Module 6: The Skeletal System Flashcards
1
Q
What tissues make up the Skeletal System?
A
Bone is an organ made up of several different tissues working together;
- Bone (osseous) tissue
- cartilage
- dense connective tissue
- epithelium
- adipose tissue
- nervous tissue
2
Q
List and Discuss the 6 functions of bones.
A
- Support
- provides a framework for soft tissue
- provides points of attachment for tendons of most skeletal muscles
- Protection
- protects internal organs from injury
- Assistance in movement
- Bones are pulled when muscles contract
- Mineral Homeostasis
- bones store minerals most notably calcium and phosphorus
- Release minerals into blood when required to assist other body parts
- Blood Cell Production
- red bone marrow is a connective tissue found in certain bone
- produces red blood cells, white blood cells and plateletes
- Triglyceride Storage
- Yellow bone marrow contains adipose cells which store triglycerides
3
Q
What is hemopoiesis?
A
The production of red blood cells, white blood cells and platelets from bone marrow.
4
Q
Classify bones on the basis of their shape and location.
A
- Long
- consist of a shaft with 2 ends
- Have greater length than width
- somewhat curved for strength
- found in thigh (femur), leg (tibia and fibula), arm (humerus), forearm (radius and ulna), and fingers and toes (phalanges)
- short
- cubed shape almost equal length and width
- wrist and ankle bones
- Flat
- generally thin and usually curved
- include cranial bones, sternum, ribs, scapula
- Irregular
- are not short, long, or flat
- complex shapes which don’t fit any other category
- vertebrae, and some facial bones
5
Q
List and discuss the major features of a long bone, including the following: diaphysis, epiphyses, metaphyses, epiphyseal line, periosteum, endosteum, medullary cavity, yellow marrow, red marrow, and articular cartilage.
A
- Diaphysis is the shaft of the bone
- Epiphyses is the distal and proximal ends of the bone
-
Metaphyses is where the diaphysis joins the epiphyses
- the Epiphyses (growth) plate, made hyaline cartilage which allows the diaphysis bone to grow in length is found here towards the proximal epiphysis
- when bone growth stops, this seals up with bone the structure is called the epiphyseal line.
-
Articular Cartilage
- thin layer of hyaline cartilage covers a part of the epiphyses of the bone responsible for articulation with another bone (a joint)
-
Periosteum
- tough sheath of dense irregular connective tissue along with blood vessels that surrounds the entire bone except areas with articular cartilage
- a connective tissue that covers the surface of the bone; it contains osteogenic cells, protects bone, assists in fracture repair, helps nourish bone tissue and serves as an attachment point for ligaments and tendons.
-
Medullary Cavity is the marrow cavity that is hollow
- found within the diaphysis
- contains fatty yellow bone marrow in adults
- Endosteum
- thin membrane which lines the medullary cavity
- Red marrow
- the site of blood production.
- Yellow marrow
- the site of fat storage.
6
Q
Describe the microscopic structures of bone.
A
- extracelluar matrix is made up of
- 25% water
- 25% collagen fibres
- 50% crystallized mineral salts
There are 4 main types of cells found in the bone tissue
-
Osteoprogenitor cells are precursor cells.
- unspecialized stem cells derived from mesenchyme
- undergo cell division which develops into osteoblasts
- found along inner position of periosteum, in the endosteum and canals within bone that contains blood vessels
-
Osteoblasts are bone-building cells.
- secrete collagen and other organic components needed to build extracellular matrix
- as they build the extracellular matrix they become stuck in it and become osteocytes
-
Osteocytes are mature bone cells, the principal cells of bone tissue.
- maintain and monitor bone tissue
-
Osteoclasts are derived from monocytes and serve to break down bone tissue.
- huge cells derived from the fusion of as many as 50 monocytes
- found in the endosteum
- release powerful lysosomal enzymes and acids that digest protein, mineral components of the bone
- breakdown extracellular matrix in bone
The matrix of bone contains inorganic salts, primarily hydroxyapatite and some calcium carbonate, and collagen fibres.
These and a few other salts are deposited in a framework of collagen fibres, a process called calcification or mineralization.
Mineral salts confer hardness to bone, while collagen fibres give bone its great tensile strength.
The process of calcification occurs only in the presence of collagen fibres.
7
Q
Discuss spongy bone in terms of trabeculae.
A
- it consists of trabeculae (columns or beams of bone of irregular latticework of thin bone), which surround many red- marrow-filled spaces.
- within each trabeculae are
- concentric lamellae
- osteocytes that lie in lacunae
- canaliculi radiating from the lacunae
- It forms most of the structure of short, flat, and irregular bones; and the epiphyses of long bones.
- Spongy (cancellous) bone does not contain osteons.
- Spongy bone tissue is light and supports and protects the red bone marrow.
8
Q
Define the term ossification.
A
this is the process of new bone formation.
this occurs in 4 principle situations;
- initial formation of bones in an embryo and fetus
- growth of bones during infancy, childhood and adolescence
- remodelling of bones - replacing old bone with new bone
- repair of fractures
Bone formation is termed osteogenesis or ossification; it begins when mesenchymal cells provide the template for subsequent ossification.
9
Q
Distinguish between intramembranous and endochondral ossification, and denote which parts of the skeleton are formed by each.
A
The two types of ossification that can occur are as follows:
Intramembranous ossification
- bone forms directly within mesenchyme arranged in sheetlike layer that resemble membranes
- flat bones of the skull, facial bones, mandible, part of clavicle
Endochondral Ossification
- Endochondral ossification is when bone forms within hyaline cartilage that develops from mesenchyme
- most bones in the body are formed this way
10
Q
Discuss the steps involved in intramembranous ossification.
A
- Development of the ossification center
- the bone development site is called the ossification center
- mesenchyme cells cluster together and differentiate
- start as osteoprogenitor cells and turn into osteoblasts
- osteoblasts then secrete the organic extracellular matrix of bone
- Calcification
- extracellular matrix fluid stops
- osteocytes are left, lie in lacunae and extend their narrow cytoplasmic processes into canaliculi that radiate in all directions.
- after a few days, calcium and other mineral salts are deposited which then hardens the area
- formation of the trabeculae
- as bone extracellular matrix forms, it develops into trabeculae, thin layers of bone, that fuse with one another which form spongy bone
- blood vessels grow into the spaces btw trabeculae
- connective tissue associated with blood vessels turn into red bone marrow
- Development of the periosteum
- mesenchyme condenses at the periphery and develops into periosteum
- eventually, a thin layer of compact bone replaces the surface layers of the spongy bone, but spongy bone still remains in the center.
11
Q
Discuss the steps involved in endochondral ossification.
A
- Development of the cartilage model
- mesenchyme cells forms the bone shape
- develop into chondroblasts which produce cartilage extracellular matrix
- this becomes the cartilage model made from (hyaline cartilage)
- a perichondrium develops on the outside of the cartilage model (hyaline cartilage)
- Growth of cartilage model
- when chondroblasts become buried in extracellular matrix they are called chondrocytes
- As growth continues, the chondrocytes in the middle of the model increase in size and the extracellular matrix begins to calcify
- this calcification causes some cells to die due to lack of nutrients to the area, bringing lacunae to form and eventually merge into small cavities
- Development of the primary ossification center
- a nutrient artery penetrates the perichondrium and the calcifying cartilage model in the middle of the model
- proceeds inwards from the external surface of the bone
- this stimulates osteoprogenitor cells in the perichondrium to change into osteoblasts
- the outer perichondrium now becomes periosteum as it is now producing bone.
- Blood vessels grow into the calcifying cartilage in the middle of the cartilage model and start the growth of the primary ossification center.
- Osteoblasts then begin depositing bone extracellular matrix over the cartilage to form trabeculae.
- The ossification center spreads to both ends of the cartilage model
- Development of the medullary (marrow) cavity
- the primary ossification center continues to grow to the ends of the bone
- Osteoclasts break down newly formed spongy bone trabeculae
- leaves a cavity the medullary (marrow) cavity
- most of the wall of the diaphysis becomes compact bone
- Development of the secondary ossification centers
- Begins when blood vessels enter the epiphyses which develops into a secondary ossification center
- the process works the same as the primary however there is no medullary cavity that forms and most of the bone remains as spongy bone
- bone formation is the same here as the primary center however it remains spongy bone, no medullary cavity is formed.
- Proceeds outwards from the center of the epiphysis to the outer surface of bone
- Formation of articular cartilage and the epiphyseal plate
- the hyaline cartilage that covers the epiphysis becomes the articular cartilage
- prior to adulthood hyaline cartilage remains btw the diaphysis and epiphysis as the epiphyseal plate is responsible for the length growth of the bone.
- once the plate becomes solid, the lengthening of the bone is completed.
12
Q
Discuss bone growth and remodelling.
A
Growth of bone can happen in 2 ways, length and thickness;
Length:
- refers to the epiphyseal plate which is responsible for growth in young people
- young chondrocytes within the plate are constantly dividing
- as new bone grows in length new chondrocytes are formed on the epiphyseal side of the plate while old chondrocytes on the diaphyseal side of the plate are replaced by bone.
- btw 18-25 this process stops. the cartilage is replaced by bone leaving the epiphyseal line.
Thickness:
- cells in the perichondrium differentiate into osteoblasts which secrete bone extracellular matrix osteoblasts develop into osteocytes lamellae are added to the surface of the bone and new osteons of the compact bone tissue are formed.
- osteoclasts in the endosteum destroy the bone tissue lining the medullary cavity which widens the cavity
Remodelling:
- bone is in a constant state of renewal replacing old bone with new bone
- Bone resorption is the destruction of the bones extracellular matrix
- Bone deposition is the formation of the bone extracellular matrix
13
Q
Discuss the nutrients and hormones involved in bone growth.
A
- Adequate minerals
- especially calcium, phosphorus, and magnesium
- Vitamins
- A, C, D, B12, K
- Several hormones
- before puberty
- human growth hormone
- insulinlike growth factors
- thyroid hormones
- insulin
- parathyroid hormone
- calcitonin
- at puberty
- estrogens, testosterone and androgens
- before puberty
- Weight-bearing exercise (bone stress)
14
Q
Fully discuss the negative feedback mechanisms involved in blood calcium (Ca++) homeostasis, and explain how this is related to bone remodelling.
A
Stimulus
- There is a decrease in the amount of Ca++ levels in the blood
Receptors
- Parathyroid gland cells detect lowered Ca++ levels and increases production of cyclic AMP
Control Center
- Parathyroid Hormone Gene turns on which increases the release of PTH
Effectors
- Osteoclasts increase bone resorption
- kidneys retain Ca++ in blood, excrete phosphate in urine and produce calcitriol
- both, in turn, increase the Ca++ levels in the blood
Without adequate calcium circulating the body would have an imbalance btw the absorption and deposition rates
15
Q
Classify the bones of the body into the axial division.
A
Axial
- Skull
- cranium
- face
- Hyoid Bone
- Auditory Ossicles
- Vertebral column
- Thorax
- Sternum
- Ribs
