Physiology - Respiratory and Renal System

What does the conducting zone consist of?

Bronchi:

• Secondary Bronchi

• Tertiary Bronchi

• Bronchioles

And Terminal Bronchioles

Describe the Secondary Bronchi

Three on right side to three lobes of right lung

Two on left side to two lobes of left lung

Describe the Tertiary Bronchi

20–23 orders of branching

Describe the Bronchioles

Less than 1 mm in diameter

Functions of the conducting zone

Air passageway: 150 mL in volume (dead space)

It increases air temperature to body temperature and humidifies air

Epithelium of the conducting zone include…

Goblet cells (secrete mucous), ciliated cells (cilia moving particles toward mouth) and mucus escalator

Functions of the respiratory zone

Exchange of gases between air and blood via diffusion

Structures of the respiratory zone include…

Respiratory bronchioles,Alveolar ducts, Alveolar sacs, Alveoli

What are the site of gas exchange called?

Alveoli

How many alveoli are there in the lungs and what are their size in total?

300 million alveoli with a size of a tennis court

Alveoli contain a ____, having capillaries form sheet over alveoli

Rich blood supply

Type I alveolar cells…?

make up wall of alveoli and are single layer of epithelial cells

Type II alveolar cells…?

secrete surfactant

Epithelium of the respiratory zone is the…

respiratory membrane

The respiratory membrane consists of…

Epithelial cell layer of alveoli (type I) and Endothelial cell layer of capillaries

it is 0.2 μm thick

The role of alveolar macrophages is

scavenging microbes such as viruses, bacteria, fungi, inhaled environmental particles like coal, silica, asbestos, tissue debris, and cancer cells

Air moves in and out of lungs by…?

Bulk flow

What drives flow in lungs?

The pressure gradient, where air moves from high to low pressure

Inspiration:

pressure in lungs less than atmospheric pressure

intra-alveolar pressure is negative (less than atmospheric)

Expiration:

pressure in lungs greater than atmospheric pressure

intra-alveolar pressure is positive (less than atmospheric)

Describe atmospheric pressure - pulmonary pressures

It is 760 mm Hg at sea level and decreases as altitude increases

It Increases under water

Other lung pressures are given relative to atmospheric pressure (set Patm = 0 mm Hg)

Describe Intra-alveolar pressure (Palv) - pulmonary pressures

It is the pressure of air in alveoli given relative to atmospheric pressure

Describe Intrapleural pressure (Pip) - pulmonary pressures

Pressure inside pleural sac, always negative under normal conditions and always less than Palv

At rest, Pip is….

-4 mm Hg

Why is Pip negative at rest?

due to elasticity in lungs and chest wall

Lungs recoil inward as chest wall recoils outward

opposing forces pull on intrapleural space

Surface tension of intrapleural fluid prevents wall and lungs from pulling apart

Transpulmonary pressure

= Palv – Pip

it is the distending pressure across the lung wall

Increase in transpulmonary pressure….

increases distending pressure across lungs, which causes lungs (alveoli) to expand, increasing volume

What does mechanics of breathing describe

describes mechanisms for creating pressure gradients

Movement of air in and out of lungs occurs due to ________

pressure gradients

force for flow = pressure gradient

What remains constant during breathing cycle?

Atmospheric pressure remains constant (during breathing cycle), thus alveolar pressure changes affect gradients

Describe Boyle’s law

pressure is inversely related to volume

If amount of gas is the same and container size is reduced, pressure will increase So pressure (P) varies inversely with volume (V)

P1V1 = P2V2

Factors determining intra-alveolar pressure

Quantity of air in alveoli and Volume of alveoli

What happens when lungs expand?

alveolar volume increases

Palv decreases

Pressure gradient drives air into lungs

What happens when lungs recoil?

alveolar volume decreases

Palv increases

Pressure gradient drives air out of lungs

What muscles increase the volume of the thoracic cavity?

Inspiratory muscles; Diaphragm and External intercostals

What muscles decrease the volume of the thoracic cavity?

Expiratory muscles; Internal intercostals and Abdominal muscles

What takes place during inspiration?

Neural stimulation of inspiratory muscles → Diaphragm contraction causes it to flatten and move downward → Contraction of external intercostals makes ribs pivot upward and outward, expanding the chest wall

a passive process (12-20 breaths/min); When inspiratory muscles stop contracting, recoil of the lungs and chest wall to their original positions decreases the volume of the thoracic cavity

What happens as a result of inspiration?

thoracic cavity volume increases

Outward pull on pleura decreases intrapleural pressure, which results in an increase in transpulmonary pressure

Alveoli expand, decreasing alveolar pressure

Air flows into alveoli by bulk flow

Events in the process of inspiration

increase in neural input →

inspiratory muscles contract →

chest wall expands →

increase pull on intrapleural fluid → decrease intrapleural pressure → increase transpulmonary pressure →

increase alveoli volume → decrease alveolar pressure → increase atmospheric pressure - alveolar pressure → increase flow of air into alveoli → increase in alveolar pressure

The pressure gradient for ventilation is represented as

atmospheric pressure - alveolar pressure

______ requires expiratory muscles (30-40 breaths/min)

Active expiration

Contraction of expiratory muscles creates a _____________ in the volume of the thoracic cavity

greater and faster decrease

What are the factors affecting pulmonary ventilation

lung compliance and airway resistance

What is lung compliance?

Ease with which lungs can be stretched

Smaller change in transpulmonary pressure needed to bring in a given volume of air

Larger lung compliance means

Easier to inspire

Factors affecting lung compliance

Elasticity (elastic recoil, ability to resist stretch: thick rubber ballon compared to thin rubber balloon)

Surface tension of lungs (force for alveoli to collapse or resist expansion)

How does Elasticity affect lung compliance

More elastic → less compliant

How does Surface tension affect lung compliance

Thin layer of fluid lines alveoli

Surface tension arises due to attractions between water molecules;

Greater tension → less compliant

How are the affects of surface tension on lung compliance overcomed

Surfactant is secreted from type II cells, which is a detergent that decreases surface tension

This then increases lung compliance, making inspiration easier

Airway resistance - as airways get _____ in diameter, they _____ in number, keeping overall resistance low

smaller; increase

Pressure gradient is needed for air flow, so resistance is normally _____

low, roughly 1 mm Hg

Does a decrease or increase to the resistance (airway resistance) happen to make it harder to breathe?

Increase in resistance makes it harder to breathe

Pressure gradient needed for air flow: > 1 mm Hg

What are the factors affecting airway resistance?

1. Contractile activity of smooth muscle

2. Mucus secretion

What is the role of the bronchiolar smooth muscle in airway resistance?

Bronchoconstriction and Bronchodilation

Bronchoconstriction

smooth muscle contracts, causing radius to decrease

Bronchodilation

smooth muscle relaxes, causing radius to increase

Describe the extrinsic control of bronchiole radius in the sympathetic nervous system

Relaxation of smooth muscle

Bronchodilation via Beta 2 receptors

Describe the extrinsic control of bronchiole radius in the parasympathetic nervous system

Contraction of smooth muscle

Bronchoconstriction via muscarinic receptors

Describe the extrinsic control of bronchiole radius in terms of hormonal control

Epinephrine, Relaxation of smooth muscle/Bronchodilation

Describe the intrinsic control of bronchiole radius in terms of hormonal control

Histamine causing bronchoconstriction

Histamine is released during asthma and allergies, which also increases mucus secretion

CO2 causes bronchodilation

Total lung volume is divided into a series of ___ volumes and ____capacities useful in diagnosing problems

4; 4

Tidal Volume (TV)

Amount of air taken in during inhalation (~500 mL)

350 mL enters alveoli + ~150 mL remains in conducting passageways (Anatomic dead space - VD)

Respiratory Rate (f) + ?

12-20 breaths per min

Minute ventilation (VE) = ?

f x TV

“# of breaths x volume of each breath”

~6 L/min

Alveolar Ventilation (VA) = ?

f x (TV – VD)

“# of breaths x (amount – dead space)”

= 12 x (500 – 150) = 4.2 L/min

Inspiratory Reserve Volume (IRV)

maximum air inspired at the end of a normal inspiration

~3000 mL

Expiratory Reserve Volume (ERV)

maximum air expired at the end of a normal expiration

~1000 mL

Residual Volume

Air left in the lungs after a maximal exhalation

~1200 mL

Hyperpnea

increase in respiratory rate/volume due to increase in metabolism

Hyperventilation

increase in respiratory rate/volume without increase metabolism

Hypoventilation

decrease in respiratory rate/volume, increase alveolar ventilation

Dyspnea

shortness of breath (difficulty breathing)

Apnea

cessation of breathing

Respiratory Capacities

Lung Capacities (4)

sums of 2 or more volumes

What is inspiratory capacity (IC)?

Maximum amount of air that can be inspired at the end of expiration

TV + IRV = 500 mL + 3000 mL = 3500 mL

What is Vital Capacity?

Maximum amount of air that can be exhaled following a max inhalation

VC = IRV + TV + ERV

= 3000 mL + 500 mL + 1000 mL = 4500 mL

OR

VC = IC + ERV

= 3500 mL + 1000 mL = 4500 mL

What is Functional Residual Capacity

Amount of air remaining at the end of normal expiration (~2300 ml)

ERV (1000 mL) + RV (1200 mL) = ~2200 mL

What is Total Lung Capacity?

Volume of air in lungs at the end of a maximum inspiration

TLC = TV + ERV + IRV + RV (or VC + RV or FRC + IC)

= 500 mL + 1000 mL + 3000 mL + 1200 mL = 5700 mL

Pulmonary Function Tests - Forced vital capacity (FVC) =

maximum-volume inhalation followed by exhalation as fast as possible

What does a low Forced vital capacity indicate?

indicates restrictive pulmonary disease

Pulmonary Function Tests - • Forced expiratory volume (FEV) =

percentage of FVC that can be exhaled within certain time frame

FEV1 =

percentage of FVC that can be exhaled within 1 second

What is a normal FEV1 percentage

80%

If FVC = 4000 mL…

should expire 3200 mL in 1 se

What does FEV1 < 80% indicate

indicates obstructive pulmonary disease

Total Pulmonary Ventilation = ?

ventilation rate x tidal volume

also known as minute ventilation (VE)

Total Pulmonary Ventilation calculation

ventilation rate x tidal volume;

12 breaths/min x 500 mL/breath = 6000 mL or 6 L/min

Some inspired air does not enter alveoli, which is known as the…

anatomical dead space, ~150 mL of air

What is Alveolar Ventilation (VA)?

movement of air into and out of the alveoli

ventilation rate x (tidal volume – dead space)

Alveolar Ventilation (VA) Calculation

ventilation rate x (tidal volume – dead space);

12 breaths/min x (500 – 150 mL/breath) = 4200 mL/min or 4.2 L/ min

What can drastically alter alveolar ventilation

Rate or depth of breathing can

What is Maximum Voluntary Ventilation?

Breathing as deeply and quickly as possible

What may happen as a result of Maximum Voluntary Ventilation?

May increase total pulmonary ventilation to ~170 L/ min

Alveoli During Breathing

Hypoventilation, Ventilation is inadequate, ↑ CO2

Hyperventilation, over breathing, ↓ CO2

Arterial blood O2 and CO2 levels remain relatively ____

constant

___ moves from alveoli to blood at the same rate it is consumed by cells

Oxygen

___ moves from blood to alveoli at the same rate it is produced by cells

CO2

What is the composition of Air?

Nitrogen (N2) ~79.04%

Oxygen (O2) ~20.93%

Carbon dioxide (CO2) ~0.03%

Dalton’s Law of Partial Pressures

Each gas contributes to the total pressure in proportion to its number of molecules Partial Pressure = total pressure x fraction of a gas

At sea level with dry air (total 760 mmHg) - PN2

= 760 mmHg x 0.7904 = 600.7 mmHg