Exercise 1 Flashcards
Define excretion. What is the difference between excretion and defecation?
Excretion is the removal of metabolic wastes from the body and is a function of the urinary system. Defecation refers to the elimination of feces from the body and is a function of the digestive system. Undigested food and bacteria contained in the feces were never part of the functioning of the body but the metabolic wastes found in urine were.
3.List and briefly explain the main functions of the urinary system as listed under “Functions of the Urinary System” on page 160.
The main functions of the urinary system are as follows: i) excretion of metabolic wastes including urea, creatinine and uric acid ii) maintenance of water-salt balance of blood which in turn affects blood pressure. The more salt in the blood, the more water in the blood. With an increase in water in the blood comes an increase in blood volume which in turn causes an increase in blood pressure. iii) maintenance of acid-base balance of blood. The normal pH of blood is 7.4. This pH is maintained by the excretion of hydrogen ions and the reabsorption of bicarbonate ions as required. iv) secretion of hormones - renin promotes secretion of aldosterone which affects the reabsorption of sodium ions; secretion of erythropoietin which regulates the production of red blood cells; the activation of Vitamin D which in turn promotes the absorption of calcium.
What are the three main nitrogenous wastes that are excreted by the urinary system? Briefly describe what each is formed from.
The main nitrogenous waste excreted by the urinary system is urea but humans also excrete some ammonium, creatinine and uric acid. i) urea – by-product of amino acid metabolism. It is formed in the liver when ammonia, a by-product of amino acid metabolism, is combined with carbon dioxide to produce urea. Note: urea is less toxic to cells than ammonia ii) creatinine – by-product of creatine phosphate metabolism in muscle iii) uric acid – by-product of nucleotide metabolism
List the four organs that form the urinary system.
The four organs that hold urine forming the urinary system are the following; two kidneys, two ureters, one urinary bladder and the urethra.
Discuss the ureters in terms of location, structure and function including the role of peristalsis.
The ureters:
Location – one ureter extends from each kidney to the bladder
Structure – two small, muscular tubes about 25 cm long, 5 mm in diameter
Function – the kidneys deliver urine to the ureters and by peristalsis,the rhythmical wavelike contraction of smooth muscle, the urine is moved within the ureters and then enters the urinary bladder in spurts.
Briefly describe what the urinary bladder looks like and its purpose. What special structures in the bladder help it do its job?
The urinary bladder is a hollow, muscular, expandable organ that stores urine. Sphincters, which are circular muscles that enclose a tube, are found at the end of the bladder where the urethra exits. They control the excretion of urine out of the bladder.
What is the role of the urethra? How does the structure of the urethra differ in males and females? What is the significance of the differences in terms of medical conditions that may result?
The urethra receives urine from the bladder and carries it out of the body. The urethra differs in the male and female in its length and the substances it carries. It is much shorter in the female and this makes bacterial infections more common in the urinary tract. In the male the urethra is approximately 20 cm long and passes through the prostate gland. As the male ages this gland often enlargens causing increased pressure on the urethra restricting the normal flow of urine. In the female the urethra is part of the urinary system only and as such carries urine. In the male the urethra is part of both the urinary and reproductive systems. During urination it carries urine out of the body and during ejaculation it carries sperm out of the body.
9.Explain how the body controls the process of urination. How does this process change as we develop?
In infants and young children the act of urination is a reflex action. When the urinary bladder fills to about 250 mL of fluid, the stretch receptors in the area send a neural impulse to the spinal cord which immediately responds by sending a neural impulse back to the bladder to contract and the sphincters to relax, allowing the excretion of urine out of the bladder and into the urethra. As we get older we learn to control this reflex.
The major organs of the urinary system are the kidneys. Give a brief description of the kidneys and indicate their location and function.
The kidneys are the primary organs of the urinary system. Description - The kidneys are bean-shaped and reddish-brown in colour, and are about the size of a fist. They are covered by tough fibrous connective tissue and adipose tissue. Location - They are found on either side of the vertebral column, just below the diaphragm. They lie in depressions against the muscles of the back just beneath the lining of the abdominal cavity. They are partially protected by these muscles and the lower ribcage, but can be damaged by a blow to the back. Function – the production and excretion of urine
