Page 158 - Physiology and Pathophysiology MNU 2024-2025 نظرى

Clinical pharmacy 2024/2025 Level 2 Pharm D Physiology and Pathophysiology (MD303)
Tunica media contains numerous layers of elastic fibers. & less Muscle
➔ can be expanded
* Contain a thicker layer of smooth muscle in the tunica
1. During contraction of heart  the artery expands when blood
media
enters the lumen.

2. During relaxation of heart  elastic wall of artery recoil to its
original position. (Go to arterioles)

2- Arterioles (resistance vessels) “small +resist +SM"

 The smallest branches of the arteries. (Near to the tissue and away from heart)
 The site of highest resistance to blood flow in the CVS (resistance vessels) هيف مكحتي ردقي مسجلاو تلاضع اهرادج نلا
Characters
 The tunica media layer consists mainly of smooth muscle ➔ so body control its diameter by sympathetic nervous system.
 Only contain (Endothelium + Tunica media) & No tunica externa
α1-Adrenergic receptors β2-Adrenergic receptors
↑Nor epinephrine ➔ Vasoconstriction (Narrowing of the ↓Nor epinephrine ➔ Vasodilatation (Widening of the
Effect of
Regulation lumen) ➔ lumen) ➔
stimulation
 Arteriolar resistance &  blood flow  Arteriolar resistance &  blood flow
 α1 effect is the predominant

3- Capillaries (exchange vessels)

Characters * Thin-walled vessels that consists of  single layer of endothelial cells. ➔ facilitate exchange
 Exchange of nutrients, water, gasses across their walls.  Link between arterioles (oxygenated blood) with Venules (no
Function
oxygenated)
Passage of substances across the capillary wall
1- Lipid-soluble substances ✓ Cross the membrane of the capillary endothelial cells by  simple diffusion. ةقاط يأ يرغ نم طيسبلا راشتنلاا

(Gases) ✓ Include  O2, CO
2- Small water-soluble ✓ Cross via the water filled clefts (gaps or pores) between the endothelial cells.
substances ✓ Include  water & glucose & amino acids.

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