Flashcards in Histology Deck (34)
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Histology
Study of the organization of tissues
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tissue
Aggregates of cells that have a particular function within the organism
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Basic Mammalian Body plan:
3 components
1. Tube-within-a-tube
Digestive tract
Body cavity/coelom
2. Two body cavities
- THORACIC
Thoracic wall
Vital organs
Heart, respiratory system
Structures of the digestive system
- ABDOMINAL
Organs of the digestive system
Spleen
Excretory system
Bladder and kidneys
3. Internal joined skeleton
Freely movable
Bones, ligaments, cartilage, tendons
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Levels of Organization
CELLS -> TISSUES -> ORGANS -> ORGAN SYSTEM
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Primary Tissue Types
Epithelial
Connective
Muscle
Nervous
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Epithelial Tissue
* Closely packed – tight junctions
* Cover the outside of the body and line organs and cavities
Functions:
1. Barrier against mechanical injury, pathogens, fluid loss
2. Secretion
3. Selective absorption
4. Excretion
5. Trans-cellular transport/ diffusion
6. Sense – smell
* Derived from the primary body tissue:
Ectoderm, mesoderm, endoderm
7. Lines cavities and body surfaces
* Anchored by a basement membrane
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How is epithelial tissue classified
According to shape and number of layers (single [simple]; many [ stratified])
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what are the 3 primary groups of epithelial tissue?
1. Squamous
2. Cuboidal
3. columnar
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squamous epithelium
Single layer
Platelike cells
Nuclei are flattened and elliptical
Thin and leaky
Allow for diffusion of substances
across the cell layer
Eg: blood vessels, air sacs of the lungs, heart’s mesothelium
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cuboidal epithelium
Dice shaped
Round central nucleus
Secretions can be made by them
Eg: glands (thyroid and salivary glad
(choroid plexus), kidney tubules
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columnar epithelium
Large, brick shaped cells
Where secretions need to be made or
absorption is important
Nuclei are elongated and towards the base
Eg: lines intestines – secretes digestive juices
and absorbs nutrients
May have specialised surface projections
Sensory reception (nose, ears, taste buds)
Secrete mucous and acts as a lubricant
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polarity
Epithelia has two different sides
1. Apical = faces the lumen or outside of the organ
Part of the epithelial tissue that is exposed to fluid or air
Specialised projections may cover this surface
2. Basal = opposite side of the epithelial tissue – connected to the
basement membrane
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pseudo-stratified epithelium
Single layer of cells
Cells are at different heights
Nuclei are at different heights
Cilia = use energy to beat and move mucous
with its sweeping motion
Locations: nose and bronchi, uterus and fallopian tubes
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stratified squamous epithelium
Multilayered
Regenerated easily and rapidly
New cells are formed by division near the basal surface
Cells push outwards and they replace the cells that have been
sloughed off the apical side
Specialisations:
Keratinized
Skin
waterproofing
Transitional
Stretchy
Location: urothelium (bladder, ureter, urethra)
Locations:
Surfaces subjected to abrasion
Outer skin
Linings of the mouth, anus and vagina
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connective tissue
Sparse population of cells scattered through an extracellular matrix
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functions of connective tissue
Holds tissues and organs together and in place
Support
Connection
Provides structure
Transport
S Patel
Matrix – ground substance:
Web of fibres embedded in a liquid (jelly like or solid foundation)
Fibroblasts present – secrete fiber proteins
Macrophages – engulf foreign particles and cell debris (phagocytosis)
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types of connective tissue fibers
Collagenous fibers
Provide strength and flexibility
Reticular fibers
Join connective tissue to adjacent tissues
Elastic fibers
Makes tissue elastic
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Loose connective tissue
Most abundant
Amorphous matrix
Has fibroblasts, macrophages, mast cells
(secrete histamines and heparin and involved in
allergic response)
Functions:
Binds epithelia to underlying tissues
Holds organs in place
Loose weave of fibres (all three types)
Location:
Skin and throughout the body
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Fibrous connective tissue
Dense with collagenous fibers
Location:
Tendons – muscles to bone
Ligaments – bone to bone @
joints
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Adipose tissue
Specialised loose connective tissue
Stores fats in adipose cells which are distributed throughout its
matrix
There is hardly any matrix
Functions:
Insulates the body
Stores fuel for the body as fat molecules
Each adipocyte contains a fat droplet – swells when the fat is
stored and shrinks when the body uses the fat as fuel
Locations:
under the skin, between organs and muscles, surrounds
blood vessels
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specialised connective tissue: Bone/ osseous tissue
Solid matrix
Mineralized connective tissue
Location:
Skeleton
Forms within and replaces the
cartilage model of the embryo and
developing baby
Hard:
Deposits of calcium, phosphate and magnesium crystals
Matrix:
Collagen and calcium phosphate laid down concentrically
Osteocytes in lacunae – initially living and are joined by canaliculi and
then they eventually die
Haversian System:
Central harversian canal
Blood vessels and nerves
Concentric lamellae
Concentric lamella of collagen fibres and calcium
Osteocytes in lacunae
Adjacent Haversian canals are joined by Volkmann’s canal
Function:
Protection
Support for muscle attachment and movement
Structure of the body
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specialised connective tissue: cartilage
Rubbery matrix
Due to chondroitin sulphate
Living chondrocytes in lacunae
Secrete collagen and chondroitin sulphate
Nutrients are exchanged through diffusion
Collagen in matrix
Firm, strong and flexible
Location: between bones, discs that act as
cushions between vertebrae, larynx, trachea
Function:
Maintains shape
Resists compression
Cushions and reduces friction @
joints
Flexible shock absorber @ vertebrae
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Specialized connective tissue: blood
Fluid matrix
Liquid extracellular matrix = plasma
Water, salts, dissolved proteins
Blood cells:
Erythrocytes
Transport of oxygen and carbon dioxide
Leukocytes
Fighting diseases
Preventing infection and getting rid of foreign matter
Platelets (thrombocytes = fragments)
Blood clotting
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Muscle tissue
Tissue responsible for all types of body movement
Cells consist of filaments of filaments containing proteins: actin and myosin
The action of a muscle is always to contract and extension is passive
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involuntary: Smooth muscle
Made up of sheets of muscle cells
Location:
many internal organs
walls of arteries and veins
digestive tract
urinary bladder
reproductive organs
myosin and actin filaments – not regularly arrayed along the length of the
cell
smooth muscle cells contracted when they are stimulated by neurons of the
ANS (autonomic nervous system)
contract and relax more slowly than skeletal muscles
Muscle activity is a response to input from the nervous system
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cardiac muscle
Involuntary muscle that needs no conscious control
Small uninucleate cells
Fibres are striated – branched
Intercalated discs: the gap junctions hold the cells together
Electrical impulses are thus allowed to cross the gap junctions
Allows synchronizes the heart beat and creates rhythmic pumping
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voluntary: skeletal muscle
Attached to bones by tendons
They are controlled by the consciousness
Multinucleated cells
Made up of bundles of skeletal muscle fibres
Fusion of many cells
Therefore, there are many nuclei in a
single muscle fiber
Myofibrils
Myofilaments of actin and myosin
Striated because they are divided into contractile
units that have thick and thin fibres
Sarcomeres = contractile units along a muscle fiber
The arrangement gives the muscle a striated appearance
Skeletal muscle → muscle fascicle → muscle fiber → myofibril (arranged
longitudinally) → myofilament → (light and dark bads alternating) → actin and
myosin
Each individual fiber is a single cell
Each fiber has multiple nuclei that are derived from the embryonic cells that fused
together and they run parallel to the length of the muscle
Move the bones and the body
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Myofibrils
Thin filaments
Consist of two strands of actin and two strands of a regulatory
protein
Thick filaments
Staggered arrays of myosin molecules
Striated = regular arrangement of myofilaments
S Patel
Creates a regular arrangement of myofilaments creates a pattern of light
and dark bands
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sarcomeres
A functional unit of a muscle
Bordered by Z lines
Where thin, actin filaments attach
Basic contractile units of a muscle
The borders of the sarcomere line up in adjacent myofibrils
Forms light and dark bands
Thick filaments are anchored in the middle – M line
Relaxed myofibril
Thick and thin filaments partially overlap
Edge of the sarcomere there are only thin filaments
Centre there are only thick filaments
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sarcoplasmic reticulum
Net like structure around the myofibrils
Contains the cytoplasm of muscle cells
Specialised endoplasmic reticulum
The cytoplasm is outside of the cell
Ease of contraction of muscles – faster
There are a lot of mitochondria – ATP provided for muscle contraction
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Muscle contraction process
Filaments slide past each other longitudinally
Produce more and more overlap between thick and thin filaments
The Z zones move more and more closer together
Sarcomere length decreases
Actin filaments move closer and closer together
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Myosin
*Myosin: has a long tail and a globular head
Head can bind to ATP and this is when it is in its low energy configuration
When the ATP is hydrolyzed then the myosin coverts to a high energy
configuration
1. The myosin head is in its low-energy configuration. This is because it is bound to
the ATP molecule
2. The myosin head hydrolyzes ATP to ADP and P and it is in its high-energy
configuration
3. The myosin head binds to actin (myosin binding site), forming a cross-bridge
with the thin filament
S Patel
4. The myosin couples release the ADP and P and there is a power stroke that
slides the thin filament along the myosin and returns the myosin head to a low-
energy state
The thin filament moves towards the center of the sarcomere
The myosin head returns to low-energy configuration
5. A new molecule of ATP releases the myosin head from the actin and a new
cycle begins
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role of calcium and regulatory proteins
- The regulatory protein tropomyosin and troponin complex bind to actin
strands on thin filaments when the muscle fiber is rest
- this prevents the actin and myosin from interacting
covers the myosin binding sites
- the troponin complex has Ca2+ binding sites
for muscle fibres to contract, myosin-binding sites must be uncovered
-this occurs when the calcium ions bind to the troponin complex and
exposes the myosin-binding sites
- contraction occurs when the concentration of calcium ions is high and stops
when the concentration is low
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