Physiology Flashcards
What is blood pressure?
The outwards (hydrostatic) pressure exerted by blood on the blood vessel walls
What is systolic arterial blood pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart CONTRACTS
What is a ideal systolic pressure?
90-120 mm Hg
What is diastolic arterial blood pressure?
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart RELAXES
What’s an ideal diastolic pressure?
60-90 mm Hg
When does hypertension occur?
When clinic blood pressure is 140/90 mm Hg or higher and day time average is 135/85 mm Hg or higher
What is pulse pressure?
The difference between systolic and diastolic blood pressures
What is a normal pulse pressure?
Between 30 and 50 mmHg
What is the mean arterial blood pressure?
The average arterial blood pressure during a single cardiac cycle which involves contraction and relaxation of the heart
How do the timings for the systolic and diastolic portions of the cycle compare?
The diastolic portion is around twice as long as the systolic portion
What are the two ways in which mean arterial blood pressure can be estimated?
MAP = [(2xdiastolic) +systolic] /3 MAP = DBP + 1/3 x (difference between SBP and DBP)
What is the normal range that MAP should be within?
70-105mmHg
What is the minimum MAP needed to perfume the brain, heart and kidneys?
60mmHg
What happens if MAP isn’t high enough?
The brain, Heart, kidney and other internal organs aren’t perfused
What happens if MAP is too high?
It can damage blood vessels and put extra strain on the heart
Describe the negative feedback reflex in MAP
Deviation in MAP > triggers Baroreceptors > which informs the cardiovascular control system (medulla) > which sends instructions to the heart and blood vessels > leading to a compensatory response (varying stroke rate in the heart, stroke volume in the heart, or systemic vascular resistance in the blood vessels)
This brings the MAP back to normal and the negative feedback shuts of the system responsible for the response.
What are the two types of baroreceptors?
- carotid receptors (carotid sinus)
- aortic baroreceptors (aorta)
How do signals from the aortic baroreceptors reach the medulla?
Aortic baroreceptors > vagus nerve > brainstem
How do the signals from the carotid baroreceptors reach the medulla?
Carotid baroreceptors > herings nerve > glossopharyngeal > brainstem
What happens to the firing rate in baroreceptors agreement neutrons when MAP increases?
It increases
What happens to the firing rate in baroreceptors agreement neutrons when MAP decreases?
It decreases
What happens in the brainstem when it receives baroreceptor signals?
> The cardiovascular control centre receives information and the nucleus tractus solitarius (NTS) is the site of the 1st synapse in the medulla.
NTS relays information to other regions of the brain
which generates a vagal (parasympathetic) outflow to the heart
regulates spinal sympathetic neurones
What is cardiac output?
The volume of blood pumped by each ventricle per minute
What is stroke volume?
The volume of blood pumped by each ventricle of the heart per heart beat
How are MAP , Cardiac output and systemic vascular resistance related?
MAP = CO x SVR
How are stroke volume, cardiac output and heart rate related?
CO = SV x HR
What is systemic vascular resistance?
The sum of the resistance of all vasculature in the systemic circulation
How can MAP be regulated?
By regulating heart rate, stroke volume and systemic vascular resistance
What is meant when the heart is described as having AUTORHYMICITY
The electrical signals which control the heart are generated within the heart itself and therefore require no extreme al stimuli to rhythmically beat.
How is heart rate modified ?
By the autonomic (involuntary) nervous system (ANS)
What do sympathetic neurones do?
Modification by the ANS which results in responses such as increased heart rate, sweating, pupil dilation etc
What do parasympathetic neurones do?
Modification by the ANS to control activities when the body is at rest (salivation, urination, digestion etc)
What happens to stroke volume when the contractile strength of the heart is increased?
It increases
What regulates stroke volume?
Autonomic nervous system
What effect do sympathetic nerves have on stroke volume?
They innervate the ventricular myocardium and stimulation increases the force of contraction, increasing stroke volume
What effect does the vagus/parasympathetic nerve have on ventricular contraction ?
Little or no direct effect
What is systemic vascular resistance (SVR) regulated by?
Vascular smooth muscles
What is the main site of SVR?
Arterioles
What happens when vascular smooth muscles CONTRACT
It causes vasoconstriction and increases SVR and MAP
What happens when vascular smooth muscles RELAX
It causes vasodilation and decreases SVR and MAP
How are vascular smooth muscles supplied?
By sympathetic nerve fibres. (The neurotransmitter is noradrenaline acting on alpha receptors.)
What is vasomotor tone?
When vascular smooth muscles are partially constricted at rest
What causes the Vasomotor tone?
The tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
(Increase in sympathetic discharge = increase in vasomotor tone = increase in vasoconstriction)
(Decrease in sympathetic discharge = decrease in vasomotor tone = increase in vasodilation)
Why can’t baroreceptors stop high blood pressure affecting somebodies wellbeing?
Baroreceptors only respond to acute changes in arterial blood pressure and their firing decreases if high blood pressure is sustained.
What is Homeostatis?
The maintenance of steady states within our bodies by coordinated physiological mechanisms. It is essential for the survival and function of cells.
What are intrinsic and extrinsic controls?
Intrinsic = local controls that are inherent in an organ Extrinsic = regulatory mechanisms initiated outside an organ. Accomplished by nervous and endocrine systems.
What is feedforward?
A term used to describe responses made in anticipation of a change (usually in combination with negative feedback)
What is feedback?
Responses made after a change has been detected. Can be positive(amplifies an initial change) or negative (opposes a initial change).
what is the haemostasis?
the arrest of bleeding and the maintenance of vascular patency
what are the requirements for haemostasis?
- permanent state of readiness
- prompt response
- localised response
- protection against unwanted thrombosis
what components are essential for a normal haemostatic system?
- formation of platelet plug (primary haemostasis)
- formation of a fibrin clot (secondary haemostasis)
- fibrinolysis
- anticoagulant defences.
how are platelets formed?
they are formed in the bone marrow by ‘budding’ from megakaryocytes.
what does endothelial damage do?
exposes collagen and released Von Willebrand Factor (VWF) and other proteins to which the platelets have receptors = platelet adhesion at the site of injury.
- there is then secretion of various chemicals from the platelets which leads to aggregation of platelets and the site of injury. (platelet plug)
what can be the causes of the failure of platelet plug formation?
- vascular’-reduced no. or function of platelets
- VWF
what are the consequences of failure of formation of the platelet plug?
- spontaneous bruising and purpura
- mucosal bleeding (epitaxes, GI, conjunctional, menorrhagia)
- intracranial haemorrhage
- retinal haemorrhages.
what happens in secondary haemostasis?
fibrin clot formation
what can cause failure to form a fibrin clot?
- single clotting factor deficiencies (e.g. haemophilia)
- multiple clotting factor deficiencies (usually acquired)
- increased fibrinolysis (plasminogen to plasmin reaction, producing fibrin degradation products)
what are consequences of failure to form a fibrin clot?
- no characteristic clinical syndrome
- may be combined primary and secondary haemostatic failure
- pattern of bleeding depends on the abnormalities and the clotting factors involved.
what are naturally occurring anticoagulants?
1 - serine protease inhibitors
2 - protein C and protein S
Describe arterial thrombosis.
- high pressure
-atherosclerosis - platelet rich thrombus
treatment = aspirin and other anti-platelet drugs
Describe venous thrombosis.
-low pressure system
-platelets not activated
- activates coagulation cascade - rich in fibrin clot.
- vichows triad = stasis, vessel wall, hypercoagulability.
treatment = heparin/warfarin/ new oral anticoagulants
