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Unit 1: Day 2 Topics: Chapter 1 Introduction to Human A & P (finish) Homeostasis (continued) General Body Plan Homeostasis Maintained by negative-feed back mechanism. Negative-feed back does not prevent variation but maintains variation within a normal range. Negative-feedback Usually 3 components: Receptor-monitors the value of variable such as blood pressure Control center-often part of the brain, which establishes the set point around which the variable is maintained. Effector or effector organ -changes the value of the variable. Blood pressure depends in part on HR (contraction). Thermostat example In order to keep the temperature in your house at the right level, the thermostat must first measure the current temperature in the house. After the thermostat measures the temperature, it compares the current value to a preset standard value. If there is no difference then there’s nothing to do. But…if it’s too hot or too cold, the thermostat has to send a signal to the furnace or air conditioner to change the temperature of the house so that it equals the standard value and then it will shut off. Homeostasis Definition: Maintenance of a dynamically stable internal environment Let’s Review. In the previous example we had a: 1. 2. 3. 4. 5. Variable temperature Measuring implement thermostat Control center also the thermostat A preset or standard value for the variable Effectors the air conditioner and furnace Similar situations arise in the human body where there are lots of variables that are maintained at certain precise levels Blood Pressure BP is a variable that we’ve got to maintain at a certain level Sensory receptors measure the BP in the body. They’re located in the aorta (the big blood vessel coming out of the heart) and in the carotid arteries (the large vessels that bring blood to the brain). These pressure receptors measure BP and then send the info (i.e., input) to a control center in the brain – the particular BP control center is in the medulla oblongata of the brain Blood Pressure The connection b/w the receptor and the control center is called the afferent pathway. In the control center, the input BP is compared with a set value. If there is a difference between the current BP value and the reference BP value then a discrepancy is detected. And the body will work to correct the discrepancy (i.e., bring the value of the variable back to normal)! Blood Pressure The control center will signal effector organs – such as the heart, in this case, to alter its activity. This process is called output. The connection b/w the control center and the effector organ is called the efferent pathway. Blood Pressure Suppose the current BP is too high. The effector must act in a way to decrease BP so the medulla oblongata (the control center) would signal the heart to decrease the force and rate of its contractions; this would decrease BP towards normal. Notice that the original stimulus was an Increase in BP and the body’s response was to act so as to Decrease BP. Note: The stimulus is opposite the response! Negative Feedback B/c the movement of a variable in one direction causes the body to enact processes that cause the variable to move in the opposite direction (so as to return the value toward the correct level) – it is called negative feedback Let’s look at BP again: Increased BP Sensed by pressure receptors in aortic arch and carotid sinus Input sent via afferent pathway to medulla oblongata BP DECREASES Heart rate & force of contraction decrease Blood vessel diameter increases Output sent along efferent pathway to heart and blood vessels Current BP compared with set point and discrepancy is detected Why is Negative Feedback so common in the body? Think about it! Every time a variable starts changing too much, the value of the variable is brought back toward normal (i.e., the body implements a process to counteract its change). THAT’S NEGATIVE FEEDBACK Other examples you will encounter: Maintenance of blood [Ca2+], blood [Glucose], blood pH, and many others When does a negative feedback process end? • A negative feedback process begins when a particular variable fluctuates from the set point. • The process ends when that variable is returned back to homeostasis. • Negative feedback processes (or loops) are self-terminating. MAKE SURE YOU UNDERSTAND WHY! Homeostasis is Important! Most of the physiological processes that occur in your body are designed to maintain homeostasis. ALWAYS KEEP THIS IN MIND! Question: Does the magnitude (i.e., size) of the error signal influence the magnitude of the response? Just to recap, let’s look at a couple more figures! Pancreas Homeostasis is DYNAMIC! What this means is that the homeostatic variables are NOT kept rigidly fixed upon a single value. They are kept within a certain range, and when they exit that range – that’s when negative feedback loops turn on to bring them back. Is your body temperature always exactly 98.6F? What about Positive Feedback? Positive feedback occurs when the response amplifies or magnifies the stimulus that produced it. In other words, a variable is altered and then the body’s response alters that variable even more in the same direction. How does this differ from negative feedback? Do you remember which is the most common in the body: positive or negative feedback? Positive-feedback Not homeostatic (rare), often times detrimental Positive implies that when a deviation from a normal value occurs, the response of the system is to make the deviation even greater. Birthing process operates under these conditions Positive Feedback in Childbirth Positive Feedback in Blood Clotting Dangerous Positive Feedback Rise in body temperature Increase in body heat production Increase in body metabolism What stops a positive feedback loop? Water, water and more H2O! About 60% of the human body is water 2/3 of this water is found within your cells so we refer to it as intracellular fluid (ICF) The other 1/3 is outside your cells so we call it extracellular fluid (ECF) The 2 main types of ECF are: 1. 2. The fluid that surrounds the cells – the tissue fluid or interstitial fluid Blood! Minor types of ECF include cerebrospinal fluid and intraocular fluid Related Fields of Study Obviously, anatomy and physiology come under the umbrella of biology – the study of life. An incredibly integral field is pathology – the study of disease. Another important field is embryology, the study of how a single zygote (i.e., a fertilized egg) turns into a fully-functioning human with trillions of cells. CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. General Body Plan includes cavities, membranes, and organ systems. cavity = space within the body membrane = sheet of tissue which lines cavities CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2 major cavities - dorsal cavity (posterior) houses brain & spinal cord - ventral cavity (anterior) houses viscera (internal organs) CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Dorsal cavity subdivisions - cranial cavity = houses brain -vertebral column= houses spinal cord - meninges = membranes lining brain & spinal cord CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ventral Cavity consists of 2 compartments divided by diaphragm (muscular sheet) 1. thoracic cavity (c) = divided by the mediastinum (space) 2. abdominopelvic c. = divided into pelvic and abdominal cavities Thoracic Cavity Subdivisions: - mediastinum = thymus, trachea, esophagus, & heart (pericardial c.) - pleural cavities = lungs Thoracic & Abdominopelvic membranes Types of membranes - parietal membrane = lines walls of c. - visceral membrane – covers organs Thoracic membranes Thoracic membranes - parietal pleural membrane - visceral pleural membrane - parietal pericardial membrane - visceral pericardial membrane Abdominopelvic membranes Abdominopelvic membranes - parietal peritoneal membrane - visceral peritoneal membrane CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Head Cavities Oral cavity Nasal Cavity Orbital cavities (eyes) Middle ear cavity Body Plan Anatomical position: standard body position - standing erect - hands at sides - palms forward - feet flat on floor - facing observer Supine - lying down in anatomical position CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Terms Universal terms which describe position of one body part relative to another Terms are paired as opposites & include: superior/ inferior medial/ lateral proximal/ distal posterior/anterior superficial/ deep CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Terms 1. superior & inferior -superior above, closer to head - inferior below, closer to feet CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Terms 2. medial & lateral -medial toward midline (imaginary line down middle of body) - lateral away from midline CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Terms 3. proximal & distal - proximal nearer to trunk of body or pt. of attachment (used w/ parts of limbs) - distal further away form trunk or pt. of attachment. CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Terms 4. posterior & anterior - posterior (dorsal) toward back surface - anterior (ventral) toward the front surface CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Anatomical Terms 5. superficial & deep - superficial near the surface - deep away from body surface CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge Which is the branch of science that studies structure? function? The thigh is ______ to the foot. Another term for dorsal is? The lips are ______ to the teeth. CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge 5. Which of the following list the structural levels from simplest to most complex? tissues, chemical, organismic, organs chemical, tissues, systems, organs chemical, tissues, organs, systems organismic, systems, tissues, organs CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge 6. The term(s) that apply to the front of the body when in anatomical position? posterior, dorsal medial, lateral back, front anterior, ventral CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge 7. The cranial and spinal (vertebral) cavity are found in the: Ventral cavity Thoracic cavity Dorsal cavity Abdominopelvic cavity CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge 8. The mediastinum is the region between the: Thoracic & two pleural cavities Thorax and abdomen Heart and pericardial membrane Lungs CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge 9. The membrane which covers the lungs is called: Parietal pleural membrane Visceral pleural membrane Pleural lung membrane Visceral peritoneal membrane CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Test Your Knowledge 10. The diaphragm, a muscular sheet, which divides the ventral cavity into a superior _____cavity and an inferior ______ cavity. CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Body Sections & Planes: Plane = imaginary line which divides the body into sections (3 body planes) 1. sagittal plane = vertical plane, producing left & right sides CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Body Sections & Planes: 2. coronal (frontal) plane vertical plane producing anterior (front) and posterior (back) body portions CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display. Body Sections & Planes: 3. transverse (horizontal) plane producing superior (top) & inferior (bottom) portions CopyrightThe McGraw-Hill Companies, Inc. Permission required for reproduction or display.
