Blood vessels autonomic control

Structures of the anterior chamber of the eye. Tissues with significant autonomic functions and the associated ANS receptors are shown in this schematic diagram. Aqueous humor is secreted by the epithelium of the ciliary body, flows into the space in front of the iris, flows through the trabecular meshwork, and exits via the canal of Schlemm arrow). Blockade of the 13 adrenoceptors associated with the ciliary epithelium causes decreased secretion of aqueous. Blood vessels (not shown) in the sclera are also under autonomic control and influence aqueous drainage. 

Physiologically, in both normal and hypertensive individuals, blood pressure is maintained by moment-to-moment regulation of cardiac output and peripheral vascular resistance, exerted at three anatomic sites (Figure 11-1) arterioles, postcapillary venules (capacitance vessels), and heart. A fourth anatomic control site, the kidney, contributes to maintenance of blood pressure by regulating the volume of intravascular fluid. Baroreflexes, mediated by autonomic nerves, act in combination with humoral mechanisms, including the renin-angiotensin-aldosterone system, to coordinate function at these four control sites and to maintain normal blood pressure. Finally, local release of vasoactive substances from vascular endothelium may also be involved in the regulation of vascular resistance. For example, endothelin-1 (see Chapter 17) constricts and nitric oxide (see Chapter 19) dilates blood vessels. 

The direction of arterial blood flow in the nose runs anteriorly against inspiration. Blood vessels are arranged in such a manner as to provide an erectile capacity to the mucosa enabling the airway to widen and narrow. Blood flow through the autonomically controlled vasculature of the nasal tissue is of importance in the conditioning of inspired air. 

Blood is supplied to the retina by the central retinal artery and choroidal blood vessels (Oyster, 1999). The central retinal artery arises from the ophthalmic artery, w hich in turn branches off the internal carotid artery. Upon entering the retina, the central retinal artery branches into deep capillary beds in the INL and superficial capillary beds in the GCL. Endothelial cells of retinal capillaries are joined by tight junctions, contributing to the blood/retinal barrier. There is litde or no autonomic regulation of the retinal circulation blood flow through these capillaries is instead primarily controlled by autoregulation (Wangsa-Wirawan and Linsenmeier, 2003). Retinal capillaries drain into the central retinal vein. 

There are three distinct types of muscle tissue in vertebrates striated, smooth, and cardiac. Striated, or skeletal, muscle is attached, at least at one end, to the skeleton via tendons. This muscle type is often referred to as the voluntary muscle, as it can be consciously controlled. Smooth muscle is usually arranged in sheets or layers in tubular systems, such as arteries and veins (see Blood Vessels), the gastrointestinal and respiratory tracts, and the genitourinary tracts. The activities of the smooth muscles are not under conscious control rather they are coordinated by the autonomic (involuntary) nervous system. The cardiac muscle comprises the bulk of the heart wall proper and small amounts are found in the superior vena cava and pulmonary vein. The cardiac muscle is not under conscious control it has an automaticity center which responds to the autonomic nervous system when needed (see section Impulse Conduction). In the heart, cardiac muscle cells are joined in a network of fibers and are connected by gap junctions, which facilitate the conduction of electrical impulses through the cardiac muscle network. In addition to the typical cardiac myocytes, there are other cardiac muscle cells that are specialized to initiate, attenuate, or accelerate the electrical impulses for coordinated contraction of the cardiac network. 

Muscular conuactiotisi ot Lite gut and secretion of acid and cn/ymes are under autonomic control. 11te enteric part of the autonomic nervous system consists of gunglionated plexuses ( ) with complex inter-connections supplying the smooih muscle, mucosa and blood vessels, fhe ganglia t > (pstrasytnpatheiic) receive extrinsic excitatory fibres from the vagus and inhibitory sympathetic fibres. Other transmitters in the gut include 5HT. Al P. nitric oxide and neuropeptide-Y. 

Spermatogenesis— process of formation of mature male germ cells Subchronic—of intermediate duration used by CERCLA to describe studies or levels of exposure for humans between 2 wk and 7 yr Sympathetic—autonomic nervous system, which controls smooth muscles, blood vessel diameter, and glandular secretion Synapse—gap between nerve axons, or between axons and effector organs Syndactylous—fusion of adjacent toes... 

Involuntary muscle does not have the characteristic striped appearance of voluntary muscle. It exists in the digestive tract, the walls of the blood vessels and in the respiratory and genito-urinary apparatus. Involuntary muscle is controlled automatically by the autonomic nervous system. 

The microvascular complications of both type 1 and type 2 diabetes melli-) tus involve the small vessels of the retina (diabetic retinopathy), the renal glomerular capillaries (diabetic nephropathy), and the vessels supplying blood to the peripheral nerves (autonomic neuropathy). The lack of adequate control of Ann Sulin s diabetic state over many years caused a progressive loss of the fdtering function of the approximately one-and-one-half million glomerular capillary-mesangial units that are present in her kidneys. 

We believe that an answer to these questions is of fundamental importance in interpreting the findings in both laboratory and applied studies. A model of the processes involved should be available in order to determine the nature of activation in autonomic space (e.g., Bemtson, Cacioppo, Quigley, Fabro, 1994). Such a model requires an adequate representation of the baroreflex blood pressure control subsystem. Increased activation of the baroreceptors in the vessel wall of the aortic arch and the carotid sinus is accompanied by an increase in vagal and a decrease in sympathetic activity, whereas decreased activation does the reverse (baroreflex). 

---