Histology

1. Nuclear Cell Structure and
Component + Cell Junctions
Dr. Rabia Inam Gandapore
Assistant Professor
Head of Department Anatomy
(Dentistry-BKCD)
B.D.S (SBDC), M.Phil. Anatomy (KMU),
Dip. Implant (Sharjah, Bangkok, ACHERS) , CHPE
(KMU),CHR (KMU), Dip. Arts (Florence, Italy)

2. Teaching Methodology
 LGF (Long Group Format)
 SGF (Short Group Format)
 LGD (Long Group Discussion, Interactive discussion with the use of models or diagrams)
 SGD (Short Group)
 SDL (Self-Directed Learning)
 DSL (Directed-Self Learning)
 PBL (Problem- Based Learning)
 Online Teaching Method
 Role Play
 Demonstrations
 Laboratory
 Museum
 Library (Computed Assisted Learning or E-Learning)
 Assignments
 Video tutorial method

3. Goal/Aim (main objective)
 To help/facilitate/augment the students about the:
1. Nuclear Structure & Components:
 Structure of the nucleus, nucleolus & chromosome, and their functions in cell
integrity
2. Cell junction:
 Define cell junction
 Describe the structure and functions of the junctions.
 Discuss the junctions on the basal and lateral surfaces of the cell.
 Enlist the junctional complex.

4. Specific Learning Objectives (cognitive)
At the end of the lecture the student will able to:
 Recognize the gross anatomical features of the Nucleus, Nucleolus &
Chromosomes
 Sketch labeled diagram of the different types of cell junctions

5. Psychomotor Objective: (Guided response)
 A student to draw labelled diagram of Nucleus & chromosome

6. Affective domain
 To be able to display a good code of conduct and moral values in the class.
 To cooperate with the teacher and in groups with the colleagues.
 To demonstrate a responsible behavior in the class and be punctual, regular, attentive and
on time in the class.
 To be able to perform well in the class under the guidance and supervision of the teacher.
 Study the topic before entering the class.
 Discuss among colleagues the topic under discussion in SGDs.
 Participate in group activities and museum classes and follow the rules.
 Volunteer to participate in psychomotor activities.
 Listen to the teacher's instructions carefully and follow the guidelines.
 Ask questions in the class by raising hand and avoid creating a disturbance.
 To be able to submit all assignments on time and get your sketch logbooks checked.

7. Lesson contents
Clinical chair side question: Students will be asked if they know what is the function of nucleus,
chromosome and gap junction.
Outline:
 Activity 1 The facilitator will explain the student's Nuclear component and Cell Junction
 Activity 2 The facilitator will ask the students to make a labeled diagram of the Gap Junction and
Nucleus
 Activity 3 The facilitator will ask the students a few Multiple Choice Questions related to it with
flashcards.

8.  Students assessment: MCQs, Flashcards, Diagrams labeling.
 Learning resources: Laiq Hussain Siddiqui, Snell Clinical Anatomy, Netter’s Atlas, BD Chaurasia’s
Human anatomy, Internet sources links.

9. Nuclear Structure &
Components
 NUCLEUS
 NUCLEOLUS
 CHROMOSOME
 FUNCTIONS IN CELL INTEGRITY

10. Objective
Nuclear structure & components:
 Describe the structure of the nucleus, nucleolus & chromosome and their functions
in cell integrity

11. Nucleus
 Contains: genetic material of cell
 Function: Has direct influence on
metabolic activities of cytoplasm
 Constant exchange of material
between nucleus & cytoplasm
 If removed cell dies
(Protein synthesis ceases)
 One nucleus per cell
(Except: Mature erythrocytes=
Incapable of protein synthesis & have
limited metabolic activity)

12.  Size: diameter range 3-10μm
 Shape: Spherical but maybe oval, fusiform, lobulated or irregular in shape
 Position in Cell: Depends on shape of cell
- Spherical & Polygonal cell= Located centerally but maybe be eccentric
- Cuboidal, Fusiform & Squamous cell= central position
- Columnar & Pyramidal Cell= Lies in basal region of cell
 Number: one nucleus per cell
- Binucleate: e.g., Liver cells
- Multinucleate: e.g., Skeletal muscle cells

13. Structure
 Nuclear Envelope: Nucleus of non-dividing cells
surrounded by it & Composed of:
1. Chromatin: Granules & particles -Basophillic
2. Nucleoli: 0ne or more darkly stained bodies
3. Ground substance or Nuclear Sap: Semifluid
material fills space within nucleus which is not
occupied by chromatin or nucleoli-Stained clear
or very pale.

15. Nuclear Envelope
 H&E stain
1. LM: Dark blue purple line
2. EM: 40nm thick, consist of 2 parallel unit membranes
separated by a narrow space called perinuclear
cisternal space.
a. Inner Nuclear Membrane: Present rigid network of
protein filaments called Nuclear Lamina. It
supports & stabilize nuclear envelope.
b. Outer Nuclear Membrane: Studded with ribosomes
and has continuity with rough endoplasmic reticulum
(RER). Hence perinuclear cisternal space is
connected to cisternae of RER

16.  Nuclear Pores: Circular opening in the nuclear envelop of
nucleus. Its formed by fusion of inner & outer membrane
layers of nuclear envelope
 Size: 50nm diameter
 Function: Serves as channels through which exchange of
materials between nucleus & cytoplasm occurs
 Nuclear pores contains nuclear pore complex which
consists of multi-domain protein structure arranged in an
octagonal symmetry with a central channel.
a. Ions & small molecules with diameter of 10nm or less pass
freely through it by simple diffusion without energy
b. Large molecules like m RNA (passing from nucleus to
cytoplasm) & histones (moving from cytoplasm to nucleus)
pass through it by a receptor-mediated transport.

17. Chromatin
H&E Stain
 LM: Fine to coarse granules distributed irregularly within nucleus,
Chromatin consists of DNA associated with protein called Histones’
 DNA exists in form of flexible rod-like structure called Chromosomes
 Chromosome: Maybe folded ,coiled or crumpled and form little
masses which are large enough to be stained ,visible under LM
called Heterochromatin or condensed chromatin. These are
inactive.
 Euchromatin or extended chromatin: straight or uncoiled parts of
chromosomes, invisible under LM. Hence nuclei containing large
amount of it gives a vesicular appearance in stained section. These
are metabolically active with regard to RNA synthesis

20.  EM: reveal smallest structural units of
chromatin are nucleosomes.
 Nucleosomes: 10nm diameter
particle consists of core of 8 histone
molecules wrapped by 2 complete
turns of DNA molecules (contains 150
base pairs)
 LINKER DNA: DNA extends to next
nucleosomes as 1.5nm filament.
 Structural organization of chromatin
referred as beads on string

22.  Chromatin Fibril: 30nm diameter, Formed by
coiling of a long strand of nucleosomes
 Each turn in coil of chromatin fibril consist of 6
Nucleosomes
 In heterochromatin: chromatin fibril are highly
folded & tightly packed on each other
 In Euchromatin: chromatin fibril are less
folded & more loosely arranged allowing
access of DNA polymerases to the DNA for
purpose of transcription

23. Chromosome
 Somatic cells (Humans): 46 chromosomes,Diploid Number
(Cell possesses 2 chromosomal sets, each set 23
chromosomes)
 Mature sex cell: 23 chromosomes, Hyploid Number (Greed
word:Single, indicates cell has one set of 23 chromosomes).
Each chromosomes in a hyploid cell has own distinctive size
& shape.
a. 1 is Sex Chromosome
b. 22 are Autosome
 Oocyte (Ovum): X sex chromosome
 Spermatozoon: X or Y sex chromosome

25.  At fertilization:
One pair contributed by spermatozoon
Other pair contributed by Ovum.
 Somatic cell Nucleus of Female: 44 autosomes & 2 X chromosomes. One of X
chromosomes remains condensed as small rounded body known as Nucleolar
satellite or bar body located close to nuclear membrane or near nucleolus.
 Somatic cell Nucleus of Male: 44 autosomes & 1X &1Y pair sex chromosomes
 Polyploid cells: Few cell types in human body have a chromosomes number more
than twice the hyploid number

28. Nucleolus
 Dense, roughly spherical intra-nuclear structure
 Not surrounded by membrane
 Only observed in resting cell (Disappears during cell division)
 Site of ribosomal RNA (rRNA) synthesis & assembly of
ribosomes.
 Variable size
 Well developed in cells engaged in active protein synthesis
 Some cell has more than one nucleoli
 H&E staining = basophilic

30.  Components: DNA, rRNA & proteins
 Nucleolar Organizer: DNA of Nucleolus
consists of portions of chromosomes that
contains genes which encode for rRNA.
 rRNA genes are transcribed by RNA
polymerase-1.
 Freshly transcribed rRNA molecules become
associated with (imported from cytoplasm) to
form ribosomal subunits,
 Ribosomal subunits pass back into cytoplasm
to aggregate into complete ribosomes.

32.  EM: Nucleolus appears as sponge like network of electron dense material.
 Pars granulosa: dense material has Granular appearance represents
maturing ribosomal subunits.
 Pars Fibrosa: densely packed filaments , represents newly transcribed rRNA
still unassociated with proteins.
 Nucleolonema: Network formed by granular & filamentous material
 Nucleolar organizer DNA: interstices of nucleolonema consists of light
stained regions. This DNA consists of portions of chromosomes which
contains genes loci that encodes rRNA. In humans exists on 5 pairs of
chromosomes i.e. 13, 14, 15, 21 and 22.

34. Cell Junctions

35. Objectives
Cell junction:
 Define cell junction
 Describe the structure and functions of the junctions.
 Discuss the junctions on the basal and lateral surfaces of the cell.
 Enlist the junctional complex.

36. Cell Junction or Intercellular Junction
 Cell is surrounded by extracellular space
 In tissues (e.g. epithelium) the intercellular
gap is reduced to about 20nm.
 Epithelial cell adhere to each other due to
presence of variety of adhesive glycoproteins
called cadherins in intercellular gaps.
 Cell or Intercellular Junction: Epithelial
(& other cells of body) shows local
specializations of cell membrane which helps
in cohesion & communication between
adjacent cells.

39. Types of Cell Junctions
 3 types
A. Occluding Junctions (Tight/occludens)
B. Adhering Junctions (Anchoring/Adherens)
C. Communicating Junctions (Gap)

41. A. Occluding Junction or Tight Junction
 Location: Found in epithelial tissues only
 Function: to join the epithelial cells tightly together, so that the epithelial sheet
forms an impermeable barrier, preventing the materials (water & other molecules)
from passing into the intercellular space
 2 types
1. Zonula occludens
2. Fascia occludens

42. 1. Zonula Occludens
 Zonula (Ring or belt shape): cell junction that encircles
the entire cell perimeter
 Function: to occlude intercellular space.
 EM: consists of series of focal fusions between the plasma
membranes of adjacent cells. More number of fusion sites
,more effective the occlusion of intercellular space (Sealing
capacity)
1. Few fusion sites: zonula occludens between epithelial
cells lining the proximal convoluted tubules of kidney
2. Several fusion sites: zonula occludens between epithelial
cells lining mucosa of intestine & urinary bladder

44.  Fusion site: Transmembrane proteins binds cell
membranes of cells.
2 types:
1. Occludins
2. Claudins
 The binding transmembrane proteins of adjacent
cell membranes traverse the intercellular space
and join in the intercellular space
 On cytoplasmic side: occludins & claudins are
reinforced by cytoplasmic zonula occludens
proteins ZO1, ZO2 & ZO3 .
 Actin filaments of cytoskeleton: attach to
zonula occludens through ZO1 proteins.

47. 2. Fascia Occludens
 Strip-like tight junction of limited extent
 Found: between endothelial cells lining the blood vessels

48. B. Adhering Junctions or Anchoring Junctions
 Function: provide adherence
cell-to-cell
or
cell-to-basal lamina
 4 Types
1. Zonula adherens
2. Fascia adherens
3. Macula adherens
4. Hemidesmosome

49. 1. Zonula adherens
 Belt like junction
 Encircles entire cell
 No fusion of cell membranes
 Intercellular gap: 20nm (Occupied by extracellular portions of
molecules of an adhesive transmembrane glycoprotein E-
cadherin.
 Extracellular portion of E-cadherin molecules of opposing cell
membranes are bound to each other inintercellular space by Ca+2
ions.
 On cytoplasmic side,tails of E-cadherin molecules are linked to
cytoplasmic anchoring proteins catenin & vinculin, which inturn bind
to actin filaments of cytoskeleton.

51. 2. Fascia adherens
 Strip like (NOT ring or belt like)
 Cardiac muscle cells are attached
to each other at longitudinal
terminations by this type cell
junctions

52. 3. Macula adherens or desmosomes
 Spot weld
 Randomly distributed along the lateral plasma membranes of
cell of simple epithelial (single layered) and throughout plasma
membranes of cell of stratified epithelia (multilayered)
 Found also between cardiac muscle cells
 EM: Cell membranes in region of cell junctions are far apart
30nm.
 Disc shaped electron dense attachment plaques are located
opposite each other on cytoplasmic aspect of plasma
membranes of 2 cells taking part in formation of desmosome.
 Fine electron dense line seems extending along midline of
comparatively wide intercellular gap
 Intermediate filaments of cytoskeleton seen anchored to
attached plaques.

54.  Intermediate filaments are either inserted into the attachment
plaque or make hairpin turns and extend back into the cytoplasm.
 In epithelial cells, keratin intermediate filaments are anchored to
the attachment plaques
 In cardiac muscle: anchoring intermediate filaments are of desmin
type.
 The attachment plaque is composed of anchoring cytoplasmic
proteins i.e desmoplakins & plakogolbins
 2 types of transmembrane glycoproteins of cadherin family provides
adherence in region of a desmosomes. These are
1. Desmocollins
2. Desmogleins

58.  The cytoplasmic aspects of these transmembrane
proteins bind to proteins of the attachement
plaque.
 Extracellular portions of desmocollins and
desmogleins extend into intercellular gap & bind
to similar proteins extending out of the cell
membrane of the adjoining cell
 Electron dense line in the middle of intercellular
gap represents the line of linkage between the
transmembrane glycoproteins of adjoining cells
 This linkage is dependent upon presence of Ca+2
ions

59. 4. Hemidesmosome
 Spot like adhering junction
 Gives appearance of half desmosomes
 Serves to anchor epithelial cells to their basal lamina
 Transmembrane linker proteins are integrins (NOT
cadherins)
 Extracellular portions of integrins bind to laminin & type
IV collagen present in basal lamina
 Intracellular parts of integrins bind to desmoplakins &
pectins present in attachment plaque of hemidesmosome
 Cytoplasmic intermediate filaments of keratin are seen to
be inserted into attachment plaque

61. C. Communicating Junctions
 Characterized by presence of minute tubular
passageways
 Function:
1. Provides direct cell –to-cell communication
2. Allow movement of ions & other small molecules
between adjacent cells.
3. Allow coordinated cellular activity by coupling the
adjacent cells metabolically as well as electrically.
 Type
1. Gap Junctions

62. 1. Gap Junctions or Nexus
 Communicating junction between epithelial cells, cardiac muscle cells, smooth muscle cells,
neurons, astrocytes & osteocytes
 No gap junction between skeletal muscle cells.
 Spot like structure
 Plasma membranes of adjoining cells are closely apposed with intercellular gap of 2nm.
 It contains closely packed array of many tubular intercommunicating channels is composed of 2
connexons: One belonging to plasmalemma of each of 2 cells participating in formation of gap
junction.
 Cylindrical wall of each connexon is formed by 6 transmembrane protein called Connexins.
 Connexon from one plasma membrane projects into intercellular gap to fuse with a connexon from
the apposing cell membrane, forming a tubular channel that directly interconnects 2 cells
 Lumens of intercommunicating channels of gap junctions have diameter 1.5nm. It permits free
passage for ions, cyclic AMP & GMP, amnino acids, sugars, and small molecules from one cell to
other.

64.  Different Connexons specifically allow passage of different ions & molecules
 This specificity depends on type of connexin protein forming connexon
wall (More than 20 connexin protein in human body identified).
 Permeability of gap junction: regulated (i.e connexons can be opened
/closed depending on intracellular conc. of Ca+2 ions & cytosolic PH.
 Normally cytosolic Ca+2 level remains below extracellular Ca+2 level. At
low Ca+2 conc. Connexons remain open
 Whenever intracellular Ca+2 conc. rises, connexons become closed.
Decrease in cytosolic PH cause closure of Connexons
 Cardiac & Smooth Muscle: gap junction function provide electrical coupling
of adjacent cells, waves of electrical excitation can spread unimpeded &
synchronous contraction of muscle take place
 Embryonic cells: gap junction helps in exchange of informational molecules
between developing cells.

66. Junctional Complex
 Junctional Complex: In many locations
e.g. Small intestinal mucosa Lateral
surfaces of adjacent Columnar epithelial
cells are bound to each other by series of
cell junctions called JC
 From apical to basal side junctional
complex has 3 components
1. Zonula Occludens
2. Zonula Adherens
3. Macula Adherens (Desmosomes)

68. Thank You

69. Multiple Choice Questions
1. Adherens junctions are specialized cell junctions that form by linking the __________ to transmembrane proteins known as __________
a) microtubule cytoskeleton . . . Cadherins
b) microtubule cytoskeleton . . . Integrins
c) intermediate filament cytoskeleton . . . Integrins
d) actin cytoskeleton . . . Cadherins*
2. Which of the following proteins forms channels that permit electrical communication between cells across gap junctions?
a) Ephrin
b) Cadherin
c) Connexin*
d) Catenin
e) Tubulin