PBL Topic 2 Case 6 Flashcards
Identify four functions of the circulation
- Transport nutrients to body tissues
- Transport waste away from body tissues
- To conduct hormones
- To maintain an appropriate environment in all tissue fluids
Identify the two types of circulation
- Pulmonary circulation
- Systemic circulation
Identify the function of the arteries
- Transport blood under high pressure to the tissues from the heart
Identify the function of the arterioles
- Control conduits through which blood is released into the capillaries
Identify the functions of the capilalries
- Exchange nutrients, electrolytes, hormones and other substances between the blood and interstitial fluid
Identify the functions of the venules
- Collect blood from the capillaries into progressively larger veins
Identify the functions of the veins
- Conduits for transport of blood from the venules back to the heart
What is the arterial pressure in the aorta?
- 100 mm/Hg
- 80 mm/Hg during diastole
- 120mm/Hg during systole
How does the arterial pressure change following the aorta?
- Decreases
- High enough to allow nutrients to diffuse through the pores
- Low enough to allow little plasma to leak through the pores
What is cardiac output and what is its typical value?
- Quantity of blood pumped into the aorta each minute by the heart
- 5 L/min
Identify two factors that determine blood flow
- Pressure difference
- Vascular resistance
How do you calculate blood pressure?
- Cardiac Output x Peripheral Resistance
How do you calculate cardiac output?
- Stroke Volume x Heart Rate
How do you calculate stroke volume?
- End Diastolic Volume - End Systolic Volume
Identify three factors that affect stroke volume
- Preload
- Contractility
- Afterload
Identify three factors that affect heart rate
- Hormones
- Temperature
- Pain
Identify three factors that affect vessel resistance
- Viscosity of the blood
- Vessel length
- Vessel radius
Identify 5 factors that increase blood flow
- Increase in metabolism
- High altitudes
- Pneumonia
- Carbon monoxide poisoning
- Cyanide poisoning
Outline Vasodilator Theory
- Increase in oxygen demand
- Formation of vasodilator substances
- Including histamine, adenosine and nitric oxide
Outline Oxygen Lack Theory
- Increase in oxygen demand
- Natural dilation of vessels in absence of oxygen
- Cyclical opening of precapillary sphincters (vasomotion)
Outline Reactive Hyperaemia
- Increase in oxygen demand
- E.g. occlusion
- Rapid blood flow through tissue for a few seconds
- Repay oxygen deficit
Outline Active Hyperaemia
- Increase in oxygen demand
- E.g. exercise
- Rate of blood flow increases through vessel
Outline Metabolic Theory of Auto-regulation of Blood Flow
- Rise in arterial pressure
- Excess flow of oxygen and nutrients
- Vasoconstriction
- Reduced blood flow
Outline Myogenic Theory of Auto-regulation of Blood Flow
- Rise in arterial pressure
- Stretching of vessel
- Vasoconstriction
- Reduced blood flow
What stimulates nitric oxide release for vasodilation?
- Rapid flow of arteries causes sheer stress due to viscous drag
- Release of bradykinin and histamine
How does nitric oxide cause vasodilation?
- Combines with guanylyl cyclase
- Formation of cGMP
- A second messenger to activate protein Kinase G
- De-phosphorylation of myosin light chains
- Sequestration of intracellular Ca2+
What is the function of prostacyclin (Prostaglandin I2)?
- Vasodilator
What is the function of endothelin-1?
- Vasoconstrictor
What is EDRF?
- Endothelium Derived Relaxing Factor
- Composed of Nitric Oxide
- Vasodilator
Identify three factors that are responsible for angiogenesis
- Vascular Endothelial Growth Factor (VEGF)
- Fibroblast Growth Factor
- Angiogenin
Outline the process of angiogenesis
- Dissolution of basement membrane
- Reproduction of endothelial that stream outward through vessel
- Formation of cords that fold over into a tube
- Formation of a capillary loop when two tubes join
- Blood flow through capillary loop
- Invasion of smooth muscle cells
Outline the process of collateral circulation
- Dilation of small vascular loops that connect the vessel above to the blocked vessel below
- Dividing of these small vascular loops forming multiple small collateral channels
Identify two ways that noradrenaline can enter the circulation
- Release from sympathetic nerve endings
- Sympathetic nerves cause adrenal medulla to secrete large amounts
Identify what occurs when noradrenaline binds to alpha receptors
- Activated G protein activates Phospholipase C
- PIP2 is converted into IP3 and DAG
- IP3 mobilises calcium ions which are involved in vasoconstriction
- DAG actives protein kinases which phosphorylate other proteins resulting in cellular response
Identify the function of a1 and a2 receptors and where they are located
- a1 receptors on smooth muscle cause vasoconstriction
- a2 receptors on presynaptic membrane cause negative feedback
Identify what occurs when noradrenaline binds to beta receptors
- Activated G protein activates adenylyl cyclase
- Conversion of ATP to cAMP
- Activation of protein kinases
- Phosphorylation of proteins results in cellular response
Identify the function of B1, B2 and B3 receptors and where they are located
- B1 receptors on sinus node and cardiac muscle increase heart rate and contraction force
- B2 receptors on smooth muscle in coronary arteries cause vasodilation
- B2 receptors on airway smooth muscle cause bronchodilation
- B3 receptors cause lipolysis
What percentage of the cardiac output do the kidneys recieve?
- 20% (1L/min)
Where and how is renin stored?
- Stored as prorenin in juxtaglomerular cells of the kidneys
What is the function of renin?
- Acts on angiotensinogen to release
- To release 10-amino acid peptide angiotensin 1
- When arterial pressure falls
What is the role of Angiotensin Converting Enzyme? Where does this function take place?
- Conversion of Angiotensin I to Angiotensin II (8-amino acid peptide)
- Lung
Identify two functions of Angiotensin II
- Powerful vasoconstrictor
- Decrease sodium and water excretion
- Thereby increasing arterial pressure
What is the function of Aminopeptidase A?
- Removes a single amino acid from Angiotensin II
- To form Angiotensin III
Identify two functions of Angiotensin III
- Stimulates aldosterone secretion
- Regulates thirst
- Increases secretion of ADH
How does Angiotensin II act on smooth muscle cells?
- Via Phospholipase C Second Messenger System
How is Angiotensin II inactivated?
- By angiotensinases
When is ANP secreted?
- Volume overload
- In response to stretching of the atria
Identify four functions of ANP
- Increase diuresis and natriuresis
- Vasodilation
- Increase vascular permeability
- Inhibit release of angiotensin II
What is the affect of ANP on renal glomerular afferent and efferent arterioles?
- Dilation of afferent arterioles
- Constriction of efferent arterioles
- Increased filtration pressure
- Increases glomerular filtration
- Enhanced sodium excretion
Identify the three regions of the vasomotor centre
- Vasoconstrictor Area
- Vasodilator Area
- Sensory Area
Identify the function of the vasoconstrictor centre
- Excites preganglionic vasoconstrictor neurons of the sympathetic nervous system
Identify the function of the vasodilator area
- Fibres project upwards
- Inhibit vasoconstrictor activity
Identify the function of the sensory area
- Receives sensory nerve signals from glossopharyngeal and vagus nerves
- Output from these helps to activate either the vasodilator or vasoconstrictor area
Identify the function of the lateral portions of the vasomotor centre
- Transmits impulses through the sympathetic nerve fibres to increase heart rate and contractility
Identify the function of the medial portions of the vasomotor centre
- Transmits parasympathetic impulses through the vagus nerve to decrease heart rate and contractility
Identify the main baroreceptors and their associated nerves
- Carotid baroreceptors, located in bifurcation of carotid artery, transmit signals via glossopharyngeal nerve (via Hering’s nerves)
- Aortic baroreceptors, located in the aortic arch, transmit signals through vagus nerve
Identify an effect of increased blood pressure on the vasomotor centre and sinus onde
- Stimulation of caridioinhibitory centre
- Inhibition of cardioaccelerator
- Increased parasympathetic activity and decreased sympathetic activity to sinus node
- Decrease in heart rate
Identify the effect of decreased blood pressure on the vasomotor centre and sinus node
- Stimulation of cardioaccelerator centre
- Inhibition of caridioinhibitory centre
- Increased sympathetic activity and decreased parasympathetic activity to sinus node
- Increase in heart rate
Explain why nicotine can stimulate postganglionic neurons
- Membranes of these neurones contain nicotinic receptors