M, M, M, M Essay

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SK277 TMA 02 Question 1 1A. GRH (growth hormone – releasing hormone) stimulates the secretion of growth hormone from the anterior pituitary, targeting the liver. From this IGF-1 is secreted by the liver. 1B. Paracrine actions – Paracrine signalling molecules act locally, exerting affects on cells close by Endocrine actions – the signalling molecules are secreted by endocrine cells and released into the bloodstream to act on target cells. Looking at IGF-1 specifically in an endocrine way, it would be secreted by the liver and transported to target cells via the bloodstream such as to growth plates of bone. An example of IGF-1 functioning in a paracrine way, is when it is secreted by proliferating cartilage cells in bone growth, acting locally without entering the bloodstream. 1C. Calcium, Magnesium and Phosphates are the minerals making up the majority of bone tissue. Their general structural purpose is for bone strength. 1D. Bone is an active living tissue, which is being constantly broken down, built up and remodelled. When we are born the human embryo skeleton is initially made up from cartilage. From the 7th week of development, bone formation will begin in a process known as ossification. Slowly the older cartilage will be replaced with harder bone tissue. To do this requires specialized cells called osteoblasts. Osteoblasts secrete collagen to form a framework of fibres within spaces where by calcium; magnesium and phosphates, which make up the majority of bone tissue can be deposited. This process is known as calcification and gives bone its hardness. The original osteoblasts will then get trapped in the new bone, which has formed and mature into what is known as osteocytes where further cell division is not possible. When a bone is fully formed it will be made up from compact bone in the middle, which is more dense and spongy bone,

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