Download Urinary System

Urinary System
Exercises 40 and 41
Organs of the Urinary System
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2 kidneys
Urinary bladder
2 ureters
Urethra
Primary function is to filter blood, and
reabsorb water and needed substances
back into blood. Remaining water and
wastes are removed in urine.
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Regulate blood volume and composition
Regulate blood pH
Regulate blood pressure
Contribute to metabolism
– Calcitriol
– Erythropoietin
– Gluconeogenesis
Location of kidneys
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Between T12 and L3
Partially protected by 11th and 12th ribs
Right kidney is lower than left
Kidneys and ureters are retroperitoneal
Protected by three layers:
– Renal capsule
– Adipose capsule
– Renal fascia
Anatomy
• Renal hilum – ureter, blood and lymphatic
vessels
• Renal sinus
• Renal cortex
• Renal medulla
– Renal pyramids
– Renal papilla
• Renal columns
Nephron
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Functional unit of kidney
Number constant from birth
Can function on 2/3 of one kidney
Forms the urine
Duct system
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Minor calyces
Major calyces
Renal pelvis
Ureter
Urine is not changed after it leaves the
collecting duct
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Kidneys = 1% of body mass
Receive 15-30 % of blood flow
Blood supplied to kidney by renal artery
Afferent arteriole divides into ball shaped
capillary network called the glomerulus.
• Capillaries rejoin to form efferent arteriole,
then peritubular capillaries
• Vasa recta
Functions of the Nephron
• Filtration
• Tubular reabsorption
• Tubular secretion
Structure of a nephron
• Renal corpuscle
– Glomerulus
– Glomerular capsule or Bowman’s capsule
• Renal tubule
– Proximal convoluted tubule
– Nephron loop or loop of Henle
– Distal convoluted tubule
– Collecting duct
Bowman’s capsule
• Outer layer - simple squamous epithelium
• Inner layer – modified simple squamous epi.
– Cells called podocytes
– Projections are pedicels
• Endothelium of capillary and podocytes form
the endothelial-capsular (filtration) membrane.
Filtration membrane
1. Fenestrated endothelium – prevents
the passage of cells
2. Basement membrane of glomerulus –
prevents passage of large proteins
3. Slit membrane (between pedicels) –
prevents the passage of medium sized
proteins
• Wall of renal tubules made up of single
layer of epithelial cells and a basement
membrane.
• Proximal convoluted tubule – cells are
cuboidal and have microvilli.
• About 65 % of water and 100 % of some
solutes are reabsorbed here.
Renal Physiology
• Glomerular filtration – most substances
easily filtered
• Filtrate = 180 L/ day but urine = 1-2 L /day
• Filter is thin
• Glomerular capillaries are long
• Capillary blood pressure is high
(afferent arteriole diameter > efferent arteriole)
• Filtration fraction is the percentage of
plasma that becomes filtrate, usually 1620 %.
• Glomerular Filtration Rate (GFR) is the
amount of filtrate formed in both kidneys
per minute; normally about 125 ml / min.
Renal autoregulation
• JGA senses Na+, Cl- and water
• When these ↓, JGA dilates afferent
arteriole, ↑ blood pressure in glomerulus
Hormonal regulation
• When BP ↓, JGA secretes renin which
converts angiotensinogen to angiotensin I,
angiotensin I is converted to angiotensin II
in the lungs. Angiotensin II is a potent
vasoconstrictor. It also stimulates the
release of aldosterone, and stimulates
the thirst center in the hypothalamus and
release of ADH from the posterior pituitary
gland.
Tubular reabsorption
• Volume of fluid that enters the proximal
convoluted tubule in ½ an hour > total
plasma volume.
• Reabsorb water, glucose, amino acids,
urea and ions, esp. Na+, Cl- and K+
• Na+ diffuses into cells, but is actively
pumped out into interstitial fluid
• Promotes reabsorption of water
DCT and collecting ducts
• By end of DCT 90 % of water and solutes
reabsorbed.
• Aldosterone causes principal cells to synthesize
sodium pumps. Also causes potassium to be
secreted into urine.
• ADH stimulates cells to put water channels into
membranes. ADH is responsible for facultative
(responding to need) water reabsorption.
Tubular secretion
• Two main functions:
• Secretion of substances to eliminate them
from body – ions, nitrogen-containing
waste (urea, creatinine) and certain drugs
• Secretion of H+ helps to maintain blood
pH
Urinary bladder
• Posterior to pubic symphysis
• Stores urine prior to micturition
• Trigone – between openings of ureters
and internal urethral orifice – mucosa is
firmly bound to muscularis.
• Muscosa, submucosa, muscularis
(detrusor muscle), and serous coat.
Evaluation of kidney function
• Blood Urea Nitrogen (BUN) – urea is a
breakdown product of proteins
– Influenced by diet
• Creatinine – end product of muscle
metabolism
– Normally constant
– Can determine creatinine clearance
Normal urine
• Transparent yellow
• Contains ions : Na+, Cl-, K+ ; nitrogenous
wastes: ammonia, creatinine, urea and
uric acid; and foreign chemicals: drugs,
pesticides, food additives, etc.
• Suspended solids in trace amounts:
bacteria, blood cells, casts.
Not normally present
• Albumin
• Glucose, Acetone– diabetes mellitus
• Bile – liver disease, obstruction of bile
ducts, hemolytic disease
• pH 4.6 -8.0
Specific gravity
• 1.001 -1.035
• Damage to tubules , s.g. fixed at 1.010 =
filtrate
• Diabetes insipidus (lack of ADH) – 1.003
• Diabetes mellitus – “sugar diabetes”
– 1.030 osmotic diuresis
• Emesis or fever –
– 1.040