Control Mechanisms 1: Hormones

Biology 5b with Chappel at University of California - Riverside

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By: michelle cruz
Created: 2011-02-04
Size: 18 flashcards
Views: 11

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Hormones

-Substances produced in one body region that

have effects in some other region: chemical messengers

Examples of animal hormones

• Endocrine hormones: produced in specialized endocrine (‘ductless’) glands, distributed in blood

• Neurotransmitters, neurohormones: released from nerve cells directly onto other cells (neurotransmitters) or into blood (neurohormones)

• “local messengers:” not produced in specialized glands; tend to have local effects on nearby cells -- paracrine signaling (histamines, prostaglandins, nitrous oxide, cytokines, etc.)

Pheromones

-chemical messengers that mediate interactions between individuals

-produced by one individual, change the behavior or physiology of other individual

Examples of Pheromones in animals

• species recognition

• group recognition

• territory marking

• navigation

• social interactions (aggression, cooperation, alarm, etc.)

• reproduction (sex recognition, attractants, receptivity indication, fertility control, etc.)

• parent offspring interactions

Hormone Functions

• Homeostatic regulation, especially blood-born substances (aldosterone, vasopressin, insulin, glucagon, leptin)

• Emergency responses ("fight or flight"), in concert with the nervous system to prepare for emergencies (epinephrine)

• Development, growth, maturation (growth hormones in vertebrates; molting hormones in arthropods)

Hormone Functions (cont.)

• Reproduction: maturation and functioning of gonads and other reproductive organs, secondary sexual characteristics, reproductive and parental behavior (testosterone, estrogens, progesterone, prolactin, oxytocin...)

• Biological rhythms, including circadian, monthly, or annual rhythms. These are often mediated by hormone activity (melatonin, etc. )

Three Basic Classes of Hormone Chemistry

• proteins or short polypeptides

• modified amino acids
• lipid-derived hormones

Proteins/Short Polypeptides

5-100 amino acids (e.g. insulin, growth hormone, vasopressin, endorphins, leptin) or glycoproteins (FSH, lutenizing hormone). A few amino acid substitutions can produce hormones with very different effects (e.g., oxytocin and vasopressin).

Modified Amino Acids

Amine hormones, such as catecholamines (epinephrine, norepinephrine), histamine, melatonin, serotonin, thyroid hormone (contains iodine)

Lipid-Derived Hormones

steroids: corticosteroids involved in homeostasis and stress responses (aldosterone, corticosterone, cortisol) and sex hormones that affect primary and secondary sexual characteristics (testosterone, estrogens; often chemically similar). Prostaglandins are chemically different but also lipid based.

Mechanisms of Hormone Function

Hormonal function involves reception, signal transduction, and response.

Reception

requires binding of hormone to a receptor protein :

• like enzymes binding substrates

• can be on cell surface or in the cytoplasm or nucleus

• different receptors for the same hormone may produce different responses, as for epinephrine:

• dilation of blood vessels with beta receptors (skeletal muscle)
• contraction of blood vessels with alpha receptors (intestine)
• glycogen breakdown in liver cells with beta receptors

Signal Transduction

‘carry’ message to effectors that produce the response.

Hormones influence their target cells in two general ways

1) Change the activity of existing proteins, transporters, etc. -This is the mode of action for most peptide hormones and amine hormones; fairly fast.
2) Change the rate of synthesis of proteins -This is the mode of action for many steroid hormones (& thyroid hormone); slower than cytoplasmic signal transduction mechanisms.

In many regulatory mechanisms mediated by hormones, there are multiple levels of feedback:

• sensing the status of the parameter of interest -- blood glucose, blood pressure, osmolarity, etc.

• sensing the levels of the hormones themselves.

Control of Sex Hormone Production

-Hypothalamus makes releasing factors .

-Releasing factors stimulate pituitary.

-Pituitary gonadotropins stimulate gonads.

-Gonads produce sex hormones.

Sex Hormone Production (cont)

-Gonadotropins may have some systemic effects.
-Sex hormones have negative feedbac on pituitary and on hypothalamus

-Gonadotropins also feed back on hypothalamic production of RFs

How do negative feedback loops maintain constant level of sex hormones when sex hormones arent constant?

- ADDITIONAL inputs to the hypothalamic regulatory center - set point adjustments• maturation
• social situation
• biological clock
• photoperiod
• food supply
• body condition

About this deck

By: michelle cruz
Created: 2011-02-04
Size: 18 flashcards
Views: 11

About StudyBlue

“I have been getting MUCH better grades on all my tests for school. Flash cards, notes, and quizzes are great on here. Thanks!”
Kathy