Calcium + Phosphate homeostasis

Describe water soluble hormones

binf to receptors on cell surface, freely soluble in plasma, activate 2nd messengers in cell, rapid actioon, short t1/2, metabolised by liver and excreted by kidney

describe lipid soluble hormones

diffuse into cell and bind to cytosolic / nuclear receptors

protein bound in plasma, less immediate action, longer t1/2, affected by disturbances in plasma protein concentration

how is growth hormone regulated

GNRH + GNIH (somatostatin)

released by hypothalamus, negative feedback loop to hypothalamys and adenohypophysis.

also stimulates insulin growth factor 1 (IGF1) from the liver, this stimulates effects of growth hormone.

List things that can increase secretion of growth hormone

• CNS inputs

• strenuous physical activity

• starvation

• stress

• decreaed glucose, ffa

• increased amino acids

• hrelin

• thyroid hormone, androgens, oestrogens

what are the actions of growth hormone

• growth of body mass

• elongation of bones

• growth of bone, cartilage and soft tissue

• inportant in lactation

• is ANABOLIC

  • stimulate protien synthesis, lipolysis, inhibits tissue uptake of glucose.

where are the main calcium pools in the body

99% bone

some intracellular fluid

some extrcellular fluid

where are the main phosphate pools in the body

85% bone

in cells

ICF + ECF

What is the source and action of vitamin D

D3 is produced by action of UV light on skin

used to improve Ca++ absorption, insulin production and sensitivity

What is the source and action of PTH

made by cheif cells of parathyroid gland

increases concentration of Ca++

• increases absorption from GI

• mobilisation from bone

• decreases urinary excretion

Decreases concentration of phosphate

• increased urinary excretion

What is the source and action of PTHrP

produced in low amounts in most body tissues naturally

same function as PTH

• cancer can cause over production and therefore hypercalcaemia

What is the action and source of calcitonin

Made by C-cells (parafollicular) of the thyroid gland.

secreted in response to increased free Ca++ in blood, reduces concentration

• increased urinary loss

• decreased absorption

• depostiton into bone

Outline how Calcium is regulates

How is Ca++ regulation different to phosphate regulation?

Ca++ depends on absorbtion from GI

phosphate relies on urinary excretion

How is phosphate regulated?

decreased Ca++ triggers release of parathyroid hormone

parathyroid hormone decerases serum phosphate by increasing urinary excretion

What can change the physiological requirements for calcium?

Lactation

Eggshell production