Cardiovascular System

BLOOD VESSELS 2 Blood Pressure

 Main factors influencing blood pressure:  Cardiac output (CO)  Peripheral resistance (PR)  Blood volume

Peripheral resistance is a major factor regulating BP and tissue perfusion Activity of Fluid loss from Crisis stressors: Bloodborne Release Dehydration, Body size muscular of ANP hemorrhage, exercise, trauma, chemicals: high hematocrit pump and excessive body epinephrine, respiratory sweating temperature NE, ADH, pump angiotensin II; ANP release Conservation Blood volume Blood pH, O , of Na+ and 2 Blood pressure CO water by kidney 2

Blood Baroreceptors Chemoreceptors volume

Venous Activation of vasomotor and cardiac return acceleration centers in brain stem

Stroke Heart Diameter of Blood Blood vessel volume rate blood vessels viscosity length

Cardiac output Peripheral resistance

Initial stimulus Physiological response Result Mean systemic arterial blood pressure

 Local control  Arterioles and capillaries vary diameters = autoregulation  A response to the chemical composition of the blood  Faster flow = faster removal of wastes Regulation of Peripheral Resistance

 Local control  Localized hypoxia  metabolites (CO2, lactic acid, adenosine)  acidic pH  inhibit smooth muscle  vasodilation  increased blood flow  Precapillary sphincters  Respond to local stimuli and vasoactive hormones  Endothelial cells & platelets  Vasodilators  NO, prostacyclin  Vasoconstrictors

 Endothelians, seratonin, thromboxane A2 Brain Heart

Skeletal muscles Skin

Kidney

Abdomen

Other Total blood flow at rest 5800 ml/min

Total blood flow during strenuous exercise 17,500 ml/min

(autoregulation) • Maintain mean arterial pressure (MAP) • Distribute blood flow to individual • Redistribute blood during exercise and organs and tissues as needed thermoregulation

Amounts of: pH Sympathetic Nerves

O2 α Receptors Epinephrine, Metabolic β Receptors norepinephrine controls Amounts of:

CO2

K+ Angiotensin II Hormones Prostaglandins Adenosine Antidiuretic hormone (ADH) Nitric oxide Endothelins Atrial natriuretic Myogenic Stretch peptide (ANP) controls

Dilates Constricts

Figure 19.15 Peripheral Resistance

 Example of autoregulation  Blood flow to skeletal muscles  During muscle activity, blood flow increases in direct proportion to the metabolic activity  Blood flow can increase 10× or more during physical activity Peripheral Resistance

 Neural control  Directed by ANS via sympathetic innervation  Vascular smooth muscle lacks parasympathetic input Peripheral Resistance

 Neural control  Vasomotor center Baroreflex Chemoreflex Ischemic reflex Peripheral Resistance

 Baroreflex  Baroreceptors (pressure receptors) in  Carotid sinuses  Aortic arch  Inhibitory signals sent to vasomotor center while stimulatory signals sent to cardioinhibitory center 3 Impulses from baroreceptors stimulate cardioinhibitory center (and inhibit cardioacceleratory 4a Sympathetic center) and inhibit vasomotor impulses to heart center. cause HR, contractility, and CO. 2 Baroreceptors in carotid sinuses and aortic arch are stimulated.

4b Rate of vasomotor impulses allows vasodilation, causing R 5 CO and R 1 Stimulus: return blood Blood pressure pressure to (arterial blood homeostatic range. pressure rises above Homeostasis: Blood pressure in normal range normal range). 1 Stimulus: Blood pressure (arterial blood pressure falls below normal range). 5 CO and R return blood pressure 4b Vasomotor to homeostatic range. fibers stimulate vasoconstriction, causing R

2 Baroreceptors in carotid sinuses and aortic arch are inhibited.

4a Sympathetic impulses to heart cause HR, contractility, and 3 Impulses from baroreceptors stimulate CO. cardioacceleratory center (and inhibit cardioinhibitory center) and stimulate vasomotor center.

Figure 19.9 Peripheral Resistance

 Chemoreflex  Excitatory or inhibitory signals to vasomotor center  Chemoreceptors are located in the  Carotid bifurcation  Aortic arch  Large arteries of the neck Activity of Fluid loss from Crisis stressors: Bloodborne Release Dehydration, Body size muscular of ANP hemorrhage, exercise, trauma, chemicals: high hematocrit pump and excessive body epinephrine, respiratory sweating temperature NE, ADH, pump angiotensin II; ANP release Conservation Blood volume Blood pH, O , of Na+ and 2 Blood pressure CO water by kidney 2

Blood Baroreceptors Chemoreceptors volume

Venous Activation of vasomotor and cardiac return acceleration centers in brain stem

Stroke Heart Diameter of Blood Blood vessel volume rate blood vessels viscosity length

Cardiac output Peripheral resistance

Initial stimulus Physiological response Result Mean systemic arterial blood pressure

 Medullary Ischemic Reflex  Triggered by low perfusion of the medulla  Hypoxia and hypercapnia  vasoconstriction in extremities  blood flow directed to head and upper body Peripheral Resistance

 Hormonal controls  Angiotensin II  Generated by kidney release of renin  Causes vasoconstriction  Atrial natriuretic peptide/factor  Causes blood volume and blood pressure to decline  Causes generalized vasodilation  Antidiuretic hormone (ADH, vasopressin)  Causes intense vasoconstriction in cases of extremely low BP  Epinephrine  Causes generalized vasoconstriction and increase cardiac output Arterial pressure

Direct renal Indirect renal mechanism mechanism (hormonal) Baroreceptors

Sympathetic stimulation promotes renin release

Kidney

Renin release

catalyzes cascade, resulting in formation of Angiotensin II

Filtration ADH release Aldosterone by posterior secretion by pituitary adrenal cortex

Water Sodium reabsorption reabsorption by kidneys by kidneys

Blood volume Vasoconstriction ( diameter of blood vessels)

Initial stimulus Physiological response Result Arterial pressure

Figure 19.10 Activity of Fluid loss from Crisis stressors: Bloodborne Release Dehydration, Body size muscular of ANP hemorrhage, exercise, trauma, chemicals: high hematocrit pump and excessive body epinephrine, respiratory sweating temperature NE, ADH, pump angiotensin II; ANP release Conservation Blood volume Blood pH, O , of Na+ and 2 Blood pressure CO water by kidney 2

Blood Baroreceptors Chemoreceptors volume

Venous Activation of vasomotor and cardiac return acceleration centers in brain stem

Stroke Heart Diameter of Blood Blood vessel volume rate blood vessels viscosity length

Cardiac output Peripheral resistance

Initial stimulus Physiological response Result Mean systemic arterial blood pressure

Figure 19.11 Questions?

 Don’t forget Homework #1 for lab!