Session 7: Bone marrow, vessels and blood

Question 1

Name the bones of the axial and appendicular skeletons

Answer 1

Axial: Skull, vertebra, thoracic cage(ribcage)
Appendicular: shoulder girdle, pelvic girdle, lower and upper limbs

Question 2

Explain how a bone is a living tissue

Answer 2

Bones have their own blood vessels, and proteins, minerals which allow them to grow, transform and repair themselves through life

Question 3

What is the function of bones?

Answer 3

1. Protects important and delicate tissues and organs
2. Haemopoiesis: holds and protects bone marrow
3. Fat storage( yellow BM), acid-base homeostasis absorbs or releases alkaline salts-has Ca, to regulate blood pH)

Question 4

How are bones formed?

Answer 4

1. Endochondral ossification: formation of long bones inside cartiliage. Continued lengthening throughout life by ossification of growth plate- called appositional growth growth at edges)
2. Intra-membrous ossification: formation of bones from clusters of mesenchymal(MSC) bone marrow cells from centre of bone. Called intersitial growth- growth begins in middle

Question 5

How do bones undergo remodelling?

Answer 5

1. Bone resorption: osteoclasts digest old bone
2. Ossification: bone formed by osteoblasts lay down new bone till resorbed bone is completely replaced

Question 6

Describe the components of bones( in a fetal skull)

Answer 6

Osteoblasts: bone deposition
Osteocytes: osteoid recycling
Osteoclasts: bone resorption
Periosteum: blood supply for bones( side 1)
Mesenchymal tissue: in bone marrow, make and repair skeletal tissue
Spicule of bone: fragments of bone marrow, connect to form tracbaculae
Osteoid: unmineralised bone tissue
Lacunae: contains osteocyte left behind by osteoblast after remodelling
Canaliculi: links lacunae with one another and with haversian canal. Also found in liver lobule
Lamellae: extracellular matrix around cells that gives compact bones it hardness.
Endosteum: lining membrane of bone marrow cavity, lines haversian canal( side 2)
Trabacular bone: porous bone connected with thin rods and plates
Haversian and Volkmann’s canals: carry blood vessels, lymph vessels and nerves

Question 7

Describe the structure of cancellous/trabecular/spongy bone and compact/cortical bone which make up every bone in the body

Answer 7

Cancellous: network of fine bony platse called trabeculae to combine strength with lightness. Spaces are filled with bone marrow
Compact: forms externla surfaces of named bones, contains Ca

Question 8

Explain the importance of Vitamin D in normal bone stability

Answer 8

Vitamin D produces calcitrol which aids in calcium absorption

Question 9

How does activity of osteocytes affect bone stability?

Answer 9

1. Activity of osteocytes( osteoid recycling): can act like osteoblasts and lay down scavenged osteoid into lacunae due to increased oestrogen or thyrois hormones OR can act like osteoclasts and degrade bone, called osteocyctic osteolysis( increased by PTH/parathormone, secreted by parathyroid gland which controls Ca levels in blood)

Question 10

How does activity of osteoblasts affect bone stability?

Answer 10

Bone deposition is stimulated by oestrogen, testosterone, thyroid hormones, vit A

Question 11

How does activity of osteoclasts affect bone stability?

Answer 11

Bone resorption is increased by PTH, releases calcium ions into blood. To counteract, calcitonin decreases Ca levels by blocking PTH at PTH receptor.

Question 12

What biological change generally causes bone disease?

Answer 12

Depletion of bone mass. Loss of mass within trabecular bone is relevant to increased suspectibility to fracture.

Question 13

Describe the genetic and phenotypical changes in osteogenesis imperfecta

Answer 13

AKA brittle bone disease. Caused due to autosomal dominant mutations in COL1A where produced mutated collagen 1 fibres do not knit together or insufficient collagen is produced. Results in:
weakened bones, short stature, blue sclera, hearing loss, loose joints, flat feet, crowded teeth

Question 14

Describe the features of bones affected by rickets and phenotypical changes, and compare with osteomalacia

Answer 14

R: mainly in children, due to Vit D deficiency. Leads to poor calcium mobilisation, weak bones, short stature, painful walk, characteristic bowed legs
O: rickets in adults, Vit D def, increased osteoid-unmineralised bone tissue, bones are weak. Leads to increased calcium resorption. Due to lack of sunlight, Ca rich food, esp when preganant. Fetus needs Ca for own tissue development as well.

Question 15

Describe the radiological and structural changes in primary and secondary osteoporosis

Answer 15

Primary
Type 1: post menopausal women due to increase in osteoclast number, loss of osetrogen in menopause- osteocyte cannot act as osteoblast anymore
Type 2: older people due to loss of osteoblast function AKA senile osteoporosis and loss of oestrogen and androgen. Incomplete filling of osteoclast resorption bay.
Secondary
Due to drugs like corticosteroids( asthma treatment), affects bone remodelling. OR due to malnutrition, space travel, lack of movement OR metabolic bone disease

Question 16

What are some modifiable risk factors for osteoporosis?

Answer 16

1. Insufficient calcium intake: recommended value for postmenopausal women is 700mg/day
2. Exercise: immobilisation of bone leads to accelarate bone loss, exercise needed to maintain bone mass.
3. Cigarette smoking: in women, smoking is correlated with increased incidence of osteoporosis

Question 17

Outline the causes and features of achondroplasia

Answer 17

Causes: inherited mutation in the FGF3 receptor gene
FGF( fibroblast growth factor) promotes collagen formation from cartilage( endochrondrial ossification affected, intramembrane ossification not affected)
Features: short stature, but normal sized head and torso AKA dwarfism as long bones cannot lengthen properly

Question 18

Describe characteristic features and functions of long bones

Answer 18

Longer than they are wider. Eg: femur, and small bones in fingers. Mostly located in apprendicular skeleton.
Function: support weight of body and facilitate movement
Require cartiilage, develop through endochondral inside cartilalge) ossification.

Question 19

Describe characteristic features and functions of short bones

Answer 19

Approximately as long as they are wide. Eg: carpals in wrists and tarsals in ankle joints
Function: provide stability and movement

Question 20

Describe characteristic features and functions of flat bones

Answer 20

Somewhat flattened, roughly parallel opposite edges. Eg: skull( occipital lobe), thoracic cage(ribs and sternum), pelvis.
Function: protect internal organs, provide large areas of attachment for muscles
Develops directly from mesenchymal tissue through intra membrane ossification

Question 21

Describe characteristic features and functions of irregular bones

Answer 21

Vary in shape and structure, but usually have complex shape.
Function: Vertebrae protect spinal cord, pelvis protects organs in pelvic cavity, provides important anchor points

Question 22

Describe characteristic features and functions of sesamoid bones

Answer 22

Embedded in tendons. Small, round bones in tendons of hand, feet, knees. Eg: patella( near knee cap), generated post natally
Function: protect tendon from stress and damage from repeat wear and tear

Question 23

What are the constituents of the bone marrow?

Answer 23

Hematopoietic cells: myeloid( creates RBC, monocytes, granulocytes and platelets) and lymphoid( creates T cells, B cells, natural killer and innate lymphoid cells)
Marrow adipose tissue: red and white
Supportive stromal cells: connective tissue

Question 24

What are the constituents of the blood?

Answer 24

Platelets
Plasma
Blood cells

Question 25

State the structure and function of bone marrow

Answer 25

semi-solid tissue found within spongy or cancellous portions of bones, produces new RBC. Stem cells can be used to treat illnesses

Question 26

What are the different kinds of blood cells? State their structure and function

Answer 26

1. Erythrocytes: no nucleus, biconcave disk, flexible-can pass through small vessels. Includse small proportion of recticulocytes, new RBC has nuc, cannot transport O2. Function- O2 transport from lungs and CO2 back. Endothelial cells in kidney sense low O2, increase erythropoietin, RBC production increase, no more hypoxia
2. Leucocytes:
   (A)granulocytes( lobed nucleus, cytoplasm with granules) and (B)mononuclear cells( normal nucleus, no granules in cytoplasm)
   (A)
   Neutrophils: pale cytoplasm, actually lysosomes with digestive enzymes. Function- phagocytosis at site of infection, process called chemotaxis. Occurs in response to other white cells singnalling. GColonySFactor increase neutrophil production, chemotaxis.
   Eosinophils: bi lobed nucleus, cytoplasm with orange granules that stain red. Ingest antigen-antibody complexes, in high levels in allergic conditions like asthma, hay fever etc.
   Basophils:granules stain blue or purple. Released into tissue at injury site- vasodilation and oedema due to hitamine and histamine prevents clotting. Both parts of basophils.
   (B)
   Monocytes: irregularly shaped nucleus, contains lysosomes. Becomes macrophages and phagocytise like in kupffer cells in liver. Return to circulation after infection subsides through lymphatic system.
   Lymphocytes: Nuclear much bigger than cytoplasm, involved in immune response to foreign materials. Contain 75% T cells that recognise antigens and kill their host cells. Also stimulate transformation of B cells into immunoblasts.

Question 27

What are the different kinds of platelets? State their structure and function

Answer 27

Cytoplasm contains alpha and dense granules.
Alpha granules: contain fibrinogen
Dense granules: contain ADP and calcium
Platelets assist in clotting. Activates prothrombin into thrombin, soluble fibrinogen to insoluble fibrin to form clot.

Question 28

Describe the structure and function of blood vessels from arteries to veins

Answer 28

Look at table in notes

Question 29

Explain the functional significance of communicating/ collateral blood vessels

Answer 29

Provide alternative path for arterial blood flow, due to tumours in arteries or blockages, or durign development. Provides protection for compormised tissues

Question 30

What is the difference between vasculogenesis and angiogenesis

Answer 30

Vasculo: formation of new blood vessels from bone marrow
eg: newly formed cancers
Angio: formation of new blood vessels from existing vessels. eg: collateral arteries

Question 31

Explain 2 possible routes of formation of vasculogenesis during embryogenesis

Answer 31

First step: production of a single vessel
Sprouting: Angiogenesis
Perictyes convert into smooth muscle cells- slow, takes hours to days, like branching off pre existing vessels
Division of primary vessel: Intussuspection
Splitting one vessel into 2, explains why arteries and veins are close together in neurovascular bundles. Quick, takes mins to hours

Question 32

Name major blood vessels of body and determine whether they are oygenated/ deoxygenated

Answer 32

Look at notes

Question 33

What are 2 connective tissue layers the bone is surrounded by?

Answer 33

Periosteum: outside
Endosteum: inside
Both vascular

Question 34

White vs red bone marrow

Answer 34

Red:
Full of developing cells, rich blood supply, only found in spongy bone. Function- haemopoiesis
Yellow: full of adipocytes, poor blood supply. Function- shock absorber and energy source, can convert to red marrow during blood loss

Question 35

Difference between immature and mature bones

Answer 35

Immature: osteocytes in random arrangments
Mature: osteocytes in concentric lamallae of osteons