Chapter 18: The Endocrine System Flashcards
Hormone
A molecule that is releases in one part of the body that regulates the activity of cells in other parts of the body.
Most enter interstitial fluid and then the bloodstream.
Exocrine Glands
Secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ, or to the outer surface of the body.
Includes: sudoriferous (sweat), sebaceous (oil), mucous, digestive glands.
Endocrine Glands
Secrete their products into interstitial fluid surrounding the secretory cells rather than ducts. From here hormones diffuse into blood capillaries and blood carries them to target cells throughout the body.
Endocrine System
All endocrine glands and hormone secreting cells. Acts on all types of cells.
Dependent on the cardiovascular system to distribute products (hormones).
Hormone Receptors
Hormones travels throughout the body in blood, affecting a specific target cell. Hormones influxes their target cells by chemical binding to specific protein receptor.
Only the target cells for a given hormone have receptors that bind and recognize that hormone.
Down-Regulation
Makes a target cell less sensitive to a hormone causing the target cells to decrease.
Receptors are constantly being synthesized and broken down.
Hormones present in excess, the number of target cell receptors may decrease.
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Up-Regulation
Makes a target cell more sensitive to a hormone so target cells will increase.
When a hormone is deficient, the number of receptors may increase.
Circulating Hormones
Most endocrine hormones are circulating as they pass from the secretory cells that move them into interstitial fluid and then into the blood.
Local Hormone
Other hormones. Example: interluekin-2
Act locally on neighboring cells or on the same cell that secreted them without entering the bloodstream.
When these hormones linger in blood, they are inactivated quickly.
Paracrines
Local hormones that act on neighboring cells.
Autocrines
Hormones that act on the same cell that secreted them.
Steroid Hormone
Lipid Soluble
Derived from cholesterol.
Each steroid hormone is unique due to the presence of different chemical groups attached at various sites on 4 rings at the core of its structure.
These small differences allow for a large diversity of functions.
Thyroid Hormones
Lipid Soluble
T3 and T4
Synthesized by attaching iodine to the amino acid tyrosine.
The presence of 2 benzene rings with a T3 or T4 molecule makes these hormones very lipid soluble.
Nitric Oxide
Lipid Soluble
This gas is both a hormone and a neurotransmitter.
Synthesis is catalyzed by the enzyme nitric oxide synthase.
Amine Hormones
Water Soluble
Synthesized by decarboxylating and otherwise modifying certain amino acids.
Called amines as they retain amino group NH3+.
Catecholamines: epi, norepi, dopamine are synthesized by tyrosine.
Histamine: synthesized from histidine by mast cells and platelets.
Peptide and Protein Hormones
Water soluble
Amino acid polymers.
Peptide: 3-49 amino acids-antidiuretic hormone, oxytocin
Proteins: 50-200 amino acids- growth hormone, insulin
Glycoproteins Hormone
Water soluble
Protein hormone
Example: thyroid stimulating hormone. Have attached carbohydrate groups.
Eicosanoid Hormones
Water soluble
20 forms. Derived from arachidonic acid, 20 carbon fatty acid.
Are important local hormones. Act as circulating hormones.
2 types: prostaglandins (PGs) and Leukotrienes (LTs).
Water Soluble Hormones in Blood
Most circulate in the watery blood plasma in free form (Not attached to other molecules).
Lipid Soluble Hormones Transport in Blood
Most molecules are bound to transport proteins which are syntheses by cells in the liver.
Transport Proteins in Blood
Have 3 functions
1. Make lipid soluble hormones temporarily water soluble thus increasing their solubility in blood.
2. Retard passage of small hormones molecules through the filtering mechanism in the kidneys, thus slowing the rate of the hormone loss in urine.
3. Provide a ready reserve of hormone, already present in the bloodstream.
Free Fraction
Where 0.1-10% of molecules of lipid soluble hormones is not bound to transport proteins.
These molecules diffuses out of capillaries, bind to receptors and triggers responses.
When free hormones leave blood, transport proteins releases new ones to replenish the free fraction.
Action of Lipid Soluble Hormones
- Free lipid soluble hormones diffuse from blood, through interstitial fluid, then through lipid bilayer of PM into a cell.
- Hormones bind to and activated receptors within the cytosol or nucleus. Hormone complex alters gene expression. (Turns on and off).
- Newly formed mRNA directs synthesis of specific proteins on ribosomes.
- New proteins alters cells activity and causes responses typical of that hormone.
Action of Water Soluble Hormones
Water soluble hormones binds to receptors embedded in the PM of target cells
1. Binding of hormones (first messenger) to its receptor. Activates G protein, which activates adenylyl cyclase.
2. Activated adenylyl cyclase converts ATP to cAMP (second messenger).
3. cAMP serves as a second messenger to activate protein kinases.
4. Activated protein kinases phosphorylate cellular proteins.
5. Millions of phosphorylated proteins cause reactions that produce physiological responses.
6. Phosphiesterase inactivates cAM.
First Messenger
Where a water soluble “hormone” binds to its receptor at the outer surface of the plasma membrane.
Second Messenger
Produced by first messenger hormone inside the cell where a specific hormone stimulated responses take place.
When cAMP is being used by this messenger it will inactivate phosphodiesterase.
Hormone Interactions
Responsiveness of a target cell to a hormone depends on
1. Hormones concentration in the blood
2. Abundance of the target cells hormone receptors
3. Influences exerted by other hormones.
Permissive Effect
Where actions of some hormones on target cells require a simultaneous or recent exposure to a second hormone.
Synergistic Effect
When the effector of 2 hormones act together is greater than the sum of their individual effects.
Antagonistic Effects
When one hormone opposites the actions of another hormone.
Hormone Secretion
Is regulated by
1. Signals from the nervous system
2. Chemical changes in the blood
3. Other hormones
Pituitary Gland
Endocrine gland. Pea shaped structure.
Secretes several hormones that control other endocrine glands.
Master is the hypothalamus. Small region below the thalamus and is a major link between nervous and endocrine system.
Anterior Pituitary
Or adenohypophysis
Secretes grimes that regulate wide range of bodily activities from growth to reproduction.
Accounts for 75 % of total weight of the gland and composed of epi tissue.
Consists of 2 parts;
1. Pars distails- larger portion
2. Pars tubealis- forms a sheath around the infundibulum
Posterior Pituitary
Or neurohypophysis
Composed of neural tissue.
Consist of 2 parts;
1. Pars nervosa- larger portion and infundibulum
2. Pars intermedia-thrid region, atrophies during human fetal development and ceases to exist as a separate lobe in adults
Growth Hormone (GH)
APH
Targets: liver
Actions: stimulates liver, muscle, cartilage, bone and other tissues to synthesize and secrete insulin like growth factors which
1. Increase growth of bones and soft tissue.
2. Acts directly on target cells to exchange lipolysis
3. Decrease glucose uptake.
Thyroid Stimulating Hormone (TSH)
APH
Target: thyroid gland
Actions: stimulates synthesis and secretion of thyroid hormones by thyroid gland.
Follicles Stimulating Hormones (FSH)
APH
Targets: ovary and testis
Actions: in females, initiates development of oocytes and induces ovarian secretion of estrogens.
In males, stimulates testes to produce sperm.
Luteinizing Hormones (LH)
APH
Target: ovary and testis
Action: in females, stimulates secretion of estrogen and progestones, ovulation and formation of corpus lutes.
In males, stimulates testes to produce testosterone.
Prolactin (PRL)
APH
Target: mammary glands
Actions: together with other hormones, promotes milk production by mammary glands.
Adrenocorticotropic Hormone (ACTH)
APH
Targets: adrenal Cortex
Actions: stimulates secretion of glucocorticoids (mainly cortisol) by adrenal cortex.
If there was an increased amount of cortisol in blood, the level of ACTh would decrease.
Melanocytes Stimulating Hormone (MSH)
APH
Targets: brain
Action: exact role in humans in unknown but may influence brain activity. When present in excess can cause darkening of skin.
Insulin Like Growth Factors (IGFs)
Small protein hormone, synthesized in the liver.
GH exerts its growth promoting effects indirectly through this hormone.
This hormone is secreted in response to GH from cells in the liver, skeletal muscles, cartilage and bones.
Tropic Hormones
Anterior pituitary hormones that act on other endocrine glands.
Inhibiting Hormones
Produced by the hypothalamus, suppress secretion of anterior pituitary hormones.
1. Growth hormone inhibiting hormone (GHIH): or somatostatin, inhibiting secretion of growth hormone.
2. Prolactin inhibiting home (PIH): dopamine, suppresses secretion of prolactin.
Hypophyseal Portal System
Blood flows from capillaries in the hypothalamus into portal vein that carry blood to capillaries of the anterior pituitary (adenohpophysis).
The hormones carried allow for communication and are an important link between the nervous and the endocrine system.
Superior Hypophyseal Arteries
Branches of the internal carotid arteries, brings blood into the hypothalamus.
Primary Plexus of the Hypophyseal Portal System
Capillary network where arteries divide at the junction of the median eminence of the hypothalamus and the infundibulum.
Hypophyseal Portal Veins
Blood drains into this vein from the primary plexus that pass down the outside of the infundibulum.
Secondary Plexus of the Hypophyseal Portal System
Another capillaries network that is formed where the Hypophyseal portal vein divides in the anterior pituitary.
Hypophyseal Veins
Drain blood from the anterior pituitary.
Neurosecretory Cells
Clusters of neurons that are located above the optic chias.
Posterior Pituitary
Does not synthesize hormones.
Stores and release 2 hormones:
(1) oxytocin (2) anti diuretic hormone
Consists of: axons and axons terminals of more than 10,000 hypothalamic Neurosecretory cells.