Renal system Flashcards
(28 cards)
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
