Vertebral column has 12 thoracic vertebrates. The joints between adjacent vertebrae is cartilaginous joint which permits limited movements. Progesterone is secreted by corpus luteum which supports pregnancy in females. Joints between adjacent vertebrae are cartilaginous joints and the opposing surfaces are connected by fibrocartil age which allows very little movement. Osteoporosis is a disease characterized by low bone mass and loss of bone tissue that may lead to weak and fragile bones. Osteoporosis occurs when there is an imbalance between new bone formation and old bone resorption. Generalized osteoporosis is common in elderly people and in women following menopause. In osteoporosis, the osteoblastic (bone forming) activity in the bone usually is less than normal and consequently the rate of bone deposition is depressed. Oestrogens inhibit osteoclastic (bone resorption) activity in the bones and therefore stimulate bone growth.After menopause, almost no oestrogens are secreted by ovaries. This oestrogen deficiency leads to increased osteoclastic activity in the bones, decreased bone matrix and decreased deposition of bone calcium and phosphate. In some women, this effect result in osteoporosis.
(i) Flagella of choanocytes maintains a regular current of water in the body (sponges).
(ii)Performs locomotion in euglenoids and other flagellarprotists (Chlamydomonas), sperm, etc.
(iii) Helps in the circulation of food.
(iv) Flagellate choanocytes brings about the circulation of water in the canal system of sponges