Overview
This lecture covers the embryonic origins of the endocrine system and explains how aging impacts hormone production, secretion, and related physiological functions.
Embryonic Origins of the Endocrine System
- The endocrine system develops from all three embryonic germ layers: ectoderm, mesoderm, and endoderm.
- Steroid hormone-producing glands (gonads, adrenal cortex) arise from the mesoderm.
- Amine, peptide, and protein hormone-producing glands develop from endoderm and ectoderm.
- The anterior pituitary arises from oral ectoderm; the posterior pituitary comes from neural ectoderm near the hypothalamus.
- The pineal gland is derived from the ectoderm.
- The adrenal cortex originates from the mesoderm, while the adrenal medulla comes from ectoderm neural cells.
- The endoderm gives rise to the thyroid, parathyroid glands, pancreas, and thymus.
Effects of Aging on the Endocrine System
- Anterior pituitary gland loses vascularization and gains connective tissue as it ages, reducing human growth hormone (hGH) production and decreasing muscle mass.
- Adrenal glands develop more fibrous tissue with age, reducing cortisol and aldosterone production, but epinephrine and norepinephrine levels stay stable.
- Menopause results from decreased ovarian sensitivity to gonadotropins, reducing estrogen and progesterone, causing reproductive cessation and increased risk for osteoporosis, atherosclerosis, and hyperlipidemia.
- Testosterone declines gradually in aging males (andropause), but sperm production typically continues into old age, albeit with reduced quality.
- Thyroid hormone production decreases with age, lowering basal metabolic rate, reducing body heat, and increasing body fat.
- Parathyroid hormone (PTH) increases, often due to lower dietary calcium, and can contribute with decreased calcitonin and estrogen to osteoporosis.
- Blood glucose spikes more and normalizes slower in elderly people, with declining insulin sensitivity contributing to increased diabetes prevalence.
Key Terms & Definitions
- Mesoderm — Middle embryonic germ layer giving rise to steroid hormone glands.
- Ectoderm — Outer embryonic germ layer forming structures including the pituitary and pineal glands.
- Endoderm — Inner embryonic germ layer forming glands like thyroid, parathyroid, pancreas, and thymus.
- Menopause — Age-related decline in ovarian function leading to low estrogen/progesterone and inability to reproduce.
- Andropause (Viropause) — Gradual decline of testosterone in aging males.
- Basal Metabolic Rate — The rate of metabolism at rest, which decreases with lower thyroid hormones.
- Osteoporosis — Weakening of bones due to hormone changes, especially decreased estrogen and increased PTH.
Action Items / Next Steps
- Review the differences in embryonic origin for each endocrine gland.
- Study the physiological consequences of decreased hormone levels in aging.
- Complete any related review or critical thinking questions from the textbook section.