The Renal System Flashcards
What are the functions of the renal system?
-Excretion of physiological waste products from body fluids
-Elimination of waste products into the environment
-Homeostatic regulation of volume and solute conc. of blood
-Also regulates BP
-Regulates plasma conc. of Na, K and Cl ions
-Helps stabilise blood pH
-Conserves valuable nutrients
-Assists liver in detoxification
What is the anatomy of the kidney?
-Fibrous capsule covering the kidney
-Cortex – superficial portion
-Medulla – composed of renal pyramids
-Renal column – band of cortical tissue which extends between and separates pyramids
-Kidney lobe – renal pyramid, overlying area of cortex and adjacent renal column
What is the nephron?
→ Functional unit of the kidney
→ Renal corpuscle – Bowman’s capsule and glomerulus
→ Renal tubule
→ Collecting system
What is the PCT
Its the proximal covulated tubule, reabsorption of ions, glucose, amino acids, vitamins, water
What is the loop of henle
-Descending limb - reabsorption of water
-Ascending limb - reabsorption of ions
-each limb of the loop has a thick and thin segment, refers to the thickness of the epithelium
-Thick segments have cuboidal epithelium
-Thin segments have squamous epithelium
What is the DCT and what is its function?
It is the distal covulated tubule, reabsorption of Na & Ca ions, secretion of acids & ammonia
What is the function of the collecting duct?
Reabsorption of water & Na ions, concentration of tubular fluid
What are the waste products in urine?
-Urea
-Creatine
-Uric acid
How is urea formed?
From breakdown of amino acids, ~21 g produced per day
How is creatine formed?
From breakdown of creatine phosphate, ~1.8 g per day
How is uric acid formed?
-Formed from recycling of RNA nitrogenous bases, ~480 mg per day
-Dissolved in blood
-Can only be excreted when dissolved– therefore this involves the unavoidable loss of water
Urine formation: Filtration
○ Blood pressure forces water & solutes across walls of glomerular capillaries
○ Sieving effect
Urine formation: reabsorption
○ Removal of water and solutes across tubular epithelium
○ Reabsorbed substances re-enter the blood
○ can be passive (water) or active (carrier proteins, glucose)
Urine formation: secretion
○ Cells produce and then discharge substances directly into the urine
○ creatinine, hormones, some drugs eg penicillin
What is hydrostatic pressure?
Fluid pressure
What is colloid osmotic pressure?
Pressure due to materials in solution on either side of the capillary walls
What conditions monitor filtration pressures?
-Fenestrations are large – even plasma proteins can pass through
-Basement membrane - only small proteins can pass through
-Filtration slits stop nearly all proteins passing
What is the glomerular filtration rate?
GFR is the amount of filtrate produced by the kidneys per minute
What is used to estimate glomerular filtration rate?
A creatine clearance test
(As creatine is filtered out in the glomerulus and is not reabsorbed it is a good indication of the rate)
What is the Renin-angiotensin-aldosterone system
· Signalling pathway responsible for regulating the body’s blood pressure
· Low renal BP causes release of renin from kidneys
· Converts angiotensinogen produced by liver to angiotensin
· Angiotensin converted to angiotensin II by angiotensin converting enzyme (ACE)
· Causes increase in sympathetic activity, resorption of Na and Cl ions and water, excretion of K ions and vasoconstriction
· Induces release of aldosterone from adrenal cortex
· Induces release of ADH from pituitary gland
What are the ureters and their function?
· Pair of muscular tubes extending from kidneys to bladder
· Ureters penetrate posterior wall of bladder at an oblique angle
· Ureteral openings are slit-like
Helps prevent backflow of urine towards ureter and kidneys when bladder contracts
What is the urinary bladder and its function?
· Hollow, muscular organ which acts as a reservoir for urine
· Urethral entrance is at the neck of the bladder
· Neck contains internal urethral sphincter
○ Involuntary control over release of urine
· When layers of muscle contract the bladder compresses and urine is expelled into the urethra
· Can contain up to 1 litre of urine
· Neck of the bladder is at the bottom of it
What is the urethra and its function?
· Extends from neck of bladder to exterior
○ Males 18-20 cm
○ Females 3-5 cm
· External urethral sphincter
· Voluntary control
· Must be relaxed to allow urination
What coordinates urination?
· Micturition reflex coordinates urination
· As the bladder fills, stretch receptors in the bladder wall are stimulated
· Results in message being relayed to cerebral cortex
○ Become aware of fluid pressure in bladder
· If volume exceeds 500 ml, bladder contractions may be so great that it forces open the internal urethral sphincter
○ Reflexive relaxation of external urethral sphincter
○ Release of urine despite voluntary opposition
· Urge to urinate usually appears when there is about 200 ml urine
What are age related changes in the renal system?
· Decrease in number of functional nephrons
· Reduction in GFR
· Reduced sensitivity to ADH
· Problems with micturition reflex
· Nephrons decrease by 30-40 % between ages 25 and 85
· GFR decrease because of fewer glomeruli, reduced renal blood flow
· With age, distal portions of tubule and collecting duct are less responsive to ADH. Water and Na ions resorbed at a reduced rate so more lost in urine
· Incontinence due to reduced muscle tone in sphincters, CNS problems like Alzheimers and stroke can cause loss of ability to control micturition reflex, in males urinary retention can be caused by enlargement of prostate which compresses the urethra
