The Cell And Its Function

THE CELL AND ITS FUNCTION Joseph R. Panaligan M.D.

CELL  the basic unit of all organisms  varies in size and shape but have similar intracellular organization and generally have the same formed structures or organelles

CELL COMPOSITION, STRUCTURE AND FUNCTIONS  the cell is made up of the nucleus and the cytoplasm. A unit membrane surrounds both the nucleus (nuclear membrane) and the cytoplasm (cell or plasma membrane. The cell forms the boundary of the cell and separates it from its environment.

A. Chemical Composition:  1. Water - 75-85% of the cell is water which may be: • Free water - water available for metabolic processes • Bound water - water loosely attached to protein molecules. – Water serves as solvent of the vehicles for suspension of cellular chemicals and particles. Since water would not allow diffusion of dissolved medium of transport of substances from one part of the cell to another.

 Proteins - 10-20% of the cell. There are two types: • Fibrous ( or structural) • Globular (enzymatic) – Proteins are responsible for the characteristic structure of the cell. Enzyme protein control the metabolic functions of the cell. A type of protein called nucleo-protein regulate cellular functions and the transmission of hereditary characteristics.

 Lipids - 2-3% – lipids are made up of fats, waxes,

phospholipids, carbohydrates, carotenoids and sterols. • Lipids serve as food reserve. They also form part of the structure of the cell like the formation of the cell membrane, and the other membranes lining te nucleus and the other organelles.

 carbohydrates - 1% – Carbohydrates in the cell are made up of: • monosaccharides (glucose, glycogen, ribose, deoxyribose) • disaccharides (sucrose, lactose) • polysaccharides (cellulose, pectin, lignin, chitin) • Mucopolysaccharides (structural materials, secreted by animal cells. Ex. intercellular cement substances; matrix of connective tissue and cartilage)

 Salt - about 1% – The most important are sodium, potassium,

calcium, magnesium, phosphates, bicarbonates, chlorides. • These electrolytes are used by the cell in many cellular reactions including those concerned with controlling mechanisms.

B. Structure and Functions of Different Parts of the Cell:  1. Nucleus - control center of the cell – contains large quantities of DNA, which we have

called genes. The genes determine the characteristics of the cell’s CHON, including the enzymes of the cytoplasm that control cytoplasmic activities. – they also control reproduction; a process called mitosis – regulates metabolic processes of the cells including synthesis of CHON and other substances

 Nuclear membrane - also called the nuclear envelope is actually two separate membranes, one layered inside the other. – The outer membrane is continuous with the

endoplasmic reticulum, and the space between the two nuclear membranes is also continuous with the compartment inside the endoplasmic reticulum.

 Endoplasmic reticulum – a network of tubular and flat vesicular

structure. – their walls are constructed of lipid bilayer membrane that contain large amounts of CHON, similar to the cell membrane. • Rough ER - attached to the outer surfaces of many parts of small granular particles called ribosomes. The ribosomes are composed of a mixture of ribonucleir acid (RNA) and CHON and they function in the synthesis of CHON in the cells. • Smoothe ER- has no ribosomes attached to it. This functions in the synthesis of lipid substances and in many other enzymatic process of the cell.

 Some of the functions attributed to the ER are the ff: – allows intercommunication between the outside

and the inside of the cell – possibly used for storage and/or synthesis of materials like CHON – membrane contains enzymes which are important in the synthesis of lipids and perhaps even glycogen – may be the means of conducting excitation from the surface of the cells to the myofibrils in the muscle

 Ribosomes – Sites of protein synthesis – particulate units in the ground substance,

usually attached to the outer surfaces of the ER. – made up of RNA attached to protein hence, sometimes referred to as ribonucleoprotein (RMP)

 Golgi apparatus (complex) – a canalicular system of various shapes with

fattened sacs (cisternae are associated with vesicles and vacuoules. The surface of the canal and sacs is always smooth.) – this structure is prominent in actively secreting cells • functions in assoc. with ER. ER vesicles continually pinch off and fuse with the golgi apparatus. In this way, subs entrapped in the ER vesicles are transported from the ER to the Golgi apparatus. The transported subs are then processed in the Golgi apparatus to form Lysosomes (secretory vesicles) or other cytoplasmic compartments

 Lysosomes - “digestive system of the cell” – granular structures surrounded by a unit

membrane – contains several hydrolytic enzymes. These enzymes are released from the lysosomes by the action of the lytic agents which destroys the membrane. • the digestive action is important for; – lysis of dying or dead useless cells – removal of structures which are no longer useful to the organism – digestion of the engulfed material, for example, those taken in by pinocytosis

 Mitochondria - “powerhouse” of the cell – the number of mitochondria reflects the energy

requirements of the cell. – the enzyme complex found in the mitochondria enables the synthesis of the high-energy phosphate compound ATP to take place • compose of mainly two lipid bilayer: outer and the inner membrane • infoldings of the inner membrane form shelves onto which oxidative enzymes are attached • the inner cavity of the mitochondrion is filled with a matrix that contains large amounts of dissolved enzymes that are necessary for extracting energy from nutrients.

• ATP is then transported out of the mitochondrion and it diffuses througout the cell to release its energy • mitochondria are self-replicative, which means that one mitochondrion can form a second one wherever there is a need in the cell for increased amounts of ATP. • indeed, it contains DNA similar to that found in the nucleus

 Microtubules and microfilaments – they may be in the outer areas of the

cytoplasm oriented with the long axis of the cell. • may serve as a framework or “skeleton” of the cell • may be contractile (as observed in cilia) • possibly serving for intracellular transport of ions and molecules

 Cilia and flagella - may be found in some animal and plant cells – consists of nine (9) pairs of peripheral

fibers sorrounding two large centrally placed fibers • provide means of locomotion. ciliated cells are also able to move subs across their surfaces

 centrioles and centrosomes – pair of cylinders whose structures are

similar to the cilia – associated with cell division

 Nucleoli/nucleolus – does not have a limiting membrane instead, it is

simply a structure that contains large amounts of RNA andCHOn of the types found in ribosomes. • becomes enlarge when the cell is actively synthesizing CHON.

 peroxisomes - physically similar to lysosomes but different in two important ways • they are believed to be formed by self-replication • they contain exidases rather than hydrolases

– oxidize subs that might be harmful to the cell

Transport of ions and molecules through the cell membrane

1. Diffusion (passive transport) > random molecular movement of substances molecule by molecule either through intermolecular spaces or in combination with a carrier protein > the energy that causes diffusion is the normal kinetic energy > Rate of diffusion is affected by : amount of substances available; velocity of kinetic motion; number of openings in the cells Simple diffusionFacilitated diffusion Osmosis- net movement of water affected by the concentration difference of water –

osmotic pressure- the amount of pressure required to stop osmosis

2. Active Transport > movement against the energy gradient (opposite to diffusion) > uphill movement > large quantities of atoms, molecules, electrolytes are needed in a compartment even if there is a minute amount in the other > transport depends on carrier protein that penetrate through the cell membrane a. Primary Active Transport > energy is derived from ATP

Na- K Pump > pumps sodium ions outward from inward > pumps K ions from outside to inside > present in all cells and is responsible for maintaining differences across the cell membrane > basis of nerve function to transmit nerve signal throughout the nervous system > controls the volume of cells > other samples: a. Calcium b. hydrogen ions > Saturation of primary active transport b. Secondary Active Transport > energy is derived secondarily from the energy stored in the form of ionic concentration differences between two sides of the membrane > Co transport and counter transport (e.g. movement of sodium)

Cell Division DNA (deoxyribonucleic acid)- composed (1) phosphoric acid, (2) a sugar called deoxyribose and four nitrogenous bases (two purines : adenine and guanine, two pyramidines: thymine and cytosine. * adenine binds with thymine * guanine binds with cytosine The phosphoric acid and deoxyribose form the two helical strands that are the backbone of the DNA molecule Nucleotides- first stage in formation of a DNA, a combination of one molecule of phosphoric acid and deoxyribose and one of the four bases Codon- three complimentary code triplets (RNA) that will be synthesized in the cytoplasm

Ribonucleic acid (RNA) Building blocks- like DNA but D is replaced by ribose Thymine is replace by uracil Formation of RNA nucleotide- same with DNA but with small changes Activation of the nucleotide- occurs by adding to each nucleotide two phosphate radicals to form the triphosphate at the far right during RNA chain formation (combined by a high energy phosphate bonds derived from the ATP of the cell) Transcription- code of DNA is transferred to RNA (RNA goes out of the nuclear pores and controls the protein synthesis in the cytoplasm (see figure 2)

Types of RNA 

Messenger RNA • •



Transfer RNA •



Long single RNA strands Carries the genetic code to the cytoplasm for controlling the formation of proteins transports activated amino acids to the ribosomes to be used in assembling the protein molecules

Ribosomal RNA •

Along with 75 different proteins forms the ribosomes, the physical and chemical structures on which protein molecules are actually assembled

Organizations of cells into Tissues: Types and functions Cells with similar fxn are often organized into larger fxnal units called tissues, and these tissues in turn associate with other dissimilar tissues to form the various organs of the body

Types of Tissues Connective tissue  The most abundant tissue of the body found in variety of forms ranging from solid bones to large cells that circulate in the vascular system

Epithelial tissue  form sheets that covers the body’s outer surface, lines internal surfaces and forms grandular tissues  is supported by a basement membrane and is avascular  must receive nourishment from capillaries in supporting connective tissues

Muscle tissue > contains actin and myosin filaments that allows it to contract and provide locomotion and movement of skeletal structures, pumping blood through the heart and contraction of blood vessels and visceral organs

Nervous tissue  provides means for controlling body function  for sensing and moving about the environment

Inflammation  is a normal protective reaction to tissue injury caused by physical trauma, noxious chemical, or microbiologic agents  is a body’s effort to inactivate invading microorganisms, remove organisms and set stage for tissue repair  Inflammation is usually triggered by the release of chemical mediators from injured tissues and migrating cells. 1. amines – histamines and 5 hydroxyptamine 2. lipids - prostaglandins 3. small peptides- bradykinin 4. larger peptide - interleukin

Local Manifestation of Inflammation  Redness (rubor)  Heat (calor)  Pain (dolor)  Swelling (tumor)  Loss of function (funcia laesa)

Inflammatory response Vascular response  movement of fluid from capillaries into tissue spaces  three patterns of responses – immediate transient response – occurs with minor

injury – immediate sustained response – occurs with more serious injury and continues for several days and damages vessels in the area – delayed hemodynamic response – the increase in capillary permeability occurs 4 to 24 hours after injury. It often accompanies radiation types of injuries, such as, sunburn

Inflammatory response Cellular response  blood flow through capillaries of the area slows as fluid is lost and viscosity rises.  Leukocytes move to the inner surface of the capillaries (margination), in amoeboid fashion, through the capillary walls ( diapedesis) and to the site of injury.  Chemicals released by injured cells exert an attractive force called chemotaxis, on white blood cells in the circulation

Exudates  is formed from both fluid and cells that move to the site as well as from cellular debris  its nature and quantity depends on the type and severity of injury and the tissues involve

Types of exudates Serous •

seen in early stage of inflammation

 Ex. Skin blisters and pleural effusions fibrinous exudates – • • •

occurs with increasing vascular permeability and fibrinogen leakage into interstitial spaces it may coat tissue surfaces and cause them to adhere adhesions may develop in the healing and bind surfaces to pleura

 Ex. Pleura adhering together secondary to pneumonia Purulent or suppurative exudates •

Pus consists of leukocytes, microorganism, (deadand alive, liquefied dead cells and other debris)

Catarrhal exudates •

Found in tissues where cells could produce mucous

Hemorrhagic exudates •

Occurs when there is rupture or necrosis of the blood vessel walls

FEVER Thermoregulation  Core temperature is a reflection of the balance between heat gain and heat loss by the body. Metabolic processes produce heat, which must be dissipated  The hypothalamus is the thermal control center- it receives information from the peripheral and central thermoreceptors and compares the information with its temperature set point  Heat loss occurs through transfer of body core heat to the surface through circulation. Heat is lost from skin through radiation, radiation, conduction, convection and evaporation  An increase in core temperature is affected by vasoconstriction and shivering, a decrease in temperature by vasodilation and sweating

FEVER Mechanism of heat production  metabolism if the body’s main source of heat production  an increase of .56 C in every 7% increase in metabolism  epinephrine and norepinephrine are released when there is a need to increase temperature, acts at thecellular level sothat energy production may be reduced and heat production increased

FEVER  is an increase in body temperature (due to vasoconstriction and shivering) due to a response to a cytokine-induced increase in hypothalamic set point  is an adaptive response to bacterial and viral infections or tissue injury. The growth rate of MO is inhibited and immune fxn is enhanced  infxn or tissue injury (exogenous pyrogen) induce the production of prostaglandins in the hypothalamus, which causes the increase in temperature set point  In response to increase inset point, the hypothalamus initiates physiologic responses to increase core temperature to match the new set point

Circulatory Failure (Shock)  Hypovolemic Obstructive  Distributive- characterized by the loss of blood vessel tone, enlargement of the vascular compartments and displacement of the vascular volume away from the heart and central circulation  Neurogenic- shock caused by the decrease in symphathetic control of the BV’s tone due to a defect in the vasomotor center of the brain stem or the symphathetic outflow of the BV ‘s. Output from the vasomotor center can be interrupted by brain injury, hypoxia, the depressant action of drugs, general anesthesia, or lack of glucose  Anaphylactic-characterized by massive vasodilation, pooling of blood in the peripheral BV’s and increased permeability caused by immunologically mediated reaction in which vasodilator substances such as histamines are released into the blood  Sepsis and septic shock- associated with severe infection and systemic response to infection, pathologic complications such as pulmonary insufficiency, DIC, and multiple organ failure.

An unpleasant sensory & emotional experience associated with actual and potential tissue damage or described in terms of such damage

THE GATE CONTROL THEORY This theory postulated the presence of neural gating mechanism at the segmental spinal cord level to account for interactions between pain and other sensory modalities

In Acute pain, therapy is directed at providing pain relief by interrupting the nociceptive stimulus

Chronic pain management requires early attempts to prevent pain and adequate therapy for acute bouts of pain

Includes nonpharmacologic, pharmacologic treatment and surgical intervention

Pain may be assessed according to nature, severity, location and radiation.

Observation of facial expression and posture may provide additional information

However, temperature and blood pressure, the nature, severity and distress of pain cannot be measured objectively. Thus, various method have been developed for quantifying a person’s pain:

1. Numeric Pain Intensity 2. Visual Analog 3. Verbal Descriptor

Pain may be classified according to location, site of referral or duration

1. CUTANEOUS PAIN

Arises from superficial structures, such as the skin and subcutaneous tissue

2. DEEP SOMATIC PAIN

Originates in deep body structures such as the periosteum, muscles, tendons, joints and blood vessels

3. VISCERAL PAIN 4. REFERRED PAIN

1. ACUTE PAIN

Pain that has its origin in visceral organs Pain that is perceived at a site different from its point of origin but innervated by the same spinal segment

2. CHRONIC PAIN Classifically defined as pain lasting 6 months or longer