9 — homeostasis & hormonal control

Question 1

Define homeostasis [2]

Answer 1

homeostasis is the maintenance of a constant internal environment [1] involving negative feedback which reverses the effects of a stimulus with the help of the corrective
mechanism to restore the condition back to the normal. [1] A stable internal environment allows an organism to be independent of changes in the external environment.

Question 2

Negative feedback definition

Answer 2

A type of corrective mechanism triggered due to a change in the internal environment detected by receptor to bring about the reverse effect of the stimulus to restore the condition back to normal.

Stimulus -> receptor -> control centre -> corrective mechanism -> set-point

Question 3

Hormones

Answer 3

Hormones r chemical substances produced in minute quantities by endocrine glands which is secreted directly into the blood stream. They are transported by blood to one or more specific target organs to alter the activity of one or more target organs and are then broken down by the liver n excreted by the kidneys after performing their functions. Hormones help to control n coordinate body activities such as growth and development of an organism

Question 4

Define Target organ [1]

Answer 4

Target organ is an effector organ with receptors to bind to specific hormone to carry out a response [1]

Question 5

Diabetes mellitus

Answer 5

Diabetes mellitus is the condition where the body is unable to maintain blood glucose level within normal range.

(disease in which there is insufficient insulin secretion hence body is unable to regulate BGC in order for it to remain within normal limits → persistently high lvl of glucose in blood, bgc^ that kidney unable to completely reabsorb all glucose → glucose excreted in urine)

Question 6

exocrine glands

Answer 6

Has duct/tube for carrying away secretions (eg salivary gland, sweat gland, pancreas)

Question 7

Define Endocrine glands + give an example [3]

Answer 7

Definition: Endocrine gland is a ductless gland [1] which produces hormones that are directly secreted into the bloodstream to the target organs.[1]

• For example, when the pituitary gland secretes more ADH, it enters the bloodstream directly without the use of ducts.
• It is carried to the kidneys, which are the target organs, and reaches nephrons,
• Causing the cells of the walls of collecting ducts to become more permeable to water so that more water is reabsorbed back into the blood.

OR

Islets of Langerhans in the pancreas is an endocrine gland that produces and releases insulin and glucagon directly into the blood plasma to be transported to the target organs (eg liver and muscles to regulate blood glucose concentration.

Question 7

Hypothalamus role + describe how hypothalamus coordinates the maintenance of a constant body temperature. [3]

Answer 7

• Regulates secretion of some hormones including the ones secreted by pituitary gland
• detects change in blood temperature
• generates nerve impulses which are transmitted to the effectors to carry out responses to return blood temperature back to normal.

Mechanism [3]:

Changes in the blood temperature stimulates thermoreceptors in the hypothalamus to generate nerve impulses [1] which are
transmitted along sensory neurone to the relay neurone in spinal cord across a synapse and across another synapse to the motor neurone [1] and to effectors such as the skin arterioles,
and sweat glands to regulate heat loss to the environment by conduction, convection and radiation and evaporation of water from sweat to remove latent heat of vapourisation.

Question 8

Pituitary gland

Answer 8

• Secretes many hormones which control the secretion of other hormones
• Secretes ADH

Question 9

Pancreas

Answer 9

• Has both endocrine & exocrine glands
• Endocrine: Islet of Langerhans secrete insulin & glucagon to control BGC levels
• Exocrine: secretes pancreatic juice thru pancreatic ducts

Question 10

Regulating blood water potential

Answer 10

Normal WP in blood → stimulus: WP of blood^ due to large intake of water → receptor: hypothalamus stimulated → corrective mechanism: less ADH released by pituitary gland into bloodstream n transported to kidneys, cells in walls of collecting ducts become less permeable to water, less water reabsorbed into blood stream, more urine produced → WP of blood decreases to normal level

Question 11

Regulating blood glucose concentration (Negative feedback mechanism) using regulation of BGC

Answer 11

Normal → stimulus: BGC ^above /decrease below normal →
receptor: Islets of Langerhans in pancreas stimulated →
Corrective mechanism: Islets of Langerhans secrete more insulin/glucagon into bloodstream transported to liver n muscles → uptake of glucose into cells increases/decreases + permeability of cell membrane to glucose increases/decreases, allowing more/less glucose to diffuse into liver n muscle cells. → stimulates liver n muscles to convert excess glucose to glycogen to be stored in liver n muscles+ rate of oxidation of glucose for cellular respiration increases/decreases + stimulates liver to convert stored glycogen to glucose + converts fats and AA to glucose→ glucose is released into bloodstream →
BGC decreases/ increase→ BGC returns to normal

Question 12

How does exercise and resting affects the BGC? [5]

Answer 12

Running:
Vigorous muscular contractions during running increase energy demand in the body. More aerobic respiration takes place to meet the increased energy demand. [1]

Glucose in liver and muscle cells is used up for aerobic respiration and the liver and muscle cells absorb more glucose from the blood. This causes the glucose concentration in the
blood to drop below normal. [1]

The change in blood glucose concentration stimulates the islets of Langerhans in the pancreas to produce and release more
glucagon and less insulin into the blood. Glucagon stimulates the liver and muscle cells to convert stored glycogen into glucose and release them into the bloodstream increasing the blood glucose level back to normal. [1]

Resting:
During resting, blood glucose concentration increases above normal due to the effect of glucagon and reduced energy demand. This stimulates the islets of Langerhans in the pancreas to release more insulin and less glucagon into the blood. [1]

Insulin stimulates the liver and muscle cells to absorb glucose from the blood and converts the excess glucose into glycogen to restore the glycogen used up during exercise. This reduces the glucose concentration in blood back to normal. [1]

Question 13

Effects of insulin (normal, lack of secretion and oversecretion)

Answer 13

Normal:
Decreases blood glucose conc by:
1. Making cell membrane more permeable to glucose, allowing more glucose to diffuse into liver n muscle cells.
2. Stimulating liver n muscle cells to convert excess glucose into glycogen for storage.
3. Increase use of glucose for aerobic respiration

Lack:
^ BGC as glucose X stored or utilised by tissue cells(subsequently lost in urine → diabetes mellitus). Muscle cells hv no reserves of glycogen, body grows weak, loses weight

Over:
Abnormal decrease in BGC
Low BGC results in shock
Seizures or fits, collapsing or pass out

Question 14

Effects of glucagon

Answer 14

• ^bgc
  
  • Stimulates conversion of glycogen into glucose
  • Conversion of fats n amino acids into glucose

Question 15

Type 1 vs type 2 diabetes

Answer 15

• Type 1 diabetes: juvenile/ early-onset diabetes, inherited, ioL unable to produce/ secrete sufficient insulin,
  
  • Treatment: insulin injection
• Type 2 diabetes: late-onset diabetes, overweight ppl more likely to dev, insulin produced but target cells do not respond well to insulin → insulin resistance
  
  • Treatment: control of dietary intake n exercising

Question 16

Signs n symptoms of diabetes

Answer 16

• persistently high blood glucose lvl
• Presence of glucose in urine
• Healing of wounds slow n difficult
• Frequent urination
• Weight loss
• Thirst

Question 17

Type 2 diabetes risk factors

Answer 17

1. Obesity (main risk)
2. Age
3. Family history
4. Blood lipid levels
5. Sedentary lifestyle

Question 18

When body tempt increases above normal

Answer 18

Stimulus: Body tempt increases above normal → receptors: thermoreceptors in skin & hypothalamus stimulated to generate nerve impulses transmitted by the sensory neurone across a synapse, to the brain, across another synapse to effector muscles such as skin arterioles, hair erector muscles and sweat gland, to carry out corrective mechanism that restore the body temperature to normal set point.

Arterioles in skin dilate during Vasodilation thus more blood flows to blood capillaries at skin surface, resulting in more heat lost from skin by radiation, convection n conduction.

Increased production of sweat by more active sweat gland, more water in sweat evaporates from skin, removing more latent heat of vaporisation from body.

Decreased metabolic rate such as respiration reduces amt of heat released within body.

Relaxation of hair erector muscles when body tempt ^ causes hairs to lie flat, allowing air to circulate over skin → removing latent heat of vaporisation from skin skin surface thru convection, radiation n conduction.

Question 19

When body tempt decreases below normal

Answer 19

Stimulus: Body tempt falls below normal. receptors: thermoreceptors in skin stimulated, producing nerve impulses which is transmitted by sensory neurones across a synapse to relay neurone that is parallel to spinal cord, to hypothalamus in brain, and across another synapse to motor neurone and to effectors such as the skin arterioles, hair erector muscles and sweat glands to increase blood temperature to normal set point. [1]

Corrective mechanism: vasoconstriction of skin arterioles occurs, skin arterioles constrict, less blood flow thru blood capillaries in skin → reducing heat loss thru radiation, convection, conduction; [1]

Sweat glands become less active → less production of sweat, less water from sweat evaporates thus less latent heat of vaporisation removed from the body; [1]

Shivering increases muscular contraction of skeletal muscles which releases more heat; [1]

Metabolic rate of body increases to release more heat within the body, increasing blood temperature. [1]

Question 20

Explain the reason for the change in concentration of insulin when a person is fasting.

Answer 20

Fasting → no glucose is absorbed into bloodstream → BGC falls below normal → stimulating islets of Langerhans in the pancreas to release more glucagon and less insulin to prevent further drop of BGC.

Question 21

Explain why it is not recommended to stay in sauna for too long. [4]

Answer 21

• ^ humidity n high tempt
• Water in sweat not evaporated due to saturation of water vapour n the air [1]
• Less heat lost via latent heat of vaporisation [1]
• May result in heat stroke

Question 22

Explain why it is very easy to get frost bites in extreme cold regions. [4]

Answer 22

• in extreme cold, to reduce heat loss thru in, the arterioles constrict [1]
• Less blood is sent to blood capillaries in the skin [1]
• Lesser oxygen n glucose reach toes n fingers [1]
• Cells in toes n fingers die overtime due to reduced respiration to release energy for cellular activities [1]

Question 23

Explain why in the desert when a person is exposed to extreme heat for prolonged period of time, he/she would gradually stop sweating and start to suffer from heat stroke. [4]

Answer 23

• high tempt in desert → excessive sweating to evaporate water in the sweat to remove excess heat via latent heat of vaporisation [1]
• Excessive loss of body fluid, reduction in water potential stimulates hypothalamus stimulating ADH n pituitary gland to release more ADH in corrective mechanism [1]
• Stimulate reabsorption of more water back into blood stream to conserve water to bring wp in blood plasma back to normal [1]
• Less water lost via urine, sweating → less heat lost. Body overheats leading to heat stroke.

Question 24

Explain the basic principles of homeostasis in terms of stimulus resulting from a change in the internal environment

Answer 24

1. A stimulus is a change from the normal condition of the internal environment.
2. Receptors detect these changes in the internal environment and are stimulated. Nerve impulses generated from the receptors are transmitted to the control centre or regulator, triggering an apppropriate response (corrective mechanism) to restore internal environment back to the norm.
3. A response counteracts the changes and returns the internal environment back to the norm
4. This response to return the internal environment to its normal levels is known as negative feedback.

Question 25

Treatment of diabetes mellitus

Answer 25

Type 1:
1. Monitor their blood glucose concentrations and test their urine regularly.
2. Regulate carbohydrate content in their diet
3. Injection of insulin

Type 2:
1. Monitor their blood glucose concentrations and test their urine regularly.
2. Regulate carbohydrate content in their diet

Question 26

Explain why temperature regulation in humans is regarded as an example of negative feedback. [2]

Answer 26

Changes in body temperature/ Rise or decrease in body temperature stimulates [1] body to carry out a series of corrective mechanism or processes to correct the body temperature to normal. [1]

Question 27

Type 2 Diabetes Mellitus patients often have impaired thermoregulation mechanism. Their core body temperatures continue to increase if they have been exposed to environment of 44°C and above. Suggest and explain what could have caused the increase in the core body temperature. [2]

Answer 27

Vasodilation of arterioles is impaired [1]
and less heat loss through conduction, convection and radiation. [1]
Or
Sweat glands activity is impaired / sweat glands are inactive / less sweat produced
[1]
heat cannot be lost through the evaporation of water in sweat. [1]
Or
Metabolic rate cannot be regulated. [1]
Release of heat energy from cellular activities remains high. [1]

Question 28

Describe the role of sweat glands in body temperature regulation [3]

Answer 28

As the blood temperature increases above normal, sweat glands
become more active and more sweat is produced; [1] more
water in sweat evaporates and more latent heat of vapourisation
is removed [1], decreasing the blood temperature back to normal.
[1]
As the blood temperature decreases below normal, sweat glands
become less active and less sweat is produced, less water in
sweat evaporates and less latent heat of vapourisation is
removed, increasing the blood temperature back to normal.

Question 29

How do you tell that the insect is cold-blooded. [2]

Answer 29

As the air temperature increases, the body temperature of the insect increases [1]; Body temperature of the insect is not maintained at a constant temperature/ lacks a homeostatic mechanism and takes on the same temperature as the air temperature. [1]

Question 30

Name the structures and explain how each structure helps to maintain a constant body temperature in cold conditions. [5] (hair, thermoreceptors, SN, adipose tissues, skin blood capillaries)

Answer 30

Hair - traps air and reduces heat loss from the body [1]

Thermoreceptors - stimulated by changes in temperature in the environment and generates nerve impulses [1]

Sensory neurone - transmits nerve impulses from thermoreceptors to the hypothalamus [1]

Adipose tissue - insulator against heat loss [1]

Skin blood capillaries -site where heat energy is lost to the environment by conduction, convection and radiation [1]

Question 31

Give an example of a homeostatic mechanism that is carried out by the kidneys under the control of a hormone. [1]

Answer 31

Osmoregulation to maintain the water potential of the blood plasma under the control of anti-diuretic hormone (ADH). [1]

Question 32

Importance of receiving dialysis and kidney transplant treatment. [3]

Answer 32

To remove metabolic waste products. [1]
Which when accumulated in excess will become toxic to the body. [1]

Question 33

If a person’s hypothalamus is damaged, describe and explain how this would affect osmoregulation in the blood. [3]

Answer 33

Hypothalamus cannot be stimulated to produce anti-diuretic hormone / produce less ADH [1] pituitary gland cannot secrete ADH.
No / less water reabsorption from collecting ducts into blood capillaries. [1]
No / less regulation of blood plasma water potential / lower than normal blood plasma water potential. [1]

Question 34

Osmoregulation

Answer 34

is The control of water potential and solute concentration (level) in the blood to maintain a constant water potential in the body

Question 35

Osmoreceptors

Answer 35

are cells in the hypothalamus that detect changes in blood water potential