Urinary System L 2, 3 Tubular Reabsorption & secretion

Prof. Madaya Dr Than Kyaw1, 8 October 2012

Micturition and micturition reflexes

• Urine transported from renal pelvis to urinary bladder by

peristalsis in the ureters

• Ureters enter the urinary bladder at an oblique angle to form

a functional valve (ureterovesicular valve)

• Back flow of urine in the bladder is prevented

Miturition reflexes• Receptors in the bladder wall stretched during filling• Have reflex ability (activation of sacral spinal cord reflex center)• Evacuation of urine through the neck of bladder and external sphincter• Brain stem reflex center

- prevent contraction of bladder and relaxation of external sphincter muscle

- normal filling occurs• When bladder is sufficiently full

- Voluntary control intervene; micturition permitted - Once micturition proceeds – complete emptying is ensured until the

bladder is empty.

Micturition and miturition reflexes

Urinary Bladder and associated organs

Urinalysis

- Important diagostic procedure- Examination of physical and chemical properties

- solute conc- microscopic exam of urine sediment

- Composition: depend on whether substances are being conserved or secreted- Colour: normally yellow – what other colours- Odour: characteristic for species; influenced by diet- Consistency: watery in most species- Nitrogenous components: mammalian – mainly – urea (formed by the liver

from ammonia (toxic to animal)- Amount and specific gravity

Volumes & specific gravity of urine

Animl Volume(ml/kg BD WT/d)

Specific gravity(mean and range

Cat 10-20 1.030 (1.030-1.040)Cattle 17-45 1.032 (1.030-1.045)Dog 20-100 1.025 (1.016-1.060)Goat 10-40 1.030 (1.015-1.045)Horse 3-18 1.040 (1.025-1.060)Sheep 10-40 1.030 (1.015-1.0450Swine 5-30 1.012 (1.010-1.050)Human 8.6-28.6 1.020 (1.002-1.040)

Measuring GFR

Renal clearance- The volume of blood plasma from which a particular waste is

completely removed in 1 minute- Two substances used

- Inulin: a polysaccharide not metabolized by the body or reabsorbed from the urine

- it is not found in the body; injected- give accurate result

- Creatinine: a breakdown product from creatine phosphate

- naturally found in the blood - not accurate as inulin (about 10% of

creattinine is reabsorbed)

• Inulin - neither reabsorbed from nor secreted into the tubule• Therefore, amount filtered into the tubules at the glomerulus

equal the amount appearing in the urineP x GFR = U x VGFR = (U x V)/P

P = plasma concentration of inulin (mg/ml)GFR = glomerular filtration rate of plasma (ml/min)U = urine concentration of inulin (mg/ml)V = rate of urine production (ml/min)

Measuring GFR

Kidney - Target organ of several hormones:

Antidiuretic hormone (ADH), Angiotensin II, Aldosterone, Atrial natriuretic peptide (ANP)Parathyroid hormone(PTH)

- Also endocrine organ - secrets renin - erythropoietin (EPO) - active form of Vit D endocrine organ

Endocrine functions of the kidney

1. Vitamin D- Becomes metabolically active in the kidney. Patients with renal disease have symptoms of disturbed calcium and phosphate balance.

2. Erythropoietin- Released by the kidneys in response to decreased tissue oxygen levels (hypoxia).

3. Natriuretic Hormone- Released from cardiocyte granules located in the right atria of the heart in response to increased atrial stretch. It inhibits ADH secretions which can contribute to the loss of sodium and water.

Renal Hormones

Endocrine functions of the kidney

Erythropoietin

- glycoprotein, secreted by fibroblasts in the renal interstitium - sensitive to PO2 (80% of EPO released from kidney, the remainder from liver)- anaemia in patient with renal failure – failure of EPO production

Endocrine functions of the kidney

• P1 primary podocyte process P2 secondary podocyte process