Homeostasis

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Homeostasis: Maintaining the Internal Environment

Homeostasis is the process of maintaining a constant internal environment within preset limits.
It is critically important because it maintains optimal conditions for enzyme action and cell function.
Sensory cells detect information about conditions inside and outside the body; if conditions change, the body responds to keep them constant.
Physiological factors controlled by homeostasis in mammals include core body temperature, blood pH, blood glucose concentration, and osmotic concentration of the blood.

The negative feedback cycle

Negative Feedback Loops

Most homeostatic control mechanisms use negative feedback loops, which reverse the effects of any change to return values to a set point.
Negative feedback maintains conditions within set limits, unlike positive feedback, which amplifies any change.
A negative feedback loop involves a receptor (detects change), a coordination system (brain and nervous system transfer information), and an effector (muscles and glands bring about a response).
The factor is continuously monitored: if it increases, the body responds to decrease it; if it decreases, the body responds to increase it.

Regulation of Blood Glucose: The Pancreas and Hormones

Blood glucose concentration is kept within narrow limits because glucose is essential for respiration and affects the osmotic balance between cells and blood.
The pancreas contains groups of cells called the islets of Langerhans, which form the endocrine tissue; the exocrine tissue produces digestive enzymes.
The islets of Langerhans contain α cells that secrete glucagon and β cells that secrete insulin.
Insulin lowers blood glucose concentration, while glucagon increases it.

Control of blood glucose

The Effects of Insulin

Blood glucose increases after a carbohydrate-containing meal; this is detected by β cells, which synthesise and secrete insulin.
Insulin is transported in the blood to target cells, mainly in the liver and muscles.
Insulin causes glucose channels in cell surface membranes to open, allowing glucose to move into cells by facilitated diffusion.
Insulin stimulates glycogenesis (conversion of excess glucose to glycogen for storage), increases the rate of respiration, and promotes conversion of glucose to fatty acids for fat storage.

The Effects of Glucagon

Glucagon is synthesised and secreted by α cells when blood glucose falls, such as after fasting or exercise.
Glucagon is transported in the blood to target cells.
Glucagon activates enzymes that hydrolyse glycogen in liver and muscle cells, releasing glucose into the blood; this is glycogenolysis.
Glucagon decreases the rate of respiration and stimulates gluconeogenesis (conversion of amino acids to glucose).

Diabetes: Type 1 and Type 2

Diabetes is a condition in which the homeostatic control of blood glucose has failed or deteriorated, allowing blood glucose concentration to rise.
Excess glucose appears in the urine because the kidneys cannot filter it all out; this causes large volumes of urine and thirst due to dehydration.
Glucose remains in the blood rather than entering cells, so cellular respiration is reduced, causing fatigue.
Dangerously high blood glucose after a meal can cause organ damage.
Type 1 diabetes is caused by an autoimmune response that attacks the β cells of the islets of Langerhans, so the pancreas fails to produce sufficient insulin; it normally begins in childhood.
Type 2 diabetes is more common and usually develops in older adults; the pancreas still produces insulin, but cell membrane receptors have reduced in number or no longer respond, causing insulin resistance.
Type 1 diabetes is treated with regular blood tests, insulin injections, and a modified diet (reduced carbohydrate intake).
Type 2 diabetes is managed with medication to lower blood glucose, a low-carbohydrate diet, and regular exercise; obesity is a major risk factor.

Opposing actions of insulin and glucagon

Thermoregulation as Negative Feedback Control

Thermoregulation is the control of internal body temperature; it is an example of negative feedback.
Peripheral thermoreceptors in the skin monitor external body temperature, while receptors inside the hypothalamus monitor internal body temperature.
Effectors respond by controlling heat loss at the skin and modifying heat generation by metabolism.
The hypothalamus regulates secretion of thyrotropin-releasing hormone, which stimulates the pituitary to release thyroid-stimulating hormone; this stimulates the thyroid gland to release thyroxin.
Thyroxin increases metabolic rate, altering heat generation by cell metabolism.
Muscle tissue shivering raises metabolic rate and releases heat; white adipose tissue provides insulation, and brown adipose tissue generates heat before shivering begins (non-shivering thermogenesis).

Responses to a change in body temperature

Mechanisms of Thermoregulation

A stable core temperature of about 37 °C is vital for enzyme activity; lower temperatures slow reactions, and temperatures that are too high cause enzymes to denature.
Endotherms (e.g. mammals and birds) maintain a constant internal body temperature using physiological mechanisms (shivering, altered metabolism) and behavioural mechanisms (seeking shade, sunbathing).
Responses to an increase in temperature include vasodilation (arteriole muscles relax, more blood flows through skin capillaries, more heat lost by radiation), sweating (cooling by evaporation), and flattening of hairs (hair erector muscles relax, allowing air to circulate).
Responses to a decrease in temperature include vasoconstriction (arteriole muscles contract, less blood flows through skin capillaries; blood diverted through shunt vessels deeper in the skin), erection of hairs (hair erector muscles contract, trapping insulating air), shivering (rapid muscle contraction and relaxation generates heat), uncoupled respiration in brown adipose tissue (energy released as heat, mainly in newborn infants), and boosting metabolic rate via thyroxine.

A cross-section of human skin

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1.Which cells in the pancreas secrete insulin?
Easy
- Aα cells
- Bβ cells
- CExocrine cells
- DAll of the above
2.Which of the following statements (I–IV) correctly describe type I diabetes? I. It usually develops in those aged 40 and over, however more and more young people are developing the condition. II. It is a condition in which the pancreas fails to produce sufficient insulin to control blood glucose levels. III. It is normally treated with regular blood tests to check glucose levels, insulin injections, and a diabetes-appropriate diet. IV. It is more common than type II diabetes.
Easy
- AII and III
- BII, III and IV
- CI, III and IV
- DI and II
3.Which of the following are roles of thyroxin? I. Targets metabolically active regions, such as adipose tissue. II. Increase the rate of protein synthesis. III. Inhibits the appetite and reduces food intake. IV. Increase the generation of body heat.
Medium
- AII only
- BI and II only
- CII and IV only
- DI, II, III and IV
4.A one-year-old child displays fatigue and excessive thirst over a period of time. A urine test reveals the presence of glucose. Which of the following would be the most likely diagnosis?
Medium
- AType I diabetes as the body is unable to respond to the presence of insulin.
- BType I diabetes as the β cells in the islets of Langerhans were destroyed.
- CType II diabetes as the body does not have sufficient insulin receptors on target cells.
- DType II diabetes as the α cells in the islets of Langerhans was destroyed.
5.In which of the following scenarios would there be an increase in the breakdown of glycogen in the liver?
Easy
- AWhen the β cells of the islets of Langerhans secrete insulin.
- BWhen the β cells of the islets of Langerhans secrete glucagon.
- CAfter eating a meal high in carbohydrates.
- DWhen the α cells of the islets of Langerhans secrete glucagon.
6.Which of the following is the best definition of homeostasis?
Easy
- AThe process of maintaining a constant internal environment.
- BThe process of amplifying changes in the internal environment.
- CThe process of controlling body temperature only.
- DThe process of producing hormones in response to external stimuli.
7.Which of the following is NOT an example of a physiological factor controlled by homeostasis in mammals?
Easy
- ACore body temperature
- BBlood pH
- CBlood glucose concentration
- DBlood group
8.Which of the following correctly describes negative feedback?
Medium
- AIt amplifies any change within a system.
- BIt reverses the effects of any change to return values to a set point.
- CIt only operates when body temperature increases.
- DIt maintains conditions without the need for receptors.

Soal lainnya

9.Which of the following is the correct sequence of components in a negative feedback control loop?
Medium
- AEffector → coordination system → receptor
- BReceptor → coordination system → effector
- CCoordination system → receptor → effector
- DReceptor → effector → coordination system
10.Which of the following statements about the islets of Langerhans is correct?
Medium
- AThey form the exocrine tissue of the pancreas and produce digestive enzymes.
- BThey contain α cells that secrete insulin and β cells that secrete glucagon.
- CThey form the endocrine tissue of the pancreas and contain α and β cells.
- DThey are found in the liver and regulate blood glucose.
11.Which of the following is the correct description of the effect of insulin on liver and muscle cells?
Medium
- AIt stimulates the hydrolysis of glycogen to glucose.
- BIt stimulates the conversion of glucose to glycogen (glycogenesis).
- CIt stimulates the conversion of amino acids to glucose.
- DIt decreases the rate of respiration.
12.Which of the following is the correct description of the effect of glucagon?
Medium
- AIt increases the rate of respiration and lowers blood glucose.
- BIt stimulates glycogenolysis and gluconeogenesis to increase blood glucose.
- CIt stimulates the conversion of glucose to fatty acids.
- DIt is secreted by β cells when blood glucose rises.
13.Which of the following are effects of insulin? (select all that apply)
Medium
- AGlucose channels in cell surface membranes open, allowing glucose to enter cells by facilitated diffusion.
- BLiver and muscle cells convert excess glucose into glycogen.
- CThe rate of respiration increases, using up glucose.
- DEnzymes that hydrolyse glycogen are activated.
- EAmino acids are converted to glucose.
14.Which of the following are effects of glucagon? (select all that apply)
Medium
- AActivation of enzymes that hydrolyse glycogen in liver and muscle cells.
- BA decrease in the rate of respiration.
- CConversion of amino acids to glucose.
- DConversion of glucose to fatty acids.
- EOpening of glucose channels in cell surface membranes.
15.Negative feedback mechanisms amplify any change within a system.
Easy
True or false?
16.Type 2 diabetes is more common than type 1 diabetes.
Easy
True or false?
17.In type 1 diabetes, the pancreas still produces insulin but the cell membrane receptors no longer respond.
Easy
True or false?
18.Glucagon is a hormone secreted by the α cells of the islets of Langerhans.
Easy
True or false?
19.Vasodilation is caused by the contraction of muscles in the arteriole walls.
Medium
True or false?
20.Shivering raises the core body temperature because the metabolic reactions required to power muscle contraction release heat.
Medium
True or false?
21.Match each term with its correct description.
Medium
- Glucagon
- Glycogen
- Glycogenesis
- Glycogenolysis
- Storage polysaccharide of animal cells
- Hormone secreted by α cells
- Conversion of glucose to glycogen
- Hydrolysis of glycogen to glucose
22.Place the following events in the correct order for the regulation of blood glucose after a carbohydrate-rich meal.
Medium
- Blood glucose concentration increases.
- β cells in the pancreas detect the increase.
- Insulin is secreted into the blood.
- Liver and muscle cells convert glucose to glycogen.
23.Which of the following are physiological factors controlled by homeostasis in mammals? (select all that apply)
Medium
- ACore body temperature
- BBlood pH
- CBlood glucose concentration
- DOsmotic concentration of the blood
- EBlood group
24.Match each component of a negative feedback control loop with its correct role.
Medium
- Receptor
- Coordination system
- Effector
- Detects a change in a physiological factor
- Transfers information between different parts of the body
- Brings about a response
25.Place the following events in the correct order for the response to a rise in blood glucose concentration.
Medium
- Blood glucose concentration rises after a carbohydrate-containing meal
- β cells in the islets of Langerhans detect the increase
- Insulin is synthesised and secreted into the blood
- Insulin binds to target cells in the liver and muscles
- Glucose channels open and glucose enters body cells by facilitated diffusion
26.Which of the following occur in the body in response to a decrease in temperature? (select all that apply)
Medium
- AVasoconstriction of arterioles near the skin
- BContraction of hair erector muscles
- CShivering of muscles
- DVasodilation of arterioles near the skin
- EIncreased sweating
27.Match each process with its correct description.
Medium
- Glycogenesis
- Glycogenolysis
- Gluconeogenesis
- Conversion of excess glucose into glycogen for storage
- Hydrolysis of glycogen to release glucose
- Conversion of amino acids into glucose
28.Place the following events in the correct order for thermoregulation when body temperature rises above normal.
Medium
- Peripheral thermoreceptors in the skin and receptors in the hypothalamus detect the increase
- The hypothalamus coordinates a response
- Muscles in the arteriole walls near the skin relax
- Arterioles dilate and more blood flows through skin capillaries
- More heat is lost to the environment by radiation
29.A person with type 2 diabetes has pancreas cells that still produce insulin. Which of the following best explains why their blood glucose remains high?
Medium
- AThe cell membrane receptors to which insulin binds have reduced in number or no longer respond.
- BThe β cells of the islets of Langerhans have been destroyed by an autoimmune response.
- CThe α cells secrete too little glucagon.
- DThe kidneys remove too much glucose from the blood.
30.Which of the following is the best explanation for why a person with untreated diabetes produces large volumes of urine and feels thirsty?
Medium
- AThe kidneys are unable to filter out excess glucose, so glucose appears in the urine and large volumes of urine are produced, causing dehydration.
- BThe kidneys reabsorb too much water, producing concentrated urine and causing thirst.
- CInsulin causes the kidneys to excrete more water.
- DGlucagon stimulates the kidneys to produce urine.
31.A person with type 1 diabetes drinks a sugary solution. Their blood glucose concentration rises and then falls back towards normal over the next few hours, even though their body produces no insulin. Which process best explains the fall in blood glucose?
Medium
- AGlucose is excreted by the kidneys in the urine
- BGlucose is used up by cells during respiration and stored as glycogen
- CGlucagon converts glucose into glycogen in the liver
- DInsulin is released from the β cells in response to the glucose
32.In an experiment, a person's blood glucose concentration was 75 mg per 100 cm³ before drinking a sugary solution. Their concentration rose to 140 mg per 100 cm³ after 30 minutes, then fell back to 75 mg per 100 cm³ after 90 minutes. Which of the following best explains the fall between 30 and 90 minutes?
Medium
- AGlucagon secretion increased, causing glycogenolysis in the liver
- BInsulin secretion increased, causing glucose uptake and glycogenesis
- CThe kidneys removed glucose from the blood and excreted it in urine
- DThe rate of respiration in cells decreased, using less glucose
33.Scientists measured insulin sensitivity in patients before and after gastric bypass surgery. The mean sensitivity for patients with type 2 diabetes rose from 0.45 to 1.17 arbitrary units. Which conclusion is best supported by these data?
Hard
- AGastric bypass surgery cures all patients with type 2 diabetes
- BGastric bypass surgery increases sensitivity to insulin in patients with type 2 diabetes
- CGastric bypass surgery causes type 2 diabetes in patients who do not have it
- DGastric bypass surgery reduces the number of insulin receptors on target cells
34.A patient's blood glucose concentration is measured every 30 minutes for 3 hours after a meal. The concentration rises to a peak at 60 minutes and then returns to the pre-meal value by 150 minutes. Which hormone is responsible for the decrease in blood glucose after the peak?
Medium
- AGlucagon, secreted by the α cells
- BInsulin, secreted by the β cells
- CThyroxin, secreted by the thyroid gland
- DThyrotropin-releasing hormone, secreted by the hypothalamus
35.A person is unable to produce insulin. Which of the following statements about their condition are correct? (select all that apply)
Medium
- AGlucose remains in the blood rather than entering the cells
- BThe kidneys produce large volumes of urine
- CThe individual may feel thirsty due to dehydration
- DCellular respiration is increased, causing weight gain
- EThe condition is treated with insulin injections
36.Which of the following would be expected in a person with untreated type 2 diabetes? (select all that apply)
Hard
- AThe pancreas still produces insulin
- BCell membrane receptors for insulin have reduced in number or no longer respond
- CThe β cells of the islets of Langerhans have been destroyed by an autoimmune response
- DBlood glucose concentration is higher than normal after a meal
- EThe condition usually develops in older adults
37.In type 2 diabetes, the pancreas stops producing insulin completely.
Easy
True or false?
38.A person with type 1 diabetes may feel fatigued because glucose remains in the blood rather than entering cells, reducing cellular respiration.
Medium
True or false?
39.The high-fat diet mice showed a smaller fall in blood glucose after the meal than the normal diet mice. Which of the following best explains this difference?
Hard
- AThe high-fat diet mice secreted less insulin in response to the meal
- BThe high-fat diet mice had more insulin receptors on their target cells
- CThe high-fat diet mice converted more glucose to glycogen in the liver
- DThe high-fat diet mice had a higher rate of respiration in their muscle cells
40.The high-fat diet mice are likely to have developed insulin resistance, similar to the reduced cellular response seen in type 2 diabetes.
Medium
True or false?
41.Name the hormone secreted by the β cells of the islets of Langerhans.
Easy
42.Name the storage polysaccharide of animal cells that is formed from excess glucose under the influence of insulin.
Easy
43.Name the process by which glucagon causes the breakdown of glycogen to glucose in the liver.
Easy
44.Name the part of the brain that contains receptors that monitor internal body temperature.
Easy
45.Complete the sentence about the control of blood glucose.
Easy
The islets of Langerhans contain α cells that secrete ____ and β cells that secrete ____.
46.Complete the sentence about thermoregulation.
Easy
When body temperature decreases, ____ occurs in the arterioles near the skin, and the hair erector muscles ____ to raise the hairs.
47.Name the three physiological factors controlled by homeostasis in mammals that are listed in the notes.
Medium
Core body temperature, blood ____, and concentration of ____ in the blood.
48.At what core body temperature do human enzymes function optimally? Give your answer in °C.
Medium
49.In an experiment, a person's blood glucose concentration was 75 mg per 100 cm³ before drinking a sugary solution. After drinking the solution, the concentration rose by 45 mg per 100 cm³. What was the blood glucose concentration after drinking the solution? Give your answer in mg per 100 cm³.
Medium
50.In an experiment, a person's blood glucose concentration was 75 mg per 100 cm³ before drinking a sugary solution. After drinking the solution, the concentration rose to 140 mg per 100 cm³. Calculate the increase in blood glucose concentration, in mg per 100 cm³.
Medium
51.A patient's insulin sensitivity was 0.45 arbitrary units before gastric bypass surgery and 1.17 arbitrary units after surgery. Calculate the increase in insulin sensitivity, in arbitrary units.
Medium
52.Complete the sentence about the control of blood glucose after a meal.
Medium
After a meal containing carbohydrate, blood glucose concentration increases. This is detected by the ____ cells in the pancreas, which secrete ____. This hormone causes liver and muscle cells to convert excess glucose into ____.
53.Describe the effects of insulin that restore blood glucose to normal levels.
Medium
54.Compare and contrast type 1 and type 2 diabetes.
Medium
55.Describe the role of the pancreas and associated hormones in the control of blood glucose concentration.
Hard
56.Explain the change in blood glucose levels for mice on a normal diet during the first 90 minutes after a meal.
Hard
57.After the first 90 minutes, mice on a normal diet show an increase in blood glucose despite no more food being eaten. Explain why blood glucose increases despite no food being consumed.
Hard
58.At what core body temperature do human enzymes function optimally? Give your answer in °C.
Medium
- A41 °C
- B45 °C
- C33 °C
- D37 °C
59.In an experiment, a person's blood glucose concentration was 75 mg per 100 cm³ before drinking a sugary solution. After drinking the solution, the concentration rose by 45 mg per 100 cm³. What was the blood glucose concentration after drinking the solution? Give your answer in mg per 100 cm³.
Medium
- A120 mg per 100 cm³
- B144 mg per 100 cm³
- C108 mg per 100 cm³
- D132 mg per 100 cm³
60.In an experiment, a person's blood glucose concentration was 75 mg per 100 cm³ before drinking a sugary solution. After drinking the solution, the concentration rose to 140 mg per 100 cm³. Calculate the increase in blood glucose concentration, in mg per 100 cm³.
Medium
- A65 mg per 100 cm³
- B79 mg per 100 cm³
- C72 mg per 100 cm³
- D58 mg per 100 cm³
61.A patient's insulin sensitivity was 0.45 arbitrary units before gastric bypass surgery and 1.17 arbitrary units after surgery. Calculate the increase in insulin sensitivity, in arbitrary units.
Medium
- A1.72 arbitrary units
- B2.72 arbitrary units
- C-0.28 arbitrary units
- D0.72 arbitrary units

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