Homeostasis Flashcards
Describe positive feedback
Levels change from normal Receptors detect change Communication (nervous or hormone) Effectors respond CHANGE IS AMPLIFIED
What is homeostasis?
The maintenance of a constant internal environment - keeps internal environment roughly constant (fluctuates around a certain level)
What is an ectotherm?
An organism that CANT control their body temperature internally
They change their behaviour to warm up or cool down
Their metabolism etc. depends on external temp
What is an endotherm?
An organism that CAN control their behaviour internally
Their metabolism is constantly high
Generate a lot of heat
Active at any temp
What is the hypothalamus and what is it involved in?
This part of the brain maintains body temp.
It receives information about temperature from thermoreceptors
Why must body temp be controlled?
Enzymes in body, in metabolism only work efficiently around 37oC
What temperature does the human body fluctuate around?
37oC
Give some ways of warming up
Hairs stand on end (layer of air)
Shiver
Why does blood glucose levels need to be controlled?
Too high = water potential of blood becomes too low! water diffuses out of cells via osmosis
Too low = cells cannot carry out their functions
Describe what happens when glucose levels are too high
Beta cells detect high concentration
Secrete hormone insulin into blood
Binds to receptor molecules on body cells (liver, muscle)
Increases membranes permeability to glucose
Liver contains insulin receptors - stimulates conversion of glucose to glycogen and glucose to fat
Glycogen can then be stored
Levels decrease
Describe what happens when blood glucose levels are too low
Low concentration detected by alpha cells
These secrete glucagon into the blood
Glucagon binds to receptors on liver cells
Activates enzymes that break down glycogen to glucose and amino acids
Also conversion of glycerol to glucose
What are islets of langerhams?
Cluster of cells in the pancreas that contain beta and alpha cells
What is glycogenesis?
Conversion of glucose to glycogen
What is gluconeogenesis?
Conversion of glycerol and amino acids into glucose
What is glycogenolysis?
Conversion of glycogen to glucose
What stimulates glycogenesis?
Activated by insulin
Or adrenaline
What stimulates gluconeogenesis?
Activated by glucagon
What stimulates glycogenolysis?
Activated by glucagon
What is adrenaline?
Protein based hormone secreted by your adrenal glands
It’s released when blood glucose concentrations are low.
Describe how adrenaline works
Binds to receptors on cell membranes forming a hormone-receptor complex - known as FIRST MESSENGER
Activates a protein that in tuen activates ADENYLATE CYCLASE (enzyme in the membrane)
This enzyme catalyses the conversion of ATP into CYCLIC AMP (this is the SECOND MESSENGER)
Camp causes a chain of reaction that eventually leads to an enzyme breaking down glycogen to glucose
What process over all does adrenaline activate to increase glucose levels in the blood?
Glycogenolysis - breakdown of glycogen into glucose
What is type 1 diabetes?
Beta cells don’t produce any insulin
What is type 2 diabetes?
Beta cells don’t produce enough insulin or cells don’t respond to insulin
What does FSH stimulate?
Stimulates the follicle to develop
What doe LH do?
Stimulates ovulation and the corpus luteum to develop from the follicle
What does oestrogen do?
Stimulates the uterus lining to thicken
What does progesterone do?
Maintains uterus lining
Where is oestrogen and progressed one secreted from?
The ovaries
Where are FSH and LH secreted from?
The anterior pituitary gland
What is a follicle?
An egg and it’s surrounding protective cells, developing in the ovary
What is ouvulation?
An egg being released
What is a corpus luteum?
A structure that forms from the remains of the follicle
What is menstruation?
If no fertilisation occurs, the uterus lining breaks down and leaves the body through the vagina
What occurs in the first stage of the mensteral cycle as the follicle develops?
Follicle develops
Releases oestrogen
Oestrogen stimulates uterus lining to thicken
Oestrogen inhibits FSH being released
So after follicle has developed, neg feedback keeps FSH conc low so no more follicles can develop
What happens in stage two of the menstrual cycle around day 14?
Ovulation occurs
Oestrogen rises to a high level.
Oestrogen no longer inhibits FSH production but instead stimulates the release of FSH and LH
LH stimulates the release of more oestrogen
Positive feedback means both of these hormone concentrations rise
Surge in LH concentration causes ovulation.
The follicle ruptures releasing the egg
What occurs in stage three of menstruation after ovulation has occurred?
LH stimulates ruptured follicle to turn into a corpus luteum
This releases progesterone so it’s conc rises
Prog. Inhibits the release of FSH and LH from the anterior pituitary gland so the conc of these fall
Uterus lining is maintained by progesterone
Negative feedback make sure no more follicle develop
If no embryo implants, corpus luteum breaks down and Prog. Is not released.
This means FSH and LH levels rise and so the uterus lining breaks down and the cycle begins again
What things signal ovulation is occurring?
LH surges
Oestrogen levels increase
Progesterone soon after is being released
Describe negative feedback
Levels change from the normal, Receptors detect change Communication (hormonal or nervous) Effectors respond Levels GO BACK TO NORMAL
