Cells Respond to Their External Environments Chapter 8

Production of Hormones

How Kidneys Works  Generation of urine during transport along the tubules of kidney  Diffusion of small molecules from capillaries to tubules of kidney through very leaky walls Filtrate: the fluid in the tubules  Transporters to reabsorb nutrient Tight junctions and microvilli Isotonic filtrate: osmotic balance between filtrate and extracellular fluid  Water impermeable, active transport of ions Dilute urine  Tubule with aquaporin channel and salt channels Concentrated urine  Bladder

Solute Transport in the Kidney

Regulation of Blood Volume and Salt Balance  Increasing water or sodium reabsorption  High blood pressure  Hormonal regulation of blood pressure  Regulation of muscle tension in the artery walls Angiotensin –Muscle contraction  increasing blood pressure Atrial natriuretic hormone (ANH) –Relaxation of muscle  decreasing blood pressure  Regulation of salt and water balance Aldosterone –Increasing retention of salt  increase blood volume and pressure Antidiuretic hormone (ADH) –Increasing retention of water

Regulation of Angiotensin and ANH  Angiotensin  Release via an enzyme cascade Secretion of renin in kidney Renin generate angiotensin I by cleavage of inactive blood protein Cleavage of angiotensin I by antiotensin-converting enzyme (ACE) to form angiotensin II  muscle contraction Conversion of antiotension II to III in kidney  stimulation of aldosterone secretion

The Renin-Angiotensin Cascade

Aldosterone and ADH  Aldosterone  Steroid hormone generated by the adrenal gland of the kidneys  Binding to receptor Increasing Na reabsorption –Increasing the activity of Na channels facing the filtrate –Increasing transcription of Na/K pump on the back of the epithelium  ADH  Small protein secreted from the pituitary gland of brain  Binding to receptor on kidney epithelial cells Increasing water absoption –Increasing aquaporins (previously stored in vesicles) on the membrane  Suppression of the release of aldosterone and renin  Alcohol inhibits ADH release

Signals for hormone release  Osmoreceptors  Sensing blood Na concentration  High Na  release of ADH  Low salt  Relase of aldosterone  Baroreceptors  Sensing blood volume  Low blood volume Release of ADH, aldosterone, angiotensin  High blood volume Release of ANH

Responses to Excess Salt increasing blood volume and pressure Stretch receptor in the heart Release of ANH Relaxation of blood vessels Activation of osmoreceptors in the hypothalamus Nerve signal to pituitary to release ADH Increase in aquaporin channels in the kidney tubules More water reabsorption Salt excess Inhibition of renin and aldosterone secretion Excretion of more salt

Blood Loss increasing blood volume and pressure Activation of baroreceptors in the kidney release of renin Increase in angiostnsin and aldosterone Blood loss Release of ADH

Failure of Salt and Water Balance  ADH failure  Excess urinating up to 16 liters/day  Diabetes insipidus  Types of problems No ADH production No response to ADH : problems in ADH receptor or aquaporin  Syndrome of inappropriate ADH (SIADH)  Too much ADH production  Water retention and low blood sodium concentration Brain swelling

Aldosterone Failure  Inactivation of aldosterone pathway  Low blood sodium concentration, dehydration  No aldosterone production  Failure to respond to aldosterone Mutation in aldosterone receptor or sodium channel  Activation of aldosterone pathway  High blood pressure Mutation in an enzyme regulating aldosterone receptor Mutation in the cytoplasmic domain of the sodium channel

Biotechnology Application  People with high blood pressure: 10 to 30 %  Can cause heart disease, stroke, and blindness  Treatment  ACE inhibitor Inhibition of angiotensin I to II conversion –Lower angiotnesin II  lower blood pressure –Lower angiotnesin III  lower aldosterone release  Angiotensin receptor blocker  Diuretics Target salt and water secretion –Blocking aldosterone receptor –Blocking sodium channel