81. What is meant by cellular secretion?
Cell secretion is the elimination to the exterior of substances produced by the cell (for example, hormones, mucous, sweat, etc.)
82. Which cell organelles are well-developed in secretory cells?
In secretory cells, like the secretory cells of endocrine glands, organelles related to production, processing and “exportation” of substances are widely present and well-developed. These organelles are the rough endoplasmic reticulum and the Golgi apparatus.
The nuclear membrane of the secretory cells generally has more pores to allow the intense traffic of molecules related to protein synthesis between the cytoplasm and the nucleus.
Rough endoplasmic reticulum Golgi apparatus
83. How do the rough endoplasmic reticulum and the Golgi apparatus act in the production and releasing of proteins?
The rough endoplasmic reticulum has in its outer membrane numerous ribosomes, structures where translation of messenger RNA and protein synthesis occur. These proteins are stored in the rough endoplasmic reticulum and later they go to the Golgi apparatus. Within the Golgi apparatus proteins are chemically transformed and when ready they are put inside vesicles that detach from the organelle. These vesicles fuse with the plasma membrane (exocytosis) in the right place and its content is liberated outside the cell.
84. What are some examples of secretory cells?
Endocrine and exocrine pancreatic cells, thyroid and parathyroid endocrine cells, adenohypophysis, adrenal and pineal endocrine cells, the many types of gastric exocrine and endocrine cells, the mucous secretory cells of the lungs and of the bowels, the salivary gland cells, the lacrimal gland cells, the sebaceous gland cells, the secretory cells of the ovaries and testicles, etc., are all examples of secretory cells.
85. What is extracellular digestion?
Extracellular digestion is that in which food breaking into utile molecules that can be internalized by the cell is done in the extracellular space, i.e., outside the cell. In extracellular digestion the cells secret substances that break big molecules into smaller ones in the external environment. Later the cell can benefit from these products of the digestion.
86. What is intracellular digestion?
Intracellular digestion, or cellular digestion, is the breaking in the interior of the cell of big molecules coming from outside or even from the own cell metabolism into smaller molecules. Products and residues of the intracellular digestion are used by the cell or excreted.
Intracellular digestion is classified into two types: heterophagic intracellular digestion and autophagic intracellular digestion.
87. What is the main cell organelle involved in cell digestion? What are the properties of that organelle that enable it to the task?
The organelles responsible for intracellular digestion are the lysosomes. Lysosomes are vesicles that contain digestive enzymes capable of breaking big molecules into smaller ones. These vesicles fuse with others that carry the material to be digested and then digestion takes place.
Cell Digestion Review - Image Diversity: lysosomes
88. What is heterophagic intracellular digestion? How is this process accomplished?
Heterophagic intracellular digestion is the breaking into smaller substances of external substances engulfed in the cell by pinocytosis or phagocytosis. Phagosomes or pinosomes fuse with lysosomes making the digestive vacuoles. Within the digestive vacuoles the molecules to be digested are hydrolyzed and the products of the digestion cross through the membrane and reach the cytoplasm or they are kept inside the vacuoles. The vacuole with residues from digestion is called residual body and by exocytosis it fuses with the plasma membrane and liberates its “waste” in the exterior space.
89. What is autophagic intracellular digestion? Why is this type of intracellular digestion intensified in an organism undergoing starvation?
Autophagic intracellular digestion is the cellular internal digestion of waste and residual materials. In general it is done by lysosomes.
Autophagic intracellular digestion is intensified in situations of starvation because in such condition the cell tries to obtain from its own constituent materials the nutrients necessary to stay alive.
90. What are some biological examples in which lysosomic enzymes play fundamental role?
The remodelation of the osseous tissue, the function of acrosomes in sperm cells and the elimination of the tadpole tail are examples of biological processes in which lysosomic enzymes are key factors.
The bone is a tissue made of osteoblast-containing matrix (osteoblasts are the secretory cells of the osseous matrix), osteocytes (mature bone cells) and osteoclasts (the remodeling cells). Osteoclasts are responsible for the the continual renovation of the osseous tissue since their lysosomic enzymes digest the osseous matrix.
The sperm acrosome, for carrying digestive enzymes within, is responsible for the perfuration of the egg cell membrane in the fertilization process. The acrosome, located in the anterior end of the sperm cell, is a specialized region of the Golgi apparatus that accumulates great amount of digestive enzymes.
In tadpoles the tail regresses while the organism develops into an adult frog. This tissue destruction is a digestion of the tail own cells and extracellular materials and it is made by lysosomes and their enzymes. The complete digestion of a cell by its own mechanisms is called autolysis, a type of apoptosis (celll suicide).
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Cell secretion is the elimination to the exterior of substances produced by the cell (for example, hormones, mucous, sweat, etc.)
82. Which cell organelles are well-developed in secretory cells?
In secretory cells, like the secretory cells of endocrine glands, organelles related to production, processing and “exportation” of substances are widely present and well-developed. These organelles are the rough endoplasmic reticulum and the Golgi apparatus.
The nuclear membrane of the secretory cells generally has more pores to allow the intense traffic of molecules related to protein synthesis between the cytoplasm and the nucleus.
Rough endoplasmic reticulum Golgi apparatus
83. How do the rough endoplasmic reticulum and the Golgi apparatus act in the production and releasing of proteins?
The rough endoplasmic reticulum has in its outer membrane numerous ribosomes, structures where translation of messenger RNA and protein synthesis occur. These proteins are stored in the rough endoplasmic reticulum and later they go to the Golgi apparatus. Within the Golgi apparatus proteins are chemically transformed and when ready they are put inside vesicles that detach from the organelle. These vesicles fuse with the plasma membrane (exocytosis) in the right place and its content is liberated outside the cell.
84. What are some examples of secretory cells?
Endocrine and exocrine pancreatic cells, thyroid and parathyroid endocrine cells, adenohypophysis, adrenal and pineal endocrine cells, the many types of gastric exocrine and endocrine cells, the mucous secretory cells of the lungs and of the bowels, the salivary gland cells, the lacrimal gland cells, the sebaceous gland cells, the secretory cells of the ovaries and testicles, etc., are all examples of secretory cells.
85. What is extracellular digestion?
Extracellular digestion is that in which food breaking into utile molecules that can be internalized by the cell is done in the extracellular space, i.e., outside the cell. In extracellular digestion the cells secret substances that break big molecules into smaller ones in the external environment. Later the cell can benefit from these products of the digestion.
86. What is intracellular digestion?
Intracellular digestion, or cellular digestion, is the breaking in the interior of the cell of big molecules coming from outside or even from the own cell metabolism into smaller molecules. Products and residues of the intracellular digestion are used by the cell or excreted.
Intracellular digestion is classified into two types: heterophagic intracellular digestion and autophagic intracellular digestion.
87. What is the main cell organelle involved in cell digestion? What are the properties of that organelle that enable it to the task?
The organelles responsible for intracellular digestion are the lysosomes. Lysosomes are vesicles that contain digestive enzymes capable of breaking big molecules into smaller ones. These vesicles fuse with others that carry the material to be digested and then digestion takes place.
Cell Digestion Review - Image Diversity: lysosomes
88. What is heterophagic intracellular digestion? How is this process accomplished?
Heterophagic intracellular digestion is the breaking into smaller substances of external substances engulfed in the cell by pinocytosis or phagocytosis. Phagosomes or pinosomes fuse with lysosomes making the digestive vacuoles. Within the digestive vacuoles the molecules to be digested are hydrolyzed and the products of the digestion cross through the membrane and reach the cytoplasm or they are kept inside the vacuoles. The vacuole with residues from digestion is called residual body and by exocytosis it fuses with the plasma membrane and liberates its “waste” in the exterior space.
89. What is autophagic intracellular digestion? Why is this type of intracellular digestion intensified in an organism undergoing starvation?
Autophagic intracellular digestion is the cellular internal digestion of waste and residual materials. In general it is done by lysosomes.
Autophagic intracellular digestion is intensified in situations of starvation because in such condition the cell tries to obtain from its own constituent materials the nutrients necessary to stay alive.
90. What are some biological examples in which lysosomic enzymes play fundamental role?
The remodelation of the osseous tissue, the function of acrosomes in sperm cells and the elimination of the tadpole tail are examples of biological processes in which lysosomic enzymes are key factors.
The bone is a tissue made of osteoblast-containing matrix (osteoblasts are the secretory cells of the osseous matrix), osteocytes (mature bone cells) and osteoclasts (the remodeling cells). Osteoclasts are responsible for the the continual renovation of the osseous tissue since their lysosomic enzymes digest the osseous matrix.
The sperm acrosome, for carrying digestive enzymes within, is responsible for the perfuration of the egg cell membrane in the fertilization process. The acrosome, located in the anterior end of the sperm cell, is a specialized region of the Golgi apparatus that accumulates great amount of digestive enzymes.
In tadpoles the tail regresses while the organism develops into an adult frog. This tissue destruction is a digestion of the tail own cells and extracellular materials and it is made by lysosomes and their enzymes. The complete digestion of a cell by its own mechanisms is called autolysis, a type of apoptosis (celll suicide).
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