Cardiorespiratory system Flashcards
What is homeostasis?
Homeostasis is the property of a system in which a variable is actively regulated to remain nearly constant. In the body it is the maintenance of the internal environment, faced with variation in the external environment, activity, and intake of nutrients
How is homeostasis maintained in the body?
The core mechanism is a negative feedback loop
What are the functions of the cardiovascular system?
Rapid transport & distribution of nutrients and waste products
Distribution of water, electrolytes & hormones
Exchange between blood vessels and interstitial fluid
Infrastructure of immune system
Temperature regulation
What is pulmonary circulation?
Blood going to the lungs under low resistance and pressure
What is systemic circulation?
Blood going to the rest of the body under high resistance and pressure
What is the arterial system?
Blood flowing away from the heat in arteries under high pressure
Why is venous return important?
The heart can only pump out blood that comes back
Define systolic blood pressure
Blood pressure when the heart contracts
Define diastolic blood pressure
Resting blood pressure when the heart isn’t contracting
Describe the atria
Thin-walled (compare with ventricles)
Receive venous blood (reservoir function)
Right atrium receives systemic venous blood, left atrium receives oxygenated venous blood
Act as pumps to fill ventricles at low pressures
Produce the hormone atrial natriuretic peptide (ANP)
Describe the ventricles
Eject blood into the arterial systems including to lungs
Left ventricle has a thicker wall than the right ventricle and generates higher pressures – blood to systemic circulation
What structure within the heart initiates the beat?
The sinoatrial node. It’s the physiological pacemaker, maintaining the heart’s rhythmicity.
What does the P wave of an ECG correspond to?
Atrial depolarisation
What does the QRS complex of an ECG correspond to?
Ventricular depolarisation
What does the T wave of an ECG correspond to?
Ventricular repolarisation
What does the PR interval of an ECG correspond to?
Atrioventricular conduction
What does the QT interval of an ECG correspond to?
Duration of ventricular activation
Define tachycardia
A fast resting heart rate (>100 bpm)
Define bradycardia
A slow resting heart rate (<60 bpm)
Cardiac output =
heart rate X stroke volume
What does cardiac output measure?
The volume of blood ejected from the heart per minute (litres per minute)
What is stroke volume?
The volume of blood pumped from the left ventricle per beat.
What factors influence stroke volume?
Intrinsic factors: preload (the initial stretching of the cardiomyocytes prior to contraction), afterload (the pressure against which the heart must work to eject blood during systole)
Extrinsic factor: contractility (via nerve input)
Starling’s law of the heart
The energy of contraction of a cardiac muscle fibre, like that of a skeletal muscle fibre, is proportional to the fibre length at rest.
Define the term ‘mean arterial pressure’
Average blood pressure at the tissues
Mean arterial pressure=
(Cardiac output x total peripheral resistance) + central venous pressure
Why is controlling blood pressure important?
BP too low: poor perfusion e.g. lack of blood to brain on standing up
BP too high: excessive pressure at the small vessels in tissues, loss of fluid to tissue; excessive afterload on heart
What are the functions of the respiratory system?
Inhalation and exhalation
Exchange of gases between the lungs and the blood, and between the blood and body tissues
What does respiration refer to?
All the processes involved in the exchange of O2 and CO2 between the cells and the external environment
Regulatory mechanisms for the respiratory system ensure that…
Ventilation of the lungs is matched with its blood supply (perfusion)
The O2 supply and CO2 removal vary appropriately with activity eg. in exercise
The regulation of respiration another example of homeostasis
Why do mammalian lungs have a large surface area?
Increased area for diffusion, making gas exchange efficient
Describe the process of respiration
Ventilation –> gas exchange in the lungs –> gas exchange between capillaries and tissues –> metabolism –> bulk transport via circulation
Pressure of a system=
The sum of the separate (partial) pressures that each gas would exert if it alone occupied the entire volume
Define the term ‘physiological dead space’
The volume of air which is inhaled that does not take part in the gas exchange
Why does some of the air inhaled not take part in gaseous exchange?
It remains in the conducting airways, or reaches alveoli that are not perfused or poorly perfused.
What is anatomical dead space?
The portion of the airways (such as the mouth and trachea to the bronchioles) which conducts gas to the alveoli. No gas exchange is possible in these spaces.
What is alveolar dead space?
Alveoli which have little or no blood flowing through their adjacent pulmonary capillaries, i.e., alveoli that are ventilated but not perfused, and where, as a result, no gas exchange can occur
Which substances is blood specialised to transport?
Oxygen and carbon dioxide
Give the equilibrium of carbon dioxide and bicarbonate in the blood
CO2 + H2O ⇌ H2CO3 ⇌ H+ + (HCO3)-
Why does the formation of bicarbonate never get to equilibrium?
It never goes to equilibrium because the products are removed by two mechanisms:
1) chloride/ bicarbonate exchange (‘chloride shift’)
2) H+ buffering by haemoglobin
Why is it important to regulate [CO2] in the blood?
If [CO2] gets too high, it could lead to the blood becoming too acidic. If the blood pH drops below 7.2, then very soon the brain won’t be able to function normally
What is hyperventilation?
An increased ventilation rate
What is hypoventilation?
A decreased ventilation rate
What are chemoreceptors?
A chemoreceptor is a specialised sensory receptor cell which responds to a chemical substance and generates a biological signal
What do the carotid and aortic bodies detect?
They detect changes primarily in oxygen. They also sense increases in CO2 partial pressure and decreases in arterial pH.
What is the pulmonary circulation loop?
The pulmonary circulation loop is the part of the circulatory system which carries deoxygenated blood away from the right ventricle of the heart, to the lungs, and returns oxygenated blood to the left atrium
What is the systemic loop?
A loop through the rest of the body to provide oxygenated blood, from the left ventricle to the right atrium.
What is the main function of the heart?
The heart produces the force that causes blood to circulate
What are baroreceptors?
They monitor blood pressure
What do baroreceptors do in response to low blood pressure?
They increase sympathetic stimulation and decrease parasympathetic stimulation of the heart, resulting in an increase in heart rate and force of contraction
