Chapter 16

Hormones interact with specific target cells and influence their function to

– Maintain fluid, electrolyte, and acid-base homeostasis \n – Promote growth \n – Regulate metabolic reactions \n – Effect function of cell from immediately to several days

What are chemical messengers?

Hormones

What is the process of exchange of arteries to veins to arteries?

1. Hormones are secreted into the interstitial fluid, after which they diffuse into blood capillaries
2. The blood transports hormones to the heart through veins
3. After leaving the heart, the blood transports the hormones to the rest of the body through the arteries
4. In capillary beds the hormones diffuse out of the blood into the interstitial fluid and bind to receptors on their target cells

Signaling Pathways - Endocrine

secreted into blood to affect distant targets

Signaling Pathways - Paracrine

chemicals secreted by cells into extracellular space, affect nearby but different types of cells

Signaling Pathways - Autocrine

chemicals secreted by cells into interstitial fluid, elicit effects from same cell or cell type

Three groups of organs

Primary organs

Secondary Organs

Neuroendocrine

What are primary organs

only endocrine functions

what are secondary organs

both endocrine and variety of non-endocrine functions

neuroendocrine are?

nervous tissue chemicals that have a hormonal function

If secondary organs are both endocrine and variety of non endocrine functions, then what are examples for it

Heart, kidneys, small intestines, testes, and ovaries

Amino-acid hormones are

\- generally hydrophilic, bind to plasma membrane receptors

\- usually free (independent traveler in blood)

\- break down quickly (seconds to minutes)

Steroid hormones are

\- generally hydrophobic hormones, binds to receptors in cytosol or nucleus

\- usually bound (bound to protein)

\- can survive for weeks

Paraneoplastic syndrome

* imbalance of electrolyte and fluid
* inappropriate amount of ADH secretion
* first sign of cancer

Types of hormones transport through the blood

free hormones

bound hormones

what are free hormones

* hydrophilic
* breakdown quickly
* used quickly
* some hydro, and growth horm are protein-bound

what are bound hormones

* bound to plasma proteins
* hydrophobic
* can be released when needed
* extends lifespan of hormone in blood

hydrophilic hormones

**cannot readily cross** plasma membrane, generally interact with receptors embedded in target cell’s plasma membrane

hydrophobic hormones

able to cross through plasma membrane, generally interact with receptors in cytosol or nucleus

Mechanisms of Hormone Action (hydrophilic amino acid based hormone)

1. hydrophilic hormone (first messenger) binds to its receptor in the plasma membrane causing the G protein to split into two subunits
2. The G-protein subunit activates adenylate cyclase
3. Adenylate cyclase catalyzes the formation of cAMP, the second messenger
4. cAMP activates protein kinase A.
5. Protein kinase A phosphorylates specific proteins

Mechanisms of Hormone (hydrophobic hormones)

1. Hydrophobic hormone diffuses into the target cell
2. hormone binds to an intracellular receptor and enters the nucleus of the cell
3. hormone-receptor complex interacts with the DNA to initiate a cellular change

Effects of hormone actions

* stimulate secretion from endocrine or exocrine cell
* activate or inhibit enzymes
* stimulate or inhibit mitosis or meiosis (cell division)
* opening or closing ion channels in cell plasma
* activate or inhibit transcription of genes that code for RNA or proteins (gene expression)
* fluid and electrolyte balance
* maintaining homeostasis

Hormones interactions - maintenance of homeostasis requires multiple hormones. What are the two types?

* synergist - act on the same target cell to exert the same effect, effect is more pronounced with interaction of multiple hormones than any one individual hormone by itself
* antagonist - act on same cells but have opposite effects

Hypothalamus influence:

* vital to many homeostatic functions
* Direct - hormone controls certain body function
* tropic - controls secretion of hormones from other endocrine glands

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Hormones of Hypothalamus

1. Hypothalamic neurons make either ADH or oxytocin
2. The hormones travel through the hypothalamic hypophyseal tract in the infundibulum
3. ADH and oxytocin are stored in the axon terminals in the posterior pituitary
4. The hormones are secreted into the capillaries in the posterior pituitary when the hypothalamic neurons fire action potentials

What does ADH do and where does it come from? (stimulus for release, inhibitor of release, target tissue, effects)

* ADH increases/decreases solute concentration of the blood, and is a hypothalamic hormones. Effects are water reabsorption from the kidney tubules, and increases blood volume.

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What is oxytocin function (stimulus for release, inhibitor of release, target tissue, effects)

* stretching of the uterus
* infant sucking at the nipple
* lack of appropriate stimuli
* uterine contractions
* milk let-down reflex

hormones of hypothalamus and anterior pituitary

* hypothalamic neurons secrete releasing and inhibiting hormones into the hypothalamic capillary bed
* hormones travel through portal veins in the infundibulum
* hypothalamic hormones exit the anterior pituitary capillary bed to bind to receptors on anterior pituitary cells
* hypothalamic hormones stimulate or inhibit secretion of hormones from the anterior pituitary cells

hypothalamus produces and releases tropic hormones either stimulates (releasing hormones) or inhibits (inhibiting hormones) release of hormones from anterior pituitary:

* first tier
* second tier
* third tier

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What is first tier

neuroendocrine cells of hypothalamus secrete releasing and inhibiting hormones

what is second tier

tropic hormones effect on anterior pituitary

third tier is

actions of anterior pituitary hormones at target tissues, target tissue glands secrete hormones that can affect various homeostatic variables

Posterior Pituitary hormones are

oxytocin and ADH

Thyroid Stimulating hormone (anterior pituitary hormone)

* Thyrotropin-releasing hormone (TRH) from the hypothalamus
* Exposure to cold
* stress
* big role for growth of thyroid gland
* synthesis of thyroid hormone

adrenocorticotropic hormone (anterior pituitary hormone ACTH)

* corticotropin releasing hormone form the hypothalamus
* stress
* growth and development of adrenal cortices
* release of adrenal steroids and catecholamines

Prolactin (anterior pituitary hormone)

* infant suckling at the nipple
* prolactin releasing hormone from the hypothalamus
* development of mammary glands
* milk production

Luteinizing hormone (anterior pituitary hormone)

* Gonadotropin-releasing hormone from the hypothalamus
* male gonad: development of gonad, testosterone production
* female gonads: development of gonads, production of estrogens and progesterone and ovulation

Follicle-stimulating hormone

* gonadotropin-releasing hormone from the hypothalamus
* production of factors that bind and concentrate testosterone
* production of estrogens maturation of ovarian follicles

growth hormone

* growth hormone releasing hormone from the hypothalamus
* stress/exercises
* ingestion of protein
* fasting
* gluconeogenesis
* fat breakdown
* production of insulin-like growth factor, stimulates cell division

Functional relationship of hypothalamus and anterior pituitary

* first tier control - hypothalamus releases GHRH
* second tier control - anterior pituitary releases GH
* effects - GH effects on liver, muscle, bone, and fat
* after effects is either hypothalamus releases soma statin/anterior pituitary decreases release of GH

growth hormone disorder is the

imbalance in GH secretion can result in various disruptions in growth

what is gigantism

hyper secretion of GH before epiphyseal plates have closed leads to extremely tall individuals. Also affects the heart tissues size

what is acromegaly

hypersecretion of GH after epiphyseal plate closure, most affected are tissues of head, face, hands, and feet as well as liver and heart

what is pituitary dwarfism

condition of GH hyposecretion, leads to individuals that are short in stature but with other wise proportional limbs and trunk

thyroid gland

secretes thyroid hormone and calcitonin

What is colloid?

protein rich, and has thyroid hormone and high concentration of iodine atoms.

what are parafollicular cells

spaces between adjacent thyroid follicles, large cells secrete calcitonin

Thyroid hormone derived from amino acid ____ bound to iodine however has _________ qualities

Tyrosine, hydrophobic

Effects of thyroid hormone are:

* Regulation of metabolic rate and thermoregulation - set basal metabolic rate
* promotion of growth an development
* synergism with sympathetic nervous system

What is hyperthyroidism?

hypothalamus and anterior pituitary gland decrease production of TRH and TSH when T3 and T4 rise

What is graves disease?

most common hyperthyroidism, immune system produces abnormal proteins that mimic TSH on thyroid

What is hypothyroidism?

Thyroid is unable to produce more T3 and T4, this problem is not recognized by the hypothalamus.

What is congenital hypothyroidism

develops when infant is born with inadequate thyroid function

Hashimoto’s thyroiditis

autoimmune disorder, immune system attacks thyroid tissue. (fatigue, sensitive to cold, pale dry, puffy face, hair loss).

What is calcitonin

produces and secreted by parafollicular cells, released when calcium ion level in blood increases above normal

Parathyroid glands

typically 3-5 separate glands (purple), on posterior surface of thyroid gland

parathyroid hormone comes from

chief cells

parathyroid increases

blood calcium levels

for calcium ion homeostasis how does it maintain balance?

* para follicular cells secrete **calcitonin** calcitonin to decrease blood calcium
* parathyroid chief cells secrete **parathyroid hormone** to increase blood calcium levels

adrenal glands

on superior aspect of each kidney, roughly pyramid-shaped, produce catecholamine and steroid

cortex is

subdivided into three distinct zones

what is zona glomerulosa of the adrenal gland

densely packed cells, produced mineralocorticoid hormones.

what is zona fasciculata of the adrenal gland

stacked on one another in columns, secrete glucocorticoids and androgenic steroids

what is zona reticularis of the adrenal gland

thin layer of cells arranged loosely in clusters, secrete glucocorticoids and androgenic steroids.

aldosterone disorders

* hypokalemia
* hypernatremia
* hypertension

what is hypokalemia?

Low blood potassium ion level

What is hypernatremia?

high blood sodium ion level

what is hypertension?

high blood pressure

Stress response

involves regulation of blood glucose levels by cortisol

cushings disease

oversecretion from adrenal cortex usually from tumor

latrogenic cushing’s syndrome

disorder caused by long-term administration of glucocorticoid-containing drugs

Chromaffin cells

(derived from nervous tissue) secrete mostly epinephrine (catecholamine); mediate immediate responses to stressor

What are pancreatic islets?

small rounded islands populated by endocrine cells, secrete hormones into bloodstream

Pancreatic islets contain three main cell types:

* Alpha
* Beta
* Delta

What are Alpha cells?

secrete peptide hormone glucagon

what are beta cells?

secrete protein hormone insulin

delta cells are

secrete peptide hormone somatostatin

exocrine acinar cells are

clustered around small ducts into which they secrete enzymes and other products; delivered to digestive tract

__ and____ regulate concentration of glucose in blood

glucagon and insulin

what is the breakdown of glycogen?

glycogenolysis

formation of new glucose in the liver

gluconeogenesis

insulin is

primary antagonist of glucagon, produces and secreted from beta cells of pancreatic islets, stimulates following responses in target cells

insulin promotes

* uptake and storage of ingested nutrients (lipids, amino acids, and glucose), lowers blood glucose levels
* synthesis of glycogen in liver, synthesis of fat from lipids and carbohydrates
* promotes satiety (feeling of fullness)

hypoglycemia is

blood glucose levels are too low, can be caused by elevated insulin levels

hypoglycemia symptoms

* weakness, dizziness
* confusion, hallucinations, seizure, coma, death

Hyperglycemia is

* blood glucose levels are too high, common causes of chronic hyperglycemia

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type 1 diabetes mellitus (insulin-dependent diabetes mellitus)

disease caused by destruction or lack of beta islet cells that produce and secrete insulin

Pineal Gland is

primary endocrine, component of epithalamus (posterior region of diencephalon of brain)

pineal gland secretes…..

secrete neurohormone melatonin, appears to be related to light and dark cycles, secretion increases in dark

Thymus is

* primary endocrine gland in mediastinum
* location where t lymphocyte mature
* secretes hormones thymosin and thymopoietin, function mainly as paracrine signals that assist in T lymphocyte maturation

Testes and ovaries are primary male and female reproductive organs of ____

gonads

Testes produces the hormone

testosterone

ovaries produces the hormone

estrogen and progesterone

What is the function of progresterone

* secretion peaks after ovulation and during pregnancy
* physiological effects include body preparation for pregnancy and supports of fetal development during pregnancy
* also has effects on smooth muscle tissue, body temperature, blood clotting, bone tissue, and metabolism

adipocytes produces the protein hormone called ____ that is able to cross blood-brain barrier, interacts with neurons in hypothalamus

Leptin

Function of leptin is

* induce satiety, prevents overfeeding


* leptin production is closely related to adipose tissue quantity, component in complex mechanisms that regulate feeding

Specific cardiac muscle cells contain stretch-sensitive ion channels, open more widely when blood volume inside heart increases, simulates cardiac muscle cells to secrete_______

ANP (atrial natriuretic peptide)

Hormones of Hypothalamus

* Hypothalamic neurons make either ADH or oxytocin
* The hormones travel through the hypothalamic hypophyseal tract in the infundibulum
* ADH and oxytocin are stored in the axon terminals in the posterior pituitary
* The hormones are secreted into the capillaries in the posterior pituitary when the hypothalamic neurons fire action potentials

glucagon secretion; prevents

hypoglycemia

GH and IGF-1 secretion

simulates protein synthesis with ingested amino acids