Flashcards in Connective Tissue Deck (197):
What does connective tissue form?
A huge continuum throughout body
What is the role of connective tissue?
What are the functions of blood?
What are the functions and cartilage?
Solid skeletal functions
Give 6 functions of connective tissues
- Provide substance and form to body and organs
- Provide medium for diffusion or nutrients and wastes
- Attach muscle to bone, and bone to bone
- Provide cushion between tissues and organs
- Defend against infection
- Injury repair
What happens to the immune cells produced in bone marrow?
What part of connective tissue is particularly important in injury repair?
What do fibroblasts do?
Lay down new cellular matrix
What are the two main cellular tissue components?
- Extracellular matrix
Is extracellular matrix present in all connective tissues?
Many, but not all
What makes extracellular matrix?
What does extracellular matrix consist of?
- Ground substance
What makes up ground substance?
Hyalurone proteoglycan aggregates
What fibres are found in the extra cellular matrix?
What do connective tissues differ in terms of?
- Types of cell they contain
- Abundance / destiny of their cells
- Constitution of the extra cellular matrix
What does the constitution of the extra cellular matrix differ in terms of?
- Ground substance composition
- Fibre type, abundance and arrangement
What are the 3 classifications of connective tissue?
What are the embryonic connective tissues?
- Mucous connective tissue
What are the regular connective tissues?
- Loose connective tissue
- Dense connective tissue
What are the types of dense connective tissue?
What are the specialised connective tissues?
What forms mesenchyme in the early embryo?
Mesodermal cells from the embryonic germ layer and few ectodermal cells migrate and proliferate to form mesenchyme
What does mesenchyme consist of?
Multipotent progenitor cells
What does mesenchyme give rise to?
How does mesenchyme give rise to it’s tissues?
Maturation and proliferation
What appearance do mesenchymal tissues from the developing foetus have?
Why do mesenchymal tissues have a tapering appearance?
Because of cytoplasmic processes
What do mesenchymal tissues have?
An abundance of viscous ground substance in the extra cellular matrix
Are mesenchymal tissues morphologically similar, or do they differ?
What will mesenchymal cells give rise to?
Cells that differentiate into a variety of different cell types
Do mesenchymal tissues persist into adulthood?
What do mesenchymal tissues do in adulthood?
Give rise to new connective tissue cells when healing required
What does mucous connective tissue have?
What does the ground substance in mucous connective tissue occupy?
Large intercellular spaces
What is found in cartilage ground substance?
What does the proteoglycan monomer consist of?
What is joined to the proteoglycan core protein?
~100 glycosaminoglycan (GAG) units
What are proteoglycan monomers attached to?
Hyaluronic acid molecules
What do hyaluronic acid molecules form?
How are proteoglycan monomers attached to hyaluronic acid molecules?
What happens to the linear aggregates of hyaluronic acid molecules?
They are interwoven with a network of collagen fibrils
What do GAGs attract?
Why do GAGs attract water?
Because of the high density of negative charges on the GAGs
What does the attraction of water to GAGs form?
A hydrated gel
What forms a hyaluronate proteoglycan aggregate?
Hyaluric acid + attached proteoglycan monomers
What is the main constituent of ground substance?
Hyaluronate proteoglycan aggregates
What lie within the ground substance consisting of hyaluronate proteoglycan aggregates?
- Cells of immune system
- Fat cells
- Blood vessels
What is the most common protein in the body?
How many types of collagen have been identified?
At least 28
What is the most widely distributed collagen type?
Describe the structure of type I collagen
Fibrils aggregate into fibres, and fibre bundles
Give 3 places type I collagen is found
How does type II collagen differ from type I?
Fibrils do not form fibres
Give 2 places type II collagen is found?
- Hyaline cartilage
- Elastic cartilage
What is type III collagen also known as?
What does reticulin do?
Forms fibres around muscle and nerve cells, and with lymphatic tissues and organs
What is type IV collagen?
A unique form present in the basal lamina of the basement membrane
What pattern does a type I collagen fibril have?
Periodic banding pattern that repeats every 68nm
What is each type I collagen fibril composed of?
Staggered collagen molecules
How big is each type 1 collagen fibril?
300nm long, 1.5nm
What is a type 1 collagen fibril composed of?
A triple helix of α-chains
What is every 3rd amino acid in a type 1 collagen fibril?
What is the result of every third amino acid of type 1 collagen molecules being glycine?
It makes it a very tough, flexible molecule
Are are fibroblasts intimately associated with?
What do collagen fibrils assemble from?
What secrete procollagen?
What do fibroblasts have lots of?
What happens to collagen fibres in dense irregular connective tissues?
Thin collagen fibres aggregate in some areas to form collagen bundles
What does the lymph nodes capsule contain?
What extends form the lymph node capsule into the node?
What is the purpose of the trabecular that extends from the lymph capsule to the node?
What kind of collagen is important in the lymph node?
What do the reticular fibres do in the lymph node?
Form an irregular anastomosing network throughout the node
What to the reticular fibres in the lymph nodes provide?
Something for the immune cells to bind to
What is densely packed in spaces between fibres in the lymph nodes?
What is elastin a primary component of?
What is elastin surrounded by?
Microfibrils called fibrillin
What is an elastic fibre composed of?
Elastin + fibrillin
Where do elastic fibres occur?
In connective tissues, to widely varying degrees
Where do elastic fibres have an important role?
- Artery walls
- Those sites bearing elastic cartilage
What is the purpose of elastic fibres in the artery walls?
It helps with blood circulation
How do elastic fibres appear an TEM’s?
- May have amorphous appearance and low electron density
- May have darkly staining fibrillin around it
Where do fibrillin lay in relation to elastic fibres?
At periphery and within elastic fibre
What is the inheritance pattern of Marfan’s disorder?
What happens in Marfan’s disorder?
Expression of fibrillin gene is abnormal, such that elastic tissue is abnormal
What is the presentation of Marfan’s disorder?
- Abnormally tall
- Exhibit arachnodactyly
- Frequent joint dislocation
- Can be at risk of aortic rupture
What are the 3 main parts of a small elastic artery?
- Tunica intima
- Tunica media
- Tunica adventita
What is present in the tunica intima?
Indistinct endothelial cells
What is in the tunica media?
What is in the tunica adventita?
What happens if the elastic fibres are compromised?
The arteries are compromised
How could the tunica media be described in the aorta wall?
What is the aortal tunica media mainly made up of?
What are aortal elastic lamallae?
Fenestrated sheets of elastic stretching around the aorta
Other than elastic lamellae, what else does the aortal tunica media contain?
- Extracellular matrix
- Smooth muscle
What is the significance of the smooth muscle in the tunica media?
They produce the elastin, collagen and matrix
What does the mammary gland consist of?
- Glandular epithelium
- Loose irregular connective tissue
- Dense irregular connective tissue
What does the loose irregular connective tissue of the mammary gland consist of?
Wispy collagen and many fibroblasts
What does the dense irregular connective tissue of the mammary gland consist of?
Thicker and more abundant collagen fibres, fewer fibroblasts
Where is loose connective tissue found in the gut?
The lamina propria between the crypts of Lieberkühn and the submucosa of the colon
What does loose connective tissue consist of?
- Lots of ground substance
- Branching elastic fibres
- Unbranching collagen fibres
- Blood vessels
- Mast cells
What do the nuclei visible in micrographs of loose connective tissues mainly belong to?
What kind of tissue is the dermis?
Loose, irregular connective tissue
How is collagen arranged in the dermis?
Bundles are collagen are densely packed but irregularly arranged. They are orientated in various directions
What is the result of the dermis having collagen having collagen fibres orientated in various directions?
The skin can resist forces in multiple directions, prevent tearing
What happens to skin after it’s been folded?
Elastic fibres show a degree of stretch and restoration to original shape
What surrounds glands?
A capsule of connective tissue
What kind of connective tissue is in the capsule surrounding glands?
Can vary from loose to dense
What does the type of connective tissue in the capsule depend on?
What feature of the capsule differs from gland to gland?
What is the purpose of the capsule?
Protects from injury and gives strength
Where is the capsule found?
- Adrenal gland
- Thymus gland
Virtually every gland
What do tendons do?
Connect muscles to bones
How do the collagen bundles lie in tendons?
In what direction is the densely packed formation of collagen bundles in tendons?
In line with the tensile force exerted by the muscle
What are tendons adapted to do?
Take pull in one direction, therefore produce tissue that can take high tensile force
What lies between collagen bundles in tendons?
Rows of elongated flattened fibroblasts
What happens between skeletal muscle and tendon collagen bundles?
They interdigitate at myotendinous junctions
What always lies between the collagen bundles and muscle fibres myofilaments?
What must be between the tendon and muscle fibre?
Very tight junctions
What do short ligaments do?
Connect bone to bone
How is collagen arranged in ligaments?
Collagen bundles densely packed in parallel arrangement, but undulate and are arranged in fascicles
What separates collagen bundles in ligaments?
Loose connective tissue
What are 6-pack muscles called?
What do rectus abdominus have?
What are aponeuroses?
Flat tendons that are like sheets
What aponeuroses are present in the rectus abdominus?
What are the muscles in the sides and hips called?
External oblique muscle
Do the external oblique muscles have aponeuroses?
What does the inguinal ligament connect?
The hip bone to the pubic bone
What can you see of fibroblasts in micrographs?
Nuclei and cytoplasm
How do fibroblasts produce collagen?
They secrete procollagen in secretory vesicles, which then self assemble into collagen fibrils
What do fibroblasts synthesis and secrete?
Ground substance, and the fibres that are within ground substance
Where are fibroblasts very important?
In wound healing
What are fibroblast cells primarily responsible for?
Formation of scar tissue
What are macrophages derived from?
Where are blood monocytes found?
Moving around in connective tissue
When are blood monocytes particularly present?
If local inflammation, especially if chronic
What kind of role to macrophages have?
What are macrophages able to do?
Degrade foreign organisms and cell debris
What are macrophages said to be professionals in?
What is meant by macrophages being professional antigen presenting cells?
They are able to present foreign material to T lymphocytes of the immune system
What do macrophages contain?
What are pinocytic vesicles important for?
What do mast cells look like?
Are mast cells derived from basophils?
What does the mast cell cytoplasm contain lots of?
What do mast cell granules contain?
- Substances that attract eosinophils and neutrophils
What is heparin?
What does histamine do?
Increase blood vessel wall permeability
What do mast cells do when there is a threat/trauma?
Release their granule contents very quickly
Where are mast cells found?
In connective tissues near blood vessels
Where are mast cells absent from?
Why are mast cells absent from the CNS?
To avoid the damaging effect of oedema there §
What do mast cells become coated with?
Immunoglobulin E (IgE)
What is IgE?
Molecules which specifically bind allergens
What happens when an allergen cross-links with the surface bound IgE molecules?
Contents of granules is rapidly released from mast cells
What can secretions of mast cell granules result in?
Immediate hypersensitivity reactions, allergy and anaphylaxis
What do some mesenchymal cells develop into that will eventually lead to the development of adipose tissue?
What are preadipocytes?
Fibroblast like cells which are committed to become lipoblasts
How does a preadipocyte become a white adipocyte?
Preadipocyte → midstage lipoblast ↔ late lipoblast ↔ mature lipoblast (white adipocyte)
What do midstage lipoblasts develop?
Numerous droplets in their cytoplasm
What has happened in white adipose tissue?
The multiple lipid droplets fuse to form a single large droplet
What does the large lipid droplet in white adipocytes do?
Displaces all other cell contents to the cell periphery
What happens in brown adipose tissue?
The multiple lipid droplets remain separate
What has happened to unilocular adipose cells (fat cells)?
They have been almost completely filled by a single fat droplet, so the cytoplasm has been displaced to the rim and the nucleus is to one side
Of what kind is most of the adipose tissue in the body?
Why do adipose tissues appear empty in typical H&E, wax embedded preparations?
Because the toluene and xylene used in tissue preparation has dissolved alway the lipid
What is the role of adipose tissue?
Where is adipose tissue found in abundance?
Does white adipose tissue have a lot of cellular matrix?
What do brown fat cells contain?
Many lipid droplets and a central nucleus
What is brown adipose tissue also known as?
Multilocular adipose cells
Where are brown adipose tissues found?
Close to scapula, sternum and axillae, especially in the newborn
Appear to be present in upper chest and neck of adults
What is the purpose of brown adipose tissue?
Why is brown adipose tissue brown?
Due to the rich vascular supply and abundant mitochondria
Why does brown adipose tissue have a rich vascular supply and abundant mitochondria?
Because it has a high respiratory capacity for generation of heat
How is the heat production of brown adipose tissue further promoted?
Uncoupling of oxidative phosphorylation
Who is non-shivering thermogenesis important in?
Where do cells of myeloid and lymphoid blood cell linages come from?
Pluripotent haemopoietic stem cell, HSC
What happens to HSC in development?
Why is blood a special form of connective tissue?
Because the extracellular matrix is a liquid
What are the different type of blood cells?
- Small resting lymphocytes
How many lobes are there in an neutrophil nucleus?
What does a stick between connecting lobes of erythrocytes indicate?
What is true of a small resting lymphocyte until it’s activated?
It’s cytoplasm is filled by nucleus
Describe the matrix of cartilage
Amorphous but firm
What do collagen fibres form in cartilage?
An imperceptible networ
What produce the cartilage matrix?
When happens when chondroblasts mature?
They turn into chondrocytes, and lie in the lacunae
What are the functions of cartilage?
- Supports and reinforces
- Resilient cushioning properties
- Resists compressive stress
Where is cartilage found?
- Forms most of embryonic skeleton
- Covers end of long bonds in joint cavities
- Forms costal cartilages of the ribs
- Cartilages of nose, trachea and larynx
Describe the matrix of bone
Hard, calcified matrix containing many collagen fibres
Where do osteocytes lie?
Is bone well vascularised or not?
Yes, very well
What is the function of bone?
- Supports and protects
- Provides levers for muscles to act on
- Stores calcium and other minerals and fats
- Marrow inside bones is site for blood cell formation