what is the route of interstitial fluid back into the blood?
- lymph capillaries
- ## lymphatic vessels
structure and properties of lymph capillaries
- blind-ended
- endothelium lined (ends of endothelial cells overlap obliquely)
- held open by anchoring filaments that attach them to surrounding tissue
- more permeable than blood capillaries
what is carried in the lymph?
- lymphocytes
- erythrocytes (rare)
- blood proteins (globulins and albumins)
- microbes
where are lymphatic vessels not found?
- CNS
- bone marrow
- cartilage
- epidermis
- alveoli
- placenta
structure of lymphatic vessels
- thinner walled than veins
- contain valves
what causes the flow of lymph fluid?
- contraction and relaxing of surrounding skeletal muscles (especially within a confined space)
- pulsing of an adjacent artery
- intrinsic smooth muscle contractility (sympathetic nerves stimulate constriction if blood pressure is low)
how do lymph vessels grow in an embryo?
- six sacs (outgrowths of veins)
- two sacs form around the jugular
- retro-peritoneal sac
- iliac sacs
- cisterna chyli
- plexi of vessels grow from sacs
- sacs shrivel EXCEPT cisterna chyli
where does the thoracic duct come from?
- diagonal connections between left and right thoracic duct (embryo)
- only caudal right and cranial left thoracic ducts remain
lymphocentres
- nodes
- all lymph passes through one (carnivores) or more (ungulates) nodes/lymphocentres
where are lymphocentres found?
places of little interference with organs e.g. behind knee/under scapula
where is the monocyte-macrophage system found? what do they do?
- cartilage (macrophages)
- blood (monocytes)
- lymph nodes
- liver (Kupfer cells)
- CNS microglia
- spleen
- phagocytose pathogens, debris, old erythrocytes
- present antigens
- store Fe
what systems are within the lymphatic system?
- macrophage-monocyte system
- lymphoid system
what are MALTs? where are they found?
- aggregations of lymphatic tissue (where fluid starts flowing into system, no inflow, only outflow)
found encapsulated around mucosa membranes:
- pharynx (tonsils)
- nose
- larynx
- third eyelids
- intestine
- vagina
- mammary glands
ungulates vs carnivore tonsils?
ungulates - tonsils lie under mucosa
carnivores - tonsils protrude (possibly sitting in a fossa)
where is the spleen? where does it derive from?
- left hand side of the stomach (long and mobile so variable positions)
- mesodermal swelling in greater omentum
what is the hilus of the spleen?
stalk that 25 splenic arteries join into
what are the internal regions of the spleen?
- capsule and muscular trabeculae (can change size)
- red pulp
- white pulp
what is the white pulp of the spleen?
lymphoid B-cell nodules or cylinders surrounded by T-cells
what is the red pulp of the spleen? what does it do?
- complex reticuloendothelial mesh and blood-filled sinusoids
- contains many monocytes
- breaks down erythrocytes
- converts iron to biliverdin to bilirubin to bile and urine
- stores resting/replacement erythrocytes –> released during exercise to increase O2 carrying capacity
- produces erythrocytes in fetuses
what innervates the spleen?
- sympathetic nerves
- few vagal fibres
- some unmyelinated sensory fibres
what is the thymus? what is its role?
- primary lymphoid organ
- where lymphocytes are formed
- where T-cells are matured
- expresses proteins to delete self-reacting cells
where did the thymus evolve from?
- gill-equivalent regions of the throat (pair in embryos)
- descend into the mediastinum (ventral to trachea, dorsal to sternum, cranial the heart )
structure of thymus
- lobulated (immature T-cells (thymocytes) infiltrate from internal thoracic artery)
- cortex (where weakly binding thymocytes are eliminated)
- medulla (exposed to Hassall’s corpuscles, epithelial whorls of endo/meso/ectoderm
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Early Development57
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Truncobrachial junction muscles32
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Spine45
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Skin76
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Imaging35
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Cartilage and bone49
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Joints52
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Muscles and tendons31
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Hoof and Claw34
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Body wall12
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Domestic animals in context23
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Shoulder and elbow muscles25
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Antebrachium muscles32
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Manus16
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Forelimb Joints23
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Hip Muscles37
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Stifle Muscles13
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Spinal Nerves49
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Autonomic Nervous System8
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Cardiovascular, Arteries and Veins26
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Lymphatics23
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Development of the Heart11
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Respiration: Thorax4
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Lungs and Pleura of the Thorax2
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Pancreas and Liver16
