lecture 7 - capillaries & lymphatics Flashcards
What is the relative thickness of capillary walls?
Very thin, to allow for easy exchange of gases and nutrients.
Why do capillary beds have a large total cross sectional area?
To maximise the rate of exchange at low pressure, speed and flow.
How do capillaries ensure slow and smooth flow of blood, despite the pulsatile pumping of the heart?
They slow down the blood and it is at low pressure
What is the basic structure of a capillary?
A tube formed by simple squamous epithelia, surrounded by a basement membrane
What is the diameter of a capillary?
The same size as a red blood cell
What feature controls the flow into capillary beds?
Pre-capillary sphincters
What are pre-capillary sphincters?
Smooth muscle cells that circumferential around the start of the capillary beds, and contract to limit flow into the beds.
What vessels supply the capillary beds?
Terminal arterioles
What feature of a capillary bed directs blood straight through the thoroughfare channel?
Vascular shunts
What is the function of vascular shunts?
They direct blood through a large thoroughfare channel, rather than into all the different parts of the capillary bed.
What are the 3 types of capillary?
Continuous, Fenestrated, Sinusoidal
What is the most widespread type of capillary?
Continuous
What are the components of a capillary that vary to control permeability?
Basement membrane, intercellular cleft, endothelial layer/tunica intima
What is the structure of a continuous capillary?
Continuous endothelial layer and basement membrane, which only allow small molecules to pass through
What is the basement membrane of a capillary?
Also called the basal lamina, it is a layer of extracellular matrix that forms the outmost layer, that molecules must pass through.
What is the approximate diameter of a continuous capillary?
8-10µm
What is the structure of fenestrated capillaries?
Capillaries with small pores/fenestrations in the endothelial layer that allow molecules to pass out. However, they have a continuous basement membrane that molecules must pass through.
Do fenestrated capillaries have continuous or discontinuous basement memebrane?
Continuous
What type of capillary are commonly found in the kidneys and small intestines?
Fenestrated capillaries
What is the leakiest type of capillary?
Sinusoidal
What is the structure of a sinusoidal capillary?
Has large intercellular gaps between endothelial cells and an incomplete basement membrane that allows for direct exchange of plasma with the ECM.
What capillary type has the largest diameter?
Sinusoidal
What is the diameter of a sinusoidal capillary?
30-40µm
What are 4 key functions of the lymph vascular system?
Drains excess tissue fluid & plasma proteins and returns to blood, filters foreign materials, screens lymph for antigens and releases antibodies, absorbs fat from intestines and transports to the blood.
How is fat absorbed using the lymph vascular system?
At the intestines, fat that has been consumed is absorbed by lymphatic drainage vessels and transported to the blood via lymph channels
How do lymphatic vessels originate?
Commence as large, blind ended capillaries
In the small intestine, what lymphatic vessels initially drain fat-laden lymph?
Lacteals
Where do lacteals drain fat-laden lymph to?
lymphatic fat collecting vessel called the cisterna chyli.
Why do lymphatic vessels have valves?
To maintain unidirectional flow.
Why are lymph channels transparent/hard to spot?
Very thin walled with transparent fluid flowing through them as contain no red blood cells.
Is fluid at high or low pressure in lymphatic vessels?
Low pressure
What are the 3 major regions of lymph nodes?
Cervical, Axillary, Inguinal
Where are cervical lymph nodes located?
The neck
Where are axillary nodes located?
In the armpit (axilla)
Where are inguinal nodes located?
In the groin
Where does the right lymphatic duct drain?
The right subclavian vein
Where does the thoracic duct drain?
The left subclavian vein and internal jugular vein
What is the process of fat absorption in the small intestine vili (Cardio vascular system)?
Lacteals (lymphatic vessels) absorb fats and then send them to the portal veins which take nutrient-rich blood to the liver
What vessels drain the lymph nodes?
Efferent lymphatic vessels
Where are immune cells held in a lymph node?
They hang onto a matrix of fibres, surveying the lymph fluid
How does cancer often spread from the breasts into others parts of the body?
Via the breast tissue lymphatic drainage system that carries cancer cells into the blood vascular system, facilitating metastasis
