Cell and Tissues Cells are the smallest living

Cell and Tissues

�Cells are the smallest living subunits of a multicellular organism such as a human being �Cells are the building blocks and functional units of all living things. �Carry out all chemical activities needed to sustain life. �Tissues are groups of cells that are similar in structure and function.

� Metabolize � Digest foods � Get rid of wastes � Reproduce � Grow � Move � Respond to a stimulus (irritability)

�Cells are not all the same but has a general structures and is formed of three main regions: �Nucleus (RBCs are exception) �Cytoplasm �Plasma membrane

I-The Nucleus � Control center of the cell, contains genetic material (DNA), RNA, & protein. � 46 chromosomes � Three regions: a-Nuclear Membrane � Consists of a double phospholipid membrane � Contain nuclear pores that allow for exchange of materials with the rest of the cell. Figure 3. 1 b

b- Nucleoli � Nucleus contains one or more nucleoli. � Sites of ribosome production �Ribosomes then migrate to the cytoplasm through nuclear pores Ribosomes are the site for protein systhesis c-Chromatin � Composed of DNA and protein � Scattered throughout the nucleus � Chromatin condenses to form chromosomes when the cell divides.

� II-Plasma Membrane : phospholipids, cholesterol (decreases the fluidity of the membrane), and proteins (channels, transporters, receptors). � Barrier for cell contents � Double phospholipid layer (permit lipid-soluble materials to easily enter or leave the cell by diffusion through the cell membrane

III-Cytoplasm � watery solution of minerals, gases, organic molecules, and cell organelles that is found between the cell membrane and the nucleus. -Cytosol , fluid that suspends other elements. -Organelles , metabolic machinery of the cell. -Inclusions , nonfunctioning units.

Cytoplasmic Organelles: the main organelles are: 1 -Ribosomes: sites of protein synthesis 2 -Endoplasmic reticulum (ER): fluid-filled tubules for carrying substances. It has two types: rough & smooth 3 -Golgi apparatus: modifies and packages proteins & carbohydrates. 4 -Lysosomes: contain enzymes that digest non-usable materials within the cell. 5 -Mitochondria: “powerhouses” of the cell. mitochondria are he site of ATP (and hence energy) production � 6 -Centrioles: rod-shaped bodies made of microtubules. Direct the formation of mitotic spindle during cell division. Their function is to organize the spindle fibers during cell division

Cellular Physiology: Membrane Transport � Membrane Transport is movement of substance into and out of the cell � The plasma membrane allows some materials to pass while excluding others � Transport is by two basic methods �Passive transport : No energy is required �Active transport: Energy is needed and must be provided by the cell

Passive (Physical) Processes • Require no cellular energy and include: • Simple diffusion • Facilitated diffusion • Osmosis • Filtration Active (Physiological) Processes • Require cellular energy and include: • Active transport • Endocytosis • Exocytosis • Transcytosis 14

Passive Transport Processes 1 -Diffusion �Particles tend to distribute themselves evenly within a solution �Movement is from high concentration to low one. �Ex: Gas exchange � Types of diffusion -Simple diffusion : solutes are lipid-soluble materials or small enough to pass through membrane pores. -Osmosis : simple diffusion of water -Facilitated diffusion: Substances require a protein carrier for passive transport. Figure 3. 9

• Movement of substances from regions of higher concentration to regions of lower concentration • Oxygen, carbon dioxide and lipid-soluble substances Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Solute molule ater moule A B (1) A B (2) Time A B (3) 16

• Diffusion across a membrane with the help of a channel or carrier molecule • Glucose and amino acids (needs carrier enzymes) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Region of higher concentration Transported substance Region of lower concentration Protein carrier molecule Cell membrane 17

Diffusion through the Plasma Membrane 2 -Filtration Water and solutes are forced from a high pressure area to a lower pressure area , a pressure gradient Figure 3. 10 must exist.

• Movement of water through a selectively permeable membrane from regions of higher concentration to regions of lower concentration • Water will naturally tend to move to an area where there is more dissolved material, such as salt or sugar. The process of osmosis also takes place in the kidneys, which reabsorb large amounts of water (many gallons each day) to prevent its loss in urines A A B B (1) (2) Time 19

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • Osmotic Pressure – ability of osmosis to generate enough pressure to move a volume of water • Osmotic pressure increases as the concentration of nonpermeable solutes increases • Isotonic – same osmotic pressure • Hypertonic – higher osmotic pressure (water loss) ? ? ? • Hypotonic – lower osmotic pressure (water gain) ? ? ? (a) (b) (c) 20 © David M. Phillips/Visuals Unlimited

Active Transport Processes Transport substances that are unable to pass by diffusion. -They may be too large -They may not be able to dissolve in the fat core of the plasma membrane -They may have to move against a concentration gradient � requires the energy of ATP to move molecules from an area of lesser concentration to an area of greater concentration.

• Carrier molecules transport substances across a membrane from regions of lower concentration to regions of higher concentration • Sugars, amino acids, sodium ions, potassium ions, etc. Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Carrier protein Binding site Cell membrane Region of higher concentration Region of lower concentration Phospholipid molecules Transported particle (a) Carrier protein with altered shape Cellular energy (b) 22

1 -Solute pumping �Amino acids, some sugars and ions are transported by solute pumps. �ATP energizes protein carriers, and in most cases, moves substances against concentration gradients �The best example is Sodium-Potassium pump

� Nerve and muscle cells constantly produce ATP to keep their sodium pumps (and similar potassium pumps) working and prevent spontaneous impulses. � Another example of active transport is the absorption. � The cells use ATP to absorb these nutrients from digested food, even when their intracellular concentration becomes greater than their extracellular concentration. n of glucose

• Active transport mechanism • Creates balance by “pumping” three (3) sodium (Na+) OUT and two (2) potassium (K+) INTO the cell • 3: 2 ratio 25

Movement of water and dissolved substances from an area of higher pressure to an area of lower pressure (blood pressure). • Smaller molecules are forced through porous membranes • Hydrostatic pressure important in the body • Molecules leaving blood capillaries Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Capillary wall Blood pressure Tissue fluid Blood flow Larger molecules Smaller molecules 26

� The blood pressure in capillaries is higher than the pressure of the surrounding tissue fluid. In capillaries throughout the body, blood pressure forces plasma (water) and dissolved materials through the capillary membranes into the surrounding tissue spaces

�Exocytosis Material inside the cell migrates to plasma membrane where a vesicle is formed. It is emptied to the outside. �Endocytosis Extracellular substances are engulfed by being enclosed in a membranous vesicle. Types of endocytosis Phagocytosis – cell eating Pinocytosis – cell drinking

• Cell engulfs a substance by forming a vesicle around the substance • Three types: • Pinocytosis – substance is mostly water • Phagocytosis – substance is a solid • Receptor-mediated endocytosis – requires the substance to bind to a membrane-bound receptor Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Cell membrane Nucleus Nucleolus Vesicle 29

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Cell Particle membrane Phagocytized particle Vesicle Nucleus Nucleolus Receptor-ligand combination Molecules outside cell Vesicle Receptor protein Cell membrane indenting Cytoplasm (a) (b) (c) (d)30

• Reverse of endocytosis • Substances in a vesicle fuse with cell membrane • Contents released outside the cell • Release of neurotransmitters from nerve cells Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Endoplasmic reticulum Golgi apparatus Nucleus 31

• Endocytosis followed by exocytosis • Transports a substance rapidly through a cell • HIV crossing a cell layer Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. HIV-infected white blood cells Anal or vaginal canal Viruses bud HIV Receptor-mediated endocytosis Lining of anus or vagina (epithelial cells) Cell membrane Exocytosis Receptor-mediated endocytosis Virus infects white blood cells on other side of lining 32

Osmosis DIFFUSION Facilitated Diffusion Active transport Filtration Phagocytosis Pinocytosis

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. • Series of changes a cell undergoes from the time it forms until the time it divide • Stages: • Interphase • Mitosis • Cytokinesis G 2 phase se a ph o Pr hase Metap Anapha se Te lop ha se S phase: genetic material replicates G 1 phase cell growth Proceed to division Remain specialized Restriction checkpoint Apoptosis 34 Cytokinesis

Cell Life Cycle � Cells have two major periods �Interphase Cell grows but no cell division. Cell carries on metabolic processes. �Cell division Cell replicates itself. Function is to produce more cells for growth and repair processes.

DNA Replication � Genetic material duplicated and readies a cell for division into two cells � Occurs toward the end of interphase � DNA uncoils and each side serves as a template. Figure 3. 14

� Cell division is the process by which a cell reproduces itself. � There are two types of cell division, mitosis and meiosis. � Although both types involve cell reproduction, their purposes are very different.

Events of Cell Division � Mitosis In mitosis, one cell with the diploid number of chromosomes (46 for people) divides into two identical cells, each with the diploid number of chromosome � The stages of mitosis are prophase, metaphase, and telophase. �Division of the nucleus �Results in the formation of two daughter nuclei � Cytokinesis �Division of the cytoplasm �Begins when mitosis is near completion �Results in the formation of two daughter cells

Figure 3. 15

� Meiosis is a more complex process of cell division that results in the formation of gametes. � In meiosis, one cell with the diploid number of chromo cells, divides twice to form four cells each with the haploid number (half the usual number) of chromosomes.

� Body Tissues � Tissues are groups of cells with similar structure and function. �Four primary tissue types -Epithelium -Nervous tissue � Epithelial - Connective tissue - Muscle Tissues, found in different areas: Body coverings Body linings Glands � Functions: Protection Absorption Filtration Secretion

� are found on surfaces as either coverings (outer surfaces) or linings (inner surfaces).

Epithelium Characteristics � Cells fit closely together � Tissue layer always has one free surface � The lower surface is bound by a basement membrane � Avascular (have no blood supply) � Regenerate easily if well nourished Classification of Epithelium � According to Number of cell layers �Simple – one layer �Stratified – more than one layer (Oral cavity) Figure 3. 17 a

� According to the Shape of cells �Squamous – flattened (alveoli) �Cuboidal – cube-shaped (thyroid gland) �Columnar – column-like (stomach lining); ciliated (trachea) �Pseudostratified Figure 3. 17 b

Glandular Epithelium � Gland – one or more cells that secretes a particular product. � Three major gland types: �Endocrine gland = Ductless Secretions are called hormones �Exocrine gland Empty through ducts to the epithelial surface Include sweat and oil glands, saliva *Mixed glands: both endo and exocrine glands as pancreas , ovaries and testes.

Connective Tissue � Found everywhere in the body � The most abundant and widely distributed tissues � Functions �Binds body tissues together �Supports the body �Provides protection �Ability to absorb large amount of water (Water reservoir). Connective Tissue shows variations in blood supply �Most conn. tissues are well vascularized. �Tendons and Ligaments have a poor supply. �Cartillages are avascular

Connective Tissues are made of : -Different types of cells. -Non-living substance that surrounds living cells. -Different types of fibers(collagen, elastin, reticular). Types of connective tissue � Conn. T. differ in their fibers present in the matrix � From most rigid to softest, C. T. major classes are: -bone - cartilage - dense c. t. as tendon, ligament & dermis of skin. - loose c. t. as areolar, adipose and reticular. -blood

Fibroblasts Bone Cartilage

Muscle Tissue Muscle is very important, specialized for contraction. It provides: � � � movement maintains posture supports soft tissue guards orifices maintains body temperature

3 Kinds of Muscle CELLs

Skeletal muscle Cardiac muscle Smooth muscle

� consists of nerve cells called neurons and some specialized cells found only in the nervous system � The nervous system has two divisions: thecentral nervous system (CNS) and the peripheral nervous system (PNS). � Neurons are capable of generating and transmitting electrochemical impulses.

Neural Tissue � Sends messages throughout the body by conducting electrical impulses � The brain and spinal cord are control centers � The neuron is the basic unit

Tissue Repair (wound healing) � Healing may be by: 1 --regeneration(injured tissues are replaced by the same type of cells 2 - -Fibrosis (the wound is repaired by scar tissue ) 3 - or both � Epith. & c. t. regenerate well. � Mature cardiac muscle & nervous tissue are repaired by fibrosis.

Developmental aspects � Growth through cell division continues through puberty. � Cells exposed to friction replace lost cells throughout life(skin , GI tract &bone marrow). � Conn. T. remains mitotic& forms repair (scar) tissue � Muscle t. becomes amitotic by the end of puberty. � Nervous t. become amitotic shortly after birth