Blood flow through arteriovenous anastomoses and its thermal function in the laying hen.

Abstract

SUMMARY1. Total (arteriovenous anastomoses +capillary) blood flow (t.b.f.) and capillary blood flow (c.b.f.) distribution were determined by 52 and 15 ,m microspheres respectively, in body organs of six unanaesthetized laying hens, exposed to thermoneutral air temperatures.2. Statistically significant differences between t.b.f. and c.b.f. were only found in the unfeathered metatarsal skin, comb and wattles. The c.b.f. constituted 22, 42 and 45 % of t.b.f. respectively, indicating significant arteriovenous anastomoses (a.v.a.) blood flow. Differences between t.b.f. and c.b.f. were small in the two larger ovarian follicles and digestive tract and were negligible in reproductive tract, liver and kidney.3. Microspheres of different size have been injected into the external ischiadic artery in order to examine the vasomotor responses of leg tissues in twenty-one hens kept in thermoneutral, cold or hot conditions. 4. In cold, thermoneutral and hot conditions 1, 16 and 35 % of whole leg blood flow respectively passed through a.v.a. Only c.b.f. was present in bone and muscle in either treatment; cold and heat reduced it in bones and cold increased it in muscles. Arteriovenous anastomoses blood flow appeared mostly in unfeathered skin; it constituted 17, 53 and 83 % of t.b.f. to this tissue in cold, thermoneutral and hot conditions, while t.b.f. increased from 1-4 to 14 % and 30 % of whole leg blood flow respectively. Blood flow to feathered skin decreased during heat and cold.

Density of arteriovenous anastomoses in some skin areas of the domestic fowl (gallus domesticus)

“…Scale = 3 mm. AVAs agrees with physiological studies which show that AVA blood flow in the normothermic hen is lower in the wattle than in the naked skin of the feet (Wolfenson, 1983).…”

Partitioning locomotor energy use among and within muscles Muscle blood flow as a measure of muscle oxygen consumption

“…The size of the microspheres is important in this context, and spheres with a diameter of 15·m are trapped in the capillaries of most tissues in mammals, birds and fish (Fan et al, 1979;Wolfenson, 1983;Schultz et al, 1999;Ellerby et al, 2005). Microsphere measures of blood flow have been extensively validated; however, implementation in a new system requires validation to determine the doses of spheres to be injected and to assure that accurate recovery from the tissues is attained [see methods described elsewhere (Ellerby et al, 2005)].…”

“…The renal circulation in these animals is complex due to the presence of renal portal flow. The amount of renal portal flow can vary due to active valving (Odlind, 1978), and renal portal flow in birds can have variable numbers of microspheres representing those that have passed through arterio-venous shunts in the legs (Wolfenson, 1983). Experimental conditions may sometimes necessitate injection into a systemic artery.…”

Development of arteriovenous anastomoses in the skin of the chicken and the influence of environmental temperature

“…Considering that the AVAs are constricted and that peripheral blood flow is low in a thermoneutral or cool environment (Hillman et a]., 1982; Wolfenson, 1983), the observed increase in AVA density after cold acclimation may seem paradoxical. There is, however, sufficient experimental evidence to indicate that the AVAs also dilate a t subzero ambient temperatures in order to prevent exposed tissues from freezing (Grant and Bland, 1931;Murrish and Guard, 1977;see also Midtggrd, 1988).…”