Lecture 3,4 and 5 terms Flashcards
Skeletal system - what is it?
The skeletal system includes the bones of the skeleton and the cartilages, ligaments and other connective tissues that stabilise or interconnect them.
What are the functions of the skeleton?
Support, movement, red blood cell formation, protection and storage of minerals and lipids
BullShit MPS (politicians have SKELETONS in their closet) - What is this acronym for?
Functions of the skeleton - Blood cell formation, Storage, movement, protection, support
Two types of bone tissue
Compact and cancellous bone
Cancellous bone
Also known as trabecular bone. Light and spongy bone that looks more disorganised (lots of fibres in different direction to deal with forces). This is a shock absorbing structure. It resists and channels forces that come from multiple directions. Spongy bone consists of an open network of struts and plates that resembles lattice work. Spongy bone is found in the inside of most bones.
Compact bone
Strong bone that is good at transmitting force in one direction (for example down its length). It is a dense organised looking bone.
Compact bone forms the outer layers and diaphysis of long bones
Long bones
These bones are longer than they are wide (elongated and slender)
Composed of wider epiphyses and a longer, narrower diaphysis
Act as levers for motion
These bones are mostly limb bones like the femur (levers are what muscles act on hence long bones are in limbs)
Short bones
These bones are close to equal width and length, they are small and boxy and often rounded or squared in appearance.
These bones are weight bearing (from multiple directions).
Made from mostly cancellous bone (taking weight from a bunch of different directions)
Examples include carpels and tarsals
Epiphysis
Distal and proximal ends of bone which make up joints (end parts of a long bone)
Made from cancellous bone
Covered in hyaline cartilage
Contain red marrow between trabeculae
The epiphysis consists largely of spongy bone. Spongy bone consists of an open network of struts and plate that resembles lattice work with a thin covering of compact bone
Metaphysis
A narrow zone that connects the epiphysis with the shaft of the bone
Diaphysis
Shaft of the bone (shaft or central part of a long bone) (long and tubular)
Compact bone (thicker bone in diaphysis)
Contains yellow marrow
Has blood vessels and nerves
Relatively dense compact bone makes up the walls of the diaphysis. It forms a sturdy protective layer around the central space.
Flat bones
The function of flat bones is usually for muscle attachment and also for protection of underlying soft tissues.
Made up of thin plates of compact bone and some cancellous too.
Example skull (protection by providing a complete encasement of organ (brain)) and scapula (muscle attachment)
Irregular bones
These are bones that don’t fit into any other category normally.
Complex shapes with short, flat, notched or edged surface e.g. vertebrae, pelvis
Various functions and shapes.
Often have a foramen/foramina (holes)
Made of thin layers of compact bone surrounding a spongy interior
Axial skeleton
The bones of the main axis of the body : cranium, spinal column and thorax( rib cage).
Function - protection of vital organs
Appendicular skeleton
The skeleton of the appendages (limbs).
Function - movement and fine motor function
Skull
Part of the axial skeleton
Consists of a number of bones of which all except the mandible (lower jaw) are fixed immovably together after infancy. i.e. the cranium and the facial bones (the cranium and facial bones are seperate structures)
Cranium (vault)
Part of the skull
This bone’s role is to give protection to the brain therefore the bones are robust.
Serves as a place for muscle attachment, larger muscles can attach due to robustness.
Facial bones
Part of the skull
Protects and supports sensory organs.
Generally small, brittle and irregularly shaped
The vertebral column
Part of the axial skeleton
Spine - composed of 24 individual vertebrae together with the sacrum and coccyx.
Keeps the trunk upright, lots of muscle and ligament attachments.
Supports head - it is balanced in the upright position
Divisions of the vertebral column and why they are named differently?
Cervical (7) Thoracic (12) Lumbar (5) Sacrum Coccyx Named differently due to different shapes of the vertebrae
Ribcage (thoracic cage)
Consists of the ribs, sternum
Known as the thoracic cage as it articulates with the thoracic vertebrae (12 vertebrae= 12 ribs)
Role is to protect the heart and the lungs. Therefore there must be some movement possible because the lungs need to inflate and deflate. This means its joints to the vertebral column are sliding joints that allow a little bit of movement. Ribs are able to slide with a little bit of room when breathing.
Describe the upper and lower limb structure
Single proximal long bone - Humerus (upper) / Femur (lower)
2 distal long bones - Radius and ulna (upper) / Tibia and fibula (lower)
Divide the upper and lower limbs into their general parts
Arm and forearm (upper)
Thigh and leg (lower)
How has bipedalism affected the form of the skeleton?
The human skeleton is the shape it is because form is related to function. We are bipedal therefore the lower limbs need to be formed to provide movement and stability. We are hands free meaning that are hands are not involved in locomotion. Less stability in the upper limbs but instead they are more mobile and are adapted for precision.
Humerus and femur in terms of relationship to bipedalism
With bipedalism this means that…
Humerus is shorter and lighter
There is deeper articulation for proximal femur than proximal humerus
All because of stability versus movement
Mobile forearms and wrists versus stability of legs
Mobile forearms and wrists
Pronation/supination radius and ulna
Shape of distal articulation for wrist mobility
More sliding is possible in wrist joint
Stability of legs
NO pronation or supination
Tibia is very robust for weight bearing
Ankle joint is stable
Hands
Carpals (8) per hand
Metacarpals (5) per hand
Phalanges (3 per finger) but in thumb only (2)
Foot
Tarsals (7) per foot
Metatarsals (5) per foot
Phalanges (3) in each toe except 2 phalanges in the big toe
What is a girdle?
Girdles are attachment points, wrapping the appendicular skeleton to the axial skeleton
Pectorial girdle
The pectorial girdle consists of the clavicle and the scapula. Pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side.
Clavicle - a stabilising strut, pushing the shoulder blades back allows for more motion.
Scapula - Freemoving and is used for muscle attachments. Allows for more mobility due to sliding motion.
Pelvic girdle
The pelvic girdle consists of the hip bones (2) and the sacrum. It attaches the axial skeleton to the lower limbs. All the force of the body is coming down the vertebral column, to pelvis to be distributed into the lower limbs. The pelvic girdle is responsible for lots of weight-bearing.
What is the hip bone made up of?
The hip bone is made up of 3 seperate bones which fuse together as a child - the ilium, pubis and ischium
Male versus female pelvis
There is sexual dimorphism displayed between the male and female pelvis.
The female pelvic cavity is more circular (like a cylinder) and the pelvic outlet is more open and wide in females. This maximises space for childbirth and it makes it easier to birth a big brained baby.
Females have a larger sub-pubic angle indicating a wider sub-pubic arch to males.
Females have a shorter, straighter sacrum compared to the male pelvis which has a more curved and longer sacrum.
Describe bone tissue composition
Bone is a connective tissue. It supports other tissues/organs and helps to maintain form. It doesn’t have a lot of cells, mostly ECM which is everything that isn’t cells (fibers etc.)
Bone has two extracellular components - an organic and an inorganic component (without one you lose a key functional aspect of bone)
Ground substance
Made up of proteoglycans, these sugars attract water molecules which provides bone with the ability to withstand compression.
Describe the organic part of bone
The organic part of bone is made up of proteins.
33% of the bone matrix is organic.
Consists of collagen (protein) which exists in fibres in different orientations (criss cross structure) surrounded by a ground substance.
Ground substance is made of proteoglycans
The function of the organic part of bone is to resist tension, if it was removed then the bone would be very brittle and would be able to be broken easier.
Describe the inorganic part of bone
The inorganic part of bone is the mineral component.
67% of the bone matrix is inorganic.
Consists of hydroxyapatite and other calcium minerals (mineral salts). The mineral component of bone makes bone hard and resistant to compression. When removed, the bone becomes too flexible.
Summary of what makes up the bone (simply)
Cells+inorganic+organic = bone
What cells make up the bone?
osteogenic cells, osteoblasts, osteocytes and osteoclasts (Both compact bone and spongy bone contain the same four types of cells.)
What percentage does the cellular component of bone make up of the bone matrix?
2%
Osteogenic cells
Osteogenic cells are stem cells that produce osteoblasts. Osteogenic cells are found in the inner, cellular layer of the periosteum.
Osteoblasts
Cells involved in the production of bone. These cells later differentiate into osteocytes. Located wherever new bone is forming. Their precursor is osteogenic cells. Osteoblasts produce new bone matrix in a process called ossification. Osteoblasts make and release the protein and other organic components of the matrix. Before calcium salts are deposited, this ‘pre-bone’ organic metric is celled osteoid. Osteoblasts also help increase local concentration calcium phosphate to the point where this calcium salt is deposited in the organic matrix. This process converts osteoid to bone. Osteocytes develop from osteoblasts that have become completely surrounded by bone matrix
Osteocytes
Mature osteoblasts.
Maintainers and communicators - recycle proteins and minerals from the matrix. Also control activity of the osteoblasts/clasts
The precursor of osteocytes are osteoblasts which become embedded in the osteoid.
Osteocytes are mature bone cells that maintain the bone matrix. These cells continually recycle the protein and minerals of the surrounding matrix. Osteocytes secrete chemicals that dissolve the adjacent matrix, and the released minerals enter the bloodstream. They then rebuild the matrix, stimulating the deposition of mineral crystals. The turnover rater varies from bone to bone. Osteocytes also take part in the repair of damaged bone. The thin layers of matrix are called lamellae. Osteocytes make up most of the cell population in bone. Each osteocyte occupies a lacuna, a pocket sandwiched between layers of matrix. Osteocytes cannot divide, and a lacuna never contains more than one osteocyte. Processes of the osteocytes extend into narrow passageways called canaliculi that penetrate the matrix. The canaliculi interconnect the lacunae and reach vascular passageways, providing a route for nutrient diffusion.
Osteoclasts
Cells involved in the destruction of bone
Remove bone matrix to maintain new healthy bone. These cells secrete enzymes and acids to dissolve the bone matrix which causes bone remodelling. These cells are located wherever bone reabsorption is occurring.
Osteoclasts are not related to osteogenic cells or their descendants. Instead, they are derived from the same stem cells that produce monocytes and macrophages, cells involved in the body’s defence mechanisms
What is the structure of compact bone?
Osteon structure
What is the structure of cancellous bone?
Trabecular structure
What is an osteon?
Longitudinal (lengthwise) unit within compact bone.
Cylindrical structure on a microscopic scale that runs down the length of your long bones.
What does an osteon provide?
Provides a pathway for nutrients to get to cells in the extracellular matrix
The function of an osteon is to maintain osteocytes by providing nutrients to them
Central canal
Contains blood vessels and nerves. This is the main way that nutrients are received.
Lamellae
Thin rings of compact bone, between which are found the lacunae.
Lamellae are tubes of ECM with collagen fibres which are aligned to resist forces. These make up the osteon, and are arranged to form a series of cylinders running longitudinally down the shaft of the compact bone
The lamellae of each osteon form a series of nested cylinders around the central canal. In transverse section, these concentric lamellae resemble a target, with the central canal as the bullseye.
Interstitial lamellae
Interstitial lamellae fill in the spaces between the osteons in compact bone. These lamellae are remnants of osteons whose matrix components have been almost completely recycled by osteoclasts during the process of bone remodelling.
Circumferential lamellae
Found at the outer and inner surfaces of the bone, where they are covered by the periosteum and endosteum, respectively. These lamellae are produced during the growth and maintenance of the bone.
Layers of bone matrix that go all the way around the bone.
Lacunae
Microscopic spaces in bone and cartilage in which cells (osteocytes) are found. (‘lakes’ for osteocytes). These cells need a blood supply therefore use canaliculi. Lacunae house individual osteocytes
Canaliculi
Canaliculi are small channels that connect the lacunae housing the osteocytes together are also connects to the central canal. These allow communication between the osteocytes and the spread of nutrient. (Canaliculi radiating through the lamellae interconnect the lacunae of the osteon with one another and with the central canal.)
Describe cancellous bone structure
Found where bones are not heavily stressed or where stresses arrive from many different direction. The trabeculae are orientated along stress lines and are cross-braced extensively. Spongy bone is much lighter then compact therefore it reduces the weight of the skeleton, making it easier for muscles to move the bones. Spongy bone makes up most of the volume of short, flat and irregular bones and the epiphyses of long bones. In spongy bone, lamellae are not arranged in osteons. The matrix in spongy bone forms struts and plates called trabeculae. The thin trabeculae branch, creating an open network. There is no vasculature in the matrix of spongy bone. Nutrients can reach the osteocytes by diffusion along canaliculi that open onto the surfaces of trabeculae. Spongy bone within the epiphyses of long bones, such as the femur, and the interior of other large bones such as the sternum and ilium contains red bone marrow. At other site, spongy bone may contain yellow bone marrow. Blood vessels within this tissue deliver nutrients to trabeculae and remove wastes generated by the osteocytes.
Where there is crossing over of line of stress, there will be a point of weakness in the bone. This is a likely place for the deterioration of trabeculae.
Marrow fills the cavities between the trabeculae. There are no blood vessels - The blood supply is from the medullary cavity (the red marrow)
This bone is synthesised outwards
Why trabecular bone? (in cancellous bone?)
Organisation of trabeculae (in a criss cross formation) resists force from multiple directions. Directs force from the body weight in a single direction down the shaft made of compact bone. This bone spreads force distally
Pelvic girdle force distribution ….explain
The trabeculae channel weight around the ilia into the femurs. This is a large weight bearing structure, carries the weight of the entire upper body from the vertebrae round laterally to where your femur articulates and down your lower limb. The trabeculae are mostly orientated to lead the weight from the vertebral column around the curve of your pelvis and into your femur, taking the weight and supporting it as it goes through your body.
What is appositional growth?
Appositional growth is the increase in the diameter of bones by the addition of bony tissue at the surface of bones. Osteoblasts add bone matrix in lamellae to bone surface. This adds successive layers of circumferential lamellae to the outer surface of the bone. Osteoblasts trapped between these lamellae differentiate into osteocytes. Over time, the deeper lamellae are recycled and replaces with the osteons typical of compact bone. As bone is being added to the outer surface through appositional growth, osteoclasts are removing and recycling lamellae at the inner surface. As a result, the medullary cavity gradually enlarges as the bone increases in diameter.
Osteoblasts at the bone surface secrete bone matrix, and osteoclasts on the inner surface break down bone.
Why is bone remodelling useful?
Because it allows bones to grow and respond to pressures around them.
If we have a lot of forces acting on our bones then we want them to get larger and wider, to deal with the force and to get wider bones they go through appositional growth.
Bone homeostasis
Bone is constantly being formed and destroyed. This allows our body to mobilse calcium, phosphate and other minerals from the bone matrix.
Remodelling allows bones to respond to stress and trauma (shape change possible to resist strain etc.)
Balance of bone destruction and formation means that the amount of bone stays the same (the same volume) (when are bones are grown)
