The Urinary System Flashcards
What does the urinary system consist of? Describe the function
Urinary system is the main excretory system and consists of:
• Two kidneys-> excrete urine
• Two ureters -> takes urine from kidneys to urinary bladder
• Urinary bladder -> collects and stores urine
• Urethra-> the urine leaves the body
Main functions of the kidneys:
• Formation urine, maintaining water, electrolyte and acid-base balance
• Excretion of waste products
• Production and secretion of erythropoietin, the hormone that stimulates formation red blood cells
• Production and secretion of renin (important enzyme in long term control of blood pressure)
Ureters:
• This carries urine from the kidneys to the urinary bladder
• Hollow muscular tubes
• Peristalsis is an intrinsic property of the smooth muscle layer that propels urine along the ureter
• The walls of the uterus consist of three layers of tissue:
1. An outer covering of fibrous connective tissue, continuous with the fibrous capsule of the kidney
2. A middle muscular layer consisting of interlacing smooth muscle fibres that form a functional unit round the ureter
3. An inner layer - the mucosa which is made of transitional epithelium
Urinary bladder:
• Reservoir to urine
• Lies in pelvic cavity
• Size and position varies depending on volume of urine it contains
• The bladder is roughly pear shaped but becomes more balloon shaped sit fills with urine
• The bladder Wall is composed of three outer layers:
1. outer layer: loose connective tissue, containing blood and lymphatic vessels and nerves
2. Middle layer: has interlacing smooth muscle fibres and elastic tissue loosely arranged in three layers.
3. Inner mucosa -composed of transitional epithelium that readily permits dimension of the bladder as it fills
Urethra:
• Canal extending from neck of bladder to the exterior at the external urethral orifice
• Male urethra - in urinary and reproductive systems
• Female urethra- apron 4cm long and 6mm. Runs downwards and forwards behind the symphysis pubis and opens at the external urethral orifice just in front of the vagina
Describe the physiological process of filtration, reabsorption and secretion with reference to the nephron
List substances that pass in or out of the nephron during filtration, reabsorption and secretion
Each kidney contains over one million microscopic filtering units called nephrons. Each nephron is made of a tubule and is responsible for ‘cleaning’ the blood by removing urea and excess water and mineral ions.
The kidney works in a number of different stages:
Stage 1
- Blood enters through the afferent arteriole, and this splits it into lots of smaller capillaries which make up the ‘glomerulus’.
- This causes a high hydrostatic pressure of the blood
- Water and small molecules, such as glucose and mineral ions are forced out of capillaries and form the ‘glomerulus filtrate’
- Large proteins and blood cells are too big to fit through the gaps of the capillary endothelium, so remain the blood.
- This then leaves the blood via efferent arteriole.
Stage 2
- Some of the cells lining the proximal convoluted tubule have adaptations such as; microvilli provide a large surface area for reabsorption. And there are lots of mitochondria to provide energy for active transport.
- This stage occurs in the proximal convoluted tubule.
- Here 85% of the glomerulus filtrate is reabsorbed back into the blood, leaving urea and excess mineral ions behind.
How does selective reabsorption happen?
- The conc of sodium ions in PCT cell decreases as the sodium ions are actively transported out of the PCT into the blood of capillaries
- PCT then has low conc of sodium, compared to the glomerulus filtrate next to it, and so these sodium ions move into PCT by diffusion.
- These sodium ions move into PCT with a co-transport protein and so glucose also attaches to this protein and goes into PCT
- High conc of glucose in PCT so it diffuses into epithelial cell in the blood stream – this is how all glucose is reabsorbed
Stage 3
- Filtrate passes through PCT into Loope of Henle (function = maintain a sodium ion gradient).
What happens at Loope of Henle:
- There are mitochondria in the walls of the cells to provide energy to actively transport sodium ions out of the ascending limb of the loop of Henle
- The accumulation of sodium ions outside of the nephron in the medulla lowers the water potential
- Therefore water diffuses out by osmosis into the interstitial space then into blood capillaries (water is then reabsorbed into the blood)
- At the base of the ascending limb some sodium ions are transported about by diffusion, as there is now a very dilute solution due to the water that has moved out
Stage 4.
- Due to all the sodium ions being actively transported out of the PCT, when the filtrate reaches the top of the PCT it is very diluted.
- This filtrate moves into the distal convoluted tubules and collecting duct, this section of the medulla surround these two parts of the nephron are very concentrated
- Therefore even more water diffuses out of the DCT and collecting ducts
- Remaining liquid in collecting duct forms urine
Outline the actions of anti diuretic hormones and aldosterone in the kidney
Identify the importance of the kidney in pH regulation
In order to maintain normal blood pH (acid–base balance), the proximal convoluted tubules secrete hydrogen ions into the filtrate, where they combine with buffers. The normal pH of urine varies from 4.5 to 8, depending on diet, time of day and other factors.
The kidneys have two main ways to maintain acid-base balance their cells reabsorb bicarbonate HCO3− from the urine back to the blood and they secrete hydrogen H+ ions into the urine. By adjusting the amounts reabsorbed and secreted, they balance the bloodstream’s pH.
Explain the role of the kidney in the elimination of nitrogenous waste
nitrogenous waste Any metabolic waste product that contains nitrogen. Urea and uric acid are the most common nitrogenous waste
The kidneys remove from the blood the nitrogenous wastes such as urea, as well as salts and excess water, and excrete them in the form of urine. This is done with the help of millions of nephrons present in the kidney. The filtrated blood is carried away from the kidneys by the renal vein (or kidney vein).
Describe the renin-angiotensinogen mechanism and its function in the body
