Session 6 - Supporting Tissues Flashcards
When is elastin made?
Elastin is only made during foetal development. It is never replaced
Name the main cells found in connective tissues and the main products
Cells: - Fibroblasts - Chondrocytes - Osteocytes/blasts/clasts - Stem cells/Progenitor cells/ Bone marrow/ blood/ adipocytes Products: - Fibres - Ground substance - Wax and gel like materials
What are the main functions of connective tissue?
1) Binding
2) Protecting
3) Insulating
4) Storing fuel reserves
5) Transporting substances
6) Separation of tissues
What is connective tissue proper and it’s subgroups?
Loose connective tissue (Areolar) - such as the lamina propria
Dense Connective tissue:
- Irregular
- Regular
- Fascia - think sheaths separate muscles
- Aponeurosis - connect muscle to muscle, tendon to tendon, ligament to tendon
Describe the structure of loose connective tissue
- Cells: fibroblasts, macrophages, other white blood cells, mast cells and adipocytes
- Mostly collagen and elastin
- Ground substance has proteoglycans and hyaluronic avid
What are the functions of loose connective tissue?
- Holds vessels that supply fluids
- Permits cell migration
- Involved in inflammation pathways
- Acts as packaging around organs
- generally hold everything in place
- Cushions and stabilises organs
Where can loose connective tissue be found?
Found under epithelial cell layers (lamina propria), around glands, capillaries, nerves and sinusoids
What are myofibroblasts?
Modified fibroblasts that contain actin and myosin. They are responsible for wound contractionq
What is the role of macrophages in loose connective tissue?
- They are derived from blood monocytes and are phagocytic cells. They move into loose connective tissue when there is local inflamation
- They are classed as “Professional antigen presenting” cells
Describe a mast cell and its properties
Look like basophils but are NOT derived from them and are strongly stained by haematoxylin.
Granular cell that contains:
- Histamine - increases blood vessel permeability
- Heparin - Anticoagulant (stops sealing of blood vessel)
- Cytokines - Attract eosinophils and neutophils
Where are mast cells not found and why?
They are not found in the CNS to avoid the damaging effects of an oedema
What is the difference between brown and white adipose tissue?
White adipocytes - Unilocular with nucleus and cytoplasm squeezed to sides
- Act as padding, shock absorber and insulation
Brown adipocytes - Multilocular with multiple lipid droplets. Nucleus and cytoplasm in center
- Insulation and fuel reserve (not really for shock absorption)
- Heat generation (Oxidative Phosphorylation uncoupling)
What are the 4 main types of collagen and describe their properties
Type 1 - Most common. Fibrils aggregate into fibres and fibre bundles (tendons)
Type 2 - Fibrils do not for fibres (present in hyaline and elastic cartilage)
Type 3 - Fibrils form fibres around muscle and nerve cells and within lymphatic tissues. It is called Reticulin
Type 4 - Unique to the basement membrane
How are fibrillin and elastin linked?
Microfibrils (fibrillin) are important scaffolding components of elastin fibres
What constitutes the extracellular matrix?
A complex extracellular structural network that consists of ground substance and fibres
What is ground substance
A viscous clear substance with a slippery feel. It is composed of proteoglycans such as glycosaminoglycans (GAGs) and hyaluronic acid
Describe the properties of dense irregular connective tissue
- Densely packed irregularly orientated collagen bundles
- Fibroblasts
- Resist forces in multiple directions
- Elastic fibres allow a small degree of stretch
Describe dense regular connective tissue
- Collagen bundles densely packed and run in parallel
- Resist tensile forces
- Fibroblasts elongated between bundles and parallel
How do tendons and muscles bind?
At the myotendinous junction the collagen fibres from the tendon pass into the muscle fibres where they form cross-links with the collagen fibres coating the muscle fibres
What is the composition of a tendon and what can this cause?
30% collagen (70% type I 30% type III reticulin)
2% elastin
68% water (as a result of this water content if someone is dehydrated this result in making the tendon brittle and more likely to snap as the fibres can’t pass over one another)
What is the difference between a tendon and a ligament?
Ligaments connect bone to bone, tendons connect muscle to bone
In ligaments collagen bundles are arranged in fascicles which are separated by loose connective tissue
What is facia and what defines it’s 3 types?
Fascia is similar to ligaments and tendons. The collagen fibres are arranged in parallel to direction of pull
3 types are based on anatomical position:
- Superficial - on the surface
- Deep - underneath something
- Visceral or parietal - next to an organ or skin (respectively)
What is an aponeurosis where are they found?
Attach - flat muscle to muscle
- tendon to tendon
- tendon to ligament
Examples - Plantar (foot), Palmar (Hand), Galea (head)
Why does vitamin C lead to scurvy?
When collagen is being formed vitamin C is required to hydroxylate proline and lysine on preprocollagen. As a result the collagen doesn’t form a proper triple helix and faulty collagen is formed
What occurs during marfans syndrome and what causes it?
This is an autosomal dominant mutation of the Fibrillin 1 gene. As a result of fibrillin malformation elastin fibres don’t form properly. This can lead to - Tall stature, arachnodactyly and aortic rupture.
The condition can be indicated by the presence of desmosine and isodesmosine in the urine (these are unique amino acids only found in elastin)
What are the three layers of the aorta?
Tunica intima (endothelial cells) Tunica media (elastin layer) Tunica adventitia (Collagen layer preventing aorta getting too big)
What occurs in osteogenesis imperfecta?
Mutation of the Col1A or Col2A gene. This results in faulty glycosylation of procollagen and as such there is faulty collagen formation. This causes:
- Weakened bones
- Short stature (dependant on the mutation)
- Blue sclera
- Hearing loss
- Hypermobility
- Poor teeth development
Describe the stages of collagen synthesis
1) Preprocollagen is translated on ribosome
2) Lysine and proline are hydroxylated which requires the use of Vitamin C
3) Preprocollagen leaves the ER and enters the Golgi
4) Procollagen is glycosylated
5) triple helix is formed
6) leaves cell by exocytosis
7) Cleavage of N and C terminals to form tropocollagen
8) Cross link formation between fibrils to form collagen
What is the parotid gland and where is it found?
This is an almost entirely serous gland and contributes to about 30% of the salivary output. They come as a pair and are located just in front of (anterior to) the ears
What are the 3 main salivary glands and how do their secretions differ?
Parotid - almost entirely serous
Submandibular - mostly serous but more mucous
Sublingual - Almost completely mucous
How are the saliva glands controlled?
Only via neural innovation:
- Parasympathetic: large amounts of watery saliva rich in enzymes (fight or flight)
- Sympathetic: Small, thick secretions of saliva, rich in mucus
Describe the hepatic blood supply (Hepatic triad)
1- Hepatic Portal Vein - brings nutrients to be filtered from the GI tract
2- Hepatic Artery - supplies liver with oxygenated blood
3- Hepatic Vein - Drains deoxygenated blood and filtered blood
Describe the 3 different types of capillary vessel and where they may be found
Continuous - Brain, most of the body
Fenestrated - Pituitary/ Kidney/ Small intestine (where small molecules need to be able to move)
Sinusoidal - Bone marrow/liver/spleen (incomplete basement membrane and intercellular gaps) Where cells need to leave
Name the main specialised cells found in the acinus of the liver and briefly outline their function
- Hepatocytes - line the sinusoids of the acinus and are found after the Space of Disse. They detoxify, metabolise etc.
- Pit Cells - a form of natural killer T cell (destroys cells like cancers)
- Dendritic Cells - Picks up bacteria/viruses and anything else and presents it to macrophages (particularly Kupffer cells)
- Kupffer Cells - Specialized macrophages
- Stellate cells (Ito) - Contain Vitamin A
What is the role of Kupffer cells?
- Trap and phagocytose damaged or aged erythrocytes and any pathogens
- They form part of the sinusoidal lining
Outline the properties of hepatocytes
- Constitute 80% of liver population
- Remarkable regeneration ability
- Contain:
- more mitochondria
- lots of peroxisomes
- Numerous free ribosomes
- Lots of RER and ER
- Glycogen deposits
What does the liver store?
- Iron
- Vitamin A,B12,D,K (lipid soluble vitamins)
- Glycogen
- Copper
Name some anabolic functions of the liver
- Production of 60% of the bodies proteins
- Major plasma proteins
- Albumen - Enzymes
- Lipid carrier proteins
- Amino acid synthesis
- Haematopoiesis in the foetus
Name some catabolic functions of the liver
Destruction/Detoxification of:
- Drugs
- Hormones, steroids, insulin, glucagon
- Haemoglobin, Bilirubin passed to gall bladder
- Poisons/Toxins
- Removal of RBCs
Outline some of the signalling roles of the liver
Autocrine - VEGF - stimulates growth of itself and angiogenesis
Paracrine - Succinate - Signals the cell next to it to grow for regeneration
Endocrine - GH, IGF1 - Stimulates muscle and bone growth
What makes hepatocytes particularly weird?
It has both exocrine and endocrine function as a single cell.
