Topic 9.1 Chemical Control Flashcards
MR H GREN
M etabolism
R esponse
H omeostasis
G rowth
R eproduction
E xcretion
N utrition
Homeostasis
The maintenance of a constant internal environment.
—> Involves constant changes around an optimum point
This involves constant fluctuations in:
-temperature
-pH
-water potential
Internal coordination
All organisms have optimal conditions under which they work optimally.
-Temperature
-Water potential
-pH
-Metabolic substrate/waste concentration
External coordination
All organisms have optimal conditions under which they work optimally.
-Temperature
-Toxins or inhibitors
-Humidity
-Light intensity
Importance of homeostasis
-Changes in pH and temperature affect proteins
–> Changes can cause a reduction in the rate of reaction or denaturation
-Changes in water potential of tissue fluid or blood can cause a change in volumes of cells due to osmosis.
Control mechanism
1) Optimum- the point at which the reaction works best
2) Receptors- detects change from the optimum
3) Coordinator- links the receptor and the effector
4) Effector- muscle or gland which brings changes to return system to optimum.
Positive feedback
A fluctuation triggers changes that result in an even greater deviation from the normal level.
-Positive feedback causes the amplification of a response
-System deviates from the optimum
-Change is detected by the receptor
-A change is then produced which causes an even greater deviation from the optimum
(Eg. Sodium channels open in a membrane)
Positive Feedback example: Oxytocin and childbirth
Negative feedback
Self-regulatory mechanisms return the internal environment to optimum when there is a fluctuation.
-System deviates from the optimum
-Change is detected by the receptor
-A change is then produced which returns the system back closer to the optimum
Hormones
-Hormones are organic chemicals produces in an endocrine glands
-They travel in the blood and can be widespread or targeted
-Protein or peptide hormones examples are insulin, ADH
-Steroid hormone examples oestrogen and progesterone
Endocrine glands
Endocrine glands can be stimulated to release hormones by both nerves or other hormones
-In particular, the pituitary gland is one which often secretes hormones which affect other glands
The pituitary and the hypothalamus
-The pituitary and hypothalamus are located in the brain
-The hypothalamus often controls the pituitary gland
Neurosecretory cells 1
-The hypothalamus contain neurosecretory cells which produce secretions from the axons
-Neorsecretory cells 1, produce substances that stimulate or inhibit the release of hormone from the anterior pitiutry
-They are known as releasing factors (if they stimulate) or release-inhibiting factors (if they inhibit).
Neurosecretory cells 2
Neurosecretory cells 2 produce secretions that are stored in the posterior pituitary and released later as hormones.
Pituitary gland
Produces growth hormone, which controls growth of bones and muscles; anti diuretic hormone, which increases reabsorption of water in kidneys; and gonadotrophin which control development of ovaries and testes.
Thyroid gland
Produces thyroxine which controls rate of metabolism and rate that glucose is used up in respiration, and promotes growth.
Adrenal gland
Produces adrenaline which increases heart and breathing rate and raises blood sugar level.
Testis
Produces testosterone which controls sperm production and secondary sexual characteristics.
Pineal gland
Produces melatonin which affects reproductive development and daily cycles.
Thymus
Produces thymosin and promotes production and maturation of white blood cells
Pancreas
Produces insulin which converts excess glucose into glycogen in the liver; and glycogen, which converts glycogen back to glucose in the liver.
Ovary
Produces oestrogen, which controls ovulation and secondary sexual characteristics; and progesterone, oestrogen, which controls ovulation and secondary sexual characteristics; and progesterone, which prepares the uterus lining for receiving an embryo.
Oxytocin
-Posterior
Stimulates the muscles of the uterus to contract during labour and also stimulates the contraction of cells in the mammary tissue so that milk is squeezed out when an infant suckles.
ADH (antidiuretic hormone)
-Posterior
Decreases the urine volume by affecting the tubules of the kidney ad also causes the arteries to constrict after haemorrhage, preventing excess blood loss and raising blood pressure.
Prolactin
-Anterior
Stimulates and maintains the production of milk by the mammory glands.
Luteinising hormone (LH)
-Anterior
Stimulates ovulation and the formation of the corpus luted in females. It prepares the uterus for implantation. In males it stimulates the testes to produce testosterone.
Follicle stimulating hormone (FSH)
-Anterior
Has different effects in males and females. In females it stimulates the ovaries to produce oestrogen and also stimulates the development of ova in the menstrual cycle. In males it stimulates the testes to produce sperm.
Adrenocorticotrophic hormone (ACTH)
-Anterior
Controls secretion of some of the hormones of the adrenal cortex of the adrenal glands.
Growth hormone (GH)
-Anterior
Stimulates the growth of body cells and increases the build-up of proteins.
Hormone action
There are 2 modes of action:
1) Release of a second messenger
2) The hormone enters the cells
General stages in negative feedback
Receptors detect deviation –> coordinator –> corrective mechanism by effector –> receptors detect that conditions have returned to normal
Why is it important that blood pH remains stable?
Maintain stable rate of enzyme-controlled reactions (& optimum conditions for other proteins).
Acidic pH = H+ ions interact with H-bonds & ionic bonds in tertiary structure of enzymes –> shape of active site changes so no ES complex form.
Explain the mode of action of adrenaline
Secondary messenger model:
1) Hormone-receptor complex forms.
2) Conformational change to receptor activates G-protein.
3) Activates adenylate cyclase, which converts ATP to cyclic AMP (cAMP).
4) cAMP activates protein kinase A pathway.
5) Results in glycogenolysis.
Explain the mode of action of oestrogen
1) Steroid hormone diffuses through cell membrane
2) Forms hormone-receptor complex with ER α receptor in the cytoplasm.
3) Complex enters the nucleus & acts as transcription factor.
