Lecture 2: Blood vessels and capillaries

Open vs closed loop

Open: Hemolymph (arthropods, mollusks)

Closed: Blood (vertebrates, earthworms, cephalopods)

From the heart

1. Artery (elastic, muscular)

2. Arteriole

3. Capillary

To heart

1. Capillary

2. Venule

3. Vein (medium-sized to large)

Capillary types

Continuous

• Basement membrane

• Water, ions, small solutes

• Muscle, skin, brain

Fenestrated

• Basement membrane

• Above rapid small molecule flow

• Kidney, intestine, endocrine glands

Sinusoidal

• No basement membrane

• Protein and cells

• Liver, bone marrow, spleen

Vessel layers (outside to inside)

Tunica externa (adventitia)

• Connective tissue

Tunica media (thickest layer)

• Muscular

• Controls vasoconstriction and dilation

Tunica intima

• Endothelium

• Elastic membrane in arteries

Lumen

• Inside vessel

Blood flows from high-low pressure

1. Pressure in atria during diastole is very low

2. Physiologic pumps increase pressure in veins

   1. 1 way valves

   2. Skeletal muscle pump- contracting of muscles in the extremities (arms/legs)

   3. Respiratory pump- blood flows in towards the heart with each breath

Vasculature health

• Varicose veins

• Arteriosclerosis: thickening and hardening of vessel walls (age)

• Atherosclerosis: Plaque build up (high fat/cholesterol diet, high blood pressure

Lymphatic system

• Open system

• Lymph originates from interstitial fluid

• Fluid leaks from blood vessels into tissues

• Carriers of nutrients, wastes, pathogens, cell debris