Physiology Flashcards
What is a tissue?
A group of cells with similar structure and specialised function.
What is an organ composed of?
Two or more types of primary tissues that function together to perform a particular function(s).
What is a body system made up of?
A group of organs that perform related functions and work together to achieve a common goal(s).
Normally, body systems work in ________ as a highly sophisticated _______ unit to maintain a healthy body.
- Harmony
- Integrated
What does normal body function require ?
Coordination of function from molecular and cellular to whole body function.
To maintain health, the human body must maintain optimum ___________ conditions.
physiological
Define human physiology
Study of the normal functions of the human body and the integrative mechanisms that control them at the level of:
- the cells
- the tissues
- the organs
- the body systems
- the whole body
Why is it important to undersatand physiology?
It is important to understand what is normal before we can understand abnormal.
Many more patients fall within normality.
Need to understand the deviations from normal.
Why is a firm understanding of physiology and its clinical application essential?
- understanding of body functions in health and disease
- understanding of patient presentations
- planning and interpretation of patient investigations
- Planning patient management options
- providing health promotion and disease prevention advice
Much of the physical control occurs at the level of the ____ ____________.
Cell membrane
Give two reasons why the physiology of the cell membrane is important
- Change in cell membrane potential (or voltage across the membrane between inside and outside a cell) is central to the functionality of nerve and muscle cells.
- Many pharmaceutical agents act at the level of cell membrane to produce their therapeutic effect.
Why are physiological control systems important?
They are important for the maintenance of stable internal environment within the body, called “homeostasis”.
What are the 2 divisions of physiological control which work to achieve a desired response?
-
Intrinsic controls
* local controls that are inherent in an organ - Extrinsic controls
- regulatory mechanisms initiated outside an organ.
- Accomplished by nervous and endocrine systems.
What are the two types of physiological control systems?
- Feedforward- term used for responses made in anticipation of a change.
- Feedback-refers to responses made after change has been detected.
What are the two types of feedback systems?
- Positive feedback systems: amplifies an initial change e.g. increasing strength of uterine contraction until a baby is born.
- Negative feedback systems: opposes an initial change- MAIN TYPE OF PHYSIOLOGICAL CONTROL MECHANISMS
Define homeostasis
Homeostasis is defined as “the maintenance of steady states within our bodies by coordinated physiological mechanisms”
Need for a constant, or near constant interntal environment is now well established and well known for the survival of the body cells and the body.
To survive and stay healthy, several __________ within the internal environment of the human body must be tightly regulated within a _________ ________.
Variables
narrow range
Why is it important to apply knowledge of homeostasis?
- One of the core concepts to understand human function in health and disease.
- Essential for the survival of body cells.
- Body cells and systems maintain homeostasis
- Many diseases are caused by deficient, inappropriate, or excessive homeostatic mechanisms.
- Disruption of homeostasis may result in disease or death.
What is the primary type of homeostatic control mechanisms within the human body?
Negative feedback control mechanisms
Do negative feedback systems amplify or oppose an initial change?
Oppose
How do negative feedback systems promote stability?
By regulation of physiological varible (regulated variable) within a narrow range.
In order to maintain homeostasis, what 3 things must a negative feedback control system be able to do?
- Sense deviations (sensor) from desired range in a regulated variable that needs to be kept within a narrow range (set point).
- Integrate this information with other relevant information (control centre).
- Make appropriate adjustments (Effector(s)) in order to restore regulated variable to its desired range set point.
Define the term ‘set point’
Range of values/range of magnitude the system desires to keep the regulated variable at.
What are the 7 steps in Negative feedback?
- Deviation in regulated variable (set point).
- Detected by sensor which informs….
- Control centre which sends instructions to…
- Effectors which bring about…
- Compensatory response which results in…
- Restoration of regulated variable to desired range.
- Negative feedback to shut off the system responsible for the response.
What is negative feedback?
A control mechanism where the action of the effector (response) opposes a change in the regulated variable and returns it back to toward the set point value.
Name 5 examples of variables regulated via negative feedback mechanisms…
- Mean arterial blood pressure
- core body temperature
- blood glucose
- blood gases (arterial Po2 and PCO2)
- Blood H+ concentrtion (pH) (acid-base balance)
Homeostasis is the maintenance of ________ stable (near-constant) _______ environment within the body.
relatively
internal
_______ feedback control mechanisms are the primary homeostatic mechanisms within the human body.
Negative
Negative feedback control mechanisms function to keep a ________ __________ relatively stable at a ___ ______ by opposing changes.
Regulated variable
Set point
What are the three components of a negative feedback control mechanism?
- A sensor
- A control centre
- Effectors
Define blood pressure
The outwards (hydrostatic) pressure exerted by the blood on blood vessel walls.
How is blood pressure measured and expressed in clinical practice?
We often measure the systemic arterial blood pressure and express it as “systolic” and “diastolic” blood pressures.
Define systemic systolic arterial blood pressure
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart contracts.
Define systemic diastolic arterial blood pressure
The pressure exerted by the blood on the walls of the aorta and systemic arteries when the heart relaxes.
Explain one way we can indirectly measure systemic arterial blood pressure?
Measuring the pressure in the brachial artery in the anti-cubital fossa using a stephascope and a sphygmomanometer.
Does the ideal normal arterial blood pressure remain the same between individuals or does it vary?
It varies
What is the range of ideal normal arterial blood pressure for adults below 80 years?
Varies between individuals from 120/80mmHg to 90/60 mmHg
In this range, what is normal for one individual may be high or low for another.
Define hypertension
Clinical blood pressure of 140/90mmHg or higher and day time average of 135/85mmHg or higher.
What is pulse pressure?
The difference beteween systolic and diastolic blood pressures
What is the normal range for pulse pressure?
Between 30 and 50mmHg
What is mean arterial blood pressure?
Mean arterial blood pressure (MAP) is the average arterial blood pressure during a single cardiac cycle, which involves contraction and relaxation of the heart.
Why is average arterial blood pressure (MAP) not obtained by averaging systolic and diastolic pressures?
Because during a normal cardiac cycle the relaxation (diastolic) portion of the cardiac cycle is about twice as long as the contraction (systolic) portion of the cardiac cycle.
What are the two formulas for calculating mean arterial blood pressure (MAP)?
- MAP= [(2xdiastolic) + systolic] divided by 3
- MAP= DBP + 1/3 pulse pressure (difference between SBP and DBP)
What is the normal range of mean arterial blood pressure (MAP)?
70-105mmHg
What is the mimimum MAP required to perfuse vital organs like brain, heart and kidneys?
At least 60mmHg
What happed if the MAP is not regulated and becomes too high?
It can damage the blood vessels or place an extra strain on the heart and other organs like the brain, kidneys and eyes.
What is the negative feedback control system used in the short term regulation of MAP?
Baroreceptor reflex
What are the sensors involved in the negative feedback system controlling MAP which send information to the control centre?
Baroreceptors
Where is the control centre located in the baroreceptor reflex which sends information to the effectors?
Cardiovascular control centre (medulla)
Which 2 effectors bring about a compensatory response in the baroreceptor negatvie feedback system?
- Heart (varying heart rate and stroke volume)
- Blood vessels (varying systemic vascular resistance)
Outline the 6 steps involved in the negative feedback system which regulates the MAP.
- Deviation in the Mean arterial pressure
- Detected by the baroreceptors
- The cardiovascular control centre (Medulla) receives info from the baroreceptors and sends it to the effectors.
- The Heart and blood vessels bring about a compensatory response by varying HR and SV and SVR.
- This result in restoration of the MAP to the desired range.
- Negative feedback to shut off the system responsible for the response.
What are baroreceptors?
Mechanoreceptors which are sensitive to stretch.
Where are baroreceptors located?
- The carotid sinus at the bifurcation of the common carotid artery into external and internal carotid artery
- Aortic arch
How do signals from the baroreceptors in the carotid sinus reach the medulla?
Via the glossopharyngeal nerve or the 9th cranial nerve
How do signals from the aortic baroreceptors reach the medulla?
Via the tenth cranial nerve or the vagus nerve
Does the firing rate in baroreceptors afferent neurons increase or decrease when the mean arterial blood pressure (MAP) increases?
Increases
The firing rate in baroreceptors in afferent neurons ___________ when the mean arterial blood pressure (MAP) decreases.
Decreases
What is the cardiovascular system in the medulla of the brainstem in charge of?
It modulates the activity of the autonomic nervous system- parasympathetic and sympathetic nervous system.
What kind of information does the cardiovascular control centre receive?
CVS afferent information
What is the site of the 1st synapse for all CVS afferents in the medulla?
The nucleus tractus solitarius (NTS)
What does the nucleus tractus solitarius (NTS) do with information from the baroreceptors?
NTS relays information to other regions in the brain e.g. medulla, hypothalamus, cerebellum
What 2 things happen when the nucleus tractus solitarius (NTS) relays info to other regions of the brain?
- Generates vagal (parasypathetic) outflow to heart- relay to nucleus ambiguus in the medulla.
- Regulates spinal sympathetic neurones: supply includes heart rate and blood vessels.
Mean arterial pressure (MAP) = Cardiac output (CO) X ____________ ____________ _______________
Systemic vascular resistance (SVR)
How can you calculate the cardiac output?
Cardiac output= Stroke volume x Heart rate
CO= SV X HR
Define cardiac output
The volume of blood pumped by each ventricle of the heart per minute.
Define stroke volume
Stoke volume is the volume of blood pumped by each ventricle of the heart per heart beat.
How else can the MAP therefore be calculated using stroke volume, heart rate and systemic vascular resistance?
MAP = Stroke volume x Heart rate x Systemic vascular resistance
What is systemic vascular resistance?
The sum of resistance of all vasculature in the systemic circulation.
Mean arterial blood pressure can be regulated by regulating which three factors?
- Heart rate
- Stroke volume
- Systemic vascular resistance
What is the heart?
An electrically controlled pump which sucks and pumps blood.
Where are the electrical signals which control the heart generated?
Within the heart
Define autorhythmicity
The heart is capable of beating rhythmitaclly in the absence of external stimuli.
What modifies the heart rate?
The autonomic (involuntary) nervous system (ANS)
What does the sympathetic division of the autonomic nervous system do? Which hormone and receptor is involved?
- Stimulation accelerates the heart rate (tachycardia)
- noreadrenaline (norepinephrine) acts on ß1 receptors
What does the parasympathetic division of the nervous system do? Which hormone and receptors are involved?
- Stimulation of the vagus nerve (10th cranial nerve) slows the heart rate (bradycardia)
- Acetylcholine acts on muscarinic receptors
Stroke Volume ________ if the contractile strength of the heart is increased.
Increases
Which nervous system regulates the stroke volume?
The autonomic nervous system.
Describe how the autonomic nervous system regulates the stroke volume
Sympathetic nerves innervate the ventricular myocardium, and stimulation increases the force of contraction and increases stroke volume.
Does the vagus (parasympathetic) nerve effect ventricular contraction?
Has little direct effect on ventricular contraction.
What is in charge of intrinsic controll of stroke volume in the heart?
The frank starling mechanism or the Starling’s law of the heart
Which vessels are the major resistant vessels in systemic vascular resistance?
Arterioles
Does vasoconstriction increase or decrease systemic vascular resistance?
Increase
What regulates systemic vascular resistance?
Vascular smooth muscles
What are the consequences of contraction of vascular smooth muscles?
- Causes vasoconstriction
- Increases SVR and MAP (i.e. pressure upstream)
What are the consequences of relaxation of vascular smooth muscles?
- Vasodilation
- Decreases SVR and MAP
The vascular smooth muscles are supplied by __________ nerve fibres. The neurotransmitter is ____________ acting on __ receptors.
- sympathetic
- noreadrenaline
- alpha
What is vasomotor tone?
Vascular smooth muscles are partially constricted at rest. This is called the vasomotor tone.
What causes vasomotor tone?
Tonic(continuous) discharge of sympathetic nerves resulting in continuous release of noreadrenaline.
How does increased sympathetic discharge impact the vasomotor tone and what are the consequences?
- Increases the vasomotor tone
- Results in vasoconstriction (increase SVR and MAP- pressure upstream)
How does decreased sympathetic discharge effect the vasomotor tone and what are the consequences of this?
- Decreases vasomotor tone
- Results in vasodilation (decrease SVR and MAP)
How are arterial smooth muscles impacted by the parasympathetic nervous system?
There is no significant parasympathetic innervation of arterial smooth muscles- exceptions are the penis and clitoris.
What does negative feedback do?
Acts to minimize any disturbances to a controlled variable e.g. mean arterial pressure
What is the only type of change in arterial blood pressure that baroreceptors respond to?
Acute changes
What happens to baroreceptor firing if high arterial blood pressure is sustained?
It decreases
What happens in relation to baroreceptors if high arterial blood pressure is sustained?
- Baroreceptors “re-set”- they will fire again only if there is an acute change in MAP above the new higher steady state level.
Baroreceptors _______ supply information about prevailing steady state arterial blood pressure.
Cannot
Define the respiratory rate
No. of breaths per minute
What do oxygen saturations refer to?
The extent the haemoglobin in the blood is saturated with oxygen.
What does AVPU stand for and what is it used for?
- A-alert
- V-response to voice
- P-response to pain
- U-unresponsibe
- Used for assessing the level of consciousness of a patient
What is the normal resting Pulse/heart rate for adults?
60-100 bpm
What else do we assess when checking the pulse?
- rhythm
- volume
- character
Name 7 commonly assessed clinical vital signs
- pulse
- blood pressure
- respiratory rate
- oxygen saturation
- temperature
- consciousness
- capillary refill time
What is an adults normal resting respiratory rate?
12-20 breaths/min
What should normal oxygen saturations be?
96% or higher
What is the capillary refill time?
A measure of the time it takes for a distant capillary bed e.g. in a fingernail or toe nail to regain colour after pressure is applied to cause blanching.
What is the normal capillary refill time?
< 2 seconds
The human body can be thought of as a ____ and an outer shell.
core
What does the outer shell of the body consist of?
Skin and subcutaneous tissue
What is the core body represented by?
The structures deep within the body
What is the “core body temperature”?
Temperature of the blood and internal organs.
The core temperature is homeostatically maintained in the structures deep within the body at about ____°C.
37.8
Why is skin temperature not a good site for monitoring body temperature?
It varies more widely than the core body temperature.
The core body temperature is kept almost _________ despite changes in the environment.
What is the narrow range it is kept within called?
- Constant
- normothermia
Normothermia is optimum for which two things?
Cellular function and metabolism
What happens to cellular metabolism when body temperature increases?
It increases
What happens when the body overheats?
Causes protein denaturation, nerve malfunction, convulsions and death.
What happens when body temperature decreases?
Slows down cellular metabolism and function, and can also be fatal.
Give 3 examples of indirect estimate of core body temperature
- infrared typanic (eardrum) thermometer
- infrared forehead
- forehead strips
Typanic thermometers are commonly used in clinical practice. What is the normal range they should be detecting?
36ºC-37.5°C
Define an abnormally high core body temperature
38ºC or above
What temperature range defines fever?
38-40°C
Define hyperthermia
Core body temp above 40°C
What is abnormally low body temperature (hypothermia) defined as?
Below 35°C
Which peripheral sites should you avoid using to estimate core body temperature?
- oral/sublingual
- axilla
How can direct estimate of body temperature be acquired?
Rectal or Oesophageal: slightly higher than tympanic temperature. May become important at extremes of body temperature e.g. very low body temperature (hypothermia)
Does normal body temperature differ slightly in different individuals?
Yes
Body temperature varies slightly throughout the day in the same individual (lowest temp in the early morning). What is this called?
Diurnal variation
Which factors may alter body temperature?
- activity
- exercise
- emotions
- exposure to extremes of temperature
- varies slightly during menstrual cycle in menstruating females (higher during the 2nd half of the cycle from the time of ovulation)
To maintin a constant core body temperature the ____ _____ and ____ ____ must be in _________.
- heat gain
- heat loss
- balance
How can heat be gained from the internal and external environments?
From internal environment
- metabolic heat gain
From External environment
- Radiation
- convection
- conduction
Heat can only be lost to the external environment. What are four ways this can occur?
- radiation
- conduction
- convection
- exaporation
What happens with heat gain and heat loss if core body temperature is decreased?
Heat gain is increased
Heat loss is decreased
The opposite is true if core body temp increases
What is metabolic heat which leads to internal heat gain?
Oxidation of metabolic fuel derived from food in the body.
What is the basic metabolic rate (BMR)? What does this lead to?
- Minimum amount of energy required to sustain vital body functions.
- Leads to basic level of heat production.
The BMR can be increased by hormones, provide three examples.
- adrenaline
- noreadrenaline
- thyroxine
How does muscle activity affect heat production?
Muscle activity increasing can increase metabolic heat production enormously.
shivering increases heat production by increasing muscle activity.
Define radiation
Emission of heat energy in the form of electromagnetic waves from a suface. Electromagnetic waves travel through the space and are transformed into heat on striking another surface.
The human body both ______ and ________ radiant heat.
- absorbs
- emits
Net heat transfer via radiation depends on what?
The relative temperature of body and surrounding objects (including the sun).
In humans, about half of the body’s heat loss is through _________.
Radiation
What is conduction?
Transfer of heat between objects in contact
In conduction does heat move from cooler to hotter objects?
No, it moves from warmer to cooler objects.
What 2 factors does heat conduction depend on?
- temperature gradient
- thermal conductivity (e.g. water is a better thermal conductor than air).
In humans does a large or small percentage of total heat exchange take place through conduction alone?
A small percentage
What is convection?
Transfer of heat energy by air (or water) currents that help to carry the heat away from the body.
What happens when convection combines with conduction?
Dissipates heat from the body
What is the impact of forced air movement across the body surface (caused by e.g. wind or a fan) on the combined effect of conduction-convection?
It increases the combined effect
What is the impact of air trapping clothes on convection?
Reduces convection
Explain the role of evaporation in cooling the body
Energy is required to convert water in the skin surface and the lining of the respiratory airways into vapour. This energy comes from the body resulting in evaporative heat loss and hence cooling of the body.
Passive evaporative heat loss occurs continuously- explain how this happens
Water molecules continuously passively diffuse from the surface of the skin and the linings of the respiratory airways.
Sweating is an ________ evaporative heat loss process controlled by the ___________ nervous system.
- active
- sympathetic
Relative humidity of the atmosphere affects the extent of evaporation and hence evaporative heat loss. Is this true or false?
True
To maintain a constant core body temperature the heat gain and heat loss must be what?
In balance
How does the human body maintain its core temperature at a set point?
The human body maintains its core temperature at a set point by homeostatic mechanisms involving a negative feedback control system.
What does negative feedback do in relation to body temperature?
Tends to cancel out any disturbance to core body temperature.
What are the sensors in the negative feedback mechanism for temperature control and where are they located?
- central thermoreceptors (in hypothalamus, abdominal organs, elsewhere)
- peripheral thermoreceptors (in skin)
Where is the control centre located for the negative control mechanism for temperature control?
In the hypothalamus, contains the body thermostat and is where set point is determined.
What are the effectors involved in the negative feedback control system of temperature control?
- Skeletal muscles
- skin arterioles
- sweat glands
The hypothalamus (small area in the brain) has a variety of neural and ________ inputs and outputs.
hormonal
The neural inputs to the hypothalamus include those from the __________ ___________ receptors for temperature regulation.
Negative feedback
The hypothalamus acts as the body’s ____________ (maintains the temperature at a set poin).
Thermostat
What temperature is the posterior hypothalamic centre activated by?
cold
What temperature is the anterior hypothalamic centre activated by?
warmth
Give 3 examples of neural connections of the hypothalamus
- Limbic system & cerebral cortex
- motor neurons which control skeletal muscles
- sympathetic nervous system
Describe the coordinated effector response when the posterior hypothalamic centre is activated by cold.
- Skin arterioles vasoconstrict (contraction of the arterioles’ smooth muscle)- blood flow to the skin surface is reduced- heat conservation (decreased heat loss).
- skeletal muscles- increased muscle tone via shivering, increased voluntary movement (behavioural)- lead to increased head production
other behavioural changes which decrease heat loss include postural changes (reduce exposed surface area) and warm clothing.
Describe the coordinated effector response when the anterior hypothalamic centre is activated by warmth
- skin arterioles vasodilate (relaxation of the arterioles’ smooth muscles)-blood flow to the skin surface is increased (increased heat loss).
- sweat glands- sweating, evaporation of sweat increases heat loss
- Skeletal muscles- Decreased muscle tone, decreased voluntary movement (behavioural), both lead to decreased heat production
Other behavioural adaptations include cool clothing to increase heat loss.
Describe how the the temperature set point changes during fever
- infection or inflammation
- release of endogenous pyrogens (from macrophages)
- stimulate the release of prostaglandins in the hypothalamus
- raise the temp. set point in the hypothalamus
- initiation of “cold response”
- increase heat production and decrease heat loss
- Raise body temp. to new set point = fever
What do endogenous pyrogens do?
Stimulate the release of prostaglandins in the hypothalmus.
What do prosteglandins do?
Act on the hypothalamic thermo-regulatotry centre to “reset” the thermostat at a higher temperature.
Where do endogenous pyrogens come from?
Chemicals released from macrophages (certain type of phagocytic white blood cells) in response to infection or inflammation act as endogenous pyrogens.
How does the hypothalamus respond to the prostaglandins acting on it to reset the thermostat?
Initiates mechanisms to heat the body“cold response” (e.g. shivering and skin vasoconstriction) to raise the body temperature to the new set point.
How does fever result when the hypothalamus initiates mechanisms to heat the body following prostaglandins acting on it?
The body temp then increases to reach the new set point resulting in “fever”.
What happens if the pyrogen release is reduced/stopped or the prostaglandins synthesis is decreased/ceased?
The hypothalamatic set point would be restored to normal.
The hypothalamus then initiates the mechanisms to cool the body “hot response” (e.g. sweating and skin vasodilatation) to reduce the body temperature to the normal hypothalamic set point.
Why might pyrogen release be reduced or stopped or prostaglandin synthesis decreased/ceased?
- body fight cause/cause treated
- body fight cause/antipyretics
The body maintains its core temperature at a set point through _____________ mechanisms involving a _________ ___________ system.
- homeostatic
- negative feedback
If the temperature set point is raised to a new higher level, what does this result in?
Fever
What is the temperature that determines fever?
38-40°C
Extreme uncontrolled increase in body temperature (elevation of body temperature beyond accepted range due to failure of heat regulating mechanisms) is known as ______________.
Hyperthermia
What temperature constitutes hyperthermia?
Temperature above 40ºC
A drop in temperature below that required for cellular metabolism and function is known as _____________.
hypothermia
What temperatures constitute hypothermia?
Temperature at or below 35°C
