ORGANS AND ORGAN SYSTEM

Organ

The group of different tissues performing same function is called organs. Different tissues are organized into the organs except simplest animals (sponges and cnidarians). Some organs have their tissue layers. For example, the stomach has four major layers.

• The lumen is lined by a thick epithelium. This epithelium secretes mucus and digestive juices.
• Outside this layer is a zone of connective tissue
• It is followed by a thick layer of smooth muscle.
• The entire stomach is encapsulated by another layer of connective tissue A laminated organization is also present in the dermis. It is the outer skin of the body.Man of the organs of vertebrates are suspended by mesenteries. Mesenteries are heets of connective tissue present in the body cavities. Mammals have an upp r thoracic cavity separated from a lower abdominal cavity by a sheet of must le called the diaphragm.

  0 an system

  The group of different organs performing same functions is called organ sys m. Organ system is a level of organization higher than organs. The organs car out major functions of vertebrates and members of most invertebrate phyla. Org n system consists of several organs. Examples are the digestive, arc latory. respiratory, and excretory system. Each system has specific func ions. But the efforts of all systems must be coordinated for the survival of ani als. For instance, nutrients are absorbed from the digestive tract. They are distr buted throughout the body by the circulatory system. But the heart itself dep nds on nutrients absorbed by the digestive tract. The respiratory system abs rbs oxygen from the air. This oxygen is transported by blood.

  DEFINITIONS AND KEY POINTS

   

  		I                             DEFINITIONS
  	ITERMS
  	Homoeostasis	The     maintenance      of a     constant    internal    environment despite fluctuations in the external environment is called homoeostasis.
  Simple	diffusion	The movement of molecules from the area of higher concentration to the area of lower concentration is called simple diffusion.
  Fac	diffusion litated ., ,	The      movement     of    molecules      through     the      protein molecules from      higher to lower concentratiOn          is called facilitated diffusion.
  	OsmoSis	The diffusion       of water across a selectively permeable ---------------------------- ---------------------------- membrane from an area of higher concentration to an area of lower concentration is called osmosis.
  Tonicity		The relative concentration of solutes in the water inside and outside the cell is called tonicity
  	Filtiation	Filtration is a process that forces small molecules across selectively     permeable      membranes     with     the     help    of hydrostatic pressure.
  Act	ye transport	The movement of molecules form the area of lower concentration to the area          higher concentration       by the expenditure of energy is called active-transport.
  Enc	ocytosis	The movement of substance inside the cell by infolding of

   

   

  	the     membrane    and     formation     of   vacuole     is    called endosytosis. The nonspecific uptake of all droplets of extracellular fluid is called pinocytosis.
  Pinocytosis
  Phagocytosis	The   uptake    of solid    particles     by  invagination     is  called
  Phagolysosome	Lysosome combines with the food vacuole to form a phagolysosome.
  Exocytosis	The removal of cell secretions from the cells by out folding is called exocytosis.
  Lysosome	Lysosome     is a     membrane-enclosed     bag    of hydrolytic enzymes that the cell uses to digest macromolecules..
  Tissues	The sheets of tightly packed           cells are called       epithelial
  Connective tissues	The tissue, with loose arrangement of cells and the cells are    scattered      in   an    extracellular      matrix    are   called connective tissue.

   

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