Blood Vessels And Nerves Flashcards
General structure
- Endothelium on a basement membrane
- Intima
- Internal elastic lamina
- Media
- External elastic lamina
- Adventitia
Loose connective tissue layers
Intima and adventitia
Thick connective tissue layer
Media- comprising smooth muscle with some fibroblasts and varying amounts of collagen and elastin
Elastic arteries
arteries near the heart eg. Aorta, pulmonary arteries
• media contains abundant concentric sheets of elastin
• Elastic recoil helps to smooth pressure surges from the heart and drives blood around the coronary circulation during diastole
• Have a blood supply of their own (vasa vasorum)
Muscular arteries
most arteries are muscular arteries
• media comprises of layers of smooth muscle and little elastin
• eg radial artery, splenic artery
Arterioles
resistance vessels
• arbitrarily defined as having 3 or fever muscle layers in the media
• up to 100um diameter
• elastic laminae poorly defined
Can be closed due completely due to contraction of smooth muscle
Criteria for an arteriole
3 or fewer muscle layers in the media
• up to 100um diameter
Capillaries
no adventitia, external elastic lamina, media, internal elastic lamina, intima
• only a layer of vascular endothelial cells resting on a basement membrane
• pericyte- layer of cells present on outside of capillary. Becomes continuous as capillary becomes larger. Cells that constrict or relax to regulate size of capillaries
• fenestrated capillaries- endothelial layer is incomplete forming pores that facilitate movement of materials into surrounding tissues eg kidney, liver
• Closed capillary substances are transported across membrane by diffusion or pinocytosis
What are fenestrated capillaries
endothelial layer is incomplete forming pores that facilitate movement of materials into surrounding tissues eg kidney, liver
Sinusoids
large diameter, thin walled vessels with a fenestrated endothelium. They have poorly developed basement membrane but are supported by surrounding tissues eg liver and spleen
Does all blood pass through capillaries
Not all blood passes through capillaries. Lots of arterio-venous shunts that allow some blood to pass directly from arteriole to venule. Most organs can control their perfusion
Venules
associated with arterioles
• Have valves
• Thin walled
No external elastic lamina
• Contractile pericytes wrap around outside of endothelial cells and form a complete layer as venules get larger
• pericytes replaced by smooth muscles as venues become veins
Veins
• no external elastic lamina
• thinner muscular wall (media) and larger lumen
• Have valves
• Smooth muscles in wall may be circular or longitudinal
Lymphatics
thin walled (similar to capillaries and veins)
• have valves
• do not contain blood - contain eosinophilic lymph and may contain lymphocytes (stains pink)
• wall of the lymph capillary is composed of endothelium in which the simple squamous cells overlap to form a simple one-way valve
Peripheral nerves
composed of neurons: consist of a cell body (often found in a ganglion) and long axons
Unipolar - 1 process
Pseudo-unipolar - apparently 1 process
Bipolar - 2 processes
Multipolar - more than 2 processes
Endoneurium
Present between individual axons
Perineurium
surrounds the groups of axons to form fascicles
Epineurium
binds fascicles together to form nerve fibres
Where are cell bodies of motor neurons
Grey matter of spinal cord
Where are cell bodies of sensory neurones
Dorsal root ganglion
Where are cell bodies of sympathetic neurons
Grey matter of spinal cord and adjacent sympathetic ganglia
Where are cell bodies of parasympathetic neurons
Brain and local ganglia
Nerve cell fibrous proteins
Microtubules- assemblies of tubulin and dynein. Transport vesicles from Golgi body in neuron cell body to end and back of axon. involved in forward (anterograde) and backward (retrograde) movement of organelles and substances along axons
Neurofilaments- determination of axon diameter
Nissl substance
rER. Well-developed in neurons as have a large surface area (cell membrane) and large number of vesicles whose neurosecretions are discharged from the cells
Mesoaxon
point where the 2 limbs of the Schwann cell or oligodendrocyte that engulf the axon fuse. It is the focal point where myelin is inserted into the myelin sheath
Satellite cells
surround nerve cell bodies and play a supportive role, plying the nerves with nutrients, growth factors etc
Neurosectretory granules
found at neuro-chemical synapse:
• two most common types: cholinergic (release acetylcholine) and adrenergic (nor-adrenaline)
Myelin
• insulates axons
• a spiral of apposed Schwann cell membranes
• one axon per Schwann Cell, multiple Schwann cells per myelinated axon
• gaps between Schwann cells = Nodes of Ranvier- depolarisation occurs at these points and action potential passes from one node to the next in a saltatory fashion
• Myelinated axons are larger and transmit faster impulses than unmyelinated ones- faster conduction velocity 10-100ms compared to 1-20m/s
• Most of myelin is extracted by conventional tissue processing leaving clear spaces or causing collapse within the nerves
Myelin structure
Myelin is membranous in nature and consists of a bilipid layer with proteins inserted into it and spanning the layers. Sphingomyelin is the predominant phospholipid. Number of proteins and lipoproteins including proteolipid proteins, myelin basic protein, PO protein and peripheral myelin protein
Schwann cells
supported by continuous chain of Schwann cells (200um long)- myelinated (one Schwann cell per axon) and unmyelinated (multiple axons per Schwann cell)
Neuromelanin
found in large quantities in neurons if substantia nigra (region of brain containing dopamine)
Lipofuscin granules
breakdown products that are not fully digested and accumulate within the perikaryon of sympathetic ganglia cells
CNS
brain and spinal cord and contains most of the cell bodies. Supporting cells = oligodendrocytes
PNS
consist of mainly axons processes passing to target organs and tissues. Supporting cells = Schwann cells
Axon hillock
contains vesicles drives from the Golgi body, site of origin of nerve stimulus. Seen as a pale zone in the perikaryon (cytoplasm surrounding nucleus) at entry to axon
Can a severed nerve regenerate
If the cell body survives, a nerve fibre can regenerate but never quite as good. Can grow at 1-2cm per week
What is the predominant myelin membrane phospholipid
Sphingomyelin
Cell bodies: motor neurons
Grey matter of spinal cord
Cell bodies: sensory neurons
Dorsal root ganglion
Cell bodies: sympathetic neurons
Grey matter of spinal cord and adjacent sympathetic ganglia
Cell bodies: parasympathetic neurons
Brain and local ganglia
