Blood vessels - general structure

• Three major types of blood vessels are : arteries, capillaries and veins

• The walls of all blood vessles except capillaries are composed of three distinct layers (tunics) surrounding a space (lumen).

• The tunics are from inside to outside – Tunic intima - endothelium, simple squamous epithelium

– Tunica media - circulary arranged smooth muscle and elastic fibers interspersed with sheets of elastin

– Tunica adventitia - collagen

Arteries

• Elastic arteries - conducting arteries– arterial pulse

• Muscular arteries - distributing arteries

• Arterioles

Capillaries

• Continous capillaries

• Fenestrated capillaries

• Sinusoids

Capillary Beds

• General structure - terminal arteriole ---------> metarteriole -------------> thoroughfare channel -----------------> postcapillary venule (PICTURE)

• Vascular shunts

• True capillaries

Veins

• Venules

• Veins

• Venous sinuses

Cardiac Output

CO = SV x HR

SV = EDS - ESV

• Therefore to regulate CO we can alter HR or SV– SV can be altered by alteruing either EDS or ESV

Regulation of SV

• Preload - Starling Law of the Heart

• Contractility

• Afterload

Regulation of HR

• Neuronal - sympathetic and parasympathetic (vagal)

• Chemical– Hormones

– ions

• Other factors

Definition of variables

• Blood pressure- P =F/A the force exerted on wall of blood vessel per unit area

• Resistance - the opposition to flow mainly in the periphery PR or TPR

• Blood viscosity - opposition to flow related to the thickness of blood

• Total BV length

• Total BV diameter

Relationships among the variables

• BP = CO X TPR

• Resistance

– directly proportional to BV L

– directly proportional to 1/r4

– Directly proportional to blood viscocity

• BF = difference in BP in different parts of the vascular system / TPR

Relationships among the variables

• MAP = dBP + 1/3 pulse pressure– pulse pressure = SBP - DBP

• BP and BF velocity in different parts of vascular system

Control of BP

• A Short term -

1 neural controls

• Cardiovascular center

• baroreceptor initiated reflexes

• chemoreceoptor initiated reflexes

• higher brain involvement

Control of BP • 2 Hormones• adrenal medulla hormones

• ANF atrail natriuretic factor

• ADH antidiuretic hormone

• Angiotensin II

• EDF endothelium derived factors

• NO nitric oxide also called endothelium derived relaxing factor EDRF

Control of BP

• 3 Drugs and chemicals• alcohol

• inflammatory chemicals -histamine , kinins

Control of BP

• B Long term -

1. kidney regulation

Capillary filtration