Module 10 – Respiratory System:
Functions of the respiratory system include:
1. Transport of oxygen from air to blood.
2. Removal of carbon dioxide from blood to air.
3. Control of blood acidity (pH)
4. Temperature regulation
5. Forming a line of defense to airborne particles.
- Located in the thoracic cavity, surrounded by the rib of cage and diaphragm.
- Airways consist of the nasal cavity and the mouth, which join at the pharynx, pharynx leads
into the voice box/larynx then trachea then two bronchi then smaller bronchioles then alveoli.
- Alveoli: site of gas exchange in the lung.
Anatomy- Blood vessels:
- Pulmonary artery delivers deoxygenated blood to the lungs.
- Pulmonary artery branches extensively to form a dense network of capillaries around each
alveolus. Capillaries have a thin endothelial walls and large total cross-sectional area.
- Form the capillaries, the oxygen-rich blood flows back to the left side of the heart through the
pulmonary vein. Anatomy – Histological Structure of an Alveolus:
- Roughly 300 million alveoli in a healthy human lung, with a diameter 0.3 mm.
- The walls of the alveoli are composed of alveolar epithelial cells (type I cells). Type II cells
secrete a fluid called “surfactant” that lines the alveoli. Large numbers of capillaries surround
the alveoli in close proximity. The region between the alveolar space and the capillary lumen is
the respiratory membrane.
- Cells of the immune system including macrophages and lymphocytes protect the body from
airborne particles that make their way into the alveoli.
Pressures of the Lungs – Intrapleural Pressure:
-There are two thin pleural membranes, one lines and sticks to the ribs (parietal pleura) and the
other surrounds and sticks to the lungs (visceral pleura).
- The two layers form the Intrapleural space, which contains pleural fluid.
- The fluid reduces friction between the two pleural membranes during breathing.
Pressures of the Lungs – Alveolar andAtmospheric Pressure:
- The pressure inside the lungs is called the alveolar pressure or intrapulmonary pressure. - The pressure in the Intrapleural space is called the Intrapleural pressure.
- The atmospheric pressure is outside the body, 760 mmHg at sea level.
- Between breaths, the alveolar and atmospheric pressures are the same at 760 mmHg
- The pressure in the Intrapleural space is roughly 756 mmHg.
Pressure of the Lungs – Transpulmonary Pressure:
- Transpulmonary pressure is the difference between the alveolar and Intrapleural pressures.
- The difference in pressure across the alveoli and Intrapleural space holds the lungs open.
- In a healthy set of lungs, the Transpulmonary pressure is positive and keeps the lungs and the
Pressures of the Lungs – Pneumothorax:
- At Transpulmonary pressure 0 there would be no pressure holding the lungs open and they
would collapse, producing a Pneumothorax.
- Generally only one lung collapses because the Intrapleural space of each lung is isolated from
Ventilation – Boyle’s Law:
- Boyle’s law states that when the volume decreases, the pressure increases.
Ventilation – Inspiration and Expiration:
- Moving air into the lungs requires an air pressure gradient.
- To move air into the lungs requires high pressure outside and low pressure in the alveoli.
- To move air out requires high alveolar pressure and low atmospheric pressure.
Ventilation – Mechanisms of Inspiration:
- To decrease the alveolar pressure, the lung volume must increase. - To increase the volume, the diaphragm contracts, moving downward, and the external
intercostal muscles of the rib contract, lifting the rib cage up and out. Both events cause the lung
volume to increase.
- Contraction of the respiratory muscles is an active process that relies on signals from the
respiratory center in the brainstem.
Ventilation – Mechanisms of Expiration:
- Mechanism of expiration depends on whether you are resting or exercising.
- At rest, the diaphragm and external intercostal muscles relax, causing lungs to recoil to their
original size.As a result, the volume decreases causing the alveolar pressure to increase above
atmospheric pressure. The pressure is high inside (761) and low outside (760) so airflows out.
Passive process = no muscle contraction occur.
- During exercise, air must be forced out, requires contraction of abdominal muscles and the
internal intercostal muscles of the ribs, which will decrease the volume of the lungs, the pressure
inside will be 763 and the pressure outside will be 760, forcing air out.
Ventilation – Model of the lung.
- Diaphragm is pulled down, volume increases, pressure decreases, air rushes in and lungs inflate
- Diaphragm relaxes, volume decreases, pressure increases, and airflows out and lungs deflate.
Note: Relaxation of inspiratory muscles will occur while exhaling during quiet breathing.
- Pulmonary compliance is the stretch ability of the lungs – the more stretchable, the more
- Pulmonary compliance is the volume change that occurs as a result of a change in pressure.
- Pulmonary compliance = volume change / pressure change.
- Pulmonary compliance determines the ease of breathing.
- Two major factors influence compliance (elastic behavior of lungs):
1. Amount of elastic tissue that is found in walls of the alveoli, blood vessels and bronchi.
2. Surface tension of the film liquid that is lining alveoli. - Both factors decrease compliance by collapsing the lungs, making breathing difficult.
- Pulmonary fibrosis: disease cause decrease in compliance, constant inhalation of fine particles.
- Normal aging/pulmonary emphysema: cause increased compliance.
Pulmonary compliance – Elastic Tissue Components:
- Fibers of elastin and collagen are present in the walls of the alveoli, blood vessels and
bronchioles. Elastin fibers are easily stretched but collagen is not.
- The more elastin, the less complaint the lungs.
Pulmonary compliance – Surface tension:
- Surface tension is due to the attractive forces between water molecules.
- Surface tension tends to collapse the alveoli, decreasing compliance and making inflation
Pulmonary Compliance – Pulmonary Surfactant:
- Pulmonary surfactant is a lipoprotein substance produced by type II alveolar cells and consists
mostly of phospholipids. Phospholipid head will be attracted to water and will balance the forces.
- The water drop will flatten out due to the decreased surface tension.
- Pulmonary Surfactant is released from type II alveolar cells during deep breathing.
Pulmonary Compliance – Pulmonary Surfactant & Infant Respiratory distress syndrome:
- Premature babies don't produce enough amount of surfactant, which will cause alveoli to
collapse making it hard to breath and causing Infant respiratory distress syndrome.
Note: Surface tension in the lungs generates a force that collapses the alveoli and is caused by
attractive forces of water Lung Volumes:
- Maximum amount of air the lungs can hold is 5 L.
- Device used to measure lung volumes and capacities.
- helpful in diagnosing pulmonary disease such as asthma, bronchitis, and emphysema.
Lung volumes and capacities:
- There are four lung volumes:
1. Tidal volume: volume of air entering or leaving the lungs during one breath at rest = 500 ml
2. Inspiratory reserve volume: max amount of air that can enter lungs in addition to tidal
Volume (2500 ml)
3. Expiratory reserve volume: max amount of air that can be exhaled beyond the tidal volume
4. Residual Volume: Remaining air in the lungs after a maximal expiration (1200mL)
- There are four lung capacities:
1. Inspiratory capacity: max amount of air that can be inhaled after exhaling the tidal volume =
tidal volume + inspiratory reserve volume.
2.Functional residual capacity: amount of air still in the lungs after exhalation of the tidal
volume = expiratory reserve volume + residual volume.
3. Vital capacity: max amount of air that can be exhaled after a maximal inhalation = inspiratory
reserve volume + tidal volume + expiratory reserve volume.
4. Total lung capacity: max amount of air that lungs can holds = vital capacity + residual
volume. Pulmonary Ventilation – calculate:
- Amount of air that enters all of the conducting and respiratory zones in one minute. Conducting
zone is the area where no gas exchange takes place because there are no alveoli.
- Respiratory zone is the region of the lings where alveoli are located.
- Pulmonary Ventilation can determine the amount of air and the amount of oxygen that is
available to the body.
- VE = tidal volume (ml) x Respiratory Rate (breaths/min).
Alveolar Ventilation – calculate:
- VAis the volume of air entering only the respiratory zone each minute.
- VArepresents the volume of fresh air available for gas exchange.
- VA(alveolar ventilation) = VE (pulmonary Ventilation) – VD (dead space ventilation)
- VE = VT x resp rate and VD = dead space volume x resp rate.
- Dead space volume = body weight.
Partial Pressure of Gases:
- Partial pressure of a gas is the pressure exerted by that one gas in a mixture of gases.
- Partial pressure of a gas = total pressure of all Gases x Fractional concentration of the one gas.
- Oxygen and carbon dioxide move down a pressure gradient, called a partial pressure gradient.
- Move from areas of high partial pressure to areas of low partial pressure.
Partial Pressures of Gases cross theAlveoli – Diffusion:
1. Blood leaving lungs has a high PO2 and low PCO2 2. Blood returns to the left side of the heart.
3. Blood enters tissue beds with high PO2 and low PCO2 still.
4. Cells have a low PO2 and high PCO2
5. As blood flow through capillaries, O2 diffuses into the cells and CO2 diffuses out.
6. Blood leaving the tissues will have a low PO2 and high PCO2.
7. Blood returns to the right side of the heart to ne pumped to the lungs. process repeats.
- Oxygen is carried in red blood cells attached to a protein called hemoglobin.
- Each molecule of hemoglobin can carry 4 oxygen molecules.
Oxygen Transport – Red Blood Cells:
- also called erythrocytes.
- RDC have a very short life span – about 120 days.
- Production of RBCs is a process called erythropoiesis in bone marrow and requires the
presence of amino acids, iron, folic acid, and vitamin B12.
- RBCs are destroyed and removed by spleen and liver.
Oxygen Transport – RBC production – Erythropoietin:
- Control of erythrocyte production requires the hormone erythropoietin (EPO).
- Roughly 90% of EPO is secreted by the kidneys and 10% secreted by the liver.
- This hormone stimulates the bone marrow to produce RBCs. - EPO is secreted in low amounts, however, EPO secretion increases when oxygen decreases in
the liver, because low level of oxygen indicates a decrease in cardiac output, decrease in RBCs or
total hemoglobin content, therefore, we need to increase the secretion of EPO which stimulates
Oxygen Transport – Hemoglobin:
- Immature RBCs contain a nucleus, but once mature and circulates in the blood, they do not.
- Each molecule of hemoglobin contains 4 subunits. Each subunit contains a single heme
molecule attached to a polypeptide. The 4 polypeptides are called globin.
- Each heme molecule can carry one oxygen atom attached to the central iron atom.
- If PO2 is high, O2 will bind to Hb forming HbO2. If PO2 is low the reaction will reverse and
O2 will unload from Hb.
- Temperature and pH also affect the dissociation of oxygen from hemoglobin.
- Increasing acidity of the blood will increase the unloading of oxygen from hemoglobin.
- Low temperatures and decreases acidity will have the opposite effect on Hb and O2.
Carbon Dioxide Transport:
- There are three forms of Carbon dioxide transport:
1. Like O2, CO2, can be dissolved and carried directly in plasma (PCO2).
2. CO2 can also be carried as a bicarbonate ion (HCO3-)
3. It can also be attached to proteins in the blood, forming carbamino compounds.
- About 70% of the total CO2 carried in the blood is carried as bicarbonate ions.
-Where oxygen is being unloaded from red blood cells, carbon dioxide is undergoing reactions
to transport it back to the lungs. CO2 will dissolve in the blood where it will remain or it can
bind to proteins to form carbamino compounds.Also, another abundant protein to bind to is
hemoglobin in RBCs forming carbamino hemoglobin (HbCO2).
- In the RBCs, CO2 can also react with water to form bicarbonate ions (HCO3-). These ions
diffuse out of the cell while Cl- diffuse in during the chloride shift. This CO2- laden blood will
return to the lungs. Origin of Respiration:
- Breathing can be either spontaneous or voluntary.
- Spontaneous respiration originates in the medullary respiration center of the medulla
oblongata of the brainstem and is produced by rhythmic activity from the neurons much like the
pacemaker of the heart.
- Voluntary center is located in the cerebral cortex. The voluntary system is capable of
overriding the center in the brainstem (when holding your breath for example).
Origin of Respiration – Inhalation:
- Medullary respiratory center in the medulla oblongata contains two areas: inspiratory center,
which activates the inspiratory muscles during inhalation. The expiratory center activates the
expiratory muscles during an active exhalation.
- Inspiration is always an active process requiring the contraction of the diaphragm and external
intercostal muscles. The inspiratory center stimulates the contraction of these inspiratory
muscles, at the same time, it also inhibits the expiratory center.
Origin of Respiration – Exhalation:
- Quiet exhalation is a passive process involving only the relaxation of the inspiratory muscles.
The lungs own elastic properties and recoiling of muscle cause exhalation at rest.
- Forceful exhalation (during exercise) requires contraction of the abdominal muscles and the
internal intercostal muscles of the ribs. Signals to these muscles originate in the expiratory center
of the medulla. While this center is active, the inspiratory center is inhibited.
Origin of Respiration – Inhalation and Exhalation Combined:
- When the body is at rest, the inspiratory center is actually active for roughly two seconds,
which is enough time to activate the muscles of inspiration (diaphragm and external intercostal
muscles), producing a small inhalation. During this time exhalation is inhibited.
- Inspiratory area will shut down after that and the expiratory center will become active.
Expiration can be either passive (inspiratory muscles relax) or active. When expiration is active,
the muscles of expiration (abdominal and internal intercostal muscles) contract and force the air
out of the lungs. During this time, the inspiratory center is inhibited.
Origin of Respiration – Apneustic and Pneumotaxic Centers: - In order to ensure proper concentrations of gas in the blood, special regions in the pons ( above
the medulla) can modify the spontaneous signals from the centers in the medulla. The
Pneumotaxic center regulates the rate of breathing while theApneustic center controls the depth
of an inhalation and exhalation.
Origin of Respiration – Voluntary Center:
- Ventilation is spontaneous, but it can also be modified voluntarily.
- For example, when jumping into water, it is necessary to stop ventilation and hold your breath
while under water.
- The site of voluntary ventilation is the cerebral cortex, which can modify ventilation by
affecting signals originating in either theApneustic center of the Pneumotaxic center.
Regulation of Respiration:
- Examine the regulatory systems responsible for maintaining gas levels, and if changes occur,
detecting them and returning levels to normal.
Regulation of Respiration – Negative Feedback:
- Regulating gas level requires the use of negative feedback.
- Negative feedback requires a set point (proper concentration of gas), a control center (brain),
sensors to detect gas levels (called chemoreceptors), an effector (muscles of respiration), and a
controlled variable (ventilation of the lungs).
- Set point ▯ Control Center ▯ Effector ▯ Controlled Variable ▯ Sensor ▯ Controlled Center.
Regulation of Respiration – Chemoreceptors: - Special receptors that detect the concentration of oxygen, carbon dioxide, or hydrogen ions
(H+) in the blood.
- There are two groups of chemoreceptors classified by their location in the body.Aperipheral
group of chemoreceptors is located in the aortic arch and carotid sinus (much like the
baroreceptors of the cardiovascular system).
- Acentral group is located in the medulla of the brainstem (close to the respiratory center). Each
group of sensors is sensitive to different gases.
Regulation of Respiration- Peripheral Chemoreceptors:
- These chemoreceptors are located in the carotid sinus and aortic arch, are sensitive to oxygen
concentrations and only slightly sensitive to carbon dioxide levels In the blood.
- Small drop of oxygen or a large increase in Co2 will be detected by these sensors, which will
send signals back to the respiratory center in the brain. The respiratory center will compare
signals with the set point value and will initiate an increase in ventilation to return the O2 and the
CO2 levels to normal.
Regulation of Respiration – Central Chemoreceptors:
- Central chemoreceptors are sensitive to H+ ion levels in the interstitial space of the brain.
Central chemoreceptors are located in the medulla, the gasses diffuse into the interstitial space
crossing the blood brain barrier (BBB). This barrier is permeable to CO2 but not permeable to
- Since CO2 can cross the BBB, it reacts with water within the interstitial space of the brain to
produce bicarbonate and H+ through the following equation:
CO2 + H2O both ways arrows H2CO3 both ways arrows HCO3- + H+
- Now the H+ produced will be detected by the central chemoreceptors.An increase in CO2 in
the blood will be detected indirectly through these chemoreceptors to signal the respiratory
center in the brainstem to increase ventilation.
Module 11 – Renal System:
- The renal system includes kidneys, ureters, bladder, and uretha.
- Principal function of kidneys: 1. Regulation of water balance.
2. Electrolyte levels.
3. pH of the blood
4. Long term regulation of arterial pressure.
Functions of the kidneys:
- Remove nonessential substances from the plasma, including waste metabolites, excess water,
- To recover any essential substances like glucose.
- Kidneys act as an endocrine gland, producing hormones or components of hormonal systems
such as erythropoietin, renin, vitamin D, and stanniocalcin.
Anatomy of the kidneys:
- Kidneys consist of an outer renal cortex, a middle renal medulla, and inner calyces that drain
into a central renal pelvis. The renal pelvis then drains into the ureter.
- Located within the renal pyramids are the functional units of the kidneys – the nephrons.
Anatomy – Blood supply of the kidneys:
- Blood flows to the kidneys through the renal artery.
- This large artery branches into several interlobar arteries that branch into arcuate arteries.
The blood in the arcuate arteries flows through the interlo