Science as a Human Endeavor Flashcards
Chp 2
Homeostasis
Homeostasis is maintaining a stable internal environment despite fluctuations in the external environment.
Endocrine
Secrete hormones into the extracellular fluid that surrounds the cells that make up the gland. Secretion passes into the capillaries to be transported by the blood. Ductless glands.
Exocrine
Secrete into a duct that carries the secretion to the body surface or to a body cavity. (sweat glands, mucous glands, salivary glands)
Characteristics of Hormones
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Chemicals secreted by endocrine glands. Transported via bloodstream. Produced in very small quantities. Alter the activity and concentration of enzymes.
Hormone Receptors
Specific – each type of receptor will bind with only 1 specific molecule.
’Lock and Key’ model.
A limited no. of receptor proteins in the membrane of each cell. Once all the receptor molecules are occupied the addition of more hormones does not produce any greater effect = SATURATION
Hormone Clearance
Hormones must be ‘turned off’ once the hormone has produced its desired effect. Hormone molecule is broken down in the target cell or the liver or kidneys – excreted in either bile or urine.
Enzyme Amplification
1 hormone molecule activates thousands of enzyme molecules.
The CASCADING EFFECT in which the no. of reacting molecules involved is increased by hundreds or thousands of times for each step.
A very small stimulus can provide a large effect.
1 hormone molecule could trigger the production of more than a billion enzyme molecules.
How do steroids affect cells?
LIPID SOLUBLE
=> Slow to have an effect
=> Long Lasting
- Hormone diffuses ACROSS the cell membrane
- Hormone attaches to a receptor located in the cytoplasm to form a hormone-receptor complex.
- The hormone-receptor complex passes through the nuclear membrane and binds to DNA.
- Effects expression of genes and thereby protein synthesis. (Stimulating or inhibiting transcription and protein synthesis.)
How do amine (protein) hormones affect cells?
WATER SOLUBLE
=> Quick to have an effect
=> Short lasting
- Attaches to receptor proteins on the cell membrane of the target cell.
- A secondary membrane is activated and diffuses through cytoplasm to attach to a cell organelle/ribosome.
- The activity of the organelle/ribosome is affected by the secondary messenger. (activates enzymes)
Hypothalamus Location + Purpose
Located at the base of the brain, below the thalamus and above Pit Gland.
=> Secretes releasing factors (stimulate secretion of a hormone) or inhibiting factors (slow down secretion of hormones)
=> Factors travel through blood vessels to APG, while hormones produced by the hypothalamus pass along the nerve fibres to PPG and are released.
=> Regulates homeostasis - temp, water balance, and heart rate, as well as increasing and decreasing the secretions of other glands.
Pituitary Gland Location + Purpose
Located under the hypothalamus and joined by a stalk called the infundibulum. APG is connected to a complex network of blood vessels lying in the infundibulum. PPG is joined by nerve fibres that come from nerve cell bodies. Not a true endocrine gland = DOESN’T secrete substances, only stores and releases.
Relationship between the Hypothalamus and the Anterior Pituitary.
- The APG is under the hormonal control of the hypothalamus.
- The hypothalamus produces releasing factors
- Travels through the blood, the blood vessels and capillary network
- To the APG
- Cause APG to produce and release hormones.
Relationship between the Hypothalamus and the Posterior Pituitary.
- PPG is under the nervous control of the Hypothalamus
- Hormones made in the hypothalamus pass long cell extensions (cell bodied of secretory cells in the hypothalamus) to the PPG
- Neurosecretory cells in the hypothalamus produce and transport it along axons.
- Where hormones are stored and released into the bloodstream
