Renal system Flashcards
Functions
Regulates body fluid volume Regulates electrolyte balance Creates urine Produces hormones (EPO) Produces enzymes (renin) Activate Vitamin D
Kidney
11cm long x 6cm wide x 3cm thick Posterior to abdominal wall Inferior to diaphragm Hilum on medial border Renal arteries enter, veins and ureters leave
Ureter
Carry urine from kidney to bladder
25-30 cm long
Thick-walled, narrow tube (3mm in diameter)
Peristaltic contractions 4-5 times a minute
Bladder
Reservoir for storing urine
Both ureters enter the bladder, while the urethra leaves at base
Holds 250-300 ml urine normally, up to 500ml
3 layers:
> Serous layer
> Muscular layer
> Inner mucous coat
Urethra
Passes urine from bladder to exterior In women = 4cm long - serves urinary system only In men = 18-20cm long - common canal for both reproductive and urinary systems
Body fluid distribution
Intracellular fluid = 25L Extracellular fluid: - interstitial = 11L - plasma = 3-5L 70% body weight = 32-40L
What are the 2 types of nephron?
Juxtamedullary
Cortical
Nephron functions
- Glomerular filtration - creates a plasma like filtrate of the blood
- Tubular reabsorption - removes useful solutes from filtrate, returns them to blood
- Tubular secretion
- removes additional wastes from blood, adds them to filtrate - Water conservation - removes water from urine and returns it to blood, concentrates wastes
Glomerular filtration
GF = filtration of protein free plasma from the glomerulus to Bowman’s capsule
Glomerular filtration rate (GFR)
Females - 115ml/min = 160 L of plasma/day
Male - 125ml/min = 180L of plasma/day
GFR = Urine conc. x urine volume/ Plasma conc.
Formation of urine
Proximal convoluted tubule - - long in length and microvilli - mitochondria for AT - reabsorbs a greater variety of chemicals than any other part of nephron: > sodium (65%) > glucose (100%) > amino acids (100%) > water (65%) Loop of Henle - > sodium (25%) > water (25%) Distal tubule & collecting ducts- > sodium (8-10%) > water (8-10%) > secretion of potassium \+ sodium and water reabsorption regulated by hormones +
Hormonal control
Aldosterone:
- stimulates sodium reabsorption and potassium secretion in DCT and collecting ducts = increase blood volume
Atrial Natriuetic Peptide (ANP):
- increase sodium excretion to decrease blood volume
ADH:
- increase ADH causes increased water reabsorption in collecting duct
- decrease ADH causes decrease in water reabsorption and increased urine excretion
What happens when plasma volume decreases?
- decrease in arterial NP
- decrease in intrarenal pressure recorded by macula densa cells in distal tubule
- causes release of renin from juxtaglomerular cells
- causes angiotensin to be converted into angiotensin 1
- angiotensin 1 converts to angiotensin II by ACE enzyme, causing a release in ADH and secretion of aldosterone = plasma volume recovers
Acid-base balance
Arterial blood = pH of 7.45
Venous blood = pH of 7.35
Acceptable range between 6.8 and 8
Acidosis - pH below 7.35 = depression of CNS, coma
Alkalosis - pH above 7.45 = convulsions, respiratory spasms
Urine
Colourless to deep amber
Odour comes from degradation of urea to ammonia if left to stand
pH range 4.5-8.2
95% water, 5% solutes eg. urea, creatinine, uric acid
Other kidney functions
Production of hormones and enzymes:
> Renin - important in control of total body fluid
> Erythropoietin - stimulates the production of RBCs in bone marrow
Activation of Vitamin D
- hormone control = Calcitriol
- kidney and liver convert Vit. D to active metabolites
- metabolite important in regulation of blood calcium and phosphorus levels
Control of bladder function
- stretch receptors in wall of bladder activated (200mls urine)
- sensory (afferent) fibres in pelvic nerve relay to sacral region of spinal cord
- an inter-neuron relays the sensation to the thalamus which further projects to the cerebral cortex (i.e. you become aware)
- a parasympathetic motor (efferent) fibre in pelvic nerve relays to a post-ganglionic neuron
- stimulating the detrusor muscle to contract
- and MICTURITION occurs after the voluntary relaxation of the external urethral sphincter
What are kidney stones?
Calcium compounds Oxalate or phosphate - nephrolithiasis - urolithiasis Symptoms: > sharp back pain, side, abdomen then groin > nausea/vomiting > haematuria > associated infection
Glomerulonephritus
Inflammation of kidney glomeruli causes impaired filtering
Blood and protein in urine
Acute kidney failure
Sudden loss of renal function Causes: - low BP - blockage of renal blood supply - toxic injury - ureter/bladder obstruction
Stages of renal failure
Chronic Kidney Disease
Normal GFR = 90-140ml/min
Stage 1 = GFR >90ml/min Stage 2 = GFR 60-89ml/min Stage 3 = GFR 30-59ml/min Stage 4 = GFR 15-29ml/min Stage 5 = GFR
What can a urinalysis detect?
Proteinuria
Most abundant protein in urine is albumin
Normally 30mg/day
Risk factors for renal failure
Race
Weight
Genetics
Treatment = control BP
Early CKD patients aim to keep BP below 130/85 mmHg
Late stage CKD patients aim to keep BP below 125/75 mmHg
ACE inhibitor is effective at lowering BP whilst protecting kidneys
Treatment = diet
Limit:
- protein causes urea build up
- phosphorus causes removal of calcium from skeleton and weakens bones
- sodium in high amounts raises BP
Treatment = haemodialysis
Haemodialysis
- blood from superficial arm vein pumped to dialysis machine
- passes over selectively permeable membrane
- balanced electrolytes solution withdraws water from blood by osmosis
- no mixing - solute and water exchange by diffusion
Positive is that it maintains patient for years
Negatives are that it is time consuming and not perfect kidney replacement
Treatment = peritoneal dialysis
Peritoneum acts as selectively permeable dialysis membrane
Dialysate fluid put into to peritoneal cavity
Exchange with blood occurs
Peritoneal fluid drained away
Positives are that it changes blood composition slowly, and can be performed at home
Negatives are that it takes much longer than haemodialysis
Treatment = transplantation
- Kidney is placed in lower abdomen
- Renal vein joined to iliac vein in the leg
- Renal artery joined to iliac artery
- Once blood vessels connected, circulation in kidney is released kidney becomes pink, will not regain normal function straight away
- urine passes out of ureter
- ureter joined to bladder to complete operation
Problems:
- requires donor
- risk of rejection
- immunosuppressive drugs increase cancer risk, and increase infection risk
