Homeostasis and Gas Exchange
Homeostasis is maintained by the respiratory system in two ways: gas
exchange and regulation of blood pH. Gas exchange is performed by the
lungs by eliminating carbon dioxide, a waste product given off by
cellular respiration. As carbon dioxide exits the body, oxygen needed
for cellular respiration enters the body through the lungs. ATP,
produced by cellular respiration, provides the energy for the body to
perform many functions, including nerve conduction and muscle
contraction. Lack of oxygen affects brain function, sense of judgment,
and a host of other problems.
Gas Exchange
Gas exchange in the lungs is between the alveolar air and the blood
in the pulmonary capillaries. This exchange is a result of increased
concentration of oxygen, and a decrease of C02....
External Respiration
External respiration is the exchange of gas between the air in the
alveoli and the blood within the pulmonary capillaries. A normal rate
of respiration is 10-20 breaths per minute. In external respiration,
gases diffuse in either direction across the walls of the alveoli.
Oxygen diffuses from the air into the blood and carbon dioxide diffuses
out of the blood into the air. Most of the carbon dioxide is carried to
the lungs in plasma as bicarbonate ions (HCO3-). When blood enters the
pulmonary capillaries, the bicarbonate ions and hydrogen ions are
converted to carbonic acid (H2CO3) and then back into carbon dioxide
(CO2) and water. This chemical reaction also uses up hydrogen ions. The
removal of these ions gives the blood a more neutral pH, allowing
hemoglobin to bind up more oxygen.
Internal Respiration
Internal respiration is the exchanging of gases at the cellular level.
The Passage Way From the Trachea to the Bronchioles
There is a point at the inferior portion of the trachea where it
branches into two directions that form the right and left primary
bronchus. This point is called the Carina which is the keel-like cartilage plate at the division point. We are now at the Bronchial Tree.
It is named so because it has a series of respiratory tubes that branch
off into smaller and smaller tubes as they run throughout the lungs.
Right and Left Lungs
Diagram of the lungs
The Right Primary Bronchus is the first portion we come to, it then branches off into the Lobar (secondary) Bronchi, Segmental (tertiary) Bronchi, then to the Bronchioles
which have little cartilage and are lined by simple cuboidal epithelium
(See fig. 1). The bronchi are lined by pseudostratified columnar
epithelium. Objects will likely lodge here at the junction of the
Carina and the Right Primary Bronchus because of the vertical
structure. Items have a tendency to fall in it, where as the Left
Primary Bronchus has more of a curve to it which would make it hard to
have things lodge there.
The Left Primary Bronchus has the same setup as the right with the lobar, semental bronchi and the bronchioles.
The lungs are attached to the heart and trachea through structures that are called the roots of the lungs.
The roots of the lungs are the bronchi, pulmonary vessels, bronchial
vessels, lymphatic vessels, and nerves. These structures enter and
leave at the hilus of the lung which is "the depression in the
medial surface of a lung that forms the opening through which the
bronchus, blood vessels, and nerves pass" (medlineplus.gov).
There are a number of terminal bronchioles connected to respiratory bronchioles which then advance into the alveolar ductsalveolar sacs. Each bronchiole terminates in an elongated space enclosed by many air sacs called alveoliAlveolar Macrophages, they ingest any microbes that reach the alveoli. The Pulmonary Alveoli are microscopic,
which means they can only be seen through a microscope, membranous air
sacs within the lungs. They are units of respiration and the site of
gas exchange between the respiratory and circulatory systems. that then become which are surrounded by blood capillaries. Present there as well, are
Cellular Respiration
First the oxygen must diffuse from the alveolus into the
capillaries. It is able to do this because the capillaries are
permeable to oxygen. After it is in the capillary, about 5% will be
dissolved in the blood plasma. The other oxygen will bind to red blood
cells. The red blood cells contain hemoglobin that carries oxygen.
Blood with hemoglobin is able to transport 26 times more oxygen than
plasma without hemoglobin. Our bodies would have to work much harder
pumping more blood to supply our cells with oxygen without the help of
hemoglobin. Once it diffuses by osmosis it combines with the hemoglobin
to form oxyhemoglobin.
Now the blood carrying oxygen is pumped through the heart to the
rest of the body. Oxygen will travel in the blood into arteries,
arterioles, and eventually capillaries where it will be very close to
body cells. Now with different conditions in temperature and pH (warmer
and more acidic than in the lungs), and with pressure being exerted on
the cells, the hemoglobin will give up the oxygen where it will diffuse
to the cells to be used for cellular respiration, also called aerobic
respiration. Cellular respiration is the process of moving energy from
one chemical form (glucose) into another (ATP), since all cells use ATP
for all metabolic reactions.
It is in the mitochondria of the cells where oxygen is actually
consumed and carbon dioxide produced. Oxygen is produced as it combines
with hydrogen ions to form water at the end of the electron transport
chain (see chapter on cells). As cells take apart the carbon molecules
from glucose, these get released as carbon dioxide. Each body cell
releases carbon dioxide into nearby capillaries by diffusion, because
the level of carbon dioxide is higher in the body cells than in the
blood. In the capillaries, some of the carbon dioxide is dissolved in
plasma and some is taken by the hemoglobin, but most enters the red
blood cells where it binds with water to form carbonic acid. It travels
to the capillaries surrounding the lung where a water molecule leaves,
causing it to turn back into carbon dioxide. It then enters the lungs
where it is exhaled into the atmosphere. | 
