Communication, Homeostasis and Energy Flashcards
14.1
What is the endocrine system?
It is a communication and control system in the body.
- It involves hormones instead of electrical impulses like the nervous system
14.1
What is the endocrine system made up of?
The endocrine system is made up of endocrine glands that synthesise and secrete hormones directly into blood vessels flowing through the glands
14.1
What are hormones?
Hormones are chemical messengers that are secreted into the blood, transported in the bloodstream, and detected by target cells and tissues
14.1
What are the different glands?
Pituitary gland, parathyroid glands (behind thyroid), thyroid gland, thymus, adrenal glands, pancreas, ovaries, testes
14.1
What are the adrenal glands?
- what does it have
The adrenal glands are endocrine glands. They are located just above the kidneys
- An adrenal gland has a central medulla surrounded by a cortex
14.1
What is the adrenal medulla?
- what does it produce and secrete
The medulla produces and secretes adrenaline in response to stress, pain and shock
14.1
What does the adrenal cortex produce?
- what is mineralocorticoids and glucocorticoids
The cortex produces steroid hormones from cholesterol. For example:
- mineralocorticoids - help control potassium and sodium ion concentration in blood
- glucocorticoids - help control metabolism of proteins and carbohydrates in the liver
14.2
What is the structure of the pancreas?
The pancreas is another example of an endocrine organ. It is a small organ found just below the stomach.
14.2
What is the function of the pancreas?
The hormone-secreting cells are arranged in the islets of Langerhans. These produce insulin and glucagon, hormones that control blood glucose concentration
14.2
Under a microscope, what would islets of Langerhans look like?
- what’s its tissue type and function
- lightly stained
- large, spherical clusters
- endocrine pancreas tissue type
- produce and secrete hormones
14.2
Under a microscope, what would pancreatic acini look like?
- what’s its tissue type and function
- darker stained
- small, berry-like clusters
- exocrine pancreas
- produce and secrete digestive enzymes
14.3
What is negative feedback?
Many homeostatic processes in the body are controlled by negative feedback. Negative feedback occurs when a change in conditions is detected and restored back to its normal level through a series of corrective measures
14.3
How is the control of glucose an example of negative feedback?
Insulin and glucagon are both involved in regulating blood glucose concentration through negative feedback mechanisms, tp keep it at its normal level of 90 mg per 100 cm3 blood
14.3
What is the body’s response when there is a decrease in blood glucose?
- A fall in blood glucose conc. below normal is detected by alpha cells in islets of Langerhans
- Alpha cells secrete glucagon
- Glucagon acts on liver cells to increase blood glucose concentration
- Blood glucose concentration returns to normal
14.3
What is the body’s response when there is an increase in blood glucose?
- A rise in blood glucose conc. above the normal is detected by beta cells in the islets of Langerhans
- Beta cells secrete insulin
- Insulin acts on target cells, particularly muscle and liver cells, to reduce blood glucose concentration
- Blood glucose concentration returns to normal
14.3
What is the role of insulin?
Insulin binds to receptors on the cell membrane of target cells, particularly muscle and liver cells. It reduces blood glucose concentration by:
1) causing more glucose channels to be inserted into the cell surface membrane, so increasing the uptake of glucose, especially by muscle cells
2) increasing the rate of respiration, so more glucose is used
3) activating enzymes involved in the conversion of glucose to glycogen - glycogenolysis - in muscle and liver cells
4) causing excess glucose to be converted into fat
14.3
What is the role of glucagon?
Glucagon works in the opposite way to insulin. Only liver cells have receptors for glucagon. Glucagon binds to receptors on the cell surface membranes of liver cells and raises blood glucose concentration by:
1) converting glycogen to glucose - glycogenolysis
2) converting glycerol and amino acids into glucose - gluconeogenesis
3) causing the body to use more fatty acids in respiration
14.3
What type of cells secrete insulin?
The secretion of insulin by beta cells has to be carefully controlled in response to changing concentrations of blood glucose
14.3
How is the control of insulin levels achieved?
- What are the first 3 stages
1) Beta cell surface membranes contain calcium ion channels, which are closed
2) there’re also potassium ion channels in beta cell-surface membranes, which are open. These allow potassium ions to diffuse out of cell. Cell’s inside becomes more negative, + sets up potential difference (p.d.) of -70mV across membrane
3) Under high blood glucose concentrations, glucose molecules diffuse into the cell + are quickly respired to release ATP
14.3
How is the control of insulin levels achieved?
- What are the last 3 stages
4) increase in ATP causes potassium ion channels to close. Potassium ions can’t move out of cell + p.d. Across membrane becomes less negative
5) change in p.d. Opens voltage-gated calcium ion channels to allow calcium ions to diffuse into the cell down their concentration gradient
6) calcium ions cause insulin-containing vesicles to move into, + fuse with, the cell surface membrane, releasing insulin by exocytosis
14.3
What is the role of the liver in controlling blood glucose concentration?
The liver is the site of 3 important processes in the control of blood glucose levels: glycogenesis, glycogenolysis and gluconeogenesis
- liver cells (hepatocytes) are target cells for the hormones insulin and glucagon
14.3
What is glycogenesis?
The conversion of glucose to glycogen under the influence of insulin
14.3
What is glycogenolysis?
The conversion of glycogen to glucose under the influence of glucagon
14.3
What is gluconeogenesis?
The conversion of non-carbohydrates to glucose under the influence of glucagon
