UHS Lahore Questions For MBBS Exam Preparation 2013
Q:1 a) Classify the functional types of blood vessels and give examples of each.
b) Give the function of each type in the light of its anatomy.
(2.5 + 2.5 marks)
- 1. Elastic Vessels: (AORTA & LARGE
- 2. Resistance Vessels: (ARTERIOLES,
- 3. Exchange Vessels: (CAPILLARIES)
- 4. Capacitance Vessels: (venules & veins)
- 5. Shunt Vessels: (Arterio-venous Anastomosis)
(0.5 mark each)
- HISTOLOGY: More elastic tissue & loose collagen fibers.
- Aorta & large arteries expand to accommodate blood by ELASTIC RECOIL à it generates & maintains diastolic B.P.
- SIGNIFICANCE: if large vessels were not elastic, there would’ve been no blood flow in diastole
Size of these vessels control blood flow to tissues. Size is controlled by nerves & local metabolic factors like lactic acid & [CO2].
- HISTOLOGY: Single layer of endothelial cells supported by a basement membrane
- Through capillary wall, there is exchange between blood & tissues.
- Pre-capillary sphincter is there at the beginning of capillary
- SIGNIFICANCE: Veins accommodate 2/3 of blood volume (64%), without increase in pressure.
- Veins are supplied by sympathetic nerve fibers.
- When veins are constricted à venous return increases
- When veins are dilated à increased amount of blood is pooled up in veins.
SHUNT VESSELS / ARTERIO-VENOUS ANASTOMOSIS:
- Pass from metarterioles à venules & bypass the capillary network.
- SIGNIFICANCE: Rapid flow of blood à Involved in temperature regulation. Normally blood flow through skin is slow BUT for temp. regulation, there must be quick flow of blood for heat loss.
- LOCATION: These are present in skin of exposed areas of body: (palm of hand, external ear & fingers).
- NERVE SUPPLY: These are supplied by sympathetic nerve fibers