Cell physiology

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

2. 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