Lecture 5 Flashcards
What are capillaries and what does their function require?
They are the site of exchange between blood and tissue, this function requires that they have very thin walls to maximize diffusion, large total cross sectional area of the capillary bed and a slow (helped by the large cross sectional area) and smooth blood flow.
What is the ultrastructure of a typical capillary?
single endonucleated cells looping on themselves with intercellular junctions to leave an 8-10 micrometer hole (enough for one red blood cell to fit across).
What is a sphincter in regards to capillarys?
Precapillary structures composed of smooth muscle which are located at the entrance (metarteriole) to the capillary bed cells which can close themselves to block off blood flow into the capillary bed.
What are the three capillary types and the main function of each?
Continuous (most widespread) Fenestrated (leaky),Sinusoidal (very leaky).
What is the structure of continuous capillaries? Where are they found? How does exchange occur?
5-10 micrometer diameter (one red blood cell), surrounded by a thing layer of extracellular matrix known as the basal lamina, found in many places (e.g cardiac or skeletal muscle). Exchange can occur through diffusion through the intercellular cleft or just directly through the membrane.
What is the structure of fenestrated and sinusoidal capillaries? Where are they found? How does exchange occur?
Fenestrated: 5-10 micrometers (one red blood cell), surrounded by a thin layer of ECM known as the basal lamina. Has holes in the cell membrane, but not the basal lamina. Can be found in the glomerulus of the kidney as the first part of bloof filtering (holes not large enough to let blood out)
Sinusoidal: 20-30 micrometers, these allow almost free exchange but still do not have large enough holes to let red blood cells out but are quite large and are known as enothelial fenestrations (which also cut into the basal lamina, these can be found in the liver.
Diffusion can occur directly, through the intercellular cleft, through the pores or active transport can be done via vesicles.
What is an arteriovenous anastomosis
A connection between arteries and veins, typically can be used to bypass circulation of areas like the extremities.
What is the difference in structure between lymph channels and other blood vessels?
Lymph channels have roughly the same diameter but are much more thin walled and contain no red blood cells (do have valves though due to the low pressure).
What are the functions of the lymph vascular system?
An open entry (drainage) system which
- drains excess tissue fluid and plasma protins from tissues (returning them to the blood)
- filters foreign material from the lymph.
- ‘screens’ lymph for foreign antigens and responds by releasing antibodies and activated immune cells.
- absorbs fat from intestine and transports it to the blood.
What is the lymphatic system structure?
Lymphatic vessels which start as large, blind ending capillaries, a special froup of lymphatic vessels known as lacteals drain fat-laden lymph into a collecting vessel called the cisterna chyli (the fluid seems like milk). The larger (thin wall) collecting vessels have numerous valves to prevent backflow. Lymph capillaries consist of endothelial cells which overlap and have filaments which anchor to connective tissue (this overlap allows materials in from one direction).
Where do lymphatic collecting vessels drain into?
The majority try to bring fluid towards the trunk, draining into the thoracic duct which connects with the left subclavean vein and is protected by a valve to prevent blood flowing back in. A minority found in the upper right of the body drains into the right subclavean vein instead.
What does the portal vein function to do?
The portal vein carries blood from the capillaries in the small intestine villi to the liver for processing.
What are lymph nodes and where are they concentrated?
Lymph nodes are structures which contain immune cells and surround the immune system, they are concentrated in many areas e.g cervical nodes in the neck, axillary nodes in the armpit, inguinal nodes in the upper thigh. These immune cells are bathed in lymphatic fluid to activate them.
Why are the axillary lymph nodes typically checked after removing breast cancer?
Breast cancer can spread throughout the body via these nodes, the surgeon needs to check the nodes for traces of these cancer cells to determine if the cancer spread.
