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 heartRelease 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