ANAT chapter 16: The Endocrine system Flashcards
The Endocrine system
- Secretes various hormones
Hormones: long-distance chemical messengers that cause a change in metabolic activity of a cell - Effects are usually long-lasting
- What is meant by “long-distance?” Enter bloodstream and travel to different part of the body. Do not bind to the same cell they are produced and released from
- Endocrine glands secrete hormones directly to blood
- Glands highly vascularized
Hormones: Chemical structure
- Chemical structure determines longevity, transport in blood, & receptivity by cell
Two major classification of hormones:
1) Amino acid-based hormones
* Molecular size variesamino acid derivatives, peptides, proteins
* Water-soluble (blood is mostly water)circulate without carrier
2) Steroid hormones
* Synthesized from cholesterol
* Gonadal hormones (testosterone, estrogen) and adrenocortical hormones are only steroid hormones in body
* Lipid-soluble–>circulate with carrier
Hormone actions
- Hormones can only affect target cells with appropriate receptors
Different cell types can have different receptors that can bind the same hormone
what are the major changes produced by hormone binding:
1) Altering plasma membrane permeability or membrane potential
2) Stimulates synthesis of enzymes/proteins inside cell
3) Activates/deactivates enzymes
4) Induces secretory activity
5) Stimulates mitosis
Two mechanisms of hormone action:
- second messenger system
- Intracellular system
Second messenger systems
- use receptors found on surface of plasma membrane
- What class of hormone uses this action? Amino based hormones
- Receptors are usually coupled to regulatory G-proteins
- G-protein activates intracellular second messenger–>causes response in cell
What is the effector enzyme in this mechanism? What is the second messenger? Cyclic AMP
This system is extremely efficient!!
Intracellular systems
- Hormone enters cell, then binds to intracellular receptors
- Receptor-hormone complex binds specific regions of DNA–>DNA transcription occurs
- Effect: certain proteins produced in larger numbers
Hormone release
Stimulating hormone release
* Hormone synthesis & release is mostly controlled by negative feedback mechs (increase hormone production and then released)
* Stimulus mechanisms:
1) Humoral stimuli:changing blood levels of critical ions & nutrients
-Ex: monitoring Ca2+ levels by parathyroid gland
2) Neural stimuli: nerve fibers stimulate hormone release
-Infrequent
-Ex: norepinephrine & epinephrine release by sympathetic nervous system
3) Hormonal stimuli: hormone released in response to other hormones
-Ex: hypothalamic hormones stimulate or inhibit anterior pituitary gland
hormone concentration in blood depends on
- How fast it is being released by endocrine organ
- How fast it is broken down
* Most hormones removed by kidneys and/or liver
* Water-soluble hormones have shortest half-life
Cellular response
- Target cells only respond to a hormone if it has a specific receptor protein for that hormone
- One hormone may only be able to interact with a few cell types, while another hormone may be able to interact with every cell type
Activation of cell depends on:
1) Blood levels of hormone
2) Number of receptors for specific hormone on/in cell
3) Affinity of receptor to the hormone
Cellular response
- amount of hormone can change number of receptors on/in target cell
- up regulation
- down regulation
up regulation
increase receptor number in response to low hormone levels (hormone will bind to at least one receptor) -more sensitive to hormones
Down regulation
decrease receptor number in response to high hormone levels. - less likely the cell becomes overstimulated -less sensitive to large amounts of hormone
Hormone interactions at Target cells
2+ hormones binding on the same target cell at the same time may result in:
1)Permissiveness: one hormone cannot have full effect without binding of a second specific hormone
* Lack of the second hormone may delay or completely inhibit effects of first
2) Synergism: 2+ hormones with similar effects bind target cell–> amplification occurs (making it more severe or enhancing it)
3) Antagonism:one hormone opposes the effect of another
* Hormones can compete for the same receptor
* Hormones act through different metabolic pathways
* Hormones can down-regulate receptor of another hormone
duration of hormone effects on target cell
- Hormone effect is not always immediateeffects seen after hours or days
- Some hormones must be activated before binding can occur
Duration of effect varies:
* Effects can disappear as levels drop or can persist for hours after levels drop
* Importance: variation of effects = strict control of hormone release
The Pituitary Gland (Hypophysis)
- Connected to hypothalamus
- Two regions of the gland:
1) Anterior pituitary: manufactures and releases several different hormones (produces its own hormones, hypothalamus produces a hormone and releases to the blood which stimulates the anterior pituitary gland)
2) Posterior pituitary:composed mostly of neural tissue and nerve fibers (storage site)
* Stores and releases neurohormones produced by hypothalamus
* Temporary
Posterior Pituitary & Hypothalamic Hormones
- oxytocin
- Antidiuretic Hormone (ADH)
Oxytocin
- Functions: stimulant for uterine contraction, milk ejection, “cuddle hormone”
- Neurotransmitter in brain–> promotes nurturing, couple bonding, trust, affectionate behavior
- Stretching of cervix during childbirth sends afferent impulses to hypothalamus–>stimulates posterior pituitary to release oxytocin
- Stimulates milk-producing glands to contract during breastfeeding
Antidiuretic Hormone (ADH)
- Diuresis means urine
- Function: inhibits formation of urine by increasing return of water to blood supply by kidneys (kidneys will put less water in urine)
- Importance: ADH will influence how much water leaves the body through urine
- Osmoreceptors in hypothalamus monitor solute concentration in the blood
Anterior pituitary hormones
Four of six hormones are tropins–> affect activity of another endocrine gland
- follicle-stimulating hormone (FSH),
- luteinizing hormone (LH),
- adrenocorticotropic hormone (ACTH),
- thyroid-stimulating hormone (TSH).
what are the six Anterior pituitary hormones:
- growth hormone
- Thyroid-Stimulating Hormone (TSH)
- Adrenocorticotropic Hormone (ACTH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Prolactin (PRL)
growth hormone:
Metabolic effects
1) Decreases glucose uptake by cells
2) Mobilizes fat storesreleases fatty acids to blood
3) Increases amino acid uptake by cells
Growth effects:
* Liver, bone, skeletal muscle, etc. produce insulin-like growth factor (IGFs) in presence of GH
IGFs stimulate growth:
1) Increase nutrient uptake by tissue
2) Formation of collagen and deposition of bone matrix
Release of GH controlled by growth hormone-releasing hormone (GHRH) or growth hormone-inhibiting hormone (GHIH)
Thyroid-Stimulating Hormone (TSH)
Function: Stimulates development and secretory activity of thyroid gland
Adrenocorticotropic Hormone (ACTH)
Function: stimulates adrenal cortex of adrenal gland to release hormones
gonadotropins
Two hormones:
4) Follicle-stimulating hormone (FSH)
5) 5) Luteinizing hormone (LH)
Function: regulate function of gonads
FSH: stimulates production of gametes
LH: stimulates production of gonadal hormones
Gonadotropin-releasing hormone (GnRH) stimulates release of FSH and LH
Gonadotropins only released after puberty
Prolactin (PRL)
- Function: stimulates milk production in breast tissue
- PRL release increases toward end of pregnancy
- Levels of PRL rise and fall in tandem with blood estrogens
- Rising estrogen stimulates PRL release
- Release controlled by dopamine–> inhibitory hormone
the thyroid gland
- Produces, secretes, and stores hormones
- Retains ~3 months normal supply of hormone
Function: produces Thyroid Hormone (TH)–>major metabolic hormone (when cell binds to TH the metabolic hormone speeds up)
Production of TH depends on presence of iodine
Low iodine causes Thyroid gland to swell
Affects virtually every body cell:
1) Increases metabolic rate and body heat production
2) Regulates tissue growth/development
3) Maintains blood pressure
The Parathyroid Gland (concern with calcium)
Secretes parathyroid hormone (PTH)
Function: contributes to calcium homeostasis in body
Falling blood Ca2+ levels stimulate PTH release by:
1) Stimulating osteoclasts to increase bone resorption
2) Enhancing Ca2+ reabsorption by kidneys
3) Activating vitamin Dincreases absorption of Ca2+ from digestive system
The Adrenal Glands
- Function: stress response, electrolyte balance (charged particles such as ions)
- Stress response hormones deal with stress
- Two areas of the gland, each functions as individual unit:
1) Adrenal Cortex:
2) Adrenal medulla
adrenal cortex
- outermost region
- Produces corticosteroids: mineralcorticoids, glucocorticoids, and gonadocorticoids
Mineralcorticoids:
regulate electrolyte concentration in ECF,especially Na+ and K+
Importance:
* Na+ influences water movement–> can affect blood volume and blood pressure
* K+ determines resting membrane potential–>imbalance affects responsiveness of neurons
Glucocorticoids
- influence energy metabolism of cells, provide resistance to stressors
- Specific types: cortisol, cortisone, corticosterone
- Cortisol release stimulated by ACTH
-Negative feedback–>rising cortisol prevents ACTH release
Stress affects cortisol release–>CNS overrides negative feedback mechanism & more cortisol released
Effects of glucocorticoids:
* Mobilizes body stores to create more glucose
* Provokes sympathetic nervous system–>vasoconstriction
Excessive release causes:
* Depressed cartilage & bone formation
* Inhibits inflammation
* Depresses immune system
* Disrupts normal cardiovascular, neural, gastrointestinal functions
Gonadocortioids:
- small amounts of androgens released by adrenal cortex
- Some converted to testosterone, others converted to estrogen
- Amount produced by adrenal cortex is very small compared to what is produced by gonads
Effects:
* Contribute to axillary and pubic hair development
* females–>contributes to sex drive, produce estrogens post-menopause
Adrenal Medulla:
- innermost region of adrenal gland
- Synthesize epinephrine & norepinephrine
Unequal amounts stored & released:
* 80% epinephrine: greater influence on metabolic activity & is a dilator of airways in lungs
* 20% norepinephrine: greater influence on blood vessel diameter
- Release is initiated by sympathetic nervous system
- Release is short-lived
- Hormones from adrenal medulla are not essential
The pancreas
- Hormones produced in pancreatic islets (alpha and beta cells)
- Function: controls blood sugar levels
Produces & secretes 2 hormones:
1. Glucagon:produced by alpha cells
* Hyperglycemic effect (increase in blood sugar)
* Effects: Stimulates liver to break down glycogen to glucose, convert non-carbohydrate molecules to glucose, release glucose from liver cells
2. Insulin: produced by beta cells
* Hypoglycemic effect (Causes blood sugar to decrease)
Release controlled by:
* Elevated blood glucose
* Rising blood levels of amino acids & fats
* Acetylcholine release from parasympathetic (rest and digest)
* Any hyperglycemic hormone
* ncrease blood—> increase insulin
* Effects: Increases glucose uptake by body cells, inhibits glycogen breakdown, inhibits conversion of non-carbohydrate molecules to glucose
Gonads
Females: ovaries produce estrogens & progesterone
* Estrogen function: maturation of reproductive organs, appearance of secondary sex characteristics, gamete maturation
* Progesterone function: breast development, cyclic changes in uterine mucosa
Males: testes produce testosterone
* Function: maturation and maintenance of reproductive organs, appearance of secondary sex characteristics, sex drive, normal sperm production
placenta
- temporary endocrine organ
- Produces estrogens, progesterone, human chorionic gonadotropin (hCG)
- Function: maintains pregnancy
