1. Homeostasis
(and some Endocrine System too)
I’m outta Cat pictures!
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2. Homeostasis and Excretion
 Homeostasis – maintaining the internal
environment at a constant level or
between narrow limits.
 Involves nervous and endocrine systems:
– Receptors monitor level of “variable”
– Brain regulates level of variable
– Effectors bring about changes as directed by
the brain
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3. Homeostasis
The parameters controlled include:
 Blood pH and CO2 concentration
 Body Temperature (Thermoregulation)
 Blood glucose concentration
 Water Balance (Osmoregulation)
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4. Negative Feedback
 Hasa stabilizing effect:
 change in “levels” always causes
an opposite change:
– Rise in levels = decrease in
production = reduction in levels
– Decrease in levels = increase =
raise the levels
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5. Thermoregulation
 Temperature regulation: thermoreceptor
– Endotherm – mammals and birds
– Ectotherm – reptiles…
 Source of heat: Aerobic Cellular Respiration
 Main methods of heat loss: Conduction,
Convection, and Radiation.
 Require coordination between nervous and
endocrine
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6. Thermoregulation
Thermoreceptors send impulses to hypothalamus which
stimulates the Pituitary Gland to release TSH into the Thyroid
Gland to release Thyroxin
Thyroxin causes the body to increase metabolic rate releasing
more heat. (less thyroxin in hot weather)
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7. Shivering
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8. Sweating
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9. Blood Glucose Level
There is a direct relationship between the digestive system
(eating), exercise, and glucose level.
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10. Type I vs. II Diabetes
Type I Type II
 Onset usually during  Can occur at any age
childhood  Target cells show
 Beta pancreatic cells insensitivity to insulin
produce insufficient  Does not require
insulin. synthetic insulin
 Must take synthetic  Correlated to obesity
insulin  Can be controlled with
 Cannot be controlled low carb diets
by diet
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11. Osmoregulation
 Control of Water Balance
 Process that keeps the osmotic pressure
of the blood and tissue fluid constant
 Depends on:
– the amount of H2O present.
– the “salt” content of the blood.
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12. Hormones and Osmoregulation
 Aldosterone
 Regulates Na reabsorption and K excretion
 Presence of hormone stimulates excretion of K and
reabsorption of Na.
– Sodium reabsorbed – Water follows to maintain proper
blood volume.
– Helps to maintain proper blood pressure.
 High Salt Level Raises Blood pressure
– Helps to control blood pH levels – secretion of H+ into
tubules.
– When K levels in blood are too high:
Aldosterone secreted – K from blood to tubule
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13. Hormones and Osmoregulation
ADH (Antidiuretic Hormone)
 Released by pituitary gland in response to
signal from the hypothalamus(brain).
 Responsible for final reabsorption of water
 In collecting duct.
– Lower levels of water: release of ADH into
blood.
– ADH causes the cell membranes in collecting
duct to become permeable to water.
– Process reverses when water level is restored.
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