Homeostasis

Question 1

Homeostasis

Answer 1

The maintenance of the internal environment of an organism, within preset limits despite fluctuations in the external environment.

Question 2

Homeostatic variables in humans/Internal conditions that are monitored and maintained in humans (4)

Answer 2

Body temperature, blood pH, blood glucose concentration, blood osmotic concentration

Question 3

Negative feedback

Answer 3

Mechanisms/responses that work against the change of the variables in order to keep it within a range, thereby maintaining homeostasis.

Question 4

Positive feedback

Answer 4

A mechanism by which a system responds to changes in its internal or external environment by amplifying the direction of the change, often leading to a cascade of events.

Question 5

Optimal blood-glucose level

Answer 5

70-100 mg/dL

Question 6

Hypoglycaemia

Answer 6

Continued low blood sugar levels

Question 7

Hyperglycaemia

Answer 7

Continued high blood sugar levels

Question 8

Endocrine tissue

Answer 8

Tissue that secretes hormones from glands into the blood, helping control body functions

Question 9

Pancreas

Answer 9

A large gland compose of the exocrine tissue and the endocrine tissue.
The exocrine tissue produces enzymes for digestion, while the endocrine tissue producest two important hormones.

Question 10

Islets of Langerhans/pancreatic islets

Answer 10

(Clusters of) pancreatic endocrine cells. Produces the hormones insulin and glucagon.

Question 11

Insulin

Answer 11

Hormone that is produced and secreted by the beta cells of the islets of Langerhans in response to rising blood glucose levels. It stimulates glucose uptake from the blood into the cells (storage).

Question 12

Glucagon

Answer 12

Hormone that is produced and secreted by the alpha cells of the islets of Langerhans in response to decreasing blood glucose levels. It stimulates the liver to release stored glucose into the bloodstream.

Question 14

Describe the regulation of blood glucose as an example of the role of hormones in homeostasis using negative feedback.

Answer 14

The opposing actions of glucagon and insulin keep the blood glucose level fluctuating within a range.

If the blood glucose level rises above the normal range:
Beta cells of the islets of Langerhans release insulin into the bloodstream.
Insulin promotes (mainly) the cells of the liver, muscles and fat tissue to take up glucose from the blood to decrease the blood glucose level.
The glucose is stored as glycogen in the cells of muscle and liver, or as fat in the cells of fat tissue, for later use.
As the blood glucose levels, decrease, the secretion of insulin also decreases.

If the blood glucose level falls below the normal range:
Alpha cells of the islets of Langerhans release glucagon into the bloodstream.
Glucagon promotes (mainly) the cells of liver and fat tissue to break down glycogen and lipids and release the glucose into the blood until the level of blood glucose increases to the normal range.
As the blood glucose levels increase, the secretion of glucagon decrease.

Question 15

Diabetes

Answer 15

The hormonal disorder that causes hyperglycaemia

Question 16

Causes of hyperglycaemia

Answer 16

Insufficient insulin production (type I) or ineffective use of insulin (type II).

Answer 17

Cells cannot obtain enough glucose from the blood.
Cells start to burn the body’s supply of fats and proteins.
Digestive system continues to absorb glucose, resulting in blood glucose concentration becoming extremely high.

Question 18

Two early signs of diabetes

Answer 18

Excessive urination and excessive thirst.

The kidneys start filtering excess glucose from the blood. The kidneys also draw water from blood to dilute the urine, causing dehydration and excessive urination.

Question 19

Risk factors of hyperglycaemia due to untreated diabetes

Answer 19

Damages cells and their process, causing:
dehydration
blindness
cardiovascular disease
kidney disease
nerve damage

Question 20

Type I diabetes

Answer 20

Insulin-dependent or early onset diabetes.

An autoimmune disorder: the immune system mistakenly attacks and destroys the beta cells in the pancreas.
Individuals are unable to producer insulin, leading to hyperglycaemia.

Early-onset, no known cure. Individuals with the condition must manage their blood glucose levels through a combination of insulin therapy, dietary modifications, and regular exercise.

Question 21

type II diabetes

Answer 21

Insulin-independent or late onset diabetes.

Cells are insensitive to insulin and are said to be ‘insulin resistant’.
In response to reduced sensitivity to insulin, pacreative beta cells start to produce more insulin and become exhausted.

Can be reversed (most of the time) by moderate weight loss, regular physical activity, healthy diet.

Question 22

Risk factors contributing to the development of diabetes

Answer 22

1. Family history (higher risk if (close) family member has diabetes)
2. Body weight (being overweight or obese - significant risk factor for type 2 diabetes as excess body weight increases insulin resistance and impairs glucose metabolism)
3. Lifestyle (lack of physical activity is linked to an increased risk of type 2 diabetes. Regular exercise improves insulin sensitivity)
4. Diet (diet high in processed foods, sugary beverages and unhealthy fats increases the risk of type 2 diabetes)
5. Age (Risk of developing diabetes increases with age (especially for type 2 - more common over age of 45)

Question 23

Thermoregulation

Answer 23

The process by which the body maintains a stable internal temperature despite changes in the external environment.

Coordinated by the nervous system.

Question 24

Hypothalamus

Question 25

Hypothalamus and pituitary gland

Answer 25

The hypothalamus is a small, almond-sized region located at the base of the brain, just above the brainstem. A crucial part of the CNS. Region of the brain that controls body temperature, hunger and thirst. Plays a vital role in maintaining homeostasis and regulating various physiological processes in the body. The pituitary gland is a pea-sized gland located at the base of the brain, just below the hypothalamus. The hypothalamus and the pituitary gland work to gether to regulate the production and release of hormonse throughout the body. The hypothalamus acts as a control centre, while the pituitary gland acts as a major endocrine gland that releases hormones into the bloodstream.

Question 26

Thermoreceptors

Answer 26

Specialised sensory neurons that can detect changes in temperature. Dispersed throughout the body. Peripheral thermoreceptors are the thermoreceptors in the skin. Central thermoreceptors are the thermoreceptors inside the body.

Question 27

Mechanisms of thermoregulation

Answer 27

The hypothalamus integrates signals from the peripheral and central thermoreceptors, initiating physiological and behavioural responses as a negative feedback mechanism t regulate body temeprature. When your body starts losing heat: The hypothalamus stimulates the pituitary gland. The pituitary gland releases thyroid stimulating hormone (TSH) to stimulate the thyroid gland. The thyroid gland produces a hormone called thyroxine, which increases the metabolic rate of body cells, resulting in more heat. When your body temperature increases: Peripheral and central thermoreceptors signal the hypothalamus to stop the pituitary gland from producing TSH. The production of TSH is an example of a negative feedback loop. The release of TSH is decreased then stopped if the levels of thryoxine produced are very high.

Question 28

Mechanisms of thermoregulation in humans in cold conditions

Answer 28

Shivering (repeated involuntary contractions of the skeletal muscles), generating heat. Muscles in the skin contract to make the hairs on the skin stand up. This traps heat in the layer of air between the skin and the hair, increasing the insulating effect of hair. Vasoconstriction reduced blood flow in peripheral blood vessels, keeping blood close to the core and vital organs, conserving heat. Fat-storing adipose tissue. Mitochondria in brown adipose tissue cells can release energy without producing ATP, increasing body heat (process is called uncoupled respiration).

Question 29

Mechanisms of thermoregulation in humans in warm conditions

Answer 29

Hairs on the skin lie flat. The glands in the skin secrete sweat. The evaporation of water in sweat carries heat out of the body (evaporative cooling). Vasodilation of the blood vessels close to the skin brings more blood to the surface of the body. Blood carries heat to the body surface to increase heat loss via convection and conduction.