Chapter 18 the Endocrine System

What is a target cell?

A cell that bears receptors for a hormone, drug, or other signaling molecule.

adenohypophysis

A major organ of the endocrine system, the anterior pituitary (also called the adenohypophysis or pars anterior), is the glandular, anterior lobe that together with the posterior lobe (posterior pituitary, or the neurohypophysis) makes up the pituitary gland (hypophysis).

synaptic communication

Across SYNAPTIC CLEFTS through NEUROTRANSMITTERS

hyposecretion of epinephrine/cortisol

Addison's disease hypotension, dehydration, hypoglycemia, weight loss caused by mutation of ACTH receptors or destruction of adrenal medulla

Refresher: We will be talking about many drugs this quarter, some of which are agonists of hormones or neurotransmitters and some of which are antagonists. Make sure you can differentiate between these two mechanisms.

An agonist is a chemical that binds to a receptor and activates the receptor to produce a biological response. Whereas an agonist causes an action, an antagonist blocks the action of the agonist, and an inverse agonist causes an action opposite to that of the agonist.

Differentiate between up-regulation and down-regulation.

An increase of a cellular component is called up-regulation. An example of down-regulation is the cellular decrease in the number of receptors to a molecule, such as a hormone or neurotransmitter, which reduces the cell's sensitivity to the molecule.

What is a hormone?

Any of various chemical substances produced by body cells and released especially into the blood and having a specific effect on cells or organs of the body usually at a distance from the place of origin.

Compare and contrast action by the nervous system with action by the endocrine system.

Both endocrine and nervous system send signals to the effector organs, tissues, or glands to maintain the homeostasis of the body. nervous system=fast, short-lived, information sent through electrical impulses/neurons, specific cell target endocrine system=slow, longer effect, hormones sent through the blood, typically organ specific

What is a corticosteroid?

Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones.

hypersecretion of epinephrine/cortisol

Cushing's Syndrome hypertension, water-retension, hyperglycemia, sweating, nervousness, complete exhaustion caused by excessive ACTH or tumor

direct communication

Direct movement through GAP JUNCTIONS linking cytoplasm of ADJACENT cells

Revisit homeostasis from chapter 1. Define negative feedback. Be able to find examples of negative feedback within the endocrine system.

Negative feedback is a reaction that causes a decrease in function. It occurs in response to some kind of stimulus. Often it causes the output of a system to be lessened; so, the feedback tends to stabilize the system. This can be referred to as homeostasis. An endocrine example is in the hypothalamo-pituitary axis. There is negative feedback of the pituitary hormone on the hypothalamus, preventing the releasing hormone from being released. For example ACTH inhibits CRH release. Similarly, there is negative feedback of the target-tissue hormone at both the pituitary and hypothalamic level. For example, cortisol from the adrenal cortex inhibits the release of ACTH from the pituitary and CRH from the hypothalamus, keeping levels of cortisol in equilibrium. Cortisol levels can never rise too high in the healthy state as the higher they get the more they inhibit the stimulation of cortisol production. Similarly they can never get too low, as the inhibition is removed and production of cortisol is stimulated. Negative feedback loops within the endocrine system prevent the systems from becoming overactive because the mechanism is inhibited by its own products. This is known as feedback inhibition and is of central importance in the control of hormone levels.

peptide hormone

Peptide hormones are chains of amino acids. Most peptide hormones are synthesized as prohormones— inactive molecules that are converted to active hormones before or after they are secreted.

Differentiate between the three phases of general adaptation syndrome.

Stage 1-alarm stage--provides a burst of energy. In Stage 2-resistance stage--body attempts to resist or adapt to the stressor Stage 3-exhaustion stage--energy is depleted

Explain how the hypothalamus responds to stress.

Stressful stimuli cause the hypothalamus to signal the adrenal medulla via nerve impulses, which mediates short-term stress responses, and to the adrenal cortex, via the hormone adrenocorticotropic hormone (ACTH), which mediates long-term stress response.

Explain why dietary iodine is critical to the synthesis of thyroid hormone.

The function of the thyroid gland is to take iodine, found in many foods, and convert it into thyroid hormones: thyroxine (T4) and triiodothyronine (T3). Thyroid cells are the only cells in the body which can absorb iodine. These cells combine iodine and the amino acid tyrosine to make T3 and T4. T3 and T4 are then released into the blood stream and are transported throughout the body where they control metabolism (conversion of oxygen and calories to energy).

Discuss the relationship between the hypothalamus and the pituitary gland.

The hypothalamus has two different connections with the pituitary gland. The connection to the adenohypophysis (the anterior lobe) is via a special portal blood system, whereas the connection to the neurohypophysis (the posterior lobe) is directly via neurones.

glucagon

The pancreas releases it when the concentration of glucose in the bloodstream falls too low; hyperglycemic

What is an endocrine reflex?

The pathways that regulate how much of which hormones are released at any particular time.

Differentiate between the anterior and posterior pituitary gland. In particular, explain the relationship between the hormones released by the hypothalamus and the hormones released by the anterior pituitary. How is the release of these hormones regulated? In other words you should understand the negative feedback loop. Specifically focus on the regulation of thyroid hormone. Explain how each hormone would be affected in hypothyroidism vs. hyperthyroidism. Identify the diseases or environmental factors associated with hypo- and hyperthyroidism.

The posterior pituitary is, in effect, a projection of the hypothalamus. It does not produce its own hormones, but only stores and releases the hormones created by the hypothalamus, whereas the anterior pituitary produces and secretes its own hormones. posterior pituitary-oxytocin, ADH(anti diuretic hormone) anterior pituitary-HGH (human growth hormone), luteinizing hormone, ACTH (adrenocorticotropic hormone), prolactin, FSH (follicle stimulating hormone), MSH (melanocyte stimulating hormone)

Differentiate between gluconeogenesis and glycogenolysis.

The two have different physiological roles. Glycogenolysis provides glucose/energy over a relatively short (I believe about ten minutes, once creatine phosphate stores are used up) period of time. Muscles will consume their own endogenous glycogen stores for energy while the liver can both consume the glucose produced itself, or export it to the blood stream. Gluconeogenesis takes place almost exclusively in the liver (a bit in the kidneys), and the glucose produced is exported to the blood stream. Gluconeogenesis only occurs during a prolonged fast when blood glucose is falling.

lipid hormone

There are two classes of lipid derivatives: eicosanoids, derived from arachidonic acid, a 20-carbon fatty acid; and steroid hormones, derived from cholesterol.

fenestrated capillaries

These are found in some tissues where there is extensive molecular exchange with the blood such as the small intestine, endocrine glands and the kidney. The 'fenestrations' are pores that will allow larger molecules though. These capillaries are more permeable than continuous capillaries.

Define thyroid-binding globulins.

Thyroxine-binding globulin (TBG) is a globulin that binds thyroid hormones in circulation. It is one of three transport proteins (along with transthyretin and serum albumin) responsible for carrying the thyroid hormones thyroxine (T4) and triiodothyronine (T3) in the bloodstream.

paracrine communication

Use of chemical messengers to transfer information from CELL TO CELL within a SINGLE TISSUE

permissive effect

a biochemical phenomenon in which the presence of one hormone is required in order for another hormone to exert its full effects on a target cell.

mineralcorticoid

a corticosteroid, such as aldosterone, that is involved with maintaining the salt balance in the body.

androgen

a male sex hormone, such as testosterone.

Define thyroglobulin.

a protein present in the thyroid gland, from which thyroid hormones are synthesized.

hypophyseal portal system

a system of blood vessels in the microcirculation at the base of the brain, connecting the hypothalamus with the anterior pituitary. Its main function is to quickly transport and exchange hormones between the hypothalamus arcuate nucleus and anterior pituitary gland.

Define transthyretin.

a transport protein in the serum and cerebrospinal fluid that carries the thyroid hormone thyroxine (T4) and retinol-binding protein bound to retinol.

thyroid hormone

act to increase the basal metabolic rate

glucocorticoid

any of a group of corticosteroids (e.g., hydrocortisone) that are involved in the metabolism of carbohydrates, proteins, and fats and have anti-inflammatory activity.

amine hormone

are small molecules that are structurally related to amino acids, the building blocks of proteins.

protein sparing

the process by which the body derives energy from sources other than protein.

Define follicular cells.

cells in the thyroid gland that are responsible for the production and secretion of thyroid hormones thyroxine (T4) and triiodothyronine (T3).

endocrine communication

cells release HORMONES into extracellular space where they are absorbed into the BLOOD STREAM, target cells must have receptors

Understand and contrast the role of epinephrine and cortisol in the stress response.

epinephrine=short term stress response cortisol=long term stress response

glucose sparing

glucose is stored as glycogen and fat to ensure that it will be available when needed.

insulin

helps control blood glucose levels by signaling the liver and muscle and fat cells to take in glucose from the blood; hypoglycemic

Differentiate between an inhibiting hormone and a releasing hormone.

hormones whose main purpose is to control the release of other hormones, either by stimulating or inhibiting their release.

What are the three major types of stimulus for an endocrine reflex?

humoral stimuli, hormonal stimuli and neural stimuli

What are the major organs/tissues of the endocrine system? (see figure 18-1)

hypothalamus, pituitary gland, thyroid, adrenal glands, pancreas, pancreas, pineal gland, parathyroid glands, thymus

permissive effect

one hormone must be present for the full effect of another hormone ex: Thyroid hormone increases the effect of epinephrine

antagonistic effect

one hormone reduces the effectiveness of a second hormone ex: During pregnancy, progesterone inhibits uterine response to estrogen

hypophysis

pituitary

glucocorticoids

promote glucose production in the liver (ex. cortisol); hyperglycemic

synergistic effect

several hormones combine to produce effects greater than the sum of their individual effects ex: Testosterone needs FSH for normal sperm production

growth hormone

spurs growth in children and adolescents; hyperglycemic

Define stress and stressors.

stress-a physical, mental, or emotional factor that causes bodily or mental tension. stressors- a stimulus that causes stress.

infundibulum

the hollow stalk that connects the hypothalamus and the posterior pituitary gland.

neurohypophysis

the posterior lobe of the hypophysis (pituitary gland), which stores and releases oxytocin and vasopressin produced in the hypothalamus.