Blood Vessels Vessels Arteries largest of blood vessels carry blood away from heart Elastic closest to heart and they have lots of resistance to blood being pumped away from heart because they are full of elastin they can expand so this helps maintain BP Muscular elastin lost as arteries move away from heart slightly smaller deliver blood to organs Arterioles greater surface area than arteries but they are smaller they branch Capillaries further branching of arterioles where gaseous exchange occurs gets smaller to where it only allows single cells to pass at a time Venules where blood is collected Veins larger and where blood is transferred back to heart Vessel Anatomy Tunica interna comprised of simple squamous epithelium continuation of cardiac endothelium the endothelium in the tunica intera are ver tightly packed which decreases friction and allows things to pass Tunica media smooth muscle layer some elastin but mostly muscle controlled by SNS when stimulated it causes vessel to constrict vasoconstriction changes in the blood vessel diameter controls the flow of blood Tunica externa predominantly collagen function is to anchor the blood vessel in place fibers that are exposed when there is a cut is the tuncia externa Vasa vasorum tiny blood vessels that feed tunica externa of really large blood vessels Lumen Capillaries Continuous Capillaries Continuous Fenestrated Capillaries Continuous Fenestrated Sinusoidal Capillary Bed Terminal arteriole away from heart so oxygen rich blood Metarteriole carries blood through capillary bed and becomes Thoroughfare channel comes through center and becomes Postcapillary venule vein side Vascular shunt True capillaries 100s off vascular shunt Precapillary sphincters one associated with each true capillary they control flow of blood into true capillaries under control of basomotor nerves which allow them to contract and also controlled by local chemical secretions Artery vs Vein Artery Vein Thick walls keep pressure moving Small lumen Thicker tunica media Lower blood volume Higher blood pressure No valves Thin walls lowest pressure Large lumen Thinner tunica media Higher blood volume Lower blood pressure Venous valves prevent backflow of blood present because of low pressure helps assisst the movement of blood even with low blood pressure Varicose Veins Additional Modifications Muscular pump muscle movement skleletal muscle contraction that helps push blood through veins Respiratory pump as we breathe we get pressure diffferences that occur in our chest when it s a low pressure the blood moves in to fill that lower pressure area and move blood to heart Collateral Channels Blood Flow volume of blood that is flowing at any given time constant varies from one organ to another controlled by capillary beds Directly proportion to differences in blood pressure Inversely proportional to peripheral resistance F P R Peripheral Resistance Blood viscosity internal resistance relatively constant can be medically treated thinning blood Peripheral Resistance Blood viscosity Vessel length larger people have longer blood vessels the longer the vessels the greater the resistance so this varies between people Peripheral Resistance Blood viscosity Vessel length Vessel diameter most imp operating system changes in vessel diameter changes the resistance smaller dia greater resistance lower flow most imp in arterioles regulates flow of blood through body Systemic Blood Pressure Anatomy Joke of the Day Mean Arterial Pressure Pressure that propels blood to tissues MAP diastolic pressure pulse pressure 3 Blood Pressure Control Counteracting Brief Fluctuations Alter blood distributions to respond to needs closing precapillary sphincters and causing blood to flow through capillary shunts Counteracting Brief Fluctuations Alter blood distributions to respond to needs Alter vessel diameter constrict blood vessel will cause increase in pressure relax blood vessel will cause lower BP Vasomotor Center Neural Reflex Arcs Baroreceptors detect change in pressure cause vasodilation to occur inhibit vasomotor center so no norepinephrine secreted which causes constriction of blood vessels opposite can also be true and they can stimulate vasomotor center short term changes and response Vasomotor center Peripheral resistance inhibited reduced Pressure reduced Side Effects Venous return reduced Cardiac output reduced less arriving less released Heart rate reduced reduces amount of contractions Contractile force reduced MAP declines Result of Side Effects Reduced MAP initiates vasodilation Also increases cardiac output Blood pressure rises Chemical Reflex Arcs Chemoreceptors detect drop in oxygen level or pH or increase in CO2 Cardioacceleratory center stimulated increases heart rate Vasomotor center stimulated causes vasoconstriction Blood pressure increases Other Chemical Controls Epinephrine and norepinephrine Other Chemical Controls Epinephrine and norepinephrine Atrial natriuretic peptide causes vasodilation reduces BP reduces blood flow also affects kidney activity increase in water loss in kidneys so water lost in blood reduces blood vol Other Chemical Controls Epinephrine and norepinephrine Atrial natriuretic peptide Antidiuretic hormone functions for water conservation increase Blood vol which will increase flow secreted by hypothalamus and typically only functions with kidneys to increase blood vol but if there is a lot of blood loss then it acts as vasoconstrictor Other Chemical Controls Epinephrine and norepinephrine Atrial natriuretic peptide Antidiuretic hormone Angiotensin II functions are vasoconstrictor which causes increase in BP linked to ADH and aldosterone Other Chemical Controls Epinephrine and norepinephrine Atrial natriuretic peptide Antidiuretic hormone Angiotensin II Endothelium derived factors chemicals secreted from endothelium of blood vessels themselves can cause vasoconstriction or vasodilation Other Chemical Controls Epinephrine and norepinephrine Atrial natriuretic peptide Antidiuretic hormone Angiotensin II Endothelium derived factors Inflammatory chemicals most imp histamine any that function like histamine will be vasodilators Other Chemical Controls Epinephrine and norepinephrine Atrial natriuretic peptide Antidiuretic hormone Angiotensin II Endothelium derived factors Inflammatory chemicals Alcohol 3 types of affect on BP 1 inhibits ADH which promotes water loss so therefore decreased BP 2 inhibits vasomotor center which promotes vasodilation