Atlas of plant and animal histology

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Glossary: G


Gametophyte: it is the haploid phase of plants. Gametophyte is formed after meiosis of macro or microspores in flowers or reproductive structures, and produces and contains the gametes. There are two types of gametophyte: male or pollen grain, and female or embryo sac.

♣ Plant organs: The flower .

Gamma cell: it is a type of cell found in the Langerhans islets. Gamma cells release somatostatin, hormone that regulates carbohydrates levels in the organism and influences the synthesis of insulin and glucagon hormones.

♣ Animal tissues: Pancreas.

Gastrulation: it is a stage of the early embryo development characterized by high cell motility and cell differentiation. Gastrulation ends with the formation of the three germ layers: endoderm, mesoderm and ectoderm.

Gelatinous connective tissue: (also known as mucous connective tissue) it is a type of connective tissue that shows low cell density and large amount of extracellular matrix. Gelatinous connective tissue is highly hydrated because it contains abundant proteoglycans. Gelatinous connective tissue can be found in the embryonary and extraembryonary tissues, such as the umbilical cord (Wharton gelatin), but it is uncommon in adults.

Geniculate nucleus: it is a nucleus of neurons found in the thalamus of the encephalon. The lateral geniculate nucleus processes primary visual information that arrives via the optic nerve.

♣ Animal organs: Senses .

Generative nucleus: (in plants) it is one of the haploid nucleus found in the pollen grain. Generative nucleus divides in two nuclei. One fuses with the egg to produce the zygote and the embryo, and the other fuses with vegetative nuclei that develops into the seed endosperm.

♣ Plant organs: Seed , Flower .

Gibberellin: (in plants) it is a type of hormone, or phytohormone, released by developing organs and seeds. Gibberellins favor cell proliferation and the development of plant organs. Lack of gibberellins results in dwarf plants.

Glandular epithelium: it is a type of epithelium specialized in the secretion of substances to the inner cavities or to the outer surfaces of the body (exocrine glands). Those cells that release substances that travel to other parts of the body through the blood stream are also included (endocrine glands).

Glia: it is a type of cell found in the nervous system. Glial cells are small and show many cellular processes that are close to neurons, blood vessels and meningeal membranes. In the central nervous system, astrocytes, microglia and oligodendroglia are glial cell types. Schwann's cells are the glia in the peripheral nervous system. Glial cells perform several functions: form the myelin, support neurons, are part of the hematoencephalic barrier, are involved in the nervous system development and are defense cells against pathogens.

♣ Animal tissues: Nervous tissue.
♣ Cell types: Astrocytes .

Glossopharyngeal nerve: (nerve IX) it is a peripheral nerve that gathers information from the taste buds located in the pharynx and posterior part of the tongue.

♣ Animal organs: Sentidos .

Gluten: it is a family of proteins found in the endosperm of seeds. Gluten is stored and used during germination.

♣ Plant organs: Seed.

Guard cell: (in plants)it is a type of cell that constitute the stomata of plants. Guard cells usually show a kidney-like morphology. In the stomata, they are arranged in a way that leaves a pore by which air and water are exchanged between the plant and the environment. Guard cells can modify their shape so that the diameter of the pore may be smaller or larger.

♣ Plant tissues: Protection, Stomata .
♣ Plant organs: Pine leaf.

Glomerulus: (in the kidney) it is a network of blood capillaries that forms part of the kidney corpuscle, a component of the nephron. The glomerulus carries out the first filtration of the blood.

♣ Animal organs: Nephron .

Olfactory glomerulus: it is a network of axonal terminals found in the olfactory bulb. The axons are sent by the olfactory receptors of the olfactory epithelium. There are many olfactory glomeruli in the olfactory bulb, all of them carry primary olfactory information.

♣ Animal organs: Senses.

Glycoproteins: it is a type of protein with chemically bound branched carbohydrates. Glycoproteins are abundant in the plasma membrane, where they orientate the carbohydrates toward the extracellular space.

♣ Animal tissues: Glandular epithelium.

Glycosaminoglycan: it is a chain of carbohydrates made up of repeated couples of monosaccharides. Gylcosaminoglycans are important components of the animal extracellular matrix because they provide lubrication and mechanical resistance. Some glycosaminoglycans are chemically bound to polypeptides chains forming the so-called proteoglycans. Glycosaminoglycans are also known as mucopolysaccharides.

♣ Animal tissues: Glandular epithelium.

Granular leukocyte: it is a type of leukocyte found in the blood characterized by having cytoplasmic granules that can be stained with basic or acid dyes. There are three types of granular leukocytes: eosinophil, basophil and neutrophil. Typically, they present nuclei with irregular morphology, particularly neutrophils.

♣ Animal tissues: Blood, Blood .

Ground meristem: (in plants) it is a region below the apical meristems that is partially committed to differentiate into ground tissues, such as parenchyma, collenchyma and sclerenchyma.

♣ Plant tissues: Meristems.

Grueneberg's ganglion: it is a sensory structure found in the rostral part of the oral cavity of some animals.

♣ Animal organs: Senses.

Gutation: it is the release of water, together with some substances, from the leaf tissues toward the epidermal surface. It is a consequence of the water pressure in the roots. Gutation is observed in plants living in watery and moist soils. The process is carried out by hydathodes, which are glands found in the leaves. Gutation forms small droplets of water in the margin and surface of the leaf, but it must not be confused with dew drops.

♣ Plant tissues: Glandular.

Gymnosperm: (in plants) type of vascular plant that does not develop true flowers. For instance, conifers.

Gynoecium: (in plants) it is part of the flower where macrospores and female gametes are produced. The gynoecium or pistil is made up of one or several carpels, as well as macrospores. Sometimes the gynoecium consists in more than one pistil.

♣ Plant organs: Flower .
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