Chapter 18 - Endocrine System Flashcards
Which two body systems act together to coordinate functions of all body systems?
Nervous System
Endocrine System
How does the nervous system act on other body systems?
Generates action potentials (nerve impulses) conducted along axons of neurons that trigger the release of neurotransmitters
What is a hormone?
A mediator molecule that is released in one part of the body but regulates the activity of cells in other parts of the body
How do hormone travel throughout the body?
Hormones enter the interstitial fluid, then the blood stream
- circulating blood delivers hormones throughout the body
How does an endocrine response differ from a nervous system response?
Endocrine system is often slower
- some hormones act within seconds, others take minutes
Nervous system effects are more brief
Nervous system acts of specific muscles or glands
Endocrine system effect are much more broad
What are exocrine glands?
Glands that secrete their products into ducts that carry the secretions into body cavities
What are some examples of exocrine glands?
Sudoriferous (sweat) glands, sebaceous (oil), mucous & digestive glands
What are endocrine glands?
Glands that secrete their products into interstitial fluid surrounding the secretory cells rather than into ducts
What are some examples of endocrine glands?
Pituitary, thyroid, parathyroid, adrenal and pineal glands
What are some examples of ORGANS that secrete hormones?
Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue and placenta
What constitutes the endocrine system?
All of the endocrine glands & hormone secreting cells (organs)
What are the functions of hormones?
- Regulate chemical composition & volume of interstitial fluid
- Regulate metabolism & energy balance
- Regulate contraction of smooth & cardiac muscle fibres
- Regulate glandular secretions
- Regulate immune system activities
- Control growth & development
- Regulate operation of reproductive systems
- Help establish circadian rhythms
What is the function of hormone receptors?
Bind to specific hormones
- specific hormone affects only specific target cells b/c of hormone receptors
What is the target cell?
The cell(s) that a specific hormone will influence
What is down-regulation?
If a hormone is present in excess, the number of target-cell receptors may decrease
- makes target cells LESS SENSITIVE to the hormone
What is up-regulation?
If a hormone is deficient, the number of receptors may increase
- makes target cells MORE SENSITIVE to the hormone
What happens if a hormone is prevented from interacting with its receptors?
The hormone cannot perform its normal functions
What are circulating hormones?
Hormones that pass from the secretory cells into interstitial fluid, & then into the blood
What are local hormones?
Hormones that act on neighboring cells or on the same cell that secreted them without first entering the bloodstream
What are paracrines?
Local hormones that act on neighboring cells
What are autocrines?
Local hormones that act on the same cell that secreted them
What are the two kinds of local hormones?
- Paracrines
2. Autocrines
Which kind of hormones is inactivated quickly, which linger longer?
(Circulating vs. Local)
Local are inactivated quickly
Circulating linger in the bood
What are the two broad classes of hormones?
- Lipid-soluble hormones
2. Water-soluble hormones
What are the three kinds of lipid-soluble hormones?
- Steroid hormones
- Thyroid hormones
- Nitric oxide (NO)
Describe steroid hormones.
Each steroid hormone is unique due to the presence of different chemical groups attached at various sites on the 4 rings at the core of its structure
- small differences allow for large diversity
- derived from cholesterol
Describe thyroid hormones.
Synthesized by attaching iodine to the amino acid tyrosine
- presence of two benzene rings makes it very lipid-soluble
Describe nitric oxide (NO).
Both a hormone & a neurotransmitter
- synthesis is catalyzed by the enzyme nitric oxide synthase
What are the three kinds of water-soluble hormones?
- Amine hormones
- Peptide & protein hormones
- Eicosanoid hormones
Describe amine hormones.
Called amines b/c they retain an amino group (NH3+)
- synthesized by decarboxylating (removing a molecule of CO2) & otherwise modifying certain amino acids
Describe peptide & protein hormones.
They are amino acid polymers
- smaller peptide chains of 3-49 amino acids
- larger peptide chains of 50-200 amino acids
Describe eicosanoid hormones.
Derived from arachidonic acid, a 20-carbon fatty acid
- important local hormones
- may act as circulating hormones
What are the two major types of eicosnoid hormones?
- Prostaglandins
2. Leukotrienes
What are the three functions of transport proteins?
- Make lipid-soluble hormones temporarily water-soluble (increase solubility in blood)
- Slow passage of small hormone molecule through kidneys (slows rate of hormone loss)
- Provide a ready reserve of hormone, already present in the bloodstream
Which hormones (water-soluble or lipid-soluble) are bond to transport proteins?
Lipid-soluble
- (water-soluble hormones circulate freely in blood plasma)
What is the “free-fraction” of lipid-soluble hormones?
- 1% - 10% of lipid-soluble hormones are NOT bound to transport proteins
- diffuse out of capillaries, bind to receptors, and trigger responses
Describe the action of lipid-soluble hormones.
- Lipid-soluble hormone diffuses into cell
- Activated receptor-hormone complex alters gene expression
- Newly formed mRNA directs synthesis of specific proteins on ribosomes
- New proteins alter cell’s activity
Describe the action of water-soluble hormones.
- Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase
- Activated adenylate cyclase converts ATP to cAMP
- cAMP serves as a second messenger to activate protein kinases
- Activated protein kinases phosphorylate cellular proteins
- Millions of phosphorylated proteins cause reactions that produce physiological responses
- Phosphodiesterse inactivates cAMP
What is a first messenger?
When a water-soluble hormone binds to its receptor at the outer surface of the plasma membrane, it acts as a first messenger
What is a second messenger?
The first messenger causes production of the second messenger inside the cell
- where specific hormone-stimulated responses take place
What is cyclic AMP?
A common second messenger
What is a G protein?
Hormone receptor complex
- acts like a switch
- activates adenylate cyclase
What does adenylate cyclase do?
Converts ATP into cyclic AMP
Why can hormones that bind to plasma membrane receptors be effective at very low concentrations?
B/c they initiate a cascade or chain reaction, each step of which multiplies or amplifies the initial effect
What does the responsiveness of the target cell to a hormone depend on?
- Hormone concentration in the blood
- Abundance of the target cell’s receptors
- Influences exerted by other hormones
What is the permissive effect?
The actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone
- the second hormone is said to have a permissive effect
- without the second hormone, the first hormone is typically very weak
How does the permissive effect work?
The permissive hormone will either:
- Increase the number of receptors for the first hormone
- Promotes the synthesis of an enzyme required for the expression of the first hormone’s effect
What is the synergistic effect?
When the effect of two hormones ACTING TOGETHER is greater or more extensive than the effect of each hormone acting alone
What is the antagonistic effect?
When one hormone opposes the actions of another hormone
How is hormone secretion regulated?
- By signals from the nervous system
- By chemical changes in the blood
- By other hormones
How do most hormone regulatory systems work?
Positive or negative feedback
Negative feedback
- except for childbirth
What is the master endocrine gland?
Hypothalamus
- major link between nervous system & endocrine system
Why is the hypothalamus the master endocrine gland?
B/c it secretes several hormones that control other endocrine glands
How does the pituitary gland attach to the hypothalamus?
By the Infundibulum
What is the infundibulum?
A stalk that connects the pituitary gland to the hypothalamus
Where is the pituitary gland located?
In the hypophyseal fossa of the sella turcica of the sphenoid bone
What are the two portions of the pituitary gland called?
- Anterior pituitary (anterior lobe)
- pars distalis
- pars tuberalis
- Posterior pituitary (posterior lobe)
- pars nervosa
- infundibulum
* third section the pars intermedia atrophies during fetal development (non-existant in adults)
What does the anterior pituitary (adenohypophysis) secrete?
Secretes hormones that regulate a wide range of body activities
- from growth to reproductions
What controls the release of hormones from the anterior pituitary?
Stimulated by releasing hormones and suppressed by inhibiting hormones from the hypothalamus
How does blood flow in the hypophyseal portal system?
Blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary
What is the function of neurosecretory cells?
They synthesize the hypothalamic releasing & inhibiting hormones in their cell bodies & package hormones inside vesicles, which reach the axon terminals by axonal transport
- nerve impulses stimulate the vesicles to undergo exocytosis
What is the human growth hormone (hGH)?
Where it is secreted from?
hGH stimulates several tissues to secrete insulinlike growth factors
- hormones that stimulate general body growth & regulate aspects of metabolism
- secreted by anterior pituitary (somatotrophs)
What is GHRH?
Where is it produced?
Growth hormone-releasing hormone (somatocrinin)
- hypothalamus
- stimulated hGH
What is GHIH?
Where is it produced?
Growth hormone-inhibiting hormone (somatostatin)
- hypothalamus
- suppresses hGH & TSH
What does the thyroid-stimulating hormone (TSH) control?
Thyrotropin
Controls the secretions & other activities of the thyroid gland
- anterior pituitary
What is TRH?
Where is it produced?
Thyrotropin-releasing hormone
- hypothalamus
- stimulates TSH
What are the two types of gonadotrophins?
- Follicle-stimulating hormone (FSH)
2. Luteinizing hormone (LH)
What does FSH act on?
The gonads
- initiates development of ovarian follicles & the secretion of of estrogens
- stimulates sperm production
What does LH act on?
The gonads
- triggers ovulation, secretion of progesterone, stimulates formation of corpus leteum
- stimulates cells in testes to secrete testosterone
What is GnRH?
Where is it produced?
Gonadotropin-releasing hormone
- hypothalamus
- stimulates secretion of FSH & LH
What does prolactin (PRL) initiate?
Initiates milk production in the mammary glands
- anterior pituitary
What is PRH?
Where is it produced?
Prolactin-releasing hormone
- hypothalamus
- Stimulates secretion of PRL
What is PIH?
Where is it produced?
Prolactin-inhibiting hormone
- hypothalamus
- suppresses secretion of PRL
What does adrenocorticotropic hormone (ATCH), also known as corticotropin stimulate?
Stimulates the adrenal cortex to secrete glucocorticoids such as cortisol
- anterior pituitary
What is CRH?
Where is it produced?
Corticotropin-releasing hormone (CRH)
- hypothalamus
- stimulates secretion of ATCH & MSH