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.