STUDY OF ANIMAL TISSUE
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Tissue : The tissue is a group of cells having the same embryonic origin, structure and function.
Organs :Various tissues combine together in an orderly manner to form a large functional unit called organs.
Organ system: Various tissues combine together in an orderly manner to form a large functional unit called organs. These organs combine together and form organ-system.
Somatic cells: All body cells of an organism except sperm and ova are somatic cells.
Germ cells: Sperm and ova are germ cells. They belong to the reproductive system.
Histology :The study of the structure coelom, etc. and arrangement of tissue is called histology.
Pavement epithelium: Cells of Squamous epithelium tissue fit together like tiles of the footpath. Hence it is called pavement epithelium.
Exocrine glands: Exocrine glands pour their secretions at specific sites e.g. Salivary gland, sweat glands etc. These are duct gland.
Endocrine glands: Endocrine glands release their secretions directly into the bloodstream. e.g thyroid gland, pituitary gland, etc. these are ductless gland.
Cell Junctions: The epithelial cells are connected to each other laterally as well as to the basement membrane by junctional complexes called cell junctions.
Tight Junctions: These junctions maintain cell polarity, prevent lateral diffusion of proteins and ions.
Gap Junctions: This intercellular connection allows passage of ions and small molecules between cells as well as the exchange of chemical messages between cells.
Hemidesmosomes :They allow the cells to strongly adhere to the underlying basement membrane. These maintain tissue homeostasis by signalling.
Desmosomes :These provide mechanical strength to epithelial tissue, cardiac muscles and meninges.
Adherens Junctions: Adherens Junctions is involved in various signalling pathways and transcriptional regulations.
White fibres: White fibres are made up of collagen. They give tensile strength to the Areolar tissue.
Yellow fibres: Yellow fibres are made up of elastin and are elastic in nature.
Achilles tendon: The Tendon that connects the calf muscles to the heel bone is called Achilles tendon.
Tendon :Tendons connect skeletal muscles to bones, It provides tensile strength to the tissue, tendons contain bundles of white fibres. E.g. Achilles tendon, Hamstring tendon.
Ligaments :Ligaments are made up of elastic or yellow fibres arranged in a regular pattern, they are present at the joint and prevent dislocation of bones.
Lacuna :In bones, Matrix is arranged in the form of concentric layers called lamellae.
Canaliculi :Fine canals that radiate from each lacuna are called canaliculi.
Ossein :Bone is characterised by a hard matrix called Ossein, which is made up of mineral salt hydroxy-apatite (Ca10(PO4)6(OH)2).
Epimysium :Skeletal muscles consist of a large number of fasciculi which are wrapped by connective tissue sheath called epimysium or fascia.
Perimysium :The covering of each individual fasciculus is called perimysium.
Myofibres : Each fasciculus consists of many muscle fibres called myofibres.
Sarcomeres :Each myofibril is made up of repeated functional units called sarcomeres.
Anisotropic band: Each sarcomere has a dark band called anisotropic or 'A' band in the centre.
H – zone: Each sarcomere has a dark band called anisotropic or 'A' band in the centre and in the centre of 'A' band is a light area called 'H' zone or 'Hensen's Zone'.
Isotropic band: Sarcomere has a dark band called anisotropic or 'A' band, On either side of 'A' band are light bands called isotropic or 'I' bands that contain only actin.
Zwischenscheibe line: The regular occurring dark bands on each myofibril is called 'Z' line (Z – Zwischenscheibe line).
Red muscles: Skeletal muscles which contain a very high amount of myoglobin are called Red muscles.
White muscles: Skeletal muscles which contain a very low amount of myoglobin are called White muscles.
Myoglobin :Myoglobin is an iron-containing red coloured pigment found only in muscles, It consists of one haeme and one polypeptide chain and It can carry one molecule of oxygen.
Intercalated discs: The points of adhesion of muscle fibres are formed by transverse thickenings of sarcolemma called intercalated discs.
Myogenic heart: Some mammalian cardiac muscles are modified are capable of generating impulse on their own, They are Myogenic e.g. mammalian heart.
Neurogenic heart: When cardiac muscles need neural stimulus to initiate the contraction, such heart is called neurogenic heart.
Neuron : A neuron is the structural and functional unit of the nervous system.
Neuroglial cells: Neuroglial cell are non-nervous supporting cells that fill in the interneuronal space, they are capable of regeneration and division.
Excitability :Neurons change action potential of their membrane on receiving any external stimulus. This property of neuron is called excitability.
Conductivity :Neurons carry a wave of electric impulse from dendron to axon, this property of a neuron is called conductivity.
Myelin sheath: Axon is enclosed in a fatty sheath called a myelin sheath.
Schwann’s cells: Outer covering of myelin sheath is known as neurilemma, Myelin sheath and neurilemma are parts of another cell called Schwann's cell, it shows nucleus at the periphery.
Node of Ranvier: The myelin sheath is absent at intervals along the axon and the place is called Node of Ranvier.
Telodendron :The terminal arborization of an axon is called telodendron.
Afferent Neuron: It carries impulses from a sense organ to the central nervous system (CNS), hence it is also called sensory neuron and is found in the dorsal root of the spinal cord.
Efferent Neuron: It carries impulses from CNS to effector organ, hence it is also called motor neuron and is found in the ventral root of the spinal cord.
Interneuron or association neuron: They are located between sensory and motor neurons, these perform processing, integration of sensory impulses and activate appropriate motor neuron to generate a motor impulse.
Myelinated / medullated nerve fibres :Myelinated or medullated nerve fibres have an insulating fatty layer called myelin sheath around the axon which makes the fibre appear white in colour.
Non Myelinated nerve fibres: Schwann cell of a non-medullated nerve fibre does not secrete myelin sheath, these fibres are grey in colour due to the absence of a fatty layer.
Synapse :Functional contact between axonal ends and dendrites of adjacent neurons is called a synapse.
Unipolar/Monopolar Neuron: It has a single process originating from cyton, both axon and Dendron arise from cyton at one point and they conduct impulses to the central nervous system. Ex. Neurons of dorsal root ganglion of a spinal nerve.
Bipolar Neuron: It has two processes, A single dendron and an axon are given off from opposite poles of the cyton and they bring about the transmission of special senses like sight, smell, taste, hearing etc. Ex. Neurons of the retina of the eye, olfactory epithelium.
Multipolar Neuron: Here cyton is star-shaped and gives out more than two processes, there is only one axon and remaining are dendrons, here axon initiates from a funnel-shaped area called axon- hillock.
