Lecture 7 - Capillaries and lymphatics Flashcards
Capillaries
Site of exchange between blood and tissues (bring oxygen in and take other gases out)
This function demands…
Very thin walls - distance the gas has to exchange across will limit the exchange processes therefore need thin walls for god gas exchange whilst maintaining the portioning of the blood and other fluid
Large total cross sectional area of capillary bed - optimises the exchange process
Slow and smooth blood flow
Large total area of the capillary bed (compared to arterioles) means much slower blood flow
Red blood cells and capillaries
Red blood cells travelling in single file down the capillary, room for one RBC to move at a time therefore diameter of capillaries is around 8-10 micrometres
This brings the RBCs as close as possible to the surrounding interstitial fluid
Precapillary sphincters
Composed of smooth muscle cells - circumferentially orientated smooth muscle running around where these branch points comes off the terminal arteriole and if these smooth muscle cells construct they then stop blood going into the side branches and the blood then gets shot across the central channel and straight out the other side and we call this a vascular shunt - contract when cold and as you warm up the precapillary sphincters open
Capillary bed
a network of capillaries
Vascular shunt
Vascular shunt allows blood to get back into the veins, made up of metaarteriole and thoroughfare channel
Three types of capillaries
The structure of capillaries varies according to the rate of exchange needed, and how controlled the exchange must be
Continuous capillaries (the most widespread) - endothelial forms a continuous barrier between the lumen and surrounding tissue Fenestrated capillaries (leaky) - endothelial cell puts little openings on its surface, allows more physical exchange between the lumen and the underlying tissues Sinusoidal capillaries (very leaky)- like the fenestrated capillaries just bigger holes, allows the cells underneath the capillary, free and direct exchange with the blood that is flowing through the capillary
Continuous capillaries
- most common, widespread
- no interruption in the barrier
- found in skeletal & cardiac muscle
- 8-10um diameter
- basement membrane - layer of connective tissue that these endothelial cells produce to help stick themselves down on the underlying tissue
Fenestrated capillaries
have pores making them LEAKY, fenestration penetrate the endothelial layer but not the basal membrane
8-10um diameter, found in Glomerulus, kidney
Basement membrane is intact - stuff still has to diffuse through this membrane like a layer of filter paper on the side of a coliander
Fenestrations are too small to allow RBCs to leave
Sinusoidal capillaries
have large openings which penetrate both the endothelial layer & basement membrane - incomplete basement layer, absent in some places so that the cells surrounding tissue are able to be up against these sinusoidal openings, no basement membrane to get in the way because we want cells to have direct and free exchange with the blood and there is also intercellular gaps
found in liver & venous system, this capillary type is less about gas exchange and more about nutrient exchange
30-40um diameter
VERY LEAKY
Movement of materials types of capillaries
Diffusion through membrane (lipid-soluble substances)
Movement through intercellular clefts (water soluble substances)
Movement through fenestrations (water-soluble substances)
Transport via vesicles or caveolae (large substances)
Continuous capillaries movement of materials
Diffusion through membrane (lipid-soluble substances)
Movement through intercellular clefts (water soluble substances)
Transport via vesicles or caveolae (large substances)
Fenestrated capillaries/sinusoidal movement of materials
Diffusion through membrane (lipid-soluble substances)
Movement through intercellular clefts (water soluble substances)
Movement through fenestrations (water-soluble substances)
Transport via vesicles or caveolae (large substances)
What is the basement membrane?
A membrane that sits over the basal surface
- not penetrated by fenestrations in fenestrated capillaries
- is penetrated in sinusoidal capillaries
Lymph vascular system
An open-entry (drainage), low pressure system
Lymphatic vascular network can pick up the fluid that has left the blood vascular space and drain it back into big veins to the right side of the heart and brings that blood back into the blood vascular volume
Lymph vascular system functions
Drains excess tissue fluid and plasma proteins from tissues and returns them to the blood
Filters foreign materials from the lymph
‘Screens’ lymph for foreign antigens and responds by releasing antibodies and activated immune cells
Absorbs fat from intestine and transports to the blood
Pulmonary vs systemic circuit
Pulmonary - from the right side of the heart, deoxygenating the blood and returning it to the left side of the heart
Systemic - from the left side of the heart back to the right side of the heart
Structure of the lymphatic system
Lymphatic vessels -
Commence as large, blind ending capillaries
From small intestines, a special group of lympahatic vessels called lacteals drain fat-laden lymph into a collecting vessel called the cisterns chyli.
Larger (thin wall) collecting vessels have numerous valves to prevent back flow
Lymph vessels
Thin walled
No RBCs
Valves - stop lymph being pushed back to the end of the tissue, ensures unidirectional flow
Lymph channels
Have thinner walls than veins
Regional lymph nodes
For the left side and everywhere else
Lymphatic collecting vessels - thoracic duct - entrance of thoracic duct into left subclavian vein.
For the upper right side
Lymphatic collecting vessels - thoracic duct - entrance of right lymphatic duct into right subclavian vein
In the small intestine lymph vessels are called lacteal which drain fat laden lymph into a collecting vessel called the cisterna chyli
Nodes to know
Cervical nodes - neck
Axillary nodes - armpit
Inguinal nodes - groin
Small intestine villus
Lacteal which then drains to the cisterna chyli - picks up fat
Takes lymph from the intestinal arteries to the vili and then takes the fat lymph back via the portal vein
Lymph node structure
Lymph flows from afferent lymphatics and then runs through a meshwork of fibres inside the node and there are immune cells suspended in this meshwork and you bathe these immune cells in the incoming lymph and then the lymph just continues out into the efferent chambers
Lymphatic drainage of the breast
Lymphatic vessels of the breast - axillary lymph nodes - right lymphatic duct - right subclavian vein
Breast tissue lymphatic drainage can carry cancer cells into the blood vascular system - metastatic cancer
