Morphology of the nutrient artery and its foramen in relation to femoral bone perfusion rates of laying and non‐laying hens

Abstract

If arteries penetrate bones through foramina, regional artery blood flow rates can be estimated from the foramen sizes. Femoral bone blood flow rates estimated from nutrient foramen sizes were previously not absolute, but only a relative blood flow index (Q i ), because the size relationship between the foramen and the occupying artery was unknown. The current study used vascular contrast and micro-computerized tomographic scanning to investigate femoral nutrient foramen and nutrient artery sizes in three groups of sub-adult chickens (non-laying hens, laying hens, and roosters) of similar ages. The results indicate that the cross-sectional area of the nutrient artery lumen occupies approximately 20.2 ± 4.1% of the foramen for femora with only one foramen. Artery lumen size is significantly correlated with foramen size. Vascular contrast imaging is capable of estimating blood flow rates through nutrient arteries, as blood flow rates estimated from artery lumen casts are similar to blood flow rates measured by infusion of fluorescent-labeled microspheres. Laying hens tend to have higher nutrient artery perfusion rates than non-laying hens, probably due to extra oxygen and calcium requirements for eggshell production, although the calculated blood flow difference was not statistically significant. Histological embedding and sectioning along with vascular contrast imaging reveal variable nutrient foramen morphology and nutrient artery location among femora with more than one nutrient foramen.

Whole‐body endothermy: ancient, homologous and widespread among the ancestors of mammals, birds and crocodylians

“…In most species, blood enters the shaft of the femur through the principal nutrient foramen, thence perfusing the endosteal cavity and bone marrow before exiting via numerous vessels in the cortical bone (Marenzana & Arnett, 2013 ). The size of the foramen can provide an index which is related to the rate of blood flow to the bone shaft (Hu, Nelson & Seymour, 2020 , 2021a , b ) and flow rate is about 10 times higher in extant mammals and birds than in extant non‐varanid reptiles (Fig. 2K ), and even higher if differences in blood pressure are considered (Seymour et al ., 2012 ; Allan et al ., 2014 ).…”

Nasal turbinates of the dicynodont Kawingasaurus fossilis and the possible impact of the fossorial habitat on the evolution of endothermy

“…Another source of information is the size of long-bone foramina through which the blood vessels passed, which are indicative of the blood flow in extinct animals. As endothermy requires a much greater blood flow and oxygen consumption, the size of long-bone foramina may provide information about the metabolic status of extinct animals (Hu et al, 2020(Hu et al, , 2021Knaus et al, 2021). Such information can also be inferred from osteohistology, which is based on the observation that the bones of modern endotherms are usually characterized by higher growth rates and the presence of fibrolamellar bone, which is absent in most ectotherms (e.g., Bakker, 1972;de Ricqlès, 1974de Ricqlès, , 1976Legendre et al, 2016;Olivier et al, 2017).…”

Blood flow rates to leg bones of extinct birds indicate high levels of cursorial locomotion

“…For example, femoral nutrient foramen areas tend to be relatively larger in young, growing kangaroos than in adults (Hu et al 2018), probably due to a higher energy demand for bone growth. Femoral bone blood flow in laying domestic fowl is higher than in subadult non-laying hens (Hu et al 2021a), possibly associated with calcium mobilization for eggshell production and provisioning the yolk for embryonic skeleton growth.…”

“…The arbitrary units of Q i (mm 3 ) were initially useful for comparative purposes, but the proportionality between the artery and foramen size was not known, and the theoretical and empirical relationships between absolute blood flow rate and arterial radius are now known to be inconsistent with Poiseuille flow (Huo and Kassab 2016; Seymour et al 2019b). This study is an improvement over the blood flow index method and represents a further improvement to the foramen technique by considering both the proportion of the foramen area occupied by the nutrient artery (Hu et al 2021a) and using an empirical relationship between absolute blood flow rate ( Q ̇ ; ml s –1 ) and arterial radius (Seymour et al 2019b).…”

“…The foramen technique was first used to relate nutrient foramen sizes on femoral bones to locomotor activity levels of living mammals and non-avian reptiles in comparison with Cretaceous dinosaurs (Seymour et al 2012). Since then, additional studies have used this technique to investigate the relationships among foramen size, regional blood flow rate, and local tissue metabolism (Allan et al 2014; Seymour et al 2015, 2016; Boyer and Harrington 2018, 2019; Hu et al 2018, 2021a, b; Newham et al 2020; Knaus et al 2021).…”