1. CYTOLOGY Membranous Cell Organelles
October 6 University
Faculty of physiotherapy
CYTOLOGY Membranous Cell Organelles

2. Objectives 1-Identify Membranous Cell Organelles 2- Recognize structure of each organelle 3- Recognize function of each organelle 4- Identify components and functions of nucleus

3. 1 - Cell membrane Definition:-
It is an ultra thin membrane that surrounds the cell i.e. it forms an envelope or a cover for the cell.
L.M:-
It is invisible by L.M as it is very thin (8-10 nm), but can be stained by Ag or PAS
EM:-
It appears as three parallel lines, two dark layers separated by a light one i.e. it is a trilamellar membrane. The cell membrane has an outer covering rich in carbohydrates called cell coat.

5. Molecular structure of the cell membrane:-
The cell membrane is composed of lipids, protein & carbohydrate:
Lipids component (30%):
Cell membrane has two types of lipids:
a) Phospholipid molecules
b) Cholesterol molecules

6. a) Phospholipid molecules:-
They are arranged into two layers. Each molecule has a polar end & a non polar end.
Polar end: It forms the head of the phospholipid molecule. It is directed to outside & carry charges. It is also called the hydrophilic end. [Has affinity to H20]
Non polar end: It forms the tail of the phospholipid molecule directed to the center of the cell membrane and not charged. It is called the hydrophobic end. [No affinity to H2O]

7. b) Cholesterol molecules:
They are present in between tails of the phospholipids molecules.
Lipid component of the cell membrane allows passage of fat soluble compounds through it.

8. 2-Protein component (60%):
Cell membrane contains two types of protein:
a) Intrinsic protein (integral protein):present in the form;
Small particles that extend for some distance within the thickness of the cell membrane.
Large globules which extend along the whole thickness of the cell membrane & act as a pathway for water soluble substances.
b) Extrinsic protein:
It is represented by small molecules which are loosely attached to the extracellular & intracellular surfaces of the cell membrane forming a non continuous layer.

9. 3- Carbohydrate component (10%):
They are polysaccharides either attached to protein molecule & form glycoprotein or to lipid one and from glycolipid. Gycolipid & glycoprotein are known as the cell coat or glycocaiyx. Cell receptors are present among the cell coat; they are responsible for entrance of drugs, hormones & bacteria to the cell. functions of cell membrane:- a- It keeps the internal composition of the cell. b- Cell coat as a part of the cell membrane is responsible for cell adhesion, cell recognition & cell immunity (functions of cell coat).

10. c- It allows passage of substance through it by:-
Passive diffusion: (e.g. gases & water). The molecules cross according to concentration gradient.
Facilitated diffusion: This diffusion needs the help of intrinsic protein which acts as a carrier e.g. glucose.
Active transport: This process needs energy & takes place against the concentration gradient e.g. Na pump outside the cell.
Selective permeability: By presence of receptors in the cell coat that allow certain substance only to enter into the cell, so it is also called receptor-mediated endocytosis.

11. Bulk transport (vesicular transport): Macromolecules enter & leave the cell by vesicular transport that involves changes in plasma membrane at a localized site & formation of vesicles from the cell membrane or fusion of vesicles with the cell membrane. Vesicular transport may be one of two processes:
- Exocytosis: in which substances leave the cell to outside.
- Endocyosis: in which substances enter the cell. If the substance that enters the cell is solid the process is called phagocytosis. If the substance that enters the cell is fluid the process is called pinocytosis.

12. 2- MITOCHONDRIA Definition:-
It is a membranous cell organelle. It is the power house of the cell responsible for cell respiration & energy production.
Number: - varies according to activity e.g. liver cells contain / cell N.B. They are present in all cells except RBCs.
Site: - at site of most activity e.g. apical part in ciliated cells.
Mitochondria appear as granules, rods or filaments. They need a special stain to be demonstrated e.g. iron hematoxylin stains them black while Janus green stains them green.

14. Each mitochondrion appears as a vesicle rounded or oval in shape & covered with double membranes, which are separated by a narrow space which is called inter-membranous space. The outer membrane is smooth while the inner one is thrown into incomplete folds, which are called shelves or cristae.
Mitochondrial matrix is the substance, which fills the internal cavity of mitochondria .The matrix, contains lipid, protein, carbohydrate, Ca & Mg as well as DNA & RNA. Oxidative enzymes are also present attached by heads to the cristae.

15. Functions:-
Mitochondria are the Power House of the cell as they contain oxidative enzymes which produce energy. This energy is stored in the form of ATP& released at time of need.
They can form their own protein & can divide, as they contain DNA & RNA

16. 3- Endoplasmic Reticulum
Definition:
It is a membranous organelle. It is formed of flattened communicating vesicles & tubules that form reticulum inside the cytoplasm. It is classified according to presence or absence of ribosomes into two types:
a) Rough (granular) E.R.
b) Smooth (agranular) E.R.

17. a. Rough endoplasmic reticulum (rE.R.)
Site: In protein forming cells e.g. pancreas, plasma cells, fibroblasts are rich in rER.
L.M.:- It appears as a basophilic (blue) structure due to presence of ribosomes = rRNA.
E.M.:- It appears as a network of parallel flattened communicating vesicles & tubules called cisternae with its outer surface covered with ribosomes.

18. Functions:-
1- Synthesis of protein by the help of the ribosomes attached to the surface of rough endoplasmic reticulum.
2- Condensation & packing of the protein formed within r.E.R.
3- Budding of the packed protein at one end of r E.R. in the form of transfer vesicle.
4- It acts as intracellular pathway for transport of protein to Golgi apparatus.
5- It shares in the formation of Lysosomes, by formation & segregation of their hydrolytic enzymes.

19. b. Smooth endoplasmic reticulum (sE.R.)
Site: - in lipid forming cells e.g. liver & cells of some endocrine glands
L.M. :- It cannot be seen by L.M.
E.M. :- It is formed of branching & anastomosing & vesicles. It is surrounded with a smooth membrane which has no ribosomes.

20. Function:
Lipid synthesis.
Steroid hormones synthesis.
Formation & storage of glycogen, e.g. in liver & muscles.
It helps muscle contraction by Ca pump.
Detoxification of drugs & hormones in liver.
Acts as intracellular pathway

22. CLINICAL APPLICATION:
Patient suffering from liver diseases should avoid the excessive use of drug
4- GOLGI APPARATUS
Definition
It is a membranous organelle. It is considered as the secretory system of the cell. So it is well developed in protein forming cells and secretory cells.
L.M.:-It is demonstrated by (Ag) stain. It appears as a dark brown network & fibrils around the nucleus (perinuclear) in nerve cell .or between the nucleus & secretory pole (supranuclear) in secretory cell. e.g. pancreas.
N.B. In sections stained with H&E the area occupied by Golgi apparatus appears as unstained area & so it is called negative Golgi Image.

23. Diagram showing Golgi apparatus

24. E.M.:- It is formed of saucer-shaped flattened saccules stacked over each other each stack has two faces:-
Immature convex surface, which is the forming surface (cis surface) that receives the transfer vesicles which carry protein budding from rE.R.
Mature concave surface from which secretory vesicles come out carrying condensed & modified protein. Also other vesicles containing hydrolytic enzymes will come out &these are called Lysosomes

25. Functions:-
Concentration of protein formed by r E.R.
Modification of protein by adding sulphates or carbohydrates.
Discharge of secretion in the form of secretory vesicles
Isolation and package of hydrolytic enzymes in the form of Lysosomes.
Formation & maintenance of cell membrane & cell coat.

26. 5- Lysosomes
Definition: - They are membranous organelles rich in hydrolytic enzymes and considered as the digestive system of the cell. So, they are numerous in phagocytic cells e.g. white blood cells
L.M.:- They can be demonstrated by using a special stain for the enzymes T rent within them, e.g. acid phosphates enzyme.
E.M.:- E.M picture of Lysosomes depends on their types.
1- Primary Lysosomes: - These are the newly formed Lysosomes. They appear as small rounded homogenous vesicles.

27. 2- Secondary Lysosomes: - They result from fusion of primary Lysosomes with intracellular macromolecules. They appear as heterogonous vesicles. They are of different types:-
Heterolysosome: - It results from fusion of a primary lysosome with a phagocytic vesicle containing food or bacteria.
Multivesicular bodies: They result from fusion of primary lysosomes with pinocytic vesicle containing fluid droplets.
Autolysosomes: They result from fusion of primary lysosomes with vacuoles containing old organelles.
Residual bodies: These are no more than secondary lysosomes containing the undigested remnants. They are either extruded outside the cell or accumulated within the cell as lipofucsin granules as in long lived cells e.g. cardiac muscle or nerve cell.

29. Functions:-
Digestion of nutrients within cell.
Defensive function, destruction of any bacteria or virus.
Removal of any degenerated old organelles.
Lysis of the cells &the body as a whole after death.
Change of inactive hormone into active one. e.g. in thyroid gland.
Help the sperm to penetrate the ovum.

30. NON MEMBRANOUS CELL ORGANELLES 1- RIBOSOMES
Definition: - Ribosomes are non membranous cell organelles. They are formed within the nucleolus, their chemical composition is ribonucleoprotein= rRNA + protein.
L.M.:- very minute structures (15-20nm) which are difficult to be seen by L.M. They appear as basophilic structures when stained by H.
Ribosome appears as small electron dense particle formed of two, one is large & the other is small both =re connected together by m RNA.

31. The large subunit has a central groove which is occupied by the newly formed polypeptide chain. There are three forms of ribosomes:- I - Free ribosomes are diffusely scattered in the cytoplasm. This form is common in immature cells, e.g. embryonic & stem cells. II - Polyribosomes:- the ribosomes are connected together by m- RNA in a spiral or rosette form. III- Attached ribosomes: - The ribosomes are attached by means of their large subunits to rER.
Polyribosomes
Ribosome

32. Functions of Ribosomes:
Ribosomes provide the intracellular site where amino acids are linked together forming polypeptide chains i.e. they are the site for protein synthesis.
Protein formed by free ribosomes is used within the cell while that formed by rER is secreted& used outside the cell (transfer vesicle from rER Golgi apparatus secretory vesicle —> cell membrane
—► outside the cell).

33. 2- CYTOSKELETON a- MICROTUBULES
Definition: non branching & rigid hollow fine tubes formed of a protein called tubulin.
L M: They are difficult to see them by L.M. except by using special stains.
E.M: They appear as fine tubules that measure about 20-25nm in diameter. The length of microtubules can be changed by adding or removal of tubulin molecules at their end.

34. Functions:
1- Maintenance of the cell shape e.g. platelets.
2- Intracelluar vesicular transport.
3- Formation of mitotic spindle during cell division.
4- Elongation & movement of the cell.
5- Formation of centrioles, cilia & flagella.
Vimentin filaments are present in connective tissue & muscle.
Desmin filaments are present in muscle.
Neurofilaments are present in nerve cells.
Glial filaments are present in glial cells.

35. Thick filaments Their diameter is about 15nm
Thick filaments Their diameter is about 15nm. They are formed of a protein called myosin & tie. are found in skeleta muscle. 3-Cell Inclusion They are classified into two groups :- a-Stored food & b- Pigments A - Stored food: The cell may store carbohydrates or Lipids: Carbohydrates:-stored in the form of Glycogen as in liver & muscles .

36. L.M.:- Glycogen cannot be demonstrated by ordinary stain (H&E) as it is water soluble, it can be seen if stained by special stain as Best's Carmine (red) or PAS (purple).
E.M.:- Glycogen is present in the form of dense partical which are present either single or in groups called glycogen rosettes
Lipids :- Lipids are stored in the form of small droplet or large globule. Fat cells are the main site for storage of lipids, other cells like liver cells may contain fat.
L. M.:- Lipids can not be demonstrated by (H&E)as it dissolves in xylol Lipid can be stained orange by Sudan III & black by Sudan black.

37. b- Pigments : may be;
1- Endogenous which are produced by the cell
a- Hemoglobin which is present in RBCs to carry gases.
b- Melanin which give the skin & hair their color
c- Lipofuscin granules are accumulated residual bodies in long lived cells e.g nerve cells & cardiac muscles.
2. Exogenous :- enter the cell from outside as
a) carotene pigments in carrots colour fats in cells
b) Dust& carbon particles in air blacken lungs

38. Nucleus
Shape :- Rounded , oval , flat , horse-shoe, kidney shaped , segmented or
lobulated.
Site:- Central , eccentric, peripheral & may be basal in position.
Number:- Single (mononucleated), two nuclei (binucleated), or many nuclei (multinucleated).
L.M. The nucleus appears as a prominent basophilic structure within the cell as it contains nucleic acids (DNA & RNA), it may be:
1 - Vesicular nucleus:- Pale stained as it has extended chromatin.
2- Condensed nucleus:-Darkly stained due to its condensed chromatin.

40. E.M.:- The nucleus is composed of:
1- Nuclear membrane.
2- Nuclear chromatin.
3- Nuclear sap.
4- Nucleolus.
1- NUCLEAR MEMBRANE:-
L.M.: It appears as a blue line because of the presence of chromatin on its inner surface& ribosomes on its outer surface.
E.M.: It consists of a double walled membrane. Its two layers are separated by a perinuclear space. Nuclear pores are present at intervals along the nuclear membrane where the two layers are fused together & they are covered by diaphragms.They are the pathway through which substances pass in between the nucleus & cytoplasm in both directions.

41. 2- NUCLEAR CHROMATIN:-
Definition :- lt consists of nucleoprotein (DNA+ protein)& forms the chromosomes of the cell.
L.M.:- Chromatin appears as a basophilic substance which fills the nucleus.
E.M.:- There are two types of nuclear chromatin according to the activity of the cell :-
1- Euchromatin :-
It is the extended type of chromatin.
It is invisible by L.M.the nucleus appears pale in staining.
It carries the active genes responsible for synthesis of protein.
Active cell has a pale nucleus with extended chromatin.

42. 3– Heterochromatirrr :
It is present in a condensed form (large masses of chromatin)
The nucleus with condensed chromatin is darkly stained.
It carries the inactive genes.
Inactive cell has a dark nucleus with condensed chromatin. Classification of chromatin according to site:
1 - Peripheral chromatin adherent to nuclear membrane.
Nucleolus associated present around the nucleolus.
Chromatin island scattered between the nucleolus & nuclea membrane.

43. 3- NUCLEOLUS:
It appears as dark basophilic structure within the nucleus.
The nucleus may contain one, two or no nucleoli according to its activity.
Functions:- Formation of ribosomal RNA (ribosomes) responsible for protein synthesis.
N.B. Protein forming cells have well defined one or two nucleoli.
4- NUCLEAR SAP:-
It is the colloidal fluid filling areas between nucleolus& chromatin islands I It acts as a transport medium to carry ribosomes from the nucleus to cytoplasm.

44. Functions of nucleus ;-
It is responsible for cell division as it contains chromosomes which carry the genetic information.
It controls all the vital processes within the cell, as protein formation.
It forms the different types of RNA (m RNA, t RNA, r RNA).

45. Objectives 1-Enumerate Membranous Cell Organelles 2- describe structure of each organelle 3- enumerate functions of each organelle 4- Enumerate components and functions of nucleus