Physiology - Human Flashcards
Define the term feedback
Refers to responses made after a change has been detected
Define the term feedforward
The term used for responses made in anticipation of a change
Give an example of a negative feedback system
Control of blood pressure
Name the three components of negative feedback systems
- Sensor - monitors magnitude of a controlled varfiable
- Control center - compares sensor’s input with a set point
- Effector - makes a response to produce a desired effect
What does positive feedback do?
Amplifies an initial change
Give an example of positive feedback
Uterine contractions during labour become increasingly stronger until the birth of baby
In relation to the negative feedback system of mean arterial pressure: state the controlled variable, sensor, control centre and effector.
Mean arterial pressure
Baroreceptors
Cardiovascular control centre (medulla)
Heart (heart rate and stroke volume) and blood vessels (total peripheral resistance)
What is blood pressure?
The outwards (hydrostatic) pressure exerted by teh blood on 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 the normal systolic pressure?
Normally <140 mmHg under resting conditions
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 is the normal diastolic arterial blood pressure?
Normally <90 mmHg
What is mean arterial blood pressure (MAP)?
The average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart.
Which portion of the cardiac cycle is longer - diastolic or systolic?
The diastolic portion is twice as long as the systolic portion.
What is the formula for estimating mean arterial blood pressure?
MAP = [(2x diastolic) + systolic] / 3
What is the other formula for estimating mean arterial blood pressure using pulse pressure?
MAP = DBP + 1/3 (pulse pressure, which is the difference between SBP and DBP)
What is the normal range of mean arterial blood pressure?
70 - 105 mmHg
What is the minimum mean arterial blood pressure needed to perfuse the coronary arteries, brain and kidneys?
At least 60 mmHg
Where are the 2 groups of baroreceptors located in?
The aortic arch and carotid sinus
How do the carotid baroreceptors signal to the medulla?
Via the IXth CN (glossopharyngeal)
How do the aortic baroreceptors signal to the medulla?
Via the Xth CN (vagus)
What kind of receptors are the baroreceptors and what are they sensitive to?
The baroreceptors are mechanoreceptors which are sensitive to stretch.
What stimulates an increase in the firing rate of baroreceptors afferent neurons?
Increases when the mean arterial blood pressure increases
Where do the baroreceptors send afferent impulses to?
The cardiovascular control centre in the medulla of the brainstem
What is the Nucleus Tractus Solitarius (NTS)?
The site of 1st synapse for all CVS afferents in the medulla
What other regions of the brain does the NTS relay information to?
The medulla, hypothalamus and cerebellum
Where is the generation of vagal outflow to the heart relayed to?
The nucleus ambiguus in the medulla
CO X TPR = ?
MAP
What is cardiac output?
The volume of blood pumped by each of the ventricles of the heart per minute
CO = ?
stroke volume (SV) x heart rate (HR)
What is stroke volume?
The volume of blood pumped by each ventricle of the heart per heart beat
What is total peripheral resistance (TPR)?
The sum of resistance of all peripheral vasculature in the systemic circulation
What three things can regulate MAP?
Heart rate
Stroke volume
Total Peripheral Resistance
What is autorhythmicity?
The heart being capable of beating rhythmically in the absence of external stimuli.
What acts on beta-1- receptors?
Noradrenaline
What does acetylcholine act on?
Muscarinic receptors
What are the major resistance vessels?
Arterioles
What are vascular smooth muscles supplied with?
Sympathetic nerve fibers
Vascular smooth muscles are partially constricted at rest - what is this called?
Vasomotor tone
What is vasomotor tone caused by?
Tonic discharge of sympathetic nerves resulting in continuous release of noradrenaline
What will an increased sympathetic discharge do to the vasomotor tone?
Increase it resulting in vasoconstriction
When the MAP is low what happens to the rate of carotid afferent nerve fibres firing?
Decreases
When the MAP is low, what happens to the rate of cardiac vagak efferent nerve fibres activity?
Decreases
When the MAP is low, what happens to the cardiac sympathetic efferent nerve fibres activity?
Increases
When the MAP is low, what happens to the sympathetic vasoconstrictor nerve fibres activity?
Increases
Acute changes in BP are only responded to by?
Baroreceptors
What is normothermia?
The normal core body temperature
What does overheating do to protein, nerves and the body?
Protein denaturation, nerve malfunctions, convulsions and death
What is tympanic temperature?
Temperature taken from the ear drum
What is oral temperature affected by?
Consumption of food and drinks
When will an individual have their lowest temperature?
In the early morning - diurnal variation in body temperature
What happens to the normal body temperature during menstrual cycle?
In menstruating females it is higher during the 2nd half of the cycle from the time of ovulation
What are the 4 ways heat can be lost to the external environment?
Convection
Conduction
Radiation
Evaporation
What leads to the basic level of heat production?
The Basal Metabolic Rate
What is the basal metabolic rate?
The minimum amount of energy required to sustain vital body functions
What 3 hormones can increase the BMR?
Adrenaline
Noradrenaline
Thyroxine
Where are the central thermoreceptors located?
In the hypothalamus and abdominal organs
Where are the peripheral thermoreceptors located?
In the skin
What are the 3 effectors in the negative feedback of temperature control?
Skeletal muscles
Skin arterioles
Sweat glands
What does the hypothalamus act as?
The body’s thermostat (maintains the temperature at a set point)
What is the posterior hypothalamic centre activated by?
The cold
What is the anterior hypothalamic centre activated by?
The warmth
What 4 things does the hypothalamus have neural connections with?
The limbic system
The cerebral cortex
The motor neurons - control skeletal muscles
The sympathetic nervous system
What acts as an endogenous pyrogen, in relation to a fever?
Chemicals released from macrophages in response to infection or inflammation
What do endogenous pyrogens do and name one?
Interleukins
Stimulate the release of prostaglandins in the hypothalamus
What do the prostaglandins act on and what does this do?
They act on the hypothalamic thermo-regulatory centre to reset the thermostat at a higher temperature
What 2 things would restore the hypothalamic set point to normal i.e. reduce it?
Stop or reduce the pyrogen release
Decrease or cease the synthesis of prostaglandins
