Ch.9: The Endocrine System Flashcards
The endocrine system is the _____ of the body.
- Second controlling system
* Nervous system is the fast-control system
Uses chemical messengers _____ that are released into the blood
Hormones
Hormones control which major processes?
- Reproduction
- Growth and development
- Mobilization of body defenses
- Maintenance of much of homeostasis
- Regulation of metabolism
Hormones are produced by:
Specialized cells
Cells secrete hormones into:
Extracellular fluids
Blood transfers hormones to:
- Target sites
* These hormones regulate the activity of other cells
Endocrinology is the scientific study of:
Hormones and endocrine organs
Hormones are classified chemically as:
- Amino acid-based
- Steroids
- Prostaglandins
What are steroids made from?
Cholesterol
What are prostaglandins made from?
Highly active lipids that act as local hormones
Hormones affect only what certain tissues or organs?
Target cells or target organs
Target cells must have specific:
Protein receptors
Hormone binding alters:
Cellular activity
Concept Link
A hormone’s relationship to its target cells resembles that of an enzyme to its substrate. Recall that enzymes interact very specifically with their substrates (Chapter 2, pp. 51‒52). Hormone interactions with target cell receptors are also very specific and fit together like two pieces of a puzzle.
When hormones arouse cells or alter cellular activity, typically, one or more of the following occurs:
- Change plasma membrane permeability or membrane potential by opening or closing ion channels
- Activate or inactivate enzymes
- Stimulate or inhibit cell division
- Promote or inhibit secretion of a product
- Turn on or turn off transcription of certain genes
Hormones act by what two mechanisms?
- Direct gene activation
• Used by steroid hormones and thyroid hormones - Second-messenger system
• Used by protein and peptide hormones
What is the process of direct gene activation?
- Steroid diffuse through the plasma membrane of target cells
- Once inside the cell, the hormone enters the nucleus
- Then, the hormone binds to a specific protein within the nucleus
- Hormone-receptor complex binds to specific sites on the cell’s DNA
- Certain genes are activated to transcribe messenger RNA
- New proteins are synthesized
What is the process of the second-messenger system?
- Hormone (first messenger) binds to a membrane receptor
- Activated receptor sets off a series of reactions that activates an enzyme
- Enzyme catalyzes a reaction that produces a second-messenger molecule (such as cyclic AMP, known as cAMP)
- Oversees additional intracellular changes to promote a specific response in the target cell
Hormone levels in the blood are maintained mostly by:
Negative feedback
A stimulus or low hormone levels in the blood trigger the release of more:
Hormone
Hormone release stops once an _____ in the blood is reached.
Appropriate level
The stimuli that activate endocrine glands fall into what three major categories?
Hormonal
Humoral
Neural
What is hormonal stimuli?
• Most common category of stimulus
• Endocrine organs are activated by other hormones
• Example:
*Hormones of the hypothalamus stimulate the anterior pituitary to secrete its hormones
What is humoral stimuli?
Changing blood levels of certain ions and nutrients stimulate hormone release
• Humoral indicates various body fluids, such as blood and bile
Examples:
• Parathyroid hormone and calcitonin are produced in response to changing levels of blood calcium levels
• Insulin is produced in response to changing levels of blood glucose
What is neural stimuli?
• Nerve fibers stimulate hormone release
• Most are under the control of the sympathetic nervous system
• Examples:
Sympathetic stimulation of the adrenal medulla to release epinephrine and norepinephrine
What are the major endocrine organs?
- Hypothalamus
- Pituitary gland
- Pineal gland
- Thyroid gland
- Parathyroid glands
- Thymus
- Adrenal glands
- Pancreas
- Gonads (testes and ovaries)
What are some glands that have purely endocrine functions?
- Anterior pituitary
- Thyroid
- Adrenals
- Parathyroids
- Other glands are mixed glands, with both endocrine and exocrine functions (pancreas, gonads)
Endocrine glands are _____ glands.
Ductless
Hormones are released directly into _____ or _____.
- Blood
* Lymph
What is the pituitary gland?
- Pea-sized gland that hangs by a stalk from the hypothalamus in the brain
- Protected by the sella turcica of the sphenoid bone
- Often called the “master endocrine gland”
The pituitary gland has what two functional lobes?
- Anterior pituitary—glandular tissue
* Posterior pituitary—nervous tissue
Hypothalamus produces _____ hormones and _____ hormones
- Releasing
- Inhibiting
- These hormones are released into portal circulation, which connects hypothalamus to anterior pituitary
The hypothalamus makes what two hormones?
- Oxytocin and antidiuretic hormone
* Carried to posterior pituitary via neurosecretory cells for storage
What is the function of the posterior pituitary gland?
- Does not make the hormones it releases
* Stores hormones made by the hypothalamus