CIRCULATION AND HEMOSTASIS

What are the properties of an Artery?

• carry blood away from the heart

• high oxygen blood

• arteriole is a small artery

• thicker muscle (tunica media) to be able to withstand higher pressure

What are the properties of a Vein?

• carry blood towards heart

• low oxygen blood

• venule is a small vein + is where capillaries converge

• thinner muscle walls due to lower blood pressure

• contains valves to prevent blood backflow

What are the properties of a Capillary?

• very thin

• composed of the tunica intima only (endothelium and basement membrane)

• site of exchange between blood plasma and cells

• varies in diameter and permeability depending on location

What are the different types of Capillaries?

• continuous, least permeable

• fenestrated, allows large molecules to pass through its pores

• sinusoid, large plasma proteins can pass through its gaps

What is Blood Pressure?

• measured on the brachial artery at the level of the heart

• systolic pressure results from blood leaving the heart (ventricular contraction; max pressure)

• diastolic lower pressure exerted after ventricular relaxation (min pressure)

normal systolic (100-140mmhg), normal diastolic (60-90mmhg)

How does an increased Cardiac Output increase Blood Flow?

• increasing heart rate, stroke volume (volume of blood pumped in each contraction), contraction strength, and blood volume in body will increase blood pressure and promote blood flow

How does a decreased Peripheral Resistance increase Blood Flow?

• shorter and wider diameter of blood vessels increases blood flow

• vessel compliance enables vessels to expand to reduce resistance

• decreased blood viscosity (less RBC + albumin), increases blood flow

How does the Nervous System regulate Blood Pressure?

• cardiovascular (increase / decrease heart rate) and vasomotor (vasodilation/constriction) centres in medulla oblongata

• autonomous nervous system

• baroreceptors detect BP change

• chemoreceptors detect CO2 and H+ concentration change

How does the Endocrine System regulate Blood Pressure?

hormones can change blood viscosity or ion levels

• nor/epinephrine increase HR/CF, vasoconstriction in exrtremeties, leading to more BP

• ADH and aldosterone lead to water retention which increases BP

• erythropoetin increases RBC which increases BP

What Autoregulation Chemical Signals regulate blood pressure?

• local levels of O2, CO2, H+, K+, lactic acid, histamines, and local body temp cause constriction or dilation capillary sphincters to determine movement of blood through specific capillary beds

• depends on requirements of the cell serviced by specific capillary bed

How does the Autoregulation Myogenic (muscle) Response regulate Blood Pressure?

• arteriole wall muscles constrict or dilate to control blood pressure within capillary beds

What is the Arterial Pulse and where can we locate one?

• the alternating expansion and recoil of an arterial muscle wall can be felt with each contraction of the left ventricle

• used to measure heart rate

• wrist - radial artery

• neck - carotid artery

• above eye - superficial temporal artery

• thigh - femoral artery

• upper arm - brachial artery

How does the Return of Blood to the Heart work?

• blood floows easily from high to low pressure areas

• veins need to maintain higher pressure

  • low pressure in atria during diastole

  • skeletal muscle pump helps vein counteract the force of gravity

  • respiratory pump helps through thoracic expansion

What are all the Major Arteries required for the class (superior to inferior)

• right and left common carotid

• right and left subclavian

• brachiocephalic trunk

• axillary

• aortic arch

• ascending and descending aorta

• pulmonary trunk to pulmonary arteries

• thoracic and abdominal aortas

• brachial

• common iliac

• femoral

What are the Main Blood Vessels supplying heart tissue?

• right and left coronary artery

• coronary sinus

What are the Major Veins required for this class (superior to inferior)?

• internal and external jugular

• subclavian

• brachiocephalic

• axillary cephalic

• superior and inferior vena cava

• right and left common iliac

• femoral

What is Hemostasis?

• reduction and stoppage of blood loss from a damaged blood vessel

• there are three mechanisms

  • vascular spasm

  • platelet plug formation

  • blood clotting or coagulation

What is the function of the Injury and Vascular Spasm phase?

• helps until longer-term mechanisms have an effect

• caused by endothelins released by damaged muscle cells

What occurs during the Injury and Vascular Spasm phase?

• blood vessel is severed

• blood and its components leak out of breaks

• smooth muscle in vessel wall contracts near injury point to reduce blood loss

What occurs during the Platelet Plug Formation Phase?

• platelets are activated by chemicals released from the injury site and by contact with underlying collagen

• platelets become spiked and stick to each other and to the wound site

What is an Initial Platelet?

• activated by chemicals released from the injured cells and by contact with broken collagen

What is a Bound Platelet?

• release chemicals that activate and attract other platelets

What is Coagulation / Blood Clotting?

• fibrinogen is converted to fibrin

  • forms a mesh that traps more platelets and erythrocytes to produce a clot

What is the Extrinsic Coagulation Pathway?

• occurs more rapidly

• clotting factor 3 is also called tissue factor

• trauma to extravascular cells

What is the Intrinsic Coagulation Pathway?

• occurs slowly

• stimulated by trauma inside the blood vessel

What is the Common Pathway of the Coagulation Phase?

• X to Xa

• Va

• Prothrombin to Thrombin

• Fibrinogen to Fibrin

• XIIIa + Ca2+

• Cross linked fibrin clot

How are Blood Clots prevented from forming in the absence of injury?

• factors circulate in an inactive form

• presence of anticoagulants

  • anti-thrombin which blocks clotting factor activity

  • heparin which boosts anti-thrombin activity

How are Blood Clots regulated during Coagulation?

• positive feedback loop begins; thrombin formation stimulates more thrombin formation

• active clotting factors work only at injury site

• all active thrombin is bound to fibrin clot

What is Clot Dissolution / Fibrinolysis?

• plasminogen (inactive enzyme) is incorporated into blood clots as they form

• various factors uncluding tissue plasminogen activator eventually activates plasminogen to form plasmin to break down the blood clot

What else can affect Blood Clotting?

• Vitamin K stimualtes liver for thrombin + other factor production

  • sourced from digestive tract bacteria + food

• anticoagulant drugs delay or prevent undesirable clots (such as ones responsible for heart attacks and stroke)

  • heparin - inactivate thrombin

  • warfarin - interferes vitamin K action

  • aspirin - inhibits vasoconstriction and platelet aggregation

• thrombolytic agents help dissolve blood clots

  • streptokinase

  • tissue plasminogen activator