Physiology 3120 Lecture Notes - Lecture 1: Extracellular Fluid, Distal Convoluted Tubule, Epiphyseal Plate
9 May 2018
School
Department
Course
Professor
Physiology 3120
Dr. Woods
Lecture 1
Hormonal Regulation of Calcium Balance
- your skeleton is not static
o your bones are very regenerative, they are always modifying
o your entire skeleton will regenerate itself within 7 years – within 6-7 years the skeleton
you have now will have completely remodeled into a new skeleton
o if you treat your skeleton well, that skeleton will be stronger than before
- we have Ca2+ that is deposited in our bones – the Ca2+ is very carefully controlled by hormones
- Parathyroid hormone regulates plasma levels of Ca2+ - the level of calcium in the extracellular
fluid volume
o One of the ways it does this is by conserving Ca2+ from the distal convoluted tubule
o So you will reabsorb more Ca2+ bc of PTH, elevating the blood Ca2+ levels
- Ca2+ is important for a lot of diff things (signaling pathways, other organs)
- Calcitrol (vitamin D) affects absorption of calcium in the gastrointestinal tract
o Vitamin D, which is activated in the form, calcitrol is a hormone will affects how much
Ca2+ we absorb in the digestive system
- Ca2+ can be stored in our bones for later and that Ca2+ serves to strengthen our bones as well –
important component of bone
- 99% of body calcium is stored in bones
- Ca2+ forms a mineral which is very good at strengthening the bone tissue and it also becomes an
easy access point
o So if at any point in your life you need to increase plasma Ca2+ levels, PTH will stimulate
your bone to degrade so that the Ca2+ gets released into your blood
o So that is the purpose for that stored Ca2+
o If that degradation is too quick, you can reduce your bone strength (not a good thing)
- Calcium is stored as hydroxyapatite crystals (calcium and phosphate salts) in bone to prevent
large changes in plasma calciums levels
o Ca2+ combines with phosphate salts and that inorganic material will be apart of the
collagen matrix of the bone that is formed
o So we have bone that is composed of both type I collagen and hydroxyapatite crystals
o And by storing that Ca2+ in the bone, it prevents really big changes in plasma Ca2+ bc
although Ca2+ is very important, you don’t want the Ca2+ levels to be too high bc it will
affect the functioning of the other cells in the body
- These crystals also provide bone strength (the crystal is the inorganic component of bone)
- Bone serves more functions than just locomotion and protection of vital organs
o Skeletal system actually serves as an endocrine organ to control ion balance,
participates in maintaining Ca2+ for example to make sure that everything is
functioning properly
- The bones that we have right now, in this age (20) are awesome
o The bones we have right now are optimal:
▪ We have amazing strength
▪ The right amount of Ca2+ phosphate
o As you age, things slow down
Types of Bone Formation
- Two types of bone formation:
o Endochondral Ossification
▪ most bones form this way
▪ creates long bones
▪ uses cartilage template that is replaced by bone tissue
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