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Chapter 1 Lecture Notes page 1 I. Homeostasis A. definition and example definition: homeostasis is the maintenance of a relatively stable internal environment example: Your body temperature stays very close to 98.6ºF (37ºC ) whether the room temperature is 72ºF (22.2ºC) or 105ºF (40.5ºC) What are some examples of body conditions that must be kept stable? B. components of a homeostatic control mechanism 1. receptors - cells or organs that monitor and detect changes in the environment (internal and external) 2. set point - a normal value or range of values within which the condition has to remain for the body to work correctly 3. control center - set of cells or organ that a. compares input from receptors to the set point to see if there is a discrepancy b. if a discrepancy exists, directs the effectors to make adjustments to the controlled condition 4. effectors - cells, tissues or organs that can change the controlled condition 5. feedback - information that tells the sensors and control center when the set point has been reached changes in output from the effectors are used by the system to determine further action: if the set point has not been reached, then the effectors continue to produce output if the set point has been reached, then the effectors stop producing output BIOL 2404 Strong/Spring 2007 Chapter 1 Lecture Notes page 2 C. types of homeostatic regulation 1. negative feedback a. if a controlled condition deviates from normal, this mechanism returns it to the set point b. negative feedback provides stable, long-term control c. it is the most common type of control mechanism in the body d. examples: body temperature, blood pressure, blood glucose 2. positive feedback a. causes rapid and extreme change in the controlled condition b. important for processes that must be completed rapidly c. temporary d. examples: blood clotting, labor D. how a homeostatic regulation mechanism works: controlled condition = body temperature deviation = hypothermia sensors = thermoreceptors in hypothalamus set point = ave. 37ºC (98.6ºF); range = 36.7 to 37.2ºC control center = hypothalamus effector output: shivering in skeletal muscle constriction of blood vessels in skin increased body temperature feedback BIOL 2404 Strong/Spring 2007 Chapter 1 Lecture Notes page 3 II. Anatomical Concepts A. anatomical position 1. upright (standing) 2. hands at sides, palms forward 3. left and right always refer to the subject, never to the observer B. directional terms front of the body back of the body towards upper part of the body towards lower part of the body towards midline of the body away from midline of the body towards an attached base away from an attached base on or nearer to the surface farther away from the surface C. planes of section 1. sagittal - splits the body into left and right sections midsagittal, median - splits body into equal left and right sections along the longitudinal midline 2. transverse - splits the body into upper and lower sections 3. frontal - splits the body into front and back sections coronal - a frontal section in the head or brain BIOL 2404 Strong/Spring 2007 Chapter 1 Lecture Notes page 4 D. body cavities and membranes 1. dorsal a. cranial walls = cranial bones contents = brain b. spinal walls = vertebrae contents = spinal cord there are connective tissue membranes called meninges surrounding the organs in the dorsal cavity BIOL 2404 Strong/Spring 2007 Chapter 1 Lecture Notes page 5 2. ventral a. thoracic the lungs are located in the lateral thoracic cavity the space between the lungs is called the mediastinum - it is not a cavity the heart is in the inferior mediastinum the thoracic cavity is separated from the abdominopelvic cavity by the diaphragm walls = ribs, muscles, vertebrae, diaphragm contents = lungs, heart, blood vessels, trachea, esophagus b. abdominopelvic abdominal - above the pelvic brim pelvic - below the pelvic brim walls = abdominal muscles, diaphragm, vertebrae contents = stomach, liver, intestines BIOL 2404 Strong/Spring 2007 Chapter 1 Lecture Notes page 6 3. epithelial membranes line the ventral cavities and cover organs in the ventral cavities a. pleura (noun singl.), pleurae (noun plural), pleural (adjective), visceral layer covers surface of lungs parietal layer lines part of inside of thoracic cavity the pleural cavity is between the visceral pleura and parietal pleura the lungs are not inside the pleural cavity, they are surrounded by it the pleural cavity contains a thin layer of fluid b. pericardium (noun singl.), pericardial (adjective) visceral layer covers surface of heart parietal layer forms a sac surrounding the heart the pericardial cavity is between the visceral pericardium and the parietal pericardium the heart is not inside the pericardial cavity, it is surrounded by the cavity the pericardial cavity contains a thin layer of fluid BIOL 2404 Strong/Spring 2007 Chapter 1 Lecture Notes page 7 c. peritoneum (noun singl.), peritoneal (adjective) visceral layer covers surface of many organs parietal layer lines part of inside of abdominal wall double layers of peritoneum called mesenteries support organs within the cavity the peritoneal cavity is between the visceral and parietal peritoneum the organs are not inside the peritoneal cavity, they are surrounded by it the peritoneal cavity contains a thin layer of fluid BIOL 2404 Strong/Spring 2007