Theme 4: Secondary Endocrine Organs, Vitamin D & Melatonin

Secondary endocrine organs

Organs with other primary functions that also release hormones or regulatory substances.

Kidney erythropoietin (EPO)

Released in response to low oxygen availability; stimulates red blood cell production in bone marrow.

Kidney renin

Released in response to low renal perfusion, low blood pressure, or related signals; activates the renin-angiotensin-aldosterone system.

Renin-angiotensin-aldosterone system

Hormonal pathway that helps raise blood pressure and conserve sodium and water.

Kidney calcitriol production

Kidneys convert calcidiol into active vitamin D, calcitriol.

Atrial natriuretic peptide (ANP)

Released by the heart in response to increased atrial stretch; promotes sodium and water loss and helps lower blood volume/pressure.

Pineal gland

Endocrine gland that secretes melatonin.

Melatonin

Hormone that helps regulate circadian rhythms and sleep-wake timing.

Effect of darkness on melatonin

Darkness promotes pineal melatonin secretion.

Effect of light on melatonin

Light detected by the retina signals pathways that suppress melatonin secretion.

Vitamin D3 skin step

Ultraviolet B exposure converts a cholesterol-derived precursor in the skin to cholecalciferol.

Liver vitamin D step

The liver converts cholecalciferol to calcidiol (25-hydroxyvitamin D).

Kidney vitamin D step

The kidneys convert calcidiol to calcitriol (1,25-dihydroxyvitamin D), the active form.

Calcitriol function

Increases intestinal absorption of calcium and supports calcium homeostasis.

How can chronic kidney disease affect red blood cells?

Reduced renal EPO production can decrease red blood cell production.

How can chronic kidney disease affect blood pressure?

Impaired renin-related regulation can disrupt blood pressure and fluid balance.

How can chronic kidney disease affect calcium absorption?

Reduced calcitriol production can reduce intestinal calcium absorption.