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Comments: Question is often rephrased as the answer; The answer lacks a definite structure.

Discuss the mechanisms that contribute to autoregulation of tissue blood flow. Maximum – 5 marks Maximum time – 10 minutes.

sawyer-summers
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Comments: Question is often rephrased as the answer; The answer lacks a definite structure.

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  1. Discuss the mechanisms that contribute to autoregulation of tissue blood flow. Maximum – 5 marksMaximum time – 10 minutes

  2. 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]

  3. 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%

  4. 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 “Multi-structural”; 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

  5. 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.

  6. 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

  7. “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.

  8. 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]

  9. Points to be noted: Point 1 • Give an example of a non-selective beta-blocker. • 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

  10. 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…

  11. 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

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