endocrine - Feb 27th to 29th Flashcards
Where is calcium found?
- bones
- soft tissues (intracellular and extracellular)
What is calcium stored as in bones? What is it made up of?
hydroxyapatite (calcium salts + phosphate)
How do you calculate total body calcium?
intake (diet) - output (kidneys)
What 3 hormones regulate movement of calcium between bone, kidneys, & intestine?
- Parathyroid hormone (PTH)
- Calcitriol (vitamin D3)
- Calcitonin
(1 & 2 most important in adults)
What is PTH? (3)
- secreted continuously by the parathyroid gland
- helps to regulate calcium
- essential for life (cannot be removed)
What are the 2 types of parathyroid gland cells?
- Chief cells (produce PTH)
- Oxyphils (function unknown)
What plasma Ca2+ falls, how does PTH get it back to normal?
- Stimulates osteoclasts to resorb bone (primary mechanism)
- Stimulates kidneys to resorb Ca2+
- Stimulates kidneys to produce enzyme needed to activate vitamin D,
which promotes better absorption of Ca2+ from food/drink across
intestinal epithelium
What is Hypocalcaemia? How is it corrected?
- Plasma calcium too low
- ↑ PTH secretion (stimulates resorption to get more Ca2+ back into blood)
What is Hypercalcaemia? How is it corrected?
- Plasma calcium too high
- ↓ PTH secretion
Describe the process of bone deposition and reposition
Bone deposition:
- Osteoblasts secrete a matrix of
collagen protein, which becomes
hardened into deposits of
hydroxyapatite
Bone resorption:
- Osteoclasts dissolve
hydroxyapatite & return the bone
Ca2+ (& phosphate) to the blood
Describe the process of vitamin D synthesis
- Vitamin D3 produced
from it’s precursor
molecule, 7-
dehydrocholesterol
under the influence of
UVB sunlight - Vitamin D3 secreted
into blood from
skin/intestine (functions
as a pre-hormone i.e.
inactive) - Vitamin D3 pre-hormone goes to liver & is chemically changed (hydroxyl group added
to C25) - Requires hydroxyl
group addition to C1
to become active
(done by enzyme in
kidneys that is
stimulated by PTH) - Active vitamin D can then stimulates intestinal absorption of Ca2+, and directly stimulates bone resorption by promoting formation of
osteoclasts
How is vitamin D synthesized in human?
- Synthesized from 7-dehydrocholesterol with UV light in skin + obtained from dietary sources
- Those far from the equator don’t have enough sunlight, so they need to ingest it via diet or suppliments
How is vitamin D synthesized in dogs and cats?
haha tricked you, it can’t be synthesized – only from diet
What is Calcitonin?
- Made in C cells of thyroid in response to high Ca2+
- Thought to only play minor role in adult humans (thyroidectomy patients are not hypercalcaemic)
How is phosphate metabolism regulated?
by the same mechanisms that
regulate Ca2+ metabolism (but not as tightly) – return/receive
phosphate to/from bone, kidney filtrate, & GI tract
Describe Hyperparathyroidism (5)
- Parathyroid too active
- Hypercalcaemia (too much
Ca2+ in blood) - Increased bone resorption
(fractures) - Mineralization of soft tissues
- Increased thirst & urination
(Ca2+ blocks ADH effects)
Describe Hypoparathyroidism (4)
- Parathyroid not active enough
- Hypocalcaemia (not enough
Ca2+ in blood) - Muscular weakness, ataxia
- Cardiac arrhythmias
Describe vitamin D deficiency (differences between adults and children, etc.)
Results in poor bone mineralization
In children = Rickets
* Bone pain, stunted growth, deformities
In adults = Osteomalacia
* Bone pain, fractures
Describe Osteoporosis (and its risk factors/treatments)
- Most common disorder of bone
- Reduction of bone quality due to excess absorption
- Risk of bone fractures
Known risk factors:
- Sex (females,
especially after menopause)
- Lack of exercise
- Calcium deficient diet
Treatment:
- Adequate calcium & vitamin D intake
- Hormone therapy, PTH, calcitonin (may be associated with cardiovascular disease, stroke, cancer)
- Exercise
- Best treatment is prevention!
What is the Somatotropic Axis?
- GH secretion inhibited by
somatostatin from hypothalamus - GHRH stimulates GH secretion from anterior pituitary
- GH has many targets (direct
or through stimulation of liver’s production of somatomedins e.g. IGF-1)
What is Growth Hormone / GH (Somatotropin)?
- Synthesized, stored, & secreted by somatotropic cells in the lateral wings of the anterior pituitary gland
- Most bound to binding protein (GHBP) but may be transported
as free hormone - Most abundant anterior pituitary hormone
- Plays an important role in growth
Describe GH secretion patterns (very brief)
- Occurs in peaks/pulse
- Largest GH peak occurs ~1 hr after
onset of sleep (circadian rhythm) - Basal levels highest early in life
What factors decrease GH secretion?
- Hyperglycemia
- Glucocorticoids
- Endocrine disruptors
What are Somatomedins?
Insulin-like growth factors
Describe Somatomedins (mostly just IGF-1)
- GH acts on the liver to produce IGFs (IGF-1, IGF-2)
- IGF-1 almost entirely bound to transport proteins (IGF-BPs)
- Some IGF-1 transport/binding proteins have an endocrine
function (i.e. there are receptors for these proteins) - GH stimulates the synthesis/release of IGF-1 in other tissues
besides the liver i.e. it is difficult to differentiate between direct
actions of GH & IGF-1 - GH & IGF-1 appear to exert opposite actions in some tissues,
suggesting independent roles
Describe the metabolic effects of GH (what does it act on and what do it do to it)
Liver:
- stimulates IGF-1to trigger bone/cartilage growth and protein synthesis in organs
Adipose Tissue:
- lipolysis
- release of fatty acids
Most other tissues:
- decreased glucose use
Basically, GH plays an especially important role in endocrine regulation of growth (muscle & bone)
What does Hypertrophy refer to (concerning GH)
increased cell size
What does Hyperplasia refer to (concerning GH)
increased cell number
What are the two types of bone growth, and what do they do?
Bone diameter increase:
* Growth occurring around the bone
* Matrix deposits on the outer surface of bone
Bone length increase:
- Growth occurring at epiphyseal plates (near end of bone)
- Epiphyseal plate contains chondrocytes (columns of collagen-producing cells)
- As collagen layer thickens, old cartilage calcifies & chondrocytes
degenerate
- Osteoblasts invade & lay bone matrix on top of cartilage base
