Chapter 18: The Endocrine System Flashcards
Nervous System vs. Endocrine System: Mediator Molecules
Nervous System: Neurotransmitters released locally in response to nerve impulses
Endocrine System: Hormones delivered to tissue throughout the body by blood.
Nervous System vs. Endocrine System: Site of Mediator Action
Nervous System: close to site of release, at synapse; binds to receptors in postsynaptic membrane
Endocrine System: far from site of release (usually); binds to receptors on or in target cells
Nervous System vs. Endocrine System: Types of Target Cells
Nervous System: muscle (smooth, cardiac, and skeletal) cells, gland cells, other neurons
Endocrine System: cells throughout the body
Nervous System vs. Endocrine System: Time to onset of action
Nervous System: typically within milliseconds (thousandths of a second)
Endocrine System: seconds to hours or days
Nervous System vs. Endocrine System: Duration of action
Nervous System: generally briefer than endocrine system (milliseconds)
Endocrine System: generally longer than nervous system (seconds to days)
Endocrine Glands
- composed of endocrine cells and tissues.
- produce and secrete hormones that move through the bloodstream to reach their target cells.
In order for a hormone to affect a target cell, a hormone must first
bind to a specific receptor
target cells
tissues that must have specific receptors to which a specific hormone binds.
List the endocrine glands
- hypothalamus (in the brain)
- pituitary gland: anterior and posterior pituitary (in the brain)
- thyroid gland (around trachea)
- parathyroid gland (on thyroid gland)
- adrenal gland: adrenal cortex and medulla (on top of kidneys)
- pancreas (tucked behind stomach)
- gonads: testes (in scrotum) and ovaries (lower abdomen)
- thymus gland (in front of the heart)
- pineal gland (in the brain)
Gastrin
- promotes secretion of gastric juice
- increases movements of the stomach
Glucose-dependent insulinotropic peptide (GIIP)
stimulates release of insulin by pancreatic beta cells
Secretin
stimulates secretion of pancreatic juice and bile
Cholecystokinin (CCK)
- stimulates secretion of pancreatic juice
- regulates release of bile from gallbladder
- causes feeling of fullness after eating
Human chorionic gonadotropin (hCG)
stimulates corpus luteum in ovary to continue production of estrogen’s and progesterone to maintain pregnancy
Estrogens and progesterone
- maintain pregnancy
- help prepare mammary glands to secrete milk
Hyman chorionic somatomammotropin (hCS)
stimulates development of mammary glands for lactation
Renin
part of reaction sequence that raises blood pressure by bringing about vasoconstriction and secretion of aldosterone
Erythropoietin (EPO)
increases rate of red blood cell formation
Calcitriol (active form of Vit D)
aids in absorption of dietary calcium and phosphorus
Atrial Natriueretic
decreases blood pressure
Leptin
- suppresses appetite
- may increase FSH and LH activity
Hormones
long distance chemical signals; travel in blood or lymph
Autocrines
chemicals that exert effects on same cells that secrete them
Paracrines
-locally acting chemicals that affect cells other than those that secrete them
What are the 3 chemical messengers?
- hormones
- autrocrines
- paracrines
Paracrines and Autrocrines are referred to as
local chemical messengers; not considered part of endocrine system
What are the 6 functions of hormones?
- Control cellular metabolism, growth and division (e.g. stimulate mitosis)
- Stimulate synthesis of enzymes &/or other proteins
- Control body fluids and electrolyte balance
- Control the secretion of other hormones
- Regulate reproductive cycles
- Regulate homeostasis by negative or positive feedback loop
What are the four types of hormones?
- Amino Acid Derivatives
- Peptide Hormones
- Lipid Derivatives
- Gas
Amino Acid Derivatives
- modified amino acid: tyrosine and tryptophan
ex) epinephrine, norepinephrine, dopamine, melatonin, histamine, serotonin, thyroid hormones (T3, and T4)
Peptide Hormones
-glycoproteins and short/small proteins
glycoproteins
- more than 200 amino acids long with carbohydrate side chains
ex) thyroid-stimulating hormone (TSH), luteinizing hormone (LH), follicle-stimulating hormone (FSH)
short/small proteins
- less than 200 amino acids
ex) antidiuretic hormone (ADH), oxytocin (OXT), growth hormone (GH), prolactin (PRL)
Lipid Derivatives
eicosanoids and steroids
eicosanoids
- derived from arachidonic acid
ex) leukotrienes, prostaglandins, thromboxanes, prostacyclins
steroids
- derived from cholesterol
ex) androgens, estrogens, progestins, corticosteroids, calcitriol
Gas Hormones
Nitric Oxide (NO): (produced by endothelial cells lining blood vessels)
Hormones act in one of 2 ways:
- Water-Soluble Hormones
2. Lipid-soluble Hormones
Water-soluble Hormones
- (all amino acid–based hormones except thyroid hormone)
- Act on plasma membrane receptors
- Act via G protein second messengers
- Cannot enter cell
Lipid-soluble Hormones
- (steroid and thyroid hormones)
- Act on intracellular receptors that directly activate genes
- Can enter cell
Steps when water-soluble hormone binds to receptor:
- binding of hormone (1st messenger) to its receptor activates G protein, which activates adenlyate cyclase
- activated adenylate cyclase converts ATP to cAMP
- cAMP serves as a 2nd messenger to activate protein kinases
- activated protein kinases phosphorylate cellular proteins
- millions of phosphorylated proteins cause reactions that produce physiological responses
- phosphodiesterase inactivates cAMP
Steps when lipid-soluble hormones binds to receptor:
- lipid-soluble hormone diffuses into cell and binds to intraccellular receptor
- the receptor-hormone complex enters the nucleus and binds to a specific DNA region
- binding initiates transcription of the gene to mRNA
- the mRNA directs protein synthesis
cAMP
- Cyclic adenosine monophosphate
- a second messenger important in many biological processes
What are the 3 stimuli that controls the release of hormones?
- humoral stimulus
- neural stimulus
- hormonal stimulus
Humoral Stimulus
hormone release caused by altered levels of certain critical ions or nutrients.
Neural Stimulus
hormone release caused by neural input
Hormonal Stimulus
hormone release caused by another hormone (a tropic hormone)
Blood levels of hormones are controlled by
negative feedback systems:
- increased hormone effects on target organs can inhibit further hormone release
- levels vary only within narrow, desirable range
What is the stimulus and response that occurs during a humoral stimulus?
Stimulus: low concentration of Ca2+ in capillary blood
Response: parathyroid glands secrete parathyroid hormone, which increases Ca2+
What is the stimulus and response that occurs during a neural stimulus?
Stimulus: action potentials in preganglionic sympathetic fibers to adrenal medulla
Response: adrenal medulla cells secrete epinephrine and norepinephrine.
What is the stimulus and response that occurs during a hormonal stimulus?
Stimulus: hormones from hypothalamus
Response: anterior pituitary gland secretes hormones that stimulate other endocrine glands to secrete hormones.
Target cell activation depends on 3 factors:
- blood levels of hormone
- relative number of receptors on/in target cell
- affinity (strength) of binding between receptor and hormone
Amount of hormone can influence the
number of receptors for that hormone
Up-regulation
target cells form more receptors or increase affinity in response to low hormone levels
Down-regulation
- target cells lose receptors or decrease affinity in response to high hormone levels
- desensitizes target cells to prevent them from overreacting to persistently high levels of hormone
Interaction of Hormones at Target Cells: 3 Types
- Permissiveness
- Synergism
- Antagonism
Permissiveness
- one hormone cannot exert its full effects without another hormone being present
ex) reproductive system development largely regulated by reproductive system hormones but need thyroid hormone for timely development of reproductive system structures
Synergism
- more than one hormone produces same effects on target cell, causing amplification
ex) glucagon and epinephrine both cause liver to release glucos
Antagonism
- one or more hormones oppose(s) action of another hormone
ex) insulin and glucagon
How does the hypothalamus regulate the internal environment through the autonomic nervous system? (4)
- helps control water balance
- controls glandular secretions
- helps control heartbeat
- helps control body temperature
What 3 ways does the hypothalamus link the nervous system and the endocrine system?
- Acts as an Endocrine Organ. Neurosecretory cells within the hypothalamus produces the hormone which then passes through the axons into the posterior pituitary where they are stored in the ends of the axon and released when needed.
- Secretes Regulatory Hormones that control the endocrine cells in the anterior pituitary.
- Exerts direct control over the endocrine cells of the adrenal gland (adrenal medulla) by means of actions potentials (sending nerve impulses, rather than through regulatory hormone