The Urinary System Flashcards
Discuss the role of the kidney in water and electrolyte balance
- The minimum urinary output is 500ml/Day and anything more is controlled by ADH released by the posterior pituitary gland.
- Sensory nerves in the hypothalamus detect changes in the osmotic pressure of blood which stimulates the release of ADH.
- Reabsorption of water by the cells in the distal convoluted tubules and collecting ducts is increased reducing pressure and ADH release.
Identify the components of the urinary system and discuss their function.
- 2 Kidneys - extreme urine, regulate body fluid volume, electrolyte balance, acid-base balance, hormone production and activation of Vit D
- 2 Ureters - Convey the urine from the kidneys to the bladder
- The Urinary Bladder - where the urine collects and is temporarily stored
- The urethra - where urine is discharged from the bladder to exterior.
How do the kidneys control sodium and potassium balance?
- Sodium is normally found in the urine and is controlled by aldosterone.
- Cells in the nephron are stimulated to produce renin by sympathetic stimulation, low BV or low BP.
- Renin converts angiotensinogen into angiotensin. Angiotensin converting enzyme (ACE) in proximal convoluted tubules convert angiotensin I into angiotensin II (powerful vasoconstrictor)
- Renin and raised blood potassium levels stimulate the adrenal gland to secrete aldosterone.
- Water is reabsorbed with sodium, increases BV leading to reduced renin secretion through negative feedback.
- Sodium Reabsorption increased, potassium secretion increased and intracellular potassium reduced.
How do they kidneys control calcium balance?
- Co-ordination of parathyroid hormone (PTH) and calcitonin.
- Distal collecting tubules reabsorb more calcium in response to PTH and reabsorb less in response to calcitonin.
Discuss the role of the kidneys in the maintenance of acid-base balance?
- The cells in the proximal convoluted tubules secrete hydrogen ions to maintain blood pH.
- In the filtrate they combine with buffers: bicarbonate forming carbonic acid, ammonia forming ammonium ions, hydrogen phosphate forming dihydrogen phosphate.
- Carbonic acid forms CO2 + H2O
Define the terms acidosis and alkalosis.
- ACIDOSIS -
When the body produces excessive quantities of acid or the kidneys are not removing enough acid from the body (too much H+) - ALKALOSIS -
When there is a decrease in H+ ions leading to an increase of bicarbonate. Not enough acid to neutralise this.
Discuss the process of micturition and explain how it is controlled.
- When the bladder is full, sensory impulses are sent to the brain and micturition begins.
- Awareness of the need to pass urine causes contraction of the external urethral sphincter and muscles of the pelvic floor inhibiting micturition.
- Micturition occurs when the detrusor muscle contracts causing reflex relaxation of the external sphincter and urination occurs
Discuss the composition and appearance of urine and appreciate how these may vary under different conditions
- COMPOSITION -
Water (96%), urea, uric acid, creatine, ammonia, sodium, potassium, oxalates, chlorides, phosphates, sulphates. (All 2% each)
Urine is clear and Amber in colour.
pH between 4.5-8 - 1000-1500ml/day - COLOUR CHANGES -
Dehydration, excess water intake, medications, diet, vitamins and infections. - ODOUR CHANGES -
Infection, kidney stones, diabetes, diet. - FREQUENCY CHANGES -
Overactive bladder, UTI, cystitis, diabetes, benign prostate enlargement, neurological disorders.
What are the main structures of the kidney?
- CAPSULE - protection
- THE CORTEX - layers of tissue
- THE MEDULLA - pale conical shaped straitions (renal pyramids)
- THE HILUM - concave medial border of the kidney where the renal blood, lymph vessels, ureter and nerves enter
- THE RENAL PELVIS - funnel-shaped structure that acts as a receptacle for urine.
What is the proximal convoluted tubule?
- long length and micro villi with mitochondria for active transport.
- reabsorbs greater variety of chemicals than any other part of the nephron:
SODIUM - 65%
GLUCOSE - 100%
AMINO ACIDS - 100%
WATER - 65%
When transport proteins in plasma membrane are saturated; glucose remains in urine.
What electrolytes are absorbed in the Loop of Henle?
SODIUM - 25%
WATER - 25%
- counter current exchange conserves electrolytes when needed!
What electrolytes are reabsorbed at the distal tubule and collecting duct?
SODIUM - 8-10%
WATER - 8-10%
Regulates by hormones
What electrolytes are secreted by the distal tubule/collecting ducts?
Potassium
What hormones act on the kidneys?
Aldosterone
Atrial Natriuretic Peptide (ANP)
Anti-Diuretic Hormone (ADH)
What substances are produced by the kidneys?
Erythropoietin
Renin
Activates Vit D
Calcitriil
What is tubular reabsorption?
Removes useful salutes from the filtrate and returns them to blood
What is tubular secretion?
Removes waste from the blood and passes it into filtrate
How does water conservation work?
Removes water from the urine and returns to blood
Describe the characteristics of the filtration membrane
- filtration takes place across the semi-permeable membrane of the glomerulus
- this consists of a single layer of flattened epithelial cells with pores penetrating through to filter plasma for waste and useful nutrients.
What is Glomerular Filtration (GF)
The filtration of protein-free plasma from the glomerulus to the Bowman’s Capsule. RBC/WBC stay in blood.
Explain the process involved in the formation of urine
FILTRATION - RBC/WBC and proteins are too big, filtrate is similar to plasma
SELECTIVE REABSORPTION - the composition and volume of the filtrate are altered during passage through nephron. Components needed for electrolyte balance and pH are re-absorbed by active transport. Regulated by PTH, ADH, aldosterone and ANP.
TUBULAR SECRETION - substances not required and foreign materials are secreted through urine.
The proximal tubule of the nephron
Reabsorbed most of the sodium ions in glomerular filtrate
ADH:
Makes the collecting ducts more permeable to water
Renin release:
Is promoted by reduced arteriolar stretch in the glomerulus
