Homeostasis

Question 1

Define homeostasis

Answer 1

maintenance of a constant internal environment

Homeostasis is the property of a system in which variables are regulated so that internal conditions remain stable and relatively constant

Question 2

What is controlled?

Answer 2

Temperature

Glucose

Blood oxygen

Hydrogen ion

Potassium

Question 3

Homeostasis model

Answer 3

slide 7

Question 4

set point

Answer 4

normal range of something

Question 5

control centre

Answer 5

compares what the level is to what the level should be

Question 6

Why is communication important in homeostasis?

Answer 6

Cells must communicate with each other to achieve homeostasis

There needs to be a co-ordinated response

Question 7

Major communication systems include

Answer 7

endocrine (hormones)

nervous (currents and neurotransmitters)

immune (antibodies, cytokines and interleukins)

Question 8

Autocrine system

Answer 8

Chemical is released from cell into the extracellular fluid and then acts upon the very cell that secreted it

cell sends a isgnal, signal travels to a recpetor on the same cell

Question 9

Paracrine system

Answer 9

Chemical messengers involved in the communication between cells, released into extracellular fluid - travel short distances, local communication.

-Cell sends a signal, Signal diffuses across gap between cells
-Inactivated locally, so doesn’t enter the blood stream
-Cells then reach a cell a short distance away from the original cell

Question 10

Examples of Paracrine

Answer 10

Acetylcholine at neuromuscular junction

Interleukins
-Signalling in the immune system
-Mainly between white blood cells

Platelet derived growth factor (PDGF)
-Released from platelets
-Regulates cell growth

Question 11

Endocrine system (secretion into blood):

Answer 11

Produce and secrete hormones, communication between cells, travel much longer distance, systemic communication, can affect the whole body.

Travel in the blood to then reach the target cell (which is elsewhere in the body relative to the endocrine cell)

Question 12

Endocrine organs/glands

Answer 12

Hypothalamus (hypothalamic hormones)
include: Dopamine

Pituitary (anterior pituitary hormones)
include: FSH, LH and thyroid stimulating hormone (TSH)

Posterior pituitary hormones
include: oxytocin (released during child birth)
ADH/ vasopressin) (in brain, master endocrine organs)

Master enocrine glands
-Thyroid (front of neck)
-Parathyroid (directly behind neck)
-Adrenals (above kidneys)
-Pancreas
-Ovaries
-Testes

Question 13

Definition of Hormone

Answer 13

Molecule that act as a chemical messenger

Question 14

Hormones are classified according to structure

Answer 14

Amino-acid derivatives

Peptide

Steroid

Question 15

Amino acid hormones

Answer 15

Synthesised from tyrosine

Acts in same way to peptide

Example; adrenaline, thyroid hormones (thyroxine (T4) and triiodothyronine (T3))

Question 16

Peptide hormones

Answer 16

Made of amino acids

Vary in size from few amino acids to small proteins

Some have carbohydrate side chains (glycoproteins)

Large, hydrophilic charged molecules that cannot diffuse across a membrane.

They bind to receptors on membranes.

Peptide hormone is pre-made and stored in cell, then released and dissolved into blood when needed. Binds to receptor on membrane then chemical reaction produces a quick response from the cell and a 2nd messenger is released in the cell

VERY FAST (minutes) (signal transduction cascade)

Examples; Insulin, growth hormone, thyroid stimulating hormone (TSH) and ADH/vasopressin

Question 17

Peptide and amino acid hormones similarity

Answer 17

Produce a quick reaction in the body

Question 18

Peptide Hormones- TSH

Answer 18

In the pituitary cell: Hormone pre-made and stored in cell ready to be released when needed

Hormone dissolved in blood.

Receptor on cell membrane

Chemical reaction produces quick response from cell.
(Signal transduction cascade)

Question 19

Steroid Hormones

Answer 19

All made from cholesterol
Different enzymes modify molecule to produce a variety of hormones

Hydrophobic- Can’t dissolve in water

Can dissolve in lipids

Question 20

How steroid hormones work?

Answer 20

Can cross membranes BUT requires transport proteins in blood, targets an intracellular receptor.

Steroid hormone is made by cell and diffuses out once made (not stored), transported in blood bound to transport proteins as it cannot dissolve in water.

Binds to receptor inside cell

RESPONSE (hours/days) since it directly affects DNA- SLOW

Examples; Testosterone, oestrogen and cortisol (long term stress hormone)

Question 21

Steroid hormones- testosterone

Answer 21

Testosterone made by cell and diffuses out once made in the testes through the phospholipid bilayer

Transported in blood bound to transport protein as can’t dissolve in water (a lot pf hormones have thoer own specific carrier protien)

Receptor is in the target cell

Slow response as directly affects DNA

Question 22

Positive feedback loop

Answer 22

Amplification of signal.

E.g. clotting cascade & oxytocin release during childbirth

Question 23

Negative feedback loop

Answer 23

Centre of homeostasis, main way endocrine hormones are controlled.

E.g. blood sugar regulation, temperature regulation, blood pressure regulation, thyroid regulation

• thyroxin, as well as going to target cell, is also sensed by the pituitary, if there is too much thyroxine in the blood then the high thyroxine levels will stimulate the pituitary to stop producing thyroid stimulating hormone (TSH)

Question 24

Define Exocrine

Answer 24

Secretion into ducts then into organ

Question 25

Key differences between endocrine and paracrine:

Answer 25

Hormones travel in blood in endocrine whereas in paracrine chemical messengers only travel in extracellular fluid.

Endocrine affects more things and travels further than paracrine