regulation of respiration

1. REGULATION OF RESPIRATION,
RESPIRATION IN UNUSUAL
ENVIRONMENT - FETAL AND
NEONATAL RESPIRATION

2. TWO MECHANISMS
1. Nervous or neural mechanisms
2. Chemical mechanisms
Nervous mechanism
•It involves respiratory centers, afferent and efferent nerves.
•Respiratory centers: The centers in the medulla oblongata and pons that collects
sensory information about the level of oxygen and carbon dioxide in the blood
and determines the signal to be sent to the respiratory muscles.
• stimulation of these respiratory muscles provide respiratory movements which
leads to alveolar ventilation.
•Respiratory centers are classified into two groups:
1. Medullary centers
2. Pontine centers

3. There are two centers in each group:
•Medullary centers:
1. Inspiratory centers
2. Expiratory center
•Pontine centers:
1. Pneumotoxic center
2. Apneustic center

4. Inspiratory center:
It is situated in upper part of medulla oblongata.
This is also called dorsal group of respiratory neurons.
It is concerned with inspiration.
Expiratory center:
It is situated in the medulla oblongata anterior and lateral to the
inspiratory center.
It is also called ventral group of respiratory neurons.
This center is inactive during quiet breathing and inspiratory center is
the active center, but during forced breathing or when the inspiratory
center is inhibited it becomes active.

5. Pneumotaxic center:
It is situated in upper pons.
it controls medullary respiratory centers, particularly the inspiratory
center through apneustic center. It always controls the activity of
inspiratory center so that duration of inspiration is controlled.
Apneustic center:
It is situated in lower pons.
Function: this center increases depth of inspiration by acting directly
on the inspiratory center.

7. NERVOUS CONNECTIONS OF
RESPIRATORY CENTERS
Afferent pathway
•Respiratory center receive afferent impulses from different parts of the body according to
movements of thoracic cage and lungs.
•From peripheral chemoreceptor impulses are carried by glossopharyngeal and vagus
nerves to respiratory center.
Efferent pathway
•Nerve fiber from respiratory center leaves the brain and descend in anterior part of lateral
column of spinal cord.
•These nerve fibers terminate in the motor neurons in the anterior horn cells of the cervical
and thoracic segments of the spinal cord.
•From motor neurons two sets of nerve fiber arise which supplies particular muscle:
1. Phrenic nerve fibers: supplies diaphragm
2. Inter coastal nerve fibers: supplies intercostal muscles

8. FACTORS AFFECTING
RESPIRATORY CENTERS
1. Impulses from higher centers: impulses from higher center can
stimulate or inhibit respiratory centers directly.
2. Impulses from stretch receptors of lung
3. Impulses from ‘J’ receptors of lungs:
•‘J’ receptors are juxtacapillary receptors which are present in wall of
the alveoli and have close contact with the pulmonary capillaries.
•These receptors get stimulated during conditions like pulmonary
edema, pulmonary congestion, pneumonia as well as due to exposure
of exogenous and endogenous chemicals like histamine, serotonin.
•Stimulation of ‘J’ receptor produces a reflex response called apena.

9. 4. Impulses from irritant receptors of lungs:
• irritant receptors are situated on the wall of bronchi and bronchioles of
lungs.
•They got stimulated by harmful chemical like ammonia and sulfur dioxide.
•Stimulation of irritant receptors produces reflex hyperventilation along with
bronchospasm which prevents entry of harmful chemicals into the alveoli.
5. Impulses from proprioceptors:
•Proprioceptors are the receptors which give response to the change in the
position of different parts of the body.
•This receptors are situated in joints, muscles and tendons. They get
stimulated during exercise and sends impulses to the cerebral cortex.
•Cerebral cortex in turn by activating medullary respiratory centers causes
hyperventilation.

10. 6. Impulses from thermorecptors:
•Thermorecptors give response to change in the body temperature.
•They are cutaneous receptors namely cold and warmth.
•When this receptors get stimulated they send signals to cerebral
cortex.
•Cerebral cortex in turn stimulates respiratory centers and causes
hyperventilation.
7. Impulses from pain receptors:
•Pain receptors give response to pain stimulus.
•Like other receptors this receptors also send impulses to the cerebral
cortex.

11. 8. Cough reflex:
•This is a protective reflex caused by irritation of parts of the
respiratory tract beyond nose like larynx, trachea and bronchi.
•Irritation of any of this part causes stimulation of vagus nerve and
cough occurs.
•Cough begins with deep inspiration followed by forceful expiration
with closed glottis.
•So the intrapleural pressure rises above 100mm Hg.
•Then, glottis is suddenly opened with explosive outflow of air at a
higher velocity. So the irritants may be expelled out of the respiratory
tract.

12. 9. Sneezing reflex:
•It is also a protective reflex which occurs due to the irritation of nasal mucus
membrane.
•During irritation of nasal mucus membrane, the olfactory receptors and
trigeminal nerve endings present in the nasal mucosa are stimulated leading
to sneezing.
•Sneezing starts with deep inspiration, followed by forceful expiratory effort
with opened glottis and the irritants are expelled out of the respiratory tract.
10. Deglution reflex:
•During swallowing of the food, the respiration is arrested for a while.
•Temporary arrest of the respiration is called apnea and apnea which occurs
during swallowing called swallowing apnea.
•This prevents entry of the food particles into the respiratory tract.

13. CHEMICAL MECHANISM
•Chemoreceptors: The primary chemical regulators of respiration are
chemoreceptors, which are specialized cells that detect changes in
the levels of oxygen (O2), carbon dioxide (CO2), and hydrogen ions
(H+). There are both peripheral chemoreceptors in the arteries and
central chemoreceptors in the brain.
•Peripheral Chemoreceptors: These are located in the carotid bodies
and aortic bodies, which are sensitive to changes in blood gases.
When blood O2 levels decrease (hypoxia) or blood CO2 levels
increase (hypercapnia), peripheral chemoreceptors send signals to the
brain.
•Central Chemoreceptors: These are primarily located in the medulla
oblongata, part of the brainstem. They are mainly responsive to
changes in the pH of cerebrospinal fluid due to the accumulation of
CO2, as CO2 can readily cross the blood-brain barrier and combine
with water to form carbonic acid, leading to increased H+ ions.

14. FEEDBACK MECHANISMS
a. Hypoxic Drive: When blood oxygen levels drop, the peripheral
chemoreceptors stimulate an increase in the rate and depth of
respiration to enhance oxygen intake. b. Hypercapnic Drive: Elevated
levels of CO2, detected by central and peripheral chemoreceptors,
trigger an increase in the rate and depth of breathing to expel excess
CO2.

16. VARIOUS PRESSURES THAT
AFFECTS THE RESPIRATION
Actually lung float like ballon in the thoracic cavity.
It is surrounded by pleural fluid, which lubricates the movement of
the lungs.
Intra alveolar pressure: when the initiation of breathing after birth,
the first inspiration causes enlargement of chest. This produces
expansion of lungs.
Inrapleural pressure: it is the pressure of the fluid in the thin space
between lung pleura and chest wall.
Transpulmonary pressure: it is the difference between the intra
alveolar pressure and intra pleural pressure.

17. Intra alveolar pressure
In the beginning of inspiration volume of lung increases and pressure decreses but it regain full
atmospheric pressure at the end of inspiration. When the expiration occurs then the intrapulmonary
pressure swing to positive.
Intra pleural pressure: it occurs within the pleural cavity.
Intrapleural pressure, also known as intrathoracic pressure, is the pressure within the pleural cavity,
the space between the two layers of the pleura that envelop the lungs. The pleura is a double-layered
membrane that lines the inside of the chest cavity (parietal pleura) and covers the surface of the lungs
(visceral pleura).
Intrapleural pressure is important in the mechanics of breathing and the maintenance of lung
expansion. It is typically lower than atmospheric pressure, and changes in intrapleural pressure are
essential for the process of ventilation, which involves inhalation and exhalation.
During inhalation, the diaphragm contracts and the external intercostal muscles between the ribs
contract, which increases the volume of the chest cavity. As the volume of the chest cavity increases,
the intrapleural pressure decreases, creating a negative pressure relative to atmospheric pressure.
This negative intrapleural pressure helps to keep the lungs inflated and allows air to be drawn into the
lungs.
During exhalation, the diaphragm and intercostal muscles relax, reducing the volume of the chest
cavity. Intrapleural pressure returns to its resting level, which is slightly below atmospheric pressure,
helping to keep the lungs in contact with the chest wall.

18. RESPIRATION IN UNUSUAL
ENVIRONMENTS
•High-Altitude Respiration: At high altitudes, the air contains lower levels of
oxygen, which can make respiration more challenging. To adapt to these
conditions, people living in high-altitude areas may have increased lung
capacity and produce more red blood cells to carry oxygen more efficiently.
•Anaerobic Respiration: In environments with extremely low oxygen levels,
some organisms switch to anaerobic respiration, which does not require
oxygen. Anaerobic respiration is less efficient in terms of energy production,
but it allows organisms to survive in oxygen-depleted environments. Some
bacteria and archaea are known to thrive in anaerobic conditions, such as
deep-sea hydrothermal vents.
•Extremophiles: Extremophiles are microorganisms that can survive and
thrive in extreme environments. Some extremophiles, like thermophiles, can
respire in very high-temperature environments, such as hot springs or
deep-sea hydrothermal vents. They have specialized enzymes and metabolic
pathways adapted to these extreme conditions.

19. •Deep-Sea Respiration: In the deep ocean, water pressure is extremely
high, and temperatures can be near freezing. Deep-sea organisms
have adaptations to withstand these conditions. They respire using
adaptations like pressure-tolerant enzymes and specialized
molecules that function at low temperatures.
•Anaerobic Digestion: In sewage treatment plants and certain
ecosystems, anaerobic digestion is used to break down organic
matter in the absence of oxygen. This process produces methane as a
byproduct, which can be harnessed as an energy source.
•Respiration in Space: Astronauts on the International Space Station
(ISS) or other spacecraft rely on carefully controlled life support
systems that maintain the right oxygen levels. In the microgravity of
space, the distribution of gases within the body is different, and
astronauts must exercise to prevent muscle and bone loss, which can
also affect their respiratory capacity.

20. •Adaptations in Extreme Cold: In extremely cold environments, like
the Arctic or Antarctica, animals may have adaptations to reduce heat
loss and maintain body temperature. For example, some marine
mammals have specialized circulatory systems that enable them to
conserve heat while still providing oxygen to vital organs.

21. FETAL RESPIRATION
•In Utero Oxygen Supply: In the womb, the fetus receives oxygen and
nutrients through the placenta. The mother's blood carries oxygen,
which diffuses through the placenta into the fetal bloodstream.
•Fetal Lungs: Fetal lungs are filled with amniotic fluid, and they are not
the primary source of oxygen exchange. Instead, the majority of
oxygen is delivered through the umbilical cord.

22. Adaptations for Fetal Respiration:
Fetal circulatory adaptations, like the ductus arteriosus and foramen ovale,
allow most of the blood to bypass the fetal lungs, as they are non-
functional.
The fetal lung is fluid-filled, preventing the exchange of gases and
maintaining a lower blood flow.
Fetal HbF: It is the main fetal protein carrying oxygen in the fetus during the
last 7 months of the fetal uterine life.
It will persist in the newborn for roughly 2 to 4 months.
Fetal Hb has more affinity than adult Hb, and it helps to give more oxygen to
the fetus from the mother’s circulation.
Fetal Hb will disappear by the 6th month
Fetal hemoglobin (HbF) consists of α2 γ2 chains

23. NEONATAL RESPIRATION
First Breath: The transition from fetal to neonatal respiration begins with the
first breath after birth. This triggers several changes:
The baby's lungs start to clear the amniotic fluid as it is expelled through
crying and coughing.
The lung tissue begins to expand and alveoli (small air sacs) start
functioning for gas exchange.
Oxygen tension in the blood increases due to the new environment.
Adaptations for Neonatal Respiration:
The ductus arteriosus and foramen ovale close within hours to days after
birth, allowing the blood to flow through the lungs to pick up oxygen.
Surfactant, a substance that reduces surface tension in the lungs, helps
maintain the alveoli's stability and prevents their collapse.

24. Breathing Rate: Neonates usually have a higher respiratory rate than
adults, which is around 30-60 breaths per minute. This rate gradually
decreases as they grow.
Diaphragmatic Breathing: Newborns primarily use their diaphragm for
breathing. Accessory muscles, such as those in the chest, are not well
developed in neonates.
Respiratory Distress: Some neonates, particularly preterm infants,
may experience respiratory distress syndrome (RDS) due to
underdeveloped lungs. This condition often requires medical
intervention, including mechanical ventilation and surfactant
replacement therapy.