Guyton Renal Tubular Filtration

Only available on StudyMode
  • Topic: Kidney, Urine, Renal physiology
  • Pages : 5 (1252 words )
  • Download(s) : 73
  • Published : January 10, 2013
Open Document
Text Preview
Chapter 26

Multiple Fxns of Kidneys in Homeostasis
1. Excretion of metabolic waste products and foreign chemicals 2. Regulation of Water and electrolyte balance
3. Regulation of Arterial pressure
--long term: excreting variable amounts of sodium and water
--short term: secreting vasoactive factors or substances such as rennin 4. Regulation of Acid-Base balance
--the only means of eliminating sulfuric acid and phosphoric acid 5. Regulation of Erythrocyte Production
--secretion of erythropoietin
6. Regulation of 1, 25-dihydroxyvitamin D3 (calcitriol) production 7. Gluconeogenesis
--synthesis of glucose from amino acids during prolonged fasting

Renal Blood Supply
=blood flow to the two kidneys is normally about 22% of the cardiac output or 1100 ml/min =renal circulation has two capillary beds: glomerular and peritubular capillaries --- arranged in series and separated by the efferent arterioles (help regulate the hyrostatic pressure in both capillaries) =glomerular capillaries have high hydrostatic pressure (60 mmHg) which causes rapid fluid filtration =peritubular capillaries have lower hydrostatic pressure (13 mmHg) which permits rapid fluid reabsorption =kidneys can regulate the hydrostatic pressure in both capillaries by: a) adjusting the resistance of the afferent and efferent arterioles b) changing the rate of glomerular filtration, tubular reabsorption, or both in response to body homeostatic demands

The Nephron is the Functional Unit of the Kidney
=each kidney contains 800,000 to 1 million nephrons
=the kidney cannot regenerate new nephrons
=after age 40, the number of functioning nephrons decreases about 10% every 10 years

Micturition
=process by which the urinary bladder empties when it becomes filled =involves two main steps:
1) bladder fills progressively until the tension in its walls rises above a threshold level; this elicits 2) 2) a nervous reflex called micturition reflex that empties the bladder, or, if this fail, at least causes a conscious desire to urinate

Micturition Reflex
= “self-regenerative” – initial contraction of the bladder --- activates the stretch receptors --- causes a greater increase in sensory impulses from the bladder and posterior urethra --- which causes a further increase in reflex contraction of the bladder --cycle is repeated again and again until the bladder has reached a strong degree of contraction --after a few seconds to more than a minute, the self regenerative reflex begins to fatigue and the regenerative cycle of the micturition reflex ceases, permitting the bladder to relax =a single complete cycle of:

1) progressive and rapid increase of pressure
2) a period of sustained pressure
3) return of the pressure to the basal tone of the bladder =an autonomic spinal cord reflex, but can also be inhibited or facilitated by centers in the cerebral cortex or brain stem 1) strong facilitative and inhibitory centers in the brain stem, located mainly in the pons 2) inhibitory but can become excitatory centers in the cerebral cortex =final control of micturition by the higher centers

1) higher centers keep the micturition reflex partially inhibited, except when micturition is desired 2) higher centers can prevent micturition, even if the micturition refelex occurs, by continual tonic contraction of the external bladder sphincter until a convenient time presents itself 3) when it is time to urinate, the cortical centers can facilitate the sacral micturition centers to help initiate a micturition reflex and at the same time inhibit the external urinary sphincter so that urination can occur =Voluntary urination: contraction of abdominal muscles-- > increases the pressure in the bladder -- > allows extra urine to enter the bladder neck and posterior urethra -- > stretching their walls -- > stimulates the stretch receptors which excites the micturition reflex and simultaneously...
tracking img