Unit 2 Cell and functions PDF

UNIT 2: STRUCTURE OF CELL & TISSUE – ITS COMPONENTS AND THEIR FUNCTIONS By: Dr. Nur Liyana Mohammed Yusof PhD Cardiovascular Science Learning objective At the end of this chapter, the students should be able to: ✓ Explain structure and characteristics of human cell ✓ Desc...

UNIT 2: STRUCTURE OF CELL & TISSUE – ITS COMPONENTS AND THEIR FUNCTIONS By: Dr. Nur Liyana Mohammed Yusof PhD Cardiovascular Science Learning objective At the end of this chapter, the students should be able to: ✓ Explain structure and characteristics of human cell ✓ Describe movements of particles across cell membrane ✓ Discuss organelles of human cell & their function Introduction  Cell is the basic living structural and functional unit of the body.  Cytology: - It is a branch of science concerned with a study of cells  The first cells were observed and named by Robert Hooke in 1665 from slice of cork under a microscope.  Some organisms consist of a single cells = unicellular organism, others are multicellular.  Diameter- 2-120µm. Cell Theory  Proposed by Matthias Schleiden and Theodor Schwann in 1839:-  Cell Theory explains about: a)All living organisms are composed of cell and cell products. b)Cell is the basic unit of structure & function of all living organisms. c)All cells come from the division of preexisting cell. d)An organism can be understood through the collective activities & interactions of its cells.  Plasma Membrane  Plasma membrane is a thin outer layer membrane, which maintains the integrity of the cell.  It is a double layered measuring about 4.5 nm and made of phospholipids, cholesterol, glycolipid, & carbohydrate (oligosaccharides). Plasma Membrane Functions: - 1.Separate the cytoplasm inside a cell from extra cellular fluid. 2.Separate cell from one another 3.Provide an abundant surface on which chemical reaction can occur. 4.Regulate the passage of materials in to and out of cells. Movement across-cell membrane  These are passive and active movements. Passive movement uses energy whereas active movement consumes energy in the form of ATP. Passive movement: a.Simple diffusion, the random movements of molecules: from area of high concentration to the area of low concentration. Example air in alveoli of lung Passive movement: b.Facilitated diffusion: larger molecules, which are not soluble in lipid need protein channel to pass through the plasma membrane. No direct energy needed. Example: - Amino acid passes through the cell membrane. c.Osmosis: a special type of diffusion referring to the passage of water through a selectively permeable membrane from an area of high water concentration to lower water concentration. d.Filtration: small molecules pass through selectively permeable membrane in response to force of pressure. Example: - filtration in the kidney in the process of urine formation. Diffusion across plasma membrane  Active movements across membranes  An active process occurs whenever a cell uses energy to move solutes across the membrane. Substances moved actively across the plasma membrane are usually unable to pass in the necessary direction by passive transport processes.  The substance may be too large to pass through the channels, incapable of dissolving in the lipid bilayer, or moving against its concentration gradient.  Therefore, it requires energy.  Active Transport Requires transport proteins that combine specifically and reversibly with the transported substances. Active transporters move solutes, most importantly ions, "uphill" against a concentration gradient. Active Transport Primary active transport: the energy to do work comes directly from the hydrolysis of ATP by transport proteins called pumps. Secondary active transport: transport is driven by energy stored in concentration gradients of ions created by Secondary active transport systems always move primary active transport more than one substance at a time using a cotransport protein. pumps. Vesicular Transport  Fluids containing large particles and macromolecules are transported across cellular membranes inside bubble-like, membranous sacs called vesicles.  Vesicular transport moves substances into the cell (endocytosis) and out of the cell (exocytosis).  Cytoplasm Cytoplasm is a matrix or ground substance in which various cellular components are found. It is thick semi transparent, elastic fluid containing suspended particles and a series of minute tubules and filaments that form cytoskeleton. Water constitutes 75-90% of the cytoplasm. It also contains solid components, proteins, carbohydrates, lipids and inorganic substances. The inorganic components exist as solutions because they are soluble in water. Organelles Organelles are specialized portion of the cell with a characteristic shape that assume specific role in growth, maintenance, repair and control. a) Nucleus  Oval in shape and is the largest structure in the cell.  Contain the hereditary factor in the cell. Hence it controls cell activity & structure.  The nucleus separated from other cell structure by double membrane called nuclear membrane.  Pores over the nuclear membrane allow the nucleus to communicate with the cytoplasm.  In the nucleus a jelly like fluid that fill the nucleus is karylymph (neucleoplasm), which contain the genetic material called chromosome.  Nucleus also contain dark, somewhat spherical, non-membrane bound mass called nucleolus.  It contains DNA, RNA and protein, which assist in the construction of ribosome. b) Endoplasmic reticulum  double membrane channel.  It is continuous with the nuclear membrane.  It involved in intracellular exchange of material with the cytoplasm.  Various products are transported from one portion of the cell to another via the endoplasmic reticulum.  So it is considered as intracellular transportation.  It is also storage for synthesized molecules.  Together with the Golgi complex it serves as synthesis & packaging center. c) Ribosome  tiny granules, composed of Ribosomal RNA (rRNA).  They are site of protein synthesis Two types: Smooth Endoplasmic Reticulum Rough Endoplasmic Reticulum ▪ Ribosomes absent ▪Contains ribosomes ▪Site of synthesis of lipid and steroid ▪Site of protein synthesis,processing hormones. and packaging. ▪Mainly present in lipid forming cells ▪Mainly present in protein forming cells such as adipocytes, interestitial cells of such as pancreatic acinar cells ,Goblet testis, glycogen storing cells of liver, cells ,antibody producing plasma cells, adrenal cortex cells, muscle cells, Nissl’s granules of nerve cells etc. leucocytes etc. d) Golgi complex It consist 4-8 membranous sacs. It process, sort, pack & deliver protein to various parts of the cell. Golgi Bodies is a collection of membrane enclosed sacs composed of four or more stacked layers of thin, flat enclosed vessels lying near the side of the nucleus. Consist of multiple discrete compartments. Consist of few functionally distinct regions: i)The cis Golgi network ii)Golgi stack –which is divided into a) The medial and b) Trans sub compartments iii)The trans Golgi network.  e) Mitochondria  A small, spherical, rod shaped or filamentous structure. It generates energy.  Each mitochondria posses two membrane, one is smooth (upper) membrane and the other is arranged with series of folds called cristae.  The central cavity of a mitochondrion enclosed by the inner membrane is the matrix.  Power generating units of the cells.  Important to maintain proper concentration of calcium ions within the various compartments of the cell.  Energy transduction through respiration.  Responsible for thermogenesis. f) Lysosomes  Appear as membrane enclosed spheres.  They are formed from Golgi complexes & have single membrane.  Diameter- 250 -750nm  These are the irregular structures surrounded by the unit membrane.  More acidic than rest of the cytoplasm and external bacteria as well as worn out cell components are digested in them. f) Lysosomes: Function  Acts as a form of digestive (lytic ) system or the cell, because enzymes present in it can digest essentially all macromolecules.  Engulf worn out components of the cells in which they are located.  Engulf exogenous substances e.g. bacteria and degrade them.  When a cell dies ,lysosomal enzymes causes autolysis of the remanant.  Thats why lysosomes are called as Suicidal Bags. Some other organelles g)The cytoskeleton: the cytoplasm has a complex internal structure consisting of a series of exceedingly small microfilaments, microtubule & intermediate filaments together referred to as the cyto-skeleton. h)Centrosme: a dense area of cytoplasm generally spherical and located near the nucleus it contain centrioles. It also contains DNA that controls their replication. Centrosmes are made of microtubules, which seam drinking straws. They are Involved in the movement of chromosome during cell division. i) Cilia/flagella: thread like appendages, which are made of microtubules. When they are beating forms rhythmic movement. They are found in female reproductive organ and upper respiratory tube.  TISSUE  Cells work together in-group of similar cells called tissue.  Tissue is a group of similar cell and their intercellular substance that have a similar embryological origin and function together to perform a specialized activity.  A science that deals with the study of a tissue is Histology.  The various tissues of the body are classified into four principal parts according to their function & structure.  These are epithelial, connective, muscular, and nervous tissue. TISSUE 1. Epithelial tissue  Epithelial tissues covers body surface, lines body cavity & ducts and form glands. They are subdivided in to: Covering & lining epithelium Glandular epithelium  Covering and lining epithelium: it forms the outer covering of external body surface and outer covering of some internal organs. It lines body cavity, interior of respiratory & gastro intestinal tracts, blood vessels & ducts and make up along with the nervous tissue (the parts of sense organs for smell, hearing, vision and touch). It is a tissue from which gametes (egg & sperm) develops. 1. Epithelial tissue  Glandular epithelium: A type of tissue that lines certain internal organs and makes and releases substances in the body, such as mucous, digestive juices, and other fluids. Glandular epithelium is commonly found in the breast, lung, stomach, colon, pancreas, prostate, uterus, and cervix.  Covering and lining epithelium are classified based on the arrangement of layers and cell shape.  According to the arrangement of layers covering and lining epithelium is grouped in to: a) Simple epithelium: it is specialized for absorption, and filtration with minimal wear & tear. It is a single layered b) Stratified epithelium: it is many layered and found in an area with high degree of wear & tear. c) Pseudo-stratified: is a single layered but seam to have many layer.  Epithelial cells vary in height, and on that basis, there are three common shapes of epithelial cells: a) Squamous: - flattened & scale like b) Cuboidal: - cube shaped c) Columnar: - tall & cylindrical Glandular Epithelium  Their main function is secretion. A gland may consist of one cell or a group of highly specialized epithelial cell.  Glands can be classified into exocrine (external secreting) and endocrine (internal secreting) according to where they release their secretion.  Exocrine: Those glands that empties their secretion into ducts/tubes that empty at the surface of covering. Their main products are mucous, oil, wax, perspiration and digestive enzyme. Sweat & salivary glands are exocrine glands.  Endocrine: They ultimately secret their products into the blood system. The secretions of endocrine glands are always hormones. Hormones are chemicals that regulate various physiological activities. Pituitary, thyroid & adrenal glands are endocrine.  Classification of exocrine glands  They are classified by their structure and shape of the secretary portion. According to structural classification they are grouped into: a) Unicellular gland: Single celled. The best examples are goblet cell in Respiratory, Gastrointestinal & Genitourinary system. b)Multicultural gland: Found in several different forms by looking into the secretary portion exocrine glands are grouped into: a. Tubular gland: If the secretary portion of a gland is tubular. b. Acinar gland: If the secretary portion is flask like. c. Tubulo-acinar: if it contains both tubular & flask shaped secretary portion. Connective tissue  Connective tissue is the most abundant tissue in the body.  The connective tissue cells are more widely separated from each other than in epithelial tissues, and intercellular substance (matrix) is present in considerably larger amounts.  There are usually fibres present in the matrix, which may be of a semisolid jelly-like consistency or dense and rigid, depending upon the position and function of the tissue.  Major functions of connective tissue are: binding and structural support protection transport insulation Connective tissue  Embryonic connective tissue Embrayonic connective tissue contains mesenchyme & mucous connective tissue. Mesenchyme is the tissue from which all other connective tissue eventually arises. It is located beneath the skin and along the developing bone of the embryo. Mucous connective tissue is found primarily in the fetus and located in the umbilical cord of the fetus where it supports the cord.  Adult connective tissue It is differentiated from mesenchyme and does not change after birth. Adult connective tissue composes connective tissue proper, cartilage, osseous (bone) & vascular (blood) tissue. Connective tissue Connective tissue Muscle tissue  Able to contract and relax, providing movement within the body and of the body itself.  Muscle contraction requires a blood supply that will provide sufficient oxygen, calcium and nutrients and remove waste products.  There are three types of specialised contractile cells, also known as fibres: 1. skeletal muscle, 2. Smooth muscle and 3. cardiac muscle 1. Skeletal muscle  Muscles that move the bones (of the skeleton), striated because striations (stripes) and voluntary as it is under conscious control.  For ex.: Diaphragm is made from this type of muscle to accommodate a degree of voluntary control in breathing.  Skeletal muscle contraction is stimulated by motor nerve impulses originating in the brain or spinal cord and ending at the neuromuscular junction. 2. Smooth muscle  Non-striated, visceral or involuntary.  It does not have striations and is not under conscious control.  Some smooth muscle has the intrinsic ability to initiate its own contractions (automaticity), e.g. peristalsis  Autonomic nerve impulses, some hormones and local metabolites stimulate its contraction.  Contraction of smooth muscle is slower and more sustained than skeletal muscle. For example: regulating the diameter of blood vessels and parts of the respiratory tract propelling contents along, e.g. the ureters, ducts of glands and the alimentary tract expelling contents of the urinary bladder and uterus. 3. Cardiac muscle  Only found only in the heart wall.  Cross-stripes (striations) characteristic of skeletal muscle can be seen.  The ends of the cells and their branches are in very close contact with the ends and branches of adjacent cells.  These ‘joints’, or intercalated discs, appear as lines that are thicker and darker than the ordinary cross-stripes.  Allow the heart to contract as a wave of contraction spreads from cell to cell across the intercalated discs. 4. Nervous Tissue