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Flashcards in Ch1-P16-24End Deck (24):

Reference man?

  • Healthy male
  • 22 years old
  • weight 70kg
  • living at 20 degrees celsius
  • engaging in light physical activity
  • consuming 2,800 kilocalories per day or 11,700 joules


Reference woman?

  • Healthy female
  • 22 years old
  • weight 58kg
  • living at 20 degrees celsius
  • engaging in light physical activity
  • consuming 2,000 kilocalories per day or 8,400 joules



The body's ability to detect change, activate mechanisms that oppose it, and thereby maintain relatively stable internal conditions.


Who observed that the internal conditions of the body remain quite constant even when external conditions vary greatly?

French physiologist Claude Bernard (1813-78)


Who coined term homeostasis?

American physiologist Walter Cannon (1871-1945)


What range does the human body temperature stay?

36-37 degrees celsius


the internal state of the body is best described as?

Dynamic equilibrium (balanced change) in which there is a set point or average value and conditions fluctuate around this point.


Negative feedback?

Keeps a variable close to its set point. The body senses a change and activates mechanisms that negate or reverse it, maintaining stability and health.


Feedback loops?

The section of a control system that allows for feedback and self-correction and that adjusts its operation according to differences between the actual output and the desired output.


How is body temperature regulated?

A group of nerve cells at the base of the brain. One heat losing mechanism is vasodilation (widening of blood vessels of the skin) which causes blood to flow closer to the bodies surface and losing heat to the environment. Sweating occurs if this is not enough.
Vasoconstriction narrows blood vessels in the skin to keep warm and if that doesn't work the body shivers (muscle tremors) to generate heat.


How is blood pressure controlled?

If blood pressure drops in an area of the body then baroreceptors (sensory nerve endings in the large arteries near the heart) detect the imbalance and send signals to the cardiac centre that regulates heart rate. The heart speeds up fixing the blood pressure imbalance. This reflexive correction of blood pressure is called baroreflex.


Three common components of a feedback loop?

  1. Receptor - senses change in the body.
  2. Integrating (control) centre - processes the information and makes a decision on what to do.
  3. Effector - cell or organ that carries out the final corrective action.


Positive feedback?

A self-amplifying cycle in which a physiological change leads to even greater change in the same direction, instead of producing the corrective affects of negative feedback. Positive feedback is often a normal way of producing rapid change. Ie in childbirth.
However sometimes positive feedback can be harmful or life threatening, ie during fever.


Explain positive feedback during childbirth?

Fetus head pushes on cervix stimulating nerve endings sending nerve signals to the brain which stimulates pituitary gland to secrete hormone oxytocin which travels in the blood and stimulates the uterus to contract. This pushes fetus downward, stimulating the cervix more and causing a positive feedback.


Explain positive feedback of fever?

Fever caused by infection is helpful to a point but if the temperature continues to rise it can cause dangerous positive feedback.


During fever at what temperature is it fatal?

45 degrees celsius



Examining body with X-rays. Records dense tissues such as teeth, bone, tumours etc. The image is called radiograph. Hollow organs can be visualised by a radiopaque substance that absorbs X-rays. Ie Barium sulfate can be drunk to examine oesophagus,  stomach, small intestine etc. Can do same by injection, ie angiography to see blood vessels.
Disadvantages - overlapping images can be confusing, slight differences in tissue density can't be easily detected and X-rays can cause mutations leading to cancer and birth defects.



Computed Tomography (CT) puts patient in ring shaped machine that emits low intensity X-rays and receives them with a detector on the opposite side. Produces thin slice that can be stacked to produce 3D image of the body. Sharper image than conventional X-ray. Virtually eliminated exploratory surgery.


CT image (picture)



Positron Emission Tomography. Tomography means imaging by sections or sectioning. So, PET is used to assess the metabolic state of a tissue and to distinguish which tissues are most active at a given moment.
Radioactive glucose is injected which emits positrons. When electrons and positrons meet they annihilate each other giving off a pair of gamma rays that can be detected by sensors and analysed by the computer, displaying a colour image showing which tissues were using the most glucose at the time. This is nuclear medicine and it can show heart problems, tumours, and cancer. PETs use same machine as CT.



Magnetic Resonance Imaging (MRI). Patient lies in cylindrical chamber surrounded by a large electromagnet creating strong magnetic field. The hydrogen atoms align in different ways giving off energy at different rates depending on the tissue to create an image. It can distinguish between white and gray matter of the nervous system and eliminates harmful X-ray exposure.


MRI scanner picture



Functional MRI shows moment to moment changes in tissue function. Ie shows shifting patterns of brain activity.



Handheld device held firmly to skin produces high-frequency ultrasound waves and receives the signals that echo back from the internal organs. Not good for bones and lungs but good for obstetrics disadvantage is that image is not very clear. Ultrasound.