57 - Excretory functions and the systems involved. Functional structure, blood supply and innervation of the kidney. Mechanism and control of glomerular filtration. Assessment of glomerular function.

sections

organs involved with excretion

function of kidney

structure of kidney

function of nephrons

blood supply of kidney

processes of urine formation

amount of urine formed and factors affecting glomerulus filtration

regulation of glomerulus filtration

organs involved with excretion

1. Kidneys - Excrete water, nitrogenous wastes ,bacterial toxins, H+, and inorganic salts

2. Lungs. Excrete CO2, heat, and a little water.

3. Skin (sweat glands). Excrete heat, water, and small quantities of salts and urea.

4. Gastrointestinal tract. Eliminates solid, undigested foods and excretes carbon dioxide, water, salts, and heat.

   • Kidneys -urinary system used in homeostasis, controls composition and volume of blood.

function of kidney

• Regulation of blood volume and composition. remove wastes from the blood. urine is formed.

• Regulation of blood pressure. --secrete enzyme renin, which activates the renin-angiotensin system. →increase in blood pressure

  • Site of glucose production

  • secreting erythropoietin, -stimulates production of red blood cells

structure of kidney

• A nephron – functional unit of the kidney

• consists of two parts: a renal corpuscle -where blood plasma is filtered and a renal tubule into which the filtrate passes.

function of nephrons

1. they control blood concentrations and volume by removing selected amounts of water and solutes;

2. they help regulate blood pH;

3. they remove toxic wastes from the blood.

   • Each corpuscle has two parts - the glomerulus (capillary network) and the glomerular (Bowman's) capsule, a double-walled epithelial capsule that surrounds the glomerulus.

     • The cells that make up the inner wall of the glomerular capsule and endothelial cells of the glomerular capillaries- form filtration membrane.

     • From the renal corpuscle, filtered blood passes into the renal tubule made of proximal convoluted tubule

     • loop of Henle (descending and ascending limb)

     • distal convoluted tubule and collecting ducts

blood supply of kidney

• Blood Supply to the Kidneys:

  • renal arteries - 1 200 ml/min

  • peritubular capillaries

processes of urine formation

• Urine formation involves three processes:

  1. glomerular filtration

  2. tubular reabsorption

  3. tubular secretion

     • Filtration - the forcing of the fluids and dissolved substances smaller than a certain size through a membrane by pressure-hydrostatic pressure - begins at the filtering membrane when blood enters the glomerulus. The resulting fluid is called filtrate.

     • Filtrate consists of all the materials present in the blood except for the blood cells and most proteins, which are too large to pass through the filtering membrane.

     • Glomerular filtration rate (GFR)

     • Glomerular Filtration Rate = Filtration coefficient x Net Filtration Pressure—inulin is commonly used

amount of urine formed and factors affecting glomerulus filtration

The volume of filtrate that forms in both kidneys per minute. In the normal adult, this rate is about 125 ml/min - about 180 liters a day.

regulation of glomerulus filtration

• several factor affect GFR:

  • changes in the size of afferent and efferent arterioles can change GFR.

  • constriction of the afferent arterioles decreases blood flow into the glomerulus , which decrease GFR.

  • constriction of the efferent arteriole, which takes blood out of the glomerulus, increase GFR.

• Regulation of Glomerulus filtration

  1. Renal auto regulation - the ability of the kidneys to maintain a constant blood pressure

  2. Hormonal regulation - angiotensin II and atrial natriuretic peptide (ANP).

  3. Neural regulation - blood vessels of the kidneys are supplied by vasoconstrictor fibers from the ANS.

• With moderate sympathetic stimulation, blood flow into and out of the glomerulus is inhibited to the same extent, which slightly decreases GFR.

• With greater sympathetic stimulation, vasoconstriction of the afferent arterioles predominates which greatly decreases GFR.