11. Urinary System Flashcards
(80 cards)
Urinary System Components
Two kidneys
Two ureters
One bladder
One urethra
Urinary System Functions
- Excretion of unwanted substances.
- Maintenance of water & electrolyte balance.
- pH regulation of body fluids (especially the blood).
- Production of hormones (erythropoietin & calcitriol).
- Regulation of red blood cell (erythrocyte) production.
- Regulation of blood glucose levels.
- Regulation of blood pressure, volume & osmolarity.
Excretion
Metabolic Wastes
1.Urea: a metabolite of protein metabolism.
2.Uric acid: product of purine metabolism.
3.Creatinine: an end product of muscle metabolism.
• All containnitrogen;the kidneys specialisein removing nitrogenous wastes.
Ions
• In particular hydrogen(H+).
Toxins
• Medications andtoxins are mostly detoxified in the liver and then excreted via the kidneys.
Water Balance
- The body’s water balance is mainly controlled by the kidneys.
- Minimum urine content required to clear body waste is 500ml/day.
- The feedback mechanism may be altered in pathologies e.g. untreated diabetes mellitus.
Electrolyte Balance
• Electrolytes are charged atoms in solution
(they can conduct electricity).
• The most important electrolytes regulated by the kidneys are: Sodium (Na+), Potassium (K+) and Hydrogen (H+).
• Electrolytes can form buffer substances. These are molecules that can buffer/regulate changes in pH.
• An excess of H+ions is an acidic solution. If a buffer is present it can bind with the free H+ions thus resisting a change in pH (resisting an increase in H+ions).
pH Balance
• Blood pH mustremain fairly constant between 7.35-7.45
• There are 2 primary pH control systems:
1. Lungs: Excrete CO2(the more CO2in blood = more acidic).
2. Kidneys: excrete H+into urine and produce the buffer HCO3-(bicarbonate).
Hormones produced by the kidneys
Calcitrol
Erythropoietin
Calcitrol
• Calcitriol is the active form of vitamin D.
• UV light activates a vitamin D precursor in the skin. The kidneys convert inactive Vitamin D into its active form.
• Increases bone formation (increases calcium):
1) Stimulates calcium & magnesium uptake from GIT.
2) Reduces calcium loss in kidneys (along with PTH).
• A deficiency can cause‘rickets’ and ‘osteomalacia’.
Erythropoietin
- A protein hormone that stimulates erythropoiesis (red blood cell synthesis) in the red bone marrow.
- Secreted by kidney interstitial cells into blood (10% produced in liver).
- Released in response to hypoxia(negative feedback).
- In renal failure, erythropoietin production is inadequate and hence results in anaemia.
- Can be measured on blood test (EPO test).
Blood Sugar Regulation
- The renal threshold for glucose is 9mmol/L.
- Above this level (in the blood), glucose cannot be reabsorbed from the nephron into the blood when passing through the kidney tubules.
- The normal blood glucose level is 4-7 mmol/L.
- Hyperglycaemia indicates pathology e.g. diabetes mellitus.
- The kidneys are able to make glucose from the amino acid glutamineto help elevate blood sugar levels when hypoglycaemic -gluconeogenesis.
Blood Volume, Pressure and Concentration
- Conserving or eliminating water in urine.
- Regulating the loss of solutein the urine which helps to maintain a constant blood concentration/osmolality.
- The kidneys help to regulate blood pressure by secreting the enzyme renin, which activates the Renin-Angiotensin-Aldosterone pathway.Increased renin causes an increase in blood pressure.
Kidney Anatomy (capsules)
- Renal Capsule
- Adipose capsule
- Renal fascia
Renal capsule
Deep layer
•Smooth, transparent sheet of connective tissue. Maintains the kidney shape.
Adipose capsule
Middle layer
• Mass of fatty tissue, providing protection and support.
Renal fascia
Superficial layer
• Thin layer of connective tissue that anchors kidneys to surrounding structures.
Renal Cortex
Superficial, light red area.
Renal medulla
Darker area composed of several cone-shaped structures called the renal pyramids.
• The apex of each renal pyramid is called a renal papilla.
• Together, the renal pyramids and renal cortex make up the ‘functional’ portion of the kidney. Within this area are the functional units of the kidney –‘nephrons’.
• Urine formed by the nephron drains into the minor and major calyces.
Hilum
On the concave kidney border. The region where blood vessels, lymph vessels, nerves and ureters enter and exit the kidney.
Blood supply
Renal artery and vein. The kidney receives 20-25% of the cardiac output (1.2L blood per minute), despite its mass accounting for 0.5% of body weight.
Nephron
The ‘nephron’ is the functional unit of the kidney.
• More than 1 million per kidney.
• Single epithelial layer throughout.
Nephron Parts
- Renal corpuscle
2. Renal Tubule
Renal corpuscle
Consists of glomerulus and Bowman’s capsule.
• The glomerulus is a tangled capillary network that receives blood from an afferent arteriole.
•The Bowman’s capsule is a double-walled epithelial cup that surrounds the glomerulus, receiving contents of filtered blood.
Renal tubule
Consists of 3 sections:
1. Proximal convoluted tubule.
2. Loop of Henle.
3. Distal convoluted tubule.
• Filtered fluid is passed through the tubule.
• Important role in reabsorption and secretion of various solutes.
• Anti-Diuretic Hormone (ADH) acts on the distal convoluted tubule to reabsorb water.
Nephron structure
- The renal corpuscle & both convoluted tubules (proximal and distal) lie in the renal cortex.
- This means that filtration of blood (takes place in the renal corpuscle) occurs in the renal cortex.
- The Loop of Henle often extends into the renal medulla, where it makes a hair pin turn & returns to the cortex.