8. Write short notes on :
(a) Goblet cell
(b) Cardiac muscle
(c) Neuron
(d) Mast cell
(e) Stratified epithelium (1) Holocrine gland
(g) Adipose tissue (h) Lymph
Q. 9. Describe the structure and the functions of three types of
epithelial tissue.
Q. 10. Describe the structure and the functions of six types of
connective tissue.
Q. 11. Describe the structure and the functions of three types of
muscular tissue.
Q. 12. Nerve impulses are conducted more rapidly in myelinated
fibres than in non-myelinated fibres,
Answers
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8. (a) Goblet cells are simple columnar goblet shaped like epithelial cells that secrete gel-forming mucins, like mucin MUC5AC. The goblet cells mainly use the merocrine method of secretion, secreting vesicles into a duct, but may use apocrine methods, budding off their secretions, when under stress. The term goblet refers to the cell's goblet-like shape. The apical portion is shaped like a cup, as it is distended by abundant mucus laden granules; its basal portion lacks these granules and is shaped like a stem.
The goblet cell is highly polarized with the nucleus and other organelles concentrated at the base of the cell and secretory granules containing mucin, at the apical surface. The apical plasma membrane projects short microvilli to give an increased surface area for secretion.
Goblet cells are typically found in the respiratory, reproductive and gastrointestinal tracts and are surrounded by other columnar cells. Biased differentiation of airway basal cells in the respiratory epithelium, into goblet cells plays a key role in the excessive mucus production, known as mucus hypersecretion seen in many respiratory diseases, including chronic bronchitis, and asthma.
(b) Cardiac muscle, also called myocardium, in vertebrates, one of three major muscle types, found only in the heart. Cardiac muscle is similar to skeletal muscle, another major muscle type, in that it possesses contractile units known as sarcomeres; this feature, however, also distinguishes it from smooth muscle, the third muscle type. Cardiac muscle differs from skeletal muscle in that it exhibits rhythmic contractions and is not under voluntary control. The rhythmic contraction of cardiac muscle is regulated by the sinoatrial node of the heart, which serves as the heart’s pacemaker.
(c) A neuron or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. It is the main component of nervous tissue in all animals except sponges and placozoa. Plants and fungi do not have nerve cells. The spelling neurone has become uncommon.
Neurons are typically classified into three types based on their function. Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord or brain. Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. A group of connected neurons is called a neural circuit.
(d) A mast cell is a migrant cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a part of the immune and neuroimmune systems. Mast cells were discovered by Paul Ehrlich in 1877. Although best known for their role in allergy and anaphylaxis, mast cells play an important protective role as well, being intimately involved in wound healing, angiogenesis, immune tolerance, defense against pathogens, and vascular permeability in brain tumours.
(e) A stratified squamous epithelium consists of squamous (flattened) epithelial cells arranged in layers upon a basal membrane. Only one layer is in contact with the basement membrane; the other layers adhere to one another to maintain structural integrity.
(f) Holocrine is a term used to classify the mode of secretion in exocrine glands in the study of histology. Holocrine secretions are produced in the cytoplasm of the cell and released by the rupture of the plasma membrane, which destroys the cell and results in the secretion of the product into the lumen.
(g) Adipose, or fat, tissue is loose connective tissue composed of fat cells known as adipocytes.
Adipocytes contain lipid droplets of stored triglycerides. These cells swell as they store fat and shrink when the fat...
Adipose tissue helps to store energy in the form of fat, cushion internal organs, and insulate the body.
There are three types of adipose tissue: white, brown, and beige adipose.
White adipose stores energy and helps to insulate the body.
(h) Lymph is the fluid that flows through the lymphatic system, a system composed of lymph vessels and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to the central circulation. Interstitial fluid – the fluid which is between the cells in all body tissues – enters the lymph capillaries. This lymphatic fluid is then transported via progressively larger lymphatic vessels through lymph nodes, where substances are removed by tissue lymphocytes and circulating lymphocytes are added to the fluid, before emptying ultimately into the right or the left subclavian vein, where it mixes with central venous blood
MAST CELL :
A mast cell (also known as a mastocyte or a labrocyte) is a migrant cell of connective tissue that contains many granules rich in histamine and heparin. Specifically, it is a type of granulocyte derived from the myeloid stem cell that is a part of the immune and neuroimmune systems.