ANAPHY LEC (ENDO)

THE ENDOCRINE SYSTEM

LABORATORY

HYPOTHALAMUS

Stimulating Hormones:

Growth hormone-releasing hormone (GHRH): Also known as somatocrinin

·       stimulates the secretion of growth hormone (GH) from the ant. pituitary.

·       GH plays a role in body growth.

Thyrotropin-releasing hormone (TRH):

·       stimulates the secretion of thyroid-stimulating hormone (TSH) from the ant. pituitary

·       TSH - regulates the thyroid gland's activity and the production of thyroid hormones.

Corticotropin-releasing hormone (CRH):

·       prompts the secretion of adrenocorticotropic hormone (ACTH) from the ant. pituitary

·       ACTH - regulates the adrenal cortex and the production of glucocorticoids like cortisol.

·

Prolactin-releasing hormone (PRH):

·       stimulates the secretion of prolactin (PRL) from the ant. pituitary

·       PRL - is involved in milk production in the mammary glands.

Gonadotropin-releasing hormone (GnRH):

·       encourages the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the ant. pituitary

·       FSH and LH are important for reproductive functions in both men and women.

Inhibiting Hormones:

Growth hormone-inhibiting hormone (GHIH):

·       Also known as somatostatin

·       GHIH inhibits the secretion of growth hormone (GH).

·       It acts as a negative feedback mechanism to control GH levels

·

Prolactin-inhibiting hormone (PIH):

·       PIH is dopamine

·       inhibits the secretion of prolactin (PRL).

·       Dopamine / PIH - regulates the release of PRL, primarily involved in milk production

PITUITARY GLAND

THYROID GLAND

·       Throxine

·       Calcitonin

PARATHYROID GLAND

·       Parathyroid Hormone

ADRENAL GLANDS

·       ALDOSTERONE

·       CORTISOL

·       ANDROGEN (DHEA)

·       EPINEPHRINE

·       NOREPINEPHRINE

PANCREAS

·       GLUCAGON

·       INSULIN

·       SOMATOSTATIN

·       PANCREATIC POLYETIDE

PINEAL GLAND

·       MELATONIN

THYMUS

·       THYMOSIN

TESTES

·       TESTOSTERONE

OVARIES

·       ESTROGEN

·       PROGESTERONE

ENDOCRINE HORMONES

ENDOCRINE SYSTEM

LECTURE

Endocrine System

·       Second messenger system of the body.

·       Uses chemical messages (hormones) that are released into the blood

o   Hormones control several major processes

o   Reproduction

o   Growth and development

o   Mobilization of body defenses

o   Maintenance of much of homeostasis

o   Regulation of metabolism

Hormones

·       Hormones are produced by specialized cells

·       Cells secrete hormones into extracellular fluids

·       Blood transfers hormones to target sites

·       These hormones regulate the activity of other cells

The Chemistry of Hormones

·       Amino acid-based hormones

o   Proteins

o   Peptides

o   Amines

·       Steroids – made from cholesterol

·       Prostaglandins – made from highly active lipids

Mechanism of Hormone Action

·       Hormones affect only certain tissues or organs (target cells or organs)

·       Target cells must have specific protein receptors

·       Hormone binding influences the working of the cells

Effects Caused by Hormones

·       Changes in plasma membrane permeability or electrical state

·       Synthesis of proteins, such as enzymes

·       Activation or inactivation of enzymes

·       Stimulation of mitosis

Steroid Hormone Action

·       Diffuse through the plasma membrane of target cells

·       Enter the nucleus

·       Bind to a specific protein within the nucleus

·       Bind to specific sites on the cell’s DNA

·       Activate genes that result in synthesis of new proteins

Nonsteroid Hormone Action

·       Hormone binds to a membrane receptor

·       Hormone does not enter the cell

·       Sets off a series of reactions that activates an enzyme

·       Catalyzes a reaction that produces a second messenger molecule

·       Oversees additional intracellular changes to promote a specific response

Control of Hormone Release

·       Hormone levels in the blood are maintained by negative feedback

·       A stimulus or low hormone levels in the blood triggers the release of more hormone

·       Hormone release stops once an appropriate level in the blood is reached

Hormonal Stimuli of Endocrine Glands

·       Endocrine glands are activated by other hormones

Humoral Stimuli of Endocrine Glands

·       Changing blood levels of certain ions stimulate hormone release

Neural Stimuli of Endocrine Glands

·       Nerve impulses stimulate hormone release

·       Most are under control of the sympathetic nervous system

Location of Major Endrocrine Organs

ENDOCRINE GLANDS

·       Hypothalamus

·       Pituitary Gland (Anterior & Posterior)

·       Thyroid Gland

·       Parathyroid Gland

·       Adrenal Gland

·       Pancreas

·       Pineal Gland

·       Thymus

·       Gonads (Testes & Ovaries)

1.     PITUITARY GLAND (HYPOTHALAMUS)

·       located below the thalamus

·       serves as the major connection between the nervous and endocrine systems

·       Hypothalamus synthesizes at least 9 hormones

·       Pituitary gland secretes 7 hormones.

o   Together, these hormones are essential for regulating various aspects of growth, development, metabolism, and homeostasis.

Stimulating Hormones:

Growth hormone-releasing hormone (GHRH): Also known as somatocrinin

·       stimulates the secretion of growth hormone (GH) from the ant. pituitary.

·       GH plays a role in body growth.

Thyrotropin-releasing hormone (TRH):

·       stimulates the secretion of thyroid-stimulating hormone (TSH) from the ant. pituitary

·       TSH - regulates the thyroid gland's activity and the production of thyroid hormones.

Corticotropin-releasing hormone (CRH):

·       prompts the secretion of adrenocorticotropic hormone (ACTH) from the ant. pituitary

·       ACTH - regulates the adrenal cortex and the production of glucocorticoids like cortisol.

Prolactin-releasing hormone (PRH):

·       stimulates the secretion of prolactin (PRL) from the ant. pituitary

·       PRL - is involved in milk production in the mammary glands.

Gonadotropin-releasing hormone (GnRH):

·       encourages the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) from the ant. pituitary

·       FSH and LH are important for reproductive functions in both men and women.

Inhibiting Hormones:

Growth hormone-inhibiting hormone (GHIH):

·       Also known as somatostatin

·       GHIH inhibits the secretion of growth hormone (GH).

·       It acts as a negative feedback mechanism to control GH levels

Prolactin-inhibiting hormone (PIH):

·       PIH is dopamine

·       inhibits the secretion of prolactin (PRL).

·       Dopamine / PIH - regulates the release of PRL, primarily involved in milk production

2.     Pituitary Gland (Anterior & Posterior)

·       a small, pea-shaped structure

·       located in the hypophyseal fossa within the sella turcica of the sphenoid bone

·       connected to the hypothalamus by a stalk known as the infundibulum.

The pituitary gland has two distinct portions:

Anterior pituitary (adenohypophysis)

·       approx 75% of the gland's total weight

·       composed of epithelial (glandular)  tissue

·

Posterior pituitary (neurohypophysis)

·       made up of nervous tissue

Anterior pituitary 2 parts:

·       pars distalis

·       pars tuberalis

·

Posterior pituitary 2 parts:

·       pars nervosa

·       infundibulum

·       3rd region of the pituitary gland called the pars intermedia

ANTERIOR PITUITARY

Hormones of the Anterior Pituitary

·       6 anterior pituitary hormones

o   Two affect non-endocrine targets (GH, PRL)

o   Four stimulate other endocrine glands (tropic hormones)

·       Characteristics of all anterior pituitary hormones

o   Proteins (or peptides)

o   Act through second-messenger systems

o   Regulated by hormonal stimuli, mostly negative feedback

ANTERIOR PITUITARY

There are five types of anterior pituitary cells, each of which secretes specific hormones:

Somatotrophs

·       secrete growth hormone (GH), also known as human growth hormone (hGH) or somatotropin.

·       GH – major effects directed towards growth of skeletal muscle and long bones

o   Amino acids  to proteins

o   Fats to energy source

Thyrotrophs

·       secrete thyroid-stimulating hormone (TSH), also known as thyrotropin.

·       TSH - controls the secretions and activities of the thyroid gland, which 8plays a crucial role in metabolism.

·

Gonadotrophs

·       secrete 2 gonadotropins:

o   follicle-stimulating hormone (FSH) – sperm/follicle development

o   luteinizing hormone (LH) – triggers ovulation; stimulate testosterone production

Lactotrophs

·       secrete prolactin (PRL),

·       PRL - initiates and regulates milk production in the mammary glands.

Corticotrophs

·       secrete adrenocorticotropic hormone (ACTH), aka corticotropin.

o   ACTH stimulates the adrenal cortex to produce glucocorticoids, including cortisol (stress response  increase energy sources

·       Some corticotrophs also secrete melanocyte-stimulating hormone (MSH).

POSTERIOR PITUITARY

·       secretion of hormones is a well-coordinated process controlled by the hypothalamus.

·       Neurosecretory cells in the paraventricular and supraoptic nuclei of the hypothalamus synthesize oxytocin and antidiuretic hormone (ADH)

·       Post. Pituitary – store and release these hormones

OXYTOCIN

During Childbirth:

·       Trigger: stretching of the cervix of the uterus during labor.

·       Effect: enhances uterine contractions  the progress of labor and the delivery of the baby

·

Breast Milk Ejection:

·       Trigger: mechanical stimulus provided by a suckling infant

·       Effect: promoting milk ejection (aka “milk letdown") from the mammary gland

ANTIDIURETIC HORMONE (VASOPRESSIN)

Decreasing Urine Production:

·       Trigger: increase solute concentration and decrease blood volume

·       Effect: promote the reabsorption of water, thus reducing urine volume

·

Increase Blood Pressure:

·       Trigger: low blood volume and low blood pressure

·       Effect: It causes the constriction of arterioles (small arteries), which increases peripheral vascular resistance

3.     Thyroid Gland

·       butterfly-shaped organ

·       located below the larynx

·       consisting of right and left lateral lobes connected by an isthmus

Microscopic:

·       Thyroid follicles

·            - spherical sacs

·            - composed of follicular cells

·            -produce 2 hormones: Thyroid

Hormones

·       thyroxine (T4)

·       triiodothyronine (T3)

·       Parafollicular cells (C cells)

·            - located between follicles

·            - produce calcitonin, which regulates calcium homeostasis.

ACTIONS OF THYROID HORMONES:

·       Increase basal metabolic rate

o   stimulate synthesis of additional Na+/K+ ATPases

o   increase the concentrations of enzymes involved in cellular respiration, which increases the breakdown of organic fuels and increase ATP production

o   increase the number and activity of mitochondria in cells, which also increases ATP production.

·       Enhance action of catecholamines

o   have permissive effects on the catecholamines (epinephrine and norepinephrine)

o   up-regulate their receptors  increase HR, increase BP, more forceful heart contractions, dilation of BV, inhibition of GIT motility

·       Regulate development and growth of nervous tissue and bones

o   Nervous system:

§  synapse formation

§  myelin production

§  growth of dendrites

o   Skeletal system:

§  formation of ossification centers in developing bones

§  synthesis of many bone proteins

§  secretion of growth hormone (GH) and insulin-like growth factors (IGFs)

REGULATION OF THYROID HORMONE

1.     Low blood levels of T3 and T4 or low metabolic rate stimulate the hypothalamus to secrete TRH.

2.     TRH enters the hypothalamic–hypophyseal portal system and flows to the anterior pituitary, where it stimulates thyrotrophs to secrete TSH.

3.     TSH stimulates virtually all aspects of thyroid follicular cell activity, including thyroid hormone synthesis and secretion

4.     The thyroid follicular cells release T3 and T4 into the blood until the metabolic rate returns to normal.

5.     An elevated level of T3 inhibits release of TRH and TSH (negative feedback inhibition).

CALCITONIN

·       produced by the parafollicular cells (C cells)

·       CT can decrease the level of calcium in the blood by inhibiting the action of osteoclasts  no bone resorption  no Ca released in the blood

o   inhibit bone resorption (breakdown of bone extracellular matrix) by osteoclasts

o   accelerating uptake of calcium and phosphates into bone extracellular matrix

4.     Parathyroid Gland

·       Partially embedded at the posterior surface of the lateral lobes of the thyroid glans

·       4 small, round masses of tissue

·- 1 pair located superiorly

·- 1 pair located inferiorly

·       Chief cell

·- aka Principal cells

·- more numerous

·- produce Parathyroid hormone (PTH) / Parathormone

·

·       Oxyphil cells

·- function not known in a normal parathyroid glans

PARATHYROID HORMONE

·       the major regulator of the levels of calcium (Ca2+), magnesium (Mg2+), and phosphate (HPO4 2−) ions in the blood.

·

·       increase the number and activity of osteoclasts  releases ionic calcium (Ca2+) and phosphates (HPO4 2−) into the blood

·

In the kidneys, PTH:

- slows the rate at which Ca2+ and Mg2+ are lost from blood into the urine

- increases loss of HPO4

- promote formation of the hormone calcitriol

·       Calcitriol, also known as 1,25-dihydroxyvitamin D3, increases the rate of Ca2+, HPO4 2−, and Mg2+ absorption from the gastrointestinal tract into the blood.

Calcium homeostasis

Increase Calcium in blood:

- PTH (Parathyroid gland)

Decrease Calcium in the blood

- Calcitonin (Thyroid gland)

5.     Adrenal Gland

·       paired adrenal glands

·       Aka Suprarenal glands,

·       lies superior to each kidney in the retroperitoneal space

·

·       two structurally and functionally distinct regions:

o   a large, peripherally located adrenal cortex, comprising 80–90% of the gland

o   a small, centrally located adrenal medulla

o

·       Adrenal cortex  - produces steroid hormones that are essential for life

·       Adrenal medulla produces three catecholamine hormones— norepinephrine, epinephrine, and a small amount of dopamine.

Adrenal Cortex

MINERALOCORTICOID (ALDOSTERONE)

·        It regulates homeostasis of 2 mineral ions

o   sodium ions (Na+)

o   potassium ions (K+)

o   Which helps adjust blood pressure and blood volume.

o

·       Aldosterone also promotes excretion of H+ in the urine; this removal of acids from the body can help prevent acidosis (blood pH below 7.35)

GLUCOCORTICOIDS

·       regulate metabolism and resistance to stress, include cortisol, corticosterone, and cortisone

·       Involved in protein breakdown, glucose formation (gluconeogenesis), lipolysis, resistance to stress, anti-inflammatory, and depression of immune responses.

Glucocorticoid secretion

·       The control of glucocorticoid secretion, primarily cortisol, operates through a standard negative feedback system.

·

·       Low blood levels of glucocorticoids trigger neurosecretory cells in the

·        

·        

·        

·       hypothalamus to secrete corticotropin-releasing hormone (CRH).

·       CRH, along with low cortisol levels, promotes the release of adrenocorticotropic hormone (ACTH) from the anterior pituitary.

·       ACTH then circulates in the bloodstream and stimulates the adrenal cortex, leading to the secretion of glucocorticoids.

·       Glucocorticoids will increase in the blood

·       ACTH also has a minor role in stimulating the secretion of aldosterone

ADRENAL CORTEX

·       The primary androgen secreted by the adrenal gland is dehydroepiandrosterone (DHEA).

·       Males, after puberty, the testes release a significant quantity of the androgen testosterone, rendering the effects of adrenal androgens negligible in males.

·       Females - adrenal androgens have important functions:

o   promote libido (sex drive)

o   can be converted into estrogens (feminizing sex steroids) by other body tissues.

o   After menopause, when ovarian estrogen secretion stops, all female estrogens come from the conversion of adrenal androgens.

·       the inner region of the adrenal gland

·       modified sympathetic ganglion of the autonomic nervous system (ANS).

·

Chromaffin cells

·       hormone producing cells

·       are innervated by sympathetic preganglionic neurons of the ANS, allowing for rapid hormone release under the direct control of the ANS.

·

·       two major hormones: 80% epinephrine (adrenaline) and 20% norepinephrine (noradrenaline

·       These hormones intensify sympathetic responses in various parts of the body.

·       In stressful situations and during exercise, impulses from the hypothalamus stimulate sympathetic preganglionic neurons.

·

·       These preganglionic neurons, in turn, stimulate the chromaffin cells in the adrenal medulla to secrete epinephrine and norepinephrine.

·       They increase heart rate and the force of heart contractions, resulting in higher cardiac output and increased blood pressure.

·       These hormones also boost blood flow to essential organs like the heart, liver, skeletal muscles, and adipose tissue, dilate airways to the lungs, and elevate blood levels of glucose and fatty acids, preparing the body for the demands of stress or exercise.

6.     Pancreas

·       The pancreas is both an endocrine gland and an exocrine gland

·       located in the curve of the duodenum, the first part of the small intestine

·       consists of a head, a body, and a tail

·       Roughly 99% of the exocrine cells of the pancreas are arranged in clusters called acini

·       four types of hormone-secreting cells:

o   Alpha or A cells make up roughly 17% of the pancreatic islet cells and secrete glucagon.

o   Beta or B cells constitute approximately 70% of pancreatic islet cells and secrete insulin.

o   Delta or D cells comprise around 7% of pancreatic islet cells and secrete somatostatin.

o   F cells account for the remaining pancreatic islet cells and secrete pancreatic polypeptide.

·       Glucagon – increases blood sugar levels

·       Insulin – decreases blood sugar levels

·       Somatostatin

o   acts in a paracrine manner to inhibit both insulin and glucagon release from neighboring beta and alpha cells.

o   also serve as a circulating hormone to slow the absorption of nutrients from the gastrointestinal tract

o   inhibit the secretion of growth hormone.

·       Pancreatic polypeptide

o   inhibits somatostatin secretion, gallbladder contraction, and the secretion of digestive enzymes by the pancreas

·       glucagon directly stimulates insulin release, while insulin suppresses glucagon secretion.

·       Growth hormone (GH) and adrenocorticotropic hormone (ACTH) indirectly stimulate insulin secretion by raising blood glucose levels.

·       Insulin secretion can be stimulated by acetylcholine, the neurotransmitter released by parasympathetic vagus nerve fibers that innervate the pancreatic islets, as well as amino acids like arginine and leucine, especially after a meal rich in proteins.

·       Glucagon secretion is stimulated by increased activity of the sympathetic division of the autonomic nervous system (ANS), such as during exercise, and by elevated blood amino acids when blood glucose levels are low, which may occur after a protein-rich meal.

7.     Pineal Gland

·       small, cone-shaped gland that hangs from the roof of the third ventricle of the brain

·       Secretes MELATONIN

o   a “sleep trigger” that plays an important role in establishing the body’s day-night cycle

·       In humans, it is believed to coordinate the hormones of fertility and to inhibit the reproductive system (especially the ovaries of females) until adult body size has been reached.

8.     Thymus

·       located in the upper thorax, posterior to the sternum

·       Large in infants and children, it decreases in size throughout adulthood.

·       By old age, it is composed mostly of fibrous connective tissue and fat

·       produces a hormone called THYMOSIN

o   essential for normal development of a special group of white blood cells (T lymphocytes, or T cells) and the immune response.

9.     Gonads (Testes & Ovaries)

TESTES

·       paired oval testes of the male are suspended in a sac, the scrotum, outside the pelvic cavity

·       In addition to male sex cells, or sperm, the testes also produce male sex hormones, or androgens, of which testosterone is the most important

·       At puberty, testosterone promotes the growth and maturation of the reproductive system organs to prepare the young man for reproduction. It also causes the male’s secondary sex characteristics (growth of facial hair, development of heavy bones and muscles, and lowering of the voice) to appear and stimulates the male sex drive.

·       In adults, testosterone is necessary for continuous production of sperm

·       Testosterone production is specifically stimulated by LH (luteinizing hormone).

OVARIES

·       paired, almond-sized organs located in the pelvic cavity

·       Besides producing female sex cells (ova, or eggs), ovaries produce two groups of steroid hormones, estrogens and progesterone.

·       ESTROGENS are responsible for the development of sex characteristics in women (primarily growth and maturation of the reproductive organs) and the appearance of secondary sex characteristics (hair in the pubic and axillary regions) at puberty

·       Acting with progesterone, estrogens promote breast development and cyclic changes in the uterine lining (the menstrual cycle).

·       PROGESTERONE

o   During pregnancy, it quiets the muscles of the uterus so that an implanted embryo will not be aborted and helps prepare breast tissue for lactation.