L5 Growth, Bones and Ageing Flashcards
what is growth?
increased length of long bones and increased size and number of cells in soft tissue; starts before birth and accelerates at two stages of development (post-natal growth spurt and pubertal growth spurt)
what are the factors that influence growth?
- Hormone levels: primarily controlled by growth hormone; other hormones (e.g. sex hormones during puberty)
- Genetics: max height determined by genetics (genetic predisposition) – whether you reach max height depends on the environment (diet, stress)
- Diet: malnourishment stunts growth- may be irreversible
- Stress: prolonged secretion of cortisol stunts growth
growth hormone is secreted by _____________
growth hormone is secreted by ANTERIOR PITUITARY
growth hormone is controlled by hormones from the _______
- stimulated by ________
- inhibited by _______
growth hormone is controlled by hormones from the HYPOTHALAMUS
- stimulated by GROWTH HORMONE RELEASING HORMONE (GHRH)
- inhibited by GROWTH HORMONE INHIBITING HORMONE (GHIH)
GH has both _____ and ____ effects
GH has both METABOLIC and GROWTH effects
GH growth effects are mediated by __________
GH growth effects are mediated by INSULIN-LIKE GROWTH FACTORS (IGFs)
GH release is _______ (higher during ______)
GH release is DIURNAL (higher during DEEP SLEEP)
what are the metabolic effects of growth hormone?
• Acts on adipose tissue, skeletal muscle and liver to conserve glucose for the brain
• Lipid metabolism
- Breaks down triglycerides (storage fat) and releases it into the blood
- Fuel for muscles
• Increases blood glucose
- Increased glucose output from the liver
- Decreased glucose uptake in skeletal muscle
how does growth hormone promote growth?
• Soft tissues (e.g. connective tissue and skin)
- Increase the number of cells (hyperplasia)
- Increase the size of cells (hypertrophy)
• Bones
- Increase in bone thickness
- Increase in bone length
not enough growth hormone?
• Children: Dwarfism
- Pituitary (not producing growth hormone)/hypothalamic defect (not stimulating release of GH)
- Abnormal GH receptors (Laron Dwarfism- proportional)- producing GH, but the receptor is mutated it won’t respond to GH
• Delayed growth
• Treatment: growth hormone drugs
• Achondroplasia: enlarged head (not proportioned with rest of the body)
select all of the correct options regarding the effects of growth hormone:
a. it stimulates the release of triglycerides into the blood
b. it increases glucose uptake into muscle cells
c. it causes the thickening of bones
d. it causes hyperplasia and hypertrophy of cells in soft tissues
e. it promotes the lengthening of bones
A, C, D, E
too much growth hormone?
• Children: gigantism
- Excessive growth of long bones
• Adults: acromegaly
- Acro = extremity; megaly = large (normal height but thicker bones and growth of soft tissues)
- Thickening of bones
- Growth of soft tissue (skin and connective tissue)
what is the functions of bone tissue and the skeleton (mechanical and metabolic)
- Mechanical: support, protection of organs, muscle attachment, facilitate movement
- Metabolic: mineral storage, calcium homeostasis, haematopoiesis
what are the general features of the bone tissue?
- composition
- high vascularity
- types
- Composition: cells (2% of mass), organic osteoid (collagen fibres and other proteins), inorganic mineral salts
- High vascularity (blood supply)- most important for calcium control
- Types: Cortical bone tissue (compact bone), trabecular bone tissue (spongy bone)
o Compact bone found in diaphysis and edge of epiphysis
o Spongy bone found in the core of the bone – epiphysis
describe the inorganic phase and organic phase of the chemical composition of bone tissue
- Inorganic phase: mineral 65-70%; hydroxyapatite crystals (calcium phosphate), storage for calcium and phosphate
- Organic phase: matrix osteoid 30-35%; collagenous fibres (95%); non-collagenous proteins (e.g. proteoglycans and glycoproteins)
describe the cellular organisation of bone tissue (osteoblasts, osteocytes, osteoclast)
- Osteoblasts (bone building cells): produce and secrete osteoid (organic component); do not calcify/mineralise bone
- Osteocytes (reside in lacunae)(mechanical sensors in bone): detect changes in mechanical environment to initiate changes in bone matrix; mature osteoblasts
- Osteoclast (multinucleated)(bone reabsorbing cells): degrade bone matrix to release calcium into blood
describe bone remodelling
Involves osteoclasts coming in to break down the bone, the osteoblasts come in and lay down new bone
why do we remodel bone?
- Maintain mineral ion homeostasis (source of Ca2+ ions)
- Adapt and shape structural organisation to alteration in biomechanical force – “mechanostat”
- Maintain structural integrity of skeleton (repair microdamage)
Bone remodelling is a balance between the ______ breaking down old bone and the ______ laying down new bone. Mature bone cells are called ______ and they monitor the mechanical forces experienced by the bone.
Bone remodelling is a balance between the OSTEOCLASTS breaking down old bone and the OSTEOBLASTS laying down new bone. Mature bone cells are called OSTEOCYTES and they monitor the mechanical forces experienced by the bone.
How is bone remodelling controlled?
• Maintaining bone mass requires a balance between osteoclast and osteoblast activity
- Regulated by the release of chemical messengers by osteoblasts (RANKL and OPG)
• If osteoblasts are more active than osteoclasts we lay down bone = increase mass
• If osteoblasts are less active than osteoclasts then we lose mass = decrease mass
T/F: The balance between osteoblast and osteoclast activity is controlled by chemical messengers released by osteoclasts.
F
T/F: Osteoprotegerin decreases osteoclast activity whereas RANKL increases osteoclast activity
T
what are the hormonal controls of bone remodelling?
- Parathyroid hormone (PTH): produced by parathyroid glands
- Vitamin D sources: skin and diet
- Calcitonin: produced by C cells in thyroid glands, minor role
- Stimulus is change in blood Ca2+
parathyroid hormone:
- secreted when ______
- increases ______ through actions on ____, _____ and ______
parathyroid hormone:
- secreted when BLOOD CALCIUM DROPS
- increases BLOOD CALCIUM through actions on BONE, KIDNEY and INTESTINE
what is the effect of parathyroid hormone on the bone? the two mechanisms?
• PTH increased blood Ca2+ by taking it out of bone storage (two places of storage: inorganic part of bone and bone fluid)
• Two mechanisms:
- Fast exchange: immediate Ca2+ regulation (from bone fluid)
- Slow exchange: response to chronic hypocalcaemia, breaks down bone
Low blood calcium -> release of parathyroid hormone -> effect on …
• Bone: ?
• Kidney: ?
• Intestine: ?
- Bone: fast exchange of calcium, slow exchange of calcium
- Kidney: increase calcium reabsorption, activate vitamin D
- Intestine: increase calcium absorption
difference between high impact sports and low impact sports on bone mineral density
- High impact sports = greater impact on bone mass, increase bone mass
- Low impact sports = not much impact on bone mass, could possibly decrease bone mass
what is osteoporosis?
Osteoporosis: the effect of aging on bone
• Reduction in mass (density) of bone and impairment of spongy bone integrity
• Weaker bone = prone to fracture
• Progression from osteopenia to osteoporosis
osteoporosis is an ______ disease with a _____ onset
osteoporosis is an ADOLESCENT disease with a GERIATRIC onset
what are the differences between men and women regarding osteoporosis?
Differences in men and women
• Peak bone mass level (greater for men than women)
• Menopause (gradual decrease for men, sharp drop at menopause for women)
what are the risk factors for osteoporosis and which ones are modifiable?
- Poor nutrition (particularly calcium)
- Sedentary lifestyle
- Low levels of oestrogen, early menopause or loss of normal menstruation
- Low levels of testosterone
- Smoking and excessive alcohol and caffeine intake
- Absence of adequate sunlight exposure (vitamin D deficiency)
- Corticosteroid use
- Aortic calcifications
Modifiable: Diet, exercise, vitamin D, smoking, drinking
prevention of osteoporosis?
- Increased peak bone mass = good nutrition and weight bearing exercise critical before the age of 30
- Maintain high dietary calcium and adequate vitamin D levels (exposure to UV)
- Maintain exercise in older age (reduce bone loss, prevent fractures, prevent falls)
