11.2B Transport of substances

Question 1

The mechanism of cardiac automaticity

Answer 1

LO: Explain the mechanism of cardiac automaticity

Question 2

Functional syncytium

Answer 2

the heart consists of individual cells, the entire mass normally responds as a unit, and all cells contract together

Question 3

Myogenic

Answer 3

• cardiac muscle can contract without nervous input, BUT the strength and the rate of contraction is modified by nervous input
• muscles or tissues that can contract on their own, without any external electrical stimulus from the brain or nervous system.

Question 4

Automaticity

Answer 4

the cardiac cell’s ability to `spontaneously generate an electrical impulse (depolarize)

Question 5

4 Valves

open only one way:
-high pressure behind – open
-high pressure in front – closed

Answer 5

• Aortic valve
• Plumonary valve
• Tricuspid valve
• Mitral(Biscupid) valve

Question 6

Chordae tendinae

Answer 6

– prevents the valves from turnig inside out under the pressure

Question 7

Transverse section of the heart apex

right ventricle| septum |left ventricle

Answer 7

LEFT ventricle is thicker because it needs to pump blood all the way around the body
Whereas the RIGHT ventricle only has to get blood to the lungs

Question 8

Electrical Activity of the Heart

Answer 8

1) SAN node
2) AV node
3) Bundle of HIS
4) Righ/Left Branch Bundles
5) Purkinje fibers

Question 9

Atrioventrical valves

Answer 9

link the atria to the ventricles

Question 10

Semi-lunar

Answer 10

valves link the ventricles to the plumonary artery & aorta

Question 11

Bundle of HIS

Answer 11

• heart muscle cells specialized for electrical conduction
• transmit electrical impulses from AV node to apex via bundle branches

Question 12

Purkinje fibers

Answer 12

cardiomyocytes that are able to conduct cardiac action potential more efficiently than other heart cells
* allow syncronized contraction of the heart ventricles
* essential for **maintaining a consistent heart rhythm **

Question 13

Heart muscle DEPOLARIZATION

Answer 13

• Influx of Na+ & Ca++ causes depolarization (positive charge inside the cell)

contraction depolarization → influx of Na+ & Ca++ → negative charge at the rest

– is when a cell membrane’s charge becomes positive to generate an action potential. This is usually caused by positive sodium and calcium ions going into the cell

Question 14

REPOLARIZATION

Answer 14

– is when a cell membrane’s charge returns to negative after depolarization. This is caused by positive potassium ions moving out of the cell

Question 15

The control of heart rhythm: SA node

Answer 15

• Signals from SA node spread through atria
• The cluster of cells — sinoatrial (SA) node or pacemaker, sets the rate and timing at which all cardiac muscle cells contract
• Impulses from the SA node first spread rapidly through the walls of the atria, causing both atria to contract in unison
• During atrial contraction, the impulses originating at the SA node reach other autorhythmic cells located in the wall between the left and right atria

SA node → atria (walls) → other autorhythmic cells

Question 16

The control of heart rythm: AV node

Answer 16

• Signals are DELAYED at AV node
• Atrioventricular (AV) node – the cells that form a relay point
• The impulses are delayed for about 0.1 second before spreading to the heart apex.
• This delay allows the atria to empty completely before the ventricles contract

AV node → impulse delayed → //atria empty// → heart apex

Question 17

The control of heart rythm: Bundle branches

Answer 17

• Bundle branches pass signals to heart apex
• Then the signals from the AV node are conducted to the heart apex and throughout the ventricular walls by specialized structures called bundle branches and Purkinje fibers

AV node → signal → Bundle branches → heart apex

Question 18

The control of heart rythm: Purkinje fibers

Answer 18

• Signals spread throughout ventricles

signal → heart apex → Purkinje fibers → ventricles

Question 19

Cardiac conduction/Cardiac cycle

Answer 19

1) Atrial DEpolarization, initiated by the SA node, causes P wave
2) with atrial DEpolarization complete, the impulse is delayed at the AV node
3) Ventricular DEpolarization begins at apex, causing the QRS complex. Atrial REpolarization occurs
4) Ventricular DEpolarisation is complete
5) Ventricular REpolarization begins at apex, causing the T wave
6) Ventricular REpolarisation is complete

Question 20

Ventricle contraction

Answer 20

wave of DEPOLARIZATION flows through the Bundle of HIS

Question 21

Cardiac cycle step by step

Answer 21

1)
* The cardiac cycle begins in the right atrium.
* The sinoatrial node (SAN) in the right atrium wall contracts and relaxes automatically, making it myogenic.
* The pacemaker’s rate can be adjusted by nerves.
2)
* The SAN produces an electrical excitation wave that sweeps through the muscle in the atrial walls, causing them to contract.
3)
* The excitation wave reaches the atrioventricular node (AVN), the only way the impulse can get down to the ventricles.
* The AVN delays the impulse for a fraction of a second, allowing the ventricles to contract after the atria.
4)
* The excitation wave moves swiftly down through the septum of the heart along Purkyne tissue fibers.
* The excitation wave arrives at the base of the ventricles and sweeps upwards through the ventricle walls, causing them to contract.
5)
* The ventricles then relax.
* The SAN contracts again, and the sequence starts anew.

Question 22

Wolff-Parkinson White Syndrome

Answer 22

• is a disorder due to a specific type of problem with the electrical system of the heart which has resulted in symptoms.
• the electrical connection passes through another accessory pathway called the bundle of Kent between the atrium and the ventricle of the heart. This pathway does not cut down the electrical activity nor delay the electrical transmission going to the ventricles. This leads to extremely rapid heartbeats.

Question 23

Facts

Answer 23

• SAN initiates heartbeat
• Beat of heart is myogenic – spontaneous not started by nervous system stimulus
• Rate of heartbeat is influenced by nervous system
• Wave of electrical activity, impulses over atria triggers contraction of atrium
• Electrical activity may only pass to the ventricles via AVN and bundle of HIS (septum)
• Fibrous tissue prevents passage beyond atria
• Delay at AVN allows ventricles to fill completely from atria

Question 24

The cardiac cycle and ECG

Answer 24

LO: Use and electrocardiogram to describe the cardiac cycle

Question 25

Cardiac cycle

Answer 25

1) An electrical impulse travels from the SA node to the walls of the atria, causing the to contract 2) The impulse reaches the AV node, which delays it by about 0.1 sec 3) Bundle branches carry signals from the AV node to the heart apex 4) The signal spread through the ventricle walls, causing them to contract

Question 26

3 stages in cardiac cycle

Answer 26

* Atrial systole * Ventrical systole * Ventical diastole

Question 27

Systole

Answer 27

contraction & ejection of blood into the aorta & plumonary trunk

Question 28

Diastole

Answer 28

relaxation & fillin gif heart chambers with blood

Question 29

**Atrial systole** – the heart is filled with blood & the muscule in the atrial walls contract

Answer 29

* both atria contract * blood flows from the atria **into the ventricles** * backflow of blood is prevented by the closure of the valves in the veins The pressure developed by this contraction is not very great, because the muscular walls of the atria are thin, but it is enough to force the *blood in the atria down through the atrioventricular valves into the ventricles*. The blood from the atria does not go back into the pulmonary veins or the venae cavae, because these have **semilunar valves to prevent backflow**.

Question 30

**Venticular systole** – about 0.1 sec after the atria contract, the **ventricles contract**

Answer 30

* *Both ventricles contract.* * The **atrioventricular valves** are pushed SHUT by the pressurised blood in the ventricles. ("LUB") * The **semilunar valves** in the aorta and **pulmonary artery** are pushed OPEN. Blood flows *from the ventricles into the arteries*. The thick, muscular walls of the ventricles squeeze the blood, **increasing its pressure** and pushing it out of the heart. When the pressure in the ventricles becomes greater than the pressure in the atria, the **atrioventricular valves shut**, preventing blood from going back into the atria. The blood rushes upwards into the aorta and pulmonary artery, pushing open the semilunar valves in these vessels.

Question 31

**Ventricular diastole** – themuscle relaxes (lasts for about 0.3 sec)

Answer 31

* *Atria & ventricles relax.* * The **semilunar valves** in the aorta & **pulmonary artery** are pushed SHUT. ("DUB") * Blood flows **from the veins through the atria and into the ventricles.** As the heart **muscle relaxes**, the **pressure in the ventricles drops**, and the semilunar valves snap SHUT to prevent backflow of blood. During diastole, the whole of the heart muscle relaxes, and blood *from the veins flows into the two atria at a very low pressure*. The atria have thin walls that are easily distended, so they provide very little resistance to the low-pressure blood flow.

Question 32

Blood flow

Answer 32

→ Oxygenated blood to all the cells IN body via **aorta** → Deoxygenated blood FROM body to **RA** through **Vena Cava** → Blood from **RA** to **RV** through **tri-cuspid valve** → Deoxygenated blood from **RV** through **plumonary arteries** TO lungs → Oxygenated blood RETURNS to **LA** via **plumonary veins** → Oxygenated blood TO **LA** via **bi-cuspid valve**

Question 33

**ECG**: ElectroCardioGram – a recording of the electrical events/changes during a cardiac cycle

Answer 33

* Assess your **heart rhythm** * Diagnose **poor blood flow** to the heart muscle (ischemia) * Diagnose a **heart attack** * Evaluate certain **abnormalities** of your heart, such as an enlarged heart

Question 34

To detect and record the **waves of excitation** flowing through heart muscle electrodes placed on the skin over opposite sides of the heart, and the **electrical potentials generated** recorded with time. The result, which is essentially *a graph of voltage against time*, is an electrocardiogram (ECG).

Answer 34

* The part labelled **P** represents the wave of **excitation sweeping over the atrial walls**. * The parts labelled **Q, R and S** represent the wave of **excitation in the ventricle walls**. * The **T** section indicates the **recovery of the ventricle walls**.

Question 35

/Graph pic/

Answer 35

**P- wave**: Depolarization of atria in response to SA node triggering (Artial contraction – systole) *PR interval*: Delay of AV node to allow filling of ventricles **QRS complex**: Depolarization of ventricles, triggers main pumping contractions (Ventricular contraction – systole) *ST segment*: Beginning of ventricle repolarization, should be FLAT **T-wave**: Ventrical (myocardium) repolarization

Question 36

Wiggers diagram – shows events **during systole, mainly ventricular systole** or contraction

Answer 36

The isovolumetric contraction phase begins at the R peak of the QRS complex on the electrocardiogram graph-line. The isovolumetric contraction phase lasts for about 0.03 seconds. After the isovolumetric contraction, the ejection phase begins immediately. During the ejection phase, ventricular volume (red graph-line) decreases as ventricular pressure (light blue graph-line) continues to increase. Once the blood is ejected from the ventricles, the pressure drops, and the heart enters diastole.

Question 37

The oxygen dissociation

Answer 37

LO: Explain oxygen dissociation curves haemoglobin and myoglobin for adults and embryos

Question 38

Haemoglobin

Answer 38

* **transport oxygen** from the gas exchange surfaces of the **alveoli in the lungs to tissues all over the body**. * supplies oxygen for aerobic respiration. * *oxygen is transported inside red blood cells in combination with the protein haemoglobin*. * each haem group can combine with one oxygen molecule. Hb + 4O2 ⇌ HbO8 (oxyhaemoglobin)

Question 39

Oxygen Binding Affinities to Haemoglobin

Answer 39

Lungs: * Oxygen high * CO2 low * pH high Tissue: * Oxygen low * CO2 high * pH low

Question 40

Cooperative Binding of Haemoglobin

Answer 40

Oxygen dissociation curves show the relationship between oxygen levels (as partial pressure) and haemoglobin saturation. Because binding potential changes with each additional O2 molecule, the saturation of haemoglobin is not linear. oxygen binding affinity: low → high Hb < HbO2 < HbO4 < HbO6 < HbO8

Question 41

S-shaped curve – due to shape of molecule being altered as each O2 molecule is taken up.

Answer 41

* After binding of first molecule shape changes so the binding of the others is easier. * Steep part of the curve - small decrease in pp oxygen results in a big fall in % saturation.

Question 42

Adult vs Fetal haemoglobin

Answer 42

* Adult hemoglobin is made up of four subunits. The most common form of adult hemoglobin, Hb A, consists of two alpha and two beta subunits **(α2 β2)**. * Mammals have a *unique form of hemoglobin for fetuses*, known as **fetal hemoglobin** (Hb F), consisting of two alpha and two gamma subunits **(α2 γ2)**. * Hb F has a **higher affinity for oxygen** compared to adult hemoglobin, allowing it to *extract oxygen from maternal circulation*. * This results in a left-shifted hemoglobin-oxygen dissociation curve for Hb F compared to Hb A. A left-shifted curve means that oxygen loading occurs **at lower oxygen concentrations**.

Question 43

Fetal oxygen transport

Answer 43

*Fetal blood has a very **low PO2**, but oxygen transport from placenta to sites of fetal need is **efficient**. * Fetal Hgb has **high O2 affinity**.

Answer 44

* Hemoglobin transports oxygen in blood while myoglobin transports or stores oxygen in muscles. * Myoglobin consists of a single polypeptide chain and hemoglobin consists of several polypeptide chains. * Hemoglobin **concentration** in red blood cells is **very high** compared to myoglobin. * Myoglobin is a monomeric protein that binds **one oxygen** molecule tightly * Hemoglobin is a tetrameric protein that can bind **four oxygen** molecules and offload both oxygen and carbon dioxide. * Hemoglobin initially binds oxygen **with difficulty** * Myoglobin binds **oxygen rapidly**.

Question 45

Adult haemoglobin

Answer 45

* rapid saturation of oxygen in the lungs * rapid dissociation of oxygen as the oxygen concentration decreases * oxygen released in the tissues where it is needed

Question 46

Fetal haemoglobin

Answer 46

* fetal haemoglobin curve **to the left** of adult haemoglobin * **higher affinity for oxygen** than adult haemoglobin * oxygen moves from adult haemoglobin to fetal haemoglobin

Question 47

Myoglobin

Answer 47

* myoglobin to the **left of fetal haemoglobin** * **higher affinity for oxygen** than adult haemoglobin * only releases oxygen at very low oxygen concentrations in tissues * acts as **oxygen reserve** in muscle cells

Question 48

high altitude where there is little O2.

Answer 48

* greater affinity to bind O2 * greater affinity to hold on to O2

Question 49

Different Haemoglobins

Answer 49

* Haemoglobins with a high affinity for oxygen. These take up oxygen more easily but release it less readily * Haemoglobins with a low affinity for oxygen. These take up oxygen less readily but release it more readily

Question 50

Q: What happens if we have an iron deficiency?

Answer 50

Answer: **Hypochromic Anemia** Is a generic term for types of anemia in which the *red blood cells are paler than normal*. Hypo – less, chromic – color.

Question 51

Bohr effect

Answer 51

LO: Describe and explain the significance of the Bohr effect

Question 52

The effect of pH on oxygen-haemoglobin loading and unloading is known as the **Bohr effect**.

Answer 52

the **decrease in the oxygen affinity** of a hemoglobin in response to *decreased blood pH* resulting from *increased carbon dioxide concentration* in the blood. * the oxyhemoglobin dissociation curve is displaced *to the right* because of **higher partial pressure of carbon dioxide and lower pH**.

Question 53

haemoglobin's oxygen binding affinity is **inversely related** both to acidity and to the concentration of carbon dioxide.

Answer 53

* blood [CO2] ↑ blood pH ↓ Hb **losing** O2 (release) CO2 + H2O → (HCO3)- + (H)+ * blood [CO2] ↓ blood pH ↑ Hb **gaining** O2 (hold) (HCO3)- + (H)+ → CO2 + H2O Since CO2 reacts with water to form carbonic acid, an increase in CO2 results in a decrease in blood pH.

Question 54

bohr effect

Answer 54

the formation of **haemoglobinic acid** means that in the presence of high CO2 conc. the dissociation curve **shifts to the right** (decrease in affinity for oxygen)

Question 55

CO2 transport

Answer 55

* 85% is transported in the plasma as dissociated *hydrogen carbonate* **H2O + CO2 ⇌ H2CO3 ⇌ (H)+ + (HCO3)-** * 15% is carried by haemoglobin as *haemoglobinic acid* **HbNH2 + CO2 ⇌ (HbNHCO2)- + (H)+** * carriage of CO2 by the plasma catalysed by **carbonic anhydrase**. Increased H+ conc. causes blood pH to drop so more oxygen is released from the haemoglobin * chloride shift balances the movement if (HCO3)- ions into the plasma

Question 56

CO2 is carried in the blood(tissues to lungs): 1) Bound to haemoglobin 2) Dissolved in the blood plasma 3) In **erythrocytes(RBC's)** as **carbonic acid**(85% of CO2 carried)

Answer 56

1. CO2 **diffuses** into erythrocyte 2. CO2 + H2O ⇌ H2CO3, catalyzed by **carbonic anhydrase**; form carbonic acid which is more soluble 3. H2CO3 **dissociates** (H)+ and (HCO3)- 4. **Chloride shift**: bicarbonate ions pumped OUT of erythrocytes & Cl- ions are pumped IN (overall charge remains the same) 5. Bicarbonate ions combine with sodium ions in the blood plasma (**NaHCO3**) – these are carried to the lungs 6. H+ ions in the erythrocyte **lower the pH**, causing haemoglobin to release oxygen (to respiring cells/tissues) 7. Haemoglobin binds excess H+ ions to **restore pH** in the erythrocyte (H+ released in lungs)