Miscellaneous Flashcards
What is lymph
Plasma like fluid
It is interstitial fluid that has been removed by the lymphatic vessels
Once interstitial fluid enters the lymph capillaries it is called lymph
Why do we return fluid to the blood
To prevent oedema and maintain normal blood pressure/ volume
Give the plan of the lymphatic system
Capillary network-> afferent vessels —> lymph node —> efferent vessels —> lymph trunk —> terminal vessels (thoracic duct/ right lymphatic trunk) —> great veins
Which lymph vessels Carey fluid to the tissue
NONE
What are lymph capillaries
Smallest lymphatic vessels which begin in tissue spaces as blind ended sacs
Where are lymph capillaries not found
Bone marrow Bone Teeth CNS tissue that lack a blood supply eg epidermis
What is the lymph capillary wall made of
Endothelium in which simple squamous cells overlap to form a simple one way valve (allowing fluid to enter but not exit)
What do lymphatic capillaries merge to form
Lymphatic vessels
Differences between lymphatic vessels and veins
Lymphatic vessels are thinner, have more valves and anastomose more frequently
Where do we think lymphatic vessels initially derived from in the embryo
Why do we think that
From the embryonic venous system
There is an intimate relationship between them
What do lymphatic vessels join to form
Lymphatic Trunks
Name the 5 lymphatic trunks
Paired lumbar Paired bronchomediastinal Paired subclavian Paired jugular trunks A single small intestinal trunk
What does the right lymphatic duct drain
Lymph from the upper right quadrant of the body
What does the thoracic duct drain
Everything other than the right upper quadrant of the body
What is the right upper quadrant of the body
Right half of head and neck, right upper limb, and right hemithorax
What does the lymphatic duct do with lymph after
Empties it into the venous circulation at the junction of the IJV and subclavian vein
Where does the thoracic duct extend from
What is the adult variation in length
L2 to the root of the neck
38-45cm
What happens if the thoracic duct is damaged
What is this called
Often it’s fine Cos it has so Many anastomoses
But if it becomes damaged by disease, lymph can leak into the pleural cavity (chylothorax)
All Lymph vessels have powerful contractile abilities. True or false?
False
Initially They rely on extrinsic forces for propulsion (a mix of muscle contraction, pressure pulse, and respiratory movement)
How is lymph flow direction maintained
Funnel shaped valves
What is the unit between lymph valves called
A lymphangion
How do collecting lymphatic propel lymph
They are contractile and the flow between lymphangions is maintained against a pressure gradient
Superficial Lymph drain in parallel to arteries. True or false?
False
They drain parallel to veins
Where are the lymph nodes
Axilla
Inguinal
Superficial cervical
What happens to superficial lymph drainage
Drains into deep system
What do deep lymphatics do
Drain organs and run parallel with arteries
Describe the structure of a lymph node
Convex surface to receive afferent lymph vessels and a convex one from which efferent leave
Each mode has a connective tissue capsule and is divided into an outer cortex and inner medulla
How does lymph travel through the nose
Enters via afferent vessel
Travels through a large sub capsular sinus and smaller sinuses to exit at the hilus through the efferent vessels
How do the number of afferent and efferent lymphatic vessels compare
Why is this
More afferent than efferent
This slows flow of lymph allowing lymphocytes and macrophages time to carry out function
What is the general pattern of lymphatic drainage in the head and neck
Superficial vessels run with superficial veins in the superficial fascia
These drain into nodes at the collar at the upper attachment of the deep cervical fascia. These nodes drain to deep cervical nodes around the IJV
What is the group of lymph nodes in the neck
Sub mental Submandibular Parotid Mastoid Occipital
Where do lymphatics draining the intestine run
Along arterial tree to reach coeliac, superior or inferior mesenteric para- aortic nodes
Where are the para aortic nodes
Lying around the Origin of the arteries in the abdomen
What are the nodes in the thorax
Mediastinal and lateral aortic
What is the chief means by which fat is absorbed from the intestine
Lymph which drain the alimentary canal
What do the alimentary canal lymphatics look like after a meal
What is the lymph called
Milky with fat
Chyle
Where do lymphatics from the lower limb and pelvis pass to
Lower limb: external iliac node
Pelvis: internal iliac node
Where do the external and internal iliac nodes drain to
Upwards into a chain of paravertebral and retroperitoneal nodes which lie laterally to vertebral bodies
What do the para vertebral and retroperitoneal nodes drain
Suprarenal glands
Kidneys
Gonads
Posterior abdominal wall muscles
What are the key nodes the limbs drain to
Upper: axillary
Lower: inguinal
What might be used as a contrast medium for x-rays
Iodine or barium
What are the five basic radiographic densities
- Black due to air eg air in lungs, gas in bowel
- Dark grey due to fat
- Light grey due to soft tissue or water
- White due to bone or calcification
- Bright white due to metal
What is the most important characteristic for definition in an x-ray
What does this mean
The presence of boundaries between densities
X-ray is good for the chest and skeletal system
Give two main advantages of radiography
They
What is the upper limit of human hearing
how does this compare to other animals
What frequency does diagnostic ultrasound work at
20kHz
Bats: 120kHz
Dolphins: 200kHz
Between 2 and 20 MHz
What is central to the theory behind diagnostic ultrasound
The piezoelectric effect
Who discovered the piezoelectric effect
What did they show
Pierre and Jacques Curie (1880) through their work on crystals eg quartz
Mechanical stress not only induced an electric current in such material but that the reverse also held true that for the emitter could also be the receiver
What principle does ultrasound technique rely upon
Ultrasound waves are either transmitted through tissues of similar acoustic quality or reflected that there is a significant difference this is called acoustic impedance
What is acoustic impedance a function of
Tissue compress ability and the speed of sound through it
How does calcified tissue react to ultrasound
What about fluid?
It is highly reflective and casts and acoustic shadow (with no information beyond)
Fluid volume is transmit sound brilliantly causing acoustic enhancement beyond them
True or false
a probe cannot be placed within blood vessals
False
they can be placed almost anywhere
What is the essential trade-off in ultrasound
Between depth penetration and spatial resolution
I.e. higher frequencies get better resolution but Are more easily attenuated
Other than the Piezoelectric affect what effect does the ultrasound technique take advantage of
Explain this effect in medicine
The Doppler effect
It causes a shift in the frequency of reflected sound according to whether there is motion towards (increase) or motion away (decrease) from its source
What are the advantages of ultrasound
It is widely available,
portable so can be used in the ITU,
safe as no ionising radiation
Give some disadvantages of ultrasound diagnosis
It is operator dependent and not good for all structures e.g. bones
When was the first CT scan performed and where
Who won the prize for it and when
1971 in Wimbledon
Hound field and McCormack
Noble prize in physiology or medicine 1979
How does a CT scan work generally
The x-ray tube rotates around the patient to pass x-rays through the body from every direction although only 180° is required for a single image
The line of a single beam passed through a body gives a numerical value representing how much it has been attenuated from the original level
These values are reconstructed to form the final 2-D image
How is the resultant axial image of a CT scan viewed by convention
When is it different
As if the observer were standing at the patient’s feet and looking towards the head as in clinical bedside examination
It was originally the other way around the neurosurgeons with their drills at the ready
True or false
single whole body scans take days to perform with CT
False
can be performed within a single breath to yield a detailed 3-D and multiplanar reconstruction
What are vital part of CT to increase the inherent contrast between structures
Why are these also useful
Iodine-based intravenous or oral contrast media
Tissues that an inflamed or malignant have abnormal vasculature with increase bloodflow and leaky vessels
How much radiation does a CT scan of the abdomen and pelvis expose the patient to
Radiation dose as high as three years of background radiation or approximately 100 chest x-rays
What are the three fundamental principles of MRI
- A large proportion of the body is fat or water
- Fat and water contain a lot of hydrogen nuclei
- Hydrogen nuclei have spin that interacts with magnetic fields and RF radiation
How strong is the magnetic field generated by MRI scanner?
3 Tesla
What is MRI good at imaging
Brain
Musculoskeletal system
Abdomen and pelvis
What is MRI not good at imaging
The chest unless cardiac gating is used to reduce movement artefact from the beating heart
Why does acquiring MRI images take longer than CT
What does this mean
Due to the multiple changes of magnetic fields required
Patients need to be able to cooperate and keep still to obtain a diagnostic image
True or false
MRI is completely safe.
False.
Anything within the body that can be magnetised may heat up or even move e.g. metallic foreign bodies such as surgical clips or prostatic heart valves
Pacemakers will stop working when they are placed inside the magnetic field produced by the MRI scanner to a patient with a cardiac pacemaker cannot go into the scanner and will have to be imaged using a different imaging modality
Generally what does nuclear medicine involve
Give an example
Administration of radiolabelled agents that undergo radioactive decay in the body which is then picked up by special cameras in 2-D or 3-D
PET
What is the most common agent used in nuclear medicine
18-FDG
What is 18-FDG
18 - fluorodeoxyglucose
Describe the course of imaging for a patient with trauma in the emergency department
X-ray initially thought fractures
May proceed to CT in more severe trauma to assess extent of bony injury and if associated soft tissue or organ is injured
How would you image someone with chest pain
Chest x-ray initially
May proceed to CT for further anatomical detail
Describe the course of imaging for abdominal pain
Ultrasound
May use CT depending on clinical question
What imaging would you use for cancer diagnosis
X-ray and ultrasound initially
May proceed to CT and/or MRI depending on disease type
Give the six steps when describing an image
- State the region of the body being imaged
- State the imaging modality
- State to view orientation
- Check the patient’s details if present
- Describe any abnormalities
- Give a diagnosis or possible list of causes
What happens if bone is understressed for long periods of time
Bone wastage occurs and the bone will become thinner
What happens if bones are suddenly subjected to high levels of stress
An increase in bone mass occurs
Describe the general structure of a bone
A hard outer casing of cortical bone and an inner trabecular bone
How much of the bone mass is cortical bone
80%
What is another name for trabecular bone
What does it consist of
Cancellous or Spongey bone
Delicate bars and sheets of bone (trabeculae) which branch and intersect to form a sponge like network
What is the structure of compact bone and where is it found
It is dense and more regular than trabecular bone and forms a thick walled tube of the shaft (or diaphysis) of long bones which surrounds a marrow cavity
A thin layer also covers the epithesis of long bones
What covers bones
Describe the vessels and nerves in this layer
And outer layer of dense connective tissue: the periosteum
It is highly vascular and densely innervated
What lines the surface of the bone facing the marrow cavity
I thin-layer of sale rich connected tissue: The endosteum
Which layers of bone possess osteogenic potency
What does this mean
The periosteum and endosteum
Following injury cells in these layers may differentiate into bone forming cells to aid in the repair of damage to the bone
Other than having osteogenic potency why is the periosteum useful
It acts as an anchoring point for tendons and ligaments
True or false:
The compressional strength of bone is greater than that of a reinforced concrete
True
The tensile strength also approaches that of reinforced concrete
True or false
Bone has a high level of torsional strength
What does this mean
False
Fractures often occur as a result of torsional forces that are exerted upon the limbs
What are the four types of bone cell
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
What are osteoprogenitor cells
Where are they pound and what do they do
Stem cells of bone
They are located in the periosteum and endosteum and differentiate into osteoblasts
What are osteoblasts
What do they form
Bone producing cells
A low columnar epitheloid layer at sites of bone deposition
As they become trapped in the form and bone they differentiate into osteocytes
What are osteocytes
Where are they found
Quiescent osteoblasts That connect with each other through canaliculi
In lacunae
What are osteoclasts
Where do they come from
Very large multinucleated bone resorbing cells
They arise from macrophage precursors in the blood
How big are osteoclasts
Up to 100μm
What are the organic components of bone matrix
Collagen fibres with type one collagen
Aim of this material including glycosaminoglycans that are associated with proteins
How much of a matrix is type one collagen
95%
What do collagen fibres do in bone
Confer tensile strength
Describe the inorganic components of bone
50% dry weight of bone matrix
Composed of calcium and phosphorus with small amounts of HCO3, citrate, magnesium, potassium and sodium
Calcium forms hydroxyapatite crystals with phosphorus
Calcium salts which are similar in physical properties to marble confer compressional strength
How are the collagen fibres in bone laid down
What do these form
Laid down by osteoblasts around the tunnels created by osteoclasts
These form concentric arrays of lamellae
What do the concentric arrays of lamellae in bone form
Osteons
What do osteons surround
The initiating blood vessel in the Haversian canal
What does the osteon and the Haversian canal together form
Haversian system
Name 2 disorders of bone matrix
Osteogenesis imperfecta
Osteomalacia
Describe osteogenesis imperfecta
This is a group of inherited diseases associated with mutations affecting collagen
Causes brittle bone that breaks easily, often the little or no apparent cause
Describe osteomalacia
A loss of skeletal mass caused by inadequate mineralisation of the normal osteoid tissue after the closure of growth plates
In children the condition is commonly known as Ricketts
Both are caused by vitamin D deficiency
What are the two mechanisms by which bone can be formed
Intramembranous ossification
Endochondral ossification
Which bones are formed by intramembranous ossification (name 3)
Bones of the skull, part of the mandible and clavicle
Name three steps for endochondral ossification
Initiates with condensation that forms a cartilage model of the bone
First visible step in ossification is hypertrophy and death of chondrocytes in the centre of the cartilage. This enables invasion by blood vassals which allow osteoprogenitor cells to enter the cartilage. He is differentiate into osteoblasts and secrete own matrix. They secrete osteoid, and ECM that binds to calcium and becomes more mineralise.Initially collagen fibres have a hazard arrangement
Differentiation of osteoblasts depend on Runx2 and Osx2. In mice where either is knocked out there is no bone made. Defects in Runx2 lead to a condition known as cleidocranial dysplasia
What are the two genes associated with endochondral ossification
Runx2
Osx2
What is the epiphyseal growth plate
I can’t imagine this region that remains at the junction between the epiphysis and diaphysis
As the bone continues to grow, how are the cartilage cells are arranged
Into zones:
Quiescent zone/stem cells
Proliferative zone of cell division
Hypertrophic zone
Which gene regulates the transition of cartilage to bone
Indian hedgehog (IHH)
Where is Indian hedgehog expressed
In pre-– hypertrophic cells and axe to promote proliferation and prevent hyperTrophy
What happens to mice that lack Indian hedgehog
They have decreased chondrocyte proliferation and short stubby bones
Which hormones act on bone growth and how
Growth hormone
Thyroid hormones
IGF-1
By acting on the germinal zone stem cells
Which hormone is deficient in Pygmies
IGF-1 levels during puberty drop to 1/3 of normal in Pygmies
How does FGF3 affect bone growth
Where is the FGF3 receptor present in bones
FGF3 inhibits growth and promotes differentiation
On chondrocytes
Achondroplasia associated with what mutation
Is it dominant or recessive
And activating mutation in the FGF3R
Dominant
When do you growth plates ossify
At the end of puberty
Give five things bone remodelling is important for
Making compact bone
Calcium homeostasis
Response to mechanical stress
Removal and replacement of ageing bone
Fracture repair
What do osteoclasts do
They are large multinucleate cells derived from haemopoietic lineage that cling to the bone matrix and erode
They can tunnel deep into the matrix, forming cavities
Name 4 key regulators of osteoclast development
Cytokines
RANKL
OPG
Calcitonin and PTH
What is RANKL
How does it affect osteoclast activity
RANK ligand
Binds to receptor RANK and promotes osteoclast activity
What is OPG and how does it affect osteoclast activity
Osteopregin
It acts as a decoy receptor binding with RANKL and inhibits osteoclast activation
How do calcitonin and PTH affect osteoclasts
Calcitonin inhibits osteoclasts when calcium is high
parathyroid hormone stimulates osteoclasts when calcium is low
How do you stimulators bone resorption affect osteoclast formation
They increase osteoclast formation by stimulating production of RANKL
Name to stimulators of bone resorption
PTH
interleukin-1 (IL-1)
How fats do groups of osteoclasts move
At 50μm a day
How are bones remodelled
Groups of osteoclasts form a cutting cone
This is followed by osteoblasts which deposit new osteoid matrix concentrically around a centrally ingrowing blood vessel. The pattern and extent of the modelling is dictated by the mechanical loads applied to the bone
What is osteoporosis
It means porous bones
Says when bones become more fragile and susceptible to fracture
An adequate supply of calcium is needed to optimise peak bone mass in early adult hood in order to protect against osteoporosis later in life
How many women have low bone density
What does this mean
About 20% of women over 50
This predisposes them to osteoporotic fractures especially of the wrist and hip and vertebrae
What is Paget’s disease of bone
Access activity of osteoclasts
A lot of women bone at the expense of compact bone
Is there a familial link in Paget’s disease of bone
What is it linked to
Familial history of it in up to 40% of patients
Linked to mutations in RANK and OPG
What are the four stages of bone healing after fracture
- Inflammation and formation of haematoma
- Formation of fibrocartilage callus
- Replacement of cartilage with lamellar bone (a bony callus)
- Remodelling of bone to normal contour
Give three factors that affect bone healing
Poor blood supply
Non-union
Infection
Give 5 bone functions
Support
Protection
Movement
Mineral/calcium storage
Hematopoiesis
What is hydroxyapatite
Calcium phosphate crystals
Which genes does brittle bones disease affect
Type 1 collagen genes
COL1A1 and COL1A2
Why all the different severities of osteogenesis imperfecta?
Null mutations in collagen genes cause a quantitive decrease in type one collagen leading to milder forms
Dominant negative mutations disrupt the triple helix structure leading to more severe forms
Give seven common symptoms of osteogenesis imperfecta
Bone fractures and limb deformities
Scoliosis
Macrocephaly
Hearing loss
Defective denition
Joint laxity
Growth retardation
Which disease do you children who are lactose intolerant to have a higher chance of getting
Osteomalacia
Give signs and symptoms of Ricketts/osteomalacia
Diffuse bone pain, tenderness and muscle weakness
X-rays commonly show decreased bone density with thinning of the cortex then maybe concavity of vertebral bodies and bowed legs
Looser’s zones
What are looser’s zones
Fractures or cracks that may appear in osteomalacia
These are incomplete fractures that are filled with unmineralised osteoid seams
True or false
More proximal limb structures commence ossification earlier
True
Phalanges and metacarpals will be late
What is Hunter Thompson Grebe type Maroteaux
When all skeletal elements are present but have abnormal growth
Why are growth plate fractures twice as frequent in boys
Female bones finish growing earlier
