Chapter Outline - Weebly



Basic Anatomy & Physiology II Dr. L. Bacha

Chapter Outline (Marieb & Hoehn 6th edition)

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15.1 The endocrine system is one of the body’s two major control systems

Hormones are chemical messengers secreted by cells into the extracellular fluids;

they travel through the blood, and regulate the metabolic function of other cells in the body.

List the 5 the major processes that hormones (these “mighty molecules”) control and integrate:

( Reproduction

( Growth and development

( Maintenance of electrolyte, water, and nutrient balance of blood

( Regulation of cellular metabolism and energy balance

( Mobilization of body defenses

define endocrinology:

= the scientific study of hormones and endocrine organs

characterize exocrine and endocrine glands with respect to what they produce and whether or not they have a duct system:

Exocrine:

- produce nonhormonal substances, such as sweat and salivary glands, and have ducts that carry these substances to a membrane surface

Endocrine:

also called ductless glands, produce hormones and lack ducts

( endocrine glands release their hormones into what?

surrounding tissue fluid

( do they have a rich vascular and lymphatic drainage that receives hormones? yes

( how are most hormone-producing cells in endocrine glands arranged?

in cords and branching networks

( what does the arrangement maximize?

contact between them and the surrounding capillaries

( observe the endocrine glands shown in Fig. 15.1

15.2 The chemical structure of a hormone determines how it acts

( nearly all of them can be classified chemically as what? amino acid based or steroids

( Amino acid based

- are most hormones amino acid based? yes

- molecular size in this group varies from what to what?

simple amino acid derivatives to peptides to proteins

- these hormones are usually water soluble and can NOT cross the plasma membrane of cells

( Steroids

- the steroids hormones synthesized from what? cholesterol

- of the hormones produced by the major endocrine organs, what ones are steroids?

gonadal and adrenocortical hormones

- these hormones are all lipid soluble and CAN cross the plasma membrane of cells

15.3 Hormones act through second messengers or by activating specific genes

( the cells where hormones have an effect are called target cells

( hormones bring about their characteristic effects by altering target cell activity (increasing or decreasing the rates of normal cellular processes)

( a hormone typically produces one or more of what 5 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

Hormones circulate through the blood to most parts of the body. If a cell is a target cell for a specific hormone, then it will have receptors for that hormone. The hormone will have no effect on cells without specific receptors.

( The type of receptor varies, depending on whether or not a hormone can pass through a cell membrane:

1. water-soluble hormones - all amino acid-based hormones except thyroid hormone:

⦁ these hormones are complex molecules that cannot pass through the cell membrane

⦁ they require a receptor on the cell membrane of the target cell and a second messenger (such as cAMP) to cause an effect (see Fig. 15.2) (insulin and other growth factors, however, do not require a second messenger)

⦁ Summary of the Cyclic AMP Signaling Mechanism:

1. a water-soluble hormone (the 1st messenger) binds to its receptor on the cell membrane of its target cell

2. this leads to the conversion of ATP into cyclic AMP (the 2nd messenger) within the target cell

3. cyclic AMP activates enzymes called protein kinases in the target cell

4. the activated protein kinases trigger some sort of response of the target cell

(e.g., activate other enzymes, activate genes, stimulate the release of cellular secretions, cause a change in membrane permeability to cause muscle contraction, etc.).

2. lipid-soluble hormones - steroid hormones and thyroid hormones

⦁ these hormones can diffuse through the cell membranes into cells (see Fig. 15.3)

⦁ if a cell is a target cell for a lipid-soluble hormone, it will have an intracellular receptor specific for that lipid-soluble hormone, and the hormone will bind to the receptor and activate genes directly

⦁ summary of Intracellular Receptors and Direct Gene Activation

1. the steroid hormone diffuses through the cell membrane of the target cell and binds to an intracellular receptor

2. the receptor-hormone complex enters the nucleus and binds to a specific DNA region

3. therefore, it directs synthesis of a new protein

4. the protein acts as an enzyme to carry out the effect of the hormone by catalyzing a certain chemical reaction in the target cell

15.4 Three types of stimuli cause hormone release

( the synthesis and release of most hormones are regulated by some type of what?

negative feedback mechanism

- in a negative feedback mechanism, some internal or external stimulus triggers hormone secretion. As levels of a hormone rise, it causes effects at the target, which then feedback to inhibit further hormone release.

As a result, blood levels of many hormones vary only within a narrow range.

Endocrine Gland Stimuli

( list the three major types of stimuli that trigger endocrine glands to manufacture and release their hormones:

humoral, neural, and hormonal stimuli

( do some endocrine glands respond to more than one type of stimulus? yes

( Humoral Stimuli

- some endocrine glands secrete their hormones in direct response to what?

changing blood levels of certain critical ions and nutrients

- give three examples:

1 parathyroid glands monitor the body’s blood calcium ion levels and release parathyroid hormone as needed

2 insulin (released in response to increased blood glucose)

3 aldosterone (released in response to low Na+ or high K+ blood levels)

( Neural Stimuli

- nerve fibers stimulate hormone release

- give the classic example of neural stimuli:

- the response to stress, in which the sympathetic nervous system stimulates the adrenal medulla to release norepinephrine and epinephrine

( Hormonal Stimuli

- many endocrine glands release their hormones in response to what?

hormones produced by other endocrine organs

- give an example:

releasing and inhibiting hormones produced by the hypothalamus regulate the secretion of most anterior pituitary hormones; many anterior pituitary hormones in turn stimulate other endocrine organs to release hormones

Nervous System Modulation

- the nervous system can make adjustments to maintain homeostasis by overriding normal endocrine controls.

15.5 Cells respond to a hormone if they have a receptor for that hormone (p. 527)

( receptors for hormones are dynamic (constantly synthesized and broken down)!

( up-regulation: persistently low levels of a hormone causes its target cells to form additional receptors for that hormone

( down-regulation: prolonged exposure to high hormone concentrations decreases the number of receptors for that hormone

- down regulation desensitizes the target cells, so they respond less vigorously to hormonal stimulation, preventing them from overreacting to persistently high hormone levels

Half-Life, Onset, and Duration of Hormonal Activity

( hormones circulate in the blood in what two forms?

- free or bound to a protein carrier

( the concentration of a circulating hormone in blood at any time reflects what two things?

(1) its rate of release

(2) the speed at which it is inactivated and removed from the body

- some hormones are rapidly degraded by what?

enzymes in their target cells

- what happens to most hormones?

- are removed from the blood by the kidneys or liver, and the body excretes their breakdown products in urine or, to a lesser extent, in feces

15.6 The hypothalamus controls release of hormones from the pituitary gland in two different ways

( what is the pituitary gland “seated” in?

( what is another name for the pituitary gland?

( the size and shape of the pituitary gland are similar to what?

( what is its funnel-shaped stalk called?

( what does the infundibulum connect the pituitary gland to superiorly?

( study the structure of the pituitary gland and its relationship with the hypothalamus in Focus Fig. 15.1 on pages 530 and 531

( name the two major lobes of the pituitary gland (and read about them on p. 529):

Pituitary-Hypothalamic Relationships

The posterior lobe is actually part of the brain; it is derived from a downgrowth of what?

( it maintains its neural connection with the hypothalamus via a nerve bundle (a bundle of axons) called what?

( this tract arises from neurons in the hypothalamus; read about the neurosecretory cells there; we will get back to them…

The glandular anterior lobe originates from what?

( although the anterior lobe loses it connection with the oral mucosa, there is a vascular connection between the anterior lobe of the pituitary and the hypothalamus by a portal system:

the hypophyseal portal system consists of three parts:

(1) a primary capillary plexus

- in the infundibulum near the hypothalamus

(2) hypophyseal portal veins

- communicate with the two capillary plexuses

(3) a secondary capillary plexus in the anterior lobe

- via this portal system, releasing and inhibiting hormones secreted by neurons in the ventral hypothalamus circulate to what and do what?

-the portal system ensures that minute quantities of hormones released by the hypothalamus arrive rapidly at the anterior pituitary without being diluted by the systemic circulation

( so, the hypothalamus, by secreting releasing hormones and inhibiting hormones, regulates the secretion of the cells in the anterior pituitary!

THE POSTERIOR PITUITARY and HYPOTHALAMIC HORMONES

( the posterior pituitary does NOT synthesize hormones

( it stores and releases two hormones (antidiuretic hormone and oxytocin) that are synthesized in the cell bodies of neurosecretory cells in the nuclei of the hypothalamus of the brain.

( the posterior pituitary consists largely of axon terminals of the neurosecretory cells

( study Focus Fig. 15.1 on page 530 and the sketches below. Note the different parts of the neurosecretory cells and their location

- cell bodies of the neurosecretory cells are in “nuclei” in the hypothalamus of the brain

- their axons form a bundle called the hypothalamic-hypophyseal tract that runs from the hypothalamus through the infundibulum to the posterior pituitary (a tract is group of axons in the central nervous system)

- axon terminals of the neurosecretory cells are in the posterior lobe of the pituitary gland; they store ADH and oxytocin and release them into nearby blood capillaries

Oxytocin

◦ from Table 15.2 on p. 532, fill in the two targets and the effects of oxytocin below:

targets effects

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Antidiuretic Hormone

◦ define diuresis:

◦ define an antidiuretic:

◦ from Table 15.2 on p. 532, fill in the target and the effects of ADH below:

target effect

- what is the effect of drinking alcoholic beverages on secretion of ADH?

◦ another target of antidiuretic hormone is the arterioles

- at high blood concentrations, ADH causes vasoconstriction of arterioles, which increases blood pressure; for this reason, ADH is also called what?

ANTERIOR PITUITARY HORMONES

( why has the anterior pituitary been called the “master endocrine gland”?

( what controls the activity of the anterior pituitary?

( there are how many distinct anterior pituitary hormones?

( are they peptides and proteins or are they steroids?

( what do tropic hormones (tropins) regulate?

- name the four out of six hormones produced by the anterior pituitary that are tropins:

Growth Hormone

◦ what is the abbreviation for growth hormone?

what is it also called?

Direct Actions of GH

targets

most cells of the body (especially skeletal muscle cells and chondrocytes)

effects

stimulates cell growth and replication by accelerating the rate of protein synthesis

Indirect Actions of GH

( growth hormone mediates most of its growth-enhancing effects indirectly by stimulating cells of the liver, skeletal muscle, bone and other tissues to produce insulin-like growth factors (IGFs; somatomedins)

( insulin-like growth factors promote growth, protein synthesis, tissue repair, breakdown of triglycerides, and increase in blood glucose

Thyroid-Stimulating Hormone

◦ what is the abbreviation for thyroid-stimulating hormone and what is it also called?

◦ target of TSH: the follicle cells of the thyroid gland

◦ effect of TSH: stimulates the follicle cells of the thyroid gland to release thyroid hormones

Adrenocorticotropic Hormone

◦ what is the abbreviation for adrenocorticotropic hormone?

- what is it also called?

◦ target of ACTH: adrenal cortex

◦ effect of ACTH: stimulates the cortex of the adrenal gland to release what type of hormones?

Follicle-stimulating hormone

◦ what is the abbreviation for follicle stimulating hormone? FSH

◦ from Table 15.2, name the target organ and effects of FSH in females:

◦ name the target and effects of follicle-stimulating hormone in males:

Luteinizing hormone

◦ what is the abbreviation for luteinizing hormone? LH

◦ from Table 15.2, name the target organ and effects of luteinizing hormone in females:

◦ name the target and effects of luteinizing hormone in males:

Prolactin

◦ what is the abbreviation for prolactin?

◦ the target is the breasts (mammary glands)

◦ what is the only well-documented effect in humans?

15.7 The thyroid gland controls metabolism

Location and Structure (of the thyroid gland)

( describe the shape and location of the thyroid gland:

( how many lobes is it composed of?

( identify the thyroid gland in Fig. 15.8 (a) and study the microscopic thyroid follicles, formed mainly of follicle cells (follicular cells) in Fig. 15.8(b)

( the follicle cells produce what glycoprotein?

( describe colloid:

- colloid is stored in the lumen of the follicle

- what is derived from iodinated thyroglobulin?

( there are also parafollicular cells (C cells) associated (in smaller numbers) with the follicles

- what hormone do the parafollicular cells produce?

Thyroid Hormone

( the term “thyroid hormone” (TH) includes the 2 hormones produced by the follicle cells:

1. thyroxine (T4)

- the major hormone produced by the follicle cells, but it gets converted to T3 at target tissues

2. triiodothyronine (T3)

- the more active form

( T4 and T3 are constructed from what?

- why do you think T4 is called T4?

- why do you think T3 is called T3?

( targets of thyroid hormone:

- are most cells in the body affected by thyroid hormone?

so, the targets of T3 and T4 are “most cells of the body”

( effects of thyroid hormone:

1. increases basal metabolic rate (the amount of energy expended while at rest) by increasing ATP production

- basal metabolic rate increases due to increased synthesis and use of ATP; as cells use more oxygen to produce the ATP, more heat is given off and body temperature rises

(this is the thyroid hormone’s calorigenic (heat producing) effect)

2. regulating tissue growth and development

- thyroid hormone is critical for what?

3. maintaining blood pressure by increasing the sensitivity of blood vessels to the sympathetic nervous system

Synthesis of Thyroid Hormone

( the thyroid gland is unique among the endocrine glands in its ability to do what?

( my summary of the synthesis of thyroid hormone (T3 and T4):

1. the follicle cells actively transport iodide ions from the blood and convert the iodide ions to iodine

2. tyrosines are linked together to form long chains of thyroglobulin

3. iodine is attached to the tyrosines of thyroglobulin to form T3 and T4; thyroglobulin is stored in the colloid in the cavity of the thyroid follicles

4. when blood levels of T3 and T4 decrease, the follicle cells take in thyroglobulin by endocytosis (specifically pinocytosis)

5. thyroglobulin is cleaved by enzymes within the follicle cells into T3 and T4

6. T3 and T4 diffuse into the blood, so that the blood level of thyroid hormone increases

Transport and Regulation

∙ most T3 and T4 released into the blood immediately binds to what protein in the blood?

( what regulates blood levels of thyroid hormones, a positive feedback loop or a negative feedback loop?

Regulation of thyroid hormone:

1. Chemoreceptors in the hypothalamus of the brain detect low blood levels of thyroid

hormone (T3 and T4).

2. The hypothalamus releases TRH (thyrotropin releasing hormone) into capillaries → hypophyseal portal system → capillaries of the anterior pituitary.

3. TRH stimulates cells of the anterior pituitary to

secrete TSH (thyroid stimulating hormone; thyrotropin) into

capillaries to the general circulation.

4. TSH circulates to the thyroid gland and stimulates follicle

cells of the thyroid gland to synthesize and secrete thyroid

hormone (T3 and T4).

5. Rising blood levels of T3 and T4 have a negative

feedback on the hypothalamus and anterior pituitary,

inhibiting further release of TRH by the hypothalamus

and of TSH by the anterior pituitary.

With a decrease in TSH, the follicle cells of the

thyroid gland stop releasing T3 and T4.

As blood levels of T3 and T4 decrease, this is detected

by the chemoreceptors in the hypothalamus....See step 1 again!

Calcitonin

( what cells of the thyroid gland produce calcitonin?

( does calcitonin have a known physiological role in humans?

( at high concentrations (pharmacological doses), calcitonin targets the skeleton, where it has what two effects?

15.8 The parathyroid glands are primary regulators of blood calcium levels

( describe the appearance and location of the parathyroid glands:

( a person usually has how many parathyroid glands?

( parathyroid cells that secrete what hormone?

( parathyroid hormone (PTH) is the single most important hormone controlling what?

( its release is triggered by what?

( its release is inhibited by what?

( From the information in Fig. 15.12 on p. 541, fill in the effects of parathyroid hormone on each target:

| | |

|Target |Effects of Parathyroid Hormone |

| | |

|bone | |

| | |

|kidney | |

| | |

|small intestine | |

15.9 The adrenal glands produce hormones involved in electrolyte balance and stress response

( study the location and structure of the paired adrenal glands (suprarenal glands) in Fig. 15.13

( describe their shape and location, and what they are enclosed in:

( the adrenal gland consists of an outer adrenal cortex and an inner adrenal medulla; each region produces its own set of hormones, but all adrenal hormones help us cope with what?

The Adrenal Cortex

( synthesizes steroid hormones collectively called what?

( the cells of the adrenal cortex are arranged in three zones that each synthesize a different category of corticosteroids:

Mineralocorticoids

( released by the outer zone; what is the essential function of mineralocorticoids?

( the major mineralocorticoid is aldosterone

target of aldosterone = kidney tubules

what are the 2 effects of aldosterone on the kidney tubules?

( a main mechanism that controls the secretion of aldosterone is the renin-angiotensin-aldosterone mechanism:

Glucocorticoids

( glucocorticoids are released by the middle zone of the adrenal cortex

( they influence what and help us do what?

- under normal circumstances, how do glucocorticoids help the body adapt to intermittent food intake?

- do glucocorticoids play a role in maintaining blood pressure?

( what is the only glucocorticoid that is produced in significant amounts in humans?

Regulation of Secretion

( what hormone produced by the anterior pituitary promotes the release of cortisol?

( cortisol secretory bursts occur in a definite pattern throughout the day and night.

- when do cortisol blood levels peak?

- when do the lowest levels of cortisol in the blood occur?

( with acute stress, there is an increase in ACTH (adrenocorticotropic hormone) release from the anterior pituitary. The resulting increase in ACTH blood levels causes what?

Targets of glucocorticoids:

( the targets of glucocorticoids are most cells of the body

Actions of glucocorticoids:

1. increase the rate of protein breakdown, which releases amino acids into the blood for production of new proteins or for ATP production

2. increase glucose formation

3. increase lipolysis (breakdown of fats from adipose tissue)

4. provide resistance to stress by:

a. increase blood glucose levels

b. increase blood pressure

5. anti-inflammatory – inhibits white blood cells that cause inflammation

6. suppress the immune system in high doses

Gonadocorticoids

The inner zone of the adrenal cortex secretes small amounts of androgens and estrogens.

The Adrenal Medulla

( list the two hormones called catecholamines synthesized by the cells of the adrenal medulla:

( effects of epinephrine and norepinephrine: Responsible for the "fight or flight" response to short term stress (along with the sympathetic nervous system)

- from Fig. 15.16 on p.546 (in the Short-term stress response) list the effects of epinephrine and norepinephrine:

( cardiovascular effects:

15.10 The pineal gland secretes melatonin

( describe the shape and location of the pineal gland:

( what is its only major secretory product?

( melatonin is thought to affect the timing of puberty and contribute to setting our “biological clock”

( changing melatonin levels may influence rhythmic variations in physiological process such as what three things?

15.11 The pancreas, gonads, and most other organs secrete hormones

The Pancreas

• study the structure of the pancreas in Fig. 15.17

• exocrine function:

- most of the cells (pancreatic acinar cells) of the pancreas form clusters called pancreatic acini that produce pancreatic juice (including digestive enzymes)

- pancreatic juice is carried to the small intestine by a duct system; this will be covered with the digestive system

• endocrine function:

- the pancreas has clusters of endocrine cells that form pancreatic islets (islets of Langerhans); - the cells of the pancreatic islets secrete insulin and glucagon (and other hormones)

Two Major Cell Types in the Pancreatic Islets:

1. alpha (α) cells – what hormone do they synthesize?

2. beta (β) cells – what hormone do they synthesize?

Glucagon

( released from alpha cells in the pancreas in response to low blood levels of glucose

( what is the major target of glucagon?

( glucagon promotes what three actions?

- the result is a rise in blood glucose to normal levels

Insulin

( released in response to high blood levels of glucose

targets effects

a. most cells of the body ◦ enables the cells to uptake glucose (by facilitated diffusion)

(especially skeletal muscle from the blood

cells and fat cells) ◦ this lowers blood glucose levels

b. hepatocytes of liver ◦ stimulates the hepatocytes to uptake glucose from the blood and convert glucose to glycogen

( insulin is not needed for glucose entry into what organs?

The Gonads and Placenta

( list the two most important hormones produced by the ovaries:

( name the primary hormone produced by the testes:

( the placenta produces estrogens, progesterone and human chorionic gonadotropin

Hormone Secretion by Other Organs

Numerous other organs, produce hormones, even though they are not classically studied as part of the endocrine system! List the 7 organs in which hormone-producing cells occur (from Table 15.6 on p. 551):

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The End

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( hormones are long-distance chemical signals that travel in blood or lymph throughout the body

( autocrines and paracrines are short distance chemical signals that may or may not be classified as part of the endocrine system:

- define autocrines:

= chemicals that exert their effects on the same cells that secrete them

- define paracrines:

= also act locally (within the same tissue) but affect cell types other than those releasing the paracrine chemicals

( Some researchers include a third class of hormones, eicosanoids:

( list the two types of eicosanoids : leukotrienes and prostaglandins

( these are biologically active lipids released by nearly all cell membranes

( what do leukotrienes mediate (promote)?

inflammation and some allergic reactions

( effects of prostaglandins:

( necessary for blood clotting, (raise blood pressure,

( promote fever, inflammation and pain,

( stimulate contraction of the uterus

( eicosanoids are considered hormonelike chemicals; why don’t eicosanoids

fit the definition of the true hormones?

because the effects are typically highly localized, affecting only nearby cells, they generally act as paracrines and autocrines and do not fit the definition of true hormones, which influence distant targets

Aspirin and related NSAIDs interfere with the synthesis of prostaglandins.

So…does it make sense that people take aspirin to decrease blood clot formation, fever, pain and inflammation?!

humor refers to moisture or body fluids

A portal system is an unusual arrangement of blood vessels in which what happens?

Milk Ejection (Milk Let-Down Reflex):

baby suckles on the nipple of the mammary gland (breast)

(

stimulates the release of oxytocin

from axon terminals of the posterior pituitary into nearby blood capillaries

(

when oxytocin circulates through the mammary glands, it stimulates contraction of the myoepithelial cells (which surround the secretory cells and ducts)

(

this causes the milk that accumulates in the ducts to be available for the child at the mother’s nipples and is known as milk ejection (milk let-down)

“tropi” = to turn on; to change

GONADOTROPINS

( Note: The next two hormones, FSH and LH, are called gonadotropinsn[?]p[?]r[?]æ[?]è[?]ê[?]ì[?]î[?][?] [?] [?] [?]´ [?]¶ [?]¸ [?]

[?][?][?][?][?]ðððÛÌÌ̽ªÛ››››Û because they are hormones that stimulate the gonads to produce their hormones. What organs are called gonads?

( the release of the gonadotropins is stimulated by gonadotropin-releasing hormone (GnRH):

GnRH is produced by the hypothalamus

target of GnRH = cells of the anterior pituitary

effect = stimulates the cells of the anterior pituitary to secrete FSH and LH

( See Table 15.2 on page 533 for the target and effects of FSH and LH!

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