A&P 1 Chapter 6

Secondary ossification centers occur in

epiphyses

Cells of the perichondrium need to take on a new role as ossification begins. They will become __________.

osteoblasts and begin to deposit bone matrix

homeostasis regulation of blood calcium

1. The homeostasis of blood calcium is regulated by a negative feedback mechanism. 2. PTH is secreted by the parathyroid glands and raises blood calcium levels that are below 8.5 mg/dL. 3. Calcitonin inhibits the action of osteoclasts while having no effect on osteoblast activity. This helps to lower the blood calcium level whenever it exceeds 11 mg/dL.

The following are important steps in the process of endochondral ossification. 1. Blood vessels grow around the edges of the cartilage and perichondrium differentiates into osteoblasts. 2. Capillaries and osteoblasts migrate to the epiphyses forming the secondary ossification centers. 3. Chondrocytes enlarge and the surrounding matrix begins to calcify. 4. Remodeling continues and the shaft becomes thicker.5. Blood vessels penetrate the cartilage and invade the central region forming the primary ossification center. What is the correct order for these events?

3,1,5,4,2

Define open fracture and closed fracture.

An open fracture is one where the bone pierces the skin; a closed fracture is one where no bone pierces the skin.

________ prevents damaging bone-to-bone contact within movable joints.

Articular cartilage

Where is articular cartilage found, and how is it nourished?

Articular cartilage is found covering both epiphyseal portions of articulating bone and nutrients diffuse from synovial fluid within the joint.

Bill, age 15, is still growing, but his older sister Andrea, age 19, has stopped. What has changed in Andrea's bones?

Her epiphyseal plates have ossified.

Which condition, due to excessive cartilage formation at the epiphyseal cartilages, results in individuals who are very tall, with long, slender limbs?

Marfan syndrome

osteoblasts and osteoclasts

Osteoblasts build bone, osteoclasts break it down

PTH vs Calcitonin

PTH is a factor that increases blood calcium level while calcitonin is a factor that decreases blood calcium level

red vs yellow marrow

Red is highly vascular and involved in production of blood cells. Yellow is adipose tissue

The intestinal response to PTH secretion when calcium ion levels are low is that calcium is

absorbed quickly

Osteocytes are embedded in a dense matrix of hydroxyapatite. Which of the following describes how osteocytes in compact bone receive nutrients?

by diffusion from nutrients released from vessels in the central canal that travel through canaliculi.

Which of the following hormones is currently thought to decrease plasma calcium levels in pregnant women and children?

calcitonin

PTH (parathyroid hormone) promotes the formation of which hormone?

calcitriol

PTH promotes the formation of which hormone?

calcitriol

Which hormone works directly in the intestine to increase plasma calcium levels?

calcitriol

The most abundant mineral in the human body is

calcium

Which substance accounts for almost two-thirds of the weight of bone?

calcium salts

The narrow passageways that contain cytoplasmic extensions of osteocytes are called

canaliculi

During the early stages of endochondral ossification, which cells enlarge, then die and disintegrate?

chondrocytes

The hormone calcitonin

decreases the level of calcium ion in the blood and inhibits breakdown of bone

During intramembranous ossification, bone replaces which type of tissue?

embryonic, or fibrous connective tissue

The articular cartilage of a typical long bone covers portions of what part of the bone?

epiphyses

After a fracture of the diaphysis has healed, the thickened region that results is called the

external callus.

Excessive growth hormone prior to puberty could result in

gigantism

appositional growth

growth in width

A hard ossified bone in an adult actually begins within the embryo as a miniature version composed of

hyaline cartilage

Which of the following would NOT be a way that parathyroid hormone (PTH) could alter plasma calcium levels? (Which one of the following is FALSE?)

increase osteoblasts on bone

What is a way that the parathyroid hormone could alter plasma calcium levels?

increase osteoclasts or increase reabsorption of calcium in the kidney

The space occupied by an osteocyte is called a

lacuna

Osteocytes

mature bone cells

Cells that are found in small depressions on the endosteal surfaces are the

osteoclasts

The process of osteolysis (bone tissue is destroyed) is performed by which cell population?

osteoclasts

The lacunae of osseous tissue contain

osteocytes

Identify the hormone that stimulates the release of calcium ions from bone matrix. Explain its mechanism of action.

parathyroid hormone; increases osteoclast break down of bone matrix

intramembranous ossification

process by which bone forms directly from mesenchymal tissue within fibrous connective tissue

endochondral ossification

process in which bone forms by replacing hyaline cartilage

ephiphyseal plate

separates diaphysis and epiphysis in early development, "growth plate"

Bones that develop within tendons are called ________ bones.

sesamoid

Which class of bones develops inside tendons and is most commonly located near joints at the knees, the hands, and the feet?

sesamoid bones

A chamber within a bone normally filled with air is a

sinus

osteogenic cells

stem cells that differentiate into osteoblasts found in periosteum or endosteum

Small, oddly shaped bones that fill gaps between bones of the skull are called ________ bones.

sutural

he three main organs that serve as the site for the regulation of blood calcium levels are

the bones, the intestines, and the kidneys

As blood vessels extend into the spaces left by dying chondrocytes, the models begin to ossify internally. Where does internal ossification begin?

the primary ossification center in the diaphysis

The large proximal projection on the femur is termed the

trochanter