BL 15 Flashcards
Recap - list the 6 types of connective tissue
Loose connective tissue
Dense connective tissue
Bones
Cartilage
Adipose
Blood
How many types of bones are there?
5 types
Name the different types of bone
Classified on basis of shape:
- Long
- Short
- Flat
- Irregular
- Sesamoid (sesame seed-like)
How can the skeleton by split?
- Axial skeleton (the part of the skeleton that consists of the bones of the head and trunk of a vertebrate)
- Appendicular skeleton (the portion of the skeleton of vertebrates consisting of the bones that support the appendages)
Long bones (describe their shape, examples, which part of the skeleton, function)
The long bones are:
• Description: longer than they are wide
• Examples: Mostly limb bones, include, the femur (the longest bone in the body) and small bones in the fingers
• Location: Long bones are mostly located in the appendicular skeleton
• Function: To support the weight of the body and facilitate movement
Short bones (describe their shape, examples, which part of the skeleton, function)
- Description: Short bones are approximately as long as they are wide
- Examples: Wrist and ankle joints.The carpals in the wrist (scaphoid) and the tarsals in the ankles (calcaneus)
- Location: Axial skeleton
- Function: Short bones provide stability and some movement
Flat bones (describe their shape, examples, which part of the skeleton, function)
- Flat bones are somewhat flattened, with roughly parallel opposite edges
- Examples: In the skull (occipital), thoracic cage (sternum and ribs), Pelvis (ilium)
- Function: Protects internal organs. Also provide large areas of attachment for muscles
Irregular bones (describe their shape, examples, which part of the skeleton, function)
•Description: Irregular bones vary in shape and structure and therefore do not fit into any other category. They often have a fairly complex shape
• Function:
- Protect internal organs.
- Vertebrae in the vertebral column protect the spinal cord
- Pelvis (sacrum) protect organs in the pelvic cavity
- Provide important ‘anchor’ points muscle groups
Seasmoid bones (describe their shape, examples, which part of the skeleton, function)
- Description: Sesamoid bones are bones embedded in tendons. Small, round bones found in the tendons of hands, knees, and feet
- Example: The patella is an example of a sesamoid bone – generated postnatally (the patella literally sits inside the tendon)
- Functions: Protect tendons from stress, and damage from repeated ‘wear and tear’ (reduces the tension in the tendon, protects the tendon from being damaged from ‘wear and tear’)
Name and describe the two types of bone in a cross section?
- Compact (compact/compressed/cortical) bone forms the external surfaces of bones and comprises ~80% of the body’s skeletal mass.
- Cancellous (cancellous/spongy/woven) bone forms a network of fine bony columns or plates to combine strength with lightness. The spaces are filled by bone marrow
Bone marrow (name, describe and the give the function of the two types)
Two types:
Red Marrow
- Full of developing blood cells
- Rich blood supply
- Only found in spongy bone
Function: To replenish cells in the blood (haemopoiesis)
Yellow marrow
- Full of adipocytes
- Poor blood supply (as doesn’t need a very good blood supply)
- At the centre of bone marrow
Function: Shock absorber and energy source Can convert to red marrow
How can bone marrow be investigated?
Cancellous bone (talk about its specific structure, name the 3 specific cells in the picture, will go into more detail in future lectures though)
Each trabeculum consists of numerous osteocytes embedded within irregular lamellae of bone Osteoblast sit on the surface of the trabeculum (blue border line in the pic below)
Osteoclasts on their surfaces act to remodel them.
Osteocytes are the dots inside the trabacule.
How do maturing cells leave the bone? (all cells except platelets)
- Determined by the speed at which blood passes throhg the bone, this determines how the cells are going to get out
- Nutrient artery enters the bone, passes into the bone marrow. There are many capillaries in the bone marrow too. ‘Normal’ capillaries then lead into a ‘mesh’ of sinusoidal capillaries (whereas, some of the capillaries lead into the compact bone layer and then enter the sinusoidal capillaries from ‘the top’
- Cells in the bone marrow (grey dotted bit of pic below) enter the blood supply through sinusoidal capillaries. The sinusoidal capillaries then enter the central marrow vein.
How do platelets leave the bone?
- MSC move to the edge of the bone and attach to the osteoblasts
- When the MSC are bound to the osteoblasts, if the osteoblasts recieve a signal
- This signal tells the MSC to divide
- The MSC then divides into cells called hematopoietic stem cells (called HPC) or HSC
- The HPC and HSC undergoes division. One of the cells go back and becomes MSC (then attached to the oestoblast etc). However, 2 of them, come together and start to develop.
- The two cells fuse, fuse again etc.
- Changing the marrow viscosity and the release of fatty acids change the phenotypes and make a really large cell called a megakaryocyte
- **Megokaryocyte then forces out parts of its cytoplasm between the epithelial cells. It enters sinusoid through fenestrations
- These fragments of the megokaryotes then become the platelets**
Summary of how cells are released
Platelets - released through fenestrations in the sinusoid
Other mature cells - released through sinusoids
List 3 types of vessels (regarding gaps in their endothelial cells etc)
- Continuous
- Fenestrated
- Sinusoid (large gaps between endothelial cells, allowsing cells to move in and out freely through these vessels - called intercellular gaps)
Look at the SEM of sinusoids
Journey of RBCs (how long does it take for RBCs to mature in the blood?)
On entering the circulation:
• Newly formed RBCs travel from: Venule intermediate vein larger vein vena cava
• During circulation RBCs become mature – 2 day
Capillaries (the other name of capillary circulation, location, function, size, how the flow in capillaries is controlled?)
- Microcirculation
- Flow in capillaries is controlled by precapillary sphincters. Contain smooth muscle - contraction - When open, blood flows freely to the capillary beds - When closed, blood is not allowed to flow through the capillary beds
- Located between arterioles and capillaries
- Function: Controls fluid exchange between the capillaries and the body tissues takes place at the capillary bed Larger cells cannot pass through capillaries and bypass the capillary bed
- Size of capillaries: Size of a RBC, RBC has to ‘squeeze’ it’s way through capillaries, WBC can’t go through microcirculation because they are too big
Vein structure (definition, layers, pressure, other structures in this structure)
- Definition: A vein is an elastic blood vessel that transports blood from various regions of the body to the heart
- Consists of 3 layers:
- Tunica intima – (inside, close to the blood) endothelial cells
- Tunica media – elastic fibres and smooth muscle cells (‘media’ - middle), this layer allows expansion of the vessel
- Tunica externa – elastic fibrous capsule (lots of collagen), this layer restricts the absolute size of the vein, so the vein doesn’t expand so much that it will break.
- Non-return fibroelastic cartilaginous valves assist flow towards the heart
- Low pressure system (relies on muscle contractions to return blood to the heart e.g. calf muscles compress to aid movement against gravity)
- Vein problems occur, due to either a blood clot or a vein defect behind the valves, e.g. deep vein thrombosis
Visualise a SEM of a vein
Arteries structure (definition, layers)
- Definition: Arteries are elastic blood vessels that convey blood away from the heart
- Consists of 3 main layers:
- Tunica Intima - composed of an elastic membrane lining and smooth endothelium (non-fenestrated)
- Tunica Media - composed of smooth muscle and elastic fibres. This layer is thicker in arteries than in veins and has two distinct elastic layers
- Tunica Externa (also called tunica adventia) - the strong outer covering composed of collagen and elastic fibres - allows arteries to stretch but prevents over expansion due to higher blood pressures than in the veins •
- Smaller lumen diameter than veins
Comparision of arteries, capillaries and veins (function, structure of the wall, lumen, valaves, function)
Comparison between artery and vein (wall structure)
Collateral blood vessels (what are they, when are they produced, give an example of what type of patient these may be seen with)
- Collateral vessels (usually arterioles) provide protection for tissues that may become compromised. They develop due to reduced blood flow often to distal part of the body or in the carotid artery and the brain
- Provide alternative path for arterial blood flow
- Some generated due to chronic disease such as ischaemia (reduced blood flow) (e.g. coronary arteries or around slow growing tumours)
- Fatty placque causing blockages will send signals to start making new blood vessels. These blood vessels join the point before and after the blockage. This helps the continuous flow of blood to tissues past the blockage.
- Some produced during development (e.g. brain and joints)
- Take time to develop
Formation of new blood vessels (name of this ‘method’, explain the process, give an example)
- Vasculogenesis
- Formation of new blood vessels angioblast precursors (bone marrow)
- Mesenchyme stem cells aggregate
Make growth factors that change the phenotype of the cells that are clustering together
They then split into cells that are around the otuside (become endothelial cells) and the cells in the middle become a primitive blood cells - Examples: During embryo development (heart and primitive vascular plexus), newly formed cancers, endometriosis, etc
Formation of new blood vessels from existing blood vessels (name of this ‘method’, explain the process, give an example)
- Angiogenesis
- Formation of new blood vessels from existing blood vessels
- Stimulus or growth factor (e.g. FGF)
Endothelial cells start migrating away from the stimulus
Smooth muscle cells move ‘out of the way’
Endothelial cells then grow towards the stimulus
Smooth muscle cells then ‘recoat’ the blood vessel - Examples: During fetal development, collateral arteries, postnatal lung development
Fetal blood vessels - look at the pic attached, what do you notice about the RBC?
These are fetal RBC because they have a nucleus, normal RBC do not have a nucleus
Formation of blood vessels during embryogenesis
First steps: Production of a single vessel
• VEGF produced by endoderm
• Generates primary plexus, which folds into a primary vessel
Sprouting: Angiogenesis
• FGF produced by mesenchymal cells
• Pericytes (stem cells) convert into smooth muscle cells
• Slow, takes hours to days (time consuming)
Division of primary vessel: Intussusception
• Twinned vessels from primary vessel (e.g. ‘splitting one vessel into two’ - one of the vessels might become an artery, one of the vessels may become a vein - this is why arteries and veins are close together in neurovascular bundles)
• Needs multiple growth factors
• Explains why arteries and veins are close together in ‘neurovascular bundles’
• Quick, takes minutes to hours
Pericyte (structure, fucntion, seen the importance in embryology, also important post-nataly)
Structure:
• Immature ‘smooth muscle-like’ cell Found inside the basal lamina close to basement membrane
• Perictye has key component of capillaries
• Have contractile properties
• Also involved in nerve cell communication
• Blood-brain barrier (stops blood entering brain tissue, as it sits in the joint between 2 adjacent endothelial cells, preventing them from leaking)
Able to differentiate into:
endothelial cell, smooth muscle cell or fibroblast
Functions:
• Prevents endothelial cell proliferation
• Maintains tight capillaries, e.g. blood brain barrier, in the retina, etc.
• It differientiates into epithelial cells if the epithelial cells get damaged, it can also turn into msucle cell or fibroblasts as it is a stem cell
NB: the extensions of the pericyte as its cytoplasmic extensions, the ‘bulby’ bits are the body of the pericyte
