D3.3  Homeostasis

Theme:  Continuity and Change

Homeostasis is process of maintaining a constant internal environment. This is achieved through Negative Feedback loops, which function to minimize change and restore the system to its original set point.

• The body maintains a continuous supply of energy by keeping blood glucose levels within a narrow range. This ensures that cells have a reliable fuel source for cellular respiration without the damaging effects of high sugar levels.
• In endothermic animals, continuity of core body temperature is vital for enzyme activity. Negative feedback ensures that if the temperature drifts, the body corrects back to the norm.
• The hypothalamus constantly monitors blood temperature and solute concentration, acting as the homeostasis control center.
• The kidneys ensure the concentration of solutes in the blood remains consistent by filtering the blood and selectively reabsorbing what the body needs to keep.
  

To keep the internal environment the same, cells and tissues must undergo rapid changes.

• Shifts in hormone levels cause changes to cells.  Insulin causes increases cell transport of glucose and glucagon triggers the breakdown of glycogen.
• The body must change its physical state to compensate for changes in temperature. For example, skin arterioles change diameter to manage heat loss from the skin.  
• Diabetes results from a change in the body's ability to produce or respond to insulin, leading to a loss of blood glucose homeostasis.
• When the hypothalamus detects dehydration, it triggers the release of antidiuretic hormone (ADH).  ADH causes a rapid change in the collecting ducts of the kidney, making them more permeable to water by initiating the translocation of aquaporins.

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How are constant internal conditions maintained in humans?
• What are the benefits to organisms of maintaining constant internal conditions​

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• For what reasons do organisms need to distribute materials and energy?
• What biological systems are sensitive to temperature changes?​ ​

Key Terms to Know: * higher level only

Active Transport*
Adipose Tissue
Antidiuretic Hormone*
Aquaporin*
Ascending Limb of Loop of Henle*
Behavioral Response
Blood Glucose Concentration
Blood Osmotic Concentration
Blood pH
Blood Plasma*
Body Temperature
Bowman'S Capsule*
Brain*
Brown Adipose Tissue
Collecting Ducts of Kidney*
Descending Limb of Loop of Henle*
Effector Cell
Endocrine Cells
Excretion*
External Environment
Filtrate*

Glomerulus*
Glucagon
Gut*
Hair Erection
Homeostasis
Hormone
Hypothalamus
Insulin
Internal Environment
Kidney*
Kidney Medulla*
Loop of Henle*
Negative Feedback Loop
Osmoles per Litre*
Osmoreceptor*
Osmoregulation*
Pancreas
Physiological Response
Pituitary Gland
Positive Feedback Loop
Proximal Convoluted Tubule*

Reabsorption*
Shivering
Skeletal Muscle
Sleep*
Sodium Ion*
Solute*
Sweating
Target Cells (of Hormone)
Thermoreceptor
Thermoregulation
Thyroxin
Toxin*
Type 1 Diabetes
Type 2 Diabetes
Ultrafiltration*
Uncoupled Cell Respiration
Urine*
Vasoconstriction
Vasodilation
Vigorous Activity*
Wakeful Rest*

D3.3.1-- Homeostasis as maintenance of the internal environment of an organism.

• Define homeostasis.
• List examples of variables that are maintained by homeostasis by humans.​​

D3.3.2— Negative feedback loops in homeostasis.

• Compare consequences of negative and positive feedback. 
• Explain how negative feedback loops maintain homeostasis.

D3.3.3-- Regulation of blood glucose as an example of the role of hormones in homeostasis.

• Explain the control of blood glucose concentration, including the roles of glucagon, insulin and the endocrine cells in the pancreatic islets.

D3.3.4--Physiological changes that form the basis of type 1 and type 2 diabetes.

• Distinguish between causes of type I and type II diabetes.
• Distinguish between treatment of type I and type II diabetes.
• Outline symptoms associated with diabetes.​

D3.3.5— Thermoregulation as an example of negative feedback control.

• Define thermoregulation. 
• ​Outline thermoregulation as a negative feedback loop. 
• Explain the process of thermoregulation in humans, including roles of  peripheral and central thermoreceptors, the hypothalamus and pituitary gland, thyroxin and muscle and adipose tissue that act as effectors of temperature change.​

D3.3.6- Thermoregulation mechanisms in humans.

• State that birds and mammals are thermoregulators. ​
• Outline physiological and behavioral responses to cold temperature, including vasoconstriction, shivering, uncoupled respiration and hair erection.
• Outline physiological and behavioral responses to heat, including vasodilation and sweating.

AHL ​​​​​​​​​​D3.3.7- Role of the kidney in osmoregulation and excretion.

• State two functions of the kidney.
• State the unit for osmotic concentration.
  
• Describe the structure of a kidney nephron. 
• Outline the processes of osmoregulation and excretion in a kidney nephron.

AHL ​​​​​​​D3.3.8-  Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion.

• Explain the process of ultrafiltration at the glomerulus and Bowman’s capsule. 
• Define filtrate.
• State why plasma proteins and blood cells are not part of glomerular filtrate.
• Explain the process of selective reabsorption at the proximal convoluted tubule. 
• Outline the mechanism of reabsorption for substances in the glomerular filtrate that are reabsorbed in the proximal convoluted tubule.

AHL ​​​​​​​D3.3.9-  Role of the loop of Henle.

• Compare the location and osmotic concentrations of the kidney cortex and medulla. 
• State the overall function of the loop of Henle.
• Describe the structure and function of the descending limb of the loop of Henle.
• Describe the structure and function of the ascending limb of the loop of Henle.

AHL ​​​​​​​D3.3.10- Osmoregulation by water reabsorption in the collecting ducts.

• Outline the effects of dehydration and hyperhydration on the osmotic concentration of blood. 
• Outline the regulation of blood osmotic concentration, including the roles of osmoreceptors, the hypothalamus, the pituitary, and antidiuretic hormone.
• Explain how the collecting ducts of the kidney increases the blood osmotic concentration.
• Explain how the collecting ducts of the kidney decreases the blood osmotic concentration.
• Outline the consequences of low blood solute concentration on the volume of urine produced, solute concentration in the urine, permeability of the distal convoluted tubule and collecting duct to water and volume of water reabsorbed.
• Outline the consequences of high blood solute concentration on  the volume of urine produced, solute concentration in the urine, permeability of the distal convoluted tubule and collecting duct to water and volume of water reabsorbed.​

AHL ​​​​​​​D3.3.11- Changes in blood supply to organs in response to changes in activity.

• Outline benefits of regulating blood supply to organs in response to changes in activity. 
• Outline the cause and consequences of vasoconstriction and vasodilation. 
• Compare blood flow to skeletal muscle, gut, brain and kidneys during sleep, vigorous physical activity and wakeful rest.