Innervation Of Blood Vessels Flashcards
Describe origin & most imp function of symp vasoconstictor fibers
Vasomotor center
They influence the caliber of resistance & capacitance vessels to maintain a normal ABP, & readjust ABP when it is disturbed.
Describe distribution of symp VC fibers
Innervate all BVs except venules & capillaries, dense in arterioles, less in veins except splanchnic veins.
The origin of symp VD center & where it recieves input from & what it innervates
Hypothalamic VD center
Cerebral cortex
Blood vessels of skeletal muscles
GR: Sympathetic vasodilator is functionally Parasympathetic
Because the have Ach as their postgamglionic transmitter
Mention functions of symp VD center
- Activated very early in exercise to allow immediate maximum muscular effort.
- In fear & terror causing fainting
- In very high rise if ABP activated by baroreceptors or in carotid sinus syndrome
Describe the role of parasympathetic fibers in ABP regulation
Has no role
Cranial parasympathetic VD fibers innervate ….
While sacral para fibers innervate ….
- Brain, heart, salivary glands & gastric mucosa
2. External genitalia responsible for erectile function
…….consititute major components of peripheral resistance.
Skeletal muscle & skin resistance vessels
Mention the functions of arterioles
- Regulation of vascular vasomotor tone
2. Regulation of blood flow to capillary vascular beds
The VC tone is highest in …… & least in ……
Resting skeletal muscle, skin, GIT splanchnic vessels
Brain, heart & kidney
What happens in case of spinal cord transection?
The sympathetic preganglionic VCs will be interrupted and VC vascular tone to the entire body mass below the lesion will be lost leading to abrup dec in peripheral resistance & dec in ABP.
GR: Vascular contrictions begins slow recovery after spinal transection
Due to intrinsic myogenic tone, as well as establishment of spinal vascualr activity of the IML gray column of spinal cord.
Describe the role of VMC in rise/fall if ABP
In fall, the VMC will be stimulated and fire high-frequency efferent impulses in symp VC nerves, leading to:
1. Arteriolar vasocontriction
2. Dec blood flow to VC vascular beds
3. A resultant dec in capillary hydrostatic pressure & inc in plasma volume
4. Venoconstriction will result in dec venous capacity thus inc venous return & COP.
Opposite in rise
Blood flow to an organ is determined by the equation:
Blood flow = Perfusion pressure / Resistance
Classify mechanisms of regulation of blood flow
Acute A) Systemic (Nervous & humoral) B) Local (Autoregulation & active & reactive hyperemia)
Chronic (Long-term reg of blood flow)
Mention the nervous reg mech if VC
Sympathetic noradrenergic fibers originate in VMC
Mention the nervous reg VD mechs
- Dec in symp noradrenergic VC nerves
- Sympathetic vasodilator cholinergic fibers
- Sympathetic beta-adrenergic VD fibers
- Parasymp VD fibers
- Antidromic VD fibers (release of histamine & substance P)
Mention the humoral VC substances
Norepinephrine
Epinephrine & ADH (only act in high conc)
Serotonin & thrombaxane A2 from blood platelets
Ang II most potent
Endothelin-1
Mention the VD humoral substances
Epinephrine (in low conc acts on b-receptors Kinins NO ANP Prostacyclin
GR: Use of ACEI also inhibits breakdown of kinins
Because kininase is the same enzyme as ACE, this may help control HTN by vasodilation but may result in complication like cough due to bronchial mucosal congestion.
NO production is enhanced by ……
Ach, bradykinin, histamine, ANP & adenosine
Organs with highest autoregulatory capacity & least neurogenic vascular tone are ……, while the opposite are ……
Brain, heart, kidney
Skin & resting skeletal muscle
Mention & explain mechanisms of autoregulation
Myogenic theory: vascular smooth muscle contracts when it is stretched
Metabolic theory:VD metabolites are CO2, H+, K+, lactate & adenosine
Tissue pressure theory: inc ABP, inc capillary hydrostatic pressure, and inc filtration, higher amount of tissue fluid around vessel dec flow & inc resistance.
Define active hyperemia and its mechanism
Process by which blood flow to active tissue is increased
Vasodilator metabolites are produced as result of tissue activity as CO2, H+,K+, lactate, adenosine dec PO2 inc osmolarity. While VD causes washout of these metabolites & subsequent VC to normal ABP.
Define reactive hyperemia
Increase in blood flow to an organ after a period of occlusion of flow.
What is the mechansim of reactive hyperemia?
O2 lack OR accumulation of metabolites
Reactive hyperemia is greatest in ….., intermediate in….., least in …..
Heart & brain
Skeletal muscle
Skin, liver & lungs
Describe long-term regulation. This adaptation is in ….., but not in ….. .
If main arterial blood supply is occluded gradually this will decrease blood flow to the organ then the collateral vessels will dilate over weeks & months and blood flow will return to normal.
Skeletal muscle
Heart & brain
The process by which O2 lack leads to blood vessel formation
Angiogenesis
If CO was evenly districuted blood flow would be .,..
8.6 ml/min/100 gm tissue
Mention the organs which recieve almost 2/3 of CO
Liver kidney skeletal muscle
Mention organs with highest blood flow per unit weight
Heart, brain, kidney ,liver.
GR: Kidneys need a very large blood flow to carry out their function
Because they are clearance organs which is associated with little oxygen extraction so the flow is non nutritional.
Mention condition in which symp nervous VC tone dominates on kidney
During stressful conditions such as severe hemorrhage
GR: Although there is no cardiac accelerator area the HR can be inc
By inhibiting CIC
By stimulation pressor area of VMC
By sympathetic nuclei which could be connected to hypothalamic symp neuclei
Parasymp originate from …., relay in .,,,
CIC
Terminal ganglia
There is preponderance of rt vagus on ….., and left on …
SAN
AVN
Symp originate from …., relay in .,,,
IML column of upper 5 or 6 thoracic & upper 1 or 2 cervical segments
Paravertebral sympathetic chain (stellate ganglion and middle cervical ganglion)
Prove that vagal para tone is predominant on HR than symp tone
Sympathectomy or BB cause slight change if HR
Vagotomy or atropine cause pronounced tachycardia
When both are removed the HR is increased to the intrinsic heart rate which is indicative of the natural frequencycof the SAN
Also, in newborns HR is 100 because there is no inhibitory vagal tone.
Veagol tone is oart of …. Reflex by ….receptors
Baroreceptor
Arterial baro
What is the function of hypotahalmus in HR reg
Conveys cortical control on HR, it controls HR by hypothalamic sympathetic & parasymp nuclei, then through parasymp nerves originate in medulla & symp nerves originate in IML columns of spinal cord
GR: Newly born infants have HR of 100 bpm
As there is no inhibitory vagal tone where ABP is 30-50 mmHg which is below threshold for firing of baroreceptors.
Describe Marey’s law
There is inverese unidirectional relationship between ABP & HR, done by baroreceptor reflex.
Site & stimulus of type B atrial receptors
Junction of right atrium with venae cavae and left atrium with pulmonary veins, also pulomnary receptors seperate from the junction.
Central venous pressure
Afferents from type B receptors are ….., efferents are …… the effect of both is ….
Vagal
Vagak & sympathetic
Tachycardia
Activation of vetricular & type A atrial receptors leads to …..
Bradycardia
Describe mechanism if respiratory sinus arrhythmia
- During inspiration the intrathiracic pressure is dec, so VR is inc leading to acceleration of the heart by Bainbridge reflex.
- Pulmonary stretch receptors stimulated by lung inflation & vagal reflex
- The respiratory center itself irradiates to the medullary center leading to stimulation of HR
High conc of epinephrine or NE lead to …..HR
Decrease
How do Hypoxia, hypercapnia & acidosis affect HR
- Locally on SAN are inhibitory leading to lowering of HR
- Reflexly on chemoreceptors cause inc HR
- Centrally act on CIC causing intial stimulation then depression result in decrease then increase in HR
Mention cases of fever associated with direct depression of SAN
Influenza, typhoid, diphtheria
Mention conditions in which inverse ABP/HR relationship is lost
When cortical stimulation is involved
Both increase in muscular exercise, mild to moderate pain, alarm reaction (anger & fight)
Both decrease in recovery to exercise, grief & terror, severe pain.
Mention conditions in which inverse ABP/HR relationship is exaggerated
Cushing reflex when intracranial pressure is increased, ABP severely inc with severe bradycardia
