Intro..Cell Phsiology PM

7/30/2019 Intro..Cell Phsiology PM

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PHYSIOLOGY

Study of normal processes and functions in livingorganisms and the mechanisms by which these are carried

out and regulated.

Medical physiology concentrates on human physiology

It Helps in maintenance ofadaptation and homeostasis, 2

fundamental features of life


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STRUCTURALORGANIZATION


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STRUCTURAL ORGANIZATIONOF CELL

3 Principal constituents of cell :

1. Cell Membrane

2. Nucleus &

its chromosomes

3. Cytoplasm &

its organelles


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Typical structures found in body cells


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CELL MEMBRANE

It is also called plasma membrane or unit membrane.

It is a flexible ,selective barrier that encloses the cell contents.

The average thickness of the membrane is 7-10 nm.

STRUCTURE OF CELL MEMBRANE

It is described using the FLUID MOSAIC MODEL.

It was discovered by SINGER and NICHOLSON in 1972 .

The molecular arrangement of the plasma membrane resembles

an ever-moving sea of fluid lipids that contains a mosaic of

many different proteins.


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COMPOSITION OF MEMBRANE

LIPIDS 42 % ( 40-45 % )

PROTEINS 55 % ( 50-60 % ) CARBOHYDRATES 3 %


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FUNCTIONSOFCELLMEMBRANE

1. Protective

2. Maintains a constant intracellular enviornment.

3. Digestive

4. Selective permeability

5. Insulating properties

6. Structural framework

7. Recognizes foreign cells


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CELL ORGANELLES


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The Endoplasmic Reticulum : is a network of

intracellular membranes connected tothe nuclear envelope , which

surrounds the nucleus.

ER has four major functions:

1. Synthesis :- Specialized regions of the ER synthesize

proteins,carbohydrates, and lipids.

2. Storage :- store synthesized molecules or materials absorbed from

the cytosol without affecting other cellular operations.

3. Transport:- Materials can travel from place to place in the ER.

4. Detoxification :- Drugs or toxins can be absorbed by the ER and

neutralized by enzymes within it


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Golgi apparatus :

Typically consists of five or six flattened membranous discs

called cisternae .

The Golgi apparatus has three major functions:

(1) modifies and packages secretions, such as hormones or

enzymes, for release through exocytosis

(2) renews or modifies the plasma membrane; and

(3) packages special enzymes within vesicles for use in the

cytoplasm.


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i. They arepower generating units of cell

ii. They provide energy for performing many functions of cell

by metabolism using nutrients and oxygen

iii. The number varies from 100-1000 depending on energyrequirement of that cell

iv. The size is 1 length varies from 5-12

v. The shape varies from globular, sausage to filamentous

form


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They are large irregular vesicular structures bounded by unit

membrane.

Size varies from 250-750 m.

They are filled with granules, size 5-8 nm which are aggregates

of protein hydrolytic enzymes mainly acid hydrolase.

They remove unwanted substances and bacteria, providing

intracellular digestive system .


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FUNCTIONSOF LYSOSOMES

1. Lysosomes also engulf worn out components ofcell forming Autophagic vacuole.

2. Lysosomal enzymes also cause autolysis of theremnants of a dead cell calledAUTODIGESTION.

Thus they are called asSUICIDAL BAGS. The lysosomes provide anIntracellular digestive system that

allows the cell to digest within itself

damaged cell structures

food particles ingested

unwanted matter e.g. bacteria


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CELL DIVISION

It is the process by which cells reproduce themselves.

2 types 1. Somatic cell division

2. Reproductive cell division

A somatic cell is any cell of the body other than a germ cell.

A germ cell is a gamete (sperm or oocyte)

Somatic cell division : a cell undergoes anuclear division called

mitosis and a cytoplasmic division called cytokinesis to produce

two genetically identical cells, each with the same number and

kind of chromosomes as the original cell.

It replaces dead or injured cells and adds new ones during tissue

growth.


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MITOSIS

Mitotic phase : Parent cell produces identical cells with identical

chromosomes.

Mitosis : Nuclear division; distribution of two sets of chromosomes

into separate nuclei.

1. Prophase : Chromatin fibers condense into paired chromatids;

nucleolus and nuclear envelope disappear; each centrosome moves to

an opposite pole of the cell.2. Metaphase :- Centromeres of chromatid pairs line up at metaphase

plate.

3. Anaphase :- Centromeres split; identical sets of chromosomes move

to opposite poles of cell.

4. Telophase :-Nuclear envelopes and nucleoli reappear; chromosomes

resume chromatin form; mitotic spindle disappears.

Cytokinesis :- Cytoplasmic division; contractile ring forms cleavage

furrow around center of cell, dividing cytoplasm into separate and equal

portions.


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Reproductive cell division : It is the mechanism that

produces gametes.

Gametes : The cells needed to form the next generation of

sexually reproducing organisms.

This process consists of a special 2 step division called

meiosis, in which the number of chromosomes in the nucleus

is reduced by half.


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MEIOSIS It is a specialized process of cell division that occurs only in the

production of gametes within the female ovary or male testes

It consists of two divisions (meiosis I and meiosis II), which result in the

formation of four gametes, each containing half the number ofchromosomes (23 single chromosomes) and half the amount of DNA (1N)found in normal somatic cells (46 single chromosomes, 2N).

Meiosis I :- Synapsis: pairing of 46 homologous duplicated chromosomes.

Crossing over: exchange of large segments of DNA.

Alignment : alignment of 46 homologous duplicated chromosomes at themetaphase plate.

Disjunction: separation of 46 homologous duplicated chromosomes from eachother; centromeres do not split.

Cell division: formation of two secondary gametocytes (23 duplicatedchromosomes, 2N).

Meiosis II. Events that occur during meiosis II include the following: Synapsis: absent.

Crossing over : absent.

Alignment: alignment of 23 duplicated chromosomes at the metaphase plate.

Disjunction: separation of 23 duplicated chromosomes to form 23 singlechromosomes; centromeres split.

Cell division: formation of four gametes (23 single chromosomes, 1N).

Intro..Cell Phsiology PM

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