BIOL 1140 1st Edition Lecture 25Outline of Last LectureI. The Muscular SystemII. Muscles Attached to Bones by TendonsIII. Muscle StructureIV. Muscle ContractionV. Regulation of Muscle ContractionVI. Muscle PlasticityOutline of Current LectureI. Functions of the Skeletal SystemII. 3 Types of Connective TissueIII. Structure of BoneIV. What Holds Bones Together?V. Cartilage is Found on Ends of BoneVI. Calcium HomeostasisVII. Bone Plasticity and RepairCurrent Lecture I. Functions of the Skeletal Systema. Support: supports soft tissues, gives structural framework and shape to bodyb. Protection: protects brain, spinal cord, heard and lungsc. Movement: determines range and direction of motioni. Joints mediate how bones can moved. Blood cell formatione. Mineral storage and homeostasis:i. Calcium and phosphate1. Recall that calcitonin and PTH regulate blood calcium levelsII. 3 Types of Connective Tissuea. Bonesb. Ligamentsc. Cartilaged. Why is bone connective tissue?i. Low density of cellsii. Scattered in an extra-cellular matrixiii. Fibers are made of proteins, mainly collagen1. Also main component of ligaments and cartilage2. Most abundant proteinThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.III. Structure of Bonea. Sometimes we think of bones as being deadb. What happens if you break a bone?i. Painii. Bleedingc. Bones are definitely alive and have plasticityd. Bone cells (osteocytes) are distributed in a matric made of mineralsi. Calciumii. Magnesiumiii. Phosphateiv. Collagene. Arranged in concentric ring pattern called osteons (also called Harversian systems)f. Central canals contain blood vesselsg. Osteocytes are in hollow chambers called lacunaeh. They have long extensions of membrane and cytoplasm in canaliculi channelsi. Adjacent cells connected by gap junctionsi. Allows diffusion of nutrients, etc. from blood vessels of central canalj. Long bones have a shaft called Diaphysis and knobby ends called Epiphysisi. Diaphysis contains yellow bone marrow (mostly fat)ii. Epiphysis contains spongy bone and red bone marrow (makes blood cells)k. Periosteum layer around outside contains bone-making cells called osteoblastsl. Central canals of compact bone contain blood vessels and nervesi. This explains why we experience pain and bleeding if we break a boneIV. What Holds Bones Together?a. Ligaments hold 2 bones to each otheri. Made of densely packed collagen fibers all oriented in same direction1. Very stiff, not stretchy2. A stretch or tear of a ligament is a spraina. Slow healing because there aren’t many cells or blood vessels in ligamentsb. Tendons connect muscles to bones, and therefore also help hold bones togetherV. Cartilage is Found on Ends of Bonesa. Cartilagei. Formed by cells called chondroblasts and made of secreted collagen and elastinproteinsii. Found where support under pressure is importantiii. Reduces friction where movement between bones occurs1. Osteoarthritis occurs when cartilage wears down and bones rub against each othera. Painful, can cause bone spurs to formVI. Calcium Homeostasisa. Thyroid gland produces calcitonini. Lowers blood calciumb. Parathyroid glands produce parathyroid hormone (PTH)i. Raises blood calciumc. Optimal blood calcium is 10mg/100 ml for normal function of Nervous System and Musclesi. Symptoms of low blood calcium are numbness, tingling, lethargy, and mental confusion, muscle crampsii. Detected by parathyroid gland1. Releases PTH2. Activates osteoclasts to break down bone and release calcium into blood3. High blood calcium causes thyroid gland to release calcitonina. Osteoblasts deposit calcium in boned. Osteoporosis is caused by an imbalance of osteoclasts and osteoblastsi. Men and women start to lose bone mass after age 35, about .4% per yearii. Postmenopausal women lose 2-3% per year for about a decade after menopause1. Recommended 1000-1500 mg calcium/day2. Do weight-bearing exerciseVII. Bone Plasticity and Repaira. New bone is made at a greater rate in regions that are under greater stressi. Bone thickness has been measured in professional athletesb. Bones can change in shape, size, and strengthi. Compression stress causes electrical current in boneii. Stimulates osteoblasts to form new bone in the area under greatest stressiii. Osteoclasts dissolve bone in areas not under stressiv. Exposure to compressive forces is reflected in shape of bonesc. Bone reshaping has been used by past societiesi. Egyptian and Mesopotamian skeletons with elongated skullsii. Ancient Mayans applied force to shape children's headsiii. Feet of girls in china from 900-191 were broken with hammers and tightly wrapped with bandages to change their