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1. TRANSPORT ACROSS THE
CELL MEMBRANE
CONTINUED FROM PREVIOUS SLIDE
1
DR.HAMISI MKINDI,MD.
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2. Cell Membrane
• Structure
• Function
Passive Transport
• Simple Diffusion
• Facilitated Diffusion
Active Transport
• Primary
• Secondary
Endocytosis and
Phagocytosis
2

3. ACTIVE TRANSPORT
3

4. When a cell membrane moves
molecules/ions against gradient
•The process is called active transport.
4

5. Active Transport divided into
•Primary active transport
•Secondary active transport
5

6. Primary active transport,
directly uses metabolic
energy for transport
6

7. In primary active transport the
energy is derived
•Directly from breakdown of ATP or
•NADH at mitochondrial level
7

8. There are a number types of ATPases
used in primary active transport:
•P-Type ATPase,
•F-ATPase, V-ATPase, and ABC
8

9. Prominent examples of P-type
ATPases
SODIUM
POTASSIUM PUMP
POTASSIUM
HYDROGEN PUMP
CALCIUM PUMP
9

10. The Na-K pump is the most important
primary active transporter in animal cells
•It is located in the plasma membrane
•Uses energy of ATP to extrude Na+ and take up K+
•Utilizes about a third of ATP consumed by body
10

11. The Na+-K+ pump mechanism
•Pumps 3Na+ outward of cell membrane
•Pumps 2K+ from outside to the inside
at the same time
11

12. 12

13. In animal cells, it is the only primary
active transport process for Na+.
• Also the most important primary active K+
transport mechanism
13

14. In cells throughout the body, is
responsible for maintaining
• A low [Na+]i and a high [K+]i relative to ECF.
•In most epithelial cells, the Na-K pump is
restricted to the basolateral side of the cell.
14

15. 15
Na-K ATPase PUMP
LUMEN
BASAL
LATERAL

16. A hallmark of the Na-K pump is that
it is blocked by cardiac glycosides,
•Examples of which are ouabain and digoxin;
•Digoxin is widely used cardiac conditions
16

17. 17

18. K+ competitively antagonizes the
binding of cardiac glycosides.
• A low [K+] in blood potentiates digitalis
toxicity in patients.
18

19. 19
PRIMARY ACTIVE TRANSPORT
OF CALCIUM IONS

20. Most if not all cells have a
primary active transporter at
the plasma membrane that
extrudes Ca2+ from the cell.
20

21. Calcium ions are normally maintained at
extremely low concentration in the ICF
•This is achieved by two active calcium pumps
•At the cell membrane (PMCA), the other
•Ca++ pump in the sarcoplasmic reticulum.
21

22. 22
PLASMA MEMBRANE CALCIUM PUMP

23. 23
Plasma Membrane
Calcium Pump (PMCA)

24. 24
SARCOPLAMIC RETICULUM CALCIUM PUMP

25. The sarcoplasmic and endoplasmic
reticulum calcium ATPase (SERCA)
•Transports two H+ and two Ca2+ ions for
each molecule of ATP hydrolyzed.
25

26. 26
PRIMARY ACTIVE TRANSPORT
OF HYDROGEN IONS

27. At two places in the body, primary active
transport of hydrogen ions is important:
•In the gastric glands of the stomach and
•In the renal distal tubule and collecting ducts.
•These segments achieve very high [H+] gradients.
27

28. There are two major types of
hydrogen ion pumps the:
• H+-ATPase pump (V-ATPase proton pump)
• H+/K+ -ATPase pump (P-Type ATPase)
28

29. In the parietal cells an
H-K pump extrudes H+
at the apical membrane.
29

30. PARIETAL CELL

31. An apical H+ pump also
secretes H+ in renal
intercalated cells.
31

32. Alpha intercalated cells
have the V-type H+ pumps
•These work independent of K+.
32

33. 33
The main
function of the
H+/K+-ATPase is
to reabsorb K+.
The H+-ATPase
helps reabsorb
filtered HCO3
−

34. SECONDARY ACTIVE
TRANSOPORT
34

35. In secondary active transport
the energy is derived from
•A concentration gradient created by
•Active transport of another substance
35

37. When a large [sodium] gradient is
created by primary active Na+ transport
• Na+ increasingly attempts to enter the cell
• Dragging with it other substances (Symport) OR
• Induce another substance move out (Antiport).
37

38. 38

39. Secondary active transport can
therefore be divided into
•Co-transport (Symporter)
•Counter-Transport (Antiporter)
39

40. GLU and many AA are transported into
most cells against concentration gradients
• The mechanism of this is entirely by co-transport
• Na+GLU co-transport is good example of symporter.
40

41. The carrier protein has
two binding sites one
for Na+ and one for
GLU.
When both Na+ and
GLU become attached,
sodium and glucose are
transported to the
inside of the cell at the
same time
HIGH [Na+]
LOW [Na+]
41

42. Sodium-GLU co-transport occurs
especially through the epithelial cells
•In intestinal tract and
•The renal tubules of the kidneys
•To promote absorption of these substances
42

43. Other cotransporters of
secondary active transporters
include the following
43

44. 44
NKCC COTRANSPORTER NCC COTRANSPORTER

45. Na/HCO3 COTRANSPORTER
177
KCC COTRANSPORTER

46. In an antiporter two solute species
are pumped in opposite directions:
•Sodium-calcium counter-transport,
•Sodium-hydrogen counter-transport.
46

47. 47
Present in nonepithelial
cells and the basolateral
membranes of epithelia
Extracellular Space Cytosol

48. 48
Na-Ca Exchanger (NCX) Cl-HCO3 Exchanger (AE)

49. Sodium-Calcium counter-transport occurs
through all, or almost all, cell membranes.
• With sodium ions moving to the interior and
• Calcium ions the exterior bound to same protein
• This is in addition to primary active transport
49

50. Sodium-Hydrogen counter transport
occurs in several tissues especially.
•In the proximal tubules of the kidneys,
•Sodium ions move from the lumen while
hydrogen ions are secreted into the lumen.
50

51. 51
TUBULAR
LUMEN
INTERSTITIAL
SPACE

52. In both primary and secondary active
transport
•Transport depends on integral (carrier) proteins,
•In active transport, the carrier protein, imparts
energy to move a substance against gradient.
52

53. ENDOCYTOSIS
53

54. Endocytosis is a cellular process in which
substances are brought into the cell.
•The material internalised is surrounded by
•An area of plasma membrane,
•Which then buds off inside the cell.
54

55. 55
Extracellular
Fluid

56. Very large particles enter the cell by a
specialized function of endocytosis.
•The principal forms of endocytosis are
•pinocytosis and
•phagocytosis.
56

57. PHAGOCYTOSIS ("CELL
EATING")
• Is the process by which
bacteria, dead tissue,
or other bits of
microscopic material
are engulfed by cells
PINOCYTOSIS ("CELL
DRINKING")
• Is a similar process
with the vesicles much
smaller in size and the
substances ingested
are in solution.
57

58. SUMMARY
58

59. The cell is the basic unit of life
•It has a cell membrane; which separates it
•From its surrounding environment
•Made up of a bilayer of phospholipids
59

60. 60
Cell membrane allows
lipid soluble substances
to enter or exit the cell
by simple diffusion
It has proteins that
provide mechanisms for
water and water soluble
substances to enter or
exit the cell

61. There are two major classes of membrane
transport proteins:
• Channel proteins: provide passage of water/ions
• Carrier Protein; that provide
• Active transport mechanisms
• Passive transport mechanisms
61

62. Passive carrier proteins facilitate the downhill
transport of substances across membranes.
• An example of a carrier protein that carries out passive
transport is the glucose transporter.
• Allows glucose to enter cells
• Allows glucose to exit liver cells
62

63. Active transport provides for transport of solutes
against electrochemical gradients. These include
• ATP-driven ion pumps
• Coupled Transporters (secondary active transporters).
• Symport
• Antiport
63

64. Active transport at the cell membrane
provides
•Maintaining composition and the volume of ICF
•Creating and maintaining membrane potentials
critical for excitable tissues
64

65. THANK YOU
65