Chapter 9: Homeostasis and Hormonal Control

Question 1

Define homeostasis.

Answer 1

• Maintenance of a
• constant internal environment to
• restore the norm
• in response to environment changes
• through corrective processes

Question 2

What is the importance of homeostasis?

Answer 2

A stable internal environment allows an organism to be independent of changes in the external environment

Question 3

Explain the principles of homeostasis.

Answer 3

• Homeostasis is the maintenance of a constant internal environment through the process of corrective mechanisms and negative feedback;
• Where a stimulus will trigger a corrective mechanism that will revert the change back to the norm

Question 4

What is meant by negative feedback?

Answer 4

Negative feedback is the body’s reaction to bring about an opposite effect to the changes detected through a negative feedback loop.

Question 5

What are the components of a negative feedback loop?

Answer 5

• Normal/set point to be maintained
• Stimulus, a change from normal conditions
• Receptors that detect the stimulus
• Corrective mechanism that brings about a reverse effect of the stimulus
• Effector, organ or cell that responds to a stimulus (carries out CM)
• Feedback to receptors that the condition has been restored to normal state (CM decreases)

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Question 6

What is the process by which blood water potential is maintained?

Answer 6

Osmoregulation

Question 7

What are the processes that occur within the body when blood water potential increases above the norm?

Answer 7

Stimulus:
- Blood water potential increases above the norm
Receptor:
- Hypothalamus in brain detects stimulus
Corrective Mechanism:
- Pituitary gland releases less ADH
- Cells in walls of distal convoluted tubule and collecting duct become less permeable to water
- Less water is selectively reabsorbed by kidney tubules back into the bloodstream
Effects:
- More water is excreted
- Urine produced becomes more diluted
- Blood water potential increases back to norm
- Feedback is sent to the hypothalamus and ADH production increases

Question 8

What are the processes that occur within the body when blood water potential decreases above the norm?

Answer 8

Stimulus:
- Blood water potential decreases above the norm
Receptor:
- Hypothalamus in brain detects stimulus
Corrective Mechanism:
- Pituitary gland releases more ADH
- Cells in walls of distal convoluted tubule and collecting duct become more permeable to water
- More water is selectively reabsorbed by kidney tubules back into the bloodstream
Effects:
- Less water is excreted
- Urine produced becomes more concentrated
- Blood water potential decreases back to norm
- Feedback is sent to the hypothalamus and ADH production decreases

Question 9

Why does blood water potential need to be kept within narrow limits?

Answer 9

blood wp too high-> body cells burst
blood wp too low-> body cells crenate

Question 10

What are the processes that occur within the body when blood glucose concentration increases above the norm?

Answer 10

Stimulus:
- Blood glucose conc. increases above norm
Receptor:
- Islets of Langerhans in the pancreas is stimulated
Corrective mechanism:
- Islets of Langerhans secrete more insulin which is transported by blood to liver and muscle cells
- Insulin
-> stimulates liver and muscle cells to convert excess glucose into glycogen for storage for liver and muscle cells
->increases permeability of cell surface membranes to glucose for increased glucose uptake by cells
->increases oxidation of glucose during tissue respiration
Effects:
- Blood glucose conc. decreases back to norm
- Feedback is sent to the pancreas and insulin production falls

Question 11

What are the processes that occur within the body when blood glucose concentration decreases below the norm?

Answer 11

Stimulus:
- Blood glucose conc. decreases above norm
Receptor:
- Islets of Langerhans in the pancreas is stimulated
Corrective mechanism:
- Islets of Langerhans secrete more glucagon which is transported by blood to liver and muscle cells
- Glucagon
-> stimulates liver and muscle cells to convert stored glycogen into glucose
-> converts fats and amino acids into glucose
Effects:
- Blood glucose conc. increases back to norm
- Feedback is sent to the pancreas and glucagon production falls

Question 12

In what situations would blood water potential be expected to rise?

Answer 12

Drinking a lot of water

Question 13

In what situations would blood water potential be expected to fall?

Answer 13

When sweating excessively due to high physical activity

Question 14

Define the term hormone.

Answer 14

Hormones are chemical substances secreted in minute quantities by endocrine glands that are transported through the bloodstream to target organs where they exert their effects.

Question 15

What is the function of a hormone?

Answer 15

• Influences the growth, development and activity of an organism
• Controls and coordinates body activities

Question 16

What happens to a hormone after performing its function?

Answer 16

• Destroyed in liver
• Excreted in kidney

Question 17

Provide some example of hormones and their respective functions in the human body.
(4 pts.)

Answer 17

1. Oxytocin helps in delivery of baby out of the mother’s womb during childbirth
2. Human Growth Hormone (HGH) increases the height of a child
3. Adrenaline prepares the body for “fight-or-flight” during dangerous encounters
4. Sex hormones are responsible for physical and emotional changes during puberty

Question 18

What are the differences between and endocrine gland and an exocrine gland?
(+ named examples of each)

Answer 18

Endocrine gland:
- Ductless glands
- Transport their secretions via the bloodstream to target organs
- e.g. adrenal gland, pituitary gland, pancreas

Exocrine gland:
- Ducts present
- Transport their secretions via ducts to target organs
- e.g. sweat gland, salivary gland, pancreas

Question 19

What are some examples of endocrine glands and their secretions? [in syllabus]
(5 pts.)

Answer 19

Pituitary gland: ADH
Hypothalamus: regulates secretion of some hormones
Ovary: Oestrogen, Progesterone
Testes: Testosterone
Pancreas: Insulin, Glucagon

Question 20

What are the effects of a lack of secretion of insulin?

Answer 20

• Abnormally high blood glucose concentration
• Tissue cells cannot store or utilise glucose
• Symptoms include weak body, continual weight loss, glucose present in urine
• Could lead to diabetes mellitus

Question 21

What are the effects of over-secretion of insulin?

Answer 21

• Abnormally low blood glucose concentration
• Symptoms include hunger, rapid heartbeat, irritability
• May lapse into a coma or even die in severe cases

Question 22

What is diabetes mellitus?

Answer 22

A condition where blood glucose conc. cannot be regulated, usually caused by insufficient insulin secretion. This leads to persistently high blood glucose concentration. As kidneys are unable to fully selectively reabsorb glucose back into blood capillaries, glucose is excreted in urine.
Signs and symptoms include:
- consistently high blood glucose conc.
- presence in glucose in urine after a meal
- healing of wounds is slow and difficult
- frequent urination
- weight loss

Question 23

What is Type 1 Diabetes?

Answer 23

• Early-onset diabetes
• Insufficient or no insulin production as cells in pancreas that produce insulin are destroyed
• Inherited condition
• Treatment: Insulin injection at early stage

Question 24

What is Type 2 Diabetes?

Answer 24

• Late-onset diabetes
• Insulin produced but target cells (e.g. muscle or liver cells) do not respond well to insulin OR
• Insufficient production of insulin
• Risk factors:
  -obesity
  -sedentary lifestyle
  -unhealthy diet
  -family history
  -high levels of bad cholesterol and low levels of good cholesterol
  -age
• Treatment: oral medication, control of dietary intake and exercising

Question 25

How do you reduce the risk of Type 2 Diabetes?

Answer 25

- eat **healthy foods** (e.g. fruits and vegetables-> low in calories, high in fibre) - engage in **more active physical activities** (use up excess glucose) -glucose provides energy for muscular contractions -liver and muscle cells become more sensitive to insulin - **avoid long periods of inactivity** (e.g. sitting for too long) - maintain a **healthy body weight** that suits age and height

Question 26

What are the similarities between endocrine and nervous controls?

Answer 26

- Contains detector that detects stimulus - Contains signal or message that is transmitted - Contains an effector (target organ/ cell that carries out response)

Question 27

What are the differences between endocrine and nervous controls?

Answer 27

**_Endocrine:_** Involves **hormones** (chemical substances) *_Nervous:_* Involves *neurones* (nerve impulses) **_Endocrine:_** **Chemical** transmission *_Nervous:_* *Chemical and Electrical* transmission **_Endocrine:_** **Hormones** transported by **blood** *_Nervous:_* *Nerve impulses* transmitted by *neurones* **_Endocrine:_** **Slower** transmission and relatively **slow-acting** *_Nervous:_* *Rapid* transmission and response **_Endocrine:_** Can cause **long-term or short-term** changes *_Nervous:_* Often causes *short-term* changes **_Endocrine:_** May be **voluntary or involuntary** *_Nervous:_* Always *involuntary* **_Endocrine:_** Usually **localised** response (e.g. one muscle) *_Nervous:_* *Widespread* responses (usually affects more than one target organ)

Question 28

What are the key structures of the skin? (state)

Answer 28

- Blood vessels - Hair follicle - Sweat glands - Sensory receptors

Question 29

What are the functions of the skin?

Answer 29

- Protection from injury - Protection from water loss - Detection of changes in the environment - Production of sweat - Temperature regulation

Question 30

What are the processes that occur within the body when body temperature increases above the norm?

Answer 30

_Stimulus:_ * Blood and skin temperatures **increase** above the norm _Receptor:_ * **Thermoreceptors on the skin** detect this change and send the information to the hypothalamus in the brain * **Thermoreceptors in the hypothalamus in the brain** also detect the increase in the temperature of *blood flowing through it* _Corrective mechanism + effect:_ 1. **Vasodilation** occurs * **Arterioles in skin dilate** * **Shunt vessels constrict** * More blood flows to capillaries in skin -More heat loss at **skin surface** through **conduction, convection and radiation** 2. **Production of sweat *increases*** * Sweat glands become **more active** -**More latent heat of vaporisation is lost due to evaporation of water in sweat** 3. **Rate of metabolic activities *decreases*** -reduced heat production -reduced heat released within the body

Question 31

What are the processes that occur within the body when body temperature decreases above the norm?

Answer 31

_Stimulus:_ * Blood and skin temperatures **decrease** above the norm _Receptor:_ * **Thermoreceptors on the skin** detect this change and send the information to the hypothalamus in the brain * **Thermoreceptors in the hypothalamus in the brain** also detect the decrease in the temperature of *blood flowing through it* _Corrective mechanism + effect:_ 1. **Vasoconstriction** occurs * **Arterioles in skin constrict** * **Shunt vessels dilate** * Less blood flows to capillaries in skin -Less heat loss at **skin surface** through **conduction, convection and radiation** 2. **Production of sweat *decreases*** * Sweat glands become **less active** -**Less latent heat of vaporisation is lost due to evaporation of water in sweat** 3. **Rate of metabolic activities *increases*** -increased heat production -more heat released within the body 4. Shivering - reflex contraction of muscles in the body - muscle cells undergo **respiration** - heat is released and transported via blood to the rest of the body 5. 'Goose Pimples' - hair erector muscles **contract** - **layer of air** trapped at skin surface to retain heat

Question 32

How do you increase heat gain by the body?

Answer 32

- Metabolic activities such as cellular respiration (esp. in liver and muscle cells) - Vigorous muscular exercise - Consumption of hot food and drinks - Being in a warm environment

Question 33

How do you lose heat within the body?

Answer 33

- Through skin surface via conduction, convection and radiation - Loss of latent heat of vaporisation through evaporation of water in sweat - Exhaled air from lungs - Faeces and urine

Question 34

Describe the relationship between the liver and the kidney in managing metabolic wastes.

Answer 34

The liver is where deamination of amino acids occurs to produce urea. Urea is carried by the renal artery to the kidney, where it is removed from the bloodstream and excreted in urine.

Question 35

Describe the relationship between the liver and the pancreas in a person whose intake is only water for 24 hours.

Answer 35

Low blood glucose stimulates the Islets of Langerhans in the pancreas to produce glucagon that is released into the blood to the liver. Glucagon stimulates the liver cells to convert stored glycogen into glucose and convert fats and amino acids into glucose for maintenance of constant blood glucose levels.