John maina - Academia.edu (original) (raw)

Papers by John maina

Research paper thumbnail of Correlations between structure and function in the design of the bat lung: a morphometric study

Journal of Experimental Biology, 1984

The lungs of five species of bat Pipistrellus pipistrellus, Miniopterus minor (Peters), Tadarida ... more The lungs of five species of bat Pipistrellus pipistrellus, Miniopterus minor (Peters), Tadarida mops (De Blainville), Cynopterus brachyotis (Muller) and Cheiromeles torquatus (Horstield) have been analysed by morphometric techniques. The mean body weight (W) ranged from 5 g in Pipistrellus pipistrellus to 173g in Cheiromeles torquatus; the lung volume (VL) ranged from 0·3 cm3 in Pipistrellus to 10 cm3 in Cheiromeles. The volume densities or the main components of the bat lung, namely the parenchyma [Vv(p,L)] (the gas exchange region) and the nonparenchyma [Vv(np,L)], were closely similar, the Vv(p,L) constituting a mean value of 84·2% and the Vv(np,L) 15·8% in the five species. The VL, the surface area of the blood-gas (tissue) barrier (St), the pulmonary capillary blood volume (Vc), and the total morphometric pulmonary diffusing capacity were all strongly correlated with body weight. The harmonic mean thickness of the blood-gas (tissue) barrier (τht) and the surface density of the...

Research paper thumbnail of The thickness of avian blood-gas barrier: qualitative and quantitative observations

Research paper thumbnail of Comparative molecular developmental aspects of the mammalian- and the avian lungs, and the insectan tracheal system by branching morphogenesis: recent advances and future directions

Frontiers in Zoology, 2012

Gas exchangers fundamentally form by branching morphogenesis (BM), a mechanistically profoundly c... more Gas exchangers fundamentally form by branching morphogenesis (BM), a mechanistically profoundly complex process which derives from coherent expression and regulation of multiple genes that direct cell-to-cell interactions, differentiation, and movements by signaling of various molecular morphogenetic cues at specific times and particular places in the developing organ. Coordinated expression of growth-instructing factors determines sizes and sites where bifurcation occurs, by how much a part elongates before it divides, and the angle at which branching occurs. BM is essentially induced by dualities of factors where through feedback-or feed forward loops agonists/antagonists are activated or repressed. The intricate transactions between the development orchestrating molecular factors determine the ultimate phenotype. From the primeval time when the transformation of unicellular organisms to multicellular ones occurred by systematic accretion of cells, BM has been perpetually conserved. Canonical signalling, transcriptional pathways, and other instructive molecular factors are commonly employed within and across species, tissues, and stages of development. While much still remain to be elucidated and some of what has been reported corroborated and reconciled with rest of existing data, notable progress has in recent times been made in understanding the mechanism of BM. By identifying and characterizing the morphogenetic drivers, and markers and their regulatory dynamics, the elemental underpinnings of BM have been more precisely explained. Broadening these insights will allow more effective diagnostic and therapeutic interventions of developmental abnormalities and pathologies in pre-and postnatal lungs. Conservation of the molecular factors which are involved in the development of the lung (and other branched organs) is a classic example of nature's astuteness in economically utilizing finite resources. Once purposefully formed, well-tested and tried ways and means are adopted, preserved, and widely used to engineer the most optimal phenotypes. The material and time costs of developing utterly new instruments and routines with every drastic biological change (e.g. adaptation and speciation) are circumvented. This should assure the best possible structures and therefore functions, ensuring survival and evolutionary success.

Research paper thumbnail of A morphological and morphometric study of the prosimian lung: the lesser bushbaby Galago senegalensis

Journal of anatomy, 1990

The lung of the lesser bushbaby (Galago senegalensis) has been investigated morphologically and m... more The lung of the lesser bushbaby (Galago senegalensis) has been investigated morphologically and morphometrically using the transmission and scanning electron microscopes. Grossly and microscopically, the bushbaby lung was found to be essentially similar to that of the other primates and the mammals in general. Subtle morphometric differences were, however, observed, with the bushbaby lung being generally structurally less sophisticated than that of the other primates on which comparable data are available, except for man. The weight-specific surface area of the blood-gas (tissue) barrier in G. senegalensis was 25 cm2 g-1. The thickness of the blood-gas barrier was 0.355 micron and the weight specific total anatomical pulmonary diffusing capacity 0.045 mlO2 sec-1 mbar1 kg-1. The morphological similarity of the galago lung to that of man gives sufficient grounds to justify its possible use in human pulmonary studies but caution has been called for in the general utilisation of primate...

Research paper thumbnail of Correlations between structure and function in the design of the bat lung: a morphometric study

Journal of Experimental Biology, 1984

The lungs of five species of bat Pipistrellus pipistrellus, Miniopterus minor (Peters), Tadarida ... more The lungs of five species of bat Pipistrellus pipistrellus, Miniopterus minor (Peters), Tadarida mops (De Blainville), Cynopterus brachyotis (Muller) and Cheiromeles torquatus (Horstield) have been analysed by morphometric techniques. The mean body weight (W) ranged from 5 g in Pipistrellus pipistrellus to 173g in Cheiromeles torquatus; the lung volume (VL) ranged from 0·3 cm3 in Pipistrellus to 10 cm3 in Cheiromeles. The volume densities or the main components of the bat lung, namely the parenchyma [Vv(p,L)] (the gas exchange region) and the nonparenchyma [Vv(np,L)], were closely similar, the Vv(p,L) constituting a mean value of 84·2% and the Vv(np,L) 15·8% in the five species. The VL, the surface area of the blood-gas (tissue) barrier (St), the pulmonary capillary blood volume (Vc), and the total morphometric pulmonary diffusing capacity were all strongly correlated with body weight. The harmonic mean thickness of the blood-gas (tissue) barrier (τht) and the surface density of the...

Research paper thumbnail of The thickness of avian blood-gas barrier: qualitative and quantitative observations

Research paper thumbnail of Comparative molecular developmental aspects of the mammalian- and the avian lungs, and the insectan tracheal system by branching morphogenesis: recent advances and future directions

Frontiers in Zoology, 2012

Gas exchangers fundamentally form by branching morphogenesis (BM), a mechanistically profoundly c... more Gas exchangers fundamentally form by branching morphogenesis (BM), a mechanistically profoundly complex process which derives from coherent expression and regulation of multiple genes that direct cell-to-cell interactions, differentiation, and movements by signaling of various molecular morphogenetic cues at specific times and particular places in the developing organ. Coordinated expression of growth-instructing factors determines sizes and sites where bifurcation occurs, by how much a part elongates before it divides, and the angle at which branching occurs. BM is essentially induced by dualities of factors where through feedback-or feed forward loops agonists/antagonists are activated or repressed. The intricate transactions between the development orchestrating molecular factors determine the ultimate phenotype. From the primeval time when the transformation of unicellular organisms to multicellular ones occurred by systematic accretion of cells, BM has been perpetually conserved. Canonical signalling, transcriptional pathways, and other instructive molecular factors are commonly employed within and across species, tissues, and stages of development. While much still remain to be elucidated and some of what has been reported corroborated and reconciled with rest of existing data, notable progress has in recent times been made in understanding the mechanism of BM. By identifying and characterizing the morphogenetic drivers, and markers and their regulatory dynamics, the elemental underpinnings of BM have been more precisely explained. Broadening these insights will allow more effective diagnostic and therapeutic interventions of developmental abnormalities and pathologies in pre-and postnatal lungs. Conservation of the molecular factors which are involved in the development of the lung (and other branched organs) is a classic example of nature's astuteness in economically utilizing finite resources. Once purposefully formed, well-tested and tried ways and means are adopted, preserved, and widely used to engineer the most optimal phenotypes. The material and time costs of developing utterly new instruments and routines with every drastic biological change (e.g. adaptation and speciation) are circumvented. This should assure the best possible structures and therefore functions, ensuring survival and evolutionary success.

Research paper thumbnail of A morphological and morphometric study of the prosimian lung: the lesser bushbaby Galago senegalensis

Journal of anatomy, 1990

The lung of the lesser bushbaby (Galago senegalensis) has been investigated morphologically and m... more The lung of the lesser bushbaby (Galago senegalensis) has been investigated morphologically and morphometrically using the transmission and scanning electron microscopes. Grossly and microscopically, the bushbaby lung was found to be essentially similar to that of the other primates and the mammals in general. Subtle morphometric differences were, however, observed, with the bushbaby lung being generally structurally less sophisticated than that of the other primates on which comparable data are available, except for man. The weight-specific surface area of the blood-gas (tissue) barrier in G. senegalensis was 25 cm2 g-1. The thickness of the blood-gas barrier was 0.355 micron and the weight specific total anatomical pulmonary diffusing capacity 0.045 mlO2 sec-1 mbar1 kg-1. The morphological similarity of the galago lung to that of man gives sufficient grounds to justify its possible use in human pulmonary studies but caution has been called for in the general utilisation of primate...