Showing posts with label Anatomy. Show all posts
Showing posts with label Anatomy. Show all posts

The Electron Transport System of Mitochondria

Thursday, May 17, 2012


Embedded in the inner membrane are proteins and complexes of molecules that are involved in the process called electron transport. The electron transport system (ETS), as it is called, accepts energy from carriers in the matrix and stores it to a form that can be used to phosphorylate ADP. Two energy carriers are known to donate energy to the ETS, namely nicotine adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD). Reduced NAD carries energy to complex I (NADH-Coenzyme Q Reductase) of the electron transport chain. FAD is a bound part of the succinate dehydrogenase complex (complex II).
It is reduced when the substrate succinate binds the complex.
What happens when NADH binds to complex I? It binds to a prosthetic group called flavin mononucleotide (FMN), and is immediately re-oxidized to NAD. NAD is"recycled," acting as an energy shuttle. What happens to the hydrogen atom that comes off the NADH? FMN receives the hydrogen from the NADH and two electrons. It also picks up a proton from the matrix. In this reduced form, it passes the electrons to iron-sulfur clusters that are part of the complex, and forces two protons into the intermembrane space.





The obligatory forcing of protons into the intermembrane space is a key concept. Electrons cannot pass through complex I without accomplishing proton translocation. If you prevent the proton translocation, you prevent electron transport. If you prevent electron transport, you prevent proton translocation. The events must happen together or not at all.
Electron transport carriers are specific, in that each carrier accepts electrons (and associated free energy) from a specific type of preceeding carrier. Electrons pass from complex I to a carrier (Coenzyme Q) embedded by itself in the membrane. From Coenzyme Q electrons are passed to a complex III which is associated with another proton translocation event. Note that the path of electrons is from Complex I to Coenzyme Q to Complex III. Complex II, the succinate dehydrogenase complex, is a separate starting point, and is not a part of the NADH pathway.
From Complex III the pathway is to cytochrome c then to a Complex IV (cytochrome oxidase complex). More protons are translocated by Complex IV, and it is at this site that oxygen binds, along with protons, and using the electron pair and remaining free energy, oxygen is reduced to water. Since molecular oxygen is diatomic, it actually takes two electron pairs and two cytochrome oxidase complexes to complete the reaction sequence for the reduction of oxygen. This last step in electron transport serves the critical function of removing electrons from the system so that electron transport can operate continuously.
The reduction of oxygen is not an end in itself. Oxygen serves as an electron acceptor, clearing the way for carriers in the sequence to be reoxidized so that electron transport can continue. In your mitochondria, in the absence of oxygen, or in the presence of a poison such as cyanide, there is no outlet for electrons. All carriers remain reduced and Krebs products become out of balance because some Krebs reactions require NAD or FAD and some do not. However, you don't really care about that because you are already dead. The purpose of electron transport is to conserve energy in the form of a chemiosmotic gradient. The gradient, in turn, can be exploited for the phosphorylation of ADP as well as for other purposes. With the cessation of aerobic metabolism cell damage is immediate and irreversible.
From succinate, the sequence is Complex II to Coenzyme Q to Complex III to cytochrome c to Complex IV. Thus there is a common electron transport pathway beyond the entry point, either Complex I or Complex II. Protons are not translocated at Complex II. There isn't sufficient free energy available from the succinate dehydrogenase reaction to reduce NAD or to pump protons at more than two sites.

Is the ETS a sequence?

Before the development of the fluid mosaic model of membranes, the ETS was pictured as a chain, in which each complex was fixed in position relative to the next. Now it is accepted that while the complexes form 'islands' in the fluid membrane, they move independently of one another, and exchange electrons when they are in mutual proximity. Textbooks necessarily show the ETS as a physical sequence of complexes and carriers. This has the unintentional effect of implying that they are all locked in place. The fluid nature of membranes allows electron exchange to take place in a test tube containing membrane fragments.
The location of ETS complexes on the inner membrane has two major consequences. By floating in two-dimensional space, the likelihood of carriers making an exchange is much higher than if they were in solution in the three dimensional space of the matrix. They are exposed to the matrix side of the membrane, of course, for access to succinate and NADH, but have limited mobility. Second, the location of the ETS on the inner membrane enables them to establish a chemiosmotic gradient.

Electron pathways and inhibition

Electron transport inhibitors act by binding one or more electron carriers, preventing electron transport directly. Changes in the rate of dissipation of the chemiosmotic gradient have no effect on the rate of electron transport with such inhibition. In fact, if electron transport is blocked the chemiosmotic gradient cannot be maintained. No matter what substrate is used to fuel electron transport, only two entry points into the electron transport system are known to be used by mitochondria. A consequence of having separate pathways for entry of electrons is that an ETS inhibitor can affect one part of a pathway without interfering with another part. Respiration can still occur depending on choice of substrate.



An inhibitor may competely block electron transport by irreversibly binding to a binding site. For example, cyanide binds cytochrome oxidase so as to prevent the binding of oxygen. Electron transport is reduced to zero. Breathe all you want - you can't use any of the oxygen you take in. Rotenone, on the other hand, binds competitively, so that a trickle of electron flow is permitted. However, the rate of electron transport is too slow for maintenance of a gradient. 




Chemiosmotic Gradient: Generation and Maintenance

Energetics of proton translocation at Compex I

The energy needed to push protons out of the matrix and into the intermembrane space comes from the oxidation of either reduced NAD (NADH) or reduced FAD (FADH2). In the case of NADH, passage of an electron pair to Coenzme Q provides a "pulling" force. That is, NADH is much less electronegative than Coenzyme Q, while the iron-sulfur protein carriers in between are intermediate in electronegativity. The amount of available free energy is 69.5 kJ/mole of NADH (kiloJoules per mole). The efficiency of electron transport can be represented by the standard reduction potential difference, namely the voltage generated by a redox reaction under standard biochemical conditions.

The standard reduction potential of NADH is -0.315V, while that of coenzyme Q is 0.045V (difference of 0.345 V). Therefore there is a strong 'pull' by Coenzyme Q on electrons through the components of Complex I.
Just for the sake of understanding the principles, let Complex I (NADH dehydrogenase complex), embedded in an intact inner membrane, be the only component of an experimental electron transport system. We'll simply take the electrons from Coenzyme Q when they reach it, so the system can keep going. The removal of protons from the matrix and deposition of protons in the intermembrane space creates a concentration difference of protons across the inner membrane. This is called the chemiosmotic gradient. As the gradient builds up, more and more energy is required to push protons across. When the amount of energy required to push protons reaches 69.5 kJ/mole, electron transport has to stop. In fact, the second law of thermodynamics requires that electron transport stop before the gradient builds up to that point. 





If there was no way of draining energy from the system, electron transport could not continue despite the presence of adequate substrate. However, a mitochondrion is always in a steady state of respiration, in which the energy lost by processes that dissipate the gradient is constantly replaced by electron transport.

Respiratory Control

The limitation placed on electron transport by the chemisosmotic gradient is termed respiratory control. Mitochondria are said to exercise respiratory control as long as they can restrict electron transport by means of the gradient. If the gradient is destroyed by damaging the membranes, respiratory control is abolished and electron transport can run freely.

Cause and effect relationship

Electron transport is driven by the free energy that is available from the energy carriers, in turn obtained from substrates such as glutamate or Krebs intermediates. It is restricted by the chemiosmotic gradient. The only way electron transport can proceed is to the extent that the energy in the gradient is dissipated. In healthy mitochondria the gradient is maintained. That is, electron transport keeps up with the utilization of the energy stored in the gradient. Even in the presence of ADP, which allows ATP synthetase to exploit the gradient, the chemiosmotic gradient is maintained at a set energy level.
Think of physical causes and effects when you attempt to describe respiratory control. What drives electron transport? It can't be driven by a "need" to maintain the gradient, because that implies a sense of purpose. The electron transport system is just a structure, complex as it is. Electron transport is driven by the increasing affinities of successive carriers for electrons, and by the availability of substrates to provide electrons and free energy. It is restricted by the chemiosmotic gradient - electron transport can only go as fast as energy is lost from the gradient. Anything that increases turnover of energy from the gradient increases the rate of electron transport proportionally.
Here is an analogy that might help with the concept. Suppose that you are trying to blow up a balloon. Blowing with all your might you succeed in filling the balloon so that it is two feet in diameter. You cannot force any more air into it so all you are doing now is holding pressure. Now some joker comes along and pokes a couple of holes in your balloon, so that air leaks out at a controlled rate. You have maintained constant pressure, so now you find yourself moving air into the balloon as it leaks out. The balloon diameter, proportional to internal pressure, remains constant. If you plug one of the holes you move less air. Open up more holes and you move more air. The electron transport system applies constant "pressure," holding the gradient at a constant level. The rate of electron tranport (analagous to air flow in the balloon example) varies as energy is drained from the system at different rates. Adding ADP in vitro, for example, opens up avenues for protons to be forced into the matrix, draining energy from the gradient. Its addition is the equivalent of poking additional holes in your balloon. Electron transport spontaneously increases.

Respiratory Control in Exercise

Sometimes in wading through all of the details, one loses sight of the big picture. Just why is all of this information about electron transport and oxidative phosphorylation so important, anyhow? Suppose you are vegging in front of the TV - in the prone position with a bag of cholesterol chips. You are very relaxed and are hardly aware that you are breathing at all. Suddenly the fire alarm sounds, and a bunch of naked people are running down the hall. This definititely provokes activity on your part, and you run down the hall also. You start breathing heavily (due to the exercise, not the sight of the naked people).
Your demand for energy is rather low when you are relaxed. However running is heavy exercise. Your muscle activity causes an immediate demand for ATP which is met in part by muscle glycogen. When that runs low you need to replace your reserves with aerobic metabolism, that is, your mitochondria need to make more ATP. Electron transport is stimulated when the ratio of ATP to ADP goes down. The rate of binding of ADP to the ATP synthetase automatically increases as more ADP is transported into the matrix. In turn, electron transport is allowed to speed up - consuming more oxygen in the process. Sensors in your cardiovascular system (primarily the carotid bodies of the carotid arteries) detect an increase in carbon dioxide (indicating an increased need for oxygen). The sensors send a signal to the brain via the nervous system that you need to speed up breathing.
So... you breathe primarily to get oxygen into the blood and to the tissues, in order to deliver oxygen to the mitochondria for cellular respiration - to make ATP. In the process, carbon dioxide is returned to the lungs and exhaled. The processes are essential to your well being, in fact, to your being at all. When you think of the effects of some of the poisons that are discussed on these pages, think of the consequences to an intact organism such as yourself.
The big picture, including regulatory pathways such as the very simplified description presented above, are in the realm of integrative disciplines such as physiology. Such disciplines are increasingly ignored in both research and academic curricula in favor of a purely molecular approach to science. Please consider the importance of knowing the consequences of molecular and cellular processes to the whole organism, and the fact that the regulatory pathways controlling those processes are still incompletely understood.

Uncoupling and the basal metabolic rate

Endotherms like ourselves (formerly called homeotherms) maintain a constant body temperature. The setpoint for that temperature is determined by a region the hypothalamus (part of the brain, for you newcomers). But just how is the temperature regulated? That is, how does the body maintain a balance between heat production and heat loss?
The answer to that one is very complex. There are many mechanisms for heat dissipation and retention (sweating, changes in distribution of the circulation, shivering, piloerection - no, it's not a dirty word, etc.). Heat production results from the loss of some of the free energy of every chemical reaction as heat - that is, every chemical reaction results in the loss of some of the total free energy in the universe. That's one of the laws of thermodynamics - I forgot which. A major source of heat production is electron transport in mitochondria.
How do mitochondria produce heat? Much of the energy released by electron transport does no useful work at all (that law of thermodynamics is at work again). That is, each exchange of electrons results in a loss of some energy as heat. Furthermore, dissipation of the chemiosmotic gradient without doing work results in the transformation of a great deal more energy to heat. The mechanism of respiratory control can be exploited to increase heat production by dissipating the gradient at a faster rate, or to slow heat production by making the ETS more efficient. One example of that type of regulation is the hormone thyroxine (thyroid hormone).
Thyroid hormone has many functions, mostly associated with promotion of anabolic activity - synthesis of compounds and cellular growth. However thyroxine is also a mildly effective uncoupling agent. Uncoupling agents dissipate the chemical gradient, usually by creating a mechanism by which protons can escape the intermembrane space (or otherwise 'short out' the gradient), allowing an increase in electron transport. In colder regions of the world a noticible change in thyroid hormone levels takes place circannually, that is, levels are higher in winter and lower in summer.

Cell physiology

Monday, January 3, 2011

The word physiology is derived from physiologicos

It means the discourse of natural knowledge

Def
It is the science, which deals with normal functions of tissues and organs of living organisms

Branches of physiology
  1. Viral physiology
  2. Bacterial physiology
  3. Plant physiology
  4. Animal physiology
  5. Human physiology

Organization of Human body
Cell----------- tissue ------ Organs ---- Organ systems---- ----human body

System

  1. CNS
  2. ANS
  3. CVS
  4. Respiratory system
  5. Digestive system
  6. Urinary system
  7. Endocrine glands
  8. Circulatory system - Blood
  9. Reproductive system
  10. Autacoids


Basic characteristics of Human  or living organisms

  1. Irritability  or excitability
  2. Conductivity
  3. Contractility
  4. Absorption
  5. Digestion
  6. Secretion
  7. Excretion
  8. Growth
  9. Reproduction


Body fluid comportments

There are two fluid comportments

  1. Extracellular fluids

               ECF is divided into 
    1. Plasma
    2. Interstitial fluid


  1. Intracellular fluids

The ECT & ICF remain separate and do not mix up by a very thin membrane  - cell membrane

ECF contains nutrients , electrolytes, oxygen and all other substances essential for survival of cells


Homeostasis
It means maintenance static or constant conditions in the internal environment

The internal environment in the human body is the ECT, in which all the cell of the body live, it constantly moves or interchanges throughout the body 

It includes blood and fluid present in between the cells


ECF contains nutrients, electrolytes, oxygen, and all other substances essential for survival of cells


Factors involved in homeostasis

  1. Maintenance of PH
  2. Maintenance of temperature
  3. Maintenance of body water
  4. Maintenance of electrolyte balance
  5. Supply of oxygen, nutrients and hormones
  6. Maintenance of normal blood volume
  7. Maintenance of normal arterial blood pressure
  8. Removal of waste products from body
  9. Maintenance constant osmotic pressure
  10. Coagulation of blood



Control mechanism of homeostasis

  1. Sensor-  Which detects or finds out the change in  the normal value and function
  2. Comparator- which compares the changed value or function with normal
  3. Effector system- which returns the changed value or function to normal
  4. Variable- Which brings down the changed value to normal value

Ex

1. Blood sugar  - Normal vale 80-120 mg/ml

1. Sensor- It senses the raised blood sugar due to excess intake of sugar from normal –  
    80-120 mg/80-120mg/100mg
2. Comparator- It compares the increased blood sugar level with normal
3. Effector system- There is increased secretion of insulin form pancreas, which brings
    the raised blood sugar to normal value
4. Variable- The variable value – raised blood sugar is brought to normal and constancy
    of internal environment is maintained

2. Body temperature- Normal value 37 degree C when a person is exposed to
    hypothermia leads to low body temperature

  1. Sensor- Detects the fall of body temperature
  2. Comparator- Compares reduced temperature with normal
  3. Effector system – There is increased secretion of thyroid hormone T3 &T4 , which raises the body temperature by caloriginic action to normal value.

Mechanism of action of Homeostatic control system
All control systems involved in homeostatic control system operate through following feedback mechanism
1.      – ve feedback mechanism – If the activity of particular system is increased regulatory mechanism will soon reduce it
2.      + VE feed back mechanism – Coagulation of blood

Various systems take part in homeostasis

1. Respiratory system – Control PH of blood
2. Skin, respiratory , digestive , renal and CNS – Involve in body temperature
3. Liver- It changes chemical composition of many absorbed substances to more useful
               form
4. Endocrine system – By secretion of various hormones such as insulin, ADH, cortisol,
    T3 & T , Aldosterone keep homeostasis normal


Cell
It is the structural and functional unit of all living beings

Cell membrane
It is a protective thin sheet  enveloping the cell body
Its thickness ranges from 75A- 110A
Composition of cell membrane
It contains of
1. Proteins                    -  55%
2. Lipids                       -  40%
3.Carbohydrates           -  5%

Structure of cell membrane
It is a 3 layered structure
  1. Lipid layer
  2. Protein layer
  3. Basement layer

1. Protein layer

1. Integral protein – Provides integrity to cell membrane
2. Channel protein- Provides channels for diffusion o water- soluble substances
    E.g – glucose, amino acids
3. Carrier protein- Helps in transport of substances across cell membrane (facilitated  
    diffusion)
4. Receptor proteins - They are receptors for hormones and neurotransmitters and they
    form receptor protein hormone complex
5. Enzyme protein- Molecules form enzymes
   Antigen protein- some proteins act as antigens and produce antibodies

2. Lipid layer
Lipid layer forms a semi permeable membrane, it allows fat – soluble substances such as oxygen, CO2, and alcohol to pass through the cell membrane
Phospholipids permit lipid-soluble materials to easily enter or leave the cell by diffusion through the cell membrane.

3. Carbohydrate layer
These molecules are attached to either protein or lipid layer- glycol- protein & glycol – lipid
Carbohydrate layer forms a covering on the cell membrane called glycocalyx
Carbohydrate molecules are negatively charged ions to keep substances outside the membrane . They form tight junctions

 Smooth endoplasmic reticulum
As sacroplasmic reticulum they play important role in skeletal and cardiac muscles

Rough endoplasmic reticulum
They contain ribosome’s and they are the sites for protein synthesis
E.g – Enzymes and hormones

Golgi apparatus
They are packaging department of the cells
They produce secretion granules, which store hormones and enzymes

Mitochondria
They are energy generating cells

Lysosomes
They act as digestive system of the cells-  bacteria, worm & exogen substances

Centrioles or centrosomes
They are concerned with movements of chromosomes during cell division

Nucleus
It is also the site of RNA synthesis. They are 3 types RNA- m, r,t RNAs
Nuclei
It contains some protein and RNA. Nuclei are sites for synthesis of ribosome’s and transfer them to cytoplasm where ribosome’s synthesize proteins

Ways of transport across cell membrane
 
Passive transport
Substances are transported from region of higher concentration to lower concentration . It is called Down Hill movement

It is 2 types

  1. Simple diffusion
  2. Facilitated diffusion

A. Simple diffusion

Diffusion through the lipid layer
Lipid soluble substances are transported through by simple diffusion across the lipid layer
E. g – O2, CO2 and alcohol

Diffusion through protein layer – Water – soluble substances diffuse through the protein layer
Eg- Glucose and electrolytes

B. Facilitated diffusion
Larger molecules of water- soluble substances cannot diffuse through protein channels such substances diffuse with the help of carrier protein, hence this type of diffusion is called facilitated or carrier mediated diffusion
E.g
Glucose and amino acids are transported by facilitated diffusion
These molecules bind with receptor protein lining the channels

 2. Active transport
The movements of substances are against the chemical or electrical or electro chemical gradient is called active transport

Substances are transported from region of lower concentration to higher concentration . It is called UP  Hill movement
It requires expenditure of energy which is liberated by breakdown of ATP into ADP and inorganic phosphate. It is faster than passive transport

Types active transport
A. Primary active transport
They directly use energy obtained from hydrolysis of ATP
They consists

1. Na- K Pump
2. Ca – pump
3. K- H  pump

1. Na – k pump
It is an electrogenic pump present in all the cells of the body
Whenever a nerve cell or nerve fiber or muscle fiber is stimulated, the Na channels open and the Na ions enter inside the cell
Simultaneously K 9ions leave the cell through K channels and come outside
It leads to depolarization of cell membrane which causes origin of action potential
The depolarization does mot and should not continue and it is followed by reploraization to obtain second stimulus
So for the repolarizaiton , Na ions must go outside the cell and K ions enter the cell, It happens with the help of Na – K pump
Na – K pump extrudes out 3 Na ions for every 2 K ions which return inside of cell membrane, resulting in a net removal of + ve charged Na ions so that inside of the cell membrane again becomes more –ve than outside
Na – K pump derives energy by breakdown of ATP into ADP + Pi with the help of ATP ase enzyme which is present in cell membrane

B. Secondary active transport
When Na is transported by carrier protein, another substance is also transported by the same protein simultaneously either in the same direction of Na or in opposite direction
This type of transport of substance along Na ion by means of carrier protein is called secondary active transport

It is of two types

A. Na – Co- transport
Along with Na ion another substance is carried by carrier protein in same direction
Substance carried by Na co-transport are glucose, amino acids, CL, I, Fe , urte ions are transported

B. Na  Counter transport
The substances are transported across cell membrane in exchange of Na ions
1. Na- Ca counter transport
2. Na- H counter transport
3. Na- Mg counter transport
4. Na- K counter transport


3. Endocytosis
The process involved in endocytosis is as follows

A.    Pinocytosis
B.     Phagocytosis

A. Pinocytosis
Large molecules are transported into the cell by cell drinking molecules dissolve in fluids bind to the outer surface of the cell membrane
Cell membrane evaginates around the droplet and they get engulfed by membrane and are converted into vacuoles
They come into contact with lysozomes and get ruptured and released inside the cell

B. Phagocytosis

The large particles are  engulfed into the cell, it is called cell eating larger bacteria are antigen when enter the body, phagocytic cell sends cytoplasmic pseudopodium around the bacteria. The particles are engulfed inside the cell and are digested

Circulatory system

Heart and blood vessels together form CVS . Blood vessels include arteries, veins and their derivatives

Artery        -- Artery is a vessel which caries oxygenated blood
Vein          -- Vein is a vessel which carries deoxygenated blood
Capillary   -- Capillary is the channel which connects the arterial system and venous
                         system together
 
Blood vessels
Histologically, a typical blood vessel shows three different areas in it
Tunica intima   
It is the innermost layer of the blood vessel lined by simple squamous epithelium or endothelium

Tunica media
It is the middle layer of a blood vessel seen just below the tunica intima
Made up of either smooth muscles or elastic fibers

Tunica adventitia
It is an outermost layer of a vessel which is made up of dense irregular connective tissue  

S No
Artery
Vein
1
Carries oxygenated blood
Carries de- oxygenated blood
2
Tunica adventitia is smaller
Tunica adventitia is larger
3
Tunica media is larger
Tunica medial is smaller
4
Lumen  is almost circular
Tunica adventitia is larger
 
Function

Endothelial layer of tunica intima is anti- thrombotic and nutritive in function
Elastic fiber of the tunica medial  expand the arterial wall thus helps in maintaining normal arterial pressure and blood flow
Connective tissue layer of the tunica adventitia prevents undue stretching and rupture of the artery

Bile secretion

Thursday, December 16, 2010



Composition of Bile

Water  - 97.5%

Solids -  2.5%

Solids contains


Organic substances                          - Bile salts
                                                            Bile pigments
                                                            Cholesteros
                                                            Fatty acids
                                                            Lecithin
                                                            Mucin


In organic substances                          Sodium
                                                            Potassium
                                                            Calcium
                                                            Chlorides
                                                            Bicarbonates
 

Formation of biles

Bile is produced continuously y by hepatocytes

Bile drains into the hepatic ducts and is stored in the gallbladder for subsequent release

Choleretic agents increase the formation of bile


Bile is formed by the following process


Primary acids

Ex – Cholic acid and chenodeoxycholic acid are synthesized from cholesterol  by hepatocytes


Secondary bile acids

In the intestine , bacteria convert a portion of each of the primary bile acids to secondary bile acids (deoxycholic acid and lithocholic acid)

Synthesis of new bile acids occurs as needed , to replace bile acids that are excreted in the feces

The bile acids are conjugated with glycine or taurine to form their respective bile salts

Ex – Taurocholic acid is cholic acid conjugated with taurine


Electrolytes and H2O are added to the bile

During the interdigestive period m the gallbladder is relaxed the sphincter of Oddi is closed and the gallbladder fills with bile

The bile is concentrated in the gallbladder as a result of isosmotic absorption of solutes and H2O

 Contraction of gallbladder

CCK

It is released in response to small peptides and fatty acids in the duodenum
It tells the gallbladder that bile is needed to emulsify and absorb lipids in the duodenum
It causes contraction of the gallbladder and relaxation of the sphincter of Oddi

 Ach

It causes contraction of the gallbladder
 
Function of bile

1.Digestive function

2. Absorptive functions

3. Excretory function

Bile pigments are the major excretory products of the bile

The other substances excreted in bile are             
Heavy metals like copper and iron
Some bacteria like typhoid
 Some toxins
Cholesterol
Lecithin

4. Laxative action

5. Antiseptic action

Bile inhibits the growth of certain bacteria in the lumen of intestine by its natural
detergent action

6. Lubrication function

The mucin in bile acts as a lubricant for the chime in  intestine

7.Maintenance of PH in GIT

It is highly alkaline, it neutralizes the acid chime which enters the intestine from stomach.
The optimum PH is maintained for the action of digestive enzymes

ELECTROCARDIOGRAM (ECG)

Sunday, November 28, 2010


It is the record or graphical registration of electrical activities of the heart

Hans Berger is considered as the father of the modern electroencephalography

EEG represents the summated electrical activity of the brain recorded from the surface of the scalp

The electrical activity recorded directly from the surface of the brain is called electrocorticogram

Usually EEG is recorded by a set of locations for electrodes placed on the skull called montage

Montages may consists of unipolar or bipolar system of electrodes

Unipolar method

In this one electrode is active and another is indifferent electrode

The indifferent electrode is applied on some part of the body at a definite distance from the cortex

Bipolar method

In this both electrodes are active and the potential difference between these two electrodes is amplified and recorded

Normal  EEG

The different waves have been identified based on their frequency and amplitude

Usually a normal EEG in a wakeful person with or without closed eyes consists of two types of waves alpha and beta waves




ELECTROCARDIOGRAH

The instrument (ECG machine) by which the electrical activities of the heart are recorded is called electrocardiograph

ELECTROCARDIOGRAH

ECG machine amplifies the elect cal signals produced from the heart and records these signals on a moving strip of paper

The markings (lines) on this paper is called ECG grid
The ECG paper has horizontal and vertical lines at regular intervals of 1 mm
Every 5 th line ( 5 mm) is thickened

Duration

The duration of different waves of ECG is donated by the vertical lines

Interval between two thick lines ( 5 mm) = 0.2 sec

Interval between two thin lines  (1 mm) = 0.04 sec

AMPLITUDE

The amplitude of ECG waves is denoted by horizontal lines

Interval between two thick lines ( 5 mm) = 0.5 m V

Interval between two thin lines  (1 mm) =0. 1 Mv

Speed of the paper

The movement of paper can be adjusted in two speeds, 25 mm/ sec and 50 mm/sec

The speed paper during recording is fixed at 25 mm/ sec

If the heart rate is very high, the speed of the paper is changed to 50 mm/sec

Waves of normal Electrocardiogram

The waves of ECG recorded by limb lead II are considered as the typical waves

Normal electrocardiogram has the following waves - P, Q, R, S and T

The P wave represents depolarization of the atria, that is the transmission of electrical impulses
from the SA node throughout the atrial myocardium.

The QRS complex represents depolarization of the ventricles as the electrical impulses spread throughout the ventricular myocardium.

The T wave represents repolarization of the ventricles (atrial repolarization does not appear as a separate wave because it is masked by the QRS complex).

P Wave
It is a positive wave and the first wave in ECG
It is also called atrial complex

Cause

It is produced due to the depolarization of atrial musculature

Duration --0. 1 sec

Amplitude

0.1  to 0. 12 Mv

QRS Complex

It is also called the initial ventricular complex

Q wave is a small negative wave

It is continued as the tail R wave,  which is positive wave
R wave is followed by a small negative wave. The S wave

Cause

QRS complex is obtained because of the depolarization of ventricular musculature

Duration --   0.08 – 0. 10 sec

Amplitude
Q wave – 0.1 to 0.2 mV
R wave – 1 Mv
S wave   - 0.4 m V

T Wave--------It is the final ventricular complex and is a positive wave

Cause

T wave is due to the repolarization of ventricular musculature

Duration ----0.2sec

Amplitude----0.2mV

Atrial replarization is not recorded as a separate wave in ECG because it is merged with QRS complex
 




Nerve cells show changes of electrical potential during their activity

The current generated by neurons in the brain is conducted by the surrounding fluids , to the scalp and can be recorded

The graphic record if such activity is called electroencephalogram (EEG)

Several types of waves have been identified which differ in frequency and potential (voltage)

Four major types of waves common in human subjects are Alpha, Beta, Theta and Delta waves

Brain Waves

Electrical recordings from the surface of the brain or even from the outer surface of the head demonstrate that there is continuous electrical activity in the brain.

Both the intensity and the patterns of this electrical activity are determined by the level of excitation of different parts of the brain resulting from sleep, wakefulness, or brain diseases such as epilepsy or even psychoses and the entire record is called an EEG (

The intensities of brain waves recorded from the surface of the scalp range from 0 to 200 microvolt, and their frequencies range from once every few seconds to 50 or more per second
.
The character of the waves is dependent on the degree of activity in respective parts of the cerebral cortex, and the waves change markedly between the states of wakefulness and sleep and coma

Much of the time, the brain waves are irregular, and no specific pattern can be discerned in the EEG..
EEG machine
It may have 8 or 16 or 32 channels for recording EEG from different areas of the scalp
It contains the following divisions

1. Electrode selector switch

This helps in selecting different electrode placements( montages) unipolar or bipolar montages are utilized for recording EEG

2. Calibrator

This is meant for calibrating the sensitivity of the instrument
Normal calibration is 7 uV/MM OR 50 uV/7 mm

3. Writing system

This consists of a pen connected to a galvanometer and ink flows into the pen from an ink reservoir. Pin writes the different waves on the chart

4. Paper moving system

This helps in movement of the paper at a constant speed
The speed of paper can be varied depending on the requirement. Normal speed is 30mm/s

5. EEG Paper

It is a graph paper with vertical lines at 3 cm intervals
It is a folded and stacked in a storage bin and is allowed to move under the writing pens

6. EEG jelly

This consists of bentonite powder mixed with saline and glycerin
This paste is applied to the electrodes to reduce the resistance between the scalp and the electrodes

7. Electrode set up

Electrodes are silver cup electrodes applied over the scalp in definite pattern
The standard set of electrodes for adults consists of 22 electrodes
The electrodes are named with  a letter and  a subscript
The letter denotes the underlying region front polar (Fp), frontal (F),  central© , parietal(P), occipital(O)
The subscript Z represent midline or zero and a number indicates lateral placement



Procedure

Fix the electrodes over the subjects scalp on a clean shaven head

Connect the electrode system to the instrument

Calibrate the instrument for a normal sensitivity of 7 mm/50 Uv

Record EEG in the following states

Resting closed eyes and open eyes

Effect of hyperventilation for 2 or 3 minutes

Effect of photic stimulation at different frequencies with the eyes open

During sleeping or in drowsy state

Analyze the EEG based on the frequency amplitude and distribution of the waves in various leads

Sources of EEG

Deep  structures like hippocampus, thalamus or brain stem do not contribute directly to the surface EEG

Pyramidal neurons are the major projection neurons in the cortex so the synaptic activity in the pyramidal cells is the principle source of EEG activity

The potential changes in the EEG are due to current flow in the fluctuating dipoles formed between the dendrites and the cell bodies of the cortical cells

The shifting dipole between the dendrites and the cell body when conducted through a volume conductor produces a wave pattern


EEG rhythm
Frequency  Hz
Amplitude voltage
Location & condition in which waves are prominent
Alpha
8-13
50
Present in parieto-occipetal areas
Waking relaxing with the eyes closed persons(synchronized waves)
Beta
14-30
5-10
Commonly seen in infants present in frontal region (desynchronized waves) seen in alert adult persons with the eyes opened
Theta
4-7
10
This may be present in parietal and temporal regions in children and also in certain brain disorders
Delta
1-4
Up to 200
Recordable during sleep and certain brain disorders

 
1. Alpha- rhythm

It is also referred as synchronized EEG

It is seen in wakeful but relaxed persons with the closed eyes

When the subject opens his eyes the alpha rhythm is replaced by low amplitude waves (beta waves)

This is referred as alpha-block

This effect is called desynchronization and can be brought abort by increasing mental activity or by applying different types of sensory stimuli

2. Beta- rhythm

It is the high frequency low amplitude EEG seen in wakeful alert active persons with the eyes open

It is also seen in infants

It is also called desynchronized EEG

These are found in parietal find frontal regions of the scalp

They have a frequency of 13-32 /sec and are of 5-10 microvolt

3. Theta- rhythm
This waves are often formed during disappointment and frustration in young children and adolescents

It is seen in parietal and temporal areas rarely but often in brain disorders

They occur at the rate of 4-7/sec and their potential is 10 microvolt

4. Delta- rhythm
These are produced during the state of unconsciousness and deep sleep

They occur at the rate of about 0.5-3.5 per second with a potential of 20-
200 microvolt

They are usually found over the parietal and temporal regions of the brain

This is the slowest wave with maximum amplitude  It is seen during sleep and certain brain disorders
Significance of EEG

1. It is utilized as a diagnostic tool in epilepsies

E.g.
    Grand mal epilepsy, petit mal epilepsy

    In petit mal epilepsy dime and spike pattern appears for few
    seconds

    In grand mal epilepsy rapid waves with spikes appear for few
    minutes

2. Localization of certain brain lesions

    Useful to localize haematomas, brain tumors, necrosed areas etc

3. It is useful in the diagnosis and prognosis of brain injuries,  
    vascular lesions

4. Useful in the diagnosis of meningitis, encephalitis congenital
    brain defects

5. Useful in neurophysiological   investigation for data collection

6. Increased intracranial pressure

    During this condition delta- waves with an amplitude up to 100
    microvolt and frequency of 3 cycles per second may be observed

7. Cerebral tumors

    Tumors cause progressive destruction of cortical tissues and as a
     result abnormally large slow delta-waves arise from the
     damaged cerebral cortex