Anatomy & Physiology

Anatomy & Physiology Study Guide kidney and directed to the urinary bladder by the ureter. The smooth muscle walls of the ureters produce a peristalsis movement that moves urine along. The urinary bladder is a sac of muscle that holds urine until it is expelled from the body. It is located in the pelvis and varies in size with the amount of urine stored. An empty bladder is shaped like a pear, but when moderately full (about 0.5 liter), it assumes an oval form. The bladder voids through an opening at its midline. There are strong muscles in this central triangle of the bladder wall, which are essential for proper voiding. The bladder is supplied with arteries, veins, and lymphatics, which are derived from abdominal blood vessels. The urinary bladder wall is stretchable to accommodate varying amounts of urine. Nerve endings, called stretch receptors , are found in the wall of the urinary bladder. Normally, the pressure within the urinary bladder is low. As the volume of urine approaches the bladder's capacity, it causes stretching of the wall, which stimulates the stretch receptors. The cycle of events controlling urination is known as the voiding reflex. The urethra voids the urine from the bladder. The male urethra is about 6-8 inches long, has two curvatures, and extends from the bladder to the penis’ end. In females, the urethra is approximately 1 1/2 inches long. There are two sphincters that control the leakage of urine. One sphincter is located around the bladder neck, and the other is around the membranous part of the urethra. The urethra is composed of a mucous membrane that is supported by submucous tissue. The urethral sphincters control the passage of the urine through the urethra. There are two sphincters: an internal urethral sphincter and an external urethral sphincter. The internal urethral sphincter is made of smooth muscle and is located on the floor of the urinary bladder. It is controlled by nerves of the autonomic nervous system. The external urethral sphincter is inferior surrounding the urethra in the region of the pelvic floor. It consists of striated muscle tissue. Controlled by the peripheral nervous system, it is crucial for the process of toilet training. 24.2 Internal Structure of Kidneys Nephrons are the functional units of the kidney. Their main functions are to remove, via filtration, certain waste materials from the body and to reabsorb water for use in the body. The two main sections of the nephron are the tubular system and the renal corpuscle . The kidney contains large quantities of renal corpuscles . There are an estimated one million of them in each kidney. A section of the renal artery, known as the afferent arteriole, carries blood to each corpuscle. This afferent arteriole divides into approximately 50 capillaries that are bent into short loops. This tangled mass of capillaries is referred to as the glomerulus. Achieve Page 332 of 368 ©2018