Histology (Tissues) Flashcards
What is Histology?
The study of Tissues
What is Tissues?
- A group of cells with similar structure and function
- Cells of most tissues are surrounded by an extracellular fluid called interstitisl fluid (mostly water and ions)
What is the 4 major tissues types?
- Epithelial Tissue
- Connective Tissue
- Muscle Tissue
- Nervous Tissue
What is Cell Junction?
- Points of contact between adjacent cells - seen in epithelial tissue, some nervous and muscle cells
- Formed by cell membrane proteins
What are the 3 examples of cell junctions?
- Tight Junctions
- Anchoring Junction (e.g. desmosomes)
- Gap Junction
Tight Junctions
- Holds cell membrane together
- Are a partial fusion of specific proteins on the lateral surface of the cell membrane
- Form ring-like tight seal
- Prevents material from passing between cells e.g. bacteria, proteins, sometimes fluid or ions (depending on the tissue)
- Stops integral proteins from moving between apical (lumen exposed surface) and basolateral (attached) surfaces of the cell
Anchoring Junction (e.g. desmosomes)
- Proteins that fasten cells to each other and/or extracellular material (“rivets” cells together)
Gap Junction
- Gaps between the cells
- Open channels (formed by proteins) through the adjacent cell membranes interconnecting the cytosois of the cells
- Allows ions/small molecules to pass from one cell to another
- Tissues can then work as a unit:
- Important in cardiac and smooth muscle (allows synchronization of contractions)
- Also found in epithelial tissue
What are the 4 Major Tissue Types? (Overview)
- Epithelial Tissue (Lining tissue)
- Connective Tissue (Connecting tissue)
- Muscle Tissue (Contractile tissue)
- Nervous Tissue (Sensation and signalling tissue)
What is the Epithelial Tissue?
- Covers body surface
- Lines body/organ cavities
- Organ cavity = lumen
What are the characteristics of Epithelia?
- Has one free surface
- Little extracellular space between cells
- Avascular - no blood vessels
- Basement membrane
- Extracellular layer
- Attaches epithelium to underlying connective tissue layer (formed by both tissues and aacts like “velcro”)
What is the classification of Epithelia?
- Most subtypes are classified and named according to:
1. The number of cell layers sitting on the basement membrane- One layer = simple
- More than one layer = stratified
- Shapes of the cells in the apical layer (= layer touching the free surface)
- Flattened = squamous
- Round or cube shaped = cuboidal
- Rectangular = columnar
What are the types of Epithelial tissues?
- Simple Epithelia ( = 1 layer)
- Stratified Epithelia ( = > 1 layer)
- Pseudostratified Epithelia
- Transitional Epithelia ( = cell shape & layering varies with stretching)
- Glandular Epithelium ( = for secretion)
Simple Epithelia ( = 1 layer)
Allow exchange of molecules (gasses, nutrients, ions) - absorption/secretion
What are the subtypes of Simple Epithelia?
- Simple Squamous
- Simple Cuboidal
- Simple Columnar
Simple Squamous
- 1 layer of squished (flat) cells
- e.g. lungs
Simple Cuboidal
- 1 layer of cube shaped cells
- e.g. kidney
Simple Columnar
- 1 layer of column shaped (tall & thin) cells
- e.g. stomach, small intestine
Stratified Epithelia ( = > 1 layer)
- Protective (areas of abrasion)
- predominant subtype is stratified squamous = apical cells squished (flat)
- e.g.epidermis of skin
Pseudostratified Epithelia
- Columnar cells that appear stratified (some cells are shorter and nuclei appear at different levels), but all cells sit on basement membrane (=simple!)
- e.g. lines most of respiratory tract (where the cells are also ciliated = ciliated pseudostratified epithelium)
Transitional Epithelia ( = cell shape & layering varies with stretching)
- Only in inner lining of urinary system
- Cuboidal to squamous when stretched
Glandular Epithelium ( = for secretion)
If the epithelial cells form a gland, the cell layer(s)/cell shape classification is no longer used & tissue is called a glandular epithelium
What are the 2 subtypes of Glandular Epithelium?
- Exocrine Glands
- Endocrine Glands
Exocrine Glands
- Secrete products onto body surface or into a body cavity
- Can be:
- Unicellular
- Multicellular
Unicellular
- e.g. Goblet cells
- Secrete mucus (into a cavity)
- In the digestive, urinary, reproductive, respiratory tracts
Multicellular
- Consists of secretory and duct cells (ducts connect secretions to surface or cavity)
- e.g. glands: sudoriferous (sweat), sebaceous (oil), mammary, digestive
Endocrine Glands
- No ducts (ductless)
- Secrete hormones into the extracellular fluid (interstitial fluid) surrounding glandular cells that then enter the blood plasma for transport to target cells/tissues
- e.g. thyroid gland secretes thyroid hormone
What are the 3 Functions of Epithelia?
- Protection
- Secretion
- Allows selective passage of materials (nutrients, waste, water, ions) across membrane
Protection
- Often stratified squamous
- e.g. epidermis of skin
Secretion
- Glandular epithelium
- e.g. thyroid gland, sweat gland
Allows selective passage of materials (nutrients, waste, water, ions) across membrane
- Typically simple epithelia
- e.g. kidney, intestine, capillaries
What is Connective Tissue?
- Mainly supports and connects tissues
- Cells far apart, separated by extracellular matrix that usually forms the bulk of the tissue.
- Extracellular material gives connective tissue subtypes their identifying characteristics
- Variable vascularity
What are CT Cell Types?
- Cell names ending in:
- BLAST
- CYTE
- CLAST
Cell Ending With BLAST
- Create matrix
- e.g. osteoblast, chondroblast, fibroblast
Cell Ending With CYTE
- Maintain matrix
- e.g. osteocyte, chondrocyte, fibrocyte
Cell Ending With CLAST
- Break down matrix
- e.g. osteoclast
What Are The Two Things In Matrix Composition?
- Fibres (proteins)
- Ground Substance
Fibres (proteins)
- collagen fibres (for strength)
- elastic fibres (containing elastin- allow stretch and recoil)
- Reticular fibres (form networks - e.g. connective tissue part of basement membrane)
Ground Substance
- water (interstitial fluid (ISF)) and large organic molecules (proteins and carbohydrates) surrounding cells and fibres
What are the classifications of Connective Tissues?
- Connective Tissue Proper
- Cartilage
- Bone
- Blood = Fluid Connective Tissue
Connective Tissue Proper
- cells = fibroblasts/fibrocytes except adipose tissue (adipocytes)
What Are The Two Types Of Connective Tissue Proper?
- Loose Connective Tissue
- Areolar connective tissue
- Adipose connective tissue
- Dense Connective Tissue
- Dense regular connective tissue
- Dense irregular connective tissue
Areolar Connective Tissue (Type of Loose Connective Tissue)
- Loosely arranged collagen and elastin fibres
- Highly vascular
- e.g. lamina propria
Adipose Connective Tissue (Type of Loose Connective Tissue)
- Very little matrix
- Cells large (adipocytes), store triglycerides - tissue looks like “chicken-wire”
- Highly vascular
Dense Connective Tissue
- Many fibres (therefore dense connective tissue is also known as fibrous connective tissue)
- Little ground substance
- Poorly vascular
Dense Regular Connective Tissue (Type of Dense Connective Tissue)
- Collagen fibres running in the same direction
- e.g. tendons and aponeuroses - connect muscle to bone
- e.g. ligaments - connect bone to bone
Dense Irregular Connective Tissue (Type of Dense Connective Tissue)
- Collagen fibres arranged irregularly
- e.g. dermis of skin
Fibrocartilage
- High in collagen fibers
- “shock absorbers”
- e.g. intervertebral discs, pubic symphysis
Cartilage
- Cells = chondrocytes (located in cavaties in the matrix called lacunae) & chondroblasts
- Large amount of matrix:
- Fibres = collagen & elastin (protein)
- Ground substance is mostly water, but is firm due to the types of organic molecules present.
What The Three Types of Cartilage?
- Hyaline Cartilage
- Elastic Cartilage
- Fibrocartilage
Hyaline Cartilage
- Most abundant
- e.g. trachea, ribs, ends of long bones
Elastic Cartilage
- Many elastic fibers
- e.g. epiglottis, ear pinna
Fibrocartilage
- High in collagen fibres
- “shock absorbers”
- e.g. intervertebral discs, pubic symphysis
Bone
- Cells = osteocytes (in lacunae), osteoblasts, and osteoclasts
- Large amounts of matrix:
- Fibres = abundant collagen
- Ground substance
- Very vascular
Ground Substance (Bone)
- inorganic calcium (Ca+) phosphate salts and organic components (proteins & carbohydrates) that make it rigid
- Little water
Blood = Fluid Connective Tissue
- Cells = red blood cells (RBC) and white blood cells (WBC), platelets
- Extracellular matrix is called plasma
- Contains soluble fibres (e.g. fibrinogen for blood clotting)
- ground substance is mostly water with ions, proteins
What are Muscle Tissues? What are the Subtypes?
- Contractile
- Subtypes:
- Skeletal (striated)
- Cardiac (striated)
- Smooth (non-striated)
What are the different cell types in Nervous Tissue?
- Neurons
- Conduct electrical impulses
- Glial Celis
- Support and protect neurons
