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صدق الله العظيم 58االسراء اية
ByBy
Dr. Abdel Aziz M. HusseinDr. Abdel Aziz M. HusseinLecturer of Medical PhysiologyLecturer of Medical Physiology
Organization of Human BodyOrganization of Human Body• The human body is made up of different systems
e.g. digestive system, whose functions are coordinated and integrated together.
• Each system consists of many organs that made up of many tissues of complementary functions.
• Each tissue consists of millions of similar cells.• The cell is the basic unit of structure and function
in the body• Each animal cell is surrounded by a cell membrane
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Cell (Plasma) MembraneCell (Plasma) Membrane
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Cell Membrane Cell Membrane
• It is a very thin elastic semi-permeable membrane (allowing some substances to pass through it and prevent others) that surrounds the cell
• It is about 7.5 nm (75 Ao = Angstrom = 10-10 of meter) in thickness.
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Functions of Cell Membrane Functions of Cell Membrane 1. It separates the cytoplasm from ECF.2. It maintains cell's internal environment.3. It transports of macromolecules into and out of the
cell.4. It controls distribution of ions e.g. Na, K extracellular
ICF and ECF.5. It generates transmembrane potentials.6. It is contains receptors for hormones and transmitter
substances which are important for signal transduction
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Components of Cell Membrane Components of Cell Membrane • It is formed of 3 components; 1.Lipids 42%.2.Proteins 55%.3.Carbohydrates 3%.
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Cell Membrane Lipids Cell Membrane Lipids
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Cell Membrane Lipids Cell Membrane Lipids
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•Form the basic structure of the membrane.
•Include mainly phospholipids, cholesterol, and glycolipids.
•Phospholipids are arranged into 2 layers (Lipid bilayer)
•Phospholipids molecules resemble the clothes-pin shape
•It consist of;
•Head (PO4 group) (face the ICF and ECF sides) relatively H2O
soluble (polar, hydrophilic).
•Tails (face each other in the interior of the bilayer) → relatively H2O
insoluble (non-polar, hydrophobic).
Cell Membrane ProteinsCell Membrane Proteins
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Functions of Cell Membrane Integral Functions of Cell Membrane Integral ProteinsProteins
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1.1. Integral or intrinsic Integral or intrinsic proteins→proteins→bind to
hydrophobic center of the lipid bilayer
2.2. Peripheral or extrinsic Peripheral or extrinsic proteinsproteins→ bind to the
hydrophilic polar heads of the lipids or to the
integral proteins
Functions of Cell Membrane Integral Functions of Cell Membrane Integral ProteinsProteins
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i)Transmembrane proteins i)Transmembrane proteins → span the entire bilayer which act
as:
a. Channels → for diffusion of small, water–soluble substances.
b. Carriers actively transport materials across the bilayer.
c. Pumps actively transport ions across the bilayer.
d.Receptors initiate intracellular reactions when activated.
Functions of Cell Membrane Integral Functions of Cell Membrane Integral ProteinsProteins
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ii)Present only on one side of the membraneThey act as enzymes that activate or inactive metabolic processes.
Functions of Cell Membrane Peripheral Functions of Cell Membrane Peripheral ProteinsProteins
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The peripheral protein may be:
i) Peripheral proteinsi) Peripheral proteins: : bind to
the intracellular surface of the
membrane and contribute to the
cytoskeleton.
ii) Peripheral proteinsii) Peripheral proteins: : bind to
the extracellular surface of the
membrane and contribute to the
glycocalyx.
Glycocalyx
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2. It acts as an attachment matrix for
other cells (cell adhesion
molecules).
•It is composed of glycolipids and
glycoproteins and covers the cell
membrane.
•Functions Functions
1. 1. It binds to the extracellular Ca to
stabilize membrane structures.
Transport through the Cell Transport through the Cell MembraneMembrane
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Transport through the Cell MembraneTransport through the Cell Membrane
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Transport through the Cell MembraneTransport through the Cell Membrane
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There are 3 mechanisms for transport of substances through cell membranes;
a) Passive transport (Diffusion):a) Passive transport (Diffusion):It is movement of substances across the cell membrane down its electrochemical gradient.
b) Active transport: b) Active transport: It is movement of substances across the cell membrane against its electrochemical gradient.
c) Vesicular transport: c) Vesicular transport: It is the process by which large sized substances are engulfed by the cell membrane to be either pushed inside the cell (endocytosis) or pushed outside the cell (exocytosis)
DiffusionDiffusion
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It is divided into 3 subtypes:1.Simple diffusion.2.Facilitated diffusion.3.Osmosis (water only)
Simple DiffusionSimple Diffusion
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It is movement of substances across the cell membrane down its electrochemical gradient by simple movement without the necessity of binding with carrier proteins
Mechanisms:Mechanisms:It occurs either
through;•The interstices of the
lipid bilayer.•The watery proteins
channels.
Simple Diffusion Simple Diffusion
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Simple DiffusionSimple Diffusion
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Characters:Characters:It is characterized by;
a) It occurs down an electro-chemical gradient.
b) It is passive i.e. no external energy is required.
Simple DiffusionSimple Diffusion
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Characters:Characters:It is characterized by;
c) It is not rate-limiting i.e. linear with concentration gradients.
d) The diffusion process is not saturable.
Osmosis or Diffusion of WaterOsmosis or Diffusion of Water
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Water diffuses through lipid bilayer of the membrane at high rate like bullets due to;
Its small size.
Its very high kinetic energy
Water moves from high to low concentrations of water
Facilitated DiffusionFacilitated Diffusion
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It is the diffusion of substances across the cell membrane (down electrochemical gradient) which needs the presence of carrier proteins→ carrier mediated diffusion
Characters
i) It occurs down an electrochemical gradientii) It is passive i.e. no energy is required.iii) It requires the presence of a transport carrier protein.iv) It is rate-limiting and saturable because it depends on the availability of a definite number of carrier or channel proteins
II) Active TransportII) Active Transport
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Def.,It is the movement of substances across the cell membranes against an electrochemical gradient.
Types:
There are 2 subtypes of active transport:i) Primary active transport → obtain its energy directly from the hydrolysis of ATP e.g. Na-K Pump, Ca ATPase, H-K ATPase
ii) Secondary active transport → use the energy stored in the Na concentration gradient e.g. Na-glucose co-transport and Na-Ca exchange
II) Active TransportII) Active Transport
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Characters
1. It occurs against the electrochemical gradient
2. It is active i.e. energy is required
3. It requires the presence of a transport carrier protein4. It exhibits stereospecificity, saturation, and competition
1ry Active Transport1ry Active Transport
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(Na-K ATPase)
Na-K pump
Ca-ATPase
(Ca-pump)
K-H-ATPase
(proton pump)
Site It presents in the
cell membranes.
It is present in
sarcoplasmic
reticulum and cell
membranes.
It presents in
stomach parietal-
cells and renal
distal tubular cells.
Importance maintains low
intracellular Na
and high
intracellular K.
It maintains the
intracellular Ca
ions concentration
low.
It transports H ions
into the lumen
against its
electrochemical
gradient.
2ry Active Transport2ry Active Transport
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Na-glucose co-
transport
Na-Ca Exchange
Site It presents in the cell
membranes.
It is present in ventricular
ms cells
Importance Transport of Na &
glucose into the cells
It transports Ca uphill from
low ICF Ca to high ECF
Ca
Differences ( ) simple diffusion, facilitated diffusion and active transport
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Simple diffusion Facilitated diffusion Active transport
Electrochemical
gradient
Downhill Downhill Uphill
Energy Doenot need energy Doenot need energy Needs energy
Rate Not limited Limited Limited
Saturation Not Saturable Saturable Saturable
Carrier Doenot need carrier Needs carrier Needs carrier
Competition Not show competition Shows competition Shows competition
III) Vesicular TransportIII) Vesicular Transport
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It is the mechanism by which the large sized substances can cross the cell membranesa) Endocytosisa) Endocytosis
It is active process which uses energy
The extracellular material is trapped within vesicles that are formed by invagination of the cell membrane
It is 3 types
III) Vesicular TransportIII) Vesicular Transport
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a) Exocytosisa) Exocytosis
It is active process which uses energy
The intracellular material is trapped within vesicles, then the vesicles fuse with the cell membrane and release their contents to the ECF
e.g. release of hormones, digestive enzymes, and synaptic transmitters
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