2.1 homeostasis, hormones

define homeostasis

the maintenance of a constant internal environment

list the basic principles (steps) of homeostasis

change in internal environment (stimulus) → receptor + control centre → corrective mechanism → negative feedback

define and describe a hormone

a chemical substance, produced by a gland, carried by the blood, which alters the activity of one or more specific target organs.

explain what is meant by an endocrine gland

they are ductless glands that transport their secretions through the bloodstream

• the islets of Langerhans pancreas is an endocrine gland which secretes insulin and glucagon

explain the importance of maintaining a constant blood glucose level

for tissue respiration (energy)

explain how the blood glucose concentration is regulated by insulin as a homeostatic mechanism

1. Stimulus: BGC increases

2. Receptor + control centre: Islets of Langerhans detect stimulus

3. Hormone secretion (effector): Islets of Langerhans (β-cells) secrete more insulin into the bloodstream

4. Corrective mechanism:

• permeability of cell surface membrane to glucose increases, more glucose is absorbed by the cells

• respiration rate of cells increases

• liver and muscle cells absorb more glucose in the same way and converts excess glucose to glycogen for storage

5. BGC decreases

explain how the blood glucose concentration is regulated by glucagon as a homeostatic mechanism

1. Stimulus: BGC decreases

2. Receptor + control centre: Islets of Langerhans detect stimulus

3. Hormone secretion (effector): Islets of Langerhans (α-cells) secrete more glucagon into the bloodstream

4. Corrective mechanism:

• liver converts stored glycogen to glucose

• glucose enters the bloodstream

5. BGC increases

describe type 2 diabetes mellitus

target cells in the body do not respond well to insulin (body’s resistance to insulin) / insufficient production of insulin → persistently higher than normal BGC

symptoms:

• slow/difficult healing of wounds

• thirst

• weight loss

• frequent urinatino

• glucose in urine

• persistently high BGC

identify the risk factors of type 2 diabetes mellitus

• Obesity/overweight

• Age

• Family history (diabetes can be inherited)

• Unhealthy blood lipid levels

• Sedentary lifestyle

identify ways to manage type 2 diabetes mellitus

• maintain healthy body weight

• avoid being inactive for long time

• engage in more active physical activities

• eat healthily:

  • consume food low in calories and high in fibre (eg fruits & veg)

which is not a function of the liver?

1. conversion of glucose to glycogen

2. storage of glycogen

3. secretion of insulin

4. synthesis of proteins from amino acids

3. secretion of insulin (pancreas)

in the control of blood glucose level, which organs are the receptor and effector?

B) receptor: pancreas | effector: liver

compare and contrast the nervous and endocrine systems (control) — (also under nervous system)

• endocrine involves hormones as signals; nervous involves nerve impulses as signals

• endocrine — hormones are transported by blood; nervous — nerve impulses are transmitted by neurones

• endocrine — usually slow responses; nervous — usually quick responses

• endocrine — always involuntary; nervous — may be voluntary / involuntary

• endocrine — may affect more than one target organ; nervous — usually localised