Chapter 6 Flashcards
(149 cards)
1
Q
(6) important functions of skeletal system:
A
- **support **(structural framework) & **point of attachment **for tendons & ligaments
- **protect **internal organs
- assist **body movement **
- **store **& **release **calcium & phosphorus
- blood cell production (hematopoiesis)
- store **triglycerides **in adipose cells of yellow marrow
2
Q
Bone is **dynamic tissue **… it is always ___
A
**remodeling **- building up & breaking down
3
Q
(2) major **bone tissues **
A
1) bone (osseous tissue)
2) cartilage
4
Q
Bone
A
highly vascularized CT with hard mineralized ECM found in 2 different arrangements
5
Q
(2) different arrangements of bone
A
1) spongy
2) compact
6
Q
Compact bone
- functions
- forms?
A
protection & support
- forms **diaphysis **of long bones & **external layer ** of all bones
7
Q
Spongy Bone
- functions
- forms?
A
lightweight
provides tissue support
forms most of epiphysis & internal cavity of long bones
8
Q
Articular Cartilage
- location
- purpose
A
thin layer of hyaline cartilage covering epiphysis of long bones
- covers part of epiphysis where bone forms joint
- reduces friction & absorbs shock
9
Q
Periosteum
A
membrane covering bone surface not covered by articular cartilage
- attached to bone by Sharpey’s fibers
10
Q
Periosteum - **purposes (4) **
A
1) protect bone
2) assist in fracture repair
3) nourish bone tissue
4) attachment point for ligaments/tendones
11
Q
(2) layers of Periosteum
A
1) tough **outer **sheath of dense, irregular CT
2) inner **osteogenic **(bone stem cells) layer
12
Q
How is **periosteum **attached to the bone?
A
by Sharpey’s Fibers
13
Q
Medullary Cavity
A
space within diaphysis of long bones that contains **fatty yellow bone marrow **in adults
14
Q
Endosteum
A
membrane that lines medullary cavity
15
Q
Various cells in **Osseous tissues **
A
osteogenic cells → osteoblast → osteocyte
osteoclast (WBC)
16
Q
Osteogenic cells
A
undergo cell division & develop into osteoblasts
17
Q
Osteoblasts
A
bone building cells
18
Q
Osteocyte
A
mature bone cells
principal cells of bone tissue
19
Q
Osteoclasts
A
derived from monocytes & serve to break down bone tissue
20
Q
Chemical Constituents of Bone
A
25% water
25% organic proteins
50% mineral salts (hydroxyapatite crystals).
21
Q
**Organic constituents **of bone
- functions
A
**collagen fibers **
- provide flexibility & tensile strength
22
Q
**Inorganic **constituents of bone
A
**Hydroxyapatite crystals (mineral salts) **
- Calcium Phosphate (Ca3PO4)2
- Calcium Carbonate (CaCO3 – marble)
- Other trace elements: Mg, F, sulphate
23
Q
Bone Structure
A
diaphyses
epiphyses
metaphyses
24
Q
Diaphysis
A
shaft or body of a long bone
25
Epiphyses
forms distal & proximal ends of a long bone
26
Metaphyses
areas where **epiphyses** & **diaphysis** join
27
Until end of active growth, epiphysis of long bones contains? forms?
hyaline cartilage & forms **“epiphyseal growth plate”**
28
In adults, epiphyseal cartilage is?
** no longer present** & **elongation** of **bones** has stopped
29
**Compact** Bone (**cortical** bone)
* contains?
contains units **osteons** (**Haversian** **systems**) formed from **concentric** **lamellae** (rings of calcified matrix) arranged around **central canal **
* **interstitial** lamellae
* **outer** circumferential lamellae
* **inner** circumferential lamellae
* **lacunae**
* **canaliculi**
* **perforating canals **
30
**Interstitial **lamellae
left over **fragments** of older osteons between osteons
31
**Outer** circumferential lamellae
encircle bone beneath periosteum
- connect to **peristeum **by **perforating (****sharpey's) fibers **
32
**Inner** circumferential lamellae
encircle medullary cavity
33
Lacunae
**small spaces** between **lamellae** which house **osteocytes**
34
Canaliculi
small channels filled with extracellular fluid connecting lacunae
35
Central canal
canal in center of osteons
- blood & lymphatic vessels
36
**Perforating** (**Volkmann’s**) canals
allow **transit** of vessels in **Central Canal** to outer cortex of bone
## Footnote
- allows vessels & nerves from periosteum to penetrate compact bone
37
Spongy bone
lacks osteons → **lamellae** arranged in lattic of thin columns (**trabeculae)**
make up **interior** bone tissue & houses **red bone marrow**
**lacunae **contain **osteocytes** (nourish mature bone tissue from blood circulating through trabeculae)
38
Spongy Bone → **Trabeculae**
structural unit of spongy bone
**-lamellae** arranged **in lattice of thin columns**
- contain **lacunae **→ contain **osteocytes** that nourish bone tissue from blood circulating through trabeculae
39
Purpose of **spongy bone**
**reduces** overall **weight**
**support**/**protect** red bone marrow → site of **hemopoiesis**
40
Blood & Nerve Supply of Bone → **periosteal** arteries & veins
supply **periosteum** & **compact** **bone**
enter **diaphysis **through **perforating **(**Volkman's**) canals
41
Blood and Nerve Supply of Bone → **nutrient **artery
near center of **diaphysis **
passes through **nutrient foramen**
enters medullary cavity & divides proximal & distal branches
42
Blood & Nerve Supply of Bone
nerves may accompany blood vessels
- periosteum is rich in sensory nerves
43
Bone formation
**ossification **or **osteogenesis = **process of formaing new bone
44
**ossification** or **osteogenesis**
* occurs in (4) situations
process of formaing new bone
## Footnote
1) formation of bone in **embryo**
2) growth of bones until **adulthood**
3) **remodeling **of bone
4) **repair **of **fracture**
45
**Osteogenesis**
* occurs by?
* when does it begin?
occurs by 2 different methods
beginning about **6th week of embryonic development**
46
**Osteogenesis **- (2) methods
1) **Intra-membranous **ossification
2) **Endochondral **ossification
47
1) **Intra-membranous **ossification
produces **spongy bone**
* subsequently**, **be remodeled to form **compact** bone
48
2) **Endochondral** ossification
**process** whereby **cartilage** is replaced by **bone**
forms both **compact **& **spongy **bone
49
**Intramembranous Ossification**
* forms?
* forms from?
used in forming **flat bones** of **skull, mandible & clavicle**
bone forms from **mesenchymal cells -**without going through cartilage stage
50
**Intra-membranous Ossification**
* steps (4)
1) Development of **ossification centre**
2) **Calcification**
3) Formation of **trabeculae**
4) Development of **periosteum**
51
**Intra-membranous ossification**
1) Development of ossification centre
chemical msgs cause **mesenchymal cells** to cluster (**ossification centre) ** & differentiate into **osteogenic** cells → **osteoblasts** - secrete ECM until surrounded
52
**Intramembranous Ossification**
2) Calcification
secretion of ECM stops
now **osteocytes** lie in **lacunae** & extend cytoplasmic processes into **canaliculi** *that radiate in all directions*
within few days: **calcium** & other mineral salts deposited & **ECM** calcifies (*hardens*)
53
**Intramembranous Ossification**
## Footnote
3) Formation of trabeculae
As bone ECM forms, develops into **trabeculae** that fuse to form **spongy bone** around network of blood vessels
CT asociated with blood vessels differentiates in **red bone marrow**
54
**Intramembranous Ossification**
## Footnote
4) Development of periosteum
In conjunction with formation of trabeculae
**mesenchyme** condenses into **periosteum**
eventually, thin layer of **compact** bone replaces surface **spongy** bone layers
*Much of newly formed bone is **remodeled** (destroyed and reformed) as bone is transformed into its adult size & shape.*
55
**Endochondral Ossification**
* steps (6)
1) **Development** of **Cartilage model**
2) **Growth** of **Cartilage Model**
3) Development of **primary ossification centre**
4) Development of **medullary** **cavity**
5) Development of **secondary ossification centre**
6) Formation of **articular cartilage** & **epiphyseal (growth) plate**
56
**Endochondral Ossification**
## Footnote
1) Development of Cartilage model
chemical msgs cause **mesenchymal** cells to crowd into general shape of bone
→ develop into **chondroblasts** - secrete cartilage ECM → produce **cartilage model** (hyaline)
- **perichondrium** develops around
57
**Endochondral Ossification**
2) Growth of Cartilage Model **(4)**
once **chondroblasts** buried in cartilage ECM → **chondrocytes**
**- interstitial/appositional growth**
as model grows, **chondrocytes** in mid-region **hypertrophy** (increase in size) & surrounding **cartilage ECM** calcifies
- chondrocytes die & spaces left behind merge into small cavities **(lacunae)**
58
2a) Interstitial (endogenous) growth
grows in **length** by continual cell division of chondrocytes & further secretions of cartilage ECM
59
2b) **Appositional** (**exogenous**) growth
growth in **thickness** due to **deposition** of **ECM** on cartilage model surface by new **chondroblasts** developed from **perichondrium**
60
**Endochondral Ossification**
3) Development of **primary ossification centre** (4)
primary ossification proceeds **inward** from external bone surface
- **nutrient artery** penetrates perichondrium & calcifying cartilage model through **nutrient foramen** → stimulates **osteogenic** cells in perichondrium to differentiate into **osteoblasts**
* (once perichondrium starts to form bone - known as **periosteum)***
- near middle of model, **periosteal capillaries** grow into calcified cartilage & induce growth of **primary ossification center** *(region where bone tissue will replace most of cartilage)*
**osteoblasts** deposit bone ECM over remnants of calcified cartilage → forms **trabeculae**
- *eventually, most of diaphysis wall replaced by compact bone*
61
**Endochondral Ossification**
4) Development of medullary cavity
as **primary ossification centre** grows towards **ends** of bone, **osteoclasts** break down **trabeculae** leaving medullary cavity in shaft
## Footnote
*eventually, most of diaphysis wall replaced by compact bone*
62
**Endochondral Ossification**
5) Development of secondary ossification centre
when branches of **epiphyseal artery** enter **epiphyses** → **secondary ossification centres** develop *(around time of birth)*
bone formation **similar** to primary oss. centres **but:**
**spongy** bone remains in interior of **epiphysis** (no medullary cavity formed) & secondary ossification proceeds **outwards** from centre of epiphysis to outer bone surface
63
**Endochondral Ossification**
6) Formation of articular cartilage & epiphyseal (growth) plate
**hyaline cartilage** that covers **epiphyses** become **articular cartilage**
before adulthood, hyaline cartilage remains b/w diaphysis & epiphysis as **epiphyseal (growth) plate** *(region responsible for lengthwise growth of long bones)*
64
During **infancy**, **childhood**, and **adolescence**, bones throughout the body grow in thickness by?
and long bones **lengthen** by?
**appositional** growth
**interstitial** growth - addition of bone material on the diaphyseal side of epiphyseal plate
65
**Growth in Length**
- (2) major events
1) **Interstitial growth** of cartilage on epiphyseal side of epiphyseal plate
2) **Replacement** of **cartilage** with **bone** on **diaphyseal side** of **epiphyseal** **plate**
66
Growth in Length
## Footnote
- **epiphyseal (growth) plate** has **(4)** zones
1) Zone of **Resting** Cartilage
2) Zone of **Proliferating** Cartilage
3) Zone of **Hypertrophic** Cartilage
4) Zone of **Calcified** Cartilage
67
**Epiphyseal (growth) plate**
## Footnote
1) Zone of **Resting** Cartilage
nearest epiphysis
- consists of small, scattered **chondrocytes**
- do not function in bone growth
- **anchor** epiphyseal plate to epiphysis of bone
68
**Epiphyseal (growth) plate**
2) Zone of **Proliferating** Cartilage
slightly larger **chondrocytes** arranged like stacks of coins
- undergo **interstitial growth** as they divide & secrete ECM
→ divide to replace those that die at **diaphyseal side** of plate
69
**Epiphyseal (growth) plate**
3) Zone of **Hypertrophic** Cartilage
consists of **large**, **maturing chondrocytes** arranged in **columns**
70
**Epiphyseal (growth) plate**
4) Zone of **Calcified** Cartilage
final zone → only few cells thick
- mostly **dead chondrocytes** b/c ECM around them is calcified
- **osteoclasts** dissolve calcified cartilage
- **osteoblasts** & capillaries from diaphysis invade area
* **osteoblasts** lay down bone ECM (replacing calcified cartilage by endochondral ossification)
- becomes **new diaphysis** firmly cemented to rest of diaphysis of bone
71
Ossification contributing to bone length usually completed by?
**18-21** years old
72
Even after epiphyseal growth plates have closed, bones still continue to? are capable of?
**thicken** & are capable of **repair**
73
Only way diaphysis can increase in length?
activity of epiphyseal plate
74
Order of Zones in Epiphyseal plate from **epiphysis to diaphysis**
Zone of:
**Resting** cartilage
**Proliferating** cartilage
**Hypertrophic** cartilage
**Calcified** cartilage
75
Growth in **Thickness/Width** by **appositional growth**
**periosteal cells** differentiate into **osteblasts** → secrete ECM
- become surrounded → **osteocytes**
- forms **grooves** around **periosteal blood vesse**l → becomes **tunnel**
- **periosteum** becomes **endosteum** that lines tunnel
- **osteoblasts** in endosteum deposit bone ECM forming new **concentric lamellae**
→ proceeds inward, filling in tunnel
- as osteon forms, **osteoblasts** under periosteum deposit new **circumferential lamellae** (further increasing thickness of bone)
- **osteoclasts** of endosteum destroy bone lining forming medullary cavity
76
**Human Growth Hormone (HGH)**
* functions (secretion)
one of body's many **anabolic hormones**
**Secretion** of HGH stimulates:
* bone growth
* muscle growth
* loss of fat
* increase glucose output by liver
*
77
**Bone remodeling**
- involves? (2)
ongoing replacement of old bone tissue by new bone tissue
involves: bone **resorption** & bone **deposition**
78
Bone Remodeling
a) Bone **resorption**
b) Bone **deposition**
a) removal of minerals & collagen fibers from bone by **osteoclasts**
(results in **destruction** of bone **ECM**)
b) addition of minerals & collagen fibers to bone by **osteoblasts**
(results in **formation** of bone **ECM**)
79
At any given time, \_\_% of total bone mass in body is being remodeled
5%
80
renewal rate for **compact** bone tissue is about \_\_\_% per year
4%
81
renewal rate for **spongy** bone tissue is about \_\_% a year
20%
82
Benefits of **Remodeling**
**(3)**
1) since strength of bone is related to degree to which it is stressed, if newly formed bone is subjected to heavy loads, it will grow thicker and therefore be stronger than old bone.
2) shape of a bone can be altered for proper support based on the stress patterns experienced during remodeling process
3) new bone is more resistant to fracture than old bone
83
**Bone Growth and Remodeling**
- balance must exist between..
actions of **osteoclasts & osteoblasts**
84
Imbalance between actions of **osteoclasts & osteoblasts** can result in? **(4)**
**1) acromegaly**
**2) osteoporosis**
**3) rickets**
**4) osteomalacia**
85
1) acromegaly
bone becomes abnormally thick & heavy b/c too much new tissue is formed
86
2) osteoporosis
excessive loss of calcium weakens bones - osteoclast activity
87
3) **rickets**
4) **osteomalacia**
excessive loss of calcium causes bones to be too flexible/soft
88
**Factors** Affecting Bone Growth and Bone Remodeling
- normal bone metabolism depends on (3)?
**adequate dietary intake of:**
1) Minerals
2) Vitamins
**sufficient levels of:**
3) Hormones
89
Factors Affecting Bone Growth and Bone Remodeling:
## Footnote
**1) Minerals**
large amounts of **Ca, P**
smaller amounts of **Mg, F** & **Mn**
- required for bone growth & remodeling
90
Factors Affecting Bone Growth and Bone Remodeling
2) **Vitamins (5)**
Vitamin A
Vitamin C
Vitamin D
Vitamin K
Vitamin B12
91
Vitamin A
stimulates activity of **osteoblasts**
92
Vitamin C
needed for synthesis of **collagen**
93
Vitamin D
promotes **absorption** of **calcium** from **foods** in **GI tract** into **blood**
94
Vitamins K & B12
needed for synthesis of bone proteins
95
3) Hormones (6)
1) HGH
2) insulinlike growth factors (IGFs)
3) estrogen
4) testosterone
5) Parathyroid hormone (PTH)
6) Calcitonin
96
3) Hormones **- most important to bone growth in childhood?**
**Human Growth Hormone (HGH -** produced by pituitary gland
**Growth Factors (IGFs)** - produced by liver
97
3) Hormones
- **HGH** & **IGFs** both... (3)
stimulate **osteoblasts**
promote **cell division** at **epiphyseal plate**
enhance **protein synthesis**
98
3) Hormones - **Thyroid hormones** (a) & **Insulin** (b)
promote bone growth
by stimulating osteoblast activity (**a**) & increasing synthesis of proteins (**b**)
99
3) Hormones - **Sex Hormones** (4)
At puberty - secretion of **estrogen & testosterone**
Responsible for:
- **increased osteoblast activity**
- **synthesis** of bone ECM
- sudden “**growth spurt**” that occurs during teen years
- closing down **epiphyseal plates**
**Estrogen** promotes widening of pelvis in females
100
During adulthood, **sex hormones** contribute to? by?
**bone remodeling** by **slowing resorption** of old bone & promoting deposition of new bone
- Estrogen slows resorption by promoting **apoptosis** (programmed death) of **osteoclasts**
101
3) Hormones - **PTH & calcitonin**
critical for **balancing** levels of **Ca & P** between **blood** & **bone**
102
Why does maintaining a **normal serum Ca2+** level take precedence over **mineralizing bone?**
too high Ca2+ → **cardiac** arrest
too low Ca2+ → **respiratory** arrest (stop breathing)
103
Ca2+ exchange is regulated by hormones, the most important of which is?
Parathyroid Hormone (PTH)
104
**PTH**
- effect on Ca2+ level
**increases** blood Ca2+ level
operates via **negative feedback system**
105
Negative Feedback System of **PTH**
stimulus causes **decrease** in **blood Ca2+ level**
PT gland cells (**receptors**) detect change → increase production of cAMP **(input)**
detected by gene for PTH within nucleus of PT gland cell (**control center**)
increased PTH synthesis (**output)** →released into blood
stimulates osteoclasts **(effectors)** → bone resorption
release of Ca2+ from bone into blood
106
How else does PTH increase Ca2+ level?
PTH acts on kidneys (**effectors)** to decrease Ca2+ loss in **urine**
PTH stimulates formation of **calcitroil** (active form of vitamin **D**) → promotes **absorption** of calcium **from food** in GI tract **into blood**
107
What Hormone works to **decrease** blood Ca2+ level?
How?
Calcitonin (CT)
increase in blood Ca2+ level → parafollicular cells in thyroid gland secrete **CT →** inhibits osteoclast activity, increase blood Ca2+ uptake by bone & Ca2+ deposition into bone
108
What hormones stimulate **osteoclast** activity & lower **serum calcium level?**
**Calcitonin**
**HGH** & **sex** hormones (to lesser exent)
109
Calcium Homeostasis
**high** blood Ca2+ level → thyroid gland **parafollicular cells** release more **CT** → **CT** inhibits **osteoclasts** → **decreases** Ca2+ level → stimulates **parathyroid chief cells** to release more **PTH**
**(1)** → **PTH** promotes **release** of Ca2+ from **bone ECM** into blood & **slows** loss of Ca2+ in **urine**
**(2)** → **PTH** stimulates release of **calcitriol** from **kidneys** → stimulates increased **absorption** of Ca2+ from food
→ **increases** Ca2+ level
110
Fractures
- different criteria for naming (3)
1) **anatomical appearance**
2) **disease/mechanism** which produced fracture
3) **common pattern of injury**
111
Fractures named by **anatomical appearance** (10)
1. **Partial**
2. **Complete**
3. **Closed** (simple)
4. **Open** (compound)
5. “**Green stick**”
6. **Impacted**
7. **Comminuted**
8. **Spiral**
9. **Transverse**
10. **Displaced**
112
1) Partial
incomplete break of bone
113
2) complete
fracture all the way through bone
114
3) closed (simple)
broken bone does **NOT** puncture skin
115
4) open (compound)
broken ends of bone puncture skin
116
5) Greenstick
partial fracture in which one side of bone is broken & other side bends
- similar to breaking green twig
- occurs only in **children** (bones not fully ossified & contain more organic than inorganic material)
117
6) Impacted
one end of fracture bone forcefully driven into interior of other
- distal part shoved up into proximal part
118
7) Comminuted
bone is splintered/crushed/broken into pieces at site of impact
119
8) spiral
occurs when rotating force applied along axis
120
9) Transverse fracture
broken straight across
121
10) displaced fracture
both ends of broken bone seperated
122
Fractures classified by **disease/mechanism** **which produced fracture**
(3)
1) Pathological
2) Compression
3) Stress
123
1) Pathological
caused by disease that led to weakness of bone structure
-chronic disease like **osteoporosis** or cancer weakens bone
124
2) Compression
produced by extreme forces such as in trauma
125
3) Stress
produced by repeated strenuous activites *such as running*
*-* series of microscopic fissures in bone that form without any evidence of injury to other tissues
126
Fractures described by **common pattern of injury** (2)
1) Colles'
2) Pott's
127
1) Colles' fracture
- usually occurs by?
Fracture of **distal end** of lateral forearm bone (**radius**) in which distal fragment is displaced **posteriorly**
- commonly caused by falling onto hard surface with **outstretched** hand
128
2) Pott's fracture
Fracture of **distal** end of lateral leg bone (**fibula**), with serious injury of **distal tibial articulation**
129
**Fracture & Repair**
- steps (4)
1) Formation of **fracture hematoma**
2) **Fibrocartilaginous callus formation**
3) **Bony callus** **formation**
4) **Bone remodeling**
130
**Fracture repair:**
1) Formation of fracture hematoma
blood vessels crossing fracture line **broken** - in **peristeoum** & **osteons**
leaking blood forms **mass** (usually clotted) around site of fracture → **fracture hematoma**
- usually forms **6-8 hours** after injury
**lack** of blood **circulation** →nearby bone cells die → **swelling** & **inflammation**
→ produces additional cellular debris →removed by phagocytes & osteoclasts
131
**Fracture Repair**
2) Fibrocartilaginous callus formation
**fibroblasts** from **periosteum** invade fracture side → produce **collagen** fibers
cells from **periosteum** develop into **chondroblasts** → produce **fibrocartilage**
- lead to development of **fibrocartilaginous (soft) callus** (mass of repair tissue consisting of collagen & cartilage that bridges broken ends of bone)
- *takes about 3 **weeks** (can take up to **6 months)***
132
**Fracture Repair**
3) Bony callus formation
* In areas closer to well‐vascularized healthy bone tissue:* **osteogenic** cells develop into **osteoblasts** → produce spongy bone trabeculae
**trabeculae** joins living & dead portions of original bone fragments
**fibrocartilage** converted to **spongy** bone →callus referred to as a **bony (hard) callus**
- lasts about 3 to 4 months.
133
**Fracture Repair**
4) Remodeling
dead portions of original broken bone fragments resorbed by **osteoclasts**
**compact** bone **replaces spongy** bone around fracture **periphery**
- fracture line disappears but thicken area on surface remains as evidence
134
Bone Tissue & Mechnical stress
bone tissue has **limited** ability to **alter strength** in **response** to **changes** in **mechanical stress**
- when stressed, can become **stronger** through **increased mineral salt** **deposition** & **production** of **collagen** fibers by **osteoblasts**
135
Main mechanical stresses on bone (2)
pull of skeletal muscles
pull of gravity
136
Unstressed bones
become weaker
- can have dramatic bone loss (up to 1% per week)
137
Aging & Bone Tissue
**decrease** in bone mass occurs as **level** of **sex** hormones **diminishes** during middle age
138
As the level of sex hormones diminishes during middle age... what happens?
- especially for who?
bone **resorption** (by **osteoclasts**) outpaces bone **deposition** (by **osteoblasts**)
- especially for womejn after **menopause**
139
Why does loss of bone mass in old age typically have a greater adverse effect in **females**?
**women's** bones generally smaller & less massive to begin with
- contributes to higher incidence of **osteoporosis** in females
140
(**2) principal effects** of **aging** on **bone tissue**
1) Loss of bone mass
2) Brittleness
141
Effects of Aging:
**1) Loss of bone mass**
- results from?
**Demineralization** - loss of calcium & other minerals from bone ECM
- usually begins after age **30** in females
- accelerates greatly around age **45** (as estrogen levels decrease)
- continues until as much as **30**% of calcium in bones is lost by age **70**
142
Once bone loss begins in females, about \_\_\_% of bone mass is lost every **10 years**
**8**%
143
For **men**:
## Footnote
Calcium loss typically does not begin until ___ , and about \_\_% of bone mass is lost every 10 years
after age **60**
**3**%
144
Effects of Aging
2) **Brittleness**
- results from?
**decreased** rate of **protein synthesis**
- **organic** part of **bone ECM** (mainly **collagen** fibers) gives bone its **tensile strength**
- loss of tensile strength causes bone to become **brittle** & susceptible to fracture
* collagen fiber synthesis slows partly due to diminished HGH production*
145
**Osteoporosis**
- often due to? (2)
condition where bone **resorption** outpaces bone **deposition**
- often due to **depletion** of **calcium** from body OR **inadequate intake**
146
Estrogen & Osteoporosis
## Footnote
**- both sexes**
Estrogen maintains **density** in both sexes (**inhibits resorption**)
**Men:** testes & adrenal glands produce estrogen
**Women:** rapid loss after menopause if:
* **body fat** too **low**
OR
* with **disuse** during **immobilization**
147
Osteoporosis
**- Treatment**
**Estrogen Replacement Therapy (ERT)**
- slows bone resorption but increases risk of breast cancer, stroke & heart disease
Best Treatment = **prevention** - exercise & calcium intake (1000-1300 mg/day) between ages 9 and 71+
- *milk = ~**300** mg/250 ml*
* Vitamin D - ~**600** IU per day*
***40** IU/100 ml milk **by law***
148
Bone difference in **late adulthood** of:
1) retired athlete
2) control
1) **2 hypotheses**
* #1 → larger circumference but thinner (**FALSE**)
* #2 → larger circumference & thicker (**TRUE**)
2) smaller circumference & thinner
149
