Endocrine and Blood (16/19) Flashcards
Endocrine system
The group of organs that secretes hormones influencing functions of other cells and tissues
Hormones
chemical messenger sent into the blood that triggers changes within its target cells
“endo”
“within” as in “within the blood”
Blood capillaries
cells of tiny blood vessels
Hormone secretion and distribution by the blood
- hormones are secreted into interstitial fluid, after which they diffuse into blood capillaries
- Blood transports hormones to the heart through the veins
- after leaving the heart, the blood transports the hormones to the rest of the body through the arteries
- in capillary beds, the hormones diffuse out of the blood, into the interstitial fluid, and bind to receptors on their target cells.
Paracrine
chemical messenger secreted into extracellular fluid to influence nearby target cells
Autocrine
chemical messenger that influences function of same cell or cell type that produced or secreted it
Endocrine glands consist of..
ductless glandular epithelial cells that secrete their hormones into the interstitial fluid for transport by the bloodstream
Exocrine glands
secrete their products into ducts that lead to body surfaces or cavities
Endocrine organs
- anterior pituitary gland
- thyroid gland
- parathyroid gland
- thymus gland
- adrenal cortex
- pancreas
- ovaries
- testes
anterior pituitary gland
situated in sphenoid bone of the skull
thyroid gland
in anterior neck
3-5 small parathyroid glands
found on posterior thyroid gland
paired adrenal cortices
located on the superior surface of the kidneys
endocrine pancreas
found in the left side of the abdominal cavity mostly posterior to the stomach
thymus
located in the superior mediastinum
paired ovaries or testes
the former in the pelvic cavity in women and the latter suspended below the pelvic cavity in men
neuroendocrine organs
an organ that consists of nervous tissue but also secretes hormones
(hypothalamus and pineal gland (brain), adrenal medulla in core of adrenal gland)
Paraneoplastic syndrome
‘the signs and symptoms that accompany hormone secretion from cancer cells’
common findings include imbalances in fluid, calcium ion, and sodium ion homeostasis
symptoms - precede other symptoms of cancer and investigating them may lead to an earlier diagnosis
amino acid-based hormones
chemical messenger consisting of one or more amino acids; most of these hormones are hydrophilic and bind plasma membrane receptors.
produced by anterior pituitary gland, pancreas, thymus, thyroid, and parathyroid glands, consist of one or more amino acids.
Which amino acid-based hormone is not hydrophilic?
thyroid hormone is hydrophobic aa, tyrosine, and does not freely interact with water.
Steroid hormones
Chemical messengers derived from cholesterol, with a core of hydrocarbon rings; hydrophobic and interact with plasma membrane or intracellular receptors
adrenal cortex, testes, and ovaries
lipid-soluble
can mix with fats and can be stored in adipose tissue
Free hormones
small, aa-based hormones that are hydrophilic and able to freely associate with water. hydrophilic nature allows them to travel freely through the water-based plasma of blood
bound hormones
which form complexes with binding proteins in the plasma, are usually hydrophobic and so do not associate with the water molecules in plasma
Receptors
the hormones can bind, receptors have 3D shapes that are highly specific for their hormones, and can bind to hormones present at extremely low concentration.
upregulation
when the level of a particular hormone in the blood declines, target cells will make more receptors for the hormone, thereby increasing the cells’ sensitivity to the hormone
downregulation
prolonged exposure to a high level of a given hormone causes the opposite effect - target cells decrease the number of receptors specific for that hormone
G-protein
When a hormone binds to a receptor linked to a G-protein, the G-protein changes shape and dissociates into two subunits. The G-protein subunit may activate or inhibit the enzyme, depending on which G-protein has been activated. if activated - catalyzes the formation of a second messenger, which then initiates a series of changes in the cell that lead to some change in its activity
steps of adenylate cyclase - cAMP system
- hydrophilic hormone (first messenger) binds to its receptor in the plasma membrane, causing the G-protein to split into two subunits
- the G-protein subunit activates adenylate cyclase
- adenylate cyclase catalyzes the formation of cAMP, the second messenger
- cAMP activates protein kinase A
- Protein kinase A phosphorylates specific proteins
mechanism of action of hydrophobic hormones via binding an intracellular receptor
- hydrophobic hormone diffuses into the target cell
- hormone binds to an intracellular receptor and enters the nucleus of the cell
- hormone-receptor complex interacts with the DNA to initiate a cellular change
effects of hormone action -
-stimulating secretion from an endocrine or exocrine cell
- activating or inhibiting enzymes
- stimulating or inhibiting mitosis and/or meiosis
- opening or closing ion channels in the cell’s plasma membrane and/or altering its membrane potential
- activating or inhibiting transcription of genes that code for RNA or proteins
half life
the amount of time it takes for the plasma concentration of the hormone to reduce by half
hormonal stimuli
Some endocrine cells increase or decrease their secretion in response to other hormones
two hypothalamic hormones: growth hormone–releasing hormone and somatostatin, which stimulate and inhibit secretion of growth hormone from the anterior pituitary gland, respectively.
humoral stimuli
Many endocrine cells respond to the concentration of a certain ion or compound in the blood or extracellular fluid, such as glucose or calcium ions.
pancreas releasing the hormone insulin in response to an elevated level of glucose in the blood.
Neural stimuli
some cells respond to signals from the nervous system
example of this is the adrenal medulla, which is stimulated by sympathetic neurons to release the neurohormones epinephrine and norepinephrine
Stimulus
A regulated physiological variable deviates from its normal range.
Receptor
Receptors on endocrine cells detect the deviation of the variable.
Control center
The stimulated control center (often the same endocrine cell) increases or decreases its secretion of a particular hormone.
Effector/response
The hormone triggers a response in its target cells that moves conditions toward the normal range.
Homeostatic range
As the variable returns to its normal range, feedback to the control center decreases the effector response.
hypothalamus
small anteroinferior portion of the diencephalon of the brain. connected to the pituitary gland by a stalk called the infundibulum.
pituitary gland
small organ, size of a bean, that sits in the sella turcica of the sphenoid bone
anterior pituitary gland/ adenohypophysis
Derived from glandular epithelium; produces many tropic hormones and growth hormone
Posterior pituitary gland/ neurohypophysis
derived from nervous tissue; stores ADH and oxytocin produced by the hypothalamus
portal veins
capillaries merge in the hypothalamus to form larger blood vessels (PORTAL VEINS) that travel through the infundibulum. These veins lead to a second group of capillaries in the anterior pituitary gland
posterior pituitary hormones
releases and stores 2 neurohormones by clusters of cell bodies in the hypothalamus, known as supraoptic and paraventricular nuclei. = Antidiuretic hormone (ADH) and oxytocin
ADH
that controls water balance; produced by hypothalamus and stored in posterior pituitary that causes the insertion of aquaporin channels in the cells of the distal tubule and collecting system to allow water reabsorption
* to increase the amount of water retained by the kidneys
ADH synthesis and release
- hypothalamic neurons make ADH
- ADH travels through the hypothalamic-hypophyseal tract in the infundibulum
- ADH is stored in the axon terminals in the posterior pituitary
- ADH is secreted into the capillaries in the posterior pituitary when the hypothalamic neurons fire action potentials
primary function of ADH
increase the amount of water retained by the kidneys
Diabetes insipidus
an abnormal lack of ADH secretion or activity results this disease