(2)Glomerular filtration is driven by the hydrostatic pressure in the glomerular capillaries and 3.As the filtrate moves through the tubules,certain substances are reabsorbed into the peritubular capillaries. (1)Substances to which the tubular epithelium is permeable are absorbed by diffusion because water reabsorption creates tubule-interstitium concentration gradients for them. ()Tubular reabsorption rates are generally very high for nutrients,ions,and water,but are lower for waste products.Reabsorption may occur by diffusion or by mediated transport. (3)Many of the mediated-transport systems manifest transport maximums,so that when the filtered load of a substance exceeds the transport maximum,large amounts may appear in the urine. 4.Tubular secretion (movement from the peritubular capillary into the tubules),like I.Renal regulation Renal function is regulated by neural and hormonal influences.The most important of these are: 1.renal sympathic nerves .renin-angiotensin system 3.aldosterone 4.atrial natriuretic peptide 5.antidiuretic hormone 6.prostaglandins parathyroid hormone IV.Clearance Clearance is an abstract concept that describes what volume of plasma passing through the kidneys has been totally cleared of a substance in a given period of time.For substances such as inulin which are neither actively absorbed nor secreted by the kidneys.clearance is equivalent to the rate(GFR).In elin isused to measure GFR. to measure the filtration rate of a substance.If less substance appears in the urine than was filtered,then some was reabsorbed by the nephrons.If more substance appears in the urine than was filtered,then there is net secretion of the substance If the same amount of the substance is filtered and excreted,then the substance is neither reabsorbed nor secreted. Clearance valu sare also used to determine how the nephron handlesa substance filtered into it.If the clearance of a substance is less than the inulin or creatinine clearances,then the substance has been reabsorbed.Conversely.if the clearance rate of the substance is greater than inulin or creatinine then it has been actively secreted into the nephron. V.Micturition spinal reflexes;these reflexes lead to contraction of the detrusor muscle,mediated by parasympathetic neurons,and relaxation of the external urethral sphincter,mediated by inhibition of the motor neurons to this muscle.(2) Glomerular filtration is driven by the hydrostatic pressure in the glomerular capillaries and is opposed by both the hydrostatic pressure in Bowman's space and the osmotic force due to the pro plasma. rption creates tubule-interstitium concentration gradients for them. y occur by diffusion or by mediated transport. substance exceeds the transport maximum, large amounts may appear in the urin ce of a substance into the tubule. gulated by neural and hormonal influences. The most important of these are: prostaglandins ct concept that describes what volume of plasma passing through the kidn which are neither actively absorbed nor secreted by the kidneys, clearance is equivalent to the FR). In clinical settings, creatinine is used to measure GFR. then it is possible to measure the filtration rate of a substance.If less substance appears in the urine than was filtered, then some was reabsorbed by the nephrons. If mor rine than was filtered, then there is net secretion of the substance. If t substance is filtered and excreted, then the substance is neither reab d. used to determine how the nephron handles a substance filtered into it. I f a substance is less than the inulin or creatinine clearances, then the substance has teins in the glomerular capillary 3. As the filtrate moves through the tubules, certain substances are reabsorbed into the peritubular capillaries. (1) Substances to which the tubular epithelium is permeable are absorbed by diffusion because water reabso (2) Tubular reabsorption rates are generally very high for nutrients, ions,and water, but are lower for waste products. Reabsorption ma (3) Many of the mediated-transport systems manifest transport maximums, so that when the filtered load of a e. 4. Tubular secretion (movement from the peritubular capillary into the tubules), like glomerular filtration, is a pathway for entran Ⅲ. Renal regulation Renal function is re 1. renal sympathic nerves 2. renin-angiotensin system 3. aldosterone 4. atrial natriuretic peptide 5. antidiuretic hormone 6. 7. parathyroid hormone Ⅳ. Clearance Clearance is an abstra eys has been totally cleared of a substance in a given period of time. For substances such as inulin glomerular filtration rate (G If a person's GFR is known, e substance appears in the u he same amount of the sorbed nor secrete Clearance values are also f the clearance o been reabsorbed. Conversely, if the clearance rate of the substance is greater than inulin or creatinine then it has been actively secreted into the nephron. V. Micturition Urine is stored in the bladder until released by urination, also known as micturition. 1. In the basic micturition reflex, bladder distention stimulates stretch receptors that trigger spinal reflexes; these reflexes lead to contraction of the detrusor muscle, mediated by parasympathetic neurons, and relaxation of the external urethral sphincter, mediated by inhibition of the motor neurons to this muscle. 17