1. Your kidney has negative feedback mechanisms that prevent GFR from increasing
ID: 3481398 • Letter: 1
Question
1. Your kidney has negative feedback mechanisms that prevent GFR from increasing if your blood pressure
increases, such as during exercise. Read about these two mechanisms (e.g., in your physiology textbook)
and describe how they work to maintain a constant GFR even if mean arterial pressure increases.
A- Myogenic regulation
B- Tubuloglomerular feedback
2. Antidiuretic hormone (vasopressin): (2 pts)
A- What stimulates release of antidiuretic hormone?
B- If antidiuretic hormone is present, how does urine volume and concentration change?
3. Aldosterone: (2 pts)
A- What stimulates release of aldosterone?
B- If aldosterone is present, how does urine volume and concentration change?
Explanation / Answer
1-) Autoregulation is a process in human body that results from an internal adaptive mechanisms working to adjust the response to any stimulus. This autoregulation is observed in Kidneys, Heart and brain. With autoregulation mechanism of these organs body can divert blood and oxygen where it is needed the most, one such condition is post workout or ny exercise.
In normal healthy young adult the value of GFR is about 130ml/minute = 180litres/day. Regulation of renal blood flow is important to maintain a stable glomerular filteration rate . During exercise kidneys work to excrete excess fluids. Normally if the perfussion pressure of blood to an organ rises be it during exercise, there should be greater flow of blood in the organs. But surprisingly, this does not happen with kidney heart and brain , even if the perfussion pressure changes mildly or moderately the blood flow does not alter. This is called autoregulation.
Normally with increased blood flow the Blood pressure increases and pressure in glomerular capillary increases thus rising the Glomerular filteration rate , but with the autoregulation and negative feedback mechanism of kidney there is no rise in the glomerular filteration rate, the mechanism lies in following processes of renal autoregulation.
A-) Myogenic regulation- Myogenic regulation or theory was founded by Starling and his disciple Bayliss, of England in 1902. This system is specially significant to kidneys where the glomerular filteration rate is sensitive to changes in blood pressure. This mechanism is the reaction of arterioles and arteries to an increase and decrease of Blood pressure to keep blood flow constant. The smooth muscle of blood vessels contracts when subjected to stretch(Arteriolar smooth muscle) Therefore when more blood during exercise tries to flow through the afferent arteriole to the glomerulus the smooth muscles of the arterioles are stretched and hence contract resulting into narrowing of arteriole and thus ------- reduction of blood flow.
B) Tubuloglomerular feedback- It is the principle mechanism responsible for Renal autoregulation. This is anegative feedback mechanism which utilizes information regarding distal tubular fluid flow rate to control the Renal blood flow and ultimately the glomerular filteration rate. When glomerular filteration rate in a single Nephron rises due to more blood flow , more fluid appears in the Bowmann's or glomerular space. More fluid and sodium appear in macula densa region------- signal generate by macula densa to fall the glomerular rate by contraction of afferent arteriole. When along with the single nephron all other glomeruli shows tubuloglomerular feedback then the Renal autoregulation shows complete effect.
2-) Antidiuretic hormone- Antidiuretic hormone is released from posterior pituitary gland.Its major effects are Conservation of body water and contraction of vascular smooth muscles.
A-) Release of antidiuretic hormone- Appropriate stimulus stimulates the hypothalamus-------Action [potential is developed in hypothalamic neurons in the hypophyseal neural tract---------- Action potentials causes bursting of storage vesciles containing Antidiuretic hormone. Two approprite stimuli works for stimulating Antidiuretic hormone. OSMORECEPTORS and VOLUMERECEPTORS.
Osmoreceptors are present in Hypothalamus. It works when body is Dehydrated be it after exercise osmolality of plasma rises causing stimulation of these receptors ---------- send signals to supraoptic and paraventricular nuclei-----stimulates------Antidiuretic hormone released.
Volumereceptors are present in Thorax in wall of Atrium. low blood volume or Hypervolemia-------- causes Atrial distension--------signals from arterial wall to hypothalamus-------causes diuresis by inhibiting antidiuretic hormone causing the correction of hypervolemia.
B-) change in concentration of urine volume- Increased blood volume prevents release od antidiuretic hormone as a result kidneys retain less water diluting the urine and increasing urine output. As fluid leaves the body the blood volume decreases and serum osmolality increases.
3-) Aldosterone- It is a main mineralocorticoid hormone released by Zona glomerulosa of adrenal cortex in adrenal gland. It helps in conservation of sodium in kidney. It regulates blood levels of electrolytes and thereby regulating blood pressure.
A-) Release of aldosterone- Major regulstor of aldosterone release is Renin angiotensin system. Renin is an enzyme secreted by kidney when blood volume in kidney falls the potassium in serum level rises ------------causing sodium levels to fall , release of renin from kidney by the Juxtaglomerular cells in the blood circulation--------Angiotensinogen in blood produced by liver gets acted by renin and is converted from angiotensin1 to angiotensin11 which is a vasoconstrictor and this stimulates release of Aldosterone from zona glomerulosa.
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