Growth Hormone and Parathyroid Hormone: Physiology

Chondrocytes

Facilitate active cartilage growth until puberty

Osteoblasts= Build Bones

Mineralize cartilage Bone

Ca2+ and PO4(3-) combine to form calcium

Osteocytes= Bone Cells

“Bone Health”

Builds bone in different locations; Acts as foremen

Osteoclasts= Breaks down bones

Reabsorbs bine to increase Ca2+

Order for Long Bone Cellular Anatomy

Blast, Cytes, Clasts

Remodeling of Bone

Adult skeleton is replaced about every 10 years

Hormonal Influences on Bone Growth and Maintenance

GH and Insulin-like Growth factor -1 (IGF): Anabolic, musculoskeletal health

Thyroid Hormone (T3)

Insulin (major anabolic hormone)

Sex hormones (estrogen and testosterone)

Cortisol (Negative regulation)- Catabolic regulation of bone growth

Effects of Growth Hormone

Promotes growth: With Insulin-Like Growth Factor (IGF-1)

Effects of Growth Hormone: Stimulates Protein Synthesis

During Fasting, GH increases glucose and lipid availability, but preserves muscles:

Stimulates gluconeogenesis

Production of new glucose

Effects of Growth Hormone: Glucose

Decreases glucose uptake (not strong because its saving)

Effects of Growth Hormone: Lipolysis

Increases lipolysis (breakdown of fat)

Effects of Estrogen

Stimulates growth at puberty through GH

Causes Epiphyseal closure (shuts down)

Cassation of Long Bone Growth

Effects of Testosterone

Stimulates growth at puberty through GH

Causes Epiphyseal closure (shuts down)

Stimulates Protein Synthesis in Males

Effects of Cortisol

Catabolic player; breakdown glucose

Major stress hormone, inhibits bone growth, stimulates protein, inhibits GI secretion

Calcium Regulation and Homeostasis: Endocrine Controls of Ca2+ Homeostasis

Critical and tightly regulated by specific hormones

These hormones act as effector sites within specific organs

Calcium Regulation and Homeostasis: Effector Sites for Ca2+ Homeostasis- Bone

Storage vs. Release

Calcium Regulation and Homeostasis: Effector Sites for Ca2+ Homeostasis- GI Tract

Absorption (site of action)

Calcium Regulation and Homeostasis: Effector Sites for Ca2+ Homeostasis- Kidneys

Reabsorption (filter the blood)

Calcium Regulation and Homeostasis: Hormonal Controls for Ca2+

Parathyroid Hormone and 1,25- dihydroxyvitamin D (Calcitron)

Parathyroid Hormone

Secreted by parathyroid glands

4 small glands located on neck on (much larger) thyroid gland

PTH is critically important for regulating of Ca2+ levels

Effects of Parathyroid Hormone (PTH)

Increases Ca2+ availability to increase plasma levels

Increases Ca2+ reabsorption in kidneys

Increases osteoclast activity

Increases formation of vitamin D, which increases uptake of Ca2+ in GI tract

Renal Regulation of Ca2+ and Phosphate

3:2 Ratio: Phosphate= Optimal for Bone Formation

Increased Ca2+ but not phosphate= Wont’ Reform Bone

Parathyroid Hormone sets the right balance for:

Increases Ca2+ reabsorption in the Kidneys

Decreases PO4(-3) reabsorption in the Kidneys

Vitamin D

Active formed produced in kidneys

Increased gene expression of Ca2+ and PO4(-3)

Calcitonin

Secreted by parafollicular cells in the thyroid glands

Decreases plasma Ca2+ concentration by inhibiting osteclasts

Secretion only stimulated by very high plasma Ca2+ levels