Week 10 Flashcards
What are the key functions of the skeletal system?
- protects internal organs: Brian and lungs
- facilitates movement: skeletal muscle, tendon, ligament, cartilage
- supports body
- stores and releases fat: bone marrow
- stores and releases minerals: Ca2+, PO4,3-
- produces blood cells
What is the axial skeleton comprised of?
- skull
- vertebrae of spine
- thoracic cage (ribs and sternum)
what is the appendicular skeleton comprised of?
- upper and lower limbs
- pelvis
- pectoral girdle (shoulder)
What are the key components of the connective tissue?
- cells - small volume
- extracellular matrix
- fibres eg. collagen, elastin
- ground substance (gel between fibres) - organic matrix in bone
What is the ground substance comprised of?
portroglycan - fills space between fibres, provides swelling pressure
glycosaminoglycan
water and electrolytes, contributes to swelling pressure
What are the two types of connective tissue?
loose, dense (skeletal tissues are dense connective tissues)
What fires are there in connective tissue?
- collagen (29 diff types), most abundant protein in body, provides tensile strength, helical
- Elastin, allows to recoil after stretch, mesh
What is the structure of the bone?
- cortical bone (very dense): outer layer- periosteum, inner layer- endosperm
- spongy bone (less dense)
- bone marrow
What are the two types of bone marrow?
red - site of production of blood cells
yellow - fat storage site
- proportion changes w age, red decreases
Explain the different type of bone cells
outside: osteogenic cells (stem cell)
route 1: differentiate into osteoblast - line surface of bone, creates ECM, lays down minerals, surround themselves with bone besides leaving small channels
route 2: differentiate into osteocytes - sense nature of bone in terms of how they respond to leading, signal other cell types to make/ break
osteoclasts - distinct form the rest, further in
What is the origin of osteoblasts and chondrocytes?
mesenchymal stem cells
what is the origin of osteoclasts?
hematopoietic stem cells
What are the two types of bone formation?
interamembranous
endochondral
How does intra-membranous ossification work?
- directly from undifferentiated mesenchymal connective tissue
- occurs only in some bones: skull, flat bones of face, clavicle (collarbone)
How does endochondral ossification work?
- via cartilage intermediary
- occurs only in most bones (except skull, collarbones)
- growth plate
What are the zones of the growth plate?
outside to inside
- reserve zone
- proliferative zone
- hypertrophic zone (cells get larger)
- calcification (mineralised cartilage, cell death)
- ossification (mineralised cartilage remodelled to form bone)
What does the growth plate allow for?
growth of bone length
How does bone formation occur for fracture healing?
- directly building new bone onto fracture site (direct or contact healing)
- heal in a process similar to endochondral ossification - via cartilage intermediate (intermediate healing)
control of bone maintenance
bone formation (osteoblast activity - reduces blood Ca2+)
bone resorption (osteoclast activity - increased blood Ca2+)
also impacts on growth plate - bone elongation
Why is it so important to maintain blood Ca?
too little
- muscle twitching/ spasm
- numbness
- paresthesia
too much
- thirst/ frequent urination
- digestive distress
- bone pain
- muscle weakness
- fatigue
- cardiac arhythmia
- kindey stones
-> needs a higher conc inside to trigger depolarisation, if conc is too similar its harder, if conc is too steep, too easy -> spasm
What hormones are involved in control of bone maintenance?
- GH - anterior pituitary - increases length, improves density
- Thyroxine -thyroid - stimulates bone growth, promotes synthesis if bone matrix
- calcitriol (vitD) - stimulates osteoclast proliferation, resorption of bone by osteoclasts
- calcitonin - thyroid - inhibits osteoclast activity and stimulates calcium uptake by bones
What does Wolff’s law state?
form follows function
What does mechanical strain lead to?
- re-distribution of Ca2+ between the blood and bone tissue
How does mechanotransduction in the bone work?
- mesenchymal stem cells
-> osteoblasts
-> osteocytes
-> intern, primary cilium, piezo1 channel
Explain the effect of growth hormone on bone maintenance
- somatotropin
- produced by pituitary, increases muscle mass, fat, radial bone growth
- liver produces insulin like growth factor 1(IGF-1) -> -ve feedback, decrease of GH
What is the difference in effect of GH in youth and adults?
youth: growth plate sill open, adds to length and thickness
adulthood: growth plate closed, adds to thickness
Explain the effect of thyroxine on bone maintenance
- no targeted effect on bone tissue, but general metabolic effects on all tissue
- promotes release of GH through positive feedback of pituitary
Explain the effect of sex hormones on bone maintenance
- promotes bone formation/ maintenance of bone density
- promotes closure of growth plate
- oestrogen in females
early growth plate closure - reduced bone length
reduction at menopause leads to loss of bone density
What are the combined actions of androgens and estrogen?
- increased trabecular mineral and thickness
- increased cortical thickness
- increased periosteral expansion
Explain the effect of vitamin D on body maintenance
- vit D3 = steroid hormone
- 7-dehydrocholesterol (via skin) -> ergocalcipherol (pre-D3) -> cholecalciferol + food intake -> via liver, kidney and parathyroid hormone -> calcitriol active vitamin D3
functions of vitamin D
- facilitates intestinal absorption of calcium (also phosphate and Mg2+)
- vit D binds to intracellular receptor - VDR + Vit D binding site, VDR also has DNA binding site
- complex of VD3-VDR bound to DNA stimulates expression of a number of proteins
-> calc transporters (calbindin)
-> bone matrix proteins (osteocaclin)
-> suppresses synthesis of type 1 collagen
What homines are in the thyroid/ parathyroid produced?
- calcitonin
- parathyroid hormone
What is the function of bone tissue?
Ca2+ reservoir
Describe the pathway for too little Ca2+
- more PTH
- more osteoclasts
- more ca 2+ uptake from blood stream
- more cholecalcipherol
- more cacitriol in liver
- more intestinal uptake
Describe the pathway for too much Ca2+
- positive feedback for CT
- positive feedback for osteoblasts
- negative feedback for osteoclasts
- osteoblasts increase uptake of Ca2+ from bone tissues
name two different bone- related disorders
- osteoporosis
- porous bones
- aging- related
- increased osteoclast activity - osteochondrosis
- abnormal growth plate
- typically in childhood and adolescence
