Arteries: carry blood away from heart. Thickest tunica media, closest to heart, exposed to higher pressure.
- Three groups of arteries:
  - Elastic: closest to heart, takes greatest pressure of blood from heart, greatest # elastin, when heart relaxes the recoil to propel blood onward during diastole.
  - Muscular: deliver blood to organs, more smooth muscle less elastin in media, actively constrict and relax. Thickest tunica media. More active in constricting than stretching.
  - Arteriole: Smallest. Tunica media is mostly smooth muscles to constrict and relax. Vasomotor fibers regulate activity of smooth muscle. Small changes in diameter greatly influence blood pressure and flow (THE RESISTANCE VESSEL).
    - Metarteriole: end of arteriole that goes to capillary junction.
Veins: farthest from heart, least pressure. Lumens larger. Tunica media smaller, Tunica externa thicker. Have valves to keep
- Venule: forms when capillaries unite, larger ones have sparse media and thin external. Small ones drain capillaries, contain endothelium where few fibroblasts congregate. Forms veins!
Capillaries: Smallest vessel, link between artery and vein. Walls have thin tunica intima, good for exchange of blood/fluids.
- Intercellular cleft: gaps of unjoined membrane allowing limited passage of membrane and small solutes.
- Capillary bed: blood flow regulation occurs here.
- pre capillary sphincter: smooth muscle fibers surrounding root of capillary, regulating blood flow.
- Capillary types:
  - Continuous: most common with endothelial cells forming continuous tube interrupted by intercellular clefts.
  - Fenestrated: in kidneys, villi of small intestine, and endocrine glands. Has pores
  - Sinusoids: form real porous channels through which blood can percolatein liver and spleen.

	Created by Stacylynn Conceicao over 6 years ago

Note on Blood Vessels-CH 19, created by Stacylynn Conceicao on 20/03/2018.