Endocrine system

Question 1

Hormone

Answer 1

A hormone (hormon 􏰔 to excite or get moving) is a mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body

Question 2

Exocrine glands

Answer 2

secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ,

Question 3

Endocrine glands

Answer 3

secrete their products (hormones) into the in- terstitial fluid surrounding the secretory cells rather than into ducts. From the interstitial fluid, hormones diffuse into blood capillaries and blood carries them to target cells throughout the body.

Question 4

Endocrine glands

Answer 4

The endocrine glands include the pituitary, thyroid, parathy- roid, adrenal, and pineal glands

Question 5

Upregulation

Answer 5

If the quantity of a hormone is deficient the number of receptors may increase

Question 6

Downregulation

Answer 6

Too much of an hormone causes the number of target cell receptors to decrease

Question 7

Paracrine

Answer 7

These are a type of local hormones that act on neighbouring cells

Question 8

Autocrine

Answer 8

These hormones act on the same cell that secreted them

These inactivate quickly

Question 9

Two types of hormones

Answer 9

• Lipid soluble

* Water soluble

Question 10

Lipid soluble hormones

Answer 10

• Steroid hormone - derived from cholesterol
• Thyroid hormone
• Nitric oxide gas

Question 11

Water soluble hormones

Answer 11

• Catecholamines (amine hormones)

* Peptide hormones

Question 12

Lipid soluble hormones in blood

Answer 12

lipid-soluble hormone molecules are bound to trans- port proteins. The transport proteins, which are synthesized by cells in the liver, have three functions:

1. They make lipid-soluble hormones temporarily water-soluble, thus increasing their solubility in blood.
2. They retard passage of small hormone molecules through the filtering mechanism in the kidneys, thus slowing the rate of hormone loss in the urine.
3. They provide a ready reserve of hormone, already present in the bloodstream.

Question 13

The function of the human endocrine system

Answer 13

Maintain homeostasis e.g. insulin and glucagon maintain the blood glucose level within tight limits - irrespective of food intake.
Respond to a wide variety of external stimuli - such as the use of adrenaline and noradrenaline in the preparation for ‘fight or flight’.
Follow various cyclic and developmental programs – sex hormones regulate sexual differentiation, maturation, the menstrual cycle and pregnancy

Question 14

Types of hormones

Answer 14

• Catecholamines - produced by the adrenal glands such as adrenaline and noradrenaline
• Peptide - insulin & parathyroid hormone
• Steroid - cortisol / sex steroid and vitamin D

Question 15

Classes of steroids

Answer 15

• Corticosteroids - released by the adrenal cortex

* Sex steroids - made by the gonads

Question 16

Coticosteroid classes

Answer 16

• Glucocorticoids - a class of corticosteroids involved in regulation of glucose metabolism
• Mineralcorticoids - a class of corticosteroids which influence the salt and water balance

Question 17

Hormones with extracellur receptors

Answer 17

Hormones which are not lipid soluble therefore cannot diffuse into the plasma membrane.
Only for water soluble hormones

Question 18

Function of water soluble hormone

Answer 18

• The hormone binds to receptor on the surface of the plasma membrane and acts as the first messenger
• The hormone receptor complex activates a membrane protein called a G protein
• The activated G protein in turn activates adenylate cyclase
• Adenylate cyclase converts ATP into cyclic AMP because the enzyme’s active site is on the inner surface of the plasma membrane.
• This reaction occurs in the inner cytosol of the cell
• Cyclic AMP (the second messenger) activates one or more protein kinases.
• The donor of the phosphate group is ATP which is converted into ADP
• Activated protein kinases phosphorylate one or more cellular proteins.
• Phosphorylation activates some of these proteins and inactivates others.
• Phosphorylated proteins in turn cause reactions which produce different physiological responses
• Different protein kinases exist within different target cells and within different organelle.
• Phosphorylisation of protein kinase may also inhibit certain proteins.

Question 19

Function of lipid soluble hormone

Answer 19

A lipid soluble hormone diffuses from the blood and through the lipid bilayer of the plasma membrane into a cell
• The hormone binds to and activates the receptors located within the cytossol or nucleus.
• The activated receptor - hormone complex then alters gene expression : it turns specific genes of the nuclear DNA on or off
• As the DNA is transcribed , new mRNA forms and leaves the nucleus and enters the cytosol
• There it directly synthesising a new protein, often an enzyme on the ribosome
• The new proteins alter the cell’s activity and cause responses typical of that hormone.

Question 20

Circadian / Diurnal rhythm

Answer 20

This is the daily cycle of biological activity based on a 24-hour period.

Question 21

Melatonin

Answer 21

• Secreted by the pineal gland
• Helps regulate biological rhythm
• Melatonin does not induce sleep / it promotes sleep and good nights rest