Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalance: Hypertension Prolonged hypertension is a major cause of heart failure, vascular disease,

Copyright © 2010 Pearson Education, Inc.

Homeostatic Imbalance: Hypertension

• Prolonged hypertension is a major cause of heart failure, vascular disease, renal failure, and stroke

• Primary or essential hypertension

• 90% of conditions

• Due ?: heredity, diet, obesity, age, stress, diabetes mellitus, and smoking


Homeostatic Imbalance: Hypertension

• Secondary is less common

• Due to identifiable disorders, including kidney disease, arteriosclerosis, and endocrine disorders such as hyperthyroidism and Cushing’s syndrome


Blood Flow Through Body Tissues

• Blood flow (tissue perfusion) is involved in

• Delivery of O2 and nutrients to, and removal of wastes from, tissue

• Gas exchange (lungs)

• Abs of nutrients (digestive tract)

• Urine formation (kidneys)

• Rate of flow is precisely the right amount to provide for proper function

Copyright © 2010 Pearson Education, Inc. Figure 19.13

Brain

Heart

Skeletalmuscles

Skin

Kidney

Abdomen

Other

Total blood flow during strenuousexercise 17,500 ml/min

Total bloodflow at rest5800 ml/min


Relative cross-sectional area ofdifferent vesselsof the vascular bed

Total area(cm2) of thevascularbed

Velocity ofblood flow(cm/s)

Aor

ta

Art

erie

sA

rter

iole

sC

apill

arie

sVe

nule

s

Vein

s

Vena

e ca

vae


Autoregulation

• Automatic adjustment of flow to tissue in proportion to its req at any given point in time

• Controlled intrinsically by modifying the diameter of local arterioles feeding the capillaries

• Is independent of MAP, which is controlled as needed to maintain constant pressure


Autoregulation

• Two types of autoregulation

1. Metabolic

2. Myogenic


Metabolic Controls

• Vasodilation of arterioles and relaxation of precapillary sphincters occur in response to

• Declining tissue O2

• Substances from metabolically active tissues (H+, K+, adenosine, and prostaglandins) and inflammatory chemicals


Metabolic Controls

• Effects

• Relax vascular smooth muscle

• Release of NO from endothelial cells

• NO is major factor causing vasodilation

• Vasoconstriction is due to sympathetic stimulation and endothelins


Myogenic Controls

• Vascular smooth muscle keep tissue perfusion constant despite fluctuatios in BP

• Passive stretch promotes increased tone and vasoconstriction

• Reduced stretch promotes vasodilation and increases blood flow to tissue


Metaboliccontrols

pH Sympathetic

a Receptors

b ReceptorsEpinephrine,norepinephrine

Angiotensin II

Antidiuretichormone (ADH)

Atrialnatriureticpeptide (ANP)

Dilates

Constricts

Prostaglandins

Adenosine

Nitric oxide

Endothelins

Stretch

O2

CO2

K+

Amounts of:

Amounts of:

Nerves

Hormones

Myogeniccontrols

Intrinsic mechanisms(autoregulation)

• Distribute blood flow to individual organs and tissues as needed

Extrinsic mechanisms

• Maintain mean arterial pressure (MAP)• Redistribute blood during exercise and thermoregulation


Long-Term Autoregulation

• Angiogenesis

• Occurs when short-term autoreg cannot meet tissue req

• Common in heart when a coronary vessel is occluded, or throughout the body in people in high-altitude areas


Blood Flow: Skeletal Muscles

• At rest, myogenic and neural mechanisms predominate

• During muscle activity

• Blood flow increases in direct proportion to the metabolic activity (exercise hyperemia)

• Local controls override sympathetic vasoconstriction

• Muscle blood flow can increase 10 or more during physical activity


Blood Flow: Brain

• Blood flow to brain is constant

• Metabolic control

• in pH, and CO 2 cause vasodilation

• Myogenic control - / in MAP cause cerebral vessels to dilate/constrict

• MAP below 60 mm Hg can cause syncope

• MAP above 160 can result in cerebral edema


Blood Flow: Skin

• Blood flow through the skin

• Supplies nutrients to cells (autoregulation)

• Helps maintain body temp (neural)

• Provides a blood reservoir (neural)

• Varies from 50 ml/min to 2500 ml/min


Blood Flow: Lungs

• Pulmonary circuit is unusual in that

• Arteries/arterioles are more like veins/venules (thin walled, with large lumens) – WHY?

• Autoreg is opposite of that in most tissues

• Low O2 cause vasoconstriction;

• High O2 promote vasodilation


Blood Flow: Heart

• During ventricular systole

• Coronary vessels are compressed

• Myocardial blood flow ceases

• Stored myoglobin supplies sufficient oxygen

• At rest, control is probably myogenic

• During strenuous exercise

• Blood flow may increase three to four times

Copyright © 2010 Pearson Education, Inc. Figure 19.16 (2 of 2)

Basementmembrane

Endothelialfenestration(pore)

Intercellularcleft

Pinocytoticvesicles

Caveolae

4 Transportvia vesicles orcaveolae (largesubstances)

3 Movementthroughfenestrations (water-soluble substances)

2 Movementthrough intercellular clefts (water-soluble substances)

1 Diffusionthrough membrane (lipid-soluble substances)

Lumen


Fluid Movements: Bulk Flow

• Extremely important in determining relative fluid vol in blood and interstitial space

• Direction and amount of fluid flow depends on two opposing forces: hydrostatic and colloid osmotic pressures


Net Filtration Pressure (NFP)

• NFP—comprises all the forces acting on a capillary bed

• NFP = (HPc—HPif)—(OPc—OPif)

• At the arterial end of a bed, hydrostatic forces dominate

• At the venous end, osmotic forces dominate

• Excess fluid is returned to the blood via the lymphatic system


HP = hydrostatic pressure• Due to fluid pressing against a wall• “Pushes”• In capillary (HPc) • Pushes fluid out of capillary • 35 mm Hg at arterial end and 17 mm Hg at venous end of capillary in this example• In interstitial fluid (HPif) • Pushes fluid into capillary • 0 mm Hg in this example

OP = osmotic pressure• Due to presence of nondiffusible solutes (e.g., plasma proteins)• “Sucks”• In capillary (OPc) • Pulls fluid into capillary • 26 mm Hg in this example• In interstitial fluid (OPif) • Pulls fluid out of capillary • 1 mm Hg in this example

Arteriole

Capillary

Interstitial fluid

Net HP—Net OP(35—0)—(26—1)

Net HP—Net OP(17—0)—(26—1)

Venule

NFP (net filtration pressure)is 10 mm Hg; fluid moves out

NFP is ~8 mm Hg;fluid moves in

NetHP35mm

NetOP25mm

NetHP17mm

NetOP25mm


Circulatory Shock

• Any condition in which

• Blood vessels are inadequately filled

• Blood cannot circulate normally

• Results in inadequate blood flow to meet tissue needs


Circulatory Shock

• Hypovolemic shock:

• large-scale blood loss

• Vascular shock: results from extreme vasodilation and decreased peripheral resistance

• Cardiogenic shock results when an inefficient heart cannot sustain adequate circulation


Signs and symptoms

Acute bleeding (or other events that causeblood volume loss) leads to:

1. Inadequate tissue perfusion resulting in O2 and nutrients to cells2. Anaerobic metabolism by cells, so lactic acid accumulates3. Movement of interstitial fluid into blood, so tissues dehydrate

Initial stimulus

Result

Physiological response

Chemoreceptors activated(by in blood pH)

Baroreceptor firing reduced(by blood volume and pressure)

Hypothalamus activated(by pH and blood pressure)

Major effect Minor effect

Brain

Activation ofrespiratory centers

Cardioacceleratory andvasomotor centers activated

Sympathetic nervoussystem activated

ADHreleased

Neuronsdepressed

by pH

Intense vasoconstriction(only heart and brain spared)

Heart rate Centralnervous system

depressed

Adrenalcortex

Kidney

Renin released

Renal blood flow

Aldosteronereleased

Kidneys retainsalt and water

Angiotensin IIproduced in blood

Waterretention

Urine outputRate anddepth of

breathing

Tachycardia,weak, thready

pulse

Skin becomescold, clammy,and cyanotic

Thirst Restlessness(early sign)

Coma(late sign)

CO2 blownoff; bloodpH rises

Blood pressure maintained;if fluid volume continues to

decrease, BP ultimatelydrops. BP is a late sign.


Circulatory Pathways

• Two main circulations

• Pulmonary circulation: short loop that runs from the heart to the lungs and back to the heart

• Systemic circulation: long loop to all parts of the body and back to the heart

Copyright © 2010 Pearson Education, Inc. Figure 19.19a

R. pulmon-ary veins

Pulmonarytrunk

Pulmonary capillariesof the R. lung

Pulmonary capillariesof the L. lung

R. pulmonaryartery

L. pulmonaryartery

Tosystemic circulation

L. pulmonaryveins

(a) Schematic flowchart.

Fromsystemiccirculation

RA

RV LV

LA


Azygossystem

Venousdrainage

Arterialblood

Thoracicaorta

Inferiorvenacava

Abdominalaorta

Inferiorvenacava

Superiorvena cava

Commoncarotid arteriesto head andsubclavianarteries toupper limbs

Aortic arch

Aorta

RA

RV LV

LA

Capillary beds ofhead andupper limbs

Capillary beds ofmediastinal structuresand thorax walls

Diaphragm

Capillary beds ofdigestive viscera,spleen, pancreas,kidneys

Capillary beds of gonads,pelvis, and lower limbs


Arteries Veins

Delivery Blood pumped into single systemic artery—the aorta

Blood returns via superior and interior venae cavae and the coronary sinus

Location Deep, and protected by tissues Both deep and superficial

Pathways Fairly distinct Numerous interconnections

Supply/drainage Predictable supply Usually similar to arteries, except dural sinuses and hepatic portal circulation

Differences Between Arteries and Veins


Developmental Aspects

• The heart pumps blood by the 4th week of development

• Fetal shunts (foramen ovale and ductus arteriosus) bypass nonfunctional lungs

• Ductus venosus bypasses the liver

• Umbilical vein and arteries circulate blood to and from the placenta


Documents

Copyright © 2010 Pearson Education, Inc. Homeostatic Imbalance: Hypertension Prolonged hypertension is a major cause of heart failure, vascular disease,