URINARY SYSTEM

KidneysUretersBladderUtrethra

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THE KIDNEY

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ROLES OF THE KIDNEY• Excretion• Homeostasis• Osmoregulation• Regulation of salts in

the body• Regulation of pH• Production of a hormone (EPO)

Kidney from a cat

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Kidneys make up 1 % of body mass, but receive about 25% of cardiac output.

Kidney has two major functions:1. Filtration of blood

Removes metabolic wastes from the body, esp. those containing nitrogen

2. Regulation of:Blood volume and compositionElectrolytesBlood pHBlood pressure

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Anatomy Hilus

Renal artery enters and vein & ureter leaves Cortex Medulla

Renal pyramids and renal papillae Major and minor calyces

Renal Pelvis Ureters

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Ureters connect kidneys to urinary bladder

Urethra leads from bladder outside the body

Urine formation

Filtration Reabsorption Secretion

The Nephron.

The Nephron is the smallest functional unit of the kidney.

The number of nephrons will vary with the size of the animal. (million in human sized animals)

The Nephron

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Nephron

Functional unit of the kidney

Filtration, tubular

reabsorption, tubular secretion

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Bowman’s capsule Receives filtrate

Proximal convoluted tubule Reabsorption of glucose, amini acids,

vitamins, proteins, urea and electrolytes.

Secretion of H+ & organic acids & bases

Loop of Henle Regulates concentration of urine Secretion of Cl-, Na+, K+< Ca++, Mg+

+, urea. Reabsorption of Water, Cl- & Na+

Distal convoluted tubule Reabsorption of water and

many electrolytes & Urea Secretion – Ammonium, K+,

H+, Collecting Duct

Secretion Water, Ammonium, K+, H+

http://en.wikipedia.org/wiki/Nephron

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Bowman’s Capsule

Blood Flow

Blood Flow

Bowman’s Capsule

Glomerulus

Water

The Proximal Convoluted Tubule.

The Filtrate composition begins to change immediately.

It contains many substances which are not waste products.

Some substances diffuse passively from the PCT back into the peritubular capillaries.

Others (e.g. Na) are actively transported through the epithelial wall.

65% of all reabsorption occurs in the PCT, including 100% of glucose and amino acids (AA’s).

Loop of Henle Reabsorption of Water to

capillaries & salts to interstitial tissues in medulla.

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Distal convoluted tubule and collecting ducts

Tubular secretion to rid body of substances: K+, H+, urea, ammonia, creatinine and certain drugs

Secretion of H+ helps maintain blood pH(can also reabsorb bicarb and generate new bicarb)

Reabsorption controlled by hormones ADH Aldosterone

The Collecting Duct. The collecting ducts pass through the

medulla and into the renal pelvis.• From here urine is drained into the ureter and into the bladder.• Water permeability is regulated in the collecting duct.• The more permeable to water the more water is reabsorbed.

Reabsorption

Erythropoitin Low Oxygen in blood stimulates kidneys

to release this hormone into blood When it reaches the red marrow of the

bone erythropoitin stimulates the production of more rbcs

Micturition (Voiding)

Slide 15.25Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Both sphincter muscles must open to allow voiding The internal urethral sphincter is relaxed

after stretching of the bladder Activation is from an impulse sent to the

spinal cord and then back via the pelvic splanchnic nerves (reflex arc)

The external urethral sphincter must be voluntarily relaxed

Terms Polyuria Anuria Oliguria Oliguria Polydipsia Micturation Cystitis Glomerular nephritis Renal