Topic 15: Histology - Study of tissues (szövettan)

Tissue:  a group of cells that are structurally similar, have the same origin and perform the same function.

Here we will be looking specifically at animal tissues, although plants also have tissues.

Each kind of animal tissue forms from one of the 3 germ layers that differentiate very early in development.
Ectoderm gives rise to skin and the nervous system, including the sense organs
Mesoderm gives rise to muscles, bones, the circulatory system, the reproductive system and the excretory system (kidneys).
Endoderm gives rise to the digestive system and the respiratory tract.

The more than 200 different cell types can be grouped into 4 tissue types:
epithelial (hám)
connective (kötő)
muscle (izom)
nerve (ideg)

EPITHELIAL TISSUE
Epithelium:  single or multiple layers of cells that cover body surfaces or line internal cavities and form glands (mirigyek).  They are attached to a basement membrane (alaplemez) of collagen (for strength) and are linked to each other by junctions.  There are no blood vessels in the epithelium, rather nutrient and gas exchange occur by diffusion.  The functions of the epithelium include protection from injury and infection, some absorption, secretion (from glands) and stimulus reception (ingerfelvétel)

Classification
A.  True epithelium (fedőhám):  single cell layer, forms thin linings
i) squamous epithelium (laphám) - flat cells that form thin sheets, permeable to diffusion. eg. line blood capillaries, alveoli (tüdőholyagocskák)

ii) cuboidal epithelium (köbhám) - single layer of cuboid cells, may have microvilli (mikrobolyhok), often involved in absorption and scecretion.  eg. line part of gut, respiratory tract and kidney tubules







iii) columnar epithelium (hengerhám) - single layer of tall cells, their surface is frequently covered with microvilli.  Secretory (goblet) cells are often found between them.  They line the digestive system.





iv) cilliated epithelium (csillóshám) - columnar cells with cilia-covered surfaces.  Line tubes and cavities where materials move.




v) stratified epithelium (többrétegű hám) - multi-layers, forms the epidermis (upper layer of the skin), lines the esophagus and vagina.






B.  Glandular epithelium (mirigyhám)
i) individual glandular cells, eg. goblet cell


ii) multicellular gland - individual goblet cells clustered together.  A gland can be exocrine (külső elválasztású) meaning that it has ducts through which the secretions are released to the surface, for example, sweat glands, or a gland can be endocrine (belső elválasztasú), which means it secretes directly into the blood stream, for example, the thyroid.

2.  Connective and Supportive Tissues (kötő- és támasztószövetek)
These tissues function to bind other tissues and organs together.  They provide protection and support and fill in spaces.  Some of these tissues carry out special roles, such as the storage of fat in fat cells, or those that form blood cells.
Connective tissue is generally formed of networks of various cell types, which often include
fibroblasts

elastin fibers

collagen fibers

macrophages


The most common kinds of connective tissues are:
connective tissue proper
skeletal tissue (cartilage and bone)
blood

a) Connective Tissue Proper (tulajdonképpeni kötőszövet)
- fibroblasts are the predominant cell type.  They produce (secrete) the ground substance and proteins for fibres

- organization:
i) Loose connective tissue (laza rostos kötőszövet)
-thin fibers, not too many fibers, quite a few cells
-found beneath skin, around organs (forms sheets around/between them)

This is an example of loose connective tissue. The elastic fibers (EF) are arranged in a random fashion and help the tissue respond to distention. The nucleus of the inactive fibroblast (IFN) is long and flat.
Source: http://bcrc.bio.umass.edu/histology/?q=node/180

Areolar Connective Tissue: MC=Mast Cell, RF=Reticular Fiber, CF=Collagen Fiber
Source:http://bcrc.bio.umass.edu/histology/?q=node/343

ii) Adipose Tissue (zsírszövet)

- found in groups surrounded by loose connective tissue

- stores fat (energy reserves)

- also pads some organs (mechanical protection) and insulates from heat loss (thermoregulation)

Source: http://www.deltagen.com/target/histologyatlas/atlas_files/musculoskeletal/adipose_tissue_white_40x.htm

iii)  Dense (fibrous) connective tissue (tömött rostos kötőszövet)

- many fibers, especially collagen.  Fibers are often tightly packed.

-  provides connections between tissues where tension is exerted in a specific direction.  

- examples are:  tendons (inak) and ligaments (izületi szalagok)

- resist tearing

Dense regular connective tissue: human tendon (BV=blood vessel)
Source:  http://bcrc.bio.umass.edu/histology/?q=node/1092

b) Supporting (Skeletal) Tissue (Támasztószövet)

i) Cartilage (porc)

- is a chondrin matrix (jelly-like) embeded with cartilage cells (chondroblasts and chondrocytes), collagen fibers and elastin fibers

Hyaline cartilage (eg. nose, trachea)

Source:  http://legacy.owensboro.kctcs.edu/gcaplan/anat/histology/api%20histo%20connective.htm

Elastic cartilage (eg. ears, epiglottis)
Source: http://legacy.owensboro.kctcs.edu/gcaplan/anat/histology/api%20histo%20connective.htm 

ii) Bone (csont)

-  harder than cartilage

- provides protection and a rigid framework

- stores mineral salts

- marrow produces red and white blood cells

- the matrix is imbedded with bone cells (osteoblasts and osteocytes) and collagen

- minerals (CaPO4, CaCO3) deposit around fibers to make bones hard

- cells and fibers provide elasticity

- 2 types of bone:  compact bone and spongy bone

compact bone

-cells are arranged in concentric circles (lamellae) around nerve and blood vessel channels (Haversian canals)

-found in long, shaft bones

http://tle.westone.wa.gov.au/content/file/969144ed-0d3b-fa04-2e88-8b23de2a630c/1/human_bio_science_3b.zip/content/003_musculo_skeletal_support/page_05.htm

http://tle.westone.wa.gov.au/content/file/969144ed-0d3b-fa04-2e88-8b23de2a630c/1/human_bio_science_3b.zip/content/003_musculo_skeletal_support/page_05.htm

spongy bone

- irregular spacing of bone cells

- red marrow fills the spaces (and produces blood cells)

- found at ends of long bones

SEM of the trabeculae of spongy bone. x40
Source:  http://www.gla.ac.uk/t4/~fbls/files/fab/tutorial/generic/bonet.html

Spongy bone 100x
Source:  http://employee.lsc.edu/faculty/BrianBich/Picture%20Library/Forms/DispForm.aspx?ID=578

End of femur bone

Source:  http://www.gla.ac.uk/t4/~fbls/files/fab/tutorial/generic/bonet.html

c) Blood

- cells in watery matrix (blood plasma), so they can move.  Plasma also transports nutrients, wastes, hormones, enzymes, dissolved gases, etc

- no fibers

- variety of cell types: 

i) Red blood cells (erythrocytes)

- biconcave disc, has lost nucleus

- contains haemoglobin (Fe gives cell red colour, haemoglobin carries O2)

http://singularityhub.com/2008/08/22/is-an-unlimited-supply-of-blood-and-no-more-need-for-blood-donors-around-the-corner/

ii) White blood cells (leukocytes)

- larger, nucleated cells

- there are fewer in the blood than red blood cells

- great diversity of types:  granulocytes, lymphocytes, etc (more later)

- help in fighting infections

Source:  http://biology.about.com/od/cellbiology/ss/white-blood-cell.htm

iii.  Platelets (vérlemezkék)

- tiny

-very important in blood clotting

Source:  http://hematologyoutlines.com/atlas_topics/165.html?topic=Agranular%20Platelets*&cb=inline_content_10

3.  Muscle Tissue
a) Skeletal Muscle
-attaches to skeleton (via tendons)
- voluntary movement
- powerful, rapid contractions, but tires quickly
- long, cylindrical cells with striations (stripes), therefore also called striated muscle
- cells are bundled together and enclosed by connective tissue to form a muscle (eg. bicep)

Organization of skeletal muscle
Source:  http://quizlet.com/3238205/muscle-tissue-flash-cards/

Source:  http://faculty.sdmiramar.edu/faculty/sdccd/kpetti/bio160/documents%20biol160.htm

Source:  http://stevegallik.org/sites/histologyolm.stevegallik.org/htmlpages/HOLM_Chapter07_Page04.html

b)  Smooth Muscle

- on walls of internal organs, such as blood vessels, bladder, intestinal wall.

- involuntary muscle, contracts slowly, fatigues slowly, contractions are weak, but long-lasting

- it contains myofibrils, but the organization is different, so no striations are visible.

Source:  http://www.mhhe.com/biosci/ap/histology_mh/nonstria.html

c)  Cardiac muscle (heart)

- striated, but fibers branch at ends and are connected to each other by junctions so signals pass rapidly between cells and they all contract together.

-  rapid, powerful contractions

- rhythmic and involuntary

- do not fatigue.

Source:  http://www.kumc.edu/instruction/medicine/anatomy/histoweb/muscular/muscle14.htm

4.  Nerve Tissue

- makes up the nervous system (brain, spinal cord, ganglia and nerves)

i) Supporting cells

- support, protect and provide nutrients to the neurones

- glial cells in brain and spinal cord: astrocytes (transport of gases, nutrients and wastes to and from 1the blood), oligodendrocytes (form myelin), microglia (role in phagocytosis)

Astrocytes
Source:  http://astrocyte.info/

Source:http://blustein.tripod.com/Oligodendrocytes/oligodendrocytes.htm

Source:  http://missinglink.ucsf.edu/lm/introductionneuropathology/Response%20_to_Injury/Microglia.htm

Source:  http://keck.bioimaging.wisc.edu/lecture-series-2006-2007.html

- Schwann cells are found in the peripheral nervous system where they form the myelin sheath

Source:  http://faculty.southwest.tn.edu/rburkett/A&P1_nervous_system_lab.htm

Source:  http://neurolex.org/wiki/Category:Schwann_Cell

ii) Neurons

- sense stimuli and control reactions to them

- send nerve impulses to organs to make them react

https://www.boundless.com/psychology/the-brain-and-behavior/neurons/introducing-the-neuron/

- impulses flow through a neuron from the dendrite to the axon

Source:  http://learnzoology.wordpress.com/tag/neuron-tissue/

- Types of neurons are based on their processes

- Bipolar neurons have 1 dendrite and 1 axon

- Unipolar neurons only have on process, typically found in the dorsal root ganglia of the spinal cord (more on that later)

- Multipolar neurons have multiple dendrites and one axon.  This are the most common type of neuron

- Pyramidal cell is a neuron found in the brain with one axon and multiple dendrites.  Its name comes from the triangular shape of the cell body

- 3 kinds:  motor neurons (mozgató), sensory neurons (erző) and interneurons (társító)

Source:  http://learnzoology.wordpress.com/tag/neuron-tissue/

- Motor neurons control effector organs, like muscles and glands

- Sensory neurons receive the sensory information from the environment.

- Interneurons connect the sensory and motor neurons to each other.

Neurons are bundled together to form nerves

Nerve fibres may be motor, sensory or mixed, depending on what kind of neurons they contain.