Archive for the ‘ L3-Cell Membrane ’ Category

L3-The cell membrane

INTRODUCTION

•The cell is the living unit of the body.

•Group of cells →Tissues→Organ→Systems→Living Organism.

BODY FLUID

Intracellular Fluid

•Fluid inside the cells of the body.

•High Na & less K

The extra cellular fluid

•Interstial fluid circulate in the spaces between the cells.

•Plasma of the blood

•High K Less Na

CELL MEMBRANE

•All animal cells are enveloped by a cell membrane

•It is composed of lipid and protein

•It is semi permeable membrane

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Function of cell Membrane

1.Separates between cytoplasm & ECF

2.Maintain cell internal environment.

3.Transport of molecules in & out the cell

4.Controls ions distribution between cytoplasm and ECF

5.It contains protein receptors for hormones &chemical transmitter.

6.Generates membrane potentials

Components of the cell membrane

•It consists of two layers of phospholipids molecules. It resemble the pin shaped.

•The head composed of protein and lipid .

•The heads are soluble in water (hydrophilic)

•The tails are insoluble in water (hydrophobic)

•They meet in the interior of the membrane

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Cell membrane protein

There are two types of proteins

(1) Integral or intrinsic protein

1.Channels through which small water soluble substance can diffuse.

2.Carrier which actively transport material across the membrane.

3.Receptors which when activated initiate intracellular reaction.

4.Enzymes.

(2) Peripheral or extrinsic protiens:

•Composed of glycolipid and glycoprotein.

•Binds to extracellular calcium to stabilize memberane.

•Acts as attachment matrix for other cells

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Transportation through cell membrane

1.Diffusion.

2.Active transport.

3.Vesicular transport.

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1.Diffusion:

•either simple diffusion or facilitated diffusion.

Simple diffusion: the substance cross the cell membrane by simple movement without binding with carrier protein.

Facilitated diffusion: carrier mediated diffusion.

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2.Active transport:

Movement of substance against concentration gradient.

•Needs energy from hydrolysis of ATP

•Either:

1-primary active transport.

2-secondery active transport

Picture7Primary Active transport:

1-Na-K pump

•Present in the cell membrane

•Transport Na (out)  from ICF to ECF

and K (in) from ECF to ICF

2- K-H ATpase (proton pump)

•Present in stomach. Transport H ions into the lumen against concentration gradient.

Secondary  Active transport:

1.Na- glucose co-transport: needs carrier which contain two binding sites for Na and glucose.

2.Na- Ca exchange: present in ventericular muscles.

3.Vesicular transport mechanism:

1.Endocytosis: (phagocytosis & pinocytosis)

2.Exocytosis: (cell vomiting)

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