Respiratory System - POSSIBLE QUESTIONS
What
are the three mechanisms by which the body uses oxygen reserves in order to
supply tissues under stress? What are the types of abnormalities present in
oxygen levels in blood and tissues?
Three
mechanisms are:
v
Pulmonary reserve > increased pulmonary
ventilation and recruiting more alveolus and capillaries mean more blood is
oxygenated and therefore greater supply to tissues
v
Circulatory reserve > increase cardiac
output and decrease TPR means more blood can perfuse tissues and therefore more
oxygen supply.
v
Erythropoetin reserve > this hormone is
released by the kidney in cases of low oxygen, which stimulates increased
production of red blood cells > more Hb present therefore more oxygen can be
carried to the tissues
The
types of abnormalities are:
v
Hypoxic hypoxia > deals with impaired
oxygen transport to pulmonary capillaries
v
Anemic hypoxia > Hb concentration is
lower than normal > may be due to reduced number of Hb, reduced number of
blood cells, rendered useless > binding of carbon monoxide, oxidation of iron
2= to Fe 3+
v
Ischemic hypoxia > usage of oxygen is
greater than availability
v
Histotoxic
hypoxia > not able to use the given amounts of oxygen
Briefly
explain the neural influences on the respiratory rate. What other influences are
present.
The
medullary rhythmicity center accounts for the breathing rhythm established.
There are a number of neural influences which affect this rhythm which will be
explained below. These influences can be separated into descending pathways and
ascending pathways.
Descending
pathways include areas of the brain, mainly the hypothalamus and cerebral
cortex. The hypothalamus can have influences on the respiratory rhythm. The
hypothalamus has a thermoregulatory center and hence can control the body
temperature. Generally, an increase in temperature causes an increase in
ventilation. The hypothalamus also controls the emotions of an individual. For
example: rage, fear anxiety and excitement all cause an increased ventilatory
response. Lastly, the hypothalamus is responsible for the release of several
hormones from the pituitary gland. These hormones can indirectly have an effect
on the ventilatory response. For example: thyroid gland and progesterone act to
increase respiration.
The
cerebral cortex can also have an effect on the voluntary control of breathing.
We all know that we can hold our breath or hyperventilate when required and
these are due to the voluntary pathways. The voluntary pathways bypass the
respiratory centers and directly synapse with the respiratory motoneurons. This
means that they can directly act in order to produce the ventilation. These
pathways travel along the lateral spinal columns of the corticospinal tracts.
There
are ascending pathways which have an effect on the ventilation rate. These are
peripheral receptors located in muscles and joints. These receptors are called
proprioceptors and are located within skeletal muscles and also in and around
joints. An increase in activity of these receptors brought about by the
increased levels of exercise, means signals are sent to the medullary
rhythmicity center and as a result cause a change in breathing pattern.
Also
there a variety of inputs located on the surfaces of lungs and respiratory
passageways. The three main types are airway irritant receptors, pulmonary
stretch receptors and pulmonary J receptors. The airway irritant receptors are
located on the epithelial surfaces of the respiratory passageways and are
activated response to increased distension of the passageways and presence of
certain chemical agents such as histamine. The pulmonary stretch receptors are
located within the connective tissue of the lungs and therefore are activated
when the lung is stretch, mainly during inspiration. They send inhibitory
signals to the inspiratory neurons and initiate expiration, known as phase
switching and this is known as the herrings breuer reflex. Also there are
pulmonary J receptors located within alveolar walls and these respond to
increased lung congestion and pulmonary odema.
The other type of factor that brings about changes in respiration are chemical factors, such as concentration of oxygen and/or carbon dioxide, and presence of chemo receptors (central and peripheral).