2. CONNECTIVE TISSUES
• Connective tissue is the medium which
surrounds and supports the other tissues of the
body.
• Composed predominantly of intercellular
material (extracellular matrix) which is
secreted mainly by the connective tissue cells.
• The cells are usually widely separated by their
matrix, which is composed of fibrous proteins
and a relatively amorphous ground substance.
3. CT intro cont…
• General functions:
– Mechanical support.
– Connect different organs and structure.
– Exchange of material.
– Storage.
– Allows different physiological processes to
take place.
– Defensive role.
5. 1) Resident cells
• Those cells which are always found residing in the
connective tissue.
• Includes;
– Fibroblasts
– Macrophages (histiocytes)
– Mast cells
– Adipocytes
– Pigment cells (melanocytes)
6. Resident cells cont…
• A ) Fibroblasts:
– Are flat, spindle shaped cells with branching of
cytoplasmic processes with elliptical and elongated
nucleus.
– The shape differs depending on activity:
– Active fibroblasts have abundant cytoplasm
– Inactive fibroblasts (fibrocytes) are smaller and
have diminished cytoplasm.
– Fibroblasts are found in nearly all types of tissues
7. Functions of fibroblasts:
• i) Synthesis:
– Secretes connective tissue fibers, these include
collagen, elastic and reticular fibers.
– They also secrete substances such as
glycosaminoglycans and glycoproteins found in
the extracellular matrix (ground substance).
• ii) Differentiation into other cells:
– Fibroblasts are capable of changing into a variety
of cell types depending on the body need.
8. Fibroblasts cont…
• iii) Wound healing:
– Fibroblasts secrete connective tissue elements
which help in remodeling the extracellular matrix,
which is important in wound healing and tissue
repair.
– During wound healing the fibroblast acquires
contractile proteins to become the myofibroblast
which play an important role during wound
healing.
– Contraction causes the wound edges to unite,
which enhances wound healing.
9. Resident cells cont…
• B) Histiocytes (tissue macrophages).
– They are polymorphic cells and can be ovoid or
irregular with short and blunt processes.
– They are derived from blood monocytes, which
migrate into the tissues and transform to become
histiocytes.
– Main role in tissue is phagocytosis and antigen
presentation.
10. Resident cells cont…
• C) Mast cells:
– Are large cells, round or oval in shape.
– Play an important role in allergic reactions.
– Mast cells are filled with secretory granules that
are filled with substances of inflammation such as
histamine and heparin, SRS-A and ECF-A.
– Heparin, is an anticoagulant and Histamine, is
released by the cells under allergic conditions give
rise to oedema, bronchospasm and other forms of
allergic reactions to the surrounding tissues.
11. Mast cells cont…
• SRS-A(slow reacting substance of anaphysis)
when released increases the permeability of
small vessels, which cause local oedema.
• The eosinophilic chemotactic factor of
anaphylaxis (ECF-A) when released enhances
eosinophils to come to the site of inflammation
thereby counteracting the allergic effects of the
molecules.
12. 2) Wondering cells
• These are the cells which are temporarily
found within the connective tissues depending
on the needs of the body, example during
infection.
• They include monocytes, lymphocytes and
granulocytes.
13. Connective tissue fibers
• There three types of connective tissue fibers;
– Collagen fibers
– Elastic fibers
– Reticular fibers
14. a) Collagen fibers
• Most abundant fibers formed by the union of many
collagen fibrils, that are made up of collagen proteins.
• They are tough, inextensible and posses a high tensile
strength.
• They appear white in fresh sections.
• Form major part of tendons, ligaments, cartilage,
teeth (Dentin and cementum) and bones.
• There different types of collagen fibers
– Type I, II, III, and IV.
15. Characteristics of collagen fibers
1. Stretching is restricted.
– Each fiber is composed of a number of fibrils. The
fibers are strong and flexible but not elastic.
2. Found in all types of connective tissue proper and
in cartilages and bones, but are especially
abundant in tendons and aponeurosis.
3. Chemically, fibers are composed of an
albuminous protein (tropocollagen) which forms
the fundamental building units of collagen and
contains gelatin.
4. They are acidophilic in their staining reaction and
therefore take up eosin stain.
16. b) Elastic fibers
• Fine fibers that can allow some degree of distention
and stretching.
• When stretched they usually recover the original form
and dimension when the force is eliminated and the
elastic limit is not exceeded.
• They are made up of elastin protein (tropoelastin)
• Appear yellow in fresh sections.
• Elastic fibers changes as the age advances where it
looses its resilience.
• Stained by special stain such as Silver stain.
17. Elastic fibers cont…
• Elastic fibers exists as accompanying
structure of collagen fibers in the capsule
of many organs, vascular walls and the
elastic cartilage.
• Also in ligamentum nuchae and
ligamentum flava
18. c) Reticular fibers:
• Smaller fibers that branch and anastomose to
form a netlike supporting framework known as
reticulum.
• They are closely related to the collagen fibers
because they contain collagen fibrils and they
show cross-banding pattern, and are sometimes
continuous with collagen fibers.
• The first connective tissue fibers to appear
during embryonic development.
19. Reticular fibers cont…
• Reticular fibers form the supporting framework in the
hemopoietic (Bone marrow) and lymphoid organs
such as the thymus, lymph node, spleen.
• In these organs the reticular fibers are
produced by reticular cells.
• Also found in endocrine glands, small blood
vessels, veins, muscle cells, fat tissue, and in spaces
between the epithelium with connective tissue.
21. Reticular fibers cont…
• In these locations the reticular fibers are
produced by fibroblasts, smooth muscle cells,
and the Schwann cells produce reticular fibers
that surround the nerve fibers.
• In wound healing the reticular fibers are the
first to be formed and as the wound improves
they gradually change to become collagenous.
22. Ground Substance
• A non-fibrillar and amorphous in nature and are secreted by
the fibroblast.
• Has the same refractive index as water; hence it is not visible
when fresh spreads are mounted on aqueous solutions.
• Serves as a diffusion medium in the spaces around the
cells and fibers.
• Its not stained by routine histological methods.
• When stained with PAS, it is found to be PAS
positive.
• The consistency of ground substance shows a wide
variation between a semifluid and jelly, and this
depends on the functions of the tissue or organ.
23. GS cont…
• G.S consists of mucopolysaccharides;
– Sulphated
– Non-sulphated.
• The sulphated mucopolysaccharides include
chondroitin sulphate A, chondroitin sulphate C,
and chondroitin sulphate B.
• The cartilage contains large amounts of
sulphated mucopolysaccharides where they
provide support and flexibility.
24. GS cont…
• The non-sulphated mucopolysaccharides
include; hyaluronic acid and chondroitin.
– Hyaluronic acid is viscous fluid-like
mucopolysaccharides.
– It has the capacity of binding down water to
the tissues and therefore controls the
permeability of the ground substance.
• Hyaluronic acid is found in synovial fluid,
umbilical cord, and vitrous humor.
• Chondroitin is present in the cornea.
25. CLASSIFICATION OF CONNECTIVE TISSUES
• Is based on the density and organization of
the connective tissue cells and non-cellular
materials (fibers).
• The composition of connective tissue also
reflects the functions of particular tissues or
organs.
• So based on these CT are classified into;
– Connective tissue proper
– Specialized connective tissue
26. Connective Tissue proper
• CT proper consists of
– Loose Connective Tissue
– Dense Connective Tissue
• a) Loose connective tissue (areolar tissue):
– Contains more cells than fibers and the fibers are thinner,
delicate, sparse and loosely arranged
– Found around vessels, between muscle fibers, lamina
propria of the intestine and in fascial spaces.
– It forms the essential medium for the nutrients and waste
materials exchange between tissues and blood, and also
maintains osmotic pressure
29. CT proper cont…
• b) Dense connective tissue:
– Contains more fibers than the cellular component.
– Fibers are densely packed with little space for
ground substance.
• Types of dense CT:
– Based on the fiber arrangement and direction;
• Regular dense CT.
• Irregular dense CT.
• Embryonic tissue.
30. CT proper cont…
• Dense Irregular CT
– Fibers are irregularly arranged.
– Fibers are mainly collagen but in some
– Made up of elastic fibers e.g. walls of elastic arteries,
and elastic ligaments e.g. ligamentum flavum and
ligamentum nuchae.
– It forms the dermis of the skin, superficial fascia, fibrous
capsule of organs, tunica albuginea of the testis,
periosteum, perichondrium, epimysium, dura matter,
and septae and trabeculae in various glands.
– Also forms sheaths and fasciae e.g. the axillary sheath and
fascia lata of the thigh.
32. CT proper cont…
• Dense regular CT
– Predominant fibers are the collagen fibers
– The fibers are densely packed and
regularly arranged parallel to each other.
– Its arrangement gives rise to a strong
structure that withstands tension exerted in
one direction.
– Comprises tendons, ligaments and aponeuroses.
38. Adipose Tissue
• Formed by aggregation of fat cells (adipocytes) with
few other cells such as macrophages, fibroblasts, and
leukocytes.
• Basically it is a storage tissue that stores nutritive
material in the form of natural fat that can be used to
produce energy when the need arises.
• Other functions includes; protection and insulation
• Two types
– White adipose tissue
– Brown adipose tissue
39. White adipose tissue
• Is made up of unilocular adipocytes i.e. each cell
contains one large lipid vacuole, which fills the entire
cells.
• The nucleus and cytoplasm are pushed to the
periphery of the cell.
• They are organized into lobes and lobules separated
by septae that are predominantly made up of collagen
fibers.
• When fat cells aggregate together they appear yellow.
• This is due to the presence of lipofuchsin pigment in
fat cells.
41. Brown adipose tissue
• Made up of aggregation of multilocular adipocytes,
i.e. one cell contains numerous vacuoles (fat
droplets).
• Richly supplied with blood vessels.
– This make it appear light brown in colour when
viewed in fresh conditions.
• Present in the infants and newborn, and decreases
with age and may be replaced by white adipose
tissue.
• Found in the posterior cervical part, axilla, suprailiac
and peritoneal regions.
• Main function is to protect newborn from cold.
43. CARTILAGE
• It’s a tough specialized CT made up of cells, fibers
and ground substances.
• These elements make cartilage firm and compact.
• Cartilage is avascular.
• Cartilage cells
– Chondroblasts
– Chondrocytes
• Ground substance (matrix)
– It is homogenous and stains with basic dyes due to
presence of chondromucoprotein.
– It surrounds the lacunae in which the cartilage cells
lie.
44. • Fibres
• Are either collagen or elastic fibers.
• > Perichondrium
– It’s a specialized membrane that covers the cartilage.
– It’s a dense regular CT with many blood vessels and
nerve fibers.
– It made up of two layers
• Outer fibrous layer containing fibroblasts.
• Inner chondrogenic layer that contains undifferentiated
cells which can become chondroblasts or chondrocytes.
45. Cartilage cont…
Types of cartilages;
• Three types based on the types of fibers it
contains and the composition of the ground
substance.
1. Hyaline cartilage
2. Elastic cartilage
3. Fibrocartilage
46. 1) HYALINE CARTILAGE.
• Most abundant type of cartilage in human body.
• Its solid but flexible and can be cut with a knife.
– Consists of collagen fibers, cells and ground substance.
• Collagen fibers (collagen type II) are in a tightly
packed ground substance, which appear shiny as
glass.
• Microscopically;
– Chondrocytes are ovoid or spherical in shape with large
spherical centrally placed nucleus.
– Cells are in lacunae.
47. Hyaline cartilage cont…
– Hyaline cartilage is found;
• In the wall of the air passages of the conducting
part of the Respiratory tract including; nose,
larynx, trachea, bronchi,
• on the sternal ends of ribs, (costal cartilages)
• covers the articular surfaces of joints.
– During embryonic life it forms the cartilage
skeleton, from which the long bones
develop.
48. Functions of hyaline cartilage:
• a) Facilitation of joint movement:
– It lines the articular surfaces of all the synovial joints,
making them to be smooth.
• b) Support to the airways:
– Its firm and does not collapse hence it assist in keeping the
tubes patent.
• c) Growth:
– It forms nearly all bones of the fetal skeleton; these are
replaced by bone tissue except at the distal ends of long
bones where they form the epiphyseal cartilage.
– The epiphyseal cartilage is responsible for the longitudinal
growth of long bones in the body.
49. 2) ELASTIC CARTILAGE
• Contains elastic fibers as major component but
few collagen type II fibers.
• Chondrocytes occurs singly and in groups.
• Ground substance contains a network of
branching and anastomosing elastic fibers.
• Its more flexible and elastic.
50. Elastic cont…
• Elastic cartilage found in;
– epiglottis, auditory tube, pinna of the ear
(external ear), and the coniculate, cuneiform
and arytenoids cartilages of the larynx.
• Functions of the elastic cartilage are to provide
support and also to maintain the shape and
flexibility of the organs.
51. 3) FIBROCARTILAGE
• Has an opaque appearance and fibrous texture.
• Has numerous visible type I collagen fibers
and sparse ground substance.
• Its not surrounded by perichondrium.
• Intercellular substance contains thick bundles
of collagen fibers which run parallel to one
another, and are separated by narrow areas of
non-fibrous matrix in which cartilage cells are
lodged.
52. Fibrocartilage cont…
• Found in areas where firm support and tensile
strength are required
• e.g. the intervertebral discs, pubic symphysis,
articular discs in joints, the cartilaginous lining
of bony grooves in which tendons are lodged
and rims of certain articular cartilages.
• Functions:
– a) Shock absorber:
– b) Joint stability.
54. Bone
• Bone is a hard and rigid tissue that forms the
bony skeleton of the body.
– Bone supports the body weight,
– it provides attachment to muscles,
– acts as lever for movements, and provides
protection to organs.
– Inside the bone there are spaces, which are filled
with the bone marrow that produce red blood cells,
platelets and cells of the immune system.
55. Bone cont…
• Cells of the immune system produced in bone
marrow include monocytes, lymphocytes, mast cells,
neutrophils, eosinophils and basophils.
• Bone consists of:
– cells,
– fibers
– ground substances.
• The only difference with other connective tissues is
that its ground substance is made up of inorganic
salts, mostly calcium ions.
• The bone is highly vascularized, and in living
conditions the bone appears pinkish in color.
56. Bone cont…
• Bone Cells
– The bone contains four types of cells namely the
osteoprogenator cells, osteoblasts, osteocytes,
and the osteoclasts.
• Bone matrix (Intercellular substance)
– It is made up of the collagen fibers
(osteocollagenous fibers), amorphous ground
substance and inorganic salts which constitute
about 74% of bone mass.
57. Classification of bone tissue
• Can be classified basing on the gross
appearance and histologically.
• Basing on gross appearance
– Long bones
– Short bones
– Flat bones
58. Bone cont…
• Histologically bone tissue is generally
classified into two types
1. Compact (cortical) bone
2. Cancellous (spongy) bone
But many bones have both the compact and
spongy portions
The compact bone is found on the outer parts and
inner to it is the spongy bone.
59. Bone cont…
• Compact (cortical) bone
– Under the microscope the compact bone is made
up of calcified matrix arranged in thin layers
known as lamellae.
• Spongy (cancellous) bone
– It is composed of bony spicules and plates that
branch and anastomose with one another to
form a meshwork.
– The spaces or cavities in the meshwork are filled
with bone marrow.
60. Bone cont…
– Microscopically the spongy bone is also
lamellated.
• HARVESIAN SYSTEM
• Harvesian canals are the longitudinal channels
that traverse the bone longitudinally and they
branch and anastomose freely.
• This ensures nutrient supply to the bone tissue
because each contains blood vessels,
lymphatics and nerve fibers.
61. Bone cont…
• The lamellae, osteocyte, and blood vessels
within the Harvesian canal form units of
bone referred to as the Harvesian system or
osteon.
62. Lacunae and Canaliculli
• Within the lamellae there are lacunae and
canaliculi:
• Lacunae;
– Are small bone cavities that contain the osteocytes
• Canaliculi;
– Are microscopic channels, which radiate from the
lacunae and are normally occupied by cytoplasmic
processes of osteocytes.
63. Inorganic matter (Salts)
• Inorganic matter constitutes about two-thirds of
the weight of bone
• The major component is calcium phosphates
(85%), calcium carbonate (10%) and small
amounts of calcium fluoride and magnesium
chloride.
• Calcium phosphate is in the form of
hydroxyapatite crystals [Ca10 (PO4)6(OH)3].
64. Periosteum
• A special connective tissue membrane that covers the
outer surface of bone.
• It is composed of mostly collagen fibers, and few
elastic fibers.
• It covers most of bone surface up to the margins of
articular surfaces where it becomes continuous with the
fibrous capsule of the joints.
• In the bones of the limbs and at the sites of attachment
of muscles, tendon and ligaments the periosteum is
firmly adherent to the bone through strong Sharpey’s
fibers.
65. • It is composed of
– Outer fibrous layer.
– Inner cellular layer.
• The inner layer (Osteogenic layer)
– Contains cells that are capable of forming bone.
– i.e. osteoprogenator cells, which are capable of
being transformed into fibroblasts and osteoblasts.
• The outer layer (fibrous layer)
– Contains mainly fibers and large vessels and
nerves that branch to enter/leave the bone.
66. Functions of the periosteum
• i) Osteogenic activity:
– The cells in the periosteum can differentiate into bone forming
cells and begin the process of lying down bone.
– This is particularly true during healing of fracture and during
bone growth.
• ii) Entry of vessels:
– It facilitates entry of blood vessels, lymphatic vessels and nerves
into the bone.
– Periosteum has many vessels, which pass to enter the bone via
the Volkman’s canals and nutrient foramina.
• iii) Muscle attachment:
– Facilitates attachment of muscles, tendons, and ligaments to the
bone.
– Tendons utilize these collagen fibers to attach to the bone.
67. Endosteal membrane
• The endosteal membrane is equivalent
to the periosteum and it lines the inner
surfaces of bone marrow cavities.
68. Bone formation
• Bone formation is commonly referred to
ossification and it occurs in two environments or
in two processes:
– within membranes and in the cartilaginous
models ossification.
• The site of bone formation is identified and bone
models are laid down either as membranes or
as cartilages; this is followed by appearance of
osteoblasts, which secrete bone matrix that
become calcified.
69. Bone formation
• Generally flat bones develop by
intramembranous ossification while long
bones develop by intracartilagenous
ossification
70. Intramembranous
ossification
• Intramembranous ossification is a process whereby
bone is formed by msc/s. into osteoblasts
• The bones that form by this process include most
of skull bones such as frontal, parietal, maxilla,
mandible, clavicle and parts of occipital and
temporal bones.
• Bone formation occurs in four main stages;
these are:
– development of the ossification centers (special
membrane),
– Formation of bone matrix
– deposition of minerals or calcification,
– formation of trabeculae and appearance of periosteum.
71. Endochondral ossification
• In endochondral ossification bone is formed from the pre-
existing hyaline cartilage that has the shape that closely
resembles the bone to be formed.
• Most long and irregular bones form via endochondral
ossification, such as the base of the skull, vertebral
column, the pelvis and bones of the extremities
(limbs).
• During this process the cartilage is gradually replaced by
bone
• Only a small amount of cartilage remains covering the
articular surfaces of the joints.
• During endochondral ossification the bone also
grows in length and width.
72. Bone remodeling
• Remodeling and reorganization
– bone undergoes continuous surface and
internal remodeling and reorganization to
maintain bone size and shape.
– Remodeling involves bone resorption and
deposition and takes place in compact as well
as trabecular bone
73. Bone marrow
• There are two types of bone marrow (Red and Yellow bone
marrow)
• Bone marrow is a connective tissue
• Location: It is located in the central part of the compact bone in
long bones and spaces between the trabeculae of spongy bones.
• It is made up of cells, (Stem cells, reticular cells,
macrophages), framework of reticular fibers and blood
vessels. The reticular cells and macrophages lie along the reticular
fibers.
• There are two types of stem cells in the bone marrow; these
are the
– haemopoietic cells which differentiate to give rise into blood cells
(leukocytes, erythrocytes and megakaryocytes) and
– mesenchymal cells.
• The mesenchymal cells are also known as ‘gatekeeper’ cells; they
are capable of giving rise into many tyepes of cells such as
osteoblasts, chondrocytes and myocytes.
74. Bone marrow
• The bone marrow contains a large number
of specialized capillaries known as
sinusoids. The sinusoids have pores in
their walls and are lined by phagocytic
cells. Pores allow the newly produced
blood cells to gain access to the
circulation.
• Lymphatic vessels have not been
demonstrated in the bone marrow.
75. Red bone marrow
• The red bone marrow is generally present in all bones up to the
time of puberty; thereafter it gradually disappears and become
replaced by the yellow bone marrow in advanced age.
• In adult bone it is mainly found in the epiphyses of long bones, in
the sternum, scapulae, pelvis, ribs, vertebrae and the cranial bones.
• The main function of the red bone marrow to generate cells of the
blood; it is a blood forming tissue. The process of blood cell
formation is also called haemopoiesis.
• The bone marrow contains multipotent haemopoietic sterm
cells (MHSC) or the haemocytoblasts that give rise to white
blood cells, red blood cells and platelets.
• Production of blood cells by the bone marrow occurs after
stimulation of the MSHC and factors and hormones such as
interleukin-7, interleukin-11, erythropoietin, thrombopoetin and
granulocyte-macrophage colony stimulating factor are known to
enhance the stem cells to begin the process of producing a specific
type of blood cell.
76. Yellow bone marrow
• The yellow bone marrow occurs in all other sites
and is mainly composed of fat tissue, which gives
its yellow color.
• It is not involved in the process of blood cell
formation.
• However, in situation where haemopoesis is over
activated the yellow marrow disappears and is
replaced by the red marrow.
• Such situation include severe haemorrhage and in
neoplastic diseases such as leukemia.
77. BLOOD TISSUE
– Blood plasma
– Blood corpuscles
• Red blood cells
• White blood cells
• Blood Platelets
