Relevant pharmacology

Gastrointestinal tract disorders are common, and many drugs are targeted at the autonomic nervous system and its effectors to control over-activity or under-activity in the smooth muscles and glands. Perhaps the most important are those controlling gastric acid secretion, those inhibiting or inducing vomiting, and those affecting intestinal motility (i.e. drugs used for the treatment of constipation and diarrhoea). 9.7.1 Drugs reducing gastric acid secretion The main pathways for...

Drugs affecting intestinal motility

Although acute diarrhoea is best treated by maintaining fluid and electrolyte balance using oral rehydration fluids, drugs reducing gastrointestinal motility can be useful in adults. The main agents used are the opiates (in particular codeine, a morphine congener, and diphenoxylate and loperamide, synthetic pethidine-like drugs), and muscarinic receptor antagonists. The opiates act on neurones in the enteric plexuses and directly on smooth muscle to increase the tone, but decrease the...

Urethra

Prostatic Urethra

In the male, the urethra is often considered as comprising four sections, the preprostatic, the prostatic, the membranous and the penile urethra (Fig. 10.11). The preprostatic urethra is about 1.5 cm long, and extends from the bladder neck to the prostate. The smooth muscle is richly supplied with noradrenergic nerve fibres, and there is only a sparse cholinergic innervation. The prostatic urethra is about 3-4 cm long and runs through the substance of the prostate. It has a crescent-shaped...

Cardiovascular and Respiratory Systems

8.1.2 Parasympathetic nervous system, 238 Mechanisms involved in slowing heart rate (negative chronotropy), 239 Mechanisms involved in reducing conduction velocity (negative dromotropy), 242 Mechanisms involved in reducing contractility (negative inotropy), 242 8.1.3 Sympathetic nervous system, 243 Mechanisms involved in increasing heart rate (positive chronotropy), 244 Mechanisms involved in increasing conduction velocity (positive dromotropy), 245 Mechanisms involved in increasing...

Components of the tract and their innervation

Structure Corpora Cavernosa

A diagram of the human male genital tract is given in Fig. 10.19. These are the organs of spermatogenesis. They are located outside the abdominal cavity in the scrotum, a thin-skinned pouch with a layer of smooth muscle (the dartos muscle), which on contraction in the cold or during exercise allows the testes to be pulled nearer to the body for protection or increased warmth, and when relaxed allows elongation and thus lowering of the testes away from the abdomen for cooling. Correct tempera-...

Kidney

In relation to its size, the kidney receives a richer innervation than almost any other organ. It is thought that the innervation is exclusively sympathetic, and the presynaptic fibres leave the spinal cord from roots T5 to L3. The innervation takes many different routes to the kidney, and there is an extensive renal plexus in association with the aorticorenal ganglion at the junction of the renal artery and the aorta. Fibres enter the kidney along the renal artery and vein at the hilum....