1. Connective Tissue

2. Most abundant and widely distributed tissue type
Connective Tissue
Most abundant and widely distributed tissue type
Four classes
Connective tissue proper
Cartilage
Bone tissue
Blood

3. Table 4.1

4. Functions of Connective Tissue
Binding structures - connects tissues to one another – Tendons & ligaments
Provide support and movement – bones
Protection – bones, cells of the immune system.
Serve as framework
Transportation -blood
Storage - fat
Insulation - fat

5. Characteristics of Connective Tissue
Connective tissues:
Most abundant tissue type
Varying degrees of vascularity
Cells separated by nonliving extracellular matrix [ECM] (ground substance and fibers)
Cells are not as abundant nor as tightly packed together as in epithelium

6. Structural Elements of Connective Tissue
The major components of CT:
Matrix
Cells

7. Structural Elements of Connective Tissue Matrix
Connective Tissues do not form cellular membranes like epithelial tissues.
Instead, scattered cells are dispersed in a substance called ECM (extracellular matrix).
The matrix constitutes the nonliving extracellular material.
The characteristics of the matrix are responsible for the nature of the specific CT.
Two materials compose the matrix:
Ground substance
Fibers

8. Structural Elements of Connective Tissue
Ground substance
Homogeneous material consisting largely of a complex mixture of proteins produced by CT cells.
Medium through which solutes (nutrients) diffuse between blood capillaries and cells
It occupies the area around the cells and fibers
Components:
Interstitial fluid
Adhesion proteins (“glue”)
Proteoglycans
Protein core + large polysaccharides (chrondroitin sulfate and hyaluronic acid)
Trap water in varying amounts, affecting the viscosity of the ground substance

9. Structural Elements of Connective Tissue
Fibers – three types
Collagenous – “white fibers”
Composed of collagen (white fibers)
Strongest and most abundant type (dense CT)
Provides high tensile strength
Holds structures together
Tendons, ligaments
Elastic – “yellow fibers”
Networks of long, thin, elastin fibers that allow for stretch & recoil
Vocal Cords and air passages
Reticular
Short, fine, highly branched collagenous fibers
Form supportive networks & provides strength

10. Structural Elements of Connective Tissue Cells
Cells – varies according to tissue
The structural cell for the tissue is commonly named according to the tissue type (prefix) and its activity (suffix)
Mitotically active and/or building cell/secretory cells = “blasts”
Mature nondividing maintenance cell = “cytes”
Fibroblasts in connective tissue proper
Chondroblasts and chondrocytes in cartilage
Osteoblasts and osteocytes in bone
Hematopoietic stem cells in bone marrow
Fat cells, white blood cells, mast cells, and macrophages

11. Structural Elements of Connective Tissue Major Cell Types Present
Fibroblasts
Fixed cell
Most common cell
large, star-shaped
Produce fibers
Macrophages
Wandering Cell
Phagocytic
Important in injury or infection
Mast Cells
Fixed cell
Release heparin
Release histamine

12. Cell types Extracellular matrix Ground substance Macrophage Fibers
• Collagen fiber
• Elastic fiber
• Reticular fiber
Fibroblast
Lymphocyte
Fat cell
Capillary
Mast cell
Neutrophil
Figure 4.7

13. Classification of Connective Tissues
CT classification is based upon these three structural characteristics of the matrix:
Types of fibers
Type of ground substance, and
The structural arrangement

14. Classification of Connective Tissues

15. Classification of Connective Tissues

16. Overview of Connective Tissues
For each of the following examples of connective tissue, note:
Description
Function
Location

17. Connective Tissue Proper
Matrix: Flexible, viscous ground substance & have abundant fibers
Cells: Structural cells called fibroblasts
Types:
Loose connective tissue – has a loose arrangement of fibers
Areolar
Adipose
Reticular
Dense connective tissue – has a dense arrangement of fibers
Dense regular
Dense irregular
Elastic

18. Loose CT - Areolar
(a) Connective tissue proper: loose connective tissue, areolar
Description: Gel-like matrix with all
three fiber types; cells: fibroblasts,
macrophages, mast cells, and some
white blood cells.
Elastic
fibers
Function: Wraps and cushions
organs; its macrophages phagocytize
bacteria; plays important role in
inflammation; holds and conveys
tissue fluid.
Collagen
fibers
Location: Widely distributed under
epithelia of body, e.g., forms lamina
propria of mucous membranes;
packages organs; surrounds
capillaries.
Fibroblast
nuclei
Epithelium
Photomicrograph: Areolar connective tissue, a
soft packaging tissue of the body (300x).
Lamina
propria
Figure 4.8a

19. Loose CT - Adipose
(b) Connective tissue proper: loose connective tissue, adipose
Description: Matrix as in areolar,
but very sparse; closely packed
adipocytes, or fat cells, have
nucleus pushed to the side by large
fat droplet.
Function: Provides reserve food
fuel; insulates against heat loss;
supports and protects organs.
Nucleus of
fat cell
Location: Under skin in the
hypodermis; around kidneys and
eyeballs; within abdomen; in breasts.
Adipose
tissue
Vacuole
containing
fat droplet
Photomicrograph: Adipose tissue from the
subcutaneous layer under the skin (350x).
Mammary
glands
Figure 4.8b

20. Loose CT - Reticular
(c) Connective tissue proper: loose connective tissue, reticular
Description: Network of reticular
fibers in a typical loose ground
substance; reticular cells lie on the
network.
Function: Fibers form a soft internal
skeleton (stroma) that supports other
cell types including white blood cells,
mast cells, and macrophages.
White blood
cell
(lymphocyte)
Location: Lymphoid organs (lymph
nodes, bone marrow, and spleen).
Reticular
fibers
Spleen
Photomicrograph: Dark-staining network of reticular
connective tissue fibers forming the internal skeleton
of the spleen (350x).
Figure 4.8c

21. Dense CT – Dense regular
(d) Connective tissue proper: dense connective tissue, dense regular
Description: Primarily parallel
collagen fibers; a few elastic fibers;
major cell type is the fibroblast.
Collagen
fibers
Function: Attaches muscles to
bones or to muscles; attaches bones
to bones; withstands great tensile
stress when pulling force is applied
in one direction.
Location: Tendons, most
ligaments, aponeuroses.
Nuclei of
fibroblasts
Shoulder
joint
Ligament
Photomicrograph: Dense regular connective
tissue from a tendon (500x).
Tendon
Figure 4.8d

22. Dense CT – Dense irregular
(e) Connective tissue proper: dense connective tissue, dense irregular
Description: Primarily
irregularly arranged collagen
fibers; some elastic fibers;
major cell type is the fibroblast.
Nuclei of
fibroblasts
Function: Able to withstand
tension exerted in many
directions; provides structural
strength.
Location: Fibrous capsules of
organs and of joints; dermis of
the skin; submucosa of
digestive tract.
Collagen
fibers
Fibrous
joint
capsule
Photomicrograph: Dense irregular
connective tissue from the dermis of the
skin (400x).
Figure 4.8e

23. Dense CT - Elastic
(f) Connective tissue proper: dense connective tissue, elastic
Description: Dense regular
connective tissue containing a high
proportion of elastic fibers.
Function: Allows recoil of tissue
following stretching; maintains
pulsatile flow of blood through
arteries; aids passive recoil of lungs
following inspiration.
Elastic fibers
Location: Walls of large arteries;
within certain ligaments associated
with the vertebral column; within the
walls of the bronchial tubes.
Aorta
Photomicrograph: Elastic connective tissue in
the wall of the aorta (250x).
Heart
Figure 4.8f

24. Connective Tissue: Cartilage
Three types of cartilage:
Hyaline cartilage
Elastic cartilage
Fibrocartilage

25. Cartilage - Hyaline (g) Cartilage: hyaline
Description: Amorphous but firm
matrix; collagen fibers form an
imperceptible network; chondroblasts
produce the matrix and when mature
(chondrocytes) lie in lacunae.
Function: Supports and reinforces;
has resilient cushioning properties;
resists compressive stress.
Location: Forms most of the
embryonic skeleton; covers the ends
of long bones in joint cavities; forms
costal cartilages of the ribs; cartilages
of the nose, trachea, and larynx.
Chondrocyte
in lacuna
Matrix
Costal
cartilages
Photomicrograph: Hyaline cartilage from the
trachea (750x).
Figure 4.8g

26. Cartilage - Elastic (h) Cartilage: elastic
Description: Similar to hyaline
cartilage, but more elastic fibers
in matrix.
Function: Maintains the shape
of a structure while allowing
great flexibility.
Chondrocyte
in lacuna
Location: Supports the external
ear (pinna); epiglottis.
Matrix
Photomicrograph: Elastic cartilage from
the human ear pinna; forms the flexible
skeleton of the ear (800x).
Figure 4.8h

27. Cartilage - Fibrocartilage
(i) Cartilage: fibrocartilage
Description: Matrix similar to
but less firm than that in hyaline
cartilage; thick collagen fibers
predominate.
Function: Tensile strength
with the ability to absorb
compressive shock.
Location: Intervertebral discs;
pubic symphysis; discs of knee
joint.
Chondrocytes
in lacunae
Intervertebral
discs
Collagen
fiber
Photomicrograph: Fibrocartilage of an
intervertebral disc (125x). Special staining
produced the blue color seen.
Figure 4.8i

28. Connective Tissue: Other
Bone
Two structural types of bone
Compact
Spongy
Blood
Atypical CT
Develops from mesenchyme
Consists of cells surrounded by nonliving matrix

29. Bone Tissue (j) Others: bone (osseous tissue)
Description: Hard, calcified
matrix containing many collagen
fibers; osteocytes lie in lacunae.
Very well vascularized.
Central
canal
Function: Bone supports and
protects (by enclosing);
provides levers for the muscles
to act on; stores calcium and
other minerals and fat; marrow
inside bones is the site for blood
cell formation (hematopoiesis).
Lacunae
Lamella
Location: Bones
Photomicrograph: Cross-sectional view
of bone (125x).
Figure 4.8j

30. Blood Tissue (k) Others: blood Description: Red and white
blood cells in a fluid matrix
(plasma).
Plasma
Function: Transport of
respiratory gases, nutrients,
wastes, and other substances.
Neutrophil
Location: Contained within
blood vessels.
Red blood
cells
Lymphocyte
Photomicrograph: Smear of human blood (1860x); two
white blood cells (neutrophil in upper left and lymphocyte
in lower right) are seen surrounded by red blood cells.
Figure 4.8k

31. Nervous Tissue
Nervous system (more detail with the Nervous System, Chapter 11)

32. Nervous tissue
Description: Neurons are
branching cells; cell processes
that may be quite long extend from
the nucleus-containing cell body;
also contributing to nervous tissue
are nonirritable supporting cells
(not illustrated).
Nuclei of
supporting
cells
Neuron processes
Cell body
Axon
Dendrites
Cell body
of a neuron
Function: Transmit electrical
signals from sensory receptors
and to effectors (muscles and
glands) which control their activity.
Neuron
processes
Location: Brain, spinal
cord, and nerves.
Photomicrograph: Neurons (350x)
Figure 4.9

33. Muscle Tissue
Skeletal muscle (more detail with the Muscular System, Chapter 10)

34. Description: Long, cylindrical, multinucleate cells; obvious
(a) Skeletal muscle
Description: Long, cylindrical,
multinucleate cells; obvious
striations.
Striations
Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression;
voluntary control.
Nuclei
Location: In skeletal muscles
attached to bones or
occasionally to skin.
Part of
muscle
fiber (cell)
Photomicrograph: Skeletal muscle (approx. 460x).
Notice the obvious banding pattern and the
fact that these large cells are multinucleate.
Figure 4.10a

35. Muscle Tissue
Cardiac muscle (more detail with the Cardiovascular System, Chapters 18 and 19)

36. Description: Branching, striated, generally uninucleate
(b) Cardiac muscle
Description: Branching,
striated, generally uninucleate
cells that interdigitate at
specialized junctions
(intercalated discs).
Striations
Intercalated
discs
Function: As it contracts, it
propels blood into the
circulation; involuntary control.
Location: The walls of the
heart.
Nucleus
Photomicrograph: Cardiac muscle (500X);
notice the striations, branching of cells, and
the intercalated discs.
Figure 4.10b

37. Muscle Tissue
Smooth muscle

38. Description: Spindle-shaped cells with central nuclei; no
(c) Smooth muscle
Description: Spindle-shaped
cells with central nuclei; no
striations; cells arranged
closely to form sheets.
Smooth
muscle
cell
Function: Propels substances
or objects (foodstuffs, urine,
a baby) along internal passage-
ways; involuntary control.
Location: Mostly in the walls
of hollow organs.
Nuclei
Photomicrograph: Sheet of smooth muscle (200x).
Figure 4.10c

39. Epithelial Membranes
Cutaneous membrane (skin) (More detail with the Integumentary System, Chapter 5)

40. (a) Cutaneous membrane (the skin) covers the body surface.
Figure 4.11a

41. Epithelial Membranes Mucous membranes Mucosae
Line body cavities open to the exterior (e.g., digestive and respiratory tracts)

42. (b) Mucous membranes line body cavities open to the exterior.
Mucosa of
nasal cavity
Mucosa of
mouth
Esophagus
lining
Mucosa of
lung bronchi
(b) Mucous membranes line body cavities open to the exterior.
Figure 4.11b

43. Epithelial Membranes Serous Membranes
Serosae—membranes (mesothelium + areolar tissue) in a closed ventral body cavity
Parietal serosae line internal body walls
Visceral serosae cover internal organs

44. (c) Serous membranes line body cavities closed to the exterior.
Parietal
peritoneum
Parietal
pleura
Visceral
pleura
Visceral
peritoneum
Parietal
pericardium
Visceral
pericardium
(c) Serous membranes line body cavities closed to the exterior.
Figure 4.11c

45. Steps in Tissue Repair Inflammation Release of inflammatory chemicals
Dilation of blood vessels
Increase in vessel permeability
Clotting occurs

46. Blood clot in incised wound Vein
Scab
Epidermis
Blood clot in incised wound
Vein
Migrating white blood cell
Inflammatory chemicals
Artery 1
Inflammation sets the stage:
• Severed blood vessels bleed and inflammatory chemicals are released.
• Local blood vessels become more permeable, allowing white blood cells, fluid, clotting proteins and other plasma proteins to seep into the injured area.
• Clotting occurs; surface dries and forms a scab.
Figure 4.12, step 1

47. Organization and restored blood supply
Steps in Tissue Repair
Organization and restored blood supply
The blood clot is replaced with granulation tissue
Epithelium begins to regenerate
Fibroblasts produce collagen fibers to bridge the gap
Debris is phagocytized

48. Regenerating epithelium
Area of granulation tissue ingrowth
Fibroblast
Macrophage 2
Organization restores the blood supply:
• The clot is replaced by granulation tissue, which restores the vascular supply.
• Fibroblasts produce collagen fibers that bridge the gap.
• Macrophages phagocytize cell debris.
• Surface epithelial cells multiply and migrate over the granulation tissue.
Figure 4.12, step 2

49. Regeneration and fibrosis
Steps in Tissue Repair
Regeneration and fibrosis
The scab detaches
Fibrous tissue matures; epithelium thickens and begins to resemble adjacent tissue
Results in a fully regenerated epithelium with underlying scar tissue

50. Regenerated epithelium
Fibrosed area 3
Regeneration and fibrosis effect permanent repair:
• The fibrosed area matures and contracts; the epithelium thickens.
• A fully regenerated epithelium with an underlying area of scar tissue results.
Figure 4.12, step 3

51. Developmental Aspects
Primary germ layers: ectoderm, mesoderm, and endoderm
Formed early in embryonic development
Specialize to form the four primary tissues
Nerve tissue arises from ectoderm
Muscle and connective tissues arise from mesoderm
Epithelial tissues arise from all three germ layers

52. 16-day-old embryo (dorsal surface view) Muscle and connective
tissue (mostly from
mesoderm)
Ectoderm
Mesoderm
Nervous tissue
(from ectoderm)
Endoderm
Epithelium
Figure 4.13