Histo block I: Lymphatic vessels, portal systems and atherosclerosis

Question 1

Where are lymphatic vessels found?

Answer 1

Lymphatic vessels are found in most organs as a one-way vascular system conveying reabsorbed lymph (excess tissue fluid) back to blood

Question 2

describe the histological characteristics of lymphatic vessels

Answer 2

*Have abundant valves
*The wall structure is very loose and less ordered than either arteries or veins
*Carry white blood cells, not red blood cells

Question 3

What is the function of lymphatic vessels?

Answer 3

Remove excess extracellular fluid from CT, and also return large molecules (proteins & lipoprotein
particles) and WBCs back to the blood and vascular system

Question 4

identify

Answer 4

Lymphatic vessel with valves

Question 5

identify

Answer 5

Lymphatic vessel with valves

Question 6

Where do lymphatic vessels originate?

Answer 6

They originate as blind ended lymphatic capillaries in close proximity to the blood capillaries. These lack a continuous basal lamina and are more permeable than blood capillaries.

Question 7

how are lymphatic vessels in the villi of small intestine called?

Answer 7

lacteals to cary large lipoprotein particles out of small intestine

Question 8

identify

Answer 8

Lacteal lymphatic vessel in small intestine

Question 9

Lymph nodes act to filter?

Answer 9

lymph

Question 10

which lymphatic vessels are associated with lymph nodes?

Answer 10

afferent and efferent

Question 11

how do lymphatic vessels drain lymph?

Answer 11

Since There is no active pump for the lymphatic vessels, Lymph is propelled passively by contraction of adjacent muscles

Question 12

what do lymphatic vessels join together form?

Answer 12

The lymphatic vessels join together to form larger vessels which eventually come together to form 2 main channels – the thoracic duct (left side drainage) and the right lymphatic trunk (right side drainage) which drain into the vascular blood system at the junction of the internal jugular and subclavian veins in the neck

Question 13

identify

Answer 13

Small afferent lymphatic in capsule of lymph node

Question 14

describe the tunica intima, media and adventitia of lymph duct

Answer 14

1. tunica intima: endothelium, collagen & elastic fibers, internal elastic lamina
2. tunica media: smooth muscle, elastic fibers
3. tunica adventitia: poorly developed longitudinal smooth muscle, vasa vasorum present

Question 15

describe the tunica intima, media and adventitia of lymph vessel

Answer 15

1. tunica intima: endothelium, thin CT, many valves
2. tunica media: 1-3 layers of smooth muscle, abundant CT
3. tunica adventitia: elastic fibers, collagen bundles

Question 16

describe the tunica intima, media and adventitia of lymph capillary (blind ended)

Answer 16

1. tunica intima: thin endothelium, few tight junctions, incomplete basal lamina
2. tunica media: none
3. tunica adventitia: none

Question 17

What is a portal system?

Answer 17

Although blood normally flows from arterioles to capillaries to venules, portal systems represent places where either a venule or vein or an arteriole or artery is interposed directly between two capillary beds.

Question 18

What are the types of portal systems?

Answer 18

1. Venous portal systems – in liver and pituitary (capillary-vein-capillary)
2. Arterial portal systems - in renal corpuscle (capillary-arteriole -capillary)

Question 19

what are arteriovenous anastomoses?

Answer 19

also known as shunts are Regions in which there is a direct connection between an artery and a vein that when open shunts blood away from the capillary bed. e.g. Skin to preserve body temp

Question 20

explain atherosclerosis

Answer 20

In this condition, low density lipids (LDLs) and very low density lipoproteins (VLDLs) are oxidized by endothelial cells.

In response to this both macrophages derived from monocytes in the blood and smooth muscle cells from the tunica media invade the tunica media and become lipid laden as foam cells.

This together with large amounts of extracellular matrix synthesized by smooth muscle cells in the tunica intima results in the formation of a fibrous plaque that may occlude the vessel.

With time necrosis and rupture of the plaque may also occur causing formation of a clot by platelets, that may occlude other vessels.

This is particularly important in Coronary Artery Disease (CAD) where it is involved in the formation of plaque and hardening of the coronary arteries leading the heart not receiving vital oxygen and nutrients.

Question 21

identify

Answer 21

Micrograph of an atheromatous lesion