Lecture 2 Flashcards
Homeostasis
Condition in which the body’s internal environment remains within certain physiological limits If the body cannot maintain homeostasis, disease occurs
Stress and homeostasis
Stress- internal or external stimuli that interrupt homeostasis External- heat, cold, loud noises, lack of atmospheric oxygen Internal- low blood glucose, increased acidity
Regulatory mechanisms to overcome stress effects: Nervous System Endocrine System
Nervous system- detects body changes and sends nerve impulses to counteract the stress effect; fast response Endocrine system- works through hormones; slower response
Regulations involved: 1. Receptor 2. Control Center 3. Effector
- Receptor - detects the changes and sends them via AFFERENT (input) pathways to the control center 2. Control Center - “thermostat” 3. Effector - recieves and executes “orders” from teh control center through EFFERENT (output) pathways i.e. Simple reflex: A pin prick to the finger activates the pain receptors which sends sensory neurons to the spinal cord (control center) which in turn sends motor neurons back to the finger (effector) to respond to the stimuli by withdrawing.
Feedback responses: Negative and Positive
Negative feedback: REVERSES the original stimulus Positive feedback: ENHANCES the original stimulus
Negative feedback example
i.e. Body temperature control Stimulus: rising body temperature Receptors: temperature sensors in the skin and hypothalamus sends information to the control center Control center: the thermoregulatory center in the hypothalamus sends commands to the effectors Effectors: sweat glands in the skin increase secretion and blood vessels in dilate (vasodilation) Response: increased heat loss through evaporation and radiation
Negative feedback: self terminating
A negative feedback process beings when a particular variable leaves the homeostatic range The process ends when that variable is back within its normal range
Positive feedback example
i.e. Blood clotting 1. Break or tear in blood vessel 2. Clotting occurs as platelets adhere to site and release chemicals 2. Released chemicals attract more platelets 4. Clotting proceeds until break is sealed by newly formed clot i.e. Labor contractions 1. Uterus contraction (labor) 2. Stretch receptors (uterine wall) 3. Control center (brain) releases oxytocin 4. Uterine muscles further contract
Positive feedback: what stops the loop?
Outside factor is required to shut off positive feedback cycle Dangerous positive feedback- i.e. fever If the body temperature rises much above 40C (104F), it may cause a dangerous feedback loop. This high temperature raises the metabolic rate, which makes the body produce more heat faster than it can get rid of it. Thus, temperature rises still further, increasing the metabolic rate and heat production still more. This “vicious circle” becomes fatal at approximately 45C (113C)
Diagnostic tools- Conventional Radiography (X-rays)
- A form of high energy radiation, 2 dimensional images
- X-rays can penetrate soft tissues of the body and darken photgraphic film on the other side
- They are absorbed, however by dense tissues such as bone, teeth, tumors, and tuberculosis nodules which leave the film lighter in these areas
- Some disadvantages of radiography are that images of overlapping organs can be confusing, slight differences in tissue density are not easily detected and x-rays can cause mutations leading to cancer and birth defects
Diagnostic tools- Computerized Tomography (CT)
formerly called a computerized axial tomographic (CAT) scan Is a more sophisticated application of X-rays 3 dimensional image The patient is moved through a ring-shaped machine that emits low intensity X-rays on one side and recieves them with a detector on the opposite side A computer analyzes signals from the detector and produces an image of a “slice” of the body, so there is little overlap of organs and the image is much sharper than a conventional X-ray CT scanning is useful for identifying tumors, aneurysms, cerebral hemorrhages, kidney stones, and other abnormalities Has virtually eliminated exploratory surgery
Diagnostic tools- Digital subtraction angiography (DSA)
A computer-assisted x-ray technique that subtracts images of bone and soft tissue to permit viewing of the cardiovascular system. radiography of blood vessels in the body after injection of contrast material
Diagnostic tools- Positron emission tomography (PET)
- Used to assess the metabolic state of a tissue and to distinguish which tissues are most active at a given moment
- The procedure begins with an injection of radioactively labeled glucose, which emits positrons (electron-like particles with a postive charge)
- When the positron and electron meet, they annihilate each other and give off a pair of gamma rays that can be detected by sensors and analyzed by computer
- The computer displays a color image that shows which tissus were using the most glucose at the moment
- PET scans are widely used to diagnose cancer and evaluate tumor status
- The PET scan is an example of nuclear medicine- the use of radioactive isotopes to treat disease or to form diagnostic images of the body
Diagnostic tools- Magnetic resonance imaging (MRI)
- The patient lies in a cylindrical chamber surrounded by a large electromagnet that creates a magnetic field 3000 -6000x as strong as the earth’s
- Hydrogen atoms in the tissues align themselves with the magnetic field
- When a field of radio waves is turned on, the H atoms absorb the additional energy and align in a different direction
- When the radio waves are turned off, the H atoms realign to the magnetic field and give off their excess energy at different rates that depend on the type of tissue
- A computer analyzes the emitted energy to produce an imageof the body
- MRI can “see” through the skill and spinal column to produce images of the nervous system
- MRI is better than the CT scan for distinguishing between the soft tissues such as the white and gray matter of the nervous system
- MRI eliminates exposure to harmful X-rays
- fMRI is a various of this technique that visualizes moment to moment changes in tissue function
Diagnostic tools- Ultrasound (Sonography)
- A handheld device held firmly to the skin produces high-frequency ultrasound waves and receives the signals that echo back from interal organs
- Not very useful for examining bones or lungs but it is the method of choice in obstetrics
- Sonography avoids the harmful effects of X-rays, and the equipment is inexpensive and portable
- Its primary disadvantage is that it does not produce a very sharp image
