9 — homeostasis & hormonal control

Question 1

homeostasis

Answer 1

homeostasis is the maintenance of a constant internal environment through an automatic corrective mechanism. Homeostasis ensures that the internal conditions of an organism are kept constant all the time. A stable internal environment allows an organism to be independent of changes in the external environment.

Question 2

Homeostatic control:

Answer 2

occurs when the body reacts to bring abt an opp effect to the change detected

Question 3

Negative feedback:

Answer 3

A type of corrective mechanism triggered which counteracts changes in the internal environment detected by receptor to bring about the reverse effect of the stimulus to restore the set- point.

Question 4

Conditions for negative feedback

Answer 4

• Normal/set point to be maintained
• Stimulus: change from normal condition in internal environment
• Receptors that detect stimulus
• Corrective mechanism: brings abt reverse effect of stimulus

Question 5

Hormones

Answer 5

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. After performing their functions, they r broken down in the liver n excreted by the kidneys. Hormones help to control n coordinate body activities such as growth and development of an organism

Question 6

Target organ

Answer 6

Target organ is an effector organ that is stimulated by the signals from the hormone to carry out a response

Question 7

Diabetes mellitus

Answer 7

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

Question 8

exocrine glands

Answer 8

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

Question 9

Endocrine glands + give an example [3]

Answer 9

Definition: Ductless glands, hormone produced is secreted directly into bloodstream n distributed around body

• 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 9

Hypothalamus

Answer 9

• Regulates secretion of some hormones including the ones secreted by pituitary gland
• Monitors and detects any changes to the temperature of the body. When the blood tempt is abnormal, thermoreceptors in hypothalamus send nerves impulses to the effectors in the sweat glands, skin arterioles, hair erector muscles, skeletal muscles and adrenal glands to carry out corrective mechanisms.

Question 10

Pituitary gland

Answer 10

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

Question 11

Pancreas

Answer 11

• Has both endocrine & exocrine glands
• Endocrine: Islet of Langerhans secrete insulin & glucagon to control BGC levels
  
  • Insulin decreases BGC by
    
    • ^ rate of glucose uptake by cells
    • ^ permeability of cell membranes to glucose
    • Stimulating liver n muscle cells to convert excess glucose into glycogen for storage
    • ^ oxidation of glucose during tissue respiration
  • Lack of insulin
    
    • Abnormally ^ bgc
    • Tissue cells cannot utilise or store glucose
    • Weak body, continual weight loss, glucose present in urine
    • Could lead to diabetes mellitus
  • Over-secretion of insulin
    
    • Abnormally low bgc
    • Hunger, rapid heartbeat, irritability
    • Death or coma
  • Glucagon ^ bgc
    
    • Convert glycoge to glucose
    • Convert fats and aa to glucose
• Exocrine: secretes pancreatic juice thru pancreatic ducts

Question 12

Ovary

Answer 12

Secretes oestrogen & progesterone

Hormones released by gonads (ovaries & testes) control dev of primary n secondary sexual characteristics → do not function until a person reaches puberty

Question 13

Testes

Answer 13

Secretes testosterone

Question 14

Regulating blood water potential

Answer 14

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 15

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

Answer 15

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^/decreases + permeability of cell membrane to glucose ^/decreases → 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 16

How does exercise cause a fall in the BGC?

Answer 16

• Exercise → muscular contractions demand large amts of energy generated by aerobic n anaerobic respiration
• Glucose is oxidised to supply increased energy demand → muscle cells use up blood glucose → BGC drops

Question 17

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

Answer 17

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 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 18

Effects of glucagon

Answer 18

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

Question 19

Diabetes mellitus

Answer 19

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 20

Type 1 vs type 2 diabetes

Answer 20

• 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 21

Signs n symptoms of diabetes

Answer 21

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

Question 22

Treatment For diabetes

Answer 22

• measure BGC n test urine regularly
• Watch diet carefully
• Type 1: inject insulin regularly into fat tissue under skin
• Type 2: oral medication & changes to diet

Question 23

Type 2 diabetes risk factors

Answer 23

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

Question 24

When body tempt increases above normal

Answer 24

Stimulus: Body tempt ^ above normal → receptors: thermoreceptors in skin & hypothalamus stimulated → corrective mechanism:

• arterioles in skin dilate -> Vasodilation: Arterioles dilate → more blood flows to blood capillaries at skin surface → more heat lost from skin by radiation, convection n conduction
• ^ production of sweat by more active sweat glands → more water in sweat evaporates from skin, removes more latent heat of vaporisation from body
• Decreased metabolic rate such as respiration → reduces amt of heat released within body
• Skin surface thru convection, radiation n conduction
  
  • Relaxation of hair erector muscles when body tempt ^ → hairs lie flat, allowing air to circulate over skin →removing latent heat of vaporisation from skin skin surface thru convection, radiation n conduction.

Question 25

When body tempt decreases below normal

Answer 25

Stimulus: Body tempt falls below normal → receptors: thermoreceptors in skin stimulated, producing nerve impulses which is transmitted to hypothalamus in brain → corrective mechanism: vasoconstriction of arterioles → less blood flow thru BCs in skin → less heat loss thru radiation, convection, conduction; sweat glands less active → less production of sweat → less latent heat of vaporisation lost; shivering due to rapid contraction of skeletal muscles occur; metabolic rate of body ^ → release more heat → keeps body warm.

Question 26

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

Answer 26

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 27

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

Answer 27

• ^ 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 28

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

Answer 28

• 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 29

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 29

• 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 30

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

Answer 30

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 31

Treatment of diabetes mellitus

Answer 31

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 32

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

Answer 32

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 33

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 33

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]