availability.
- Activation of StAR and CYP11A1 enzymes.
- Enhanced fat particle uptake.

Gene Expression Regulation in Steroid Synthesis

ACTH regulates cortisol synthesis through cAMP response elements in gene promoters.

Conversion Pathway of Steroids

Pregnenolone is converted to 11-deoxycortisol in the cytoplasm, with further conversion to cortisol occurring in mitochondria.

Receptor Information

Glucocorticoid receptor (GR) functions as an intracellular receptor, mediating the effects of glucocorticoids like cortisol.

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Description

Test your knowledge on steroid hormone synthesis with these flashcards. Learn how steroid hormones are made as needed and their sources, focusing on cholesterol. Perfect for students studying endocrinology or related fields.