The Endocrine System Flashcards
(24 cards)
What is the endocrine system?
Includes all of the endocrine cells and tissues of the body
Endocrine cells are glandular secretory cells surrounded by an extensive network of capillaries that facilitates diffusion of hormones from the secretory cells in the blood stream
Also known as ductless glands because hormones diffuse directly into the bloodstream and not by a duct they are not exocrine cells because they don’t release secretions onto epithelial surfaces
What are hormones
Hormones are chemical messengers that are released into the blood which are then carried to target tissues and organs where they influence cell growth or metabolism
What is homeostasis and what maintains it
Homeostasis is the a Ability to maintain a dynamic equilibrium resulting in a stable internal environment using negative feedback mechanisms
It is maintained partly by the autonomic nervous system and partly by the endocrine system.
The autonomic nervous system is concerned with rapid changes while the endocrine control involved is mainly slower and uses more precise adjustments
What a are the two broad classes of hormones?
Lipid soluble hormones and water soluble hormones, according to this classification, hormones perform their actions differently
What type of hormone are steroids and thyroid hormones?
Lipid soluble hormones
Receptors for lipid soluble hormones are inside the cell which is why the hormones need to be lipid soluble so they can penetrate the phospholipid bi layer
What type of hormone are amine, peptide and protein hormones an example of
Water soluble hormones
The receptors for water soluble hormones are found on the cell membrane
When and why are hormones released
A hormones are usually released in response to s specific stimulus and its action normally reverses or negates the stimulus a negative feedback mechanism. This may be controlled either directly by blood levels of the stimulus or indirectly through the release of hormones by the hypothalamus and the anterior pituitary gland.
How is positive feedback used to control hormone levels
The effect of a positive feedback mechanism is ampflication of the stimulus and increasing release of hormone until a particular process if complete and the stimulus ceases
What do hormones cause to happen or change
Typically produces one or more of the following changes
Alters plasma membrane permeability or membrane potential, or both by opening or closing ion channels.
Stimulates synthesis of enzymes and other proteins within the cell
Activates or deactivates enzymes
Induces secretory activity
Stimulates Mitosis
Describe the location and function of the hypothalamus and pituitary gland
Both act as a unit regulation the activity of most of the other endocrine glands
The hypothalamus is a small part of the brain below the thalamus.it secretes several releasing (stimulatory) and suppressing (inhibitory) hormones that regulate nearly all aspects of growth, development, metabolism and homeostasis
The pituitary gland lies in the hypophyseal fossa of the sphenoid bone, below the hypothalamus, to which it is attached by a stalk (the infundibulum)
It is the size of a pea and consists of two main parts that originate from different types of cells.
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What are the anterior and posterior pituitary gland made up of
The anterior pituitary is a growth of glandular epithelium from the the Pharynx
The posterior pituitary is a down growth of nervous tissue from the brain
There is a network of nerve fibers between the hypothalamus and the posterior pituitary
Describe the vasculature of the anterior pituitary
Is supplied indirectly with arterial blood that has passed through the capillaries of the hypothalamus
As well as providing oxygen and nutrients, this blood transports releasing and inhibiting hormones secreted by the hypothalamus.
These hormones specifically influence, release or inhibit secretion of other hormones formed in the anterior pituitary
What are the tropic hormones that control the secretion of many other endocrine glands that the anterior pituitary gland secretes?
Growth hormone: a protein hormone that stimulates the growth of bone and muscle in growing children. It promotes protein synthesis and fat metabolism and acts as an insulin antagonist.
Prolactin: a protein hormone that is essential for lactation in the female
Luteinising hormone (LH): a glycoprotein that stimulates the production of testosterone in the testis and the ovulation and secretion of estrogen and progesterone by the ovary
Follicle stimulating hormone (FSH): a glycoprotein that stimulates the formation of sperm in the testis and the maturation of the ovarian follicles and estrogen in the ovary
Thyroid stimulating hormone (TSH): a glycoprotein that stimulates the synthesis and secretion of thyroid hormones T4 and T3.
Adrenocorticotropic hormone (ACTH): a peptide hormone that stimulates the synthesis and secretion of the glucocorticoid and adrenal androgens by the adrenal cortex.
Describe the function of the posterior pituitary and its vascular supply
the posterior pituitary does not synthesizehormones but stores and releases hormones produced by the cells of the hypothalamus
There is a network of nerve fibers between the hypothalamus and the posterior pituitary through which these hormones are transported from the hypothalamus to the posterior pituitary
The posterior pituitary is supplied by arterial blood directly by a branch from the internal carotid arteries
What are the two hormones released by the posterior pituitar?
Vasopressin or antidiuretic hormone (ADH): a short peptide that is secreted in a response to elevated plasma osmolarity (high salt or low water content)or decreased blood volume. It acts in the kidney tubules to enhance water reabsorption from the tubular fluid and the formation of more concentrated urine
Oxytocin: stimulates uterine contraction during Labour and the contraction breast ducts during lactation .
Describe the external anatomy of the thyroid gland
The thyroid gland is a butterfly shaped endocrine gland, located on the anterior surface of the neck, just below the larynx and in front of the trachea.
It has a deep red colouration because of the large number of blood vessels serving the glandular cells
The thyroid gland is made up of two lobes (left and right lobes) connected by the isthmus
Four arteries supply blood to the thyroid, two on each side, superior and inferior thyroid arteries
There is also extensive venous return from the gland
Describe the internal anatomy of the thyroid
The gland is made up of small spherical sacs called thyroid follicles
The wall of the follicle consists primarily of cuboidal epithelial cells called follicular calls that are surrounded by a basement membrane
These cells are under the effect of thyroid stimulating hormone (TSH) from the anterior pituitary.
TSH is produced under the stimulating effect of the hypothalamic hormone thyrotropin releasing hormone (TRH)
When the follicular cells are stimulated they secrete two hormones : thyroxine (T4) and tri-iodothyronine T3
T3 and T4 together are called thyroid hormones
What are the functions fit the thyroid hormones T3 and T4
Regulate growth, development and reproduction
Stimulate, metabolic activity’s (proteins carbohydrates and fat), energy production and utilization
Increase sensitivity of the cardiovascular and nervous system to adrenaline and noradrenaline.
What is the function of parafollicular cells?
Also know as C cells, they lie between follicles
These cells secrete the hormone calcitonin which helps in regulating calcium homeostasis
The main function of calcitonin is to lower raised blood calcium levels by promoting the storage of calcium in bone cells and inhibiting its reabsorption in the kidney tubules
Describe the anatomy and philosophy of the parathyroid glands
Two pairs of tiny masses of tissue embedded in the posterior surfaces of the thyroid gland
One superior and one inferior parathyroid gland are attached to the right and left thyroid lobes
They contain two types of epithelial cells
The more numerous chief cells, produce parathyroid hormones (PTH)
The function of the other type is not known
Blood calcium levels regulate PTH secretion. When they fall secretion of PTH is increased and visa versa
The main function of PTH is to increase blood calcium levels (the opposite of calcitonin) this is achieved by increasing the calcium absorption from the small intestine and calcium reabsorption from the kidney tubules. It also releases calcium from the bones and into the blood by stimulating osteoclasts (bone destroying cells)
PTH and calcitonin act in a complimentary manner to maintain blood calcium levels within the normal range which is needed for Muscle contraction Transmission of nerve impulses Blood clotting Normal action of enzymes
Describe the anatomy of the adrenal glands
The paired adrenal (suprarenal) glands one of which lies superior to each kidney have a flattened pyramidal shape
The glands are composed of two parts that have different structures and function. The outer is the cortex and the inner part is the medulla
A connective tissue covers the gland. The adrenal glands like the thyroid glands are highly vascular
What are the three zones of the adrenal cortex and what do they each secrete
The outer zone secretes mineralocorticoids
The middle zone secretes glucocorticoids
The inner zone secretes sex hormones
What is the function of the hormone Aldosterone
The main mineralocorticoid, it is involved in maintaining water and electrolyte balance
It stimulates the reabsorption of sodium ions by the renal tubules and excretion of potassium ions in the urine. Sodium reabsorption is also accompanied by water retention
High blood potassium levels stimulate the secretion of aldosterone from the adrenal cortex.
Angiotensin also stimulates the secretion of aldosterone through the renin-angiotensin-aldosterone system
When blood volume and blood sodium levels are low, juxtaglomerular cells in the kidneys secrete renin directly into circulation
Plasma renin then carries out the conversion of angiotensinogen released by the liver to angiotensin I.
Angiotensin I is subsequently converted to angiotensin II by the help of another enzyme called Angiotensin converting enzyme, which is found in the lungs
Angiotensin II stimulates the secretion of aldosterone
