Lecture 19 - Gas transport and respiratory control

Question 1

Oxygen transport

Answer 1

Oxygen is carried in the blood in two forms - dissolved oxygen in the plasma or bound to haemoglobin in RBCs

Oxygen dissolves poorly, especially because blood is warm - also because plasma is mostly water and oxygen does not dissolve well in water

Only about 3mL of oxygen per litre of blood, so about 15 mL total … we need about 250mL/min

Carbon dioxide is better dissolved in cold (think about bubbles in a cold drink vs a warm drink)

Question 2

Cardiovascular side of oxygen transport

Answer 2

Saturated blood with oxygen by the alveoli and this blood gets taken through the pulmonary veins, left atrium of the heart and left ventricle and then through the systemic arteries to deliver the oxygen to all the tissues in the body

Question 3

Functions and characteristics of erythrocytes

Answer 3

Also called red blood cells

Contain large amounts of haemoglobin, it is one third of the weight of a RBC
Uses iron as part of the heme structures to bind oxygen
Four heme units, so each haemoglobin can bind four oxygen molecules
Binds cooperatively which means that the most difficult oxygen for each haemoglobin molecule to bind is to bind the first, with each bound oxygen the affect for the next oxygen becomes much greater

Question 4

Haemoglobin binding curve

Answer 4

Sigmoidal relationship for haemoglobin due to cooperative binding of oxygen molecules

At the average pressure of oxygen in the blood that is leaving the peripheral tissues - binding becomes cooperative and affinity has skyrocketed

At the average pressure of oxygen in the blood that is enetering the systemic circuit - most binding sites are occupied and each additional oxygen molecule that wants to bind haemoglobin has trouble finding a spot (haemoglobin is filled with oxygen at this point)

Oxygen is distributed to the tissues that need it the most! Skeletal muscle for example

Question 5

How can the haemoglobin binding curve be shifted?

Answer 5

Lower pH i.e. more acidic reduces oxygen affinity
Higher temperature reduces oxygen affinity

Means greater release of oxygen to the working muscles for example during exercise, better release

Question 6

Exercises causes what in skeletal muscle?

Answer 6

Causes pH to drop and temperature to rise in skeletal muscle

Lactic acid but also lots of CO2 is produced which is a waste product of metabolism and then the carbon dioxide then gets turned into bicarbonate which lowers the pH as we are liberating the proteins —> the more active a tissue becomes, the more carbon dioxide produced and the more acidic the tissue gets and this helps haemoglobin to release more oxygen to replenish

Question 7

Carbon dioxide is transported in 3 forms…

Answer 7

Dissolved in plasma
Bound to haemoglobin
Converted to bicarbonate

Question 8

Formation of bicarbonate

Answer 8

Carbon dioxide + water —>*** this card does not work

Question 9

Control of breathing

Answer 9

We need to maintain normal levels of oxygen and carbon dioxide for metabolic and biochemical stability e.g. pH
But oxygen usage and carbon dioxide production is quite variable
Despite this, oxygen and carbon dioxide are normally kept within close limits
How? - by the tight control of ventilation

Question 10

Feedback loops for the control of breathing

Answer 10

Central controller - pons, medulla, other part of brain
Central controller sends efferent signal to the effectors and the sensors such as chemoreceptors, baroreceptors, lung stretch receptors and protective reflects sense the effectors actions.
The sensors send afferent signals to the central controller

Question 11

Chemoreceptors

Answer 11

Carbon dioxide receptors are the most important in determining respiratory activity

Question 12

Homeostasis disturbed by increasing arterial carbon dioxide

Answer 12

Receptor = chemoreceptors in arteries and medulla oblongata
Chemoreceptors stimulated by the increased carbon dioxide and the decreased pH
Effector = respiratory muscles stimulated
This results in increased respiratory rate with increased elimination of carbon dioxide at alveoli which result in decreased arterial carbon dioxide pressure which means that homeostasis is restored

Question 13

Homeostasis disturbed by decreasing arterial carbon dioxide

Answer 13

Receptor = chemoreceptors in arteries and medulla oblongata
Chemoreceptors inhibited by the decreased carbon dioxide and the increased pH
Effector = respiratory muscles inhibited
This results in decreased respiratory rate with decreased elimination of carbon dioxide at alveoli which result in increased arterial carbon dioxide pressure which means that homeostasis is restored

Question 14

Baroreceptors

Answer 14

Blood pressure receptors located on the carotid artery and the aortic arch

Question 15

Arterial blood pressure goes down….

Answer 15

Arterial blood pressure goes down which reduces flow
Sensed by the baroreceptors
Respiratory minute volume goes up (increase in the amount of air into lungs, pushes a little more carbon dioxide out that arrives)
Increased uptake of air

Question 16

Arterial blood pressure goes up….

Answer 16

Arterial blood pressure goes up, which increases flow
Sensed by the baroreceptors
Respiratory minus volume goes down
Decreased uptake of air

Question 17

Inflation and deflation and the brain

Answer 17

As the lungs inflate or deflate, they send afferent input from stretch receptors
The brain then sends efferent output preventing them from stretching too far either way!

Question 18

Protective reflexes

Answer 18

Receptors also detect irritation
Brain sends efferent signal that triggers a sneeze or cough - protects alveoli, expels the irritants and protects the system

Question 19

What receptors send afferent input to the brain so that it can manage respiratory function?

Answer 19

Chemoreceptors, baroreceptors, lung stretch receptors, and protective reflex receptors

Question 20

Real card for the formation of bicarbonate

Answer 20

Carbon dioxide + water (double headed arrow) carbonic acid (double headed arrow) hydrogen ion + bicarbonate ion

In words …
Carbon dioxide and water combine to form carbonic acid
Carbonic acid dissociates into bicarbonate and a hydrogen ion
This lowers the pH - the blood is getting more acidic (proton formed lowers the pH in the area in which it is being formed so it makes the blood more acidic

occurs in RBCs