Chapter 16- The endocrine system Flashcards
Hormones
Long distance chemical messengers that cause a change in metabolic activity of a cell. Effects are usually long lasting and are diverse
What factors do hormones control (4)
- Reproduction- gametes
- Growth and development- bone growth, mitotic activity, etc.
- Immune system activation- when pathogens get in
- Maintenance of various blood components (glucose, electrolytes, water, etc.).
Autocrine
Short distance chemical messengers- affect the same cells that secrete the messenger
Paracrine
Short distance chemical messengers- affect different cells that secrete the messenger in the same tissue
What does the chemical structure of hormones determine? (3)
Chemical structure determines longevity, transport in blood, and receptivity
Two major classifications of hormones
- Amino acid based
2. Steroids
Amino acid based hormones
Molecular size varies- amino acid derivatives, peptides, proteins. Epinephrine is an example of an amino acid derivative. Water soluble- can circulate without a carrier (chaperone to get to target cells/tissues). This is because blood is water based.
Steroid hormones
Synthesized from cholesterol. Lipid soluble- circulate with a carrier molecule. Can pass straight through the membrane of the target cell
What are the only steroid hormones in the body?
Gonadal hormones and adrenocortical hormones are the only steroid hormones in the body
Hormones can only affect a cell if
Hormones can only affect target cells with appropriate receptors. Different receptors= different response
Changes produced by hormone binding (5)
- Altering plasma membrane permeability or membrane potential, caused when ion channels open
- Stimulates synthesis of enzymes/proteins inside cell
- Activates/deactivates enzymes
- Induces sensory activity
- Stimulates mitosis
Two mechanisms of hormone action
- Second messenger systems
2. Intracellular systems
Second messenger systems
Uses receptors found on surface of plasma membrane. A ligand (hormone in this case) binds to a receptor, which then activates the G-protein inside the cell. The G-protein activates intracellular second messenger- causes response in cell. This is extremely efficient- a single hormone binding a receptor results in millions of product molecules being produced
Mechanism of action for amino acid based hormones
Second messenger systems
Intracellular systems
Hormone enters cell, binds to intracellular receptors. Receptor hormone complex- binds specific regions of DNA- DNA transcription occurs. Effect- certain proteins produced in larger numbers
Intracellular systems steps (5)
- The steroid hormone diffuses through the plasma membrane and binds an intracellular receptor
- The receptor hormone complex enters the nucleus
- The receptor hormone complex binds a specific DNA region
- Binding initiates transcription of the gene to mRNA
- The mRNA directs protein synthesis
How is hormone synthesis and release controlled?
Hormone synthesis and release is controlled by negative feedback mechanisms. Importance- hormone levels need to be precisely regulated. If we produce too much or too little, homeostatic imbalances would result very quickly.
Stimulus mechanisms for hormone release (3)
- Humoral stimuli
- Neural stimuli
- Hormonal stimuli
Humoral stimuli
Changing blood levels of critical ions and nutrients. Ex- monitoring calcium levels by the parathyroid gland
Neural stimuli
Nerve fibers stimulate hormone release, this is infrequent. Ex- norepinephrine and epinephrine release by sympathetic nervous system
Hormonal stimuli
Hormone released in response to other hormones. Ex- hypothalamic hormones stimulate or inhibit anterior pituitary gland
Target cells only respond to a hormone if
It has a specific receptor protein for that hormone. Can be specific (only cells of a certain tissue) or broad (all body cells)
Hormone activation of a cell depends on
- Blood levels of hormone
- Number of receptors for specific hormone on/in cell
- Affinity of receptor to hormone
Up regulation
Increased receptor number in response to low hormone levels. This increases the sensitivity of the receptors to the hormone, so the receptors are more likely to respond.
Down regulation
Decreased receptor number in response to high hormone levels
Hormone concentration in the blood depends on (2)
- How fast it is being released by endocrine organ
2. How fast it is broken down by the body
Which organs remove hormones?
Kidneys, liver. Hormones are circulated through the blood, so they must be broken down that way too.
What type of hormones have the shortest half life?
Water soluble hormones (amino acid based)
Duration of hormone effects on the target cell
Hormone effect is not always immediate- effects seen after hours or days. Some hormones must be activated before binding can occur, and the duration of the effect varies.
What happens if a hormone isn’t activated?
If the hormone isn’t activated, it will not bind regardless of how much of the hormone is released.
Importance of the variation of hormone effects
Importance- variation of effects= strict control of hormone release. Effects can disappear as levels drop or can persist for hours after levels drop
Hormones binding on the same target cell at the same time may result in (3)
- Permissiveness
- Synergism
- Antagonism
Permissiveness
One hormone cannot have full effect without binding of a second specific hormone. Lack of the second hormone may relay or completely inhibit effects of first
Synergism
2+ hormones with similar effects bind target cell- amplification occurs. Not the same as positive feedback the response- doesn’t fly out of control
Antagonism
One hormone opposes the effect of another- hormones can compete for the same receptor, act through different metabolic pathways, or they can down-regulate the receptor of another hormone
How is the pituitary gland connected to the hypothalamus?
By the infundibulum
Two regions of the pituitary gland
- Anterior pituitary
2. Posterior pituitary
Anterior pituitary
Manufactures and releases several different hormones
Posterior pituitary
Composed mostly of neural tissue and nerve fibers. Releases neurohormones received from hypothalamus
How is the release of hormones from the pituitary controlled by the hypothalamus? (1 of 2)
- Action potentials from the hypothalamus cause hormone release from axon terminals in the posterior pituitary
- Hypothalamic hormones released into the hypophyseal portal system- stimulate or inhibit hormone release from the anterior pituitary
Posterior pituitary and hypothalamic hormones (2)
- Oxytocin
2. Antidiuretic hormone (ADH)
Oxytocin functions
Functions- stimulant for uterine contraction, “cuddle hormone”. Neurotransmitter in brain- promotes nurturing, couple bonding, trust, affectionate behavior. Also stimulates milk producing glands to contract during breastfeeding
What stimulates the posterior pituitary to release oxytocin during childbirth?
Stretching of cervix during childbirth sends afferent impulses to the hypothalamus- stimulates posterior pituitary to release hormone. Release increases as labor progresses, stops soon after birth. Speeds up labor overall
ADH function
Function- prevents formation of urine by the kidneys- the kidneys reabsorb more water
Importance- prevents dehydration or water overload
What are the stimuli for ADH release?
Osmoreceptors in hypothalamus monitor solute concentration. If the solute concentration is high- release ADH. If it’s low- prevent ADH release. Other stimuli for ADH release includes pain, low blood pressure, some drugs (nicotine, morphine, barbiturates)
Tropins
Hormones that affect the activity of another endocrine gland. 4/6 of the anterior pituitary hormones are tropins. The anterior pituitary is not considered the master endocrine gland because it is controlled by the hypothalamus, however.
Anterior pituitary hormones (6)
- Growth hormone
- Thyroid stimulating hormone
- Adrenocorticotropic hormone (ACTH)
- Follicle Stimulating hormone (gonadotropin)
- Luteinizing hormone (gonadotropin)
- Prolactin
Growth hormone general function
Aids in metabolic and growth promoting actions
Growth hormone metabolic effects (3)
- Decreases glucose uptake by cells- anti insulin effect
- Mobilizes fat stores- binds to adipocytes- releases fatty acids to blood
- Increases amino acid uptake by cells
Growth hormone growth effects
Liver, bone, skeletal muscle, etc. produce insulin-like growth factor (IGF) in presence of growth hormone
How do IGFs stimulate growth? (3)
- Increase nutrient uptake by tissue
- Increases mitotic activity
- Formation of collagen fibers and deposition of bone matrix (osteoid), allows for bone growth
Too much or too little growth hormone can result in
Gigantism or dwarfism
Release of growth hormone is controlled by
Growth hormone releasing hormone (GHRH) or growth hormone inhibiting hormone (GHIH).
Thyroid stimulating hormone (TSH) function
Stimulates development and secretory activity of the thyroid gland.
What hormone stimulates TSH release?
Thyrotropin releasing hormone
Adrenocorticotropic hormone (ACTH) function
Stimulates adrenal cortex to release hormones
What hormone stimulates ACTH release?
Corticotropin-releasing hormone
What 2 hormones are gonadotropins?
Luteinizing hormone (LH) and follicle stimulating hormone (FSH)
FSH function
Stimulates production of gametes
LH function
Stimulates production of gonadal hormones (estrogen, progesterone)
What hormone stimulates the release of LH and FSH?
Gonadotropin releasing hormone (GRH) stimulates release of FSH and LH, rising gonadal hormone blood levels inhibit release
Gonadotropins are only released after
Puberty
Prolactin function
Stimulates milk production in breast tissue in XX individuals, function is unclear in XY individuals.
What stimulates the release of prolactin?
Release controlled by dopamine- inhibitory hormone. PRL release increases substantially toward the end of pregnancy. Levels of PRL also rise and fall in tandem with blood estrogens- rising estrogen stimulates PRL release
Functions of the thyroid gland
Produces, secretes, and stores hormones (extracellularly). Stores about a 3 month supply of hormones. Also produces produces thyroid hormone (TH)- major metabolic hormone
What 2 hormones make up thyroid hormone?
Thyroxine (T4) and triiodothyronine (T3)
Production of TH depends on the presence of
Iodine
Affects of TH on body cells (3)
- Increases metabolic rate and body heat production
- Regulates tissue growth/development
- Maintains blood pressure- increases the number of adrenergic receptors on blood vessel walls.
Parathyroid gland
Secretes parathyroid hormone (PTH)
PTH function
Controls calcium balance in the blood- calcium homeostasis
What stimulates PTH release?
Falling blood calcium levels
How does PTH increase calcium levels in the blood? (3)
- Stimulates osteoclasts to increase bone degradation- increasing calcium release to blood
- Enhances calcium reabsorption by the kidneys- the kidneys reabsorb calcium ions
- Activates vitamin D- increases absorption of calcium from the digestive tract. Need vitamin D to absorb calcium in the digestive tract
Hyperparathyroidism cause
Usually a parathyroid tumor
What is the effect of hyperparathyroidism?
Calcium is leached from the bones. Osteoclasts go into overdrive and osteoblasts can’t keep up. The bone is replaced by fibrous connective tissue, which is tough, but not as tough as bone. Therefore, bones can fracture spontaneously. There is also excess calcium in the blood.
What are the effects of excess calcium in the blood (as a result of hyperparathyroidism)? (2)
- Depress the nervous system- abnormal reflexes and weak skeletal muscle contraction
- Calcium crystalizes and forms salts in kidneys- kidney stones
Causes of hypoparathyroidism
Trauma to parathyroid glands (attached to the back of the thyroid glands) or removal of parathyroid glands. If you have a tumor and the thyroid gland is removed, the parathyroid glands are removed with it.
Effects of hypoparathyroidism
Low blood calcium. This results in highly excitable neurons- tetany (unwanted, hard skeletal muscle contraction), tingling, convulsions, coma. If untreated- respiratory paralysis, death
Location of adrenal glands
One on top of each kidney
Function of adrenal glands
Stress response, electrolyte balance
Regions of the adrenal gland
Two areas, each functions as different gland. The adrenal cortex is the outermost region and the adrenal medulla is the innermost region.
3 subdivisions of the adrenal cortex
- Zona glomerulosa- produce mineralocorticosteroids
- Zona fasciculata- produce glucocorticoid
- Zona reticularis- produce adrenal sex hormones
Function of the adrenal cortex
Produces corticosteroids
Glucocorticoids
Specific types- cortisol, cortisone, corticosterone- we are most concerned with cortisol. We release periodic bursts of cortisol throughout the day. Cortisol is a stress hormone- “fight or flight”- CNS overrides normal release mechanism in these situations
Effects of glucocorticoids (2)
- Want glucose available in stressful situations
2. SNS- vasoconstriction
Excessive release of glucocorticoids causes (3)
- Depressed cartilage and bone formation
- Inhibits inflammation and depresses the immune system overall- more susceptible to infection
- Disrupts normal cardiovascular, neural, GI functions if excessive release occurs over a long period of time
Gonadocorticoids
Small amounts of androgens released. Some converted to testosterone, others converted to estrogen. The amount produced is insignificant to the amount produced by gonads.
Effects of gonadocorticoids (2)
- Contribute to axillary and pubic hair development
2. Women- contributes to sex drive, produce estrogens post menopause
What hormones are secreted by the adrenal medulla?
Epinephrine and norepinephrine. Unequal amounts are stored and released. 80% is epinephrine, 20% is norepinephrine.
Epinephrine function
Greater influence on metabolic activity, dilator of airways in lungs. This is the treatment for people with asthma or anaphylaxis.
Norepinephrine function
Greater influence on peripheral vasoconstriction, blood pressure
What initiates the release of epinephrine and NE?
Release is initiated by sympathetic nervous system- this is short lived. Hormones are not essential- the sympathetic nervous system will work without adrenal medulla hormones. However, excessive secretion is problematic- long term “fight or flight” symptoms
Pineal gland function
Secretes melatonin
Melatonin function
Regulates night day cycles, sleeping schedule
What controls the release of melatonin?
Release controlled indirectly by visual pathways- intensity and duration of sunlight
The pancreas
Also an exocrine gland, largest dual gland in the body. Hormones are produced in pancreatic islets. Function- controls blood sugar levels
Hormones secreted by the pancreas
- Insulin
2. Glucagon
Glucagon
Produced by the alpha cells of the pancreas. Glucagon has a hyperglycemic effect- causes an increase in blood sugar. It stimulates the liver to break down glycogen, convert non-carbohydrate molecules to glucose, and release glucose from liver cells
What controls the release of glucagon?
Dropping blood sugar levels
Insulin
Produced by beta cells of the pancreas. Hypoglycemic effect- causes a decrease in blood glucose levels. It increases glucose uptake by body cells, inhibits glycogen breakdown, and inhibits conversion of non-carbohydrate molecules to glucose
What causes insulin release? (4)
- Elevated blood glucose
- Rising blood levels of amino acids and fats
- Acetylcholine release from parasympathetic division
- Any hyperglycemic hormone
Diabetes mellitus
Inadequate (or absent) release of insulin by pancreas. Effect- consistently high blood sugar levels
Normal blood sugar levels
90-110 mg glucose/dl blood
Type 1 diabetes
Autoimmune condition- no insulin released. Individual’s WBCs see beta cells as foreign cells so they are destroyed. Do not produce insulin at all. Several genes contribute to this condition
Type 1 diabetes treatment
Treatment- insulin shots before meals, or continuous fusion pumps
What long term issues can be caused by type 1 diabetes?
Development of vascular and neural problems if not taking the correct amount of insulin as needed. A large amount of glucose is circulating through the blood and will stick to the inside of the blood vessels
Type 2 diabetes
Insulin resistance- insulin released, but cells do not respond. The pancreas is fine, they are producing normal amounts of insulin. Correlated more with lifestyle- there is some genetic component, but almost all patients are overweight and underactive. Similar complications to type 1 diabetes
Treatment for type 2 diabetes
Can be managed by diet and exercise
What hormones do the gonads produce?
In females, the ovaries produce estrogen and progesterone. In males, the testes produce testosterone.
Estrogen function
Maturation of reproductive organs, appearance of secondary sex characteristics
Progesterone function
Breast development, cyclic changes in uterine mucosa (mucosa is necessary for implantation of a fertilized egg).
Testosterone function
Maturation and maintenance of reproductive organs, appearance of secondary sex characteristics, sex drive, normal sperm production
Placenta
Only temporary endocrine organ. Produces estrogens, progesterone, human chorionic gonadotropin (hCG)
hCG function
hCG is only produced and released during pregnancy. Function- maintains pregnancy
What hormone does adipose tissue release?
Releases leptin.
Leptin function
Function- alerts brain as to how much body fat is being stored- influences hunger and satiety, energy expenditure. The more leptin released, the higher the body fat percentage and the less hungry the person feels
Atrial natriuretic peptide (ANP)
Released by the heart. Function- decreases blood volume- blood pressure drops. This occurs because the kidneys put more water into urine. Has the exact opposite effect of antidiuretic hormone (it is a diuretic hormone)
What hormones are released by the kidneys?
Erythropoietin and renin
Erythropoietin function
Stimulates blood cell formation in red bone marrow
Renin function
Increases blood pressure
Thymus function
Gland that releases several types of peptide hormones. Function- promotes normal and timely development of white blood cell T-lymphocyte
