resp and cardiac

Functions of the lungs

Gas exchange. Requires good matching beteeen ventilation and perfusion

Acid base balance by regulation of C02

Pathogen defence via mucociliary escalator

Ventilation

Flow of gas into alveolus that participates in gas exchange

Perfusion

Flow of fluid through organ or tissue that can participate in gas change. Blood flow of pulmonary circulstion that is available for gas exchange

Ventilation/perfusion matching

Matching between ventilation and perfusion must occur for gas exchange. If mismatch, causes hypoxaemia

Hypoxaemia and hypoxia

Hypoxaemia- lock of oxygen in blood

Hypoxia- lack of oxygen in tissue

Lobes of the lungs

Right lung has upper middle and lower lobe

Left lung has upper and lower lobe

Inhaled fluid is more likely to go into right lung as right lung is straighter and more vertical

Structures of respiratory system

Nasal cavity

Naso, oro, laryngo pharynx

trachea- c shaped cartilage and smooth muscle around it so that it stays open

Bronchus

Bronchioles

Alveoli

Extrapulmonary and intrapulmonary pressure

Extrapulmonary-outside lung

Pressure that influence on trachea is different from intrapulmonary airways

Alveoli: type 1 and 2

The gas exchange units. Has 2 types of cells in alveoli

Type 1: make up 95% of epithelial lining and responsible for gas exchange

Type 2:production of surfactant

Alveoli has high surface area and thin walls to optimise diffusion

Surfactant (type 2 alveolar cells)

Reduces surface tension by lining the interface between air and liquid in alveoli. Surfactant reduces surface tension and prevents alveoli from collapsing by coating inside of alveoli

Collateral ventilation

Air travelling through tiny connects to reach alveolus

Pathogen defence

In upper respiratory tract:

Goblet cells produces mucus, trapping bacteria and dust

Ciliated epithelium- tiny hair like structures called cilia moves mucus up the throat. It does not brush out debris, it moves a layer of mucus

In lower respiratory tract:

Alveolar macrophages eats up all foreign particles

Pleura

Visceral pleura-membrane covering lungs (inner)

Parietal pleura-lines thoracic cavity

Intrapleural space is the space between parietal and visceral pleura. Negative pressure

Collapsed lung happens when positive pressure is in intrapleural space. Pneumothorax is when there is positive pressure and air in intrapleural space.

Structures and functions of respiratory system

Trachea- c shaped cartilage with cilinated epithelium and goblet cells. Warms, humidifies and filters inspired air. Mucociliary escalators traps and removes debris

Bronchi-distributed air, filters, humidify and warm air

Bronchioles-walls have smooth muscles that can construct and dilate. Collateral ventilation

Alveoli-type 1 alveolar cells produces epithelial lining for gas exchange. Type 2 produces surfactant reducing surface tension. Gas exchange units has large surface tension and thin walls.

Muscles of respiration

Inspiration is active- muscles have to contract whereas expiration is passive due to lungs elastic recoil properties.

External intercostals helps ribs move up increasing horizontal diameter

Diaphragm-flattens and decends increasing vertical volume

Increased thoracic volume decreases Intrapleural pressure pulling air into lungs

accessory muscles are SCM, serratus anterior, scalenes

Muscles of expiration

Quiet expiration is passive, muscles only being used if forced expiration

Internal intercostals

Abdominals

Breathing is governed by body attempt of equalising pressure

Intrapleural pressure

Transpulmomary pressure-pressure difference between alveoli and pleural cavity (space around lungs)

intrapulmonary pressure-pressue of air inside alveoli

Atmospheric pressure

Boyles law in respiration

Thoracic volume increases, expanding chest pulls on pleura making Intrapleural pressure more negative which is transmitted to alveoli. Pressure gradient formed between alveolar pressure and atmospheric pressure which forces air into the lungs

In expiration, diaphragm relaxes, thoracic volume decreases causing intrapulmonary pressure to increase and be greater than atmospheric pressure causing air to flow out

Compliance

Elastic recoil- lungs returning to resting volume

Compliance-how easy it is for lungs to be expanded. High compliance, very easy for lungs to expand, small increase in pressure produces large increase in lung volume

High compliance= less work or breathing as lungs easier to inflate.

Factors affecting lung compliance

Lung volume

Surfactant-reduces surface tension of alveoli, easier to expand lungs

Pulmonary blood flow

Age; age increases compliance due to loose elastic recoil but decreases compliance of chest wall so overall requires higher WOB

Disease

Obesity-reduces compliance by stiffening of chest wall and lungs

Airway resistance

Determined by length, radius and cross sectional area. Decreases diameter increases resistance.

Parasympathetic NS causes bronchocontriction

B2 adrenergic receptors causes bronchodilation

Control of breathing

Neural controls: respiratory centre in medulla controls breathing rate and depth. Done by sending message via phrenic nerve and intercostal nerve to contract and relax.

Higher centres (cerebral cortex, hypothalamus, limbic systems) can voluntary control breathing eg holding breath, singing

Primary drive to breathe is the elimination of C02 as it is 4x more soluble than oxygen. C02 dissolves to form carbonic acid which lowers pH. Central chemoreceptors sense decrease in pH and stimulate resp centre to increase depth and rate of breathing.

ANS:

SNS: during stress or exercise, stimulates B2 causing bronchodilation, reducing airway resistance, allow more air to flow in

PNS:Vagus nerve. Causes bronchocontriction and increases mucus secretion during rest

Lung volumes

The amount of air exchanged during ventilation

4 lung volumes:

Tidal volume

Inspiratory reserve volume

Expiratory reserve volume

Residual volume

4 lung capacity (2 or more volumes)

Functional residual capacity

Inspiratory capacity

Vital capacity

Total lung capacity

Tidal volume Vt

Resting inspiration to resting expiration. Amount of air moves in and out lungs each breath

About 500ml

Inspiratory reserve volume IRV

Max amount of air that can be inhaled from resting inspiration. Rest inspiration to max inspiration

Expiratory reserve volume ERV

Max volume of air exhaled from resting expiration. Resting expiration to max expiration

Residual volume RV

Volume of air in lungs after max expiration. Can’t be measured by spirometer

Functional residual capacity FRC

Volume of air remaining at end expiration. Residual volume + expiratory reserve volume

Inspiratory capacity IC

Sum or Inspiratory reserve volume and tidal volume

Vital capacity VC

Max amount of air that can be forcibly exhaled from point of max inspirstion

Total lung capacity TLC

Amount of air lungs can hold. Max inspiration to max expiration and remaining air in lungs RV

Spirometry

One of many pulmonary function tests

Measures flow rates (how much and how quick air can b exhaled) and some lung volumes.

Aids diagnosis and help categorization of lung diseases being obstructive or restrictive

Obstructive- can’t get air out

Restrictive- can’t get air in

FEV1

Forced expiratory volume in 1st second of exhalation. How much air person can get out in 1st second

FVC-forced vital capacity

Ratio FEV1/FVC: relationship between values is called ratio. Allows for diagnosis of common lung diseases

Partial pressures and gas exchange

partial pressures changes throughout the respiratory system. Diffusion of O2 and CO2 occurs across pressure gradient (low to high).

PaO2 raised after gas exchange between alveoli and capillaries

PaCO2 reduced after gas exchange beteeen capillaries and alveoli

Drive to breath is controlled by central and peripheral chemoreceptors in response to pH and carbonic acid

Gas transport

Oxygen transport- getting energy to cells

Ventilation of lungs, air flows in and out of lungs and diffusion of O2 occurs from alveoli to capillary blood. Perfusion of systematic capillaries with oxygen blood and diffuses from systematic capillaries into cells.

98% of O2 transported with haemoglobin

Carbon dioxide transport- getting waste out of body

Diffusion of CO2 from cell to systematic capillaries to perfusion of pulmonary capillary blood by venous blood to diffusion of CO2 in alveoli then ventilation air out.

30% with haemoglobin, 10% dissolved state, 60% bicarbonate

gas transport percentages

Oxygen:

98% transported with haemoglobin, forming oxyhemoglobin

2% in dissolved state

CO2

30% transported with haemoglobin, carboxyhemoglobin

10% dissolved state

60% as bicarbonate

Role of haemoglobin

1.O2 diffuses from alveoli across alveolar cap membrane and moves to blood. There is high PaO2 in alveoli and lower PaO2 in incoming blood so O2 diffuses from alveoli to blood

2.O2 binds with haemoglobin in red blood cells. Each haemoglobin can hold 4 O2 molecules. Binds until Hb is saturated (holding 4)

3.O2 transported to body tissue. It dissociates from Hb and diffuses into body tissue

PaO2 and O2 bound to Hb (saturation)

S shaped graph. When O2 binds to Hb it makes it easier for next O2 to bind to Hb.

Affinity

Strength at which haemoglobin binds to oxygen

Can be affected by CO2 levels, pH, temperature,

Left shift of graph is higher affinity: Hb and O2 bind more readily when:

pH increases

CO2 decreases

Body temp decreases

CO2 transport

CO2 also binds with Hb. CO2 diffuses out cells to capillaries and is 4 times more soluble than O2.

Haldane effect: O2 released in tissue capillaries leads to CO2 binding with Hb. O2 binding with Hb in lungs facilitates release of CO2 into plasma

Flow of blood between blood and lungs

Deoxygenated blood:

Inferior and superior vena cava to R atrium to tricuspid valve to R ventricle to pulmonary arteries to pulmonary capillary network for gas exchange

Oxygenated blood:

Pulmonary capillary network to pulmonary veins to L atrium to mitral valve to L ventricle to organs and tissues via systemic circulatory system

Characteristics that facilitate gas exchange

Alveoli:

Single cell wall- thin wall

Fluid lining

Large suface area

Good ventilation

Pressure gradient

Pulmonary capillaries

Single cell wall

High Hb levels

Dense capillary bed

Good perfusion

Pressure gradient

Distribution of ventilation and perfusion

Ventilation and perfusion are usually preferentially distributed to lower lung region, where there is more blood and greater change in volume of lungs

Lower region is called dependent region: at top of lungs alveoli is stretched whereas at bottom has greater potential to stretch and more blood flow

Dependent vs non-dependent region

Describes position in relation to gravity. Eg in standing, bottom of lungs is dependent and top is non dependent. In supine, posterior part of body is dependent and anterior is non dependent

Factors affecting distribution of ventilation

Weight of lungs

Elastic properties of lungs

Gravity

How does weight of lungs affect distribution of ventilation

Dependent portion is more compressed so alveoli is more compliant requires less pressure change to create larger change in volume

Non dependent regions is already fully expanded and less compliant. Requires larger pressure chsnge to create small change in volume

How does gravity affect distribution of ventilation

Intrapleural pressure is negative and lungs are under influence of gravity. At non dependent regions are more negative and dependent regions are less negative so lower dependent regions have greater potential for change.

Dependent region has greater potential for change and to be more negative causing pressure gradient for air to flow in

How does elastic properties of lungs affect ventilation

Upper non dependent regions are more stretched than lower dependent regions and so lower dependent region have more potential of stretch so greater compliance

Characteristics of pulmonary blood vessels

Short and wide: low resistance and low pulsatile pressure

Thin and compliant: ease of diffusion and distension

Surrounded by air

Pulmonary blood vessels are surrounded by air

Transmural pressure (pressure difference between inside and outside of wall) effects pulmonary vascular resistance. If alveolar pressure is greater than pressure of capillaries, capillaries will collapse

What is blood gas analysis

Type of pulmonary function test

Provides info for metabolic state and respiratory status

Gold standard for measuring O2 and CO2 in arterial blood

ABGs (PaO2 and PaCO2) used to evaluate gas exchange in lungs

Normal ranges of ABGs

pH:7.35-7.45

PaCO2: 35-45mmHg

PaO2: 80-100mmHg

HCO3: 24-28mmol/L

BE: -2-2 mmol/L

SaO2: 96-100%

Key structures of the heart

Aorta

Right atrium

Tricuspid valve

Right ventricle

Pulmonary artery

Left atrium

Mitral valve

Left ventricle

Differences between autonomic and somatic NS

Autonomic controls unconscious perceived visceral sensations. Needs 2 neurons to connect CNS to organ

Somatic is voluntary movements and only needs 1 neurons to connect CNS to organ

Role of autonomic NS

Maintain homeostasis by adjusting vital visceral functions:

Regulation of heart (BP, HR and Contractility)

Reglation of secretory glands

Regulation of smooth muscle fibres

Hypothalamus is control centre for ANS functions

Neurotransmitters of the sympathetic division

2 pathways:

1.acetylcholine transmitted thought preganglionic axons to synaptic ganglion and is received by nicotinic receptors. Noradrenaline and adrenaline released through post ganglionic axons to effector organs

2.acetylcholine transmitted through preganglionic receptors to adrenal gland. Adrenal cortex releases aldosterone and adrenal medulla release noradrenaline to effector organs

Short preganglionic, long post ganglion’s

Neurotransmitter of PNS

Acetylcholine transmitted through preganglionic axons to synaptic ganglion received by nicotinic receptors and releases acetylcholine through postganglionic axons to effector organs received by muscarinic receptors

Long preganglionic and short postganglionic

Blood pressure meaning

Force originating in pumping action of the heart exerted by blood against walls of blood vessels

Systolic BP

Maximum pressure in arteries as heart is pumping

Diastolic BP

Minimum pressure in arteries when heart is at rest

BP formula

BP = CO x TPR/SVR

TPR/SVR

Total peripheral resistance. Resistance to blood flow in systematic circulation

Systematic vascular resistance. Force which heart must overcome to pump blood through systematic circulation

The amount of force exerted on circulating blood by vasculature of body

TPR/SVR determined by

Length of blood vessels

Diameter of vessels

Viscosity of blood

Pressure in pulmonary vs systematic system

Pressure in pulmonary system is lower than systematic because there are more pathways for blood to flow in pulmonary

Systematic: 120/80

Pulmonary: 25/8

Hypertension and hypotension

Hypertension: high BP 140/90

Hypotension: Low BP 90/60

Regulation of BP

Chemoreceptors in carotid and aortic bodies and central chemoreceptors in medulla detects changes in pH and ABGs

Peripheral baroreceptors in carotid sinus, aortic arch and R atrium detect changes in pressure

Juxtaglomerular apparatus detects changes in blood flow in kidney

Higher cortical areas alter BP in response to exercise, stress and emotion

What are the systems which regulate blood pressure

Heart via cardiovascular centre and ANS

Blood vessels via SNS

Kidneys via RAAS

RAAS

Renin, angiotensin 2, aldosterone system

Juxtaglomerular cells in kidney detects decreased blood flow and releases renin.

liver releases angiotensinogen

Renin converts angiotensinogen to angiotensin 1

Angiotensin converting enzyme converts angiotensin 1 to angiotensin 2

Angiotensin 2 is a powerful vasoconstrictor, increases TPR, increasing BP.

Angiotensin 2 stimulates release of hormones: Aldosterone from adrenal glands (adrenal cortex) and antidiuretic hormone ADH from pituitary gland.

Aldosterone simulates soul retention, increasing water retention and blood volume, increasing BP

ADH stimulates thirst which increases water intake, increasing blood volume, increasing BP