Discuss the mechanisms that
contribute to autoregulation of
tissue blood flow.
Maximum – 5 marks
Maximum time – 10 minutes
• Tissue blood flow is the blood going to the
tissues. It is autoregulated. There are so many
mechanisms for regulating it. They are
complex. Ultimately, blood flow is maintained
everywhere. Defects in this mechanism can
lead to problems like death which can be
dangerous.
Comments:
Question is often rephrased as the answer;
The answer lacks a definite structure.
Deserves 0 – 20% marks
Level 1 – Lacking a definite structure [Unstructured]
• Tissue blood flow is regulated by local autoregulatory
mechanisms – i.e. each tissue is capable of regulating
its own blood flow independent of neural influences.
There are several autoregulatory mechanisms
contributing to maintenance of tissue blood flow.
• Comments: Only one aspect of the process that is
being discussed here – ie., autoregulation of TBF
(namely what is meant by autoregulation of tissue
blood flow) is clear and correct. Other parts of the
answer are missing or vague.
• Level: “Unistructural”
• Marks: 21-40%
• Each tissue has the ability to regulate its blood flow based on
its demand independent of neural mechanisms. It is achieved
by varying local vascular resistance.
• There are two mechanisms contributing to autoregulation:
– The myogenic mechanism
– Effect of products of tissue metabolism
• When tissue blood flow increases as a result of an increase in
BP, blood vessels in a tissue are stretched and the response is
constriction.
• Lack of oxygen, drop in tissue pH also cause local vasodilation.
• Comments: Multiple aspects of tissue blood flow
regulation are presented here. This answer is “Multistructural”; however, the relation between various
aspects of a process (here between metabolic and
myogenic mechanism, or the consequences of a
mechanism) are not presented. Deserves 41-60% marks
• When changes in perfusion pressure affect blood
flow, a tissue is able to maintain its blood flow by
changing local vascular resistance. This is called
autoregulation and can occur even in denervated
tissues.
• TBF = BP / local vascular resistance.
• 2 distinct mechanisms contribute:
• The myogenic mechanism: A rise in flow due to a rise
in arterial pressure stretches the arterioles and the
reflex response to this is vasoconstriction, the effect
of this is to restore flow toward normal in the steady
state.
• The metabolic mechanism:
• In actively metabolizing tissue with increased demand,
products of tissue metabolism such as low PO2, a drop in
tissue pH >>>> local vasodilation, thereby meeting
increased blood flow requirements.
• Autoregulation is quantitatively much more important as
a mechanism for augmenting blood flows during exercise
compared to a rise in arterial pressure.
• In contrast, in metabolically quiescent tissues, lack of
accumulation of products of metabolism result in
vasoconstriction and this prevents the tissue from being
overperfused.
The answer has multiple aspects and the relation between
one aspect of the answer and other aspects is evident;
cause-effect relationships are correctly presented. Level –
Relational; 61-80% marks
“Highly Developed” Answer..
Also called extended abstract
[81-100% marks]
• Will contain inferences and predictions that can be
made from facts presented in the answer.
• Besides the facts and mechanisms and the
relationships between aspects of the process
(mentioned in the previous response) the answer
would contain statements like this:
• It follows that administration of drugs causing
vasodilation or vasoconstriction will interfere with
autoregulation or reset the limits of autoregulation
of tissue blood flows.
Bigg’s Structure of the Observed
Learning Outcome (SOLO) Taxonomy
•
•
•
•
•
•
No answer [0 marks]
Lacking a structure [0 – 20% marks]
Unistructural [21 – 40% marks]
Multi-structural [41 – 60% marks]
Relational [61 – 80% marks]
Highly Developed (also called Extended Abstract]
[81 – 100% marks]
Points to be noted:
Point 1
• Give an example of a non-selective betablocker.
• Ans: Propranolol
• What level is this in SOLO Taxonomy?
• Point 1 - Not all questions can be evaluated
using the SOLO taxonomy.
• This is an objective type question
Point 2:
• When two different answers are at the same
SOLO level (let us say relational), then, they
may still be awarded different marks
depending on the expected length of the
answer.
• Two answers may be relational and one may
contain more relevant points than the other,
and therefore given higher marks…
Point 3:
Take this question:
• Discuss the physiological changes that occur during
dynamic exercise and the underlying mechanisms
involved. [Max time – 30 min; Max – 20 marks]
• A response may contain an account of only respiratory
changes during exercise and this part of the response
may be highly developed [SOLO Level 5]; however, the
student may have missed changes in cardiovascular
function (HR, BP, SV, venous return, cardiac output)
completely [SOLO Level Zero for this part!] – then the
marks awarded will be correspondingly low depending
upon the number of subheads such as: CV changes;
respiratory changes etc