Lecture 7- Circulatory system anatomy, capillaries and lymphatics

Question 1

What does the exchange function of capillaries demand in terms of their structure?

Answer 1

• Very thin walls (allows to readily get into tissue)
• Large total cross sectional area of capillary bed (more surface area= greater chance for exchange)
• Slow & smooth blood flow

Question 2

How does the total area of the capillary bed compare to arterioles and what does this allow?

Answer 2

• Large total area of the capillary bed (compared to arterioles) means much slower blood flow.
• Imagine going form a river (arterioles) to lake (capillary bed)

Question 3

How is a capillary formed?

Answer 3

Endothelia cells wrapped around and bonded to neighboring cells via tight junctions to make a tube

Question 4

How big is the lumen of a capillary?

Answer 4

• Size of a red blood cell so 8-10 micrometers (go in single file)
• Means there is less distance for gas exchange into the tissues as cells press against edge (makes more efficient)

Question 5

What are the rings surrounding the vessels that branch from arterioles called? What are their function?

Answer 5

• Called precapillary Sphincters
• They constrict to stop blood flowing into the capillary bed and dilate to allow blood in
• When they constrict blood goes through an alternative pathway called the vascular shunt going straight from the supply network to drainage. This conserves heat as doesn’t go through the exchange network that sits in the epidermis closer to surface sticks to the dermis.

Question 6

What are precapillary Sphincters made of?

Answer 6

Smooth muscle as control involuntary movement

Question 7

What is the last part of the supply network called?

Answer 7

Terminal arteriole

Question 8

What is the first part of drainage network called?

Answer 8

Postcapillary venule

Question 9

Why do the structures of capillaries vary?

Answer 9

Vary according to the rate of exchange needed, and how controlled the exchange must be.

Question 10

What are the three types of capillaries?

Answer 10

Continuous capillaries (the most widespread).
Fenestrated capillaries (leaky).
Sinusoidal capillaries (very leaky).

Question 11

What is the structure of a continuous capillary like?

Answer 11

• Lumen has 8-10 micrometer diameter (allows only 1 red blood cell), wall is thin
• Has basement membrane surrounding outside, then an endothelial layer (tunica intima).
• Endothelial cells are joined together by intercellular clefts which create the tube shape

Question 12

What is the basement membrane of a capillary?

Answer 12

• Extracellular connective tissue produced by endothelial cells
• Described as a velvet collagen layer whose function is to help bond it to the underlying tissues

Question 13

When diffusing through a capillary what are the two things blood cells have to diffuse through?

Answer 13

Cellular (endothelial cells) and extracellular layer (basement membrane)

Question 14

What is the movement that can occur across continuous capillaries?

Answer 14

• Diffusion through membrane (lipid soluble)
• Movement through intercellular clefts (Water-soluble substances)
• Transport via vesicles or caveolae (large substances)

Question 15

What is the structure of fenestrated capillaries like?

Answer 15

-Structurally designed to bring blood cells close to wall
as again are 8-10 micrometers in diameter, wall is thin
-Wall has little pore like openings (in cytoplasm of endothelium) like a sieve. These openings are not large enough for blood cells to pass through so does not lead to hemorrhage.

Question 16

What can be send through the fenestrations of the capillaries?

Answer 16

The basement membrane this ultimately decides what can enter and leave

Question 17

What is the structure of sinusoidal capillaries like?

Answer 17

• Lumen is much greater at 30-40 micrometers, therefore not as interested in bringing blood close to wall for diffusion. Instead bathes the liver in nutrient rich blood from the gut to be processed.
• Openings still do not allow blood cells through but are bigger than fenestrations, also basement membrane is incomplete so a lot leakier

Question 18

What is the movement that can occur across fenestrated and sinusoidal capillaries?

Answer 18

• Diffusion through membrane (lipid soluble)
• Movement through intercellular clefts (Water-soluble substances)
• Transport via vesicles or caveolae (large substances)
• Movement through fenestrations (water-soluble)

Question 19

Describe the lymphatic system…

Answer 19

-Fluid that has left the blood vascular system is brought back back the lymph system
-Finger like projections sit amongst capillary bed and
mop up fluid
-They then lead to lymph nodes which survey the contents of the lymph

Question 20

What are the functions of the lymph vascular system?

Answer 20

1. Drains excess tissue fluid & plasma proteins from
   tissues and returns them the blood.
2. Filters foreign material from the lymph.
3. ‘Screens’ lymph for foreign antigens & responds by
   releasing antibodies & activated immune cells.
4. Absorbs fat from intestine and transports to blood.

Question 21

What are the special features of the lymph system that allow it to absorb fats from the small intestine?

Answer 21

-A special group of lymphatic vessels
called lacteals drain fat-laden lymph (looks white) from the gastrointestinal mucosa into collecting vessels called the cisterna chyli.
-Therefore, there is a more indirect path for lymph containing fat to got the liver

Question 22

What is the structure of lymph vessels like?

Answer 22

-Commence as large, blind ending capillaries
-Larger (thin wall) collecting vessels have numerous
valves to prevent backflow.

Question 23

In a diagram how do you tell which are the lymph vessels in cross section?

Answer 23

• Very thin walls
• sometimes not even visible as pushed together
• absence of blood vessels

Question 24

What is the path for lymph fluid to drain from the left side of the body? (2/3)

Answer 24

-Tissues drains via lymph collecting vessels into the  
thoracic duct (part of lymphatic system)
-Goes into the left subclavian vein (part of blood vascular system). 
-There will be a valve between the lymph system and vascular system to prevent backflow.

Question 25

What is the path for lymph fluid to drain from the right side of the body? (1/3)

Answer 25

Right lymphatic duct into the right subclavian vein

Question 26

Afferent lymphatics…

Efferent lymphatics…

Answer 26

lymph goes into lymph node

lymph goes out of lymph node

Question 27

What is a lymph node?

Answer 27

A cage of fibers that holds lymphoid cells

Question 28

What is the pathway for lymph drainage from the breast?

Answer 28

• Lymphatic vessels of the breast
• Axillary lymph nodes
• Right lymphatic duct
• Right subclavian vein

Question 29

How can breast cancer highjack the lymph system?

Answer 29

• Breast cancer cells break of and get inside the lymphatic vessels. They can then enter the blood vascular system and spread throughout the body (metastatic cancer)
• This explains why when they remove the primary tumour they also remove the lymph nodes. If they see cancer cells in there then they know the cancer has likely spread and they need alternative forms of treatment

Question 30

Where do you most commonly find the 3 different types of capillaries?

Answer 30

• Continuous= cardiac and skeletal muscle
• fenestrated= small intestine
• Sinusoidal= liver