Physiology 1 22

Question 1

There are two components to respiration what are they ?

Answer 1

The two compenents of respiration = Internal and External

External respiration = external environment to tissue

• Ventilation = bulk transport of external media across a gas exchange surface
• respiratory exchange - diffusion
• circulation
• cellular exchange

Internal respiration = cellular metabolism

Question 2

What is Dalton’s law ?

Answer 2

Daltons law

• the partial pressue of gas
• the total pressure of a gas is equal to the sum of the partial pressures of the individual gases in a mixture

With altitude as the total pressure decreases, the partial pressure of a particular gas will decrease.

Partial pressure of oxygen = PO₂

_{The partial pressure of any gas will change with environment.}

Question 3

What is Henry’s law ?

Answer 3

Henrys law

The amount of gas dissolved in a liquid is afftected by the gases partial pressure and solubility coefficient of that gas.

gas dissolved = pressure of gas in the media * solubility coefficient

• gas and liquid are in equilibrium
• only free gas molecules (physically dissolved contribute to the partial pressure of gas in liquid)
• gases will always diffuse down their partial pressure gradients.

Question 4

What is Fick’s law, and what four factors affect the rate of diffusion ?

Answer 4

Describes the net diffusion rate of a gas across a fluid membrane.

• gases move down their partial pressure across a semi permeable membrane

Rate of diffusion

• surface area
• thickness or distance (T)
• pressure gradient (P)
• Diffusion coefficient (D)

Question 5

What is Boyle’s law ?

Answer 5

Boyle’s law

For a fixed amount of an ideal gas kept at a fixed temperature, pressure and volume are inversly proportional.

Question 6

What is tidal breathing and flow through breathing ?

Answer 6

Flow through breathing

• unidirectional flow of media, yeilds greater O₂ uptake
• birds, fish and some crocodiles

Tidal breathing

• relatively inefficient as external medium moves in and out through the same opening
• mammals (bidirectional).
• fresh media is mixed with depleted media

Question 7

Describe concurrent, cross current and countercurrent gas exchange ?

Answer 7

Concurrent exchange

• external medium and blood flows in the same direction
• partial pressure gradient declines
• does not exist in a biological system

Cross current exchange

• external medium and blood travels at right angles to each other
• diffusion occurs through-out declines gradually
• PO₂ is higher in blood then external medium at the end
• birds

Coutercurrent exchange

• external medium and blood flows in the opposite direction and parallel to each other
• partial pressure gradient is maintained and diffusiin is constant
• fish highly efficient

Question 8

Describe gas exchange in fish through the use of gills ?₂

Answer 8

Gills

• countercurrent exchange system
• flow through
• at every point O₂ is diffused into blood - great efficiency in gas exchange
• four gill arches - filaments - lamella
• large surface area which is proportional to how active the fish is

Buccal pressure pump - fish opens and closes mouth

Opercular suction pump - fish open and close opercular flaps

Question 9

Describe the upper and lower respiratory tract, what are these systems purpose?

Answer 9

Upper respiratory tract

• located outside the chest cavity
• no gas exchange anatomical deadspace
• covered with mucus and ciliated epithelium
• trachea and bronchi supported by cartilage
• smooth muscle lines trachea, bronchi and bronchioles.

Function = conditioning of air (warm, humidification), and filtration muco-ciliary escalator

Lower respiratory tract

• alveolar surface thin layer of squamous epithelial cells (type one)

Contains three cell types

• Type one alveolar cell - assist in gas exchange
• Type two - large cuboidal produce surfactant
• Alveolar macrophage - phagocytic patrol the alveolar surface.

Question 10

Hoe does air move into the lungs ?

Answer 10

By creating negative pressure. Increasing volume by contraction of the diaphragm and external intercostal muscles.

Question 11

Describe the histological sections of the upper respiratory tract ?

Answer 11

Trachea = C shaped cartilage

Bronchi = cartiliginous plates

Bronchioles do not have cartilage

The amount of smooth muscle increase from the trachea to the bronchioles.

Question 12

Describe the histology of the alveolar ?

Answer 12

Alveolar

• Alveolar surface covered by a dense capillary surface, lung interstitium has mast cells, connective tissue and elastic tissues to hold the alveolar open.
• mainly composed of type one alveolar cells - single layer of a single layer of sqaumous epithelial cells.
• Type two alveolar cells are cuboidal and secrete surfactant and the fluid layer which lines the lungs
• Alveolar macrophage

Question 13

What effect does the parasympathetic and sympathetic nervous system have on the lungs ?

Answer 13

Sympathetic

• air way relaxation
• blood vessel constriction
• inhibition of glandular secretion through beta 2 receptors

Parasympathetic

• air way constriction
• blood vessel dilation
• increased glandular secretion
• vagus nerve

Question 14

Describe the intrapleural space and the intrapleural pressure, and what they do?

Answer 14

Intrapleural space

• pleura anatomically seperates the lungs from the thoracic wall
• enables friction free movement between the lungs and the thorax
• lung is mechanically connected to the thoracic cage and pleura by the pleural fluid
• pressure of fluid is negative (intrathoracic pressure) holds the lungs open
• -3mmhg
• intrapleural space of the two lungs is seperated in most species
• cause for negativity is the mechanical interaction between the lungs and chest wall.

During quiet inspiration the intrapleural pressure becomes more negative, while during expiration it becomes less negative.

Question 15

What is the intrapulmonary pressure (Palv) ?

Answer 15

Alveolar or intrapulmonary pressure is the pressure of the air inside the lung alveoli

Normal respiration alveolar pressure decreases to about -1 mmhg (inspiration) and rises to about 1mmhg during expiration.

Question 16

What is the transpulmonary pressure ?

Answer 16

Transpulmonary pressure

Is the difference between the alveolar pressure and the pleural pressure (distending pressure)

• the more positive the distending pressure ptp becomes the more the lungs are distended or inflated
• ptp= Palv -Ppl

Question 17

Describe Pulmonary ventilation in mammals ?

Answer 17

Inspiration

• diaphragm and intercostal muscles contract
• lung volume increases
• lung pressure decreases belwo atmospheric pressure
• air flows down its concentration gradient
• inspiration is always active as it requires muscle contraction
• 1-2% of the total energy metabolism

Expiration

• diaphragm and intercostal muscles recoil
• lung volume decreases
• lung pressure increases
• internal intercostal muscles may contract to assist with expiration
• passive process in rest

Question 18

What is eupnea ?

Answer 18

normal quiet breathing

Question 19

What is Hyperpnea ?

Answer 19

increased depth and frequency of breathing during exercise

Question 20

What is Tachypnea ?

Answer 20

excessive rapidity of breathing

Question 21

What is bradypnea ?

Answer 21

abnormal slowness of breathing

Question 22

What is polypnea ?

Answer 22

rapid shallow breathing, as occurs during panting

Question 23

What is dyspnea ?

Answer 23

Difficult, painful or laboured breathing - pathological

Question 24

What is apnea ?

Answer 24

cessation of breathing, in clinic refers to transient state of cessation of breathing

Question 25

What are adventitious sounds ?

Answer 25

crackles and wheezes abnormal sound superimposed on normal breath sounds.

Question 26

Why do birds need a more efficient gas exchange system when compared to mammals ?

Answer 26

Birds are exothermic with a higher body temperature - 40-41 degrees Highly active - flying high altitudes where the partial pressure of oxygen is lower.

Question 27

How do birds achieve a greater efficiency in respiration when compared to humans ?

Answer 27

Greater efficiency of respiration in birds * narrow diffusion distance air capillaries * flow through breathing unidirectional * cross current breathing

Question 28

How does the bird's respiration system work ?

Answer 28

Bird * During inspriration both the anterior and posterior air sacs expand * During expiration both the anterior and exterior air sacs deflate * allows for flow through breathing * lung relatively rigid and the air sacs act as bellows * both inspiration and expiration are active even at rest * respiratory muscles act upon the sternum to reduce or increase pressure within the air sacs * air exchange occurs in the parabronchi ( air capillaries) Requires two cycles to move a single bolus of air through the entire system.

Question 29

What is lung compliance ?

Answer 29

Lung compliance is a measure of how much force is required to distend the lung. * the greater the change in volume, with a smaller force = greater compliance * lung and thoracic structures * alveolar surface tension

Question 30

Why is the surfactant produced by type two alveolar cells so crucial ?

Answer 30

Surfactant Surface tension acts to reduce the surface area collapsing the alveolar. Surfactant reduces surface tension . * prevents alveolar from collapsing * reduces effort to expand lungs * prevenst adhesion of adjacent respiratory surfaces Barker syndrome = in piglets and horses is caused by too low a production of surfactant during gestation. The animal requires excessive force to extend lungs and rapid expiration.

Question 31

What is a restrictive disease of the lungs, provide an example and type of breathing pattern this will generally cause ?

Answer 31

Restrictive disease * results in restriction of lung expansion * pulmonary fibrosis - progressive scarring of the lungs seen in older terriers * causes rapid shallow breathing

Question 32

What is an obstructive lung disease, provide an example and what type of breathing pattern this will generally cause ?

Answer 32

Obstructive lung disease * Causes obstruction within the airways - decreasing airway diameter * decrease in airway diameter occurs during expiration (due to positive intrapleural pressure) * expiratory dyspnoea * animals abnormally slow and deep breathing pattern. Examples * Heaves in horses = hypersensitive to allergens * Feline asthma inflammation and constriction of the bronchioles

Question 33

In a spirogram we can obtain four lung volumes of TV, IRV, ERV and RV difine these volumes.

Answer 33

The four volumes obtained in a spirogram. ## Footnote Tidal volume (TV or VT) = volume of air inhaled or exhaled per breath Inspiratory reserve volume (IRV) = amount of additional air that can be taken into the lungs after a normal inspiration. ERV = amount of additional air than can be taken from the lungs after a normal expiration. Residual volume = amount of air remaining in the lungs after maximal expiration (can not be measured by spirometry).

Question 34

Describe what will happen if lung compliance becomes abnormal ?

Answer 34

Higher than normal compliance * Lung inflates easily but due to reduced elastic recoil it becomes difficult to expire * emphysema Lower than normal compliance * Requires increased force to expand alveoli * pulmonary fibrosis

Question 35

Define the four lung capacites inspiratory capacity, functional residual volume, vital capacity and total lung capacity obtained in a spirogram ?

Answer 35

Four lung capacity ## Footnote Inspiratory capacity = IRV + TV Functional residual capacity = ERV + TV Vital capacity = ERV + IRV + TV Total lung capacity (TLC) = VC + RV

Question 36

Define PEFR and PIFR ?

Answer 36

Peak flow rate can be taken as a quick measurement and is useful to monitor obstructive diseases. ## Footnote PIFR = Peak inspiratory flow rate The fastest flow rate achieved during inspiration PEFR = Peak flow rate achieved with maximal force during expiration after a complete inspiration.

Question 37

Define minute ventilation ?

Answer 37

Minute ventilation Minute ventilation = The volume of air breathed in or out within one minute. _mV = RR \* TV * increases during physical activity * gives the volume flow throughout the entire respiratory tract including lungs

Question 38

Define respiratory dead space, anatomical dead space, and physiological dead space ?

Answer 38

Respiratory dead space = air that enters the lungs but dose not participate in gas exchange. ## Footnote Anatomical dead space = air which fills conducting airways, conditioning, thermoregulation Alveolar dead space = gases which enter the alveolar but do not participate in gas exchange eg no perfusion. Physiological dead space = alveloar dead space + anatomical dead space In a normal healthy lung the physiological dead space = anatomical dead space as a healthy lung has no alveoli dead space.

Question 39

Define alveolar ventilation ?

Answer 39

Alveolar ventilation accounts for the fact that not all minute ventilation contributes to gas exchange Alveoli ventilation = (TV - dead space volume) \* RR It is the rate at which the alveolar air is replaced by atmospheric air.

Question 40

What is the V_a / Q ration and why is it important in respiration ?_a

Answer 40

For gas exchange to occur efficiently the ventilation of th lungs to perfusion ratio must be matched V_a / Q = 1 Maximum gas exchange * If perfusion of the lungs increases the bronchioles, alveoli will dilate in response to increase ventilation: and vice versa * local control mechanisms * bronchiole dilates - arterioles dilate * bronchiole constricts - arterioles constrict Mismatching of the V_{a and Q are the main causes of hypoxemia}

Question 41

What happens during mismatching of ventalation and perfusion, and provide an example ?

Answer 41

Ventalation V_a and perfusion Q mismatching occurs in abnormal conditions * healthy perfusion ventilation ratio = 1 * as the degree of mismatching increases, O2 exchange becomes less efficient * most common cause of hypoxemia decreased 0₂ in the blood Eaxamples * Shunt = blockage of the airway (mucous plug) so perfusion without ventilation * embolism = blockage of an artiole ventilation without perfusion

Question 42

Why would impairment of partial pressure gradient affect 0₂ but not CO_2?

Answer 42

Diffusion coefficient is higher in CO_2, than O₂

Question 43

Describe how O_2, and CO₂ are transported around the body and it what proportions ?

Answer 43

Blood needs to carry more gas than can dissolve in plasma. Oxygen is carried in two forms * bound to haemoglobin 98.5% * unbound dissolved 1.5% Carbon dioxide is carried in two forms * carbaminohemoglobin (3) as bicarbonate form Oxygen bound to hemoglobin dose not contribute to PO₂ * this maintains oxygen gradient in the lung * the amount of Hb in blood determines the oxygen carrying capacity of blood * each HB molecule binds four O_{2 molecules when fully saturated}

Question 44

What shape is the hemoglobin oxygen disociation curve, why dose the flat part occur ?

Answer 44

The oxygen haemoglobin dissociation curve is sigmoid in shape. The saturation of HB is related to the PO₂ of the blood The flat part * Favors loading of oxygen and is due to a high PO₂ * occurs in the lungs * no significant change in % saturation between 60 - 100 mmHg * at normal PO_{2 complete saturation of hemaglobin occurs} * _{large plateau of curve provides a large safety margin.}

Question 45

The sigmoid oxygen haemoglobin dissociation curve has a steep part why dose this occur.

Answer 45

Steep part * curve shows steep decline in % saturation between 40 to 10 mmHg * helps dissociate oxygen from the haemoglobin molecule

Question 46

What four factors affect the affinity of Hb for O_{2, how would these facotors be changed to cause a decrease in affinity ?}

Answer 46

The four factors * temperature * PH * 2,3 DPG * PO₂ To cause a decrease in affinity * temperature increases * PH decreases * 2,3 DPG increases * PCO_{2 increases}

Question 47

What is the BOHr affect ?

Answer 47

An increase in carbon dioxide in the blood and a decrease in PH results in a reduction of the affinity of haemoglobin for O_2.

Question 48

What affect will exercise have on the oxygen - haemoglobin dissociation curve why dose this occur ?

Answer 48

Exercise right shift of sigmoid curve decreased affinity - favoring unloading of oxygen to the tissues note = at rest only 25% of oxygen bound to HB is released to the tissues in one circuit - so there is a large reserve of oxygen for increased metabolic rate. Factors * PO_{2 reduced metabolically active tissues / reduced saturation of HB 10-40mmHG} * CO₂ increases in tissues * acidity increases * when tissues need more they get more

Question 49

Dose the form of haemoglobin vary, and why would this occur ?

Answer 49

Haemoglobin form varies between species and life stages Animals have varying form of Hb suited to their metabolic rate and environment * small animals with fast metabolism have HB with low affinity - favoring oxygen unloading in tissues * animals at high altitudes - HB higher affinity of for oxygen as the partial pressure of oxygen is lower * The effect of CO2, H+ causes different affects on HB depending upon its form * effect of 2,3 DPG varys depending on form * Fetal HB often has a lower affinity for oxygen than in its adult form.

Question 50

Describe the diffusion of oxygen at the tissue level ?

Answer 50

O_{2 diffusion tissue level} * Tissue PO₂ at rest = 40 mmhg * partial pressure of O₂ systemic 100 mmhg * partial pressure gradient = 60 mmhg Oxygen diffuses from blood into the tissue down its partial pressure gradient. Tissues with a higher demand for oxygen will be more highly vascularised.

Question 51

Describe the diffusion of CO₂ at tissue level ?

Answer 51

Tissue diffusion of PCO₂ * _{tissue partial pressure = 45mmhg} * _{systemic blood partial pressure = 40mmhg} CO₂ moves into blood from the tissues down its partial pressure gradient

Question 52

Describe the three forms carbon dioxide is transported in, within the blood ?

Answer 52

* Bicarbonate 60% * Bound to HB 30% * Dissolved 10%

Question 53

What does carbonic anhydrase do?

Answer 53

Carbonic anhydrase located within red blood cells * CO2 + H2O - H2CO3 - H+ and HC)3- * Carbonic anhydrase converts CO2 into HCO3- within the red blood cell close to the tissue * This liberates H+ ions (increasing acidity) which bind to HB causing the further release of O_{2 (Bohr effect) Chloride shift = the HCO3- ions are transported out of the cell in exchange for CL- Note the reverse happens at alveoli.}

Question 54

What is the Haldane effect ?

Answer 54

Haldane effect * CO2 binds to a different site then oxygen = CO2 binds to the globin site where as O₂ binds to the heme component. * removal of oxygen from HB in tissues increases affinity for CO2 - favouring the loading of CO2 in tissues

Question 55

What is hypoxemia ?

Answer 55

A condition where arterial oxygen tension or partial pressure (PAO2) is below normal.

Question 56

What is hypoxia ?

Answer 56

Inefficient O2 at the cellular level

Question 57

What is cyanosis ?

Answer 57

refers to a blue-purple discolouration of the skin and mucous membranes, caused by elevated concentration of deoxygenated hemoglobin.

Question 58

What is Hypercapnia ?

Answer 58

* excess CO2 in the artial blood * affects acid base balance * occurs during hyperventilation

Question 59

Name the three components that regulate the respiratory system ?

Answer 59

Respiratory system Regulated tightly to maintain concentration of O2, CO2 and H+ at constant levels independant of varying external conditions * Control centre = rhythmic neural discharge for automatic control * Chemical receptors = regulate the magnitude of ventilation to match physiological needs * modification of respiration to meet other physiological needs

Question 60

Describe the central respiratory centre

Answer 60

Pons and medulla central respiratory centre * rhythmic neural discharge for automatic control * respiratory rhythmicity originates in the brain stem : respiratory central pattern generator located pons and medulla * neurons in medulla signals inspiratory muscles * Stimulate diaphragm via phrenic nerve * stimulate intercostal muscles by the intercostal nerve.

Question 61

How does the central respiratory centre regulate expiration ?

Answer 61

Expiration * at rest expiration is due to inhibition of inspiratory neurons * when physiological demand increases expiratory neurons become activated to enhance ventaltion * Signal nerves innervate the internal intercostal muscles and abdominal muscles

Question 62

Describe how the higher brain regions can act on the respiratory centre to alter respiration ?

Answer 62

Voluntary control is innervated by the cerebral cortex * phonation, swallowing, partuition and defacation have altered respiratory signals voluntary control * cerebral cortex

Question 63

Where are respiratory central and peripheral chemoreceptors located, and what affect do theses receptors have ?

Answer 63

Central chemoreceptors = medulla close to respiratory centre Peripheral chemoreceptors = carotid bodies and aortic arch Chemical chemoreceptors regulate the magnitude of ventilation to match physiological needs * goverened by PO2, PCO2 and H+ in arterial blood which is detected by chemoreceptors.

Question 64

Describe central chemoreceptors and how they are activated ?

Answer 64

Central chemoreceptors * situated in the medulla close to the respiratory centre * Hypercapnia (high CO2) is the primary driver for activation of central chemoreceptors its action is carried out through H+ * CO2 can not cross the blood brain barrier, where as H+ can * Increased H+ in interstitual fluid of the brain stimulates central chemoreceptors * stimulates hyperventilation

Question 65

Describe peripheral chemoreceptors and how they are activated ?

Answer 65

Peripheral chemoreceptors * Located the aortic arch and carotid bodies * stimulated by a decrease in arterial PO2, increase in H+ (especially non CO2 generated as in metabolic acidosis) and increase in PCO2 * hyperventilation by stimulating the respiratory center in the medulla * increases ventilation Note - adjustment for acid base balance stimulated by an increase in H+. will stimulate peripheral chemoreceptors to a major extent and to a lesser extent central chemoreceptors. Diabetes mellitus

Question 66

Describe the evolution of the cardiovascular system ?

Answer 66

Evolution of the cardiovascular system * simple small organsisms simple diffusion * multicellular flow through system eg sponges * Fish simple two chambered heart * Amphibians three chambered heart - lead to a seperate circuit for the first time - one ventricle two atrium - some mixing of deoxygenated blood and oxygenated blood in the one atrium * mammals, birds and crocodiles eveolved a four chambered heart - two atria and two ventricles - oxygenated and deoxygenated blood completely seperated

Question 67

Name the four layers of the heart ?

Answer 67

Pericardium - contains fluid Epicardium Myocardium endocardium

Question 68

Describe the heart valves of the mammalian heart and their function - location ?

Answer 68

Heart valves Functions to ensure one way flow of blood and prevent mixing of oxygenated and deoxygenated blood Pulmonary valves = Atriventricular valves = prevented from closing by chordae tendineae supported by papillary muscles. (tricupsid valve) * the valves open and close passively * forward pressure gradient opens valves * backward pressure gradient closes valves * valvular disease will reduce cardiac output

Question 69

Describe the structure of the myocardium in the mammalian heart ?

Answer 69

Myocardium * middle layer the thickest * consits of myocardial cells which comprise 99% of the heart Myocardial cells * cardiac muscle cells * excitable, striated, mononucleated and has abundant mitochondria * intercalated disc = gap junctions which allow molecules and small ions to move between cells * The intercalated disk allows quick spread of action potentials The myocardium acts as functional syncytium contracts as a single unit. Atrial and ventricular syncytia are seperated by a layer of connective tissue

Question 70

Describe auto-rythmic cells location and their pathway through the heart ?

Answer 70

The heart depends on auto-rythmic (pacemaker cells) for rythmic beating, and does not require activation by the nervous system. * situated in the sinoidal node, aventricular node and conduction pathways of the heart * do not have a constant resting membrane potential * pacemaker activity * slowly depolarises between action potentials - declines to the firing level - pace maker potential or pre potential The SA node is the usual pace maker as HR is determined by the fastest pacemaker.

Question 71

Describe phase four action potential in the SA node ?

Answer 71

Phase four = pre potential ## Footnote Funny Na+ channels open allowing Na+ into the cell - this is unusual as it occurs while the cell is relatively polarised (if) This causes transient Ca2+ channels to open which causes further depolarisation (ica), which occurs during the second half of phase four.

Question 72

Describe what happens during phase 0 and 3 during the action potential of the SA node ?

Answer 72

Phase 0 rapid depolarisation * occurs due to opening of long lasting voltage gated CA2+ channels once the threshold potential is meet -40mV Phase 3 repolarisation * Due to opening of K+ channels and closing of Ca2+ channels * as the membrane reaches -65mV, the if Na+ channel start to reopen.

Question 73

Describe the parasympathetic activity on the SA node ?

Answer 73

Parasympathetic * Acetylcholine * Parasympathetic nerves cause a slower rate of rise in the pacemaker cells * phase four SA node prolonged * deacrease in HR

Question 74

Describe sympathetic activity on the heart ?

Answer 74

Sympathetic * catecholomines * sympathetic nerves release catacholomines which act on the beta receptors of heart muscle * increase the rate of depolarisation * increase heart rate

Question 75

Describe the conduction pathways within the heart ?

Answer 75

Conduction pathway within the heart * SA node - internodal path - AV node - AV bundle (HIS bundle) - bundle branches and purkinje fibres * atrioventricular node delays the impulse (AV node delay) * AV node and AV bundle provide the only route for the propagation of action potentials from the atria to ventricles * AV bundle splits into left and right bundle branches * purkinje fibres arising from the bundle spread impulse over the ventricular wall * rapid to allow synchronous depolarisation.

Question 76

Describe the five phases of the action potential in the cardiac contractile cell ?

Answer 76

Contractile cell * Phase 0 rapid depolarisation * opening of voltage gated Na+ channels * Phase 1 initial rapid repolarisation * opening of transient K+ channels * Phase 2 plateau phase * opening of long lasting Ca 2+ channels * Phase 3 rapid repolarisation * K+ influx by the opening of voltage gated K+ channels * Phase 4 resting phase

Question 77

In cardiac muscle what is the refractory period, compare this to the refractory period in skeletal muscle ?

Answer 77

Refractory period Occurs immediately after the initiation of an action potential, and last until the action potential is complete * no response to further excitation until the refractory period has ended. Contrast skeletal and cardiac refractory period * skelatal short 5 msec * prolonged in cardiac muscle 300msec * contractile time in cardiac muscle is longer than in skeletal muscle (as action potential duration is longer) this ensures adequate time for the ejection of blood

Question 78

What are the benefits to having a prolonged refractory period in cardiac muscle ?

Answer 78

Refractory period * cardiac muscle can not be restimulated until contraction is over - unable to have sustained contraction or summation of contraction * can not fatigue cardiac muscle * provides sufficient time to empty and refill cardiac chambers

Question 79

What physiological differences are apparent in cardiac muscle excitation coupling compared to skeletal muscle ?

Answer 79

* T tubules are wider * sarcoplasmic reticulum less extensive * Ca2+ from the ECF induces the release of Ca2+ from SR

Question 80

What is an electrocardiogram ECG, and how do we attch it ?

Answer 80

ECG is the record of electrical activity of the heart * word 'lead' in ECG recording refers to the tracing of the voltage difference between two electrodes * ECG waveforms are produced by momentary changes in voltage differences during the spread of cardiac excitation. Connection * Lead 1 right foreleg to left foreleg * Lead 2 right foreleg to left hindleg * Lead three left foreleg to left foreleg

Question 81

Describe normal ECG waves ?

Answer 81

Waves P wave * atrial depolaristation - small positive deflection * atrial repolarization is a slow process, hence dose not usually produce a significant visible wave (may be obsecured by QRS) QRS complex * ventricular depolarisation * Q first negative deflection, R large positive deflection and S negative deflection following R. T wave * ventricular repolarisation * pattern of ventricular repolarisation varies between animals and may be positive or negative.

Question 82

Describe the mechanical events which follow the electrical events on an ECG ?

Answer 82

Mechanical events which follow * p wave followed by atrial contraction * QRS followed by ventricular contraction * T wave followed by ventricular relaxation The delay of cardiac impulse conduction at the AV node prevents overlap of atrial and ventricular contraction

Question 83

In an ECG describe the PR interval, if this interval was prolonged what disease would you expect ?

Answer 83

PR interval * Longer than normal signifies a delay in impulse from SA node to ventricles * Duration of conduction from the SA node to ventricles

Question 84

QT interval in an ECG what does this signifiy ?

Answer 84

QT interval * electrical activity in ventricles - repolarisation and depolarisation * interval of QRS to T wave * influenced by electrolyte balance, drugs, ischemia

Question 85

Describe the RR interval what does it signify ?

Answer 85

RR interval * interval between two successive RR * duration is equal to one cardiac cycle * HR/min = 60/RR interval

Question 86

What is a Wiggers diagram, and describe the four phases of a Wiggers diagram ?

Answer 86

The four phases of a Wiggers diagram ## Footnote 1 = ventricular filling + gradual rise in left ventricular pressure 2a = isovolumetric contraction phase = steep rise in pressure as both valves remain closed 2b = ejection phase + left ventricular pressure is higher than in the aorta 3 = isovolumetric relaxation phase + no change in volume + both valves remain closed + steep drop in ventricular pressure

Question 87

Describe a first degree AV block - conduction block

Answer 87

First degree block * AV node block is a common dysfunction of cardiac impulse conduction * may be caused by cardiac trauma, toxins, bacterial infections etc * Three dgrees of severety of AV block are recognised First degree AV block slowed conduction through AV node PR interval prolonged

Question 88

Describe a second degree, and third degree AV block ?

Answer 88

Second degree AV block * some P waves are not followed by a QRS complex As the degree of AV block increases until the AV node fails completely and no QRS wave is seen Third degree AV block * complete conduction block * no impulse goes through the AV node * the atrium and ventricles beat at their own intrinsic rate * purkinje fibres initiate ventricular contraction * cardiac out put and blood pressure is compromised - animals will be weak and may collapse. * treat by using a pace maker

Question 89

Describe a cardiac arrhythmia and how they may be identified on an ECG ?

Answer 89

Cardiac arrhythmias Any variation in the normal rythm of the heart , requires treatment if animal develops clinical signs such as syncope * impaired impulse formation * impaired impulse conduction As seen on an ECG * no P wave * P wave not followed by a QRS * abnormal P wave * prolonged PR interval * irregular waves as in ventricular fibrillation

Question 90

Describe a cardiac arrhythmia - ectopic pacemakers and atrial fibrillation ?

Answer 90

Atrial fibrillation * frequency of the generation of action potentials is too high * common in older animals and horses * continuous random passage of action potentials within the atrium * well tolerated, few AP manage to get through the AV node Complications = blood may pool in parts of the atria forming clots

Question 91

Describe ectopic pacemakers - ventricular fibrillation ?

Answer 91

Ventricular fibrillation * electric chaos, random voltage fluctuations generated by fibrillating ventricles * no coordinated ventricular contraction * reduced cardiac out put and arterial pressure Defibrillation = CPR

Question 92

Describe parasympathetic innervation of the heart invlude function, receptors and the location of where the nerves act ?

Answer 92

Parasympathetic innervation * right vagus supplys SA node * left vagus supplys AV node and Bundle of His * Inervation of atrial muscles, but very few connections to ventricular muscle Function * reduce HR * reduce conduction of impulses * Increase delay in AV node Vagus nerve acts by releasing acetylcholine which acts upon muscarinic M2 receptors on the heart muscle

Question 93

Describe the sympathetic innervation of the heart, including function, what receptors it acts upon and where the nerves are located ?

Answer 93

Sympathetic innervation * SA and AV node * Bundle of HIS branches and ventricular muscle Function * quicker, stronger and faster * increase HR * increase force of contraction * speeds up relaxation * increases cardiac conduction velocity of impulses Sympathetic nerevs act upon beta one and two in ventricular muscle, which respond to circulating adrenaline and noradrenaline

Question 94

What creates the arterial pulse, and where can it be measured ?

Answer 94

Arterial pulse A pressure wave travels along the artery when blood is forced into the aorta during systole * pressure wave extends arteriole walls as it travels and this expansion is palpable * felt at femoral artery, facial artery, radial artery and carotid artery

Question 95

Describe S1 and S2 of the four heart sounds ?

Answer 95

Heart sounds S1 * Lub closure of atriventricular valves * denotes the onset of ventricular systole * low pitch, soft, relatively large Lub S2 * closure of aortic valves and pulmonary valves * signals onset of ventricular diastole * shorter, sharper and of a slightly higher pitch DUB

Question 96

What is a heart murmer ?

Answer 96

Heart murmer Abnormal heart sounds resulting from turbulant flow of blood through heart defects * narrowed stenotic valves * injured, leaky insufficient valves

Question 97

Define cardiac output and how is it determined ?

Answer 97

Cardiac out put It is the volume of blood pumped out by each ventricle per minute * both ventricles simulaneously pump the same amount of blood * continually adjusted to meet biological needs cardiac out put (vol/min) = stroke vol (vol pumped) \* HR (beats/min)

Question 98

Define cardiac reserve ?

Answer 98

Cardiac reserve The maximum percentage that the cardiac output can increase above normal is known as the cardiac reserve * cardiac out put can be increased up to a limit * low cardiac reserve may indicate heart disease such as cardiac failure

Question 99

Define ejection fraction ?

Answer 99

Ejection fraction This can be defined as the end fraction of duystole that is ejected juring systole SV/EDV = EF * normal EF values between 50% and 80% * index of ventricular function

Question 100

What is stroke volume and what three factors dose it depend on ?

Answer 100

Stroke volume = is the volume of blood pumped by each ventricle per beat. SV = EDV (end dystolic vol) \* ESV (end systolic volume Stroke volume depends upon three factors * pre load * after load * cardiac muscle contractility

Question 101

Describe preload and what factor affects it?

Answer 101

Pre load = extent of diastolic filling or end diastolic volume is preload. * the strength of contraction is increased by increased filling of the heart * increase in preload increases force of contraction * within limits stretching of the ventricular fibres optimizes overlap between myosin and actin filaments increasing the strength of contraction. * also increases the amount of CA2+ released from the sacroplasmic reticulum.

Question 102

What is afterload, and how can it be adjusted ?

Answer 102

Afterload = is the tension developed in the ventricular wall during ejection * determined by arterial resistance (arterial pressure) * increase in afterload - the more difficult it becomes for ventricles to eject blood * sustained high arterial pressure increases left ventricular workload - eventually leading to heart failure Higher afterload reduses stroke volume in a heart that is failing.

Question 103

Name the four organ systems involved in excretion ?

Answer 103

Four organ systems * respiratory system * digestive system * integument glands and skin * renal organs

Question 104

State the four functions of the kidney ?

Answer 104

The four functions of the kidney ? * removal of waste materials * maintenance of the composition of body fluids * production of hormones (vitamin D3, renin and erythropoietin) * production of pheramones

Question 105

What is a nephron, and what is its functional components ?

Answer 105

The nephron is the function component of the kidney. It is composed of * glomeralus * proximal collecting tubule * distal collecting tubule * collecting duct * medulla and cortex of the kidney * macula denser * Bowmans capsule

Question 106

Name and describe the two different types of nephron ?

Answer 106

Two types of nephron Juxtamedullary * specialised for the formation of concentrated urine * renal corpscles lie just above the junction of the cortex and medulla * long hoop of Henle extends into the inner medulla * supplied by vasa recta which runs parallel to the loop of Henle * varies between species eg cat 100%, pig 3% Cortical nephron * renal corpuscles lie in the outer layer of the cortex * short loop of Henle * % of cortical nephrons varies between species

Question 107

How is the renal system stimulated ?

Answer 107

Stimulation of the renal system * supplied by sympathetic nerves * primarily supply the afferent and efferent arterioles * also proximal and distal tubules, loop of Henle and juxtaglomerula cells * powerful stimulation decreses bllod flow The effect is a increase in renin, increase in Na+ reabsorption and decrease in EBF/GRF

Question 108

How is the vascularisation of the kidney unique, and what is the function of this unique system?

Answer 108

Vascularisation of the kidney and its function * kidney highest blood flow per unit mass among major organs 20-25% * mainly for the rate of glomerula filtration * double capillary network in series Glomerulus = high pressure capillary bed favors filtration (60mmhg) Pertubular capillary network = low pressure capillary network (20mmhg) permits rapid reabsorption. Note afferent arterioles are shorter and wider than efferent arterioles, which is required for the high pressure within the glomerulus.

Question 109

Describe the three basic steps of urine formation ?

Answer 109

Glomerular filtration tubular reabsorption tubular secretion

Question 110

How does the glomerular barrier prevent the filtration of proteins and cells?

Answer 110

All molecules and ions are filtered at the same concentration as in plasma except protein and cells. What prevents protein and cells being filtered the glomerular barrier * endothelium capillary (fenestrated negative charge) * Basement membrane or basal laminar capillary (negatively charged, collagen and proteoglycans) * epithelial cells of the Bowman's capsule (negatively charged) which have podocytes

Question 111

What is a podocyte ?

Answer 111

Podocyte * Within the epithelial cells of the Bowman's capsule * has foot processes * negatively charged * prevents the filtration of proteins and cells

Question 112

What determines the net filtration pressure ?

Answer 112

Net filtration pressure * glomerula hydrostatic pressure * Glomerula protein osmotic pressure (colloid osmotic pressure opposes filtration). * hydrostatic pressure of the Bowman's capsule (opposes filtration) The colloid osmotic pressure of the Bowman's capsule is negligible as proteins are not filterred in a healthy kidney. The changes in glomerular hydrostatic pressure is the main means for physiological control regulation of GFR.

Question 113

Describe the glomerular filtration ?

Answer 113

Glomerular filtration * fenestrated capillaries * high capillarie hydrostatic pressure * capillary tuft inbetween two arterioles The afferent arterioles are shorter and wider than efferent arterioles - which is required for high pressure within the glomerulas * glomerular filtration is a passive process * filtrate is identical to plasma (PH, osmolality) **but protein free** *

Question 114

Describe the juxta glomerular apparatus ?

Answer 114

Juxtar glomerular apparatus * autoregulation * GFR and RBF are primarily determined by the glomerular hydroastaic pressure * constriction of afferent arteriole increases GFR, but severe constriction decreases GFR Composed of -ve feedback mechanism * juxta glomerular cells (granular cells). Located mostly around the afferent arteriole, and act to secrete renin * Lacis cells which are located between the afferent and efferent arteriole. These cells are involved in the renin-angiotensin-aldosterone system. * Macula densa - afferent arteriole or modified distal tubule. The macular densa detects changes in tubular fluid Na+ and Cl-

Question 115

Desribe how GFR may be measured ?

Answer 115

Glomerular filtration rate GFR is the sum of filtration rates of all nephrons = total glomerular filtration rate . Measurement of GFR is the best single means of assessing kidney function. Criteria for a substance to be used to measure GFR are * freely filtered (not reabsorbed or secreted) * non toxic, not metabolised or stored within the kidney * substance which meet these criteria inulin, iohexol and endogenous creatine. * Plasma creatine concentration is a good indicator of GFR as it is freely filtered, produced continuously and excreted in urine.

Question 116

What is renal clearance ?

Answer 116

Renal clearance It is a measure of the kidneys ability to remove substances from the plasma * of a substance is the volume of plasma from which that substance is removed by the kidneys per minute.

Question 117

Describe how you could obtain a estimate of GFR ?

Answer 117

Estimate of GFR Creatine Criteria for a substance to be used in estimation of GFR * freely filtered (not secreted or absorbed) * non toxic, not metabolised in the body or stored in the kidney * inulin, iohexol and endogenous creatine Why is creatine suitable * continuous production, being a byproduct of muscular metabolism * freely filtered * excreted in urine * frequently used to measure GFR

Question 118

Describe tubular function ?

Answer 118

Tubular function Glomerular filtration is non selective (to a large extent) process but tubular reabsorption and secretion are highly selective processes. * modulating the volume and composition of urine * structure of each tubule section is adapted to its specific function * transport proteins present on the cell membrane of tubular lining in each part of the tubule varies - which is the reason for the different function by different parts of the tubule.

Question 119

Describe the process behind tubular reabsorption ?

Answer 119

Process of tubular reabsorption Process * driven by sodium - potassium ATPase (generates Na+ gradient inside of the cell) * reasorption and secretion of most substances inside the tubule is driven by ATPase system. * Cotransport - Na+ and solute same direction * Counter transport - Na+ and solute moves in opposing directions Process of solute transport * paracellular reabsorption * transcellular reabsorption * carrier mediated transport

Question 120

Describe carrier mediated transport across the apical membrane ?

Answer 120

Carrier mediated transport in the kidney * 5-10% of mammalian genes code for transport proteins * lack of causes many kidney diseases * numerous transport proteins are crucial drug targets

Question 121

Describe the glucose reabsorption and where it occurs ?

Answer 121

Glucose reabsorption in the proximal tubule Normally glucose is completely reabsorbed by the proximal tubule * secondary active transport, which prevents nutritive loss * sodium ion and glucosetransported into PT cell by sodium-glucose transporter (SGLT) on luminal side * glucose is then transported out of the cell by Glut2 transporter * eventually glucose enters the blood

Question 122

What is glycosuria, and what dose it cause ?

Answer 122

Glycosuria It is the pressence of glucose in urine * a common cause is diabettes mellitus due to rise in blood glucose conc * may also occur in tubular two dysfunction (SGLT mutations) * also causes an excessive water loss into the urine, a process called osmotic diuresis (osmotic effect of glucose) * carrier mediated transport is saturable - renal threshold filtered load \> reasorbing capacity of the proximal tubule

Question 123

Describe the function of the proximal tubule ?

Answer 123

Function proximal tubule * 65% of filtered Na+, CL- and water reabsorbed * osmotically reabsorbed * reabsorbs glucose, amino acids, Na+, K+, CL-, Ca++ and HCO3- * 40% of urea reabsorbed via pinocytosis * secretes organic anions and cations.

Question 124

Describe the function of the loop of Henle

Answer 124

Describe the function of the loop of Henle Descending * highly permeable to water and moderately to urea Ascending part * thin impermeable to water, but permeable to sodium * thick reabsorbs 25% of Na+, Cl- and K+ Both thin and thick ascending parts are impermeable to water

Question 125

Describe the function of the distal part of the tubule ?

Answer 125

Function of distal tubule ## Footnote The first part of the distal tubule resembles that odf the ascending loop of henle - permeable to water and reabsorbing Na+ and Cl- **The late distal tubule and collecting duct reabsorb sodium and is impermeable to water.** Avid absorption of salts without water absorption produces a hypotonic tubule fluid, thus, these segments are sometimes called diluting segments.

Question 126

Describe the function of the medullary collecting duct ?

Answer 126

Medullary collecting duct Crucial in determining the final output of urine and solutes * permeability to water depends on ADH * permeable to urea contains urea transporters * secretes hydrogen ions against a lrage concentration gradient

Question 127

Describe the function of principle cells, intercalated disks and where are they located ?

Answer 127

Both principle cells and intercalated disks are located in the late distal tubule and collecting tubule Principal cells * reabsorb sodium from the lumen * secretes potassium * may become permeable to water in the pressence of ADH Intercalated disks * key role acid base balance * alpha cells secrete H+, reabsorb bicarbonate * Beta cells secree bicarbonate and reabsorb H+

Question 128

The kidney acts to regulate four physiological parameters simultaneously, what are these parameters ?

Answer 128

Four physiological parameters * water balance * osmolality * ECF volume * blood pressure

Question 129

Discuss Na+ reabsorption within the proximal tubule ?

Answer 129

Proximal tubule * 65% of the mass of filtered sodium is reabsorbed * isosmotic tubular fluid Angiotensin 2 * enhances Na+ reabsorption from the proximal tubule * early Na+ reabsoprtion is linked to nutrient transport and H+ secretion

Question 130

Describe Na+ reabsorption by The thick ascending limb of loop of Henle and early distal tubule ?

Answer 130

Ascending limb and distal tubule. Thick ascending limb reabsorbs Na+ and Cl- but is virtually impermeable to water. * hypo-osmotic (more dilute fluid) tubular fluid when compared to the plasma **ADH vasopressin** = enhances Na+ reabsorption from thick ascending limb

Question 131

Describe the reabsorption of Na+ by the late distal tubule and collecting tube ?

Answer 131

Na+ reabsorption in the late distile tubule and collecting duct ## Footnote **Principal cells** = Na+ entry from the lumen is via an ion channel epithelial sodium channel (ENaC) **Aldosterone** = increases the absorption of Na+ and increases K+ secretion in principal cells

Question 132

What affect does Natriuretic peptide have on sodium reabsorption ?

Answer 132

Natriuretic peptide reduses sodium reabsorption in the principal cells of the later distal tubule and collecting duct. In response to a high ECF volume the atrial wall becomes distended. This results in the release of atrial natriuretic peptide (ANP) which decreases sodium absorption from principal cells.

Question 133

Describe the RAAS Renin-angiotensin, aldosterone system and what it achieves ?

Answer 133

Renin-angiotensin aldosterone system * important salt conserving system * important role in regulating Na+ balance * ECF palsma volume * regulation of arterial pressure. Angiotensin two stimulates the production of * ADH vasopressin, acts upon the ascending loop of Henle to incrase Na+ absorption * aldosterone acts upon principal cells to increase Na+ absorption.

Question 134

Identify the six effects of Angiotensin 2.

Answer 134

Angiotensin two acts to increase ECF volume in several ways. (defends against a decrease in ECF volume). * increase water retension * increase thirst * vasocontriction of the systemic circulation * stimulate secretion of ADH posterior pituitary * stimulate secretion of aldosterone secretion * increase proximal tubule Na+ absorption + increase action of principle cells to increase Na+ absorption Aldosterone and ADH is released from the zona glomerulosa

Question 135

Describe the actions of ADH (antidiuretic hormone) on the renal tubule ?

Answer 135

ADH Acts to decrease volume and increase concentration * increase in plasma osmolality (concentrated) results in increased secretion of ADH * inserts urea transporters increasing urea uptake * stimulates reabsorption of Na+ thick ascending loop of Henle * Inserts aqau porins in the luminal membrane of principal cells increasing water reuptake * negative feed-back mechanism

Question 136

What is the affect of aldosterone on the kidney?

Answer 136

Aldosterone