A&P Exam 2 (Part 1)

Function of hormonal control of bone metabolism

to maintain blood calcium levels within a narrow range

What range is the blood calcium level kept between?

9-11 mg/ 100ml

The maintenance of blood calcium levels can be at the expense of the skeleton. (T/F)

true

What is calcium important for in the body?

muscle contraction, nerve pulse transmission, blood clotting, secretion of glands and near cells, and cell division

What is calcium vital for in the body?

muscle contraction (i.e. heart and lungs) and nerve pulse transmission

Parathyroid hormone (PTH)

most important hormone in bone metabolism

When is PTH secreted?

when the calcium level in the blood is too low

What is PTH secreted by?

parathyroid gland

hypocalcemia

low blood calcium levels

hypercalcemia

high blood calcium levels

What are the effects of PTH being released?

stimulates osteoclast reabsorption, increases calcium absorption in the intestine and reabsorption in the kidney

Osteoclasts reabsorbing bone allows for what?

the release of calcium into circulation (increase in blood calcium)

How does the absorption of calcium into the intestine happen?

through the activation of vitamin D in the kidney

In calcium homeostasis, what are the effectors?

osteoclasts, kidneys, and intestines

In calcium homeostasis, what is the efferent pathway?

the liver and kidneys

In calcium homeostasis, what is the control center?

the parathyroid gland

PTH activates vitamin D to D3 (T/F)

true

Osteoblasts are part of the calcium homeostasis process (T/F)

false

When is calcitonin secreted?

when calcium levels in the blood are too high

What is calcitonin secreted by?

parafollicular cells of the thyroid gland

calcitonin is only secreted once calcium levels exceed ___%

20

Calcitonin

inhibits osteoclasts and acts to accelerate bone deposition, decreasing calcium levels

Calcitonin’s effects are short lived and it does not have an important role in calcium homeostasis (T/F)

true

Calcium levels are homeostatically regulated, but bone metabolism is not. (T/F)

true

All people will have normal bone loss throughout life, with women being greater at risk. (T/F)

true

Osteoporosis

a disease where bone reabsorption is greater than bone deposition to the point that bones become porous and lighter

Peak bone mass generally occurs between what ages?

25-35

During osteoporosis the composition remains normal, but the bone mass is reduced. (T/F)

true

X-rays are unable to pick up on osteoporosis until what percent of bone mineral is lost?

30-50

Trabecular bone loss begins at what age?

20

What becomes more likely with trabecular bone loss?

compressional fractures of the vertebrae and hip fractures

The femoral neck is what percent trabecular bone?

45

The most important thing to prevent osteoporosis is to increase the consumption of what?

dietary calcium

What type of calcium is the best for preventing osteoporosis?

calcium (carbonate) with vitamin D

How much calcium do you need in a day?

1000-1200 mg

How much vitamin D do you need in a day?

500 IU

What is the second most influential factor on osteoporosis?

Estrogen and testosterone levels

Sex hormones like estrogen and testosterone _____ (promote/restrain) osteoclast activity

restrain

Testosterone decline is must more dramatic than estrogen decline (T/F)

false

Because estrogen declines sharply, women are more vulnerable to osteoporosis (T/F)

true

Amenorrhea

irregular menstruation of women

Why are women who menstruate less more likely to have calcium deficiency and osteoporosis?

they are not producing enough estrogen to stop bone mass loss

Estrogen and progesterone birth control

stops ovulation, but allows for estrogen intake

Progesterone only birth control

inhibits menstruation completely, no estrogen intake

How to minimize bone mass decline?

regular calcium intake and weight-bearing exercise

What outside factors can cause calcium loss?

smoking, excessive protein intake, and sodium chloride intake

The human skeleton is initially made up of what?

cartilage and fibrous membranes

In the human skeleton, cartilage eventually becomes bone (T/F)

false

Before ___ weeks the embryo’s skeleton is entirely fibrous membranes and cartilage

8

Intramembraneous ossification

bone develops from a fibrous connective tissue membrane producing the membrane bones

General steps for intramembraneous ossification

fibrous c.t. cells become osteoblast → formation of ossification center → mineralization of osteiod → trapped osteoblasts become osteocytes → formation of the rest of the bone elements

Intramembraneous ossification deals with osteoclasts (T/F)

false

Intramembraneous ossification is use to form what type of bones?

flat and irregular bones

Intramembraneous ossification can be used to form long bones, but usually is not (T/F)

false

Heterotopic bones

bones that develop in unusual places

Myositis ossificans

muscle inflammation causes bone deposition around the skeletal muscle

Fibrodysplasia ossificans progressiva

bone deposition that occurs outside the skeletal system and into connective tissue; congenital disease

Heterotopic bone is formed by the same process that membraneous bone is created (T/F)

false

fibrous connective tissue is made up of what types of connective tissues?

dense regular and dense irregular connective tissues

Endochondral ossification

hyaline cartilage is used as a model for bone construction, producing cartilage bones

What kind of bones does endochondral ossification form?

long bones and sesamoid bones

Mesenchymal cells

crowding together of connective tissue cells, differentiate into chondroblasts which make a cartilage matrix; young cells

The cartilage “model” does not grow in length or thickness (T/F)

false

General steps of endochondral ossification

cartilage cells under periosteum specialize into osteoblasts → cartilage cells enlarge and calcify → periosteal bud forms → osteoclasts break down new spongy bone (medullary cavity formation)

In endochondral ossification osteoblasts form the bone collar and produce bone that moves to the inside (T/F)

false

Does creation of a medullary cavity occur in the epiphysis of bones? (yes/no)

no

Bone collar

forms around the shaft of the forming bone, encasing the cartilage; for support

What signals the calcification of the matrix?

pH changes within the shaft

What makes up a periosteal bud?

vessels, nerve fibers, lymphatic, red marrow, osteoclasts, and osteoblasts

Osteoclast function in endochondral ossification

erode calcified cartilage matrix and new spongy bone, creating the medullary cavity

Osteoblast function in endochondral ossification

secrete osteoid that calcifies into hard, spongy bone

The secondary ossification centers in the epiphyses of long bones are formed _____ (before/after) birth

before

What places does hyaline cartilage remain after endochondral ossification

on the ends of bones where there is a junction (articulation) with another bone and between the diaphysis and epiphysis

Epiphyseal places (growth plates)

the hyaline cartilage that remains between the diaphysis and epiphysis of long bones, where growth of bones occurs after birth

Important hormone for bone growth after birth

human growth hormone (hGH)

Where is hGH secreted from?

the anterior pituitary gland

Bone growth is also affected by the release of what two hormones?

estrogen and testosterone

High levels of testosterone and estrogens induce ________.

the closure of the epiphyseal plate

Bone growth can occur in thickness, especially in response to stress (T/F)

true

Bone remodeling

microscopic areas of bone are continuously broken down, reabsorbed, and reconstructed

How does bone remodeling work?

“remodeling units” of adjacent osteoclasts and osteoblasts

Where does bone remodeling occur?

at the periosteal and endosteal surfaces of bone (internal and external surfaces of the bone)

Remodeling is uniform (T/F)

false

Remodeling occurs in some bone areas more frequently than others (T/F)

true

Example of bone remodeling

distal end of femur is totally replaced more than twice a year

No remodeling would cause only the bone ends to grow without shaping of the bone occurring as well (T/F)

true

When does bone remodeling occur?

through the lifetime of an individual

The rate of bone deposition increases with what?

injury or stress on the bone

Large bony projections occur where heavy, active muscles attach (T/F)

true

Why does bone remodeling occur?

to respond to mechanical and gravitational forces

Atrophy in bones increases with what?

when bones are not stressed by weight bearing exercise or stretch of muscles

Why does bone remodeling occur?

to maintain calcium homeostasis in extracellular fluid

Malformation of bones is a reflection of a malfunction of what bodily system?

the endocrine system

Giantism

over secretion of hGH (hyper hGH) before puberty

Dwarfism

under secretion of hGH (hypo hGH) before puberty

Achondroplastic dwarfism

genetic; only affects the epiphyseal plates of long bones, no response to hGH; normal size of head and torso

Acromegaly

hypersecretion of hGH just after puberty, increased thickness of bones

The knee joint is not enclosed anteriorly by the joint capsule (T/F)

false

What makes up the joint capsule?

fibrous dense irregular connective tissue and inner synovial membrane

The joint capsule ____ the joint cavity

forms