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)

key:

• 1. Elastic Vessels: (AORTA & LARGE 

        ARTERIES)

 

• 2. Resistance Vessels: (ARTERIOLES, 

       METARTERIOLES &

      PRE-CAPILLARY SPHINCTERS)

 

• 3. Exchange Vessels: (CAPILLARIES)

 

• 4. Capacitance Vessels: (venules & veins)

 

• 5. Shunt Vessels: (Arterio-venous Anastomosis)

 

(0.5 mark each)

ELASTIC VESSELS:

• 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

RESISTANCE VESSELS:

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

EXCHANGE VESSELS:

• Through capillary wall, there is exchange between blood & tissues.

 

• Pre-capillary sphincter is there at the beginning of capillary

CAPACITANCE VESSELS:

• 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

 

 

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