Unit 7 - histology Flashcards
What is histology
The study of tissues
Tissue
- a group of cells with similar structure and function
- cells of most tissues are surrounded by an extracellular fluid called interstitial fluid (mostly water and ions)
4 major tissue types
- Epithelium
- Connective
- Muscle
$. Nervous
Cell junctions
- points of contact between adjacent cells
- seen in epithelial tissue, some nervous and muscle cells
- formed by cell membrane proteins
3 examples of cell junctions
- Tight junctions
- Anchoring junctions
- Gap junctions
Tight junctions
Are a partial fusion of specific proteins on the lateral surface of the cell membrane
What do tight junctions form
Ring-like tight seals (seal everything)
What do tight junctions prevent
- material from passing between cells
- ex. Bacteria, proteins, sometimes fluid or ions (depending on the tissue)
What do tight junctions stop
- integral proteins from moving between apical (lumen exposed surface) and basolateral (attached) surfaces of the cell
What are anchoring junctions
- proteins that fasten cells to each other and/or extracellular material
- anchors cells together
- ex. Demosomes
What do gap junctions do
- open channels (formed by proteins) through the adjacent cell membranes interconnecting the cytosols of the cells
- allow ions/ small molecules to pass from one cell to another
- tissues can then work as a unit (important in cardiac and smooth muscle) (also found in epithelial tissue)
Why are gap unctions important in cardiac and smooth muscle
Tissues can work together to allow synchronization of contractions
Epithelial tissue
- Covers body surface
- Lines body/ organ cavities
Lumen
Organ cavity
Characteristics of epithelia
- has one free surface
- little extracellular space between cells
- avascular (no blood vessels)
- basement membrane
basement membrane
- extracellular layer
- attaches epithelium to underlying connective tissue layer
- formed by both tissues
- acts like Velcro
Subtypes of epithelia are classified by
- The number of cell layers sitting on basement membrane
a) one layer = simple
b) more than one layer = stratified - Shape of cells in the apical layer
a) flattened = squamous
b) round/cube shaped = cuboidal
c) rectangular = columnar
Apical layer
Layer touching the free surface
Types of epithelia
- Simple epithelia = 1 layer
- Stratified epithelia = more than one layer
- Pseudostratified epithelia
- Transitional epithelia
- Glandular epithelia
Simple epithelia
- allows exchange of molecules (gasses, nutrients, ions)
- absorption/secretion
- produces gasses
Subtypes of simple epithelia
- Simple squamous
- Simple cuboidal
- Simple columnar
Simple squamous epithelia
- 1 layer of squished, fat cells
- ex. Lungs
Simple cuboidal epithelia
- 1 layer of cube shaped cells
- ex. Kidneys
Simple columnar epithelia
- 1 layer of column shaped (tall and thin) cells
- ex. Stomach and small intestine
Stratified epithelia
- more than one layer
- provides protection
- predominant subtype = stratified squamous
- ex. Epidermis of skin
Pseudostratified epithelia
- columnar cells that appear stratified
- cells sit on the basement membrane (simple)
- some cells are shorter and nuclei appear at different levels
- lots of nuclei
- ex. Lines most of respiratory tract, found in trachea
- respiratory tract = cells are ciliated = ciliated Pseudostratified epithelium
Transitional epithelia
- cell shape (and layering) varies with stretching
- only in inner lining of urinary system
- cuboidal to squamous when stretched
Glandular epithelia
- for secretion
- if the epithelial cells form a gland, the cell classification is not longer used and the tissue is called glandular epithelium
- subtypes:
1. Exocrine glands
2. Endocrine glands
Exocrine glands
- secrete products onto body surface or into a body cavity
- can be:
1. Unicellular
2. Multicellular
Unicellular exocrine glands
- ex. Goblet cells
- secrete mucus (into a cavity)
- in the digestive, urinary, reproductive and respiratory tracts
Multicellular exocrine glands
- consists of secretory and duct cells
- ducts connect secreted ions to surface or cavity
- ex. Sudoriferous (sweat) gland, sebaceous (oil) gland, mammary glands, digestive glands,
Endocrine glands
- no ducts
- secrete hormones into the ECF (interstitial fluid) surrounding glandular cells that then enter the blood plasma for transport to target cells/tissues
- ex. Thyroid gland secretes thyroid hormone
Functions of Epithelia
- Protection: often stratified squamous
- ex. Epidermis of skin - Secretion: glandular epithelium
- ex. Thyroid glands, sweat glands - Allows selective passage of materials across membranes: typically simple epithelia
- ex. Kidneys, intestine, capillaries
Connective tissue
- mainly supports and connects tissues
- cells far apart, separated my extracellular matrix that usually forms most of tissue
- variable vascularity
Extracellular material
- gives connective tissue subtypes their identifying characteristics
CT cell types
Cell names ending in:
1. BLAST= create matrix
- ex. Osteoblast, chondroblast, fibroblast
2. CYTE= maintain matrix
- ex. Osteocyte, chondrocyte, fibrocyte
3. CLAST= break down matrix
- ex. Osteoclast
matrix composition
- Fibres
- Ground substance
Types of Fibres in matrix
- collagen fibres (for strength)
- elastic fibres (containing elastin- allow stretch and recoil)
- reticular fibres (form networks) (ex. CT part of basement membrane)
Ground substance
- water (interstitial fluid (ISF)) + large organic molecules surrounding cells and fibres
Classification of CT
- Connective tissue proper
- Cartilage
3.bone - Blood
Connective tissue proper
- cells = fibroblasts/fibrocytes except adipose tissue
- types:
1. Loose connective tissue
2. Dense connective tissue
Loose connective tissue subtypes
- Areolar connective tissue
- Adipose connective tissue
Where is loose connective tissue found
In dermis of skin
Areolar connective tissue
- loosely arranged collagen and elastin fibres
- Highly vascular
- ex. Laminated propria
Adipose connective tissue
- very little matrix
- large cells, store triglycerides
- tissue looks like chicken wire
- vascular
Dense connective tissue
- many fibres
- also knows as fibrous connective tissue
- little ground substance
- vascular
Dense connective tissue subtypes
- Dense regular connective tissue
- Dense irregular connective tissue
Dense regular connective tissue
- collagen fibres running in the same direction
- ex. Tendons and aponeuroses, ligaments
Tendons
Connect muscle to bone
Ligaments
Connect bone to bone
Dense irregular connective tissue
- collagen fibres arranged irregularly
- ex. Dermis of skin
Cartilage
- no blood vessels (avascular)
- cells = chondrocytes and chondroblasts
- large amounts of matrix
Where are chondrocytes located
In cavities in the matrix called lacunae
Cartilage matrix
- Fibres = collagen and elastin (proteins)
- Ground substance is most water, but is firm due to the types of organic molecules present
Does cartilage heal fast or slow
Slow (avascular)
3 types of cartilage
- Hyaline cartilage: most abundant, reduces friction between bones
- ex. Trachea, ribs, ends of long bones - Elastic cartilage: many elastic fibres, main function is to recoil
- ex. Epiglottis, ear - Fibrocartilage: high in collagen fibres, shock absorbers so spinal cord doesn’t get injured
- ex. Intervertebral discs, pubic symphysis
Bone cells
- Osteocytes (in lacunae)
- osteoblasts
- osteoclasts
Bone matrix
- Fibres= abundant collagen
- Ground substance: contains calcium, salts and phosphates that make it rigid
- contain little water
Is bone vascular or avascular
Very vascular
Blood
Is fluid connective tissue
Blood cells
- Red blood cells
- White blood cells
Extracellular matrix in blood
Plasma
- contains soluble fibres
- used for blood clotting
- ground substance is most water with ions and proteins
Muscle tissue
Is contractile
Subtypes of muscle tissue
- Skeletal - striated
- Cardiac - striated
- Smooth - non-striated
Nervous tissue cell types
- Neurons- conduct electrical impulses
- Glial cells- support and protect neurons
