Histology Flashcards
Histology
Study of the organization of tissues
tissue
Aggregates of cells that have a particular function within the organism
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
- Internal joined skeleton
Freely movable
Bones, ligaments, cartilage, tendons
Levels of Organization
CELLS -> TISSUES -> ORGANS -> ORGAN SYSTEM
Primary Tissue Types
Epithelial
Connective
Muscle
Nervous
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
- Lines cavities and body surfaces
* Anchored by a basement membrane
How is epithelial tissue classified
According to shape and number of layers (single [simple]; many [ stratified])
what are the 3 primary groups of epithelial tissue?
- Squamous
- Cuboidal
- columnar
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
cuboidal epithelium
Dice shaped Round central nucleus Secretions can be made by them Eg: glands (thyroid and salivary glad (choroid plexus), kidney tubules
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
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
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
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
connective tissue
Sparse population of cells scattered through an extracellular matrix
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)
types of connective tissue fibers
Collagenous fibers Provide strength and flexibility Reticular fibers Join connective tissue to adjacent tissues Elastic fibers Makes tissue elastic
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
Fibrous connective tissue
Dense with collagenous fibers Location: Tendons – muscles to bone Ligaments – bone to bone @ joints
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
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
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
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
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
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
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
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
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
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
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
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
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
- A new molecule of ATP releases the myosin head from the actin and a new
cycle begins
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
role of calcium and regulatory proteins
- The synaptic terminal of the motor neuron releases the neurotransmitter,
acetylcholine (ACh) - ACh depolarizes the muscle and causes it to produce an action potential
- the action potential travels through the plasma membrane down the T(transverse)-
tubules - this causes the Ca2+ to be released from the SR
- Ca2+ binds onto the troponin and this causes the tropomyosin to shift from the
position over the myosin binding sites - Muscle contraction is allowed as the myosin forms cross bridges with the actin
- After the action potential ends, cytosolic Ca2+ is removed by active transport into
the SR - Once all the calcium
ions are removed the
tropomyosin returns to
its original position and
blocks the myosin
binding sites on the
actin - Contraction ends
- Muscle fiber relaxes
