1. Laboratory Exercise 5
“Histology”

2. Histology
In this exercise, you will identify the four major types of tissues and their subtypes (histology), and relate characteristics of each tissue type with its function and location in the human body.
These terms should be familiar to you: Epithelial (simple, stratified, psedostratified, squamous, cuboidal, columnar, transitional; cilia, villi, goblet), Connective (loose [areolar or adipose], dense, cartilage [chondrocytes, lacunae, chondroitin], bone [osteocytes, lacnae, canaliculi, fluid [RBC, WBC, plasma), Muscle (skeletal, smooth, cardiac; striations, nuclei, intercalation) and Nervous tissue (neurons, glia; soma, axon, dendrite).
This laboratory exercise correlates with Chapter 4 of your lecture textbook; Exercise 5 of your laboratory manual

3. Laboratory Lecture

4. An Introduction to Tissues (Histology)
Tissues are structures with discrete structural and functional properties
Tissues in combination form organs, such as the heart or liver
Organs can be grouped into 11 organ systems
Histology is the study of tissues

5. There are Four Types of Tissue
Tissues are collections of cells and cell products that perform specific, limited functions
Four types of tissue
Epithelial tissue covers the body, lines body cavities, internal passages and forms glands
Connective tissue provides protection, support, immunity, energy storage (fat) and transportation
Muscle tissue facilitates body movement, heat generation and material movement
Neural tissue detects stimuli and responds

6. Epithelial Tissue
Epithelial tissue is composed of epithelia and glands:
Epithelia are layers of cells covering internal or external surfaces (singular – epithelium)
Glands are structures that produce secretions
The functions of epithelial tissue include:
Providing Physical Protection
Controlling Permeability
Providing Sensation
Produce Specialized Secretions (from the glandular epithelium)

7. Note: We will not examine gland histology in lab.

8. Epithelia is characterized by:
Polarity (apical and basolateral surfaces) – necessary for cellular (epithelial) function
Intercellular connections (at cell junctions) – facilitating support and communication
Attachment to a structural element (basement membrane or basal lamina)
Avascularity (no blood vessels) – blood has to diffuse to these tissues
Regeneration – germinative cells near the basement membrane divide by mitosis and replace cells

9. A little more about polarity, connections and attachment…
Apical surfaces
Microvilli increase absorption & secretion
Cilia move fluid
Basolateral surface
Cell attachment to the basement membrane and adjacent epithelia

10. 2. Intercellular Connections
Support and communication is facilitated by extracellular proteins (ropes that tie cells together)
CAM’s (cell adhesion molecules) are transmembrane proteins
Proteoglycans are intercellular cement
Glycosaminoglycans – made of (hyaluronic acid)
The contact points are termed Cell junctions
Tight junctions
Gap junctions
Desmosomes

11. Animation: Tight Junctions
Tight junctions prevent
fluid from moving
across a layer of cells
0.5 µm
Tight junction
Animation: Desmosomes
Intermediate
filaments
Desmosome
Desmosome
Gap
junctions
1 µm
Figure 6.32 Intercellular junctions in animal tissues
Animation: Gap Junctions
Extracellular
matrix
Space
between
cells
Gap junction
Plasma membranes
of adjacent cells
0.1 µm

12. supplemental slide
At tight junctions, membranes of neighboring cells are pressed together, preventing leakage of extracellular fluid
They are usually found near the apical surface of a cell
Isolates contents of the lumen from the basolateral side
Desmosomes (anchoring junctions) fasten cells together into strong sheets
Hemidesmosomes attach cells to the basal lamina
Gap junctions (communicating junctions) provide cytoplasmic channels between adjacent cells
They allow rapid communication between cells, like in cardiac and smooth muscle tissue (functional syncytium)

13. supplemental slide tight junction gap junction hemidesmosome
Interlocking junctional proteins
Tight junction
tight junction
Adhesion belt
Terminal web
Spot desmosome
Adhesion belt
Gap junctions
Hemidesmosome
gap junction
Embedded proteins (connexons)
Intermediate filaments
Clear layer
Basement membrane
Dense layer
Dense area
hemidesmosome
Cell adhesion molecules (CAMs)
Proteoglycans
spot desmosome 13

14. 3. Attachment to a structural element
The clear layer (lamina lucida) is composed of thin fibers
It is secreted by epithelia and is a barrier to proteins
The dense layer (lamina densa) is composed of thick fibers
It is produced by connective tissue, providing strength and filtration

15. Classification of Epithelia
(Singular = Epithelium; Plural = Epithelia)
There are two classes of epithelia
The first is based on shape
Squamous epithelia is thin and flat
Cuboidal epithelia is square shaped
Columnar epithelia is tall, slender rectangles
The second is based on layers
Simple epithelium has a single layer of cells
Stratified epithelium has several layers of cells

16. 16

17. …the upcoming slides show the different kinds of epithelia in our bodies they are a blending of shape and layering! This is PERFECT lab practical exam material!

18. Figure 4-3a Squamous Epithelia
Simple Squamous Epithelium
LOCATIONS: Mesothelia lining ventral body cavities; endothelia lining heart and blood vessels; portions of kidney tubules (thin sections of nephron loops); inner lining of cornea; alveoli of lungs
FUNCTIONS: Reduces friction; controls vessel permeability; performs absorption and secretion
Cytoplasm
Nucleus
Connective tissue
LM  238
Lining of peritoneal cavity
One flat layer of cells – permeability; i.e. capillaries! 18

19. Figure 4-3b Squamous Epithelia
Stratified Squamous Epithelium
LOCATIONS: Surface of skin; lining of mouth, throat, esophagus, rectum, anus, and vagina
FUNCTIONS: Provides physical protection against abrasion, pathogens, and chemical attack
Squamous superficial cells
Stem cells
Basement membrane
Connective tissue
Surface of tongue
LM  310
Many flat layers of cells – physical protection; i.e. skin! 19

20. Figure 4-4a Cuboidal and Transitional Epithelia
Simple Cuboidal Epithelium
LOCATIONS: Glands; ducts; portions of kidney tubules; thyroid gland
Connective tissue
FUNCTIONS: Limited protection, secretion, absorption
Nucleus
Cuboidal cells
Basement membrane
Kidney tubule
LM  650
One cuboidal layer of cells – secretion and absorption; i.e. kidney tubule cells! 20

21. Figure 4-4b Cuboidal and Transitional Epithelia
Stratified Cuboidal Epithelium (RARE)
LOCATIONS: Lining of some ducts (rare)
FUNCTIONS: Protection, secretion, absorption
Lumen of duct
Stratified cuboidal cells
Basement membrane
Nuclei
Connective tissue
Sweat gland duct
LM  500
(RARELY SEEN) Many cuboidal layers of cells – permeability; i.e. sweat gland duct! 21

22. Transitional Epithelium is an unusual stratified type:
It tolerates repeated cycles of stretching and recoiling and returns to its previous shape without damage
The Appearance changes as stretching occurs
Transitional Epithelium
LOCATIONS: Urinary bladder; renal pelvis; ureters
FUNCTIONS: Permits expansion and recoil after stretching
Epithelium (relaxed)
Basement membrane
Connective tissue and smooth muscle layers
Empty bladder
LM  400
Epithelium (stretched)
Basement membrane
LM  400
Connective tissue and smooth muscle layers
Full bladder
LM  400
Urinary bladder
Many unusual cuboidal layers of cells – expansive; i.e. bladder! 22

23. Figure 4-5a Columnar Epithelia
Simple Columnar Epithelium
LOCATIONS: Lining of stomach, intestine, gallbladder, uterine tubes, and collecting ducts of kidneys
Microvilli
Cytoplasm
FUNCTIONS: Protection, secretion, absorption
Nucleus
Basement membrane
Loose connective tissue
Intestinal lining
LM  350
One columnar layer of cells – permeability; i.e. intestinal lining! 23

24. Figure 4-5b Columnar Epithelia
Pseudostratified Ciliated Columnar Epithelium is an unusual cellular type:
It is composed of several different types of cells
Pseudostratified Ciliated Columnar Epithelium
LOCATIONS: Lining of nasal cavity, trachea, and bronchi; portions of male reproductive tract
Cilia
Cytoplasm
FUNCTIONS: Protection, secretion, move mucus with cilia
Nuclei
Basement membrane
Loose connective tissue
Trachea
LM  350
Several cellular layers of cells – movement, i.e. mucociliary escalator of the lung! 24

25. Figure 4-5c Columnar Epithelia
Stratified Columnar Epithelium
LOCATIONS: Small areas of the pharynx, epiglottis, anus, mammary glands, salivary gland ducts, and urethra
Loose connective tissue
Deeper basal cells
FUNCTION: Protection
Superficial columnar cells
Lumen
Lumen
Cytoplasm
Nuclei
Basement membrane
Salivary gland duct
LM  175
Many columnar layers of cells – protection; salivary gland duct! 25

26. Characteristics of Connective Tissue
Connective tissues are found deeper in the body
They have very few cells (there is much intercellular space) with an expansive extracellular matrix
The extracellular matrix consists of:
Ground substance (fluid, rubbery or solid stuff)
Determines the specialized function
It is clear, colorless and viscous
Connective Tissue Fibers (next slide…)

27. The different types of Connective Tissue Fibers
Collagen fibers are the most common type
They are long, strong, flexible and resist stretching
They are in the tissues of the dermal layer of the skin, tendons, ligaments, cartilage and bone
Reticular fibers are a thin network (stroma) of interwoven fibers
They are strong and flexible, and resist force in many directions (stabilize functional parenchymal cells)
They are in the tissues of the lymph nodes, spleen and basement membranes (acts as an organ sheath)
Elastic fibers are elastic, branched and wavy (elastin)
They are in the tissues of the skin, lungs and arteries
This reflects a balance between tension and flexibility

28. The Cells and Fibers of Connective Tissue Proper (cartoon)
Reticular fibers
Mast cell
Melanocyte
Elastic
fibers
Fixed macrophage
Plasma B cell
Free macrophage
Collagen fibers
Blood in vessel
Fibroblast
Adipocytes (fat cells)
Mesenchymal cell
Ground substance
Lymphocyte 28

29. Connective Tissues have defined functions…
Establishing a structural framework for the body
Transporting fluids and dissolved materials
Protecting delicate organs
Supporting, surrounding, and interconnecting other types of tissue
Storing energy reserves, especially in the form of triglycerides
Defending the body from invading microorganisms

30. Classification of Connective Tissues
Connective tissue proper - connect and protect
Categorized as loose or dense connective tissue
Loose: has more ground substance (i.e. fat)
Dense: has more fibers (i.e. tendons)
Fluid connective tissues – transport stuff
i.e. Blood and lymph
Supporting connective tissues – structural strength
i.e. Cartilage and bone

31. Connective Tissue Proper Cell Popluations
Permanent residents:
(don’t move about)
Fibroblasts: are the most abundant cell type, are found in all connective tissue proper populations and produce proteins of the matrix
Fibrocytes: are the second most abundant cell type, are found in all connective tissue proper populations and maintain matrix proteins
Adipocytes: are fat cells; they store triglycerides (fat molecules)
Mesenchymal cells: are stem cells that respond to injury or infection; they differentiate into fibroblasts, macrophages, etc…
Fixed Macrophages: are fixed phagocytic cells; engulf pathogens, dead or dying cells
Non-permanent residents:
(motile)
Mast cells: reside near blood vessels; they secrete histamine (inflammatory mediator) and heparin (anti-coagulant)
Free Macrophages: are free phagocytic cells; engulf pathogens, dead or dying cells
Lymphocytes: are specialized immune cells in the lymphatic system (T and B cells - includes immune protective and antibody secreting cells)
Microphages: are phagocytic blood cells that destroy pathogens (neutrophils, eosinophils)
Melanocytes: produce melanin (brown pigment)
Plasma B Cells: antibody producing White Blood Cells

32. The Cells and Fibers of Connective Tissue Proper (cartoon)
Reticular fibers
Mast cell
Melanocyte
Elastic
fibers
Fixed macrophage
Plasma B cell
Free macrophage
Collagen fibers
Blood in vessel
Fibroblast
Adipocytes (fat cells)
Mesenchymal cell
Ground substance
Lymphocyte
free vs. fixed cell types 32

33. Loose Connective Tissues
Loose Connective Tissues are the “packing materials” of the body; they fill spaces between organs
There are three types in adults
Areolar
Adipose
Reticular

34. 1. Areolar Tissue (little space)
Areolar tissue provides padding and is flexible, allowing for stretching
It is a loose arrangement of fibers and cells in an abundant viscous ground substance
Thus, it serves as a passageway for nerves and blood vessels
It is widely distributed; it underlies all epithelia, is between muscles and forms a subcutaneous layer with adipose tissue

35. Adipocytes (white adipose cells)
2. Adipose Tissue
Adipocytes (fat cells) take up most of the space
They do not divide; they expand to store more fat (don’t we know it!) and shrink as fat is released
Mesenchymal cells divide and differentiate to produce more fat cells when more storage is needed
Adipose Tissue
LOCATIONS: Deep to the skin, especially at sides, buttocks, breasts; padding around eyes and kidneys
FUNCTIONS: Provides padding and cushions shocks; insulates (reduces heat loss); stores energy
Adipocytes (white adipose cells)
LM  300
Adipose tissue

36. there is white fat and there is dark fat…
Most common
Stores fat molecules
Absorbs shock(s)
Slows heat loss (insulation)
Brown fat
More vascularized
Adipocytes have many mitochondria
When it is stimulated by the nervous system, fat breakdown accelerates, releasing energy as heat
Children have more brown fat

37. 3. Reticular Tissue
Reticular tissue is a loose network of reticular fibers that is filled with fibroblasts and white blood cells
Reticular tissue forms a supportive framework (stroma) for the functional cells (parenchyma) of the lymphoid organs
The reticular organs include the spleen, liver, lymph nodes, thymus and bone marrow
Reticular Tissue
LOCATIONS: Liver, kidney, spleen, lymph nodes, and bone marrow
FUNCTIONS: Provides supporting framework
Reticular fibers
Reticular tissue from liver
LM  375
Reticular Tissue

38. Dense Connective Tissues
Dense Connective Tissues are tightly packed with high numbers of collagen or elastic fibers
There are three types in adults:
Dense regular connective tissues
Are tightly packed, parallel collagen fibers
Dense irregular connective tissues
Are interwoven networks of collagen fibers
Elastic tissues
Are made of elastic fibers

39. 1. Dense Regular Connective Tissue is tightly packed and contains parallel collagen fibers
Tendons attach muscle to bone
Ligaments connect bone to bone and stabilize organs
Aponeuroses attach in sheets to large flat muscles
Dense Regular Connective Tissue
LOCATIONS: Between skeletal muscles and skeleton (tendons and aponeuroses); between bones or stabilizing positions of internal organs (ligaments); covering skeletal muscles; deep fasciae
Collagen fibers
FUNCTIONS: Provides firm attachment; conducts pull of muscles; reduces friction between muscles; stabilizes relative positions of bones
Fibroblast nuclei
Tendon
LM  440

40. 2. Dense Irregular Connective Tissue is densely packed, randomly arranged collagen fibers
It withstands stresses applied in different directions
Found in the deep layer of the skin (dermis), the thick fibrous capsules around organs such as the kidney, and around bone (periosteum) and cartilage (perichondrium)
Dense Irregular Connective Tissue
LOCATIONS: Capsules of visceral organs; periostea and perichondria; nerve and muscle sheaths; dermis
FUNCTIONS: Provides strength to resist forces applied from many directions; helps prevent overexpansion of organs such as the urinary bladder
Collagen fiber
bundles
Deep dermis
LM  111

41. Figure 4-11c Dense Connective Tissues
3. Elastic Tissue is made of elastic fibers
Elastic Tissue
LOCATIONS: Between vertebrae of the spinal column (ligamentum flavum and ligamentum nuchae); ligaments supporting penis; ligaments supporting transitional epithelia; in blood vessel walls
Elastic fibers
FUNCTIONS: Stabilizes positions of vertebrae and penis; cushions shocks; permits expansion and contraction of organs
Fibroblast nuclei
Elastic ligament
LM  887 41

42. 2. Fluid Connective Tissue Cell Populations
Fluid Connective Tissues include the blood and lymph, which are composed of a watery matrix of dissolved proteins and cells
The blood contains formed elements (cells or cell fragments)Red blood cells (erythrocytes)White blood cells (leukocytes)Platelets
The lymph forms as interstitial fluid enters the lymphatic vesselsThis material is returned to the venous system of the heartIt is monitored by the immune system (lymph nodes; lymphocytes)

44. 3. Supporting Connective Tissues
Supporting connective tissues buttress soft tissues and body weight, and are composed of:
Cartilage – a gel-type ground substance that aids in shock absorption and protection
Bone – a calcified material that is made rigid by the incorporation of calcium salts and minerals
Bone aids in weight support

45. Cartilage
Cartilage is composed of chondrocytes, which produce the rubbery gel matrix of proteoglycan (chondroitin sulfate) and protein fibers
Chondrocytes are surrounded by lacunae
Cartilage is avascular:
Cartilage damage is difficult to repair (chondrocytes produce antiangiogenesis factor)
The perichondrium is a surrounding layer, offering protection, attachment to other tissues, maintenance and growth
Cartilage grows by two mechanisms (next slide)

46. There are three types of cartilage…
Hyaline cartilage
Elastic cartilage
Fibrocartilage (fibrous cartilage)

47. 1. Hyaline Cartilage offers stiff, flexible support
It reduces the friction between bones
Found in synovial joints, rib tips, sternum, and trachea

48. 2. Elastic Cartilage is supportive but bends easily
Found in external ear and epiglottis

49. 3. Fibrocartilage (Fibrous Cartilage) limits movement
It prevents bone-to-bone contact
It pads knee joints, is found between pubic bones and between intervertebral discs

50. Bone Bone (osseous tissue) is strong and resists shattering
The functional unit of bone is the osteon with a centrally located canal that feeds the bone cells through canaliculi tributaries
Bone cells (osteocytes) are arranged in circular lacunae within a matrix of calcified calcium salt deposits and flexible collagen fibers
The periosteum covers bone surfaces

51. A Comparison of Cartilage and Bone51

52. Muscle Tissue
Muscle Tissue is specialized for contraction and produces all body movement
There are three types of muscle tissue:
Skeletal muscle tissue
Large body muscles responsible for movement
Cardiac muscle tissue
Found only in the heart
Smooth muscle tissue
Found in walls of hollow, contracting organs (blood vessels; urinary bladder; respiratory, digestive, and reproductive tracts)

53. Muscle cells are classified by three criteria:
Striation
Do the cells have a banded appearance or not?
Nucleation
Do the cells have a single nucleus or many?
Control
Are the cells controlled voluntarily (consciously) or involuntarily (autonomically)

54. Skeletal Muscle cells (myofibers)
Long and thin striated cells that are multinucleated (what does multinucleated and striated mean?)
Under voluntary (somatic) control
New fibers are produced by stem cells (myosatellite cells)

55. Cardiac Muscle cells (cardiocytes)
Short and branched, striated cells with a single nucleus
The branching networks are connected at intercalated discs
They are under involuntary (autonomic) control and are egulated by pacemaker cells
It is difficult to regenerate cardiac muscle cells

56. Smooth Muscle cells
Small and tapered, non-striated cells with a single nucleus
Can divide and regenerate! Very important!

57. Neural Tissue
Neural Tissue is also called nervous or nerve tissue and is specialized for conducting electrical impulses
Rapidly senses internal or external environment
Processes information and controls responses
Neural tissue is concentrated in the central and peripheral nervous system
CNS: Brain & spinal cord (integrative nerves)
PNS: Senses and nerves (afferent and efferent nerves)

58. There are two types of neural cells in the CNS
Neurons
Nerve cells - Perform electrical communication
Neuroglia
Supporting cells - Repair and supply nutrients to neurons

59. Neurons are generally composed of:
Cell body
Contains the nucleus and nucleolus
Dendrites
Short branches extending from the cell body
Receive incoming signals
Axon (nerve fiber)
Long, thin extension of the cell body
Carries outgoing electrical signals to their destination

60. NEUROGLIA (supporting cells)
Figure Neural Tissue
NEURONS
NEUROGLIA (supporting cells)
Nuclei of neuroglia
• Maintain physical structure
of tissues
Cell body
• Repair tissue framework
after injury
• Perform phagocytosis
• Provide nutrients to neurons
• Regulate the composition of the
Axon
interstitial fluid surrounding neurons
Dendrites
Nucleolus
Nucleus of neuron
LM  600
Dendrites (contacted by other neurons)
Axon (conducts information to other cells)
Microfibrils and microtubules
Mitochondrion
Nucleolus
Nucleus
Contact with
other cells
Cell body (contains nucleus and major organelles)
A representative neuron (sizes and shapes vary widely) 60

61. What procedures are we doing?
You will observe simple stained slides, identify different tissues in the human body, and correlate a relationship of those tissues with their location and function.

62. Resources available…
Anatomy and Physiology Laboratory Study Pages; submenu: Tissues

64. Classifying Epithelia according to the shape of the cells64

65. Classifying Epithelia according to the layering of the cells65